Drilling discharges in the marine environment

[From the U.S. Government Printing Office, www.gpo.gov]

-e

Drilling Discharges

in the Marine Environment

6..
TL
Q.R I.

CDDL. C.."T .'.-O

....................:..::......COASTAL tONE INFORMATION CENTER

COASTAL ZONE
INFORMATION CENTER

Drilling Discharges

in the Marine Environment

Panel on Assessment of Fates and Effects of Drilling Fluids
and Cuttings in the Marine Environment
Marine Board
Commission on Engineering and Technical Systems
National Research Council

COASTAL ZONE

Property of CSC Library

NATIONAL ACADEMY PRESS DEPARTMENT OF COMMERCE NOAA
~"~ ~9 Washington, D.C. 1983 U.S. DEPARTMENT OF COMMERCE NOAA
x+s n 18 COASTAL SERVICES CENTER
e O-- =: 2234 SOUTH HOESON AVENUE
-L�1 " CHARLESTON, SC 29405-2413

National Academy Press 9 2101 Constitution Avenue, N.W. 0 Washington, D.C. 20418

NOTICE: The project that is the subject of this report was approved
by the Governing Board of the National Research Council, whose members
are drawn from the councils of the National Academy of Sciences, the
National Academy of Engineering, and the Institute of Medicine. The
members of the panel responsible for the report were chosen for their
special competences and with regard for appropriate balance.

This report has been reviewed by a group other than the authors
according to procedures approved by a Report Review Committee
consisting of members of the National Academy of Sciences, the
National Academy of Engineering, and the Institute of Medicine.

The National Research Council was established by the National Academy
of Sciences in 1916 to associate the broad community of science and
technology with the Academy's purposes of furthering knowledge and of
advising the federal government. The Council operates in accordance
with general policies determined by the Academy under the authority of
its congressional charter of 1863, which establishes the Academy as a
private, nonprofit, self-governing membership corporation. The
Council has become the principal operating agency of both the National
Academy of Sciences and the National Academy of Engineering in the
conduct of their services to the government, the public, and the
scientific and engineering communities. it is administered jointly by
both Academies and the Institute of Medicine. The National Academy of
Engineering and the Institute of Medicine were established in 1964 and
1970, respectively, under the charter of the National Academy of
Sciences.

This report represents work supported by Contract 14-12-0001-29063
between the U.S. Department of the Interior and the National Academy
of Sciences.

Library of Congress Catalog Card Number 83-62998
International Standard Book Number 0-309-03431-0

Printed in the United States of America

Panel on Assessment of Fates and Effects of Drilling Fluids
and Cuttings in the Marine Environment

John D. Costlow, Chairman Jerry M. Neff
Duke University Marine Laboratory Battelle New England Marine
Beaufort, North Carolina Research Laboratory
Duxbury, Massachusetts
Robert C. Ayers, Jr.
Exxon Production Research Company James P. Ray
Houston, Texas Shell Oil Company
Houston, Texas
Donald F. Boesch
Louisiana Universities Marine Hal Scott
Consortium ECO/Interface Evaluations
Chauvin, Louisiana Orlando, Florida

Thomas R. Gilbert Judith Spiller*
Northeastern University University of New Hampshire
Boston, Massachusetts Durham, New Hampshire

James G. Gonders Kenneth R. Tenore
Cities Service Company Skidaway Institute of
Oklahoma City, Oklahoma Oceanography
Savannah, Georgia
Donald W. Hood
Consultant David C. White
Friday Harbor, Washington Florida State University
Tallahassee, Florida
Kenneth D. Jenkins*
California State University
Long Beach, California

Staff

Charles A. Bookman, Senior Staff Officer
William Kirby-Smith, Consultant
Phyllis Johnson, Secretary
Delphine D. Glaze, Word Processer

*Appointed in September 1982.

iii

Preface

ORIGIN OF THE STUDY

A variety of wastes are generated in drilling oil and gas wells,
including drill cuttings and used drilling fluids.' The disposal of
these wastes is licensed by the U.S. Environmental Protection Agency
(EPA) under the National Pollutant Discharge Elimination System
(NPDES) (40 CFR 122-125). Permitting such discharges on the outer
continental shelf (OCS)2 has occasioned considerable public debate
about how much they may harm the marine environment.
To improve the technical basis for decision making about
discharging drilling fluids and cuttings in the marine environment,
the Bureau of Land Management' turned to the National Research
Council for a critical review of the subject. In response, the
Assembly of Engineering'4 of the National Research Council convened
the Panel on Assessment of Fates and Effects of Drilling Fluids and
Cuttings in the Marine Environment under the auspices of the Marine
Board. Members of the panel were selected for their experience in

'Drilling fluid is also called mud or drilling mud, because it
often looks like mud. All these terms are commonly used in the oil and
gas industry. For consistency, the term drilling fluid is used
throughout this report.

?The OCS is that portion of the submerged continental margin that
is subject to U.S. jurisdiction. For the purpose of this report, the
OCS extends from a state's offshore boundary (3 miles offshore except
off Texas and west Florida where state boundaries extend 3 leagues--9
nautical miles--offshore) out to the limit of economic exploitation.

3 In a subsequent federal reorganization, the sponsorship of this
study was transferred to the newly created minerals Management Service.

I1n a reorganization of the National Research Council in the
spring of 1982, the Assembly of Engineering was subsumed by the newly
created Commission on Engineering and Technical Systems.

marine biology, marine environmental analysis, toxicological studies
of marine animals, chemical oceanography, benthic ecology, the
technology and chemistry of drilling fluids, and offshore drilling
operations. Consistent with the policies and procedures of the
National Research Council, appropriate balance of perspectives was an
important consideration in choosing panel members.

SCOPE OF STUDY

The charge to the panel was to establish a credible technical basis for
decisions about discharging drilling fluids and cuttings in the marine
environment. The panel proceeded by reviewing and critically apprais-
ing the available knowledge concerning the fates and effects of drill-
ing fluids and cuttings on the OCS. It assessed the adequacy and
applicability of existing research and the transferability of research
results to different sites and hydrodynamic regimes. The panel also
considered additional needed research as well as various means to
mitigate the potential effects of drilling discharges.
In agreement with its charge the panel focused on discharges made
during exploratory and development drilling, as opposed to those made
during other phases of OCS operations. It did not consider the fates
and effects of the formation waters primarily produced during oil and
gas production, nor those of certain specialty drilling fluids used
infrequently and in limited quantities during periodic maintenance
operations and in preparing wells for production. The panel further
restricted its study to water-based drilling fluids, since these are
the fluids used in the vast majority of OCS wells and are the only kind
of fluids currently permitted to be discharged on the OCS.
Drilling discharges are but one impact on the marine environment
from petroleum resource development. In addition to specialty drilling
fluids (not covered in this report as explained above), waters from
hydrocarbon-bearing formations are discharged during production, and
spills or blowouts may occur. Also, petroleum development may compete
with other resource uses, such as fishing. It is the combination of
factors that contribute to the effects of OCS petroleum development.
The assessment was limited to the OCS. Nevertheless, substantial
oil well drilling activity occurs on state lands, and, often similar
oceanographic conditions prevail in state waters as on the OCS. Thus,
the application of the data and results in the report to state waters
(or any other marine environment) is appropriate where the physical
conditions that prevail in the state waters are similar to those of the
OCS, expecially those reported in OCS field studies. The fates and
effects of discharged drilling fluids and cuttings in restricted near-
shore waters, such as in estuaries and embayments, were not a subject
of this study. The panel's work on the nature of drilling fluids, on
considerations in using the available scientific information, and on
mitigating measures applies to all marine environments.

METHOD OF THE STUDY

Available data on the fates and effects of drilling fluids in the
marine environment were of paramount importance throughout this study.
Panel members initially received four comprehensive, and in some cases
critical, reviews of the available literature (Houghton, et al., 1981;
Neff, 1981, Petrazzuolo, 1981; Rieser and Spiller, 1981) for a broad
overview of current knowledge in the field and attendant technical and
Public issues. Several panel members had such a long and consistent
involvement in the subject that they were also familiar with virtually
all the abundant original literature on the subject (a bibliography of
this literature is available [IMCO Services, 1982]).
The panel considered all available literature and even current
(unpublished) work related to its charge. It found that some aspects
of the problem, such as ocean dispersion, were best treated by older
well-established literature, while others, such as the toxicity of
particular fluids or fluid additives, were discussed only in draft
reports that had not yet passed through normal publication procedures.
The panel also considered conventional peer-reviewed journal articles
and the vast amount of so-called "gray literature,' which may have been
subjected to various levels of review, but which is limited in circula-
tion and availability. It relied on peer-reviewed literature when such
literature was available, but also used the gray literature when its
quality could be established. An important aspect of the panel's work
was weighing the quality of all these scientific contributions.
Another of equal importance, but often more difficult to achieve, was
determining the applicability of the research to the problem under
consideration. Some of the research reviewed was designed to test a
hypothesis; other research had been conducted to satisfy regulatory or
other mandates. The panel attempted to accommodate these diverse
sources by evaluating the literature on its scientific merit and on its
applicability to the objectives of this study.
At the outset the panel solicited public comments on the issues it
should address (Federal Register, Oct. 23, 1981); 33 sets of comments
were received. With this initial guidance, the panel then conducted
its review of the technical literature and summarized this review in a
set of discussion papers. About 200 copies were distributed for
review, and 46 substantive written reviews were received. An open
meeting of the panel provided additional opportunity for interested
persons to identify and discuss related issues. Seventy people
attended the day-long meeting. The panel then sought additional
information to address concerns the public had raised and to complete
its assessment.
Thus, the panel's report and its conclusions and recommendations
are based on its review of the primary and secondary scientific
literature, on the public comments that were received, on additional
data and information sought by the panel, and on the professional
experience of panel members.

vii

ACKNOWLEDGMENTS

The panel benefited greatly from the interest, material contributions,
intellectual challenges, and encouragement of a number of individuals
and organizations. In addition to the many reviewers and commenters,
the following made especially important contributions to the panel's
work: the American Petroleum Institute, Michael Connor (Harvard School
of Public Health), Tom Duke (Environmental Protection Agency), William
Grant (Woods Hole Oceanographic Institute), Maurice Jones (IMCO
Services Division, Halliburton Company), Burt Keenan (National Advisory
Committee on Oceans and Atmospheres), Gary Petrazzuolo (Technical
Resources), and Robert Spies (Lawrence Livermore Laboratories). The
panel also wishes to acknowledge the contributions of the liaison
representatives of several government agencies: James Cimato, (Minerals
Management Service), Joseph Kravitz (National Oceanic and Atmospheric
Administration), Douglas Lipka (Environmental Protection Agency), and
Edward Tennyson (Minerals Management Service).

REFERENCES

Houghton, J.P., et al. 1981. Fate and effects of drilling fluids and
cuttings discharges in lower Cook Inlet, Alaska, and on Georges
Bank. Report prepared for Branch of Environmental Studies,
Minerals Management Service. Dames & Moore, Inc., Seattle, Wash.

IMCO Services. 1982. Environmental Aspects of Drilling Fluids: A
Bibliography. 3d ed. Technical Bulletin. Houston, Tex.: IMCO
Services Division, Halliburton Company.

Neff, J.M. 1981. Fate and biological effects of oil well drilling
fluids in the marine environment: a literature review. Draft
report (15-077) to the U.S. Environmental Protection Agency.
Environmental Research Laboratory, Gulf Breeze, Fla.

Petrazzuolo, G. 1981. Preliminary report: an environmental
assessment of drilling fluids and cuttings released onto the Outer
Continental Shelf. Vol. 1: Technical assessment. Vol. 2:
Tables, figures, and Appendix A. Draft report prepared for
Industrial Permits Branch, Office of Water Enforcement and Ocean
Programs Branch, Office of Water and Waste Management, U.S.
Environmental Protection Agency, Washington, D.C.

Rieser, A., and J. Spiller. 1981. Regulating Drilling Effluents on
Georges Bank and the Mid-Atlantic Outer Continental Shelf: A
Scientific and Legal Analysis. Boston, Mass.: New England States/
New England River Basins Commissions. 130 pp.

viii

Contents

Page

Summary, Conclusions, and Recommendations 1

1. Introduction 9

2. Drilling Discharges 11
Offshore Oil and Gas Drilling and Development 11
Characteristics and Functions of Drilling Fluids 13
Discharges of Drilling Fluids 14
The Compositions of Discharges 17
Components of Water-Based Drilling Fluids 15
The Chemistry of Drilling Fluids 24
Drilling-Fluid Components as Commercial Products 25
Trends in Operating Practices: Generic Drilling Fluids 26
The Regulation of Drilling Fluids 34
The Mass Loading of Drilling Discharges in Relation to
That of Other Inputs to the Marine Environment 37
References 44

3. The Fates of Drilling Discharges 49
Introduction 49
Behavior of the Discharge Plume 51
Fates of Drilling Fluids and Cuttings 56
References 69

4. The Biological Effects of Drilling Discharges 75
Introduction 75
The Toxicities of Drilling Fluid Components 75
The Toxicities of Used Drilling Fluids 84
Bioavailability 105
Conclusions 112
References 112

5. Considerations in Using the Information Available on the
Fates and Effects of Drilling Discharges 129
Laboratory Evaluations of Toxicity 129
Bioaccumulation 132

CONTENTS (continued)

The Variability of Drilling Fluids 133
Field Studies of the Fates and Effects of Drilling Fluids 133
Extrapolation of Results 137
Long-Term Fates and Effects 137
Other Information 139
References 141

6. Alternative Operating Practices 147
Shunting 147
Dilution Requirements and Limitations on
Rates of Discharge 149
Offloading and Transport for Distant Discharge 149
Other Transport Techniques 151
Disposal on Ice 151
Substitutions 151
Other Alternatives 152
The "No Discharge" Alternative--A Case Study 153
References 156

Appendix A 157
Appendix B 171

Tables and Figures

Table

I Offshore Wells in the United States 12
2 Mineral Composition of a Shale-Shaker Discharge
from a Mid-Atlantic Well 17
3 Representative Fluid Compositions 18
4 Representative Metal Compositions 20
5 Drilling Fluid Components and Additives Used in
the United States 20
6 How Specialty Additives Are Used to Solve
Drilling Problems 22-23
7 Generic Fluid Systems (EPA Region 11) 28-29
8 Characterizations of Field Drilling Fluids Used in the
Joint Industry Mid-Atlantic Bioassay Program 30-31
9 Summary of Bioassay Results of Mid-Atlantic Generic
Drilling Fluids 32-33
10 Average Discharge of Particulate Solids, Barium and
Chromium from OCS Wells 39
11 Drainage Area and Water and Suspended Sediment
Discharges of North America's Major Rivers 40
12 Estimates of Mass Emissions of Particulate Solids,
Barium, and Chromium from OCS Drilling Discharges
and from Rivers 42
13 Ocean Disposal of Various Wastes by Geographic Areas,
1973 to 1980 43
14 Dilution and Dispersion of Discharge Plumes 58
15 Typical Sea Waves 62
16 Mass Balance of Total Excess Sediment Barium
Surrounding Offshore Drilling Sites 64-65
17 Effect of Environmental Factors on Study Results 67
18 Acute Toxicity of Drilling Fluid Components to
Estuarine and Marine Organisms 77-78
19 Summary of Results of Acute Lethal Bioassays With
Drilling Fluids and Marine/Estuarine Organisms 89-90
20 Summary of Investigations of Sublethal and Chronic
Effects of Drilling Fluids on Marine Animals 91-95

Table

21 Summary of Major Field Investigations of the
Environmental Fate and Effects of Drilling Fluids and
Cuttings Discharged to the Environment 99
22 Trace Metal Concentrations in Drilling Fluids from
Different Sources 106
23 Summary of Biological Effects of Drilling Fluids and
Drilling Fluid Ingredients on Marine Animals11
24 Discharge Alternatives 148
25 Percentage of Time that Drilling Discharges Cannot be
Transferred to Barges or Supply Boats 150
26 Estimated Costs of the "No Discharge' Alternative 155
A-1 Chemicals Commonly Used in Drilling Fluid Lubricants 164
A-2 Chemicals Commonly Used in Drilling Fluid Surfactants 166
A-3 Chemicals Commonly Used in Drilling Fluid Emulsifiers 166
B-l Comparable Drilling Fluid Products by Tradenames 172-180

Figure

1 Drilling Fluid Circulation System 15
2 Idealized Jet Discharge 52
3 Variance as a Function of Time in Dye Diffusion
Experiments 5
4 Barium Concentration as a Function of Transport Time 59
5 Relationship Between Current Speed, Particle Diameter,
and Sediment Erosion, Transport, or Deposition 68

xii

Summary, Conclusions, and Recommendations

The discharges made in drilling outer continental shelf (OCS) oil and
gas wells have recently been the subject of research and public debate
with regard to their potential effects on the marine environment. A
lack of scientific consensus about the physical fates and biological
effects of these discharges has led to actions contesting the permit-
ing of some drilling discharges. At the request of the U.S.' Department
of the Interior, the National Research Council convened the Panel on
Assessment of Fates and Effects of Drilling Fluids and Cuttings in the
Marine Environment with the charge of establishing a credible technical
basis for making resource management decisions.
This section presents the panel's summ~ary, conclusions and recoin-
specific findings concerning fates and effects and inadequacies or gaps
in available information. These are noted throughout the report. Many
of these findings represent an incomplete understanding of basic
oceanic or biological processes. The panel has taken these findings
and limitations into account. Those which it considers to be the most
salient and relevant are discussed in this section.

THE USE AND COMPOSITION OF DRILLING FLUIDS

Drilling fluids are required in rotary drilling for oil and gas
exploration and development to remove cuttings from beneath the bit,
to control pressure in the well, to cool and lubricate the drill
string, and to seal the well. There are no alternatives to using
drilling fluids in this rotary drilling. Although drilling fluids are
recirculated during drilling and sometimes can be held and reused in
drilling multiple production wells, eventually they must be disposed
of because of their contamination with suspended material or their
loss of important properties or because of weight and space
limitations on drilling vessels. Cuttings from the formation drilled
are removed from the drilling fluid and must also be disposed of.
Although drilling discharges can be barged ashore or to other sites at
sea for disposal, cost and operational considerations favor onsite

disposal, by either overboard discharge or shunting through a pipe to
some depth. Land disposal is now required for certain drilling fluids
(for example, oil-based drilling fluids), and in certain state waters
(for example, some state waters of California and Alabama).
Drilling fluids used on the OCS are composed of bulk constituents
and special purpose additives. The principal bulk constituents are
water, barite (barium sulfate), clay minerals, chrome lignosulfonate,
lignite, and sodium hydroxide. All of these constituents are nontoxic
to marine organisms at the dilutions reached shortly after discharge.
There is limited information on the compositions and quantities of
additives in used fluids discharged on the OCS. Several common drill-
ing-fluid additives, including biocides and diesel fuel (No. 2 fuel
oil), are much more toxic to marine organisms than the bulk constit-
uents.
Approximately two million metric tons (dry weight) of drilling-
fluid components are discharged annually on the U.S. OCS, more than 90
percent of this amount in the Gulf of Mexico. Corresponding figures
in the future will depend on government leasing policies, successes in
exploration, and economic factors, but in the near future most drilling
discharges are likely to occur in the Gulf of Mexico and of f southern
California and Alaska. Compared to the mass emissions of river sedi-
ments and those of municipal wastes and dredged material, the quantity
of drilling fluids discharged in the ocean is small. For example,
total particulate loading in the Gulf of Mexico from drilling fluids
represents about I percent of that from the Mississippi River. Annual
discharges of dredged material, of sludge, and of industrial wastes in
U.S coastal waters exceed those of drilling fluids.

THE CHEMICAL TOXICITY OF DRILLING FLUIDS

The first step in evaluating a material's potential harm to marine
organisms and ecosystems is usually the acute lethal bioassay.* In
this kind of test, organisms are exposed to graded concentrations of
the material. Mortalities are recorded, and on the basis of these
data the concentration causing 50-percent mortality after a predeter-
mined exposure time (usually 96 hours) is estimated statistically and
recorded as the median lethal concentration (LC5O).
More than 96 percent of the whole drilling fluids tested in short-
terra experiments (from 44 to 144 hours) have LC5O values greater than
1,000 ppm and are classified as "slightly toxic" or "practically non-
toxic" by the IMCO et al. (1969) characterization of toxicity (see
Chapter 4). More than 98 percent of the tests that have used the
suspended particulate phase of drilling fluids found their LC50 values
greater than 10,000 ppm (in the range of "practically non-toxic").

*A bioassay is a quantitative determination of the concentration
of a substance by its effect on an organism under controlled
conditions.

This distribution of toxicities, representing over 70 drilling fluids
and more than 60 species of marine organisms, indicates that most
water-based drilling fluids are relatively nontoxic.
Fewer than 4 percent of the tests of whole fluids and only 2
percent of those using the suspended particulate phase found the sub-
stances "moderately toxic,' that is, having LC50 values between 100 and
10,000 ppm. Most of this toxicity is probably attributable to the use
of diesel fuel (No. 2 fuel oil) in the drilling fluids, but the fluids
tested for toxicity have not always been fully analyzed chemically.
Acute toxicity bioassays are only the first step in hazard assess-
ment. The results of these tests indicate the relative toxicities of
used drilling fluids and the relative sensitivities of different
species. They do not, for example, indicate sublethal signs of stress.
Nor have such tests reproduced the exposure levels and intervals that
characterize the dispersing plumes of discharged drilling fluids in the
field.
Drilling fluids have recently been used in tests of sublethal
toxicity. Such tests have measured changes in the growth and develop-
ment of organisms in embryonic and larval stages and changes in the
behavior of adults. In most cases, these effects are observed at con-
centrations of 10 to 1,000 ppm, about one-to-two orders of magnitude
below LC5O values determined in acute bioassays. Expressed as an
application factor of chronic to acute ratios, most species fall above
a factor of 0.22; the highest ratio observed was 0.033. Unfortunately,
the experimental designs of the tests of sublethal toxicity have also
relied on exposure regimes that do not simulate the rapid dispersion
of discharged drilling fluids or their movement along the bottom as
measured in the field. Thus, hazard assessments using these biological
data must extrapolate from them; yet there are no well-established
relationships between responses and exposure intervals. The results
of benthic microcosm experiments are also difficult to interpret. In
these tests, responses to the chemical properties of drilling-fluid
solids have not routinely been isolated from responses to physically
altered substrates.
Predicting the effects of marine organisms' accumulation (through
bioaccumulation) of substances in drilling fluids have relied on
measurements of total tissue and body burdens and have not considered
the organisms' mechanisms for sequestering and detoxifying contami-
nants. Nor have they taken into account whether contaminants are
present at intracellular sites of toxic action. Furthermore, the
potential increase of accumulated contaminate body burdens with
increasing trophic levels has not been addressed, although research on
other discharges containing the same metals suggests that the metals
commonly found in drilling discharges are not biomagnified. The
potential for biomagnification may be greater for organic compounds or
organic complexed metals.
In toxicity tests, organisms from any one OCS region appear to be
no more sensitive to drilling effluents than comparable ones from any
other region, indicating that test results usually may be applied from
one region to another. In addition, some nearshore organisms have

shown sensitivities to drilling effluents similar to those exhibited
by morphologically similar species from offshore areas; also, some
species that have been tested are found both near and offshore. These
results suggest that some nearshore species are appropriate surrogates
for testing the effects of drilling effluents. It is desirable to
tailor drilling-fluid regulations to take account or advantage of
environmental conditions or to protect sensitive or valuable habitats,
but there is no evidence that justifies different regulatory policies
concerning the use of drilling-fluid additives in different geographic
regions.

THE PHYSICAL PATES OF DRILLING FLUIDS

Discharges of drilling fluids and cuttings into OCS waters take place
in a wide range of marine environments, which vary greatly in water
depth, ice cover, tidal and nontidal currents, waves, geological
history, land runoff, and biotic characteristics. Thus, the physical
fates of dischar~ged drilling fluids and cuttings vary greatly.
On the continental shelf, approximately 90 percent of the parti-
cles in discharged drilling fluids, and almost all of the cuttings,
settle rapidly, passing through a stage of convective descent until
encountering the seabed or becoming neutrally buoyant. In addition to
the main, or lower plume, a visible or upper plume is also formed.
Most observations of water column fate have focused on the upper plume
and on the dispersion of dissolved components. Based on observations
of upper plumes, the plumes spread out at some depth appropriate to
density characteristics and are rapidly dispersed by the turbulent
diffusion characteristic of the ocean. Horizontal turbulent diffusion
results in dilution of the plumes by a factor of 10,000 or more within
an hour of release and even greater dilution of suspended components
because of settling.
Although dilution may be inhomogeneous at thermoclines or
pycnoclines, the high dilutions predicted in mathematical models take
Place in the field. Theoretical considerations and empirical observa-
tions yield the same values for dispersion rates in the water column.
Given such rapid dilution within tens of meters of the discharge, toxic
responses in organisms in the water column would be anticipated only
if short-term exposures (of around one hour) result in acute effects
at concentrations lower than 100 ppm. Although very few short exposure
experiments have been conducted, longer term experiments (over 96
hours) have seldom identified lethal or sublethal effects at concentra-
tions less than 100 ppm. Direct assessments of the effects on plankton
and nekton in the water column have not been attempted and, given
natural variability and the difficulty of sampling, are probably not
feasible. Thus, even sublethal effects on pelagic biota moving past
the point of discharge are confined to a very small area (within tens
of meters) around the point of discharge. This finding suggests that
restrictions on the dilutions or rates of discharges are not justified
in most OCS areas.

At most depths typical of the continental shelf the majority of
discharged fluids and cuttings are initially deposited on the seabed
within 1,000 meters of the point of discharge. This material may
persist as initially deposited or may undergo rapid or prolonged dis-
persion, depending on the energy of the bottom boundary layer. In
high-energy environments, such as the tidally active Lower Cook Inlet
in Alaska, the resuspensive and tractive dispersion of sedimented
materials will take place very quickly. in relatively quiescent
environments this dispersion will be slow and the fluids and cuttings
may be physically or chemically detectable for a number of years.
Storm events on the continental shelf probably control the accumulation
of fluids and cuttings as much as any other environmental factor. In
any case, the ultimate fates of the deposited materials depend on
processes acting after deposition, which have not been treated in the
conventional plume dispersion models.
The effects of drilling fluids and cuttings on benthic habitat,
communities and organisms may be physical (burial or substrate change)
and chemical (toxicity). In practice, it is difficult to separate
physical and chemical effects based on either field surveys or labora-
tory experiments. Most laboratory experiments on the effects of
drilling fluids on benthic organisms have not been very successful in
mimicking realistic exposure conditions. Effects on benthos have been
observed in the field, under low to moderate energy regimes, within
1,000 meters of the discharge point. Only one study has yet described
environmental changes over time after drilling operations ceased; while
the fauna had been altered, recovery was nearly complete within one
year. Because the effects of drilling discharges are probably largely
physical, recovery times should be similar to those following other
physical seabed disturbances. These times vary widely; recovery may
take weeks in frequently disturbed shallow-water communities, several
months to several years in continental shelf communities, and many
years on the continental slope and in deep sea. The resuspensive
transport of deposited drilling-fluid components may produce effects
beyond the area of immediate burial, but at the same time it reduces
the concentrations of potentially toxic substances. As the material
disperses, organisms that feed at the sediment-water interface may
nonetheless be exposed to higher concentrations of such substances than
bulk analysis of sediments would suggest.
Shunting drilling discharges to the near-bottom, as an alternative
to surface disposal, may increase the exposure of benthic organisms to
wastes. It may be effective, however, in restricting wastes from
topographic rises with sensitive biota like reef corals. In contrast,
surface discharges ensure dispersion and limit the duration and amount
of organism exposure. Predilution of such discharges is generally
unnecessary given the speed with which they are diluted, except
possibly in low-energy or shallow-water environments.
The long-term benthic effects of drilling discharges from multiple
wells during intensive exploration or development are difficult to
distinguish from the effects of other discharges and activities
(including oil and gas production) on the continental shelf and from

natural variations. Comprehensive studies of these various effects are
not available. Results of platform monitoring studies have demon-
strated spatially limited effects on the benthos. However, these
effects cannot be directly ascribed to discharges of drilling fluids.
Long-lived communities, which are characteristic of hard substrate
epibiota, may be particularly susceptible to long-term effects if they
are exposed to large concentrations of deposited fluids and cuttings,
but many of these communities are not very likely to accumulate such
materials unless the materials are deposited directly on them.

CURRENT KNOWLEDGE OF DRILLING-FLUIDS FATES AND EFFECTS

The information base for assessing the fates and effects of drilling
discharges in OCS waters has some notable deficiencies, many of which
pertain equally to the effects of other pollutants in the coastal
ocean. These deficiencies include variable quality of research, limits
to the realism and relevance of laboratory experiments, difficulties
in unequivocally ascribing effects observed in field studies to given
causes, and a poor understanding of ecosystem processes. These limi-
tations do not invalidate most of the results that have been produced,
but must be taken into account in interpreting them. Our knowledge of
the fates and effects of drilling fluids and cuttings is not notably
inferior to that of the fates annd effects of dredged materials and
other wastes dumped in the ocean, even though the latter have been
studied considerably longer.
Our understanding of the fates and effects of drilling discharges
in the marine environment is limited more by the state of our general
understanding of marine pollution than by specific deficiencies in our
knowledge of drilling fluids and cuttings. Our understanding of this
narrow problem may be advanced most rapidly by conducting research on
the broader topics of the accumulation and transfer of materials in the
marine environment. With this understanding of where research emphasis
should be placed, the panel concludes that extensive further research
focused specifically on the fates and effects of drilling fluid dis-
charges is not needed.
Any additional research on drilling fluids should include acute,
sublethal, and chronic bioassays using techniques and contaminant
exposures that reflect actual discharge and exposure conditions, field
studies that take into account inventories and chemical analyses of
discharges, and studies of resuspensive transport of particulate
contaminants.
The panel's review of existing information on the fates and
effects of drilling fluids and cuttings on the OCS shows that the
effects of individual discharges are quite limited in extent and are
confined mainly to the benthic environment. These results suggest that
the environmental risks of exploratory drilling discharges to most OCS
communities are small. Discharges from oil and gas field development
drilling introduce greater quantities of material into the marine
environment over longer periods of time. Results of field studies

suggest that the accumulation of materials from these longer-term
inputs is less than additive and therefore the effects of exploratory
drilling provide a reasonable model for projecting the effects of
development drilling. Uncertainties regarding effects still exist for
low energy depositional environments, which experience large inputs of
drilling discharges over long periods of time.
To minimize effects, care needs to be exercised in the following:

* Discharges should be prevented from burying particularly
sensitive benthic environments, especially hard substrate epibiota,
which are not exposed to significant natural sediment flux.
* The use of more toxic additives, such as diesel fuel (No. 2
diesel oil), should be monitored or limited. Fluids that show signi-
ficant toxicity should be analyzed chemically to determine their toxic
components.

Introduction

This report seeks to answer two questions:

* Are drilling fluids and cuttings as they are released into the
outer continental shelf (OCS) toxic to marine organisms or do they
cause deleterious sublethal responses in these organisms that may
adversely affect the ecosystem, or are they innocuous?
*Are the heavy metals or organic materials in drilling fluids
or cuttings bioaccumulated or biomagnified so that they are harmful to
organisms or to those who consume them, including man?

Chapter 2 of the report, "Drilling Discharges," provides an over-
view of offshore drilling, and of the use, composition, and chemistry
of drilling fluids and cuttings. It describes the regulation of drill-
ing discharges and examines the quantities and frequencies of these
discharges and their components in relation to other inputs to the
marine environment.
Succeeding chapters review what is known about the fates and
effects of drilling fluids and cuttings in the marine environment.
Chapter 3, "The Fates of Drilling Discharges," discusses the transport
forces of the ocean, the behavior of dissolved and particulate
materials in seawater, and the physical fates of drilling fluids and
cuttings in the marine environment. Chapter 4, "Biological Effects of
Drilling Discharges," summarizes and critically evaluates the scien-
tific literature on the toxicities of drilling fluids and on the
impacts on OCS ecosystems of discharging used drilling fluids and
cuttings.
After reviewing the available information on these topics the
report discusses the limitations in using this information for decision
making. Chapter 5 reviews the adequacy and applicability of the
available information. It reviews considerations in conducting and
interpreting laboratory evaluations of toxicity and field studies,
problems of extrapolating from laboratory to field and between geo-
graphic regions, and the topics of bioaccumulation and the long-term
fates and effects of drilling discharges.
The final chapter considers the operations, cost, and risk of
disposing drill discharges overboard.
The conclusions and recommendations of the panel appear in the
summary.

Drilling Discharges

OFFSHORE OIL AND GAS DRILLING AND DEVELOPMENT

Since 1947 nearly 22,000 wells have been drilled on the OCS in
exploring for and developing oil and gas resources. Table I indicates
that those in the Gulf of Mexico (offshore' Florida, Louisiana, and
Texas) account for 83.2 percent of all offshore wells; those offshore
Louisiana alone account for 73.3 percent. Two-thirds of all offshore
wells (67.1 percent) have been drilled in federal waters, although this
percentage varies widely by geographic region, from 100 percent in the
offshore Atlantic to 5 percent offshore Alaska. Exploratory wells
account for 24.6 percent of the wells in federal waters and for 23.2
percent of those in state waters. These figures also vary widely by
region: all wells drilled in the Atlantic, where there have been no
commercial discoveries, have been exploratory; 91.2 percent of wells
drilled offshore California, where offshore development began in the
1890s, have been development wells.
OCS oil and gas production now accounts for 8 percent of domestic
oil production and 24 percent of domestic gas production (Minerals
Management Service, 1982). The U.S. Geological Survey estimates that
as much as 41.3 percent of the nation's undiscovered recoverable oil
and 28.1 percent of its natural gas lie offshore (Dolton et al., 1981).
In the future, major new discoveries of oil and gas are more
likely to occur offshore than on land, because the OCS has been less
completely explored. Such large discoveries, like those recently made
offshore California and Alabama, are also more cost-effective to
develop than multiple smaller discoveries (which characterize the
majority of past Gulf of Mexico developments). Thus, the sites of
future oil and gas development are likely to be those areas that have
not yet been thoroughly explored, and that have geologic potential for
large accumulations of oil and gas (Edgar, 1983). Offshore Alaska is
one area that meets these criteria. By 1990, 22 percent of domestic
oil is expected to come from future discoveries, 45 percent by the year
2000 (Palmer and Kelly, 1983).

'The term "offshore" is used in this report to refer to state and
federal offshore lands together, "OCS" to federal lands only.

TABLE 1 Offshore Wells in the United StatesArb

Exploratory Development Total

Alaska
State 80 281 361
Federal 19 - 19
Total 99 281 380

California
State 161 3,185 3,364
Federal 145 299 444
Total 306 3,484 3,790

Oregon
Federal 8 - 8

Washington
State 2 - 2
Federal 4 - 4
Total 6 6

Florida
State 15 - 15
Federal 9 - 9
Total 24 24

Louisiana
State 977 2,904 3,881
Federal 3,186 12,134 15,320
Total 4,163 15,038 19,201

Texas
State 762 252 1,014
Federal 888 656 1,544
Total 1,650 908 2,558

Atlantic
Federal 21 - 21

Total
State 1,997 6,622 8,619
Federal 4,280 13,089 17,369
State and federal 6,277 19,711 25,988

aCumulative through 1981. New wells are now drilled on the OCS at the
rate of approximately 1,000 per year.
bOffshore wells are defined as those beyond natural shorelines.

SOURCE: Adapted from American Petroleum Institute (1982).

CHARACTERISTICS AND FUNCTIONS OF DRILLING FLUIDS

Commercial oil and gas exploration and production wells an the OCS are
drilled with rotary equipment. In rotary drilling, the well is drilled
by a rotating bit to which downward force is applied. The bit is
fastened to and rotated by a hollow drill stem made of pipe, through
which drilling fluid is circulated.
Drilling fluids are essential to drilling operations, performing
the following major functions :2

0 Removing cuttings from beneath the bit and transporting them
to the surface where they can be separated from the drilling fluid for
disposal
* Preventing formation fluids from flowing into the wellbore by
maintaining a hydrostatic pressure in excess of the fluid pressure in
the formation
* Coating the borehole wall with an impermeable filter cake to
prevent fluid loss in permeable formations
* Having sufficiently high gel properties to suspend cuttings
and fluid solids when circulation is interrupted
* Helping to support the weight of the drill string
* Lubricating and cooling the drill bit and drill string
a Having properties that do not interfere with the accurate
geological evaluation of the formation or the production of
oil and gas.

Drilling fluids are classified as either water-based or oil-based,
depending on their principal liquid-phase component. Consistent with
the scope of this report, this section is concerned with water-based
drilling fluids.

2In completing wells for production and in workover operations
(periodic maintenance) special fluids may be used:

* A packer fluid may be placed in the well to counter formation
pressures over a long period of time.
* in workover operations, special drilling fluids may be circu-
lated continuously for the limited duration of the operation.
* Special fluids may be used in stimulation procedures such as
fracturing. (In this operation, fluids can sometimes be displaced into
the formation. The potential for their discharge exists when the well
is returned to production.)

Some fluids used in these operations, such as seawater, are
innocuous and discharged routinely. others are oil-based and disposed
of onshore or are fluids containing high concentrations of soluble
salts (e.g., CaCl2/CaBr2 and CaCl2/CaBr2/ZnBr2)' These
discharges are quite small relative to other drilling discharges and
are beyond the scope of this report.

A schematic diagram of a drilling fluid circulation system is
shown in Figure 1. The fluid's components are added through the hopper
and mixed in the tanks. The fluid is then pumped from the tanks down
the drill string and through the bit. It sweeps the crushed rock
cuttings from beneath the bit and carries them back up the annular
space between the drill string and the borehole or casing to the
surface. This permits drilling to continue and is the fluid's most
important function.

DISCHARGES OF DRILLING FLUIDS3

After the drilling fluid has circulated through the well and has
returned to the surface, it is passed through solids control equipment
to remove the formation drill solids (Cuttings). The solids control
equipment is an integrated system that consists of shale-shaker
screens4 that remove the coarse particles and hydrocycloness that
remove the sand and silt fractions from the fluid. The drill solids
separated by the solids control equipment are discharged to the ocean.
This type of discharge is continuous in that it occurs while drilling
is in progress. Typically, these discharges occur about half the time
the rig is on location.
The rates of this type of discharge vary from about 1 to 10
bbl/h6 (Ayers, 1981). The higher number is more characteristic of
the shallow part of the hole when drilling is fast and the bit diameter
is large. Over the life of a well, some 3,000 to 6,000 bbl of wet
solids are discharged from the solids control equipment (Ayers, 1981).
After the fluid passes through the solids control equipment and
the solids are separated, it is returned to the tanks for
recirculation. At this point another type of discharge may be
required. The solids control equipment cannot remove the fine clay

3This section presents information on discharges from wells. A
discussion of mass loading--cumulative discharge quantities--appears
in the the final section of this chapter.

4A series of trays with sieves that vibrate to remove cuttings
from the circulating fluid. The size of the openings in the sieves is
selected to match the size of the solids in the drilling fluid and the
anticipated size of cuttings (Petroleum Extension Service, 1979).

'A centrifugal device used to remove fine particles of sand from
drilling fluid. it operates on the principle of a fast-moving stream
of fluid being put into a whirling motion inside a cone-shaped vessel
(Petroleum Extension Service, 1979).

6A measure of volume for petroleum products. one barrel (bbl)
equals 42 U.S. gallons. one m3 equals 6.2897 bbl (Petroleum
Extension Service, 1979).

Constituents
0 Barite � Lignite
Bentonite 0 Caustic
Hopper * Lignosulfonate * Water
7.bTank * Specialty Additives

T Pump * Drill String

I ~' I
Bulk Discharge To Ocean
� Intermittent
* 100-1000 bbl/discharge
� 500-2000 bbl/hr ,
� 5000-30,000 bbl/well . I ---- Casing
- Annular Space

IT C41--Bore Hole

fargee To ' 41-<~~~~~~~~~~ - -- Formations

Solids Control Equipment Discharges To Ocean Solids Control Equipment T
* Continuous During Actual Drilling � Shale Shakers
* 1-10 bbl/hr * Desanders - Bit
* 3000-6000 bbl/well * Desilters

Source: Ayers, 1981.
Y Drill Solids

FIGURE 1 Drilling Fluid Circulation System

and colloidal particles7 that are generated in drilling through for-
mations. As the fluid is recirculated the concentration of these fine
particles continues to increase and eventually the fluid becomes too
viscous for further use. At this time, a portion of the fluid is dis-
charged and the discarded volume is replaced with water and appropriate
quantities of additives to bring the concentration of fine solids back
to an acceptable level. This method of reducing the fine solids in the
system is called "the dilution method." Less frequently, bulk dis-
charges are made when the type of fluid needs to be changed as when
the bit will be penetrating a particular formation or when the
rheological properties of the fluid become altered. (The chemistry of
drilling fluids is discussed below.) It is also necessary to
discharge the entire fluid system at the end of drilling each
exploratory well, and sometimes after drilling development wells.
Bulk discharges occur only intermittently. Their volumes normally
range from 100 to 1,000 bbl per discharge (Ayers, 1981). A small
volume, 100 to 200 bbl, is usually discharged every I to 3 days (Ayers,
1981). A discharge of 1,000 bbl is typical on completing a well or
when the fluid system must be changed for some reason.
The rate of bulk discharges ranges from 500 to 2,000 bbl/h (Ayers,
1981). Over the life of an exploratory well, some 5,000 to 30,000 bbl
of fluid are discharged (Ayers, 1981). Because development wells are
normally shallower, smaller in diameter, and require less time to drill
than exploratory wells, less fluid is discharged in drilling them.
The volume of fluid discharged ranges widely. The dilution method
is an efficient way to control the concentration of colloids and fine
particles in low-density fluids, which contain a minimum of barite and
additives. (These fluids are adequate for shallow drilling through
competent rock formations.) Discharge volumes will usually be high for
this type of system, since the bulk of the material discharged is water
and the fluids cost is low. On the other hand, high-density drilling
fluids have appreciable quantities of barite and additives, and are
expensive. For economic reasons, it is desirable to minimize the bulk
discharge of these fluids. This is accomplished by the more extensive
use of solids control equipment and by increasing the concentration of
chrome lignosulfonate to deflocculate the fine clay particles and to
reduce fluid viscosity. Thus, the discharge volumes of such
high-density fluids are low compared to those of less expensive
low-density systems.
The variation in quantity of discharged material from well to well
is much less if one considers only the quantity of solids--everything
but water--that is discharged. About 1,000 m3 (2,000 tons) of dry
solids (formation solids and fluid additives) are discharged both in
bulk and from solids control equipment over the life of a typical

7A colloid is a liquid mixture in which the particles of one
substance are dispersed in another in a continuous phase without being
dissolved. The size of colloidal particles is in the approximate
range of 10-5,000 Angstroms (Adam, 1956).

exploratory well (Ayers, 1981). The quantity of discharges from
development wells is likely to be as much as 25 percent less than that
of discharges from exploratory wells (Ayers, 1983). Fluid components
account for about half the quantity of discharges in dry weight and
formation solids for the other half.

THE COMPOSITIONS OF DISCHARGES

The discharges from solids control equipment and those made in bulk
have different compositions. The first contain primarily formation
solids, and the second fluid components. Table 2 gives the mineral
composition of a shale-shaker discharge. This sample and others dis-
cussed below are representative of solids discharges from drilling
operations in that the primary constituents are naturally occurring

TABLE 2 Mineral Composition of a Shale-Shaker Discharge From a
Mid-Atlantic Wella

Mineral Percentage by Weight (Dry Basis)

Barium Sulfate 3

Montmorillonite 21

Illite 11

Kaolinite 11

Chlorite 6

Muscovite 5

Quartz 23

Feldspar 8

Calcite 5

Pyrite 2

Siderite 4

a-iSixty-five percent solids, density 1.7 g/cm3.

SOURCE: Adapted from Ayers, Sauer, Meek, and Bowers (1980).

clay and quartz minerals. This sample was obtained from a well drilled
in the mid-Atlantic region, about 100 miles East of Atlantic City, New
Jersey. The small amount of barium sulfate results from barite parti-
cles that have adhered to the cuttings particles. The montmorillonite
clay comes from both added bentonite and from formation clays. The
remaining material represents the formation being drilled at that time
and consists primarily of clays, quartz, and low concentrations of
calcite, pyrite, and siderite. This particular shale-shaker sample
contained 65 percent solids and 35 percent water. The amount of water
in these discharges ranges from 20 to 50 percent.
The compositions of drilling fluids vary with both the depth and
the location of the well. In the shallow portion of the hole the fluid
used usually consists of low concentrations of bentonite and sodium
hydroxide in seawater ("spud mud"). As hole depth increases, the
system may be converted to fresh water with more bentonite, lignite,
lignosulfonate, and barite added. Also, if problems in drilling occur,
specialty chemicals may be required (see Table 6). The vast majority
of fluids discharged on the OCS are like the two compositions shown in
Table 3. One is a low-density and the other a high-density fluid. The
high-density sample represents the final composition of the fluid used
in a well in the Gulf of Mexico, and the low-density one represents a
fluid used in the late stages of drilling a mid-Atlantic well. The
high-density fluid weighs 2.1 g/cm3 and contains 62 percent barite

TABLE 3 Representative Fluid Compositions

Concentration (wt%)

Low Density aHigh Densityt
Component (1.19 g/cm ) (2.09 g/cm3)

Barite 15.0 62.0
Low gravity solids 6.5 5.9
Chrome lignosulfonate 1.0 0.9
Lignite 1.0 0.9
Inorganic salts 0.7 0.5
Water 75.8 29.8

a pH 11.4.
b pH 12.4.

SOURCE: Adapted from Ayers (1981).

and 30 percent water. The low-density fluid weighs 1.2 g/cm3 and
contains 15 percent barite and 76 percent water. The concentrations
of other ingredients in the two fluids--low-gravity solids, chrome
lignosulfonate, and lignite--are similar. The low-gravity solids are
bentonite clay and formation solids.
Trace metals in drilling discharges originate from both formation
solids and fluid additives. Representative metal concentrations for a
shale-shaker sample and a fluid sample are shown in Table 4. These
samples were taken from a well in the mid-Atlantic. The presence of
barite causes the barium concentration to be much higher than that of
any other metal. Chromium also occurs in concentrations higher than
those normally seen in formation solids or sediments. The chromium
comes from the additive chrome lignosulfonate. Both barium and
chromium concentrations are higher in the fluid than in the shale-
shaker sample because these metals come from fluid additives, and only
a small quantity of fluid additives adheres to the cuttings when they
are screened out.8 The other metals shown in Table 4 are present in
concentrations comparable to those normally found in formation solids
or sediments.

COMPONENTS OF WATER-BASED DRILLING FLUIDS

Five major components (barite, clays, lignosulfonate, lignite, and
caustic soda) account for over 90 percent of the solid components of
water-based drilling fluids (Perricone, 1980), as is illustrated in
Table 5. Appendix A provides a review of the functional components of
drilling fluids. These five components and water account for over 98
percent of the mass (or volume) of drilling fluid discharged to the
OCS. These components, in decreasing order of use, are the following:

* Barite, a mineral containing 80 to 90 percent barium sulfate,
which is used to increase the density of the drilling fluid to control
formation pressures. In some cases, concentrations as high as 700
lb/bbl may be used. Depending on its source, barite may contain low
concentrations of quartz, chert, silicates, and other minerals and also
trace levels of metals.
* Bentonite, the clay most commonly used in drilling fluids.
Sodium montmorillonite clay in concentrations of 60 to 80 percent is
the predominant ingredient. Silica, shale, calcite, mica, and feldspar
are common impurities in bentonite deposits. Bentonite is used to
maintain the rheological properties required to remove the cuttings
from beneath the bit and carry them to the surface. Bentonite also

'The quantity of additives that adheres to cuttings depends on
the depth of water in which the cuttings are discharged (residence
time), and the mixing energy of the water column. As much as 20
percent of additives may adhere to cuttings in a shallow water, low
energy environment.

TABLE 4 Representative Metal Compositions

Concentration (mg/kg)
Metal Shale Shaker- Fluidb

Barium 3,160 37,400
Chromium 44 191
Cadmium <2 <1
Lead 10 3
Mercury <1 <1
Nickel 15 4
Vanadium 11 5
Zinc 80 50

a 77.1 percent solids, 1.9 g/cm3.
b 21.0 percent solids, 1.16 g/cm3.

SOURCE: Adapted from Ayers, Sauer, Meek, and Bowers (1980).

TABLE 5 Drilling Fluid Components and Additives Used in the
United States

Component Percentage of Total

Barite 63.0

Clays 24.0

Lignosulfonate 2.0

Lignite 1.5

Sodium hydroxide 1.5

Other additives- 8.0

aSpecial additives to oil-based drilling fluids are included
in this estimate.

SOURCE: Adapted from American Petroleum Institute (1978).

prevents fluid loss by providing filtration control while drilling
through permeable zones. The concentration of bentonite in drilling
fluids normally ranges from 5 to 35 lb/bbl.
� Lignosulfonates, which are normally used in drilling fluids in
concentrations ranging from 1 to 15 lb/bbl. Lignosulfonates are
derived from the sulfite pulping of wood chips to produce paper and
cellulose. Chrome lignosulfonates, the most widely used deflocculant
in drilling fluids, are prepared by treating lignosulfonate with sul-
furic acid and sodium dichromate. Sodium dichromate oxidizes the
lignosulfonate and cross-linking occurs. Hexavalent chromium intro-
duced by the chromate is reduced during the reaction to the trivalent
state and complexes with the lignosulfonate. Lignosulfonates control
viscosity in water-based drilling fluids by acting as thinning agents
or deflocculants for clay particles. The chrome appears to bind onto
the edges of clay particles at high downhole temperatures, reducing the
formation of colloids (Skelly and Dieball, 1970).
� Lignite (soft coal) which is used in drilling fluids as a clay
deflocculant and to control filtration rate. The concentration of
lignite in drilling fluids normally ranges from 1 to 15 lb/bbl. Most
of the drilling-grade lignite, leonardite, is mined in North Dakota.
The chief constituent of this naturally occuring oxidized lignite is
humic acid.
* Sodium hydroxide (caustic soda), which is normally used in
drilling fluids in concentrations sufficient to maintain a pH of 9 to
12. A pH greater than 9.5 is needed to obtain maximum deflocculation
from the chrome lignosulfonate and to keep lignite in solution. A
basic pH also lowers corrosion rates and provides protection against
possible hydrogen sulfide contamination by suppressing microbial
growth.

A large number of other additives are available for use in water-
based drilling fluids (American Petroleum Institute, 1978). These
additives, which have been formulated to meet specific needs, range in
complexity from simple inorganic salts to organic polymers of high
molecular weight. Typically, only a few are used on any one well, and
they are used in low concentrations (Moseley, 1981). Table 6 gives the
operating objectives of the most frequently used and environmentally
significant additives in water-based drilling fluids, and indicates
their ranges of concentration and frequencies of use.
Water-based drilling fluids and drill cuttings sometimes contain
quantities of hydrocarbons (usually diesel fuel [No. 2 fuel oil]) in
greater than trace amounts. This occurs when diesel fuel is added to
the fluid system to reduce torque and drag. As much as 2 to 4 percent
diesel may be added to the bulk fluid system to improve lubricity (a
relatively common operating practice in the Gulf of Mexico). A
standard technique for freeing the drill pipe should it become stuck,
is to pump a "pill" of diesel fuel or oil-based drilling fluid down
the drill string and "spot" it in the annulus area where the pipe is
stuck. The pill may or may not be kept separate from the bulk drilling
fluid system, recovered, and disposed of onshore. Even when the pill

TABLE 6 Special Additives and Their Uses

Additive Operating Objective Concentration Frequency of Usea
(lb/bbl)

Sodium bicarbonate Eliminate excess calcium ions 0.1-4 Very common
due to cement contamination
by precipitating calcium as
calcium carbonate.

Sodium chloride Minimize borehole washout in 10-125 Rare
salt zone by preventing
dissolution of salt formation.

Ground nut shells, mica, Minimize loss of drilling fluid 5-50 Common
or cellophane to the formation by adding
material to plug the "thief"
zone.

Cellulose polymers or Counter thick, sticky filter 0.25-5 Very common
starch cake; decrease filtrate loss
to formation.

Aluminum stearate or Minimize foaming. 0.05-0.1 Common
alcohols

Sodium chromate Reduce viscosity increase 0.1-2 Rare
in high temperature wells; aid
deflocculation of lignosulfonate.

Diesel, vegetable, or Reduce torque and drag on the 2-50 Common
mineral oil lubricant drill string by preventing it
from sticking.

Pill of oil-based Counter differential pressure 100-300b Common
spotting fluid sticking of drill string. (Pill
is placed downhole opposite
contact zone to free pipe. After
pipe is free, the oil-contaminated
mud is collected and may or may not
be discharged to the ocean depending
on operational circumstances.)

Paraformaldehyde Retard bacterial degradation in 0.2-2 Very common
bactericide polymer starch fluid systems;
prevent casing string corrosion 0.2-2 Very common
in development drilling when added
to fluid left behind the casing.

Zinc compounds Counter hydrogen sulfide contami- 0.5-5 Common
nation by precipitating sulfides.

Potassium Chloride Prevent shale swelling and 20-95 Rare
sloughing; improve wellbore
stability.

Biopolymer Provide viscosity in drilling fluids 0.2-2 Rare
with high salt concentrations.

AsbestosS_ Improve solids-carrying capacity; 1-10 Very rare
lift formation drill solids out
of the hole.

a Characterizations are expert judgments, based in part on the quantities of additives sold in
1978 and the concentrations of additives used.
b Concentration of oil in the pill of fluid.
C The use of asbestos is prohibited in most OCS regions under EPA's NPDES program.

SOURCE: Adapted from American Petroleum Institute (1978) and Moseley (1981).

is recovered, a small amount of diesel fuel from the pill may become
mixed with the bulk drilling fluid. Discharges of water based drilling
fluids containing diesel fuel are not prohibited in the Gulf of Mexico
Provided the discharge does not cause an oil sheen on the water surface
or an oily sludge on the seafloor.

THE CHEMISTRY OF DRILLING FLUIDS

The chemistry of drilling fluids is complex because of the diversity
of components that may be used and the high temperatures and pressures
that may be encountered at depth. As slurries, drilling fluids have
some attributes of liquids, yet tests used in aquatic chemistry are
often inappropriate for them because of their high solids contents.
To confound the chemists further, soil chemistry procedures are often
not appropriate because of the high water content of drilling fluids.
Further complicating matters, the high temperatures and pressures
encountered in some wells can dramatically affect chemical equilibria.
Water-based drilling fluids are colloids, suspensions of fine
particles in solution. Understanding their chemistry begins with
understanding the behavior of colloidal clays in water. Organic
colloids are also present in drilling fluids, and, like inorganic
colloids, are chemically active. The particle sizes of these chemical
groups are so small that properties like viscosity and sedimentation
velocity are controlled by surface chemistry phenomena. Furthermore,
the surf icial layers of the clay particles, and in some cases organic
molecules, are charged. Clays particularly have high surface area to
volume ratios and therefore high charge to mass ratios. End-to-end,
side-to-side aggregations that form as a result are the basic
mechanisms of flocculation and viscosity, and are essential to under-
standing thinning mechanisms. Gray et al. (1980) provide several good
sections on clay chemistry and discuss colloidal interactions, as does
van Olphen (1977) .
With the exception of electrochemical changes in clays, most
drilling-fluid solids do not undergo chemical changes as a result of
the temperatures and physical conditions that occur in drilling. Even
so, maintaining rheological properties with increasing depth of
drilling is a major technical challenge because of the increased
tendency of clays to flocculate at the higher temperatures encountered.
Carney and Harris (1975) grouped drilling-fluid additives according
to their thermal stability. Their discussion of thermal degradation
of lignosulfonates and the work of Skelly and Kjellstrad (1966) are
important to understanding drilling-fluid chemistry. Clay particles,
which in slurry form provide lubrication, tend to aggregate. To retard
this process, the drilling fluid may be diluted with water if it
contains a minimum of solids; in heavier fluids, chemical thinners like
ferrochrome lignosulfonate may be added (McAtee and Smith, 1969).
Chrome lignosulfonate adsorbs on the edges of clay particles and
prevents them from flocculating (Skelly and Dieball, 1970). At high
temperatures, higher concentrations of chrome lignosulfonate are
required (compare drilling fluids 7 and 8 in Table 7) because the

chrome lignosulfonate undergoes thermal degradation (some polymeriza-
tion occurs in this reaction, releasing carbonates, bicarbonates, and
* ~~sulfates). When the concentration of fine particles becomes so great
* ~~that flocculation can not be controlled through the use of additives,
the drilling fluid must be replaced.

DRILLING-FLUID COMPONENTS AS COMMERCIAL PRODUCTS

The drilling-fluids industry has grown to be a major oilfield service
industry worldwide. Four U.S. companies control approximately 90
percent of the world market. In the United States, smaller companies
are better able to compete and may capture 25 percent of domestic sales
(Escott and Walker, 1981). Each of the four major companies is inte-
grated to the extent that it mines, processes, packages, distributes,
stores, and delivers to the well site the major bulk products (e.g.,
bar ite and bentonite). These companies also provide onsite consulting,
including operating recommendations and product information and

Some of the components of drilling fluids (e.g., caustic soda) are
commodity chemicals widely produced and used. Others are specialty
products developed for and used exclusively in drilling fluids. While
the commodity chemicals do not represent a large number of available
drilling-fluid products, they do represent the major part of drilling
fluid additives by weight and are present in nearly all drilling
fluids.
The significance of the distinction between commodity chemicals
and specialty products relates to the information available on chemical
composition. Chemical information on commodity chemicals is widely
available and usually appears in detail on product containers or tech-
nical data sheets issued by the responsible company. Chemical informa-
tion on specialty products may or may not be as specific, depending on
the product's patent status. Information on patented products and
systems is usually available and in the public domain. Products not
patentable or for which patents have not been issued are usually
described in less chemical detail. However, chemical family names at
least are available, and more specific data may be released if required
for product registration or approval.
If regulated hazardous substances are included in the product,
these compounds will be listed in the required terms on the container,
in the product literature, or on the Material Safety Data Sheet
(Occupational Safety and Health Administration (OSHA) Form 20). Com-
plete information on the composition of bactericides is required under
the Federal Insecticide, Fungicide, and Rodenticide Act. With these
exceptions, however, neither chemical formulas nor manufacturing
processes are described. This allows the manufacturing company to
maintain a stronger market position with regard to a product or system.
The development of drilling fluid products is driven by the same
forces that drive the development of other specialty chemicals--
availability of resources, proven product performance, proven market-
ability, available technology, and favorable return on investment

(McGuire, 1973). Their constraints are similar--competition, changing
markets, government regulations, and customer demands. Drilling-fluid
service companies undertake the majority of product-related research
and development, but much is also performed by major oil companies,
chemical companies, and academic and research institutions. As in the
chemical industry generally (Ashford and Heaton, 1979), government
regulations protecting the health of the worker, the public, and the
environment have caused the development of additional health and safety
data, product substitutions or modifications, and removals of products
from the market. These regulations have prompted the development of
some products that are designed to be not only functional but more
"environmentally acceptable" (Jones et al., 1980), for example, by
substituting mineral or vegetable oil for diesel.
In part because of the numbers of commercial chemicals used in
drilling fluids, drilling fluid companies seek to protect their market
positions through the use of trade names. A list of drilling-fluid
components (Wright and Dudley, 1982) suggests there are thousands of
such components, but the profusion of trade names makes the list con-
siderably redundant (American Petroleum Institute, 1978). Appendix B
lists functionally equivalent products of the four leading drilling-
fluid service companies.

TRENDS IN OPERATING PRACTICES: GENERIC DRILLING FLUIDS

While numerous products are available for use in drilling-fluid
systems (Wright and Dudley, 1982), in practice the number of generic
chemicals (as opposed to trade-name products) is limited. In 1978 the
Offshore operators Committee (OOC) and the U.S. Environmental Protec-
tion Agency (EPA), Region II, capitalized on this uniformity by
developing the generic drilling-fluid concept. Eight basic drilling-
fluid systems were designated that encompass most drilling fluid types
commonly used offshore. These systems are described in Tables 7 and 8
(Ayers, Sauer, and Anderson, 1983). The impetus behind identifying and
using these categories is to address the toxicity of drilling dis-
charges under Sec. 403 of the Clean Water Act by providing EPA with an
understanding of, and control over, drilling-fluid formulations and
discharges without requiring operators to perform redundant bioassays
and chemical tests for every permitted discharge. The concept also has
been adopted in EPA Regions I (for Georges Bank), II (Baltimore Canyon
region), and IX (for California), and is being considered for use in
EPA regions III (mid-Atlantic), IV (eastern Gulf of Mexico), VI
(Western Gulf of Mexico), and X (Alaska).
The eight generic drilling fluids in the tables were identified by
reviewing permit requests in EPA Region II and selecting the minimum
number of fluid systems which would cover all of the prospective
permits. The eight generic fluids contain primarily major components
and do not consider specialty additives. Therefore, lists of fre-
quently used additives have also been developed in each region. EPA
has required that bioassays of both generic drilling fluids and addi-
tives be completed as a condition of their initial approval (see, for

example, Table 9). Drilling operators may use an additive that is not
on the approved list if data are submitted to EPA prior to its use on
its chemical composition, rates of use, and toxicity. Such special
discharges are approved case by case. Once bioassay tests on an addi-
tive have been completed, the additive may be added to the approved
list, provided it does not significantly alter drilling-fluid toxicity
(Jones and Hulse, 1982). All permits provide for "emergency use" of
specialty additives.
Two or three generic drilling fluids may be used in a well. For
example, initial drilling is usually conducted with a spud fluid. As
drilling progresses, increasing amounts of weighting agents and
thinners are added. Thus, one drilling program may call successively
for a spud fluid, a lightly treated lignosulfonate fluid, and then a
lignosulfonate freshwater fluid. Another program may call for a
potassium chloride (KC1) system. This system makes extensive use of
polymers to control viscosity, with bactericides sometimes added to the
system to keep the polymers from degrading (IMCO Services, 1978).
Some generic fluids are saltwater fluids, others are freshwater.
Saltwater fluids, commonly with concentrations of salt greater than
10,000 ppm, are used when drilling salt sections that would collapse
if freshwater fluids were used, when resistivity control is needed,
when drilling through bentonite shales, or when fresh water is not
available in large quantities. The addition of saltwater to freshwater
fluids increases viscosity and reduces gel strength with resulting loss
of fluid. Certain properties are more difficult to maintain in salt-
water than in freshwater fluids. Saltwater fluids require more dis-
persants and deflocculants to control viscosity and to maintain gel
strength. For these reasons, calcium salt or lignosulfonate is
frequently added to them.
Drilling fluids may also be either inhibitive or noninhibitive
(Houghton, 1981). The first does not alter the formation once it is
cut by the bit. In contrast to the simpler noninhibitive fluids, they
inhibit disintegration and retard hydration of drilled solids and
commercial (added) clays, and they stabilize the borehole.
Brief descriptions, drawn largely from IMCO Services (1978),
indicate the natures and utilities of the eight generic fluids
described in Table 7.

1. Potassium/polymer fluids are inhibitive fluids used for
drilling through soft formations like shale where sloughing may occur.
Polymers are used to maintain their viscosity. These fluids require
little thinning with fresh or salt water.
2. Seawater/lignosulfonate fluids are inhibitive fluids that
function well under a variety of conditions. They are thought to
maintain viscosity by binding lignosulfonate cations onto the broken
edges of clay particles, reducing flocculation and maintaining gel
strength. They control fluid loss and maintain borehole stability.
They are easily altered for more complicated downhole conditions,
e.g., higher temperatures.

TABLE 7 Generic Fluid Systems (EPA Region II)

Type of Fluid Components Permissible Content
(lb/bbl)

(1) Potassium/ Barite 0-450
polymer Caustic soda 0.5-3
Cellulose polymer 0.25-5
Drilled solids 20-100
Potassium chloride 5-50
Seawater or fresh water As needed
Starch 2-12
XC polymer 0.25-2

(2) Seawater/
lignosulfonate Attapulgite or bentonite 10-50
Barite 25-450
Caustic soda 1-5
Cellulose polymer 0.25-5
Drilled solids 20-100
Lignite 1-10
Lignosulfonate 2-15
Seawater As needed
Soda ash/sodium
bicarbonate 0-2

(3) Lime Barite 25-180
Bentonite 10-50
Caustic soda 1-5
Drilled solids 20-100
Fresh water or seawater As needed
Lignite 0-10
Lignosulfonate 2-15
Lime 2-20
Soda ash/sodium
bicarbonate 0-2

(4) Nondispersed Acrylic polymer 0.5-2
Barite 25-180
Bentonite 5-15
Drilled solids 20-70
Fresh water or seawater As needed

(5) Spud (slugged Attapulgite or bentonite 10-50
intermittently Barite 0-50
with seawater) Caustic soda 0-2
Lime 0.5-1
Seawater As needed
Soda ash/sodium
bicarbonate 0-2

TABLE 7 (continued)

Type of Fluid Components Permissible Content
(lb/bbl)

(6) Seawater/ Attapulgite or bentonite 10-50
freshwater gel Barite 0-50
Caustic soda 0.5-3
Cellulose polymer 0-2
Drilled solids 20-100
Lime 0-2
Seawatey or fresh water As needed
Soda ash/sodium
bicarbonate 0-2

(7) Lighly treated Barite 0-180
lignosulfonate Bentonite 10-50
freshwater/ Caustic soda 1-3
seawater Cellulose polymer 0-2
Drilled solids 20-100
Lignite 0-4
Lignosulfonate 2-6
Lime 0-2
Seawater-to-freshwater ratio 1:1 approximately

(8) Lignosulfonate Barite 0-450
freshwater Bentonite 10-50
Caustic soda 2-5
Cellulose polymer 0-2
Drilled solids 20-100
Fresh water As needed
Lignite 2-10
Lignosulfonate 4-15
Lime 0-2
Soda ash/sodium
bicarbonate 0-2

SOURCE: Adapted from Ayers, Sauer, and Anderson (1983).

TABLE 8 Characterizations of Field Drilling Fluids Used in the Joint Industry Mid-Atlantic Bioassay Program

General Fluid Types
(1) (2) (3) (4) (5) (6) (7) (8)
KC1/ SW Ligno- LT Ligno- Ligno-
Polymer sulfonatea Lime Nondispersed SW Spud SW/FW Gel sulfonate sulfonate FW

Components (lb/bbl)

Barite 18.0 176 64.0 10.8b 2 21.2 9.0 15.1
Bentonite/drill solids 18.0 32.1 20.0/30.0 20.0b-49.0 22.0/52.0 9.7�14.1� 25.0/48.0 15.1/28.1
Chrome lignosuulfonate 0 1.8-b(2.8)C 3.5 0 0 0 4.0 1.7b
Lignite 0 0.9b 1.8 0.1 0 0 5.0b 2.8b
Polyanionic cellulose 1.0 0.2b 0 1.0 0 0.5 0.5 0
Caustic soda 2.0 0.9b 1.5 d d 0.4b e 1.2�
Other KCl (16.0) (10.0)/ (1.5)b (0.1)/ (0.1)/
Salt Lime CMS Lime

Properties

Fluid density (lb/gal) 9.3 12.1 10.4 9.4 9.2 9.1 9.6 9.3
Percent solids (wt %) 18.3 43.5 27.8 21.0 21.7 11.6 24.1 16.4
pH 11.5 e 10.0 e e e 10.8 9.0
Chlorides (mg/l) 38,000 e e 1,200 e 250 7,500 1,800
Calcium (mg/l) e 650 lime e e 40 e 40

Oil and greasef 2,200 1,800 180 290 70 40 50 80

Metalse
(ppm--whole fluid)

Arsenic 1 2 3 2 3 2 1 3
Barium 24,800 141,000 76,200 13,000 2,800 25,600 11,500 14,000
Cadmium 1 1 1 1 1 1 1
Chromium 14 227 192 10 16 2 265 48
Copper 2 11 8 7 5 2 26 4
Lead 2 1 4 2 4 1 24 9
Mercury 1 1 1 1 1 1 1 1
Nickel 6 8 3 4 6 1 6 8
Vanadium 9 18 27 22 35 6 30 18
Zinc 20 181 58 16 21 12 82 15

a Acronyms explained in Table 7.
b Estimated concentration outside range designated in generic fluid systems (Table 1).
c Chrome lignosulfonate concentration estimate from chromium content calculation (3% Cr in chrome lignosulfonate).
d Other components in DC1 fluid: soda ash (4.0), aluminum stearate (0.5), sawdust (<.1), lime (<.1), surfactant (<.01), no
paraformaldehyde.
e Not measured.
f Oil and grease analyses conducted by Energy Resources, Cambridge, Mass.
2 Metals analysis conducted by SCR, Houston, Tex.

SOURCE: Adapted from Ayers, Sauer, and Anderson (1883).

TABLE 9 Summary of Bioassay Results of Mid-Atlantic Generic Drilling Fluidsa

96 hour LC50 in ppm Percent Survival of
For Mysid Shrimpa Hard Shell Clams

Type of
Drilling Fluid Liquid Phase Suspended Particulate Phase Solid Phase (Controls)

(1) Potassium/polymer 66,000c. 25,000b 90(99)c
58,0004 70,900d 88(100)d

(2) Lignosulfonate sea- 283,500 53,200 83(100)e
water 880,000 870,000 70(94)e

(3) Lime 393,000 66,000 100(100)
1,000,000 860,000 94(100)

(4) Nondispersed >1,000,000 >1,000,000 100(100)
>1,000,000 >1,000,000 100(100)

(5) Seawater spud >1,000,000 >1,000,000 100(100)
>1,000,000 >1,000,000 100(100)

(6) Seawater/fresh- >1,000,000 >1,000,000 100(100)
water gel >1,000,000 >1,000,000 100(100)

(7) Lightly treated >1,000,000 >1,000,000 97(98)
lignosulfonate >1,000,000 >1,000,000 100(100)
fresh water/sea-
water

(8) Lignosulfonate >1,000,000 506,000 99(100)
fresh water >1,000,000 >1,000,000 99(100)

NOTE: Characterization of Toxicity (IMCO/FAO/UNESCO/WMO, 1969)

LC50 Value (ppm) Toxicant Classification

>10,000 Practically nontoxic
1,000-10,000 Slightly toxic
100-1,000 Moderately toxic
1-100 Toxic
<1 Very toxic

a LC50 values are expressed as ppm and must be multiplied by 0.20 to obtained values for
drilling fluid used to formulate phases.
b Physical phases of drilling fluids were extracted from a 1:4 mixture by volume of fluid and
synthetic or natural sea water. Test organism for the liquid and suspended particulate phases
was the mysid shripm (Mysidopsis bahia), and for the solid phase was the hard shell clam
(Mercenaria mercenaria). Protocol for testing was established by EPA Region II in conjunction
with the Mid-Atlantic Operators.
c First values given in these columns were determined by Energy Resources, Cambridge,
Massachusetts.
d Second values given in these columns were determined by Normandeau Associates, Bedford, New
Hampshire.
e Statistically significant differences (a = 0.05) in survival between clams exposed to the
solids phase of fluid and control sediment.

3. Lime (or calcium) fluids are inhibitive fluids in which calcium
binds onto clay. The clay platelets are pulled together, dehydrating
them and releasing absorbed water. The size of the particles is
reduced, and water is released, resulting in reduced viscosity. More
solids may be maintained in these systems with a minimum of viscosity
and gel strength. These fluids are used in hydratable, sloughing shale
formations.
4. Nondispersed fluids are inhibitive fluids in which acrylic
serves to prevent fluid loss and maintain viscosity. They also provide
improved penetration, which is impeded by clay particles in dispersed
fluids.
5. Spud fluids are noninhibitive, simple mixtures used in the first
1,000 (300m) or so of drilling.
6. Seawater/freshwater gel fluids are inhibitive fluids used early
in drilling or in simple drilling situations. They provide good fluid
control, shear thinning, and lifting capacity. Prehydrated bentonite
that flocculates is used in such freshwater or saltwater fluids.
Attapulgite is used in saltwater fluids when fluid loss is not
important.
7. Lightly treated lignosulfonate freshwater/seawater fluids
resemble seawater/lignosulfonate fluids (type 2) except that the salt
content is less. The viscosity and gel strength of these fluids are
adjusted through additions of lignosulfonate and caustic soda.
8. Lignosulfonate freshwater fluids resemble fluid types 2 and 7,
except that lignosulfonate concentrations are higher. These fluids are
suited to high-temperature drilling. Increased concentrations of
lignosulfonate will result in heavily treated fluids of this type.

As the descriptions of the generic fluids indicate, these fluids
share numerous properties. The major ones are containing either fresh
water or seawater, being inhibitive or noninhibitive, and being non-
dispersed or lignosulfonate-treated polymers. Certain components are
shared by fluids in each of these categories, for example, the weight-
ing agent barite, and the caustic soda used to control pH.
The concept of generic drilling fluids was developed initially for
exploratory wells. Its application to development wells (the majority
of those drilled) is recent. The differences between discharges from
exploratory and development wells have been assessed (Boothe and
Presley, 1983), and can be addressed within the framework of generic
drilling fluids.

THE REGULATION OF DRILLING DISCHARGES

Principal authority to regulate the discharge of drilling fluids and
cuttings in offshore oil and gas activities rests with EPA through its
National Pollutant Discharge Elimination System (NPDES), which was
established under Section 402 of the Clean Water Act (formerly the
Federal Water Pollution Control Act Amendments). The Minerals
Management Service (MMS) of the Department of the Interior also
controls discharges through lease stipulations and OCS operating

3 5

orders under the authority of the Outer Continental Shelf Lands Act
Amendments of 1978.9
The Clean Water Act requires that point-source discharges of pol-
lutants achieve effluent limitations through use of the "best practi-
cable control technology currently available" (BPT). EPA determines
BPT limitations for categories of industrial discharges and promulgates
national guidelines for regional permits concerning the pollution
control a discharger will achieve while utilizing BPT.
BPT limitations relevant to drilling fluids are contained in the
limitations for the oil and gas extraction industry (40 CFR 435).
Current limitations mention only oil and grease. These adopt the "no
free oil standard' established under the oil discharge liability pro-
vision of Section 311 of the Clean Water Act. This standard prohibits
any discharge that would cause a film or sheen on the surface of the
water or a sludge or emulsion to be deposited beneath the surface of
the water (40 CFR 110). Discharges that cannot meet this standard are
to be disposed of an land at a dump site approved under RCRA.
Under Sec. 301(c) of the Clean Water Act, EPA is currently develop-
ing standards concerning the Best Available Technology Economically
Achievable (BAT). These standards may include a prohibition on the use
of diesel fuel, requirements for bioassays, the use of generic fluid
categories, and new compliance tests.
Section 306 of the Clean Water Act requires new source performance
standards for discharges through application of the "best available
demonstrated control technology", reflecting the greatest degree of
effluent reduction. Such standards have yet to be promulgated for
drilling fluids.
NPDES permits, which are issued through EPA's regional offices,
must be preceded by determinations under Section 403(c) of the Clean
Water Act that the discharges will not result in unreasonable degrada-
tion of the marine environment. This section, and its implementing
regulations, the Ocean Discharge Criteria (40 CFR Part 125) issued in
1980,10 provide a two-tiered test of degradation. Based on informa-
tion supplied by the applicant and other relevant material, the
regional administrator assesses the potential for "unreasonable degra-
dation": significant adverse changes in ecosystem diversity and pro-
ductivity and in the stability of the biological communities within and
surrounding the area of discharge; threats to human health through
direct exposure to pollutants or consumption of exposed aquatic
organisms; or loss of aesthetic, recreational, scientific or

91n territorial waters, states may also impose requirements on
discharges, either through administration of NPDES permit programs
(where states have been delegated such authority by EPA), or through
separate state regulations. States cannot be less restrictive than the
EPA in administering NPDES permit programs.

10Prior to 1980, the issuing of permits was guided by the ocean
dumping regulations, 40 CFR 227, which require bioassays and the cal-
culation of the 'limiting permissible concentration" (LPC) of the
discharge following dilution.

economic values unreasonable in relation to the benefits derived from
the activities leading to the discharge. Such determinations depend
on the location of the discharge, the presence of special aquatic
sites, and the nature of the discharge, including its composition,
potential toxicity through bioaccumulation, and persistence and
transport in the marine environment.
If the proposed discharge is found not likely to cause unreason-
able degradation, then it may be permitted. If information is insuf-
ficient to determine whether unreasonable degradation will occur, no
permit may be issued unless another determination is made that the
discharge will not cause " i rpaal harm." Irreparable harm is
defined as significant undesirable effects, occurring after permit
issuance, that will not be reversed by ceasing or modifying the dis-
charge (Section 125.121(a) of the Clean Water Act). In such cases, it
must be judged that the discharge will not result in irreparable harm
during the period in which monitoring can be conducted, and that there
are no reasonable alternatives to onsite disposal of the wastes. The
discharge must meet a number of conditions, among them: it may not
exceed a limiting permissible concentration (LPC) for the liquid and
suspended particulate phases of the waste following dilutions measured
from the boundary of a mixing zone(defined as 100 m from the point of
discharge); it may not exceed the LPC for the solid phase or result in
bioaccumulation; permit conditions may require environmental monitoring
of discharges or other appropriate conditions.
Drilling fluids determined unacceptable for disposal under the
Ocean Discharge Criteria or under State authority in territorial waters
may be considered for ocean dumping at a designated ocean dump site for
land disposal. In federal notes of discharges and dumpsite designa-
tions are authorized under Title I (The "Ocean Dumping Act") of the
Marine Protection, Research and Sanctuaries Act. The regulations that
implement this Act (40 CPR 220-229) provide for the calculation of a
limiting permissible concentration based on liquid, suspended particu-
late, and solid phase bioassays. Land disposal is regulated under the
Reseource Conservation and Recover, Act (RCRA).
EPA's Region IX (San Francisco) issued the first offshore NPDES
permit, to the Shell Oil Company, in 1976. It later issued permits for
the Atlantic and the Gulf of Mexico. Also, wells have been drilled
offshore Alaska with EPA concurrence. It developed a general permit
now in force in the Gulf of Mexico and California but also issues in
these regions individual permits that are designed to protect biologi-
cally sensitive areas (e.g., the Flower Garden Banks in the Gulf of
Mexico).
In addition to, or as adjuncts to, the Ocean Discharge Criteria
and the effluent limitations, NPDES permits may make special prohibi-
tions (e.g., on the use of pentachlorophenol or asbestos), require
special discharge practices (e.g., shunting to the nepheloid layer or
predilution), and require biological or other studies to monitor the
marine environment for changes as the result of discharges. These
conditions may complement those imposed by MMS. For example, EPA and
MMS jointly required and aided in developing a biological monitoring
program for Georges Bank.
Before EPA exercised its authority over offshore drilling dis-
charges, the Bureau of Land Management and the Conservation Division

of the U.S. Geological Survey (now combined as MMS) placed special
requirements on operators through lease stipulations and OCS operating
orders (Rieser and Spiller, 1980). Lease stipulations commonly give
the MMS district supervisor the authority to require special discharge
practices when appropriate, for example, district supervisors may
specify monitoring programs and depths at which discharges are to be
released in biologically sensitive areas. The objective of operating
orders is to ensure safe operations. MMS Operating Order 7 specifi-
cally addresses pollution, and, while noting that fluid disposal is
subject to the requirements of EPA, this order also requires informa-
tion on the constitutents of drilling fluids and additives. The use
offshore of pentachlorophenol is prohibited under this MMS authority.
The NPDES permits of the Environmental Protection Agency and the
operating orders and other requirements of the Minerals Management
Service (and consequently industrial operating practices, including the
use of additives) vary according to geographic regions. For example,
in 72 percent of wells in a sample in the Gulf of Mexico in 1982,
additives were used that were not approved for use in EPA Region II (a
mid-Atlantic region), where the concept of generic drilling fluids has
been adopted (Dalton, Dalton, Newport, 1983). Regional differences
have been taken into account because of environmental conditions, or
to protect sensitive or valuable habitats.'" (See Table 23.)
Government regulation has spurred extensive research, both in
anticipation of permit conditions and as a result of those conditions.
EPA's initial attempts to regulate drilling discharges were repeatedly
challenged by industry. More recently, however, there has been growing
cooperation between industry and government, resulting in the develop-
ment of monitoring programs (e.g., the Georges Bank monitoring pro-
gram), the Region II bioassay protocol (U.S. Environmental Protection
Agency Region II, 1978), a program for sampling used drilling fluids
("PESA muds") and for conducting toxicity testing and chemical analyses
of them, and the specification of generic drilling fluids (Ayers,
Sauer, and Anderson, 1983).

THE MASS LOADING OF DRILLING DISCHARGES IN RELATION TO
THAT OF OTHER INPUTS TO THE MARINE ENVIRONMENT

As part of the review of the discharge of drilling fluids and cuttings,
the quantities and frequencies of these discharges and their components
will be examined in light of their mass loading into the coastal ocean
compared to that of sediments and trace metals from other natural and
anthropogenic sources. Because these inputs vary greatly with time and
place, the comparisons that follow do not necessarily reflect relative
effects. They are useful, however, in considering the magnitude of

"1An alternative explanation for the difference in regulations
for the Gulf of Mexico and EPA Region II is that the list of approved
additives for EPA Region II was not up to date in 1982 because there
had been no drilling there since 1981.

drilling-fluid discharges on the OCS. Caution is advised concerning
the estimates used--most are approximations.

Drilling Discharges

Several estimates of the magnitude of drilling-fluid discharges on the
OCS are available (see Table 10). These result from theoretical calcu-
lations or product use inventories from exploratory, development, and
production wells in the Gulf of Mexico, mid-Atlantic, and North
Atlantic (Georges Bank) OCS areas. These statistics display approxi-
mately a fourfold range in mean total solids and chromium discharged
per well, but a much narrower range in mean barium discharge. Most of
the variation is due to the fact that smaller discharges are made from
the shallower development and production wells in the Gulf of Mexico.

River Inputs

Table 11 compares the average annual discharges of water and sediments
of major rivers in North America. Although sediment discharge is
generally related to drainage area and water discharge, some rivers
(e.g., the Bel River in northern California and the Copper River in
Alaska) contribute disproportionately large loads of sediment to the
sea. Sediment discharges are frequently episodic and highly variable
from year to year. For example, in 1969 the Santa Clara River in
California flooded and discharged Ilx 108 metric tons (t of sediment
during 2 weeks, compared to an annual average discharge of 2 x 106
t. This event increased sedimentation in the Santa Barbara Basin 10
to 100 mm compared with the long-term annual sedimentation rates of 1
to 5 mm.
The total loading in 1980 of particulate material from drilling
discharges on the U.S. OCS is estimated as 1.85 x 106 t, compared to
over 4 x 108 t per year for North American rivers. Most of the load
from drilling discharges was in the northern Gulf of Mexico, and was
equivalent to approximately 0.8 percent of the Mississippi River's
input to the Gulf.
Barium, added as barite (BaSO4), is commonly present in drilling
fluids at much higher concentrations than in marine or riverine sedi-
ments and thus serves as an effective tracer of drilling-fluid contam-
ination of marine sediments. Barium is present in an average concen-
tration of 62 P.g/l in Mississippi River water (Hanor and Chan, 1977),
but most of the barium discharged by rivers is in relatively insoluble
particulate material in an average concentration of 600 i'g/g (dry
weight) of suspended sediment (Martin and Maybeck, 1979).
The average mass emission of barium by the Mississippi River is
approximately 1.5 x l05 t per year, almost all of which is particu-
late (Table 12). The release of barium from OCS drilling activities
has been estimated to be 3.2 x l0~ t per year. Since these estimates
are approximations, it is perhaps more appropriate to say that the mass
emissions of barium from OCS drilling discharges appear to be of the
same order of magnitude as those from the Mississippi River.

TABLE 10 Average Discharges of Particulate Solids, Barium, and Chromium from OCS Wells

Gulf of Mexico, Gulf of Mexico, Mid-Atlantic, Georges Bank, Gulf of Mexico,
Average Well Five Exploratory Exploration Well Eight Exploratory Forty-Nine Exploration,
(Gianessi and Wells (Petrazzuolo, (Ayers et al., 1980) Wells (Danenberger, Development and
Arnold, 1982) 1981) 1983) Production Wells
(Boothe and Presley, 1983)

Depth of well (m) 5,486 3,329 4,970 4,900 3,121

Total solids (t) 1,140 2,160 1,220a 598

Barite -600 752 715 492

Barium b (t) 312 391 372 256

Chrome lignosulfonate - 20 45 26 10

Chromium c (t) - 0.6 1.3 0.8 0.3

a Drilling fluid solids only (does not include cuttings).
b Barium estimated at 52 percent of barite weight.
c Chromium estimated at 2.9 percent of chrome lignosulfonate weight.

TABLE 11 Drainage Area and Water and Suspended Sediment Discharges of North America's Major Rivers

Water Sediment
Drainage Area Discharge Discharge
River (millions of km2) (km3 per year) (t per year)

St. Lawrence (Canada) 1.03 447 4

Hudson (USA) 0.02 12 1

Mississippi (USA) 3.27 580 191

Brazos (USA) 0.11 7 15

Colorado (Mexico) 0.64 20 0.1

Eel (USA) 0.008 - 13

Columbia (USA) 0.67 251 7

Fraser (Canada) 0.22 112 18

Yukon (USA) 0.84 195 55

Copper (USA) 0.06 39 64

Susitna (USA) 0.05 40 23

Mackenzie (Canada) 1.81 306 91

SOURCE: Adapted from Milliman and Meade (1983).

Chromium, added mainly in the form of chrome lignosulfonate, may
also be more concentrated in drilling fluids compared to riverine
sources (Table 12). Mass emissions of chromium associated with sus-
pended sediments in North American rivers are estimated as 76 x10
t per year, while the dissolved input has been estimated at 22 x10
t Per year. Emissions of chromium from drilling operations (estimated
from usage of additives or analysis of discharged material) averages
about 580 jig/g dry weight of solids. In contrast to barium,
however, much of the chromium in drilling fluids is soluble and will
disperse differently from particulate components when discharged into
the ocean. Drilling discharges of chromium equal just over I
percent of the input of North American rivers.

Anthropogenic Wastes

A broad variety of other wastes, including municipal sewage, industrial
wastes, and dredged material, is introduced into both coastal and OCS
waters via pipelines, barges, ships, and offshore drilling vessels and
Platforms. Table 13 compares direct waste inputs into the U.S. coastal
ocean, including drilling-fluid discharges. It should be kept in mind
that the concentrations, bioavailabilities, and geographic locations
of such inputs vary greatly and consequently so do their effects.
Thus, Table 13 does not compare the environmental significance of these
wastes. It does indicate that the mass emissions of dredged materials,
sewage sludge, and industrial wastes exceed those of drilling fluids.
The amount of suspended solids in southern California municipal
waste discharges is approximately 2.5 x l05 t per year (Bascom,
* ~~1982), that in drilling-fluid discharges on the California OCS is 1.7
x 104 t per year. These municipal wastes include approximately 230
t per year of chromium; the figure for California drilling discharges
* ~~is roughly 10 t per year. The introduction of chromium from U.S. OCS
drilling discharges, approximately I x l0~ t per year (Table 12),
* ~~approaches that from waste disposal in the New York Bight, I1.4 x 103
t per year (Mueller et al., 1976).

Other Human Impacts

Discharged drilling fluids and cuttings may settle on the bottom and
harm benthic organisms within some area around the rig. These effects
may be primarily physical and, providing that bottom sediments are not
modified over a long period of time, may disturb the seabed much in the
way that storms, dredging, the disposal of dredged material, and
certain fishing activities do.
Dredging for surf clams Spisula solidissma covers average swathes
* ~~1 5 m wide by 46 cm deep (Ropes, 1972), which might disturb 4.3 x 103
m of sediment per vessel per day. There were 98 surf clam boats
working along the U.S. east coast in 1974 (Ropes, 1982). In contrast,
Gianessi and Arnold (1982) estimated that an average of 442 m3 of
drill solids are discharged per well over approximately 90 days.
(Regarding this comparison, it needs to be kept in mind that fishing

TABLE 12 Estimates of Mass Emissions of Particulate Solids, Barium, and Chromium
from OCS Drilling Discharges and from Rivers

Sediment Barium Barium Chromium Chromium
Discharged Concentration Loading Concentration Concentration
Source (t per year) (mg/g) (t per year) (ug/g) (t per year)

U.S. OCS Drilling Fluids 1.3 x 106 250a 3.2 x 105a 580 1.1 x 103

North American Rivers 4 x 108-b 190 76 x 103

Mississippi River 2.1 x 108b 0.74d 1.5 x 105 150C 31 x 103

aEstimated from the average barium discharge per OCS well inventoried (Table 10) and 1,033 wells drilled in
1981. It is not known how representative these wells are with regard to barium concentration.
bMilliman and Meade (1983).
CGoldberg (1980).
-Trefry et al. (1981).

TABLE 13 Ocean Disposal of Various Wastes by Geographic Areas, 1973 to 1980 (Millions of Tons)

Atlantic Ocean Gulf of Mexico Pacific Ocean Total
1973 1976 1980 1973 1976 1980 1973 1976 1980 1973 1976 1980

Industrial Wastes-a 3.643 2.633 2.928 1.408 0.100 0 0 0 0 5.051 2.733 2.928

Sewage Sludgea 4.898 5.271 7.309 0 0 0 0 0 0 4.898 5.271 7.309

Construction and 0.974 0.315 .089 0 0 0 0 0 0 0.974 0.315 0.089 .
Demolition Debrisa

Dredged Wastesb - - - - 89.376 92.485 60.866

Wood Incinerationa 0.011 0.009 0.011 0 0 0 0 0 0 0.011 0.009 0.011

Drilling FluidaC 0 0 0.008 1.94 1.85 1.67 0.12 0.082 0.17 2.06 1.932 1.848
and Cuttings (2.01%) (1.88%) (2.5%)

102.87 102.695 73.051

a Source: EPA (1980).
b Source: U.S. Army Corps of Engineers (1982). Original values of million cubic yards of material converted to tons by applying multiplier of
1.33 tons/yd3. This value can vary significantly depending on material. This multiplier was delivered from 1980 data given in this source.
_ Source: Quantities based on estimated value of 2,000 t per well (dry weight) of fluids and cuttings solids. Pacific includes wells drilled
off Alaska.

dredges and trawls disturb in situ sediment, with attendant physical
effects; the discharge of drilling fluids and cuttings adds foreign
substances to the marine environment.)
These comparisons to river inputs, anthropogenic wastes and other
human impacts are made not to suggest that the effects of drilling
discharges are minimal by comparing them to traditional uses of the
ocean's natural resources; rather they indicate that the use of natural
resources virtually always results in some potentially undesirable side
effects. With each activity, appropriate and effective pollution pre-
vention and mitigation measures are needed. Regardless of the relative
contributions of pollutants to the marine environment from other
sources, it is the mandate of this study to provide an effective
assessment of the environmental risks of drilling fluids and cuttings.
In meeting that charge, the chapters of this report provide more
detailed consideration of the compositions, locations, and frequencies
of drilling discharges; their fates, including dispersion and chemical
transformation; and their effects on marine biota.

REFERENCES

American Petroleum Institute. 1978. Oil and gas well drilling fluid
chemicals. 1st ed. API Bull. 13F.

American Petroleum Institute. 1982. Total number of offshore wells
drilled in the United States. In: Basic Petroleum Data Book.
Washington, D.C.: American Petroleum Institute. Vol. 3, No. 1,
Sec. H, Table 7.

Ashford, N.A., and G.R. Heaton. 1979. The effects of health and
environmental regulation on technological change in the chemical
industry: theory and evidence. In: C.T. Hill (ed.), Federal
Regulation and Chemical innovation. American Chemical Society
Symposium Series 109, September 14, 1978, Miami Beach, Fla.
Washington, D.C.: American Chemical Society. Xv + 200 pp. Pp.
4 5-66.

Ayers, R.C., Jr. 1983. Characteristics of drilling discharges. in:
Proceedings of Workshop on Modeling, Santa Barbara, Calif.
Reston, Va.: Minerals Management Service. in press.

Ayers, R.C., Jr. 1981. Fate and effects of drilling discharges in
the marine environment. Proposed North Atlantic OCS oil and gas
lease sale 52. Statement delivered at public hearing, Boston,
Mass., November 19, 1981. Bureau of Land Management, U.S.
Department of the Interior.

Ayers, R.C., Jr., T.C. Sauer, Jr., and P. Anderson. 1983. The
generic mud concept for offshore drilling for NPDES. Paper
presented at the IADC/SPE 1983 Drilling Conference. Paper No.
IADC/SPE 11399. Available from SPE, 6200 North Central Causeway,
Drawer 64706, Dallas, TX 75206.

Ayers, R.C., Jr., T.C. Sauer, Jr., R.P. Meek, and G. Bowers. 1980.
An environmental study to assess the impact of drilling discharges
in the mid-Atlantic. In: Proceedings of a Symposium on Research
on Environmental Fate and Effects of Drilling Fluids and
Cuttings. Washington, D.C.: Courtesy Associates. P. 382.

Bascom, W. 1982. The effects of waste disposal on the coastal waters
of Southern California. Environ. Sci. Techol. 1664:226A-236A.

Boothe, P.N., and B.J. Presley. 1983. Distribution and behavior of
drilling fluid and cuttings around Gulf of Mexico drill sites.
Draft final report. API Project No. 243. Washington, D.C.:
American Petroleum Institute.

Carney, L.L., and L. Harris. 1975. Thermal degradation of drilling
mud additives. In: Proceedings, Environmental Aspects of Chemical
Use in Well-Drilling Operations, May 21-23, 1975, Houston, Tex.
EPA-5601/1-75-004. Washington, D.C.: Office of Toxic Substances,
U.S. Environmental Protection Agency. vi + 604 pp.

Dalton, Dalton, Newport. 1983. Analysis of drilling muds from 74
offshore oil and gas wells in the Gulf of Mexico. Draft report
dated May 6, 1983. Available from Monitoring and Data Support
Division, Office of Water Regulations and Standards, U.S. Environ-
mental Protection Agency, Washington, D.C.

Danenberger, Elmer P. 1983. Georges Bank exploratory drilling
1981-1982. n.p. Available from Minerals Management Service,
Offshore Division, Reston, Va.

Dolton, G.L., et al. 1981. Estimates of undiscovered recoverable
resources of conventionally producible oil and gas in the United
States, a summary. Open File Report 81-192. Reston, Va.: U.S.
Geological Survey. 17 pp.

Edgar, N. Terrance. 1983. Oil and gas resources of the U.S.
continental margin. In: Gerald J. Mangone (ed.), The Future of
Oil and Gas from the Sea. New York: Van Nostrand Reinhold Co.,
Inc. Pp. 25-79.

Escott, T.A., and J.B. Walker. 1981. The drilling fluids market:
status report. Oil Service Monthly Bulletin, June 1981. Paine,
Webber, Mitchell, Hutchins, Inc. 11 pp.

Gianessi, L.P., and F.D. Arnold. 1982. The discharges of water
pollutants from oil and gas exploration and production activities
in the Gulf of Mexico region. Draft report prepared by Resources
for the Future, Washington, D.C. Contract NA-80-SAC-00793.
Office of Ocean Resources Coordination and Assessment, NOAA.

Goldberg, E.D. (ed). 1980. Proceedings of a Workshop on
Assimilative Capacity of U.S. Coastal Waters for Pollutants,

Crystal Mountain, Washington, July 29-August 4, 1979. Working
Paper No. 1: Federal Plan for Ocean Pollution Research
Development and Monitoring, FY 1971-1985. Second Printing--
Revised. Environmental Research Laboratory, NOAA, U.S. Department
of Commerce, Boulder, Colo.

Gray, G.R., H.C.H. Darley, and W.F. Rogers. 1980. Composition and
Properties of Oil Well Drilling Fluids. 4th ed. Houston, Tex.:
Gulf Publishing Co. xii + 630 pp.

Hanor, J.S., and H.L. Chan. 1977. Non-conservative behavior of
barium during mixing of Mississippi River and Gulf of Mexico water.
Earth Planet. Sci. Lett. 37:242-250.

IMCO Services. 1978. Applied Mud Technology. Houston, Tex.: IMCO
Services, Halliburton Co.

Intergovernmental Maritime Consultative Organization, et al. 1969.
Abstract of first session report of Joint Group of Experts on the
Scientific Aspects of Marine Pollution. Water Res. 3:995-1005.

Jones, M., C. Collins, and D. Havis. 1980. Trade-offs in traditional
criteria vs. environmental acceptability in product development:
an example of the drilling fluids industry's response to environ-
mental regulations. Environ. Prof. 2:94-102.

Jones, M., and M. Hulse. 1982. Drilling fluid bioassays and the OCS.
Oil Gas J. 80(25):241-244.

McGuire, E.P. 1973. Evaluating new product proposals. Conference
Board Report No. 604. New York: The Conference Board.

Martin, J., and M. Maybeck. 1979. Elemental mass balance of material
carried by major world rivers. Mar. Chem. 7:173-206.

Milliman, J.D., and R.H. Meade. 1983. Worldwide delivery of river
sediments to the oceans. J. Geol. 91:1-21.

Minerals Management Service. 1982. Approval of five-year OCS oil and
gas leasing program announced. News Release, July 21, 1982.
Washington, D.C., Department of the Interior. 7 pp.

Moseley, H.R., Jr. 1981. Chemical components, functions, and uses
of drilling fluids. In: Proceedings of UNEP Conference, Paris,
France, June 2-4, 1981. P. 43.

McAtee, J.L., and N.R. Smith. 1969. Ferrochrome lignosulfonates.
J. Colloid Interface Sci. 29(3):389-398.

Mueller, J.A., J.S. Jeris, A.R. Anderson, and C.F. Hughes. 1976.
Contaminant inputs to the New York Bight. Technical Memorandum
ERL MESA-6. Rockville, Md.: NOAA. 347 pp.

Palmer, C.R., and P.L. Kelley. 1983. America's five-year offshore
leasing plan--its importance in increasing domestic petroleum
reserves. Presentation to 23d Annual Institute in Petroleum
Exploration.

Perricone, C. 1980. Major drilling fluid additives. In:
Proceedings of a Symposium on Research on Environmental Fate and
Effects of Drilling Fluids and Cuttings. Washington, D.C.:
Courtesy Associates. P. 15.

Petrazzuolo, G. 1981. Preliminary report. An environmental
assessment of drilling fluids and cuttings released onto the outer
continental shelf. Vol. 1: Technical assessments. Vol 2:
Tables, figures and Appendix A. Prepared for Industrial Permits
Branch, Office of Water Enforcement and Ocean Programs Branch,
Office of Water and Waste Management, U.S. Environmental Protection
Agency, Washington, D.C.

Petroleum Extension Service. 1979. A Dictionary of Petroleum Terms.
Austin, Tex.: University of Texas Petroleum Extension Service.
129 pp.

Ropes, J.W. 1972. The Atlantic coast surf fishery--1965-1969. Mar.
Fish. Rev. 34(7-8):20-29.

Ropes, J.W. 1982. The Atlantic coast surf fishery--1965-1974. Mar.
Fish. Rev. 44(7-8):1-4.

Skelly, W., and D.E. Dieball. 1970. Behavior of chromate in drilling
fluids containing chrome lignosulfonate. J. Soc. Pet. Eng.:
140-144.

Skelly, W., and J.A. Kjellstrand. 1966. Thermal degradation of
modified lignosulfonates in drilling mud. In: Proceedings, API
Production Department, Spring Meeting, March 2-4, 1966, Houston,
Tex. Dallas, Tex.: American Petroleum Institute. 12 pp.

Trefry, J.H., R.P. Trocine, and D.B. Meyer. 1981. Tracing the
fate of petroleum drilling fluids in the northwest Gulf of Mexico.
Oceans '81. Available from Marine Technology Society, Washington,
D.C. Pp. 732-736.

U.S. Army Corps of Engineers. May 1982. Report to Congress on
administration of ocean dumping activities. Pamphlet 82-P1.

U.S. Environmental Protection Agency. 1978. Bioassay procedures for
the Ocean Disposal Permit Program. Report No. EPA-600/9-78-010.
U.S. Environmental Protection Agency, Washington, D.C.

U.S. Environmental Protection Agency. 1980. On administration of the
Marine Protection, Research, and Sanctuaries Act of 1972. Annual
report to Congress.

Van Olphen, H. 1977. An Introduction to Clay Colloid Chemistry. 2d
ed. New York: Wiley & Sons. xvii + 318 pp.

Wright, T.R., Jr., and R.D. Dudley (eds.). 1982. Guide to Drilling
Completion and Workover Fluids. World Oil. Houston, Tex.: Gulf
Publishing Co.

The Fates of Drilling Discharges

INTRODUCTION

The fates of drilling fluids and cuttings discharged in the marine
environment are determined by diverse physical processes (current,
gravity), chemical processes (reaction, sorption), and biological
processes that all serve to disperse or concentrate constituent
materials. The various dissolved and particulate constituents behave
in different ways when encountering seawater and transport forces in
the ocean. Even so, some generalizations can be made, and they allow
predicting the fates of drilling fluids.
Although the ocean is a continuous liquid with a long time scale
for mixing, it remains an inhomogeneous solution. Inhomogeneities are
caused by energetics that set up horizontal density gradients of liquid
(fronts) and vertical ones (pycnoclines) through which transfer is
relatively slow. Within the boundaries established by density gradi-
ents, inhomogeneities tend to be less as a consequence of the conser-
vative nature of the major components of seawater; yet heavy metals,
nutrients, dissolved gases and organic matter may be non-conservative
both in quantity and chemical form as a result of geochemical and bio-
logical processes. The forces of the ocean, however, are continuously
at play, reducing these gradients and producing more constant composi-
tion. While molecular diffusion' in any liquid brings about
homogeneity, the rate is slow (10-5 cm2/s) compared to the rates

1Molecular diffusion is the gradual mixing of molecules of two
or more substances through random thermal motion. In a solution in
which the concentration of a substance varies in space, the amount of
that substance which per second diffuses through a surface area of 1
cm2 is proportional to the change in concentration per cm along a
line normal to that surface (dM/dt = 6de/dn). The proportionality
constant (6) is the diffusion coefficient, which for seawater is
about 2 x lo-5.

produced by mixing or eddy diffusivity2 in the ocean (approximately
1 cm2/s in the vertical and 105 to 107 cm2/s in the horizontal)
(Okubo, 1971).
The ocean's properties and composition are nonuniform because of
many factors. Major among these are heat exchange with the atmosphere,
which leads to evaporation and surface cooling, which both increase
density; and surface warming, river runoff, and rainfall, which all
decrease density. Changes in density cause mixing both vertically and
horizontally, and, together with winds and tides, provide most of the
energy for ocean mixing. Other factors that are not very important to
physical mixing also cause inhomogeneities. Phytoplankton growth
decreases concentrations of nutrient elements and alters the carbon
dioxide components, causing an increase in pH. River runoff adds
sediment and dissolved materials, including anthropogenic components
derived from various uses of water. Sorption processes, in which trace
metals and organic compounds selectively adhere to or exchange on sur-
faces, also result in the inhomogeneous distribution of materials. For
example, trace metals may adsorb to clay minerals, which then are
deposited on the seafloor, while other materials, such as polychlor-
inated biphenyls (PCBs), may concentrate at the sea surface. In addi-
tion, fine particulate solids and the associated sorbed materials in
suspension often flocculate when mixed with seawater, thereby increas-
ing the settling rate of the solids and altering the physical and
chemical characteristics of deposited sediment.
When discharged into the ocean, a material composed of finely
divided insoluble materials or solutes immediately is subject to a
process of dilution in a concentration gradient decreasing from the
point of discharge. To reverse this process (for instance, by bio-
accumulation) requires sufficient energy to overcome the dilution
process. Components that are held in solution or suspension are
rapidly diluted by a factor of 105 to 106 within the first hour
(Sverdrup et al., 1942) from the eddy diffusion resulting from the
ocean turbulence generated mainly by geostrophic flow3, tidal
currents, and wind mixing (Hill, 1962). Neutrally buoyant or dissolved
materials will form a dispersion (dilution) plume, riding the path of
currents through the ocean, always decreasing in concentration. Those

2The rate of transfer of mass in water is proportional to the
gradient of concentration. The proportionality coefficient is called
eddy diffusivity. It is not a physical constant, but depends on the
nature of the turbulent motion. (This motion is that of a liquid
having local velocities and pressures that fluctuate randomly. It is
also called turbulent flow.) The ranges of eddy diffusivity per unit
mass are about 0.1 to 100 cm2/s in the vertical and about 106 to
108 cn/s in the horizontal direction (Sverdrup et al., 1942).

3The oceanic flow resulting from the earth's rotation.

materials that are negatively buoyant separate from the suspended plume
according to their Specific settling characteristics. They may then
be reconcentrated by gravity on the seafloor, where they may be buried
by physical and biological Processes, resuspended and transported, or
chemically altered by benthic processes.
The fates of materials discharged into the marine environment are
influenced heavily by the dispersive and transport energy of the ocean
at the discharge site. This energy dominates the rate of dispersion
after the dynamic energy induced by the actual discharge has decayed.
In ocean discharge operations this dynamic energy has been used exten-
sively to cause rapid dilution. Discharges in the wakes of moving
barges (Hood et al., 1958; Ketchum and Ford, 1952), outfall diffusers
(Colonell, 1981; Yudelson, 1967) and high-pressure jets (Brandsma et
al., 1980) are very effective ways to reach dilutions of several orders
of magnitude within only a few meters of the place of discharge.
Dispersion from a point source into the marine environment varies
with site location and depth of discharge because of the variability
of several important factors influencing the turbulence (eddy diffusi-
vity) of the water column and the bottom boundary layer:

o Vertical or horizontal stratification by temperature, salinity,
and suspended sediments
* Wind and tidal energy interaction
* The topography of large-scale bed forms
* Variable bed conditions (bioturbation, bed forms, and near-bed
transport).

These factors vary not only from site to site; storm events also affect
ambient flow conditions. These factors together provide a general
framework for analyzing the fates of drilling fluids and cuttings.

BEHAVIOR OF THE DISCHARGE PLUME

The phenomena observed during drilling-fluid discharges are explained
by the Offshore Operator's Committee model (Brandsma et al., 1980)
which is illustrated in Figure 2. The initial plume is denser than
seawater and goes through a stage of convective descent until it
encounters the seabed or becomes neutrally buoyant from loss of solids
and water entrainment. As a result of the density gradient of the
plume, the plume then collapses and goes into a stage of passive dif-
fusion. The same plume behavior would be observed in subsurface or
shunted discharges except that, because of its density, the plume would
be confined to that part of the water column deeper than the point of
discharge. in addition to the main or lower plume, a visible or upper
plume is also formed. This results from turbulent mixing of the lower
plume with seawater as it descends. The upper plume contains only a
small fraction (less than 10 percent of the dishcarged material.
Fractionation of the contaminants may occur during any of the
stages in dispersion, depending on whether the materials are soluble
or solids heavier or lighter than seawater. Neutrally buoyant solids

� :.'., ~-.:.~ .--.... - ..A...--'....,..:.":
C'.' ".' ~ -' %-'. o � -

Convective Descent - - � Dynamic Collapse - Passive Diffusion

Encounter Diffusive Spreading
Neutral Greater than
Buoyancy Dynamic Spreading

Source: Brandsma, et al., 1980,

FIGURE 2 Idealized Jet Discharge

may settle to an appropriate density discontinuity, where they may be
transported at an intermediate depth for long distances from the site
of disposal.
Rapid flocculation and aggregation of the clay-sized particles
occur when drilling fluids encounter seawater. These finely divided
particles are dispersed in drilling fluids by the electrical charges
between particles and lignosulfonate, which is used in drilling as a
deflocculant. This suspension is destabilized by decreasing lignosul-
fonate concentration and by particle ion exchange with seawater
electrolytes, particularly polyvalent ions. The rate at which agglom-
eration occurs depends on the frequency of collisions and on the
efficiency of particle contacts. Particles in suspension collide with
each other as the result of two mechanisms of particle movement. Par-
ticles move relative to each other because of thermal energy (brownian
motion) and because of the turbulence of the seawater. In the oceans,
if colloids are large (0.1-2jjM) or the fluid shear rate is high (10-
200 cm2/s), the relative motion of particles created by turbulence
far exceeds brownian motion and thus flocculation depends essentially
on turbulence.
The decrease in number of particles in a well-mixed (velocity
gradient) fluid from agglomeration is expressed by the equation (Stumm
and Morgan, 1970):

n
n du
with = -K t+, K V
LnNo o o o m d
withN -aZ

where n is the number of particles, N. is the initial number of par-
ticles, Vm is volume of total solid mass suspended per volume of
medium, a. is the fraction of collisions leading to permanent
agglomeration, t is time, and du/dz is the velocity gradient. In a
practical way this expression indicates that, for a medium containing
107 particles per cm3, of diameter approximating lpm, V becomes
approximately 5 x 10-6 cm3/cm3. For a = 1 and agitation char-
acterized by a velocity gradient of 10/s (equivalent to a "medium"
stirred beaker, but generally less than ambient ocean turbulence), K.
is of the order 1.5 x 10-5/s. In this example, half the particles
would agglomerate in a period of approximately 4.5 h. The high dilu-
tion rates in the ocean will reduce the rate of flocculation downstream
by reducing the concentration of particles. Materials will be precipi-
tated for extended periods of time because of the complex interactions
of microscopic particles suspended in highly ionic solutions.
In the case of drilling fluids, most of the discharged material
(barite, flocculated clays, and formation solids) sinks to the bottom
near the well site with the distance from the discharge point (within
500 m for most OCS areas) dependent on depth of water, lateral
transport, particle size, and density of material (Ayers et al., 1980a;
Ayers et al., 1980b; Ray and Meek, 1980; Trefry et al., 1981; Trocine
and Trefry, 1982). How long the settled material remains at the well
site depends on environmental factors (such as water depth and energy
regime) that govern sediment resuspension, transport, and dispersion.

A smaller portion of the discharged material, less than 10 percent
of the solids and some of the water and soluble components (Ayers et
al., 1980b), remains in the water column. This fraction of the dis-
charge, which breaks away from the fast-descending main plume to form
the upper plume, is transported away from the well by ambient currents.
The fate of the upper plume (as well as the main plume if it reaches
neutral buoyancy before encountering the seabed) depends largely on
oceanic dispersion processes. Diffusion as a physical process in the
environment has been the subject of considerable study over the past
several decades. Batchelor (1952), Ichye (1963), Joseph and Sender
(1958), Richardson (1926), and Stommel (1949), developed the theory
of this process. In the 1950s the use of fluorescent dyes to measure
diffusion directly (Seligman, 1955; Moon et al., 1957; Prichard and
Carpenter, 1960) provided many data on the rates of dispersion (dilu-
tion) under different oceanographic conditions. In a summary of dye
diffusion studies, Okubo (1968) compared the horizontal variance in dye
concentration in the upper mixed layer of four geographically separated
areas of the continental shelf and two estuaries (Figure 3). These
experiments show that, regardless of the detailed oceanographic condi-
tions, variance" exhibits a general trend. Specifically, it
increases with time by power between 2 and 3 in different scale diffu-
sion fields, current regimes, and sea surface conditions. Thus, local
variability appears to have a relatively minor influence on dispersion
compared to generic hydrodynamic processes, those common to continental
shelf and estuarine waters.
in one of the classical experiments in open ocean diffusion, Folsom
and Vine (1957) measured the 3spread of a radioactive tracer over a
horizontal area of 40,000 km3 in 40 days. During this time it mixed
vertically through 60 m. This mixing corresponded to eddy diffusivi-
ties of l07 cm2/s in the horizontal and of I cm2/s in the verti-
cal direction. The effect of bottom friction and resulting mixing by
tidal and other bottom currents was not seen in these data because of
the great water depths in the area observed.
The energy for mixing dilutes any contaminants by mixing them with
uncontaminated water. From this it follows that populations of non-
motile or weakly motile organisms like phytoplankton, zooplankton,
larvae, and eggs will be exposed to the contaminated plume while other
exposed organisms will be carried out of the plume as diffusion of the
plume progresses.
The discussion of dispersion thus far has largely focused on the
mixed layer and relates primarily to dilution of the buoyant plume.
This plume represents less than 10 percent of the discharged material
in drilling fluids and cuttings. The bulk of the material, which

4A statistical term denoting the mean of the squares of varia-
tions from the mean of a frequency distribution. In this report,
variance refers to the square of the mean of dye concentration varia-
tion in a horizontal field from the peak concentration at the center.

I014 I I~ | m 100 km
o RHENO
, 1964 7
E 1962 m NORTH SEA t
0 1962 TT
o 1961 I
101o3- � I
OFF
CAPE @
KENNEDY
* .5
/
@ 6
O12- 0 NEW YORK BIGHT @ - lOkm

~~~~2
2 e a
arc e *b
a o c OFF
(cm2) o * d CALIFORNIA @
i1011 - a
@
0 BANANA RIVER /
[0 MANOKIN RIVER

60
I lol� � /�[9- Ikm

O0 /
e/

108- - lOOm

HOR i@t DAY WEEK MONTH

7o~ ,Ig I I
10 03 104 105 106 107
I (sec)

FIGURE 3 Variance as a function of time in dye diffusion experiments.

rapidly sinks to the bottom, is dispersed or remains in place depending
on the eddy diffusivity of the bottom boundary layer. A reasonable
model for the eddy diffusivity of the bottom boundary layer has been
developed (Businger and Arya, 1974; Grant and Glenn, in press; Long,
1982):

Vt = * Z/h

m
where No is von Karmens constant (equals 0.4), U* is shear
velocity, %m is stratification correction, h is boundary layer
thickness and Z is roughness length established by measuring
near-bottom average velocity profiles.
Thus, as this expression indicates, mixing is affected by all of
the following: the depth of discharge (since eddy diffusion has a
maximum); how the sediment is distributed over the water column when
resuspended; how stratified the flow is (since stratification decreases
mixing, thus increasing %m); and the boundary shear stress U*.

U* is a critical parameter for sediment transport because it encom-
passes the interaction among wind (waves), tides (currents), and
sediment.
In considering the fates of those materials that reach the bottom,
resuspension and transport are of primary interest. For this reason,
parameter U* becomes very important. U* determines the mean fric-
tion on the large-scale flow field and the eddy viscosity. Eddy vis-
cosity is related to eddy diffusivity by a parameter known as
Richardson's number, which represents that fraction of the turbulent
energy (eddy diffusivity) generated by the shearing stresses that
maintain turbulent mixing against the density gradient. U* is also
related to the transport of the resuspended sediment through the mean
flow.
On the continental shelf, mean flow usually is determined by the
combination of winds and tides. Against a solid boundary the average
velocity profile of mean flow is logarithmic (Bowden, 1962). The eddy
diffusivity generated by frictional losses from the interaction of flow
with the bottom then provides turbulence for the transport of sediments
along the bottom boundary layer.
Instantaneous stress, if great enough, resuspends sediment. This
stress is associated with the combined wave and current flow, which is
coupled through the nonlinear interaction of steady and oscillatory
f lows. The time-mean-stress determines the friction of the mean flow.
Above the wave boundary layer, time-mean-stress is enhanced by wave-
current interaction above that value determined solely by current.
This enhancement has been established theoretically by Grant and Madsen
(1978, 1979) and Smith (1977), and in the field by Cacchione and Drake
(1982), Grant et al. (1982), and in the laboratory by Kemp and Simons
(1982) and Bakker and Doomn (1978).
The other important feature of the system is the sediment type.
The initiation of motion is clearly related to it, as is seabed rough-
ness, a parameter of considerable importance in flow-solid phase
interactions. Bed forms develop under combined flows over sand beds.
Under low flow conditions, silty-sandy beds are primarily controlled
by bioturbation (Grant et al., 1982), which influences seabed roughness
by causing mounds and furrows and adhesion in the sediment. The fates
of drilling fluids in different sediments may vary greatly.

FATES OF DRILLING FLUIDS AND CUTTINGS

The discharge into the ocean of heterogeneous drilling fluids and
cuttings results in much fractionation. The biota of the water column
are affected by that portion of material that becomes and remains
waterborne, the portion that depends on passive diffusion and convec-
tion for dispersion. The rates of dispersion are a critical deter-
minant of the fates of these materials in the water column and their
effects on the pelagic biota. Effects on the benthos result from that
portion of material that settles to the bottom where it can be incor-
porated into the sediments, resuspended, transported, and dispersed.

Pates in the Water Column

The preceding brief synopsis of the nature of dispersion in the ocean
and the behavior of materials discharged at sea provides a background
for considering more specifically the fates of drilling fluids and
cuttings that are discharged into the waters of the continental shelf.
In the case of cuttings discharges, the relatively large particles
settle rapidly near the well. Soluble and particulate fluid additives
adhering to the cuttings are to some extent washed off as the larger
particles settle. When whole fluid is discharged, most of the material
forms a plume which descends rapidly until it encounters the seabed or
reaches neutral buoyancy due to water entrainment and solids loss to
settling. In addition, a visible or upper plum is formed due to tur-
bulent mixing of the lower plume with seawater. Ayers et al. (1980b)
have estimated that the amount of material remaining in the upper plume
on discharge is 5 to 7 percent of the total discharge. Under most
conditions on the OCS, this portion is of primary concern in consider-
ing the fates of materials in the water column. In deeper water (about
80 m or more depending on site conditions), the lower plume will reach
neutral buoyancy before encountering the bottom. In this case, both
plumes will be of concern in considering water column fates. That
portion of the settled material that is resuspended through sedimentary
processes will be considered later along with the fates of settled
material.
Many field studies have traced the dispersion of the materials
contained in the buoyant plume. The studies of Ayers et al. (1980b),
Ecomar (1978), Ray and Meek (1980), and Trefry et al. (1981) generally
agree with those of Ayers et al. (1980a) and Trocine and Trefry (1982),
which will be considered in some detail here as representative studies
on the dispersion to be expected under continental shelf conditions.
The data obtained in the Ayers et al. (1980a) study are summarized in
Table 14, which represents two widely different discharge rates from
an exploratory platform at 23 m depth in the Gulf of Mexico. The study
was conducted in the summer under calm sea conditions, conditions that
did not favor rapid dispersion. For the two discharge rates studied,
the rates of change of solids concentration at first decreased rapidly
with distance (primarily because of settling), within 45 m in the first
study and 152 m in the second; this was followed by a much slower
average change in their concentration (primarily because of passive
diffusion) of approximately 0.1 mg/l/m or less. Depending upon the
discharge rate, the rapid bulk discharge of whole fluids resulted in
an initial dispersion of the fluid to between 30 and 50 ppm (solids
concentration) within these distances. Further dilution of the plume
occurred, approaching ambient total solids concentrations between 350
and 1,500 m from the discharge. At the low discharge rate the trans-
missivity values persisted below ambient values for somewhat longer
than did the values of total solids concentration. This is because
fine colloidal material has relatively little mass, but is very
effective in scattering light.
The time required for a pollutant to disperse to near-ambient
levels is an important parameter in assessing the impact of that pol-
lutant. Since time and distance are related by the velocity of the

TABLE 14 Dilution and dispersion of discharge plumes-a

Suspended Trans- Change in
Distance from Depthb Solids- mittance Suspended
Discharge Rate Source (m) (m) (mg/1) (%)c solids (mg/l/m)

275 bbl/hd 0 -- 1,430,000 -- --
6 8 14,800 -- --
45 11 34 2 378.6
138 9 8.5 56 0.31
150 9 7.0 48 0.013
364 9 1.2 37 0.06
625 9 0.9 71 0.001
Background 0.3-1.9 76-85
1,000 bbl/h 0 (Whole mud) -- 1,430,000 -- --
45 11 855 0 --
51 12 727 0 21.3
152 11 50.5 2 6.7
375 16 24.1 4 0.12
498 14 8.6 23 0.13
777 13 4.6 21 0.01
878 2 1.2 71 0.028
957 12 0.83 76 0.005
1,470 11 2.2 82 --
1,550 9 1.1 82 --
Background 0.4-1.1 80-87 --

A.Dilution and dispersion of two plumes produced by high-rate high-volume
discharges of used chrome lignosulfonate drilling fluid from an offshore
exploratory platform in the Gulf of Mexico.
_Depth at which highest plume concentration was found.
PMaximum solids concentration and minimum transmittance observed at the noted
distance.
d250 bbl discharged.

SOURCE: Adapted from Ayers et al. (1980a).

ambient currents, a plot of the distance from discharge divided by
current speed reflects the required time (transport time) to reach
given dilution. Ayers et al. (1980a) used this type of analysis to
determine the concentration over time of barium in the plume of the
rapidly discharged bulk drilling fluids (Figure 4). In this study
barium concentration was reduced to between 0.001 and 0.01 percent of
its concentration in the drilling fluid within 5 min of discharge.
Similar dispersion rates for chromium were also reported.

Whole Fluid Barium Concentration

5-
� = 1000 bbl/hr Test

-
C.)

E
.- 2-

o 1

0- � U

-1- �*
Control Barium Concentration

0 10 20 30 40 50 60 70 80 90 100 110 120

Transport Time (Minutes)

Source: Ayers, et al., 1980a.

FIGURE 4 Barium Concentration as a Function of Transport Time

The studies of Trefry, Trocine, Proni (in press) and Trocine and
Trefry (1982) focused on the careful analysis of particulate barium,
chromium, and iron in the surface plume as drilling particle tracers.
Barium is a particularly useful tracer because it is present in drill-
ing fluids in high concentrations (up to 449,000 pg/g of solids), it
has relatively low concentrations in the uncontaminated environment
(from 200 to 600 ug/g in near-shore sediments in the northern Gulf
of Mexico), and its primary anthropogenic source is drilling fluids.
On occasion, chromium has been used as a tracer. Iron is associated
with ferrochrome lignosulfonates and other components of drilling
fluids and has been found to be a good tracer of bentonite clays with
which it associates. Iron was found at levels of 200 ng/l in seawater
and 250 ig/g in ambient Gulf of Mexico sediments. Particulate
chromium and iron concentrations in the upper water column 200 m down-
stream of the discharge showed dispersion ratios of 0.5 x 106 at the
surface and 1.5 x 106 at 10 m depth. These ratios were similar to
those for fluid solids and show that chromium and iron closely follow
the dispersion of the fluid solids. Particulate barium, on the other
hand, showed a dispersion ratio of 1.4 x 106 at the surface and of
3.0 x 106 at 10 m, which is two to three times greater than that for
the other drilling-fluid solids. Barium thus behaves differently than
drilling solids, probably because of its relatively high density. The
data indicate a dispersion (dilution) ratio of 106 for drilling
solids within a distance of 200 m of a platform with a surface current
of 30 to 35 cm/s. Although the fluids were discharged in this case in
the form of a fine spray 10 m above the sea surface, the results of
this study substantiate those of Ayers et al. (1980a,b). The analyti-
cal techniques used here, combined with data comparing metal ratios in
drilling fluids and in natural sediments, provide a powerful tool for
tracing drilling fluids in the ocean for long distances from the dis-
charge site. Particulate barite was detected in one sample at 3.2 km
from the site at a concentration of 750 ng/l in an ambient concentra-
tion of 50 to 100 ng/1. The dispersion ratio at this distance was
found to be 109.
In the studies described above, components of the drilling fluids
investigated had either settled to the bottom or diffused by a factor
of 106 to less than 1 mg/l within 100 to 200 m less than 1 h after
discharge. A concentration of 30 to 50 mg/l of mud solids was reached
within a few minutes after discharge.
At water depths at which the main plume encounters the seabed (50
m or less, depending on site-specific conditions) it may be inferred
that less than 10 percent of the drilling fluids (143,000 g/l in the
Ayers et al. [1980a] experiments) eventually become transported by the
water column plume. Dilution of this portion of the discharge to 30
to 50 mg/l indicates mixing with a volume of seawater 2,500 to 5,000
times greater between 5 and 20 min after discharge. These conditions,
which occur soon after discharge, place bounds on the possible extent
of exposure of pelagic organisms such as phytoplankton, zooplankton,
and micronekton to discharges of drilling fluids.
In deeper water, the lower plume reaches a condition of neutral
buoyancy before it encounters the seabed. Thus, both plumes are of

interest in water column fate considerations. At this time, virtually
all field measurements of drilling fluid solids and soluble component
concentrations in the water column have been made on the upper plume.
Laboratory measurements and model calculations indicate that concentra-
tions in the lower plume are approximately an order of magnitude higher
than in the upper plume (Brandsma amd Sauer, 1983).

Benthic Fates

Ayers et al. (1980a) showed that over 90 percent of discharged
drilling-fluid solids settled directly to the bottom. The distance
from the well site and settlement time are primarily a function of
current and water depth. Several studies have evaluated the deposition
and accumulation of the solids on the seabed (Boothe and Presley, 1983;
Bothner, 1982; Dames and Moore, 1978; Ecomar, 1983; EG&G Environmental
Consultants, 1982; Gettleson and Laird, 1980; Meek and Ray, 1980;
Northern Technical Services, 1983; Trocine et al., 1981). Usually
these studies have included analyses of sediment samples for such
metals as barium, chromium, iron, lead, and mercury. Of these metals,
barium has proven to be the most useful tracer of drilling fluids.
Most other metals show moderate to no elevation and are restricted to
near-rig (within 125 m) sediments (Boothe and Presley, 1983). In most
of the studies total sedimentary concentrations of the elements were
determined and no attempt was made to distinguish among metals present
as sulf ides or hydrous oxides, those sequestered in organic matrices,
or those adsorbed on the surfaces of clay particles. Barium would
likely persist as particles of BaSO4, although the gradual
dissolution of this phase should occur since seawater is undersaturated
with respect to BaSO4 (Chow, 1976; Church and Wolgemuth, 1972). In
surface waters, biogeochemical scavenging would minimize increases in
the concentrations of dissolved barium.
The redistribution and ultimate fates of the settled drilling
solids depends upon many environmental factors. The most important
factor, as discussed earlier, is the shear velocity, which depends on
the shear between the bottom forms and the flow fluid. The sediment
type, bioturbation, bottom configuration, and suspended sediment-
established stability layers are the primary factors involving the
solid phase that influence the shear velocity. The flow field charac-
teristics are determined by the interaction of waves and currents. The
highest energy is imparted to the surface water particles by wave
action, which induces oscillatory motion. The effect of waves on par-
ticle motion decreases with increasing depth, and at depth D it is only
a fraction, exp (-2TrD/L), of that at the surface. L is the
distance between a wave crests, i.e., the "wavelength." This factor
becomes about 1/2 for a depth of one-ninth of a wavelength, 1/4 for
two-ninths of the wavelength and so on. Some motion is contributed to
water par- tidles by wave action until D is about half the
wavelength. Charac- teristics of typical sea waves are shown in Table
15.

TABLE 15 Typical Sea Waves

Period Wavelength Velocity Group Velocity
Type of Wave (s) ( m) (m/s) (m/s)

Ground swell 15 350 23.4 11.7

Swell 10 156 15.6 7.8

Ocean waves 7 76 10.9 5.5

In anchorages 3 14 4.7 2.3

SOURCE: Adapted from Barber and Tucker (1962).

The continental shelf regions are subjected not only to these
typical waves, but to storm swells with periods of 14 to 20 s. Such
swells impart motion to particles in the water column, and trigger
interactions with the bottom sediments over most of the shelf.
The potential effects of storms on sediment transport or movement
of drilling solids are very important. Drilling solids may build up
for extended periods at certain times of the year, but one major storm
event may be sufficient to move the entire layer the solids have
formed. Whether this happens depends of course on depth of water,
intensity of storms, biological stabilization or destabilization,
texture of the ambient sediments and stratification of the flow by
suspended sediments. These are the important factors to consider in
predicting the fates of deposited drilling solids.
Concern about the sensitivity of hard-substrate epibiota to the
physical and toxic effects of drilling fluids has prompted special
studies and regulatory restrictions, such as those related to the
Flower Garden Banks off the Texas coast. Exploratory drilling activi-
ties around the Flower Garden Banks have been monitored to determine
the possible effects of these activities on the coral reef ecosystem
associated with these banks. In these activities drilling fluids and
cuttings had to be shunted to within 10 m of the bottom to protect the
banks from the possible plume fallout of materials dispersed in the
water column. Studies by Continental Shelf Associates (1975, 1976) and
Gettleson (1978) indicate that barium concentrations in ambient sedi-
ments vary from 10 to 600 ppm of whole sediment. Postdrilling analysis
showed the average barium concentration at 100 m from the drill site
to be 3,000 ppm; at 1,000 m from the drill site, the average barium
concentration was 1,000 ppm. From 100 to 1,000 m, the concentration
decreased inversely with the square root of the distance, and was

radially symmetrical around the discharge. The relatively weak
currents and low wave energy at the site (bottom currents had a value
of about 10 cm/s) resulted in the settlement of most of the solids
associated with drilling fluids and cuttings within 1,000 m of the
discharge.
Stronger currents were observed in the Tanner Bank area off
southern California (Ecomar, 1980; Meek and Ray, 1980). Maximum bottom
currents reached 36 cm/s and averaged 21 cm/s. Approximately 863,290
kg of solids were discharged over 85 days. It was inferred from sedi-
ment trap data that 12 percent of the solids settled within 50 m. It
was estimated that between 44 and 94 percent of this material was in
turn transported directly or by resuspension from the drill site by
currents, since little accumulation was observed.
Even stronger currents were observed during a study conducted in
the Lower Cook Inlet, Alaska (Dames and Moore, 1978). Maximum bottom
currents of tidal origin reached 99 cm/s. Sediment trap samples showed
that the cuttings and some drilling-fluid particles (barite) were
carried initially to the seafloor. However, because of the strong
tidal current, dispersion of the settled material was rapid. Tele-
vision examination of the seafloor at the well site immediately after
drilling showed no visible accumulation of cuttings. Barium levels
were not elevated. On the other hand, different results were observed
in a study conducted in the mid-Atlantic OCS (EG&G Environmental Con-
sultants, 1982). Maximum bottom current reached 18 cm/s and the bottom
was too deep (120 m) to be affected by storm waves. In this case,
elevated piles of cuttings and sediment barium levels an order of mag-
nitude above ambient levels were both observed in the area of the well

site immediately after drilling and 1 year later.
Data from six types of drilling operations, three in shallow water
dphwas a major controlling factor on bottom deposition (Boothe and
Presey,1983). Detailed sediment analyses revealed that the only
component of the drilling discharge remaining in the sediments at a
statistically significant level beyond 125 in was barium. A mass
balncestudy showed that only 11.6 percent of the total barium dis-
chagedfrom 25 wells still remained within 500 m of the platform. As
ca eseen in Table 16, shallow water locations have approximately 10
tmsless total barium remaining within 500 in. Little (5-10 times)
tnoelevation of other drilling related metals was seen in near-
platormsediments, and only a few stations showed any hydrocarbon

Two areas of particular interest in oil and gas development are the
nearshore Beaufort Sea in the Arctic Ocean and Norton Sound in the
Beaufort Sea. These areas differ from the others studied because they
are covered with ice for a large part of the year, and drilling in the
immediate future will occur in both areas shoreward of the 20-in depth
contour. A drilling-fluids discharge study was conducted in the
Prudhoe Bay area of the Beaufort Sea in the winter of 1979, in which
discharge tests were conducted both below and above the ice (Northern
Technical Services, 1981). In the below-ice discharge, rapid disper-
sion was observed in the 8 m water column, with only loose flocs of

TABLE 16 Mass Balance of Total Excess Sediment Barium Surrounding Offshore Drilling Sites

Total
Barium Mean Total Excess Barium (TEB) in
Water Used (TBU) BAEXAC Sediments (10' kg) within Percent of TBU within
Drilling Depth Mode of in Drilling 0-500m Radius (m)s Radius (m)
Site' Type2 (m) Discharge3 Activities Radius Ref.
(10' kg) (g/m2)4 500 1000 2000 3000 500 1000 2000 3000

West Cameron ES 13 Surface 2,414 25.8 20.3 -- -- 131 0.84 -- -- 5.5 Boothe ana
294 Presley, 1983

Vermilion ED 102 Surface 229 28.0 22.0 -- -- 193 9.6 -- -- 84.0
381

Matagorda DS 29 Surface 2,334 27.5 21.6 -- -- 131 0.93 -- - 5.6
686

High Island DD 76 Surface 1,518 173.0 136.0 -- -- 1,093 9.0 -- -- 72.0
A-341

Brazos PS 34 Surface 1,041 19.2 15.1 -- -- 70 1.5 -- -- 6.7
A-1

Vermilion PD 79 Surface 4,964 732.0 575.0 -- -- 2,330 11.6 -- -- 47.0
321

High Island ES 55 Shunted 127 8.8 6.9 21 -- -- 5.4 16.5 -- -- Gettleson and
A-502 Lairo, 1980

Mustang Island ED 75 Shunted 820 14.0 11.0 31 -- _ 1.3 3.8 -. _
A-85

High Island ED 95 Surface 574 12.7 10.0 19 46 90 1.7 3.4 8.1 16.0
A-367

High Island ED 112 Shunted 396 143.0 117.0 129 161 -- 30.0 33.0 41.0 -- Continental
A-3 84 Shelf Asso-
ciates, 1983

High Island ED 124 Shunted 618 43.4 34.0 78 -- -- 5.5 12.6 -- -- Gettleson and
A-389 Laird, 1980

New Jersey ED 120 Surface 443 8.2 6.4 16 42 86 1.5 3.7 9.5 19.0 EG&G, 1982
(18-3) 684

'All drilling sites are in the northwest or north central Gulf of Mexico, except for New Jersey 684, which is located in the western Atlantic 156 km oft
the coast off New Jersey.

2Exploratory (E), development (D), or production (P) in shallow (S) or deep (D) water.

'Shunted discharge pipes were located within 10-15 m of the seafloor.

"Mean total excess barium in the sediment column areal concentration (BAEXAC) within a 500-meter radius of the drilling site = TEB500/27t(500)2.

'All TEB data were estimated using the procedure described in Boothe and Presley, 1983 except for the TEB3000 values for this study. These TEB3000
values were estimated by fitting a power curve of the form y=axb to the BAEXAC data for all stations including the 3000m ones. These regressions were
significant (p < 0.01) for all six drilling sites based on an F test. The range of R2 values was 0.34 to 0.62. The area (representing TEB) under each
power curve rotated 360� and from 500-3000 m radius was integrated. This value was added to the TEB500 value to get the TEB3000 values given. No
actual samples were collected between 500 and 3000 m radii from the drilling sites.. These TEB3000 values are included for comparison purposes to give an
estimate of the TEB present within 3000 m of these drilling sites.

SOURCE: Boothe and Presley, 1983

drilling materials collecting on the bottom. These were then resus-
pended and transported by episodic events (probably from changes in
barometric pressure) that produced bottom currents of up to 10 cm/s.
The determination of trace metals and barium concentrations in the
sediment before discharge and 2 to 3 weeks following showed no change.
The study of discharge disposal on ice, in which fluids and cuttings
were discharged onto the ice surface and allowed to remain until the
spring breakup of the ice, caused a broad ultimate dispersal of the
materials. A recent open-water study (in an area without ice cover)
at the Tern artificial ice island in the Beaufort Sea confirmed the
earlier studies (Northern Technical Services, 1983). Drilling fluids
and cuttings were prediluted with 30 times their volume of ambient
seawater and discharged at the rate of 60 bbl/min into the current
impinging on the island. The suspended sediment concentrations were
reduced by a factor of 1,000 within 100 m and 15 min of discharge, and
no statistically significant patterns of increase in barium, chromium,
or lead concentrations were found in the surrounding sediments.
A recent open-water study was made in Norton Sound (Ecomar, 1983)
giving further data on the behavior of drilling fluids and cuttings
discharged into shallow waters. This study was conducted under
extremely adverse weather conditions unlike those of any other similar
study, and therefore may serve as a limiting case in analyzing the
dispersal of fluids and cuttings in general. Currents at the site were
between 18 cm/s at 11 m depth and 80 cm/s at the surface in a southwest
direction, and wave-induced motion reached 750 cm/s. These conditions
can be compared to those in a Gulf of Mexico study, in which the
currents reported were similar, but wave-induced motion was only 9
cm/s. The main difference observed in dispersion patterns was that,
in the first study, the wave motion increased the quantity of fluids
and cuttings supported by the surface plume longer than at other sites;
otherwise, the decrease in ratio of solid concentrations in the fluid
to that in the plume was about 5 x 105 for all cases studied 20 min
after the discharge.
Table 17 summarizes the important role of environmental factors in
determining the fates of settled materials around a well site. The
relatively dispersive energy of the areas is represented by the maximum
bottom currents. Water depth is important because it affects how much
wave-induced oscillatory currents above the seabed interact with bottom
currents to induce sediment resuspension (Grant and Madsen, 1978). In
the studies reported in the table, visual evidence of discharged fluids
and cuttings was sought through bottom television or submersibles. In
Cook Inlet, there was no visual evidence of drilling as soon as the rig
left. On Tanner Bank, there was also no visual evidence of discharged
material. In the mid-Atlantic, discharges at the well site were still
visible I year after the rig had moved off location.
Increased barium levels in the sediment immediately after drilling
provide another indication of the fates of settled materials. In Cook
Inlet, barium levels did not increase. in this area, the energy was
so high that the barite particles were rapidly swept away. On Tanner
Bank, barium concentrations in the sediment were increased near the

TABLE 17 Effect of Environmental Factors on Study Results

Cook Inlet Tanner Bank Mid-Atlantic

Environmental factors

Maximum bottom 99 36 18
current (cm/s)

Water depth (in) 62 55 120

Study results

Visual evidence of
discharged material No No Yes
immediately after
drilling

Increased barium
levels in sediment No Yes Yes
immediately after
drilling

SOURCE: Adapted from Ayers (1981).

well site. In the low-energy mid-Atlantic area, increased barium
levels in the sediment around the well site were still found 1 year
after drilling. These results show that the length of time the settled
material remains concentrated at the well site depends on environmental
factors that govern resuspension and dispersion after settlement. This
period of time ranges from hours to years.
The processes that govern resuspension of settled particles and
their subsequent dispersion are known in theory but have not generally
been applied to the fates of deposited drilling fluids and cuttings.
Particles are eroded from the seabed when the eddy diffusivity becomes
great enough to overcome the adhesive forces of the sediment and the
effect of gravity. Eddy diffusivity, as discussed earlier, is a
complex function of current velocity, roughness of the sediment, and
turbulence induced by waves. The adhesive forces of the sediment are
a function of sediment composition, sediment fabric, sedimentation
rates, and biological processes, including bioturbation, tube con-
struction, and microbial binding. In some studies, only current
velocity and particle size distribution have been used to predict
sediment erosion from the seabed (Figure 5). According to these

Q iWter
Content (%)eposition

I
CLAY SILT SAND
1 4 20 60 200 2000
PARTICLE DIAMETER (Am)

FIGURE 5 Relationship between current speed, particle diameter, and
sediment erosion, transport, or deposition (after Kennett, 1982)

criteria, the critical entrainment velocity decreases with decreasing
grain size down to fine sand size particles, thereafter varying greatly
depending on the cohesiveness and consolidation of sediments. It is
now well established that shear stress (closely related to eddy vis-
cosity), and not velocity, is the variable of interest since it takes
into account the seabed roughness factor and turbulent motion from
waves; velocity alone does not. Figure 5 indicates that a velocity of
100 cm/sc or more is required to erode consolidated clay-sized sedi-
ments from the seabed. Most of the time on the shelf, mean flow is
insufficient to move sediments, but waves resulting in bottom orbital
velocities, which cause sufficient shear stress to erode sediments, are
common. Storm waves during seasons of heavy weather are the main
determinant of sediment transport in many continental shelf environ-
ments.
Both settling and erosion of particles on the seabed is related to
a nondimensional fall diameter S* of a sediment particle in the con-
ventional Shields' diagram (Madsen and Grant, 1976). The term S* is
a function of both particle diameter, particle density, and density of
the fluid medium. While the Shields' diagram fails to consider seabed
roughness, biological effects, and sediment mixtures, it is useful in
showing that particles of considerably different densities (e.g., ben-
tonite, barite, shales, and sandstones), such as those in drilling
fluids and cuttings, will undergo selective dispersion under prevailing
continental shelf current (10 to 50 cm/s) and wave (5 to 15 s) condi-
tions. Furthermore, the effects of organisms, from microbes to large
mammals, may increase or decrease the critical eddy viscosity by
changing bottom roughness and sediment cohesiveness (Grant el al.,
1982; Nowell et al., 1981).

REFERENCES

Ayers, R.C., Jr. 1981. Fate and effects of drilling discharges in
the marine environment. Proposed North Atlantic OCS Oil and Gas
Lease Sale 52. Statement delivered at public hearing, Boston,
Mass., November 19, 1981. Bureau of Land Management, U.S.
Department of the Interior.

Ayers, R.C., Jr., T.C. Sauer, Jr., D.O. Steubner, and R.P. Meek.
1980a. An environmental study to assess the effect of drilling
fluids on water quality parameters during high rate, high volume
discharges to the ocean. In: Proceedings of a Symposium on
Research on Environmental Fate and Effects of Drilling Fluids and
Cuttings. Washington, D.C.: Courtesy Associates. Pp. 351-391.

Ayers, R.C., Jr., T.C. Sauer, Jr., R.P. Meek, and G. Bowers. 1980b.
An environmental study to assess the impact of drilling discharges
in the mid-Atlantic. I. Quantity and fate of discharges. In:
Proceedings of a Symposium on Research on Environmental Fate and
Effects of Drilling Fluids and Cuttings. Washington, D.C.:
Courtesy Associates. Pp. 382-418.

Barber, N.F., and M.J. Tucker. 1962. Wind waves. In: M.N. Hill
(ed.), The Sea. Vol. 1. New York: Interscience. Pp. 664-699.

Batchelor, G.K. 1952. Diffusion in a field of homogeneous turbu-
lence. Proc. Camb. Philos. Soc. 48:345-362.

Bakker, W.T., and T.H. Doom. 1978. Near bottom velocities in waves
with a current. In: Proceedings of a Coastal Engineering
Conference. Pp. 1394-1413.

Boothe, P.N., and B.J. Presley. 1983. Distribution and behavior of
drilling fluid and cuttings around Gulf of Mexico drill sites.
Draft final report. API Project No. 243. American Petroleum
Institute, Washington, D.C.

Bothner, M.H., et al. 1982. The Georges Bank monitoring program.
Analysis of trace metals in bottom sediments. First year final
report to the New York OCS Office, Minerals Management Service,
U.S. Department of the Interior. Interagency Agreement No.
AA851-IA2/8. Geological Survey, U.S. Department of the Interior,
Woods Hole, Mass.

Bowden, K.F. 1962. Turbulence. In: M.N. Hill (ed.), The Sea.
New York: Interscience. Pp. 802-825.

Brandsma, M.G., L.R. Davis, R.C. Ayers, Jr., and T.C. Sauer, Jr. 1980.
A computer model to predict the short-term fate of drilling dis-
charges in the marine environment. In: Proceedings of a

Symposium on Research on Environmental Fate and Effects of
Drilling Fluids and Cuttings. Washington, D.C.: Courtesy
Associates. Pp. 588-610.

Brandsma, M.G., and R.C. Sauer. 1983. The OOC model: prediction of
short term fate of drilling fluids in the ocean. Part two: model
results. In: Proceedings of Minerals Management Service Workshop
on Discharges Modeling, Santa Barbara, Calif., February 7-10, 1983.

Businger, J.A., and S.P.S. Arya. 1974. Height of the mixed layer in
the stably stratified planetary boundary layer. In: Advances in
Geophysics. New York: Academic Press. Pp. 73-92.

Cacchione, D.A., and D.E. Drake. 1982. Measurements of storm
generated bottom stresses on the continental shelf. J. Geophys.
Res. 87(C3):1952-1961.

Chow, T.J. 1976. Barium in Southern California coastal waters: a
potential indicator of marine drilling contamination. Science
193:57-58.

Church, T.M., and K. Wolgemuth. 1972. Earth Planet. Sci. Lett.
15:35-44.

Colonell, J.M. (ed.). 1981. Port Valdez, Alaska: environmental
studies 1976-1979. Occasional Publication No. 5. Institute of
Marine Science, University of Alaska, Fairbanks, Alaska. 373 pp.

Continental Shelf Associates. 1975. East Flower Garden Bank
environmental survey. Rep. No. 1: Pre-drilling environmental
assessment, Vol. 1, II. Rep. No. 2: Monitoring program and post-
drilling environmental assessment. Vols. I, II, III, IV. Reports
submitted to Mobil Oil Corp. for lease OCS-G2759.

Continental Shelf Associates. 1976. Pre-drilling survey report.
Results of gravity core sediment sampling and analysis for barium.
Post-drilling survey report. Results of gravity core sediment
sampling and analysis for barium. Block A-85, Mustang Island
Area, East Addition. Reports submitted to Conoco, Inc.

Continental Shelf Associates. 1982. Environmental monitoring program
for platform "A,' Block A-85, Mustang Island Area, East Addition,
near Baker Bank, March 1978 to March 1981. Report submitted to
Conoco, Inc.

Dames & Moore, Inc. 1978. Drilling fluid dispersion and biological
effects study for the lower Cook Inlet C.O.S.T. well. Report
submitted to Atlantic Richfield Co. Dames & Moore, Inc.,
Anchorage, Alaska. 309 pp.

Ecomar, Inc. 1978. Tanner Bank mud and cuttings study. Conducted for
Shell Oil Company, January through March 1977. Ecomar, Inc.,
Goleta, Calif. 495 pp.

Ecomar, Inc. 1980. Maximum mud discharge study. Conducted for
Offshore Operators Committee, Environmental Subcommittee, under
direction of Exxon Production Research Co. Ecomar, Inc., Goleta,
Calif. 495 pp.

Ecomar, Inc. 1983. Mud dispersion study, Norton Sound Cost Well No.
2. Conducted for Arco Alaska, Inc., Anchorage, Alaska. 91 pp.

EG&G Environmental Consultants. 1982. A study of environmental
effects of exploratory drilling on the Mid-Atlantic Outer
Continental Shelf--final report of the Block 684 Monitoring
Program. EG&G Environmental Consultants, Waltham, Mass.
Available from Offshore Operators Committee, Environmental
Subcommittee, P.O. Box 50751, New Orleans, LA 70150.

Folsom, T.R., and A.C. Vine. 1957. On the tagging of water masses
for the study of physical processes in the oceans. In: Natl.
Acad. Sci.-Natl. Res. Counc. Publ. 551:121-132.

Gettleson, D.A. 1978. Ecological impact of exploratory drilling: a
case study. In: Energy/Environment 1978. Society of Petroleum
Industry Biologists Symposium, 22-24 August, 1978, Los Angeles,
Calif. 23 pp.

Gettleson, D.A., and C.E. Laird. 1980. Benthic barium in the
vicinity of six drill sites in the Gulf of Mexico. In:
Proceedings of a Symposium on Research on Environmental Fate and
Effects of Drilling fluids and Cuttings. Washington, D.C.:
Courtesy Associates. Pp. 739-788.

Grant, W.D., and S.M. Glenn. In press. Continental shelf bottom
boundary layer model: theoretical model. Vol. I. Woods Hole
Oceanographic Institution Technical Memorandum. 160 pp.

Grant, W.D., S.M. Glenn, and A.J. Williams. In press. Near
bottom velocity profile measurements under combined wave and
current flows. Comparison with theory. Woods Hole Oceanographic
Institution Technical Memorandum. 160 pp.

Grant, W.D., L.F. Boyer, and L.P. Sanford. 1982. The effects of
bioturbation on the initiation of motion of intertidal sands. J.
Mar. Res. 40:659-677.

Grant, W.D., and S.M. Glenn. 1983. Continental shelf bottom
boundary layer model. Vol. I: Theoretical model development.
Final report to the American Gas Association PR-153-125. Depart-
ment of Ocean Engineering, Woods Hole Oceanographic Institution.
163 pp.

Grant, W.D., and O.S. Madsen. 1979a. Combined wave and current
interaction with a rough bottom. J. Geophys. Res. 84:1797-1808.

Grant, W.D., and O.S. Madsen. 1979b. Bottom friction under waves in
the presence of a weak current. NOAA TM ERL/MESA-29. 150 pp.

Grant, W.D., and O.S. Madsen. 1982. Moveable bed roughness in
unsteady oscillatory flow. J. Geophys. Res. 87(C1):469-481.

Gross, M. Grant. 1975. Trends in waste solid disposal in U.S. coastal
waters, 1968-1974. In: Thomas M. Church (ed.). Marine Chemistry
of the Coastal Environment. American Chemical Society ACS
Symposium Series 18. 710 pp.

Hill, W.N. (ed.). 1962. Physical oceanography. In: The Sea. Vol.
1. New York: Interscience. 864 pp.

Hood, D.W., B. Stevenson, and L.M. Jeffery. 1958. Deep sea disposal
of industrial wastes. Ind. Eng. Chem. 50:885-888.

Ichye, T. 1963. Oceanic turbulence. Technical Paper No. 2.
Prepared for Office of Naval Research by Florida State
University. 200 pp.

Joseph, J., and H. Sendner. 1958. Uber die horizontale diffusion im
meere. Dtsch. Hydrogr. Z. 11:49-77.

Judson, S., and D.F. Ritter. 1964. Rates of regional denudation in
the United States. J. Geophys. Res. 64:3395-3401.

Kemp, P.H., and R.R. Simons. 1982. The interaction between waves and
a turbulent current: waves propogating with the currents. J.
Fluid Mech. 116:227-250.

Kennett, J.P. 1982. Marine Geology. Englewood Cliffs, N.J.:
Prentice Hall. 813 pp.

Ketchum, B.H., and W.L. Ford. 1952. Rate of Dispersion in the Wake
of a Barge at Sea. Trans. Am. Geophys. Union 33(5):680-684.

Long, C.E. 1981. A simple model for time-dependent stably stratified
turbulent boundary layers. Special Report No. 95. Department of
Oceanography, University of Washington, Seattle. 170 pp.

Madsen, O.S., and W.D. Grant. 1976. Sediment transport in the
coastal environment. Rep. No. 209. Ralph M. Parsons Lab.,
Massachusetts Institute of Technology. 105 pp.

Meek, R.P., and J.P. Ray. 1980. Induced sedimentation, accumulation,
and transport resulting from exploratory drilling discharge of
drilling fluids and cuttings. In: Proceedings of a Symposium on

Research on Environmental Fate and Effects of Drilling Fluids and
Cuttings. Washington, D.C.: Courtesy Associates. Pp. 259-284.

Moon, F.W., Jr., C.L. Bretschneider, and D.W. Hood. 1957. A method
for measuring eddy diffusion in coastal embayments. Inst. Mar.
Sci. l(Pub. Univ. Tex.)IV:14-21.

Northern Technical Services. 1981. Beaufort Sea drilling effluent
disposal study. Prepared for the Reindeer Island stratigraphic
test well participants under the direction of SOHIO Alaska
Petroleum Company.

Northern Technical Services. 1983. Open water drilling effluent
disposal study, Tern Island, Beaufort Sea, Alaska. Conducted for
Shell Oil Co. 87 pp.

Nowell, A.R.M., P.A. Jumars, and J.E. Ekman. 1981. Effects of
biological activity on the entrainment of marine sediments. Mar.
Geol. 42:133-153.

Okubo, A. 1968. A new set of oceanic diffusion diagrams. Chesapeake
Bay Inst. Tech. Rep. 38.

Okubo, A. 1971. Horizontal and vertical mixing in the sea. In:
D.W. Hood (ed.), Impingement of Man on the Ocean. New York:
Wiley-Interscience. 738 pp. Pp. 89-168.

Petrazzuolo, G. 1981. Preliminary report. An environmental assess-
ment of drilling fluids and cuttings released onto the outer con-
tinental shelf. Vol. 1: Technical assessments. Vol. 2: Tables,
figures and Appendix A. Prepared for Industrial Permits Branch,
Office of Water Enforcement and Ocean Programs Branch, Office of
Water and Waste Management, U.S. Environmental Protection Agency,
Washington, D.C.

Prichard, D.W., and J.H. Carpenter. 1960. Measurements of turbulent
diffusion in estuarine and inshore waters. Bull. Int. Assoc. Sci.
Hydrol. 20:37-50.

Ray, J.P. 1979. Offshore discharge of drilling muds and cuttings.
In: Outer Continental Shelf Frontier Technology: Proceedings of
a Symposium. Washington, D.C.: National Academy of Sciences.

Ray, J.P., and R.P. Meek. 1980. Water column characterization of
drilling fluids dispersion from an offshore exploratory well on
Tanner Bank. In: Proceedings of a Symposium on Research on
Environmental Fate and Effects of Drilling Fluids and Cuttings.
Washington, D.C: Courtesy Associates. Pp. 223-258.

Ray, J.P., and E.A. Shinn. 1975. Environmental effects of drilling
muds and cuttings. In: Environmental Aspects of Chemical Use in
Well Drilling Operations. EPA-560/1-75-004. Washington, D.C.:
U.S. Environmental Protection Agency. Pp. 533-545.

Richardson, L.F. 1926. Atmospheric diffusion shown on a distance-
neighbor graph. Proc. R. Soc., Lond. A110:709-727.

Seligman, H. 1955. International Conference on the Peaceful Uses of
Atomic Energy. Paper No. 419.

Smith, J.D. 1977. Modeling of sediment transport on continental
shelves. In: The Sea. Vol. 6. New York: Wiley-Interscience.

Stommel, H. 1949. Horizontal diffusion due to oceanic turbulence.
J. Mar. Res. 8:199-225.

Stumm, W., and J.J. Morgan. 1970. Aquatic Chemistry. New York:
Wiley-Interscience. 583 pp.

Sverdrup, H.U., M.W. Johnson, and R.H. Fleming. 1942. The Oceans.
Englewood Cliffs, N.J.: Prentice Hall. 1060 pp.

Trefry, J.H., R.P. Trocine, and D.B. Meyer. 1981. Tracing the fate of
petroleum drilling fluids in the northwest Gulf of Mexico. In:
Conference Record: Oceans 81, Boston, Mass. Vol. 2. Available
from Marine Technology Society, Washington, D.C. Pp. 732-736.

Trefry, J.H., R.P. Trocine, and J.R. Proni. In press. Drilling
fluid discharges into the marine environment. Presented at Third
International Ocean Disposal Symposium, Woods Hole Oceanographic
Institution, October 12-16, 1981. In: Wastes in the Ocean. New
York: John Wiley & Sons.

Trocine, R.P., and J.H. Trefry. 1983. Particulate metal tracers of
petroleum drilling fluid dispersion in the marine environment.
Environ. Sci. Technol. 17(9).

Yudelson, J.M. 1967. A survey of ocean diffusion studies and data.
W.K. Kech Laboratory of Hydraulics and Water Resources Tech. Mem.
No. 67-2. California Institute of Technology, Pasadena, Calif.

Zingula, R.P. 1975. Effects of drilling operations in the marine
environment. In: Environmental Aspects of Chemical Use in Well
Drilling Operations. EPA-560/1-75-004. Washington, D.C.: U.S.
Environmental Protection Agency. Pp. 433-448.

The Biological Effects of Drilling Discharges

INTRODUCTION

There are two major environmental concerns about discharging used
drilling fluids to the oceans: (1) that these fluids may kill marine
organisms, produce harmful sublethal responses in them, or alter eco-
systems; and (2) that some of these fluids may contain metals and
organic compounds that accumulate in marine organisms to concentrations
that could harm them or their consumers, including humans. A substan-
tial body of scientific research addresses these concerns. The purpose
of this chapter is to summarize and critically evaluate this litera-
ture.
Evaluating the effects of a complex mixture on the marine environ-
ment requires many kinds of information. The acute lethal and chronic
toxicities of the complex mixture and of its ingredients must be known.
Biological responses of marine organisms to sublethal concentrations
of the mixture must be not only measured but also evaluated in terms
of their ecological significance and implications for human health.
Chemical compositions of mixtures resulting in acute and sublethal
effects need to be determined. Laboratory studies of the mixture's
acute, chronic, and sublethal effects should be interpreted in the
context of expected or measured concentrations and exposure durations
in the field. Finally, the long-term responses of marine organisms,
communities, and ecosystems exposed to these mixtures should be docu-
mented in the field. The information available on drilling fluids with
regard to all these points provides the basis for evaluating these
fluids' effects on the marine environment.

THE TOXICITIES OF DRILLING FLUID COMPONENTS

Acommon practice in evaluating the toxicity of such a complex mixture
as a drilling fluid is to determine the toxicities of its components
in bioassays. The assumption is made that the toxicities of the indi-
vidual components are approximately additive and that no physical or
chemical interactions among ingredients affect the toxicity of the
mixture during its formulation or use. These assumptions are probably
invalid with regard to used treated drilling fluids. Sprague and Logan
(1979) showed that the calculated sum of toxicities of ingredients in
a used drilling fluid was not always a good predictor of the acute

toxicity of the whole used fluid to freshwater fish. In spite of these
limitations, bioassays with drilling-fluid ingredients are likely to
be useful in identifying the relative toxicities of components. If
these toxic or physically damaging ingredients are identified, they can
in some cases be replaced by less harmful substitutes. The ocean dis-
charge of fluids containing such ingredients also can be regulated.

Acute Lethal Toxicity

Acute lethal bioassays (usually run over 96 hours) are used to compare
the relative acute toxicities of different drilling fluids and
drilling-fluid ingredients and the relative sensitivities of different
species. They establish the basis for determining quantitative rela-
tions between exposures and effects. They are quick and inexpensive
and therefore a very popular means of initially screening and ranking
the potential hazards of chemicals that might be released to the envi-
ronment in substantial quantities. They also help determine the ranges
of concentrations to be used in studies of chronic and sublethal
effects.
Acute lethal bioassays cannot be used alone, however, to predict the
environmental effects of discharging drilling fluids to the ocean (see
extended discussion of limitations in Chapter 5). In such bioassays,
animals often are exposed to drilling-fluid ingredients, drilling
fluids, or drilling-fluid fractions in concentrations substantially
higher and for much longer than in the field. High concentrations and
long exposure times are often needed to produce statistically signifi-
cant results with a reasonably small number of test animals. If
chronic as well as acute bioassay data are generated, it may be possi-
ble to extrapolate (using application or safety factors) to environ-
mentally more realistic exposure concentrations.
Table 18 presents some of the data available on the acute lethal
toxicities of drilling-fluid ingredients to marine and estuarine
organisms.

Major Ingredients

Of the five ingredients that make up more than 90 percent of most
water-based drilling fluids, namely, barite, bentonite, lignite, chrome
lignosulfonate, and sodium hydroxide (Perricone, 1980), only chrome and
ferrochrome lignosulfonates and sodium hydroxide are moderately toxic
(LC50 of 100 to 1,000 ppm) to any but the most sensitive species and
life stages of marine organisms (Table 18). The 96-h LC50 of NaOH for
rainbow trout in fresh water is 105 to 110 ppm (Logan et al., 1973;
Sprague and Logan, 1979). The toxic effects of this material are
attributed to elevation in pH. Chaffee and Spies (1982) report that
adding sufficient NaOH to seawater to increase pH from 7.8 (control)
to 8.5 or 9.0 reduced the growth rate and increased the incidence of
developmental anomalies in embryos of the starfish Patiria miniata.
Because of the higher buffer capacity of seawater 2xl0-eq/Z/pH
unit compared to that of fresh water, no significant change in pH

TABLE 18 Acute Toxicity of Drilling Fluid Components to Estuarine and Marine Organismsa

Compound Bioassay Organism 96-1 LC50(ppm) Reference

Aquagel� (Wyoming Oyster Crassostrea virginica >7,500 Daugherty, 1951
bentonite) Shrimp Pandalus hypsinotus 100,000 Dames and Moore, 1978
Copepod Acartia tonsa 22,000 EG&G Bionomics, 1976a
Alga Skeletonema costatum 9,600 EG&G Bionomics, 1976a

Barite (barium Several fish an6 invertebrates >7,500 Daugherty, 1951
sulfate) Sailfin molly Mollieniasis Grantham and Sloan,
latipinna >100,000 1975
Shrimp Pandalus hypsonotus >100,000 Dames and Moore, 1978
Copepod Acartia tonsa 590 EG&G Bionomics, 1976a
Alga Skeletonema costatum 385-1650 EG&G Bionomics, 1976a

Calcite (calcium Sailfin molly M. latipinna >100,000 Grantham and Sloan,
carbonate) 1975

Siderite (iron Sailfin molly M. latipinna >100,000 Grantham and Sloan,
carbonate) 1975

Carbonox (lignitic Several fish and invertebrates >7,500 Daugherty, 1951
material)

Lignite Sailfin molly M. latipinna >15,000 Hollingsworth and
Lockhart, 1975

Chrome lignosulfonate Sailfin molly M. latipinna 12,200 Hollingsworth and
Lockhart, 1975

Chrome-treated White shrimp Penacus setiferus 465 Chesser and McKenzie,
lignosulfonate 1975

Ferrochrome Dungeness crab Cancer magister 210b Carls and Rice, 1980
lignosulfonate Dock shrimp Pandalus danae 120b Carls and Rice, 1980

Iron lignosulfonate White shrimp Penaeus setiferus 2,100 Chesser and McKenzie,
1975

Cellulosic calcium White shrimp Penaeus setiferus 1,925 Chesser and McKenzie,
caronate workover 1975
additive

TABLE 18 (continued)

Compound Bioassay Organism 96-1 LC50(ppm) Reference

Jelflake� (shredded Several fish and invertebrates >7,500 Daugherty, 1951
cellophane)

Impermee (pregela- Several fish and invertebrates 500-7,500 Daugherty, 1951
tinized starch)
Oyster Crassostrea virginica 3,000 Daugherty, 1951

Fibertex� (shredded Several fish and invertebrates >7,500 Daugherty, 1951
cane fiber)

Mica Several fish and invertebrates >7,500 Daugherty, 1951

Low-molecular-weight White shrimp Penaeus setiferus 3,500 Chesser and McKenzie,
polyacrylate 1975

Quebraco (tannin) Sailfin molly M. latipinna 158 Hollingsworth and
Lockhart, 1975

Modified hemlock bark White shrimp Penaeus setiferus 265 Chesser and McKenzie,
extract (tannin) 1975

Sodium acid pyrophos- Sailfin molly M. latipinna 7,100 Grantham and Sloan
phate (Ha2H2P207) 1975

Oilfot (Na tetra- Several fish and invertebrates >7,500 Daugherty, 1951
phosphate)

Quadrafot (Na poly- Several fish and invertebrates 500-7,500 Daugherty, 1951
phosphate)

Oil well cement Several fish and invertebrates 70-450 Daugherty, 1951

White lime Several fish and invertebrates 70-450 Daugherty, 1951

Formaldehyde Pompano Trachinotus carolinus 25-31 Birdsong and Avault,
1971

Dowacide G � Sheepshead minnow Cyprinodon 0.52 Borthwick and Schimmel,
(79% Na penta- variegatus (2 wk. fry) 1978
chlorophenate)
Pinfish Lagodon rhomboides 0.066 Borthwick and Schimmel,
(48-h prolarvae) 1978

Diesel fuel Many fish and invertebrates 0.1-1,000 Neff and Anderson, 1981

aIMCO et al. (1969) defines LC50 toxicities as follows: very toxic, <lppm; toxic, 1-100 ppm;
moderately toxic, 100-1,000 ppm; slightly toxic 1,000-10,000 ppm; practically nontoxic, >10,0900
ppm.
b144-h LC50.

occurs when drilling fluid is discharged to the ocean. Based on the
evidence to date, barite, bentonite, and lignite can be classified as
practically nontoxic (having LC50 values greater than 10,000 ppm).
Although EG&G Bionomics (1976a,b) reported that barite was moderately
toxic (96-h LC50 of 385 to 1,650 ppm) to a copepod, Acartia tonsa, and
an alga, Skeletonema costatum, mortality in these bioassays can
probably be attributed to physical abrasion by suspended barite parti-
cles and not to chemical toxicity.

Chromium

Drilling fluids may contain chromium in a variety of chemical forms,
but mostly complexed with lignosulfonate. It is generally believed
that virtually all the chromium in a drilling fluid that has been used
for an extended period will be in the trivalent state, even though it
may have been added as inorganic hexavalent chromium (Skelly and
Dieball, 1969). This may not always be the case. In a chromate-
treated chrome lignosulfonate fluid maintained at a pH of 9 to 11,
hexavalent chromium may persist for a long time at room temperature (23
to 240C). At higher temperatures typical of those encountered near
the drill bit (50 to 1200C), chromate is reduced rapidly to trivalent
chromium and becomes complexed with the lignosulfonate molecule (Skelly
and Dieball, 1969). Chromium-lignosulfonate complexes are quite stable
at normal operating temperatures and pHs, and chromium is not readily
released (McAtee and Smith, 1969). At temperatures above about
1500C, chrome lignosulfonates lose their ability to thin drilling
fluids, primarily because of thermal degradation of the organic portion
of the molecule and not because of a change in the physical or chemical
form of the chromium (Carney and Harris, 1975).
Thermodynamic calculations indicate that when chromate-treated
chrome lignosulfonate drilling fluid is discharged to the ocean and
diluted with seawater any chromium ions in the trivalent state,
Cr(III), should be transformed to the hexavalent state Cr(VI), and any
Cr(VI) discharged with the fluid should remain in that valence state
(Cranston and Murray, 1980; Nakayama et al., 1981a,b,c; van der Weijden
and Reith, 1982). The oxidation of Cr(III) to Cr(VI) occurs very
slowly in normally oxygenated seawater, however, and Cr(III) tends
rapidly to adsorb to or complex with suspended organic material and
clay. In the complexed state, Cr(III) is very resistant to oxidation.
Manganese oxides in seawater or sediments may accelerate the oxidation
of Cr(III) to Cr(VI), while oxidizable materials like H2S and many
natural organic compounds readily reduce Cr(VI) to Cr(III) (Nakayama
et al., 1981b; Smillie et al., 1981). Cr(VI) is also reduced rapidly
to Cr(III) in anoxic sediments (van der Weijden and Reith, 1982). As
a result of these interactions, seawater may contain dissolved chromium
in the form of Cr(III), Cr(VI), and organically bound chromium
(Nakayama et al., 1981c).
Trivalent chromium salts are not very soluble in seawater and have
low toxicities (see, for example, Oshida et al., 1981). Most species
of marine animals are much more sensitive to hexavalent chromium salts
than to trivalent salts, although species vary greatly in their

sensitivities to the first (Eisler and Hennekey, 1977; Frank and
Robertson, 1979; Reish et al., 1976). Some species appear to be
equally sensitive to Cr(VI) and Cr(III). The 48-h LC50s of Cr(VI), as
Na2CrO4, and of Cr(III), as CrO3, are 16.37 and 19.27 ppm
respectively for the marine copepod Acartia clausi (Moraitou-
Apostolopoulou and Verriopoulos, 1982). The reported LC50 value for
CrO3 is about 385 times higher than the value at which this Cr(III)
salt is soluble in seawater, so the bioassay has no environmental
meaning. Published values for the acute lethal toxicity (usually 96-h
LC50) of inorganic hexavalent chromium salts to marine animals
typically fall in the range of 0.5 to 250 mg/l. Polychaete worms are
very sensitive; teleost fish are not.
Slightly soluble hexavalent chromium salts, such as calcium chromate
and zinc chromate, are carcinogenic in mammals following tracheal
inhalation and intramuscular or intrapleural injection (Norseth, 1981).
Chromates also show evidence of genetic toxicity in several in vitro
tests. Trivalent chromium salts have shown little or no evidence of
carcinogenicity and genetic toxicity. When ingested in small amounts
by marine animals or man chromates would be reduced to the trivalent
state by organic materials in the digestive tract, and therefore would
not represent an important carcinogenic hazard.
In used chrome lignosulfonate drilling fluids, the proportion of
total or dissolved chromium present in ionized inorganic form is not
known (Liss et al., 1980). Since most of the chromium is associated
with the lignosulfonate, or clay fractions of the fluid or both, data
on the toxicity of ionic chromium species do not accurately indicate
the contribution of chromium to the toxicity of drilling fluids.

Hydrocarbons

Diesel fuel (No. 2 fuel oil) sometimes is added to water-based drilling
fluids to improve the lubricating properties of the fluid when drilling
a slanted hole. As much as 2 to 4 percent diesel fuel may be added
under some circumstances. Because much of the added diesel fuel
quickly becomes adsorbed to particles in the drilling fluids,
discharging these fluids to the ocean rarely results in an oil sheen
on the surface. In some circumstances, a "pill" of diesel fuel or oil-
based fluid is used to help free stuck pipe. This pill may or may not
be kept separate from the bulk fluid system, recovered, and disposed
of onshore. Even when the pill is kept separate, a small amount of
diesel fuel from the pill may become mixed with the bulk drilling
fluid.
There is growing evidence that diesel fuel may contribute signifi-
cantly to the toxicity of drilling fluids that contain it. Conklin et
al. (in press) reported a statistically significant inverse relation-
ship (r = -0.58, p<0.05) between the 96-h LC50 of 18 drilling fluid
samples collected at different depths from an exploratory well in
Mobile Bay, Alabama, to molting grass shrimp Palaemonetes pugio, and
the concentrations in these fluids of petroleum hydrocarbons identified
as derived from a no. 2 fuel oil. The drilling fluids contained 170 to

8,040 pl of petroleum per liter of whole fluid, and had acute
toxicities of 14,560 to 360 Pl/l, respectively.
The toxicities of crude and refined petroleums to marine organisms
have been studied extensively (see the reviews of Baker, 1976; Malins,
1977; Neff and Anderson, 1981; Rice et al., 1977). The acute toxici-
ties of different petroleums to different species of marine organisms
are extremely variable. Most 96-h LC50s fall in the range of 1 to
1,000 mg of oil per liter. Some very sensitive larval and early life
stages of marine animals may have LC50s of about 0.1 to 1 mg/l.
Sublethal responses to petroleum hydrocarbons, especially behavioral
modifications, have been reported following acute exposure to petroleum
concentrations in the low microgram per liter (parts per billion)
range. Because the most toxic major components of petroleum are the
light aromatics (i.e., benzenes, naphthalenes, and phenanthrenes) and
closely related heterocyclic compounds, the acute toxicity of a parti-
cular crude, refined, or residual petroleum product is usually directly
correlated with the concentration in it of these compounds.
No. 2 diesel fuel is a petroleum hydrocarbon distillate of moderate
volatility used in medium and high speed engines in industrial and
heavy mobile service (such engines commonly power drilling rigs). No.
2 diesel fuel has a boiling range of 350-7000F. While the properties
of U.S. diesel fuels are generally defined by ASTM Specification
D-975, the exact composition of a sample of No. 2 diesel fuel will vary
with the source, refining techniques, seasonal climatic requirements
and the demand for other products at the processing facility. No. 2
diesel fuel may include 20-40 percent cracked components and 15 to 50
percent by weight aromatic hydrocarbons. No. 2 diesel fuel may also
contain a variety of additives, used in providing properties such as
oxidation inhibition, dispersancy, corrosion protection, cetane
improvement, and anti-static protection. The toxicity and environ-
mental effects of additives to diesel fuel are evaluated, as an element
of registering the products with the EPA.
Most of the aromatic hydrocarbons in diesel fuels are benzenes and
naphthalenes, with much smaller amounts of polycyclic aromatic hydro-
carbons (aromatics containing three or more fused aromatic rings.) An
American Petroleum Institute reference No. 2 diesel fuel for biological
effects research contained 38.2 percent by weight aromatic hydrocarbons
(Neff and Anderson, 1981). A total of 39 percent of the chemical com-
ponents in the fuel were identified by gas chromatography/mass spec-
trometry. Of the identified components, 22,000 ppm were benzenes,
65,190 ppm were naphthalenes and biphenyls, and 11,962 ppm were poly-
cyclic aromatic hydrocarbons. A comprehensive review of the fates and
effects of petroleum hydrocarbons was published by the National Academy
of Sciences in 1975 (National Academy of Sciences, 1975) and is
currently being updated (publication is anticipated late in 1983).
A sample of drilling fluid which had been treated with diesel fuel
and IMCO Free Pipe from an exploratory well on Georges Bank contained
481 ppm total hydrocarbons, 31.6 percent of which were in the aromatic
fraction. Of the identified components 8.7 ppm were benzenes, 20.1 ppm
were naphthalenes and biphenyls, 3.1 ppm were polycyclic aromatic
hydrocarbons, and 0.8 ppm were dibenzothiophenes (2 ring sulfur hetero-
cyclics). Thus, the hydrocarbon composition of the drilling fluid

sample resembled that of diesel fuel except that it was deficient in
benzenes which are quite volatile and probably had evaporated during
usage or during extraction/clean-up for analysis.

Biocides

Halogenated phenol biocides, such as Dowicide B and Dowicide G, which
have been used as drilling-fluid additives in the past, are quite toxic
to benthic invertebrates (Land, 1974; Zitko, 1975). Their use is now
prohibited in drilling fluids and all other drilling or production
operations on the OCS (Federal Register, 1979). The use of parafor-
maldehyde is permitted. Its acute and chronic toxicities to marine
animals are much lower than those of chlorinated phenol biocides (Table
18). Paraformaldehyde is used in amounts up to 300 g/bbl (about 1,500
ppm). Paraformaldehyde depolymerizes to formaldehyde, the active
biocide, upon contact with water. Formaldehyde is suspected of being
a carcinogen when administered to rats via inhalation, but the
carcinogenicity of traces of formaldehyde in solution to marine
organisms is unknown.

Surfactants

Surfactants are used in small amounts in some drilling fluids to aid
the dispersion of poorly soluble components, such as aluminum stearate
and gilsonite, in the aqueous phase of the fluid. Polyethoxylated
alkyl phenols like Aktaflo-E or Aktaflo-S may be added to drilling
fluids at concentrations of 1 to 10 lb/bbl (2,850 to 28,500 ppm)
(American Petroleum Institute, 1978). Structurally related polyoxy-
ethylene esters and ethers have acute toxicities in the range of 1 to
40 ppm for Atlantic salmon Salmo salar and of 2.5 to 14,000 ppm for the
amphipod Gammarus oceanicus (Widlish, 1972). Anionic surfactants of
the linear alkylate sulfonate and alkyl aryl sulfonate types are some-
times used in drilling fluids. They have acute toxicities (96-h LC50)
to freshwater and marine invertebrates and fish of 0.4 to 40 ppm (Abel,
1974). Toxicity increases with decrease in water hardness (or salin-
ity) and decrease in alkyl side chain length.

Chronic and Sublethal Effects

Relatively little research has been performed on the chronic and
sublethal effects of individual drilling-fluid ingredients on marine
animals. The research that has been done has focused on barite,
hydrocarbons, and various biocides.

Barite

Several experiments studied the effects of barite on recruiting benthic
invertebrates from the plankton to sandy sediments in experimental

aquaria receiving unfiltered estuarine water (Cantelmo et al., 1979;
Tagatz et al., 1980; Tagatz and Tobia, 1978). The abundance of most
species of meiofaunal animals was significantly decreased by the
presence of barite on the sand. A 5-mm layer of barite significantly
inhibited recruitment of macrofaunal polychaetes and molluscs. The
grain size distribution, mineralogy, texture, and organic content of
sediments have a profound effect on settlement of planktonic larvae
(Thorson, 1957, 1966). Much of the effect of barite on recruitment of
benthic invertebrates owed to barium-mediated changes in sediment
texture, and not to the chemical toxicity of barite. Barite has a much
finer grain size (mean less than 60 Pm) than sand. The sand sub-
strate in control aquaria contained no silt-clay fraction, whereas in
aquaria containing sand-barite mixtures, the clay-silt fraction was 5.6
to 16.3 percent (Cantelmo et al., 1979). Such changes in sediment
characteristics render the sediment more suitable for some species and
less suitable for others.
Exposed to a substrate of particulate barite for periods up to 106
days, shrimp Palaemonetes pugio ingested the barite (Brannon and Rao,
1979; Conklin et al., 1980). Although this did not affect survival of
the shrimp, they were observed to show several sublethal responses.
Barite ingestion caused damage to the epithelium of the posterior
midgut, possibly by abrasion. The shrimp accumulated barium in the
exoskeleton and soft tissues. Barium concentrations in the carapace
and other tissues of intermolt shrimp exposed to barite for 21 days
were higher than corresponding concentrations in control shrimp. The
chemical form and physiological significance of elevated barium con-
centrations in barite-exposed animals is unknown.
Thompson and Bright (1977) applied separately barite and bentonite
clays to small colonies of three reef corals, Diploria strigosa,
Montastrea cavernosa, and Montastrea annularis. The surface of the
corals was heavily coated, but they were able to clear their surfaces
rapidly. D. strigosa cleared itself faster than did the other species.
Barite and bentonite clays were cleared at about the same rate as
natural calcium carbonate sand. During exposure for 29 days to 10 and
100 ppm ferrochrome lignosulfonate in a flowthrough system, polyp
retraction in corals Madracis decactis was significantly greater than
in controls (Thompson, 1980).
Morse et al. (1982) described histological damage to delicate gill
ctenidia of sea scallops Placopecten maqellanicus exposed for up to 20
days to suspensions of 100 ppm or greater of attapulgite clay or to
solutions of 500 ppm or greater of ferrochrome lignosulfonate.
Ferrochrome lignosulfonate, but not attapulgite, caused a decrease in
the rate of the cilia-mediated particle movement across the frontal
surface of the gill filaments.

Hydrocarbons

Because of the low bioavailability of sediment-adsorbed hydrocarbons,
most benthic marine animals are able to tolerate higher nominal con-
centrations of hydrocarbons in sediments than in seawater. Chronic
exposure to sediments initially containing 500 to 1,200 ppm crude oil

resulted in weight loss and hepatocellular vacuolization in English
sole Paralichthys vetulus (McCain et al., 1978), reduced condition
index and altered tissue-free amino acid ratios in clams Protothaca
staminea and Macoma inquinata (Augenfeld et al., 1980; Roesijadi and
Anderson, 1979), and reduced feeding rate in the polychaete Abarenicola
pacifica (Augenfeld, 1980). Anderson et al. (1978) contaminated
natural marine sediments with Prudhoe Bay crude oil, either as a
surface layer (5,000 to 6,000 ppm oil initially) or by mixing the oil
with the sediments (100 ppm oil initially), and placed the sediments
in trays in the intertidal zone of the Washington State coast for 100
days. The oil treatments did not substantially affect recruitment of
benthic animals to the sediment trays. When three experimental eco-
systems at the Marine Ecosystems Research Laboratory at the University
of Rhode Island were dosed with 190 Iig/l (ppb) No. 2 fuel oil in the
water column for 25 weeks, 109 mg/kg (ppm) petroleum hydrocarbons
accumulated in the bottom sediments (Grassle et al., 1980; Oviatt et
al., 1982). The macrofauna and meiofauna in the benthos of the oiled
tanks declined significantly compared to those in control tanks. The
greater effect of No. 2 fuel oil than crude oil on recruitment may owe
to the higher concentration of toxic aromatic hydrocarbons in the first
or to damage to pelagic larvae caused by the presence of petroleum
hydrocarbons in the water column in the experimental ecosystem tanks.
More than 5 years after a spill of No. 2 fuel oil near Falmouth,
Massachusetts, effects of the oil were still detectable in salt marsh
biota where the oil came ashore, probably because the petroleum hydro-
carbons persisted in the marsh sediments (Sanders et al., 1980).

Biocides

Tagatz et al. (1979) studied the effects of three biocides on recruit-
ment of benthic invertebrates to sandy substrates in aquaria. Recruit-
ment of most species to the sand substrate was diminished by two
chlorophenol biocides prohibited for ocean disposal, Dowicide G-ST and
Surflo B-33. The paraformaldehyde biocide, Aldacide, which is approved
for discharge, had no effect on recruitment at concentrations of 14 and
273 pg/l.

THE TOXICITIES OF USED DRILLING FLUIDS

Bioassay Procedures

A used drilling fluid, especially a treated one used in a deep hole,
is an extremely heterogeneous mixture. It contains water-soluble
materials, clay-sized particles of moderate density that settle slowly
in seawater, and larger or denser particles that settle rapidly. In
addition, montmorillonite and attapulgite clays in fluids flocculate
upon contact with seawater, forming larger particles that tend to
settle more rapidly than dispersed clay. These fractions tend to
separate rapidly when the drilling fluid is added to seawater in a

bioassay aquarium, as they do when they are discharged from a drilling
rig. Flocculation makes it extremely difficult to design a bioassay
protocol in which test organisms are exposed uniformly and reproducibly
to a drilling fluid-seawater mixture of known concentration or that at
least roughly simulates the kind of exposure an organism might
encounter in the vicinity of the drilling-fluid discharge in the field.
Because of the complexity of the chemical and physical processes that
take place when a used drilling fluid is discharged to the ocean, none
of the bioassay protocols used to date are completely satisfactory;
however, these protocols are at least consistent with currently
accepted bioassay procedures.
The simplest approach has been to add different volumes of whole
drilling fluids to a volume of seawater to achieve several concentra-
tions. Test organisms are then exposed to these mixtures, which are
aerated, mixed, or left unmixed during the bioassay (Houghton et al.,
1980; McLeay, 1976; Tornberg et al., 1980).
Another approach is to evaluate the toxicity of different drilling-
fluid fractions or mixtures of drilling fluids and seawater that
roughly simulate the likely exposures of organisms in different marine
habitats. These bioassay protocols are similar to those recommended
for evaluating the environmental impact of dredged material (EPAN/COE,
1977). The latter assays have been adopted with minor modifications
by EPA for bioassays to comply with NPDES permits for discharging
drilling fluids on the mid- and North-Atlantic OCS (Jones and Hulse,
1982). In these EPA bioassay protocols one part drilling fluid is
mixed with four parts seawater, and the phases are allowed to separate
for one hour. The supernatant is called the suspended particulate
phase, and the sedimented fraction the solid phase. A liquid phase is
prepared by centrifuging and filtering the suspended particulate phase
through a 0.45--v m filter. Other investigators have used an initial
dilution of 1 part drilling fluid with 9 parts seawater and a settling
period of 20 h (Gerber et al., 1980; Neff et al., 1980, 1981).
Protocols using even greater initial dilutions of drilling fluids are
being evaluated by investigators associated with the EPA laboratory in
Gulf Breeze, Florida.
There is growing evidence that the degree of initial dilution of the
drilling fluid has important effects on the composition, and therefore
the toxicity, of the three drilling fluid fractions (Neff, unpublished
observations). Because of the particulate attraction among clay
materials in a drilling fluid slurry, a 4:1 dilution of fluid does not
realistically separate into appropriate phases (i.e., suspended parti-
culate and settled solid phases), but rather unnaturally partitions the
solid and chemical components of the drilling fluid into the two
phases. Field data have shown that drilling fluids are diluted by
1,000 times within a transport period of less than I min after
discharge (the corresponding distance from the discharge pipe is a
function of current, e.g., 4 m at a current velocity of 15 cm/s). This
high initial dilution means that the discharge phases occuring in the
field would be significantly different than those observed in the
protocol of 4:1 dilution. Thus, the method of preparing the bioassay
mixture may substantially influence the estimated toxicity of the
drilling fluid or drilling-fluid fraction. Bioassay techniques now
used also present difficulties in filtering the suspended particulate

phase (excess solids stay in suspension) and in the opaqueness of their
test solutions (especially of chrome lignosulfonate fluids), which
seriously interferes with making bioassay observations on juvenile
crustaceans (e.g., mysids). During the course of the bioassay,
drilling-fluid solids may accumulate on the bottom of test chambers,
creating a viscous zone in which small zooplankton become entrapped.
Small copepods, such as Acartia tonsa, have been observed mired in
layers of settled drilling-fluid solids (Gilbert, 1981), a situation
unlikely to occur in nature.
There is some confusion in the literature on the toxicities and
biological effects of drilling fluids about the appropriate units to
express exposure concentrations and LC50 values. The units most
frequently used in the general aquatic toxicology literature are parts
per million (ppm), which for liquid or semiliquid solutes in water may
be calculated in milligrams or microliters of solute per liter. For
solutes with densities near 1.0 kg/l the differences in nominal con-
centrations calculated in the two ways are not great. The density of
used drilling fluids, however, varies from 1.07 to 2.27 kg/l (9 to 19
lb/gal). Large discrepancies can arise in expressing concentrations
of drilling fluids in seawater or concentrations of ingredients in
drilling fluids as either mg/l or pl/1. A 19-lb fluid might be
reported to have a 96-h LC50 value of 1,000 u1 fluid/l seawater or
one of 2,270 mg fluid/l seawater. The two values are equivalent, but
when the numbers are expressed only as "ppm," substantial errors can
arise in comparing the toxicities of different fluids. The units
expressing exposure concentrations should be clearly defined and
standardized. Results are also occasionally reported as ppm phase.
If a predilution of 4:1 was used in preparing the phase, then the
actual phase concentration has to be multiplied by 0.20 to correct back
to whole drilling fluid concentration.
Flow-through exposure systems also have been used for studying long-
term and sublethal effects (Conklin et al., 1980; Rubenstein et al.,
1980). There is the danger that drilling fluids may fractionate in
such systems, and particularly that drilling-fluid solids may accumu-
late in exposure tanks. No measurements have been made of the varia-
tions over time in the concentrations and compositions of drilling
fluids in these tanks.

Acute Lethal Toxicity

The acute lethal toxicities of more than 70 used water-based drilling
fluids have been evaluated with 62 species of marine animals from the
Atlantic and Pacific Oceans, the Gulf of Mexico, and the Beaufort Sea
(Carls and Rice, 1980; Conklin et al., in press; ERCO, 1980; Gerber et
al., 1980, 1981; Gilbert, 1981; Houghton et al., 1980; Marine Bioassay
Labs, 1982; McLeay, 1976; Neff, 1980; Neff et al., 1980, 1981; Tornberg
et al., 1980). Five major animal phyla found in the marine environment
were represented by the bioassay organisms, including Chordata (12
species of fish), Arthropoda (30 species of crustaceans), Mollusca (12
species of molluscs), Annelida (6 species of polychaetes), and
Echinodermata (1 species of sea urchin). Larvae and other early life
stages (considered to be more sensitive than adults to pollutant

stress) were also included. The results of these bioassays are
summarized in Table 19. Nearly 80 percent of the 400 LC50 values
resulting were higher than 10,000 ppm. Two LC50 values were below 100
ppm, both for the copepod Acartia tonsa exposed to heavily treated
drilling fluids from Mobile Bay, Alabama (Gilbert, 1981). The
estuarine copepod Acartia tonsa and the oceanic copepod Centropages
typicus were the most sensitive species tested (EG&G Bionomics 1976b,c;
Gilbert, 1981). Other relatively sensitive species included larvae of
the dock shrimp Pandalus danae, pink salmon fry Oncorhynchus gorbuscha,
larvae of the lobster Homarus americanus, juvenile ocean scallops
Placopecten magellanicus and mysid shrimp (Mysidopsis, Neomysis,
Acanthomysis [sic Holmeimysis], and Mysis). In most cases, organisms
in larval and early juvenile life stages were more sensitive than
adults. Molting crustaceans were more sensitive than intermolt animals
(Conklin et al., 1980). Crustaceans as a group, and in particular,
copepods, mysids, and shrimp, were more sensitive than other major taxa
to drilling fluids. This is probably in part because more bioassays
were performed with crustaceans in sensitive early life stages than
with organisms in other taxonomic groups at these stages. There were
no discernible differences in tolerance to drilling fluids among
animals from the Atlantic Ocean, Gulf of Mexico, Pacific Ocean, and
Beaufort Sea.
Whenever comparisons were made, species were found more sensitive
to suspended particulate phase preparations than to liquid phase
preparations, indicating that suspended particles or sorbed materials
in the drilling fluids contributed substantially to their toxicities.
The liquid phase of certain drilling fluids was also toxic. These
toxicities may be due to a combination of the chemical toxicity of the
liquid phase fluid ingredients and chemicals associated with the
particulate phase or the physical toxicity in the form of irritation
and damage to delicate gill and other body structures of drilling-fluid
particles. Physical abrasion by particles may increase the uptake and
therefore the chemical toxicity of soluble components of drilling
fluids.
Drilling fluids vary in their toxicities. Information about the
types and compositions of drilling fluids used in bioassays is incom-
plete. Fluids that have been treated heavily with chrome or ferro-
chrome lignosulfonate, chrome lignosulfonate-bichromate mixtures,
surfactants, sulfide scavengers, or diesel fuel are the most toxic.
Both the soluble and particulate phases of such fluids are toxic
(Conklin et al., in press). Fluids and "spud fluids" (used during
initial drilling) have a minimum of additives and toxicities that, in
most cases, are not markedly different from that of suspended clay
(McFarland and Peddicord, 1980). The soluble fractions of these fluids
are usually nontoxic (Neff, 1980; ERCO, 1980).
In summary, LC50s are useful primarily for ranking and comparing the
relative toxicities of different chemicals or mixtures and for compar-
ing the sensitivities of different species or life stages to a parti-
cular pollutant. The joint IMCO et al. group of experts on the
scientific aspects of marine pollution (1969) has used LC50 values to
classify different grades or degrees of the acute lethal toxicity of
chemicals to marine animals: very toxic chemicals have LC50 values of

less than 1 ppm; toxic ones of 1 to 100 ppm; moderately toxic ones of
100 to 1,000 ppm; slightly toxic ones of 1,000 to 10,000 ppm; and
practically nontoxic ones of greater than 10,000 ppm. The summary of
the results of acute lethal bioassays presented in Table 19 can be
interpreted using this classification. Larval, juvenile, and molting
crustaceans are more sensitive to drilling fluids than are organisms
in most other life stages and of most other species.

Chronic and Sublethal Effects

Investigations of the chronic and sublethal effects of drilling fluids
have been performed with 35 species of marine animals, including 10
species of corals, 5 species of molluscs, 15 species of crustaceans, 1
species of polychaete worm, 2 species of echinoderms, and 2 species of
teleost fish. Results of these investigations are summarized in Table
20. The lowest concentrations that elicit a particular response are
given. In some experiments, however, this concentration was the lowest
concentration tested. Responses to sublethal concentrations of drill-
ing fluids that have been measured include alterations in burrowing
behavior and chemosensory responses in lobsters; patterns of embryo-
logical or larval development or behavior in several species of shrimp,
crab, lobsters, sand dollars, and fish; feeding in larval and adult
lobsters and cancer crabs; food assimilation and growth efficiency in
opossum shrimp; growth and skeletal deposition in corals, scallops,
oysters, and mussels; respiration and nitrogen excretion rates in
corals and mussels; byssal thread formation in mussels; tissue enzyme
activity in crustaceans; gill histopathology in shrimp and salmon fry;
tissue-free amino acid ratios in corals and oysters; and polyp retrac-
tion, mucus hypersecretion, ability to clean surfaces, photosynthesis,
extrusion of zooanthellae and survival of corals. All the drilling
fluids evaluated were chrome or ferrochrome lignosulfonate fluids, the
type used most frequently for exploratory drilling on the U.S. OCS.
Several of the drilling fluids tested, including the most toxic ones,
are known to have contained diesel fuel or other petroleum material.
These include several of the fluids from Mobile Bay, Alabama (Conklin
et al., in press; Gilbert, 1981 and Jay Field, Florida (Atema et al.,
1982; Bookhout et al., 1982; Dodge, 1982; Szmant-Froelich et al., 1982;
White et al., 1982) and a medium weight fluid from the Gulf of Mexico
(Gerber et al., (1980, 1981); Neff, (1980). Diesel fuels, including
No. 2 fuel oil, are known to be quite toxic to marine organisms
(Malins, 1977; Neff and Anderson, 1981), and undoubtedly contribute
significantly to the toxicity and sublethal effects of those fluids
containing them.
Studies of chronic and sublethal effects are often better predictors
of the potential environmental impact of a pollutant than are acute
lethal bioassays because the first may employ exposure conditions that
simulate those organisms might encounter in their natural environment.
In most of the investigations summarized in Table 20, this ideal was

TABLE 19 Summary of results of acute lethal bioassays with drilling
fluids and marine/estuarine organisms.a

Number of Number of Number of
Species Fluidsc Bioassays
Organism Tested Tested Bioassays

Phytoplankton 1 9 12

Invertebrates
Crustaceans
Copepods 2 17 39
Isopods 2 4 6
Amphipods 4 8 19
Mysidsb 5 18 35
Shrimp- 10 40 76
Crabsb 6 18 35
Lobstersb 1 2 7

Molluscs
Gastropods 5 5 10
Bivalvesb 7 14 33

Echinoderms
Sea Urchins- 1 2 4

Polychaetes 6 14 28

Finfishb 12 32 90

TOTALS 62 72 400

.aMost median lethal concentration (LC50) values are based on 96-hour
bioassays and results are expressed as parts per million (mg/l or
p 1/1) mud added (Based on review of Petrazzuolo, 1981, with data
from Carls and Rice, 1980; ERCO, Inc., 1980, Gilbert, 1981, Marine
Bioassay Labs, 1982 and Conklin et al., in press, added).

bIncludes results for embryonic, larval and early life stages.

CIn many cases, the same drilling fluid was used for bioassays with
several species. In a few cases, more than one investigator evaluated
the toxicity of a single drilling fluid.

TABLE 19 (continued)

Number of LC50 Values (ppm)
Not 100- 1,000- 10,000-
Organism Determinable 100 999 9,999 99,999 100,000

Phytoplankton 5 6 0 7 0 0

Invertebrates
Crustaceans
Copepods 4 2 11 15 7 0
Isopods 0 0 0 0 1 5
Amphipods 0 0 0 0 5 14
Mysids- 1 0 1 0 21 18
Shrime 0 0 12 15 31 18
Crabs- 1 0 0 5 16 13
Lobstersb 0 0 0 1 3 3

Molluscs
Gastropods 0 0 0 0 2 8
Bivalvesb 0 0 0 1 15 17

Echinoderms
Sea Urchins-b 0 0 0 0 1 3

Polychaetes 0 0 0 0 9 19

Finfishb 0 0 0 3 52 35

TOTALS 11 2 24 47 163 153

Percentage, as a fraction
of the total number of
drilling fluid bioassays. 2.8 0.50 6.0 11.75 40.75 38.25

aMost median lethal concentration (LC50) values are based on 96-hour
bioassays and results are expressed as parts per million (mg/l or p 1/1)
mud added (Based on review of Petrazzuolo, 1981, with data from Carts and
Rice, 1980; ERCO, Inc., 1980, Gilbert, 1981, Marine Bioassay Labs, 1982
and Conklin et al., in press, added).

_Includes results for embryonic, larval and early life stages.

Cin many cases, the same drilling fluid was used for bioassays with
several species. In a few cases, more than one investigator evaluated the
toxicity of a single drilling fluid.

TABLE 20 Summary of Investigations of Sublethal and Chronic Effects of Drilling Fluids on Marine Animals (the Lowest Concentration
of Drilling Fluid Eliciting a Particular Response)

Exposure
Concentration
Species Drilling Fluid Tvpe and Duration Responses References

Coelenterates (corals)
Montastrea cavernosa Used FeCr-lignosulfonate 25 ml., 1:1 Unable to clear horizontal Thompson and eright, 1977
Montastrea annularis seawater:fluid surfaces
Diploria strigosa

Montastrea annularis Freshly prepared FeCr- 2-4 mm layer applied Decreased growth rate Hudson and Robbin, 1980
lignosulfonate 4 times at 2.5 h at 6 months
intervals

Montastrea annularis Used Cr-lignosulfonate, Burial under 10-12 All colonies dead Thompson, 1980
Porites asteroides offshore Louisiana cm for 8 h after 10 days

Montastrea annularis Used Cr-lignosulfonate, Thin covering Partial clearing in 26 h, Thompson, 1980
offshore Louisiana some dead polyps,
extruded zooanthellae

Madracis decactis Used Mobil Bay Cr- 100 ppm Depressed respiration Krone and Biggs,
lignosulfonate with and NH3 excretion 1980
added Cr-lignosulfonate rate

Porites furcata, P. Used Cr-lignosulfonate, 100 ppm, 96 h Partial polyp retraction, Thompson, 1980;
astroides, Montastrea offshore Louisiana excess mucus production Thompson and
Bright, 1980;
annularis, Acropora Tright, 1980;
Thompson et al.,
cervicornis, Agaricia 1980
agaricites

Porites divaricata Used Cr-lignosulfonate, 316 ppm, 96 h Partial polyp retraction, Thompson, 1980;
offshore Louisiana excess mucus production Thompson and
Bright, 1980;
Thompson et al.,
1980

Dichocoenia stokesii Used Cr-lignosulfonate, 1,000 ppm, 96 h Partial polyp retraction Thompson, 1980;
offshore Louisiana Thompson and
Bright, 1980;
Thompson et al.,
1980

Montastrea annularis Used Cr-lignosulfonate with 100 ppm, 6 weeks, 84% reduction in calcifi- Szmant-Froelich et
diesel, Jay Field, Fla. flowthrough cation rate, 40% reduction al., 1982
in respiration rate, 26%
reduction in photosyn-
thesis, 49% reduction in
NO3 and NH3 uptake,
inhibition of feeding

Montastrea annularis Used Cr-lignosulfonate with 100 ppm, 6 weeks, Reduction in skeletal growth Dodge, 1982
diesel, Jay Field, Fla. flowthrough rate

Montastrea annularis Used Cr-lignosulfonate with 1-100 ppm, 6 weeks, Growth inhibition, alteration White et al., 1982
diesel, Jay Field, Fla. flowthrough of biochemical pathways and
composition, bacterial
infection

TABLE 20 (continued)

Exposure
Concentration
Species Drilling Fluid TYPe and Duration Responses References

Molluscs
Pacific oyster Crasso- Used medium- and high-weight 5,000 ppm, 6 weeks, Decreased shell growth, Neff, 1980
strea gigas Cr-lignosulfonate, Gulf of static decreased condition index
Mexico

Atlantic oyster Used Cr-lignosulfonate, 100 ppm, 100 days, Reduced rate of shell Rubenstein et al., 1980
Crassostrea virginica Mobile Bay, Ala. flowthrough regeneration

C. virginica Unidentified Cr- 4,000 ppm Altered tissue-free amino Powell et al., 1982
lignosulfonate acid concentrations and
ratios

Mussel Modiolus modiolus Used high-weight Cr- 30,000 ppm Reduced rate of byssus thread Houghton et al., 1980
lignosulfonate, Cook formation
Inlet, Alaska

Mussel Mytilus edulis Used medium- and high-weight 33,000 ppm Decreased filtration rate, Gerber et al., 1980
Cr-lignosulfonate, Gulf of increased rate of respiration
Mexico and NH3 excretion

M. edulis Used medium- and high-weight 250 ppma Decreased rate of shell growth Gerber et al., 1980, 1981
Cr-lignosulfonate, Gulf of
Mexico

Ocean scallop Placopecten Used medium- and high-weight 49.4 ppma Decreased rate of shell growth Gerber et al., 1981
magellanicus (juveniles) Cr-lignosulfonate, Gulf of
Mexico

P. magellanicus (2-day Filtered suspension (liquid 1,000 ppm, 96 h Significant inhibition of Gilbert, 1981
larvae) phase) of used Cr- shell formation
lignosulfonate, Mobile Bay,
Ala., May 15 fluid

May 29 fluid 100 ppm, 96 h Significant inhibition of Gilbert, 1981
shell formation

P. magellanicus (2-day Liquid phase of used Cr- <100 ppm, 96 h Signific at inhibition of Gilbert, 1981
larvae) lignosulfonate fluid, shell formation
Mobile Bay, Ala.,
September 4 fluid

P. magellanicus (2-day Liquid phase of used 3,000 ppm, 96 h Significant inhibition of Gilbert, 1981
larvae) "Gilsonite" fluid shell formation

P. magellanicus (2-day Liquid phase of used low- 10,000 ppm, 96 h Significant inhibition of Gilbert, 1981
larvae) density lignosulfonate shell formation

Crustaceans
Opossum shrimp Mysidopsis Used Cr-lignosulfonate 50 ppm, 42 days, 50% survival from postlarva Conklin et al., 1980
bahia Mobile Bay, Ala. flowthrough to adult

M. almyra Liquid phase of used Cr- 10,000 ppm, 7 days Decreased food assimilation Carr et al., 1980
lignosulfonate, Gulf of and growth efficiency,
Mexico reduced growth rate

Coonstripe shrimp Pandalus Used high-weight Cr- 100,000-ppm Gill histopathology Houghton et al., 1980
hypsinotus (adults) lignosulfonate, Cook Inlet, suspension
Alaska

P. hypsinotus Used FeCr-lignosulfonate 2,000-ppm suspen- Cessation of swimming by 50% Carls and Rice, 1980
(Stage I larvae) Cook Inlet, Alaska sion, 144 h, of larvae
3,250-ppm liquid
phase, 144 h

Dock shrimp Pandalus Used FeCr-lignosulfonate 500-ppm suspen- Cessation of swimming by 50% Carls and Rice, 1980
danae (Stage I larvae) Cook Inlet, Alaska sion, 144 h, of larvae
1,050-ppm liquid
phase, 144 h

Kelp shrimp Eualus suckleyi Used FeCr-lignosulfonate 5,000-ppm suspen- Cessation of swimming by 50% Carls and Rice, 1980
(Stage I larvae) Cook Inlet, Alaska sion, 144 h of larvae

Grass shrimp Palaemonetes Used medium- and high-weight 10,000-15,000 ppm No effect on duration of any Neff, 1980
pugio larvae Cr-lignosulfonate, Gulf of liquid phase for intermolt periods or on dur-
Mexico duration of ation of larval development,
larval development significantly increased
mortality at molting

Sand shrimp Crangon Used low-weight Cr- 33,000-ppm liquid Decrease in activity of the Gerber et al., 1980
septemspinosa lignosulfonate, phase, 96 h enzyme glucose-6-phosphate
mid-Atlantic OCS dehydrogenase in muscle tissue

Atlantic Cancer crab Liquid phase of used Cr- 100 ppm, 20 days, No effect on survival or Gilbert, 1981
Cancer irroratus lignosulfonate, Mobile Bay, flowthrough molting rate
Ala., September 4, 1979

C. irroratus (Stage III Liquid phase of used Cr- 100 ppm, 4 days Temporary inhibition of feeding Gilbert, 1981
larvae) lignosulfonate, Mobile Bay,
Ala., September 4, 1979

Cancer crab Cancer Used medium-weight Cr- 160,000-ppm suspen- Increase in activity of enzymes Gerber et al., 1981
borealis lignosulfonate, Gulf of sion, 96 h aspartate aminotransferase and
Mexico 33,000-ppm liquid glucose-6-phosphate dehydrogenase
phase, 96 h in heart tissue

TABLE 20 (continued)

Exposure
Concentration
Species Drilling Fluid Type and Duration Responses References

Crustaceans (continued)
Green crab Carcinus maenus Used low-weight Cr- 33,000-ppm liquid Increase in activity of Gerber et al., 1980
lignosulfonate, phase, 96 h enzymes aspartate
mid-Atlantic OCS aminotransferase and
glucose-t-phosphate dehydro-
genase in muscle

King crab Paralithoides Used FeCr-lignosulfonate, 2,800-ppm suspen- Cessation of swimming by 50% of larvae Carls and Rice, 1980
camschatica (Stage I Cook Inlet, Alaska pension, 144 h
larvae) 12,900-ppm liquid
phase, 144 h

Tanner crab Chionoecetes Used FeCr-lignosulfonate, 2,800-ppm liquid Cessation of swimming by 50% of larvae Carls and Rice, 1980
bairdi (Stage I larvae) Cook Inlet, Alaska phase, 144 h

Mud crab Rhithropanopeus Used low-weight Cr- 100,000-ppm fluid No effect on survival or development Bookhout et al., 1982
harrisii larvae lignosulfonate, Jay aqueous fraction rate to first crab stage
Field, Fla. and suspended
particulate
phase, complete
larval development

Blue crab Callinectes Used low-weight Cr- 50,000-ppm fluid Significant decrease in survival of Bookhout et al., 1982
sapidus larvae lignosulfonate, aqueous fraction megalopa, altered larval behavior
Jay Field, Fla. and suspended
particulate phase,
complete larval
development

American lobster Homarus Used low-weight Cr- 10,000-ppm liquid Increase in activity of the enzyme Gerber et al., 1980
americanus (adults) lignosulfonate, phase, 96 h aspartate aminotransferase and
mid-Atlantic OCS decrease in activity of enzyme
glucose-6-phosphate dehydrogenase
in heart tissue

B. americanus (larvae) Used medium-weight Cr- 2,000-ppm liquid Increase in duration of larval Gerber et al., 1981
lignosulfonate, Gulf of phase development by 3 days
Mexico

H. americanus (adults) Used medium- and high-weight 10-ppm suspension, Decreased chemosensory response of Derby and Atema, 1981
Cr-lignosulfonate, 3-5 min walking leg chemosensors to food cues
Mobile Bay, Ala.

H. americanus (adults) Unknown 1-2 mm layer, 4 days Inhibition of feeding behavior Atema et al., 1982

Crustaceana (continued)
H. americanus (adults) Used Cr-lignosulfonate, 7-mm layer, 4 days No effect on feeding behavior Atema et al., 1982
Mobile, Ala.,
June 26, 1979

H. americanus (Stage IV Used Cr-lignosulfonate, Jay 7.7-ppm suspen- Partial inhibition of molting, delayed Atema et al., 1982
larvae) Field, Fla., sion, 36 days detection of food cues
July 29, 1980

H. americanus (Stage IV and Used Cr-lignosulfonate 1-4 mm layer Delays in burrow construction, altered Atema et al., 1982
V larvae) fluids, Jay Field, Fla., burrowing behavior
and Mobile Bay, Ala.

Polychaete Worms
Lugworm Arenicola cristata Used Cr-lignosulfonate 10-ppm suspension 33% mortality Rubinstein et al., 1980
fluids, Mobile Bay, flowthrough with
Ala. an accumulation of
4.5 mm at 100 days

Echinoderms
Sand dollar Echinarachnius Used Cr-lignosulfonate, 3,816-ppma sus- Depressed fertilization, delayed Crawford and Gates, 1981
parma (embryos) MobileBay, Ala., pension, duration development, developmental anomalies
June 26, 1979 of development

Bat starfish Patiria 13 used Cr-lignosulfonate 500-100,000 ppm significant decrease in growth rate, Chaffee and Spies, 1982
miniata (embryos) fluids, Santa Barbara fluid aqueous increased incidence of developmental
Channel, Calif. fraction, 48 h abnormalities

Teleaost Fish
Killifish Fundulus Used Cr-lignosulfonate, 3,816-ppme a s us - Retarded embryonic development, Crawford and Gates, 1981
heteroclitus (embryos) MobileBay, Ala., pension, duration depressed embryonic heart beat rate
June 26, 1979 of development

F. heteroclitus (embryos) Used freshwater Cr- 10,000-ppm liquid Depressed hatching success, depressed Sharp et al., 1982
lignosulfonate phase, duration embryonic heart beat rate,
Gulf of Mexico of development developmental anomalies

Pink salmon Oncorhynchus Used high-weight Cr- 30,000-ppm sus- Gill histopatholoqy Houghton et al., 1980
gorbuscha lignosulfonate pension
Cook Inlet, Alaska

aConcentrations originally reported as ppm suspended solids, converted here to estimated ppm total fluid added.

not met. Pelagic and some benthic animals were exposed to suspensions
or soluble (liquid phase) preparations of drilling fluids continuously
for periods of time much longer than they would be in the water column
near an exploratory rig. Benthic animals were exposed to layers of
whole drilling fluids or to fluids mixed with natural uncontaminated
sediments. Unless a drilling fluid is shunted directly to the bottom,
it will fractionate as it descends through the water column. Soluble
fractions of the fluid not tightly sorbed to clay particles, including
the more soluble and toxic aromatic fractions of diesel fuel, may not
reach the bottom at all. Lighter clay fractions will be carried
farther away than dense barite fractions. Thus, it is unlikely that
benthic fauna on the OCS will ever encounter a layer of unfractionated
drilling fluid on the bottom. Despite the methodological shortcomings
of these studies, however, several of them provide useful insights into
the subtle biological responses of marine animals when exposed to sub-
lethal concentrations of drilling fluids. They also suggest the types
of responses to look for in field studies of the effects of drilling-
fluid discharges on marine communities. It is worth noting, also, that
all major taxa have not been treated in a parallel manner in the tests
reported in Table 20. Life cycle tests have not been run on indigenous
or surrogate fish species.
A difficulty in performing studies of chronic and sublethal
responses of marine animals to drilling fluids is that there is no
completely satisfactory method for precisely measuring actual exposure
concentrations of drilling fluids and their variation over the course
of the experiment. Thus, results are presented giving nominal exposure
concentrations, based on amount of drilling fluid or fluid fraction
added per unit volume of seawater.
Discharges may result in considerable concentrations of suspended
solids in the water column (see Table 14), which are rapidly dispersed
(see Chapter 3). While the suspended solids themselves may not be
toxic, investigators have shown in laboratory studies that solids con-
centrations may interfere with survival and reproduction of aquatic
species (Nimmo et al., 1979; Paffenhofer, 1972; Wilber, 1971). Concen-
trations of solids that interfered with reproduction in laboratory
studies (45 uamg/l)l (although differences in reproduction were
negligible) are shown in Table 14 to occur as much as 152 m from the
point of discharge (assuming a high rate, high volume discharge).
However, exposures in the laboratory experiments have been weeks,
whereas exposures in the field are minutes.
Biological responses to whole used drilling fluids were recorded at
concentrations ranging from 1 to 160,000 ppm and to fluids distributed
as a 1-mm to 12-cm layer on natural sediment. In some cases, sublethal
responses were observed only at concentrations slightly lower than
those that were acutely lethal. For example, the 144-h LC5Os of
suspended and liquid phase preparations of a used chrome lignosulfonate
drilling fluid from Cook Inlet, Alaska, were 1.4 to 3 times higher than

'Del Nimmo, personal communication, July, 1983.

the concentration of this fluid that in the same period of time caused
swimming to cease in 50 percent of Stage I larvae of six species of
marine crustaceans (Carls and Rice, 1980). In several other species,
however, significant sublethal responses were recorded at concentra-
tions 10 to 100 times lower than the acutely lethal concentrations.
These species include the American lobster Homarus americanus and
several molluscs, particularly the ocean scallop Placopecten
magellanicus (Table 20).
There have been several investigations of the behavioral and
physiological responses of reef corals to sublethal concentrations of
drilling fluids (Table 20). Exposure to drilling fluid elicits partial
or complete polyp retraction in the corals, accompanied in many cases
by hypersecretion of mucus. These are defensive reactions that, if
they persist for long because of continued pollutant insult, lead to
decreased nutrient assimilation and production, altered biochemical
composition, depressed respiration and nitrogen excretion, partial or
complete inhibition of growth and deposition of calcium carbonate
skeleton, bacterial infection, and, eventually, death (Table 20).
These responses are elicited by chronic exposure to concentrations of
100 ppm or less, though there are large interspecies differences in
sensitivity to drilling fluids. Reef corals are sensitive to drilling
fluids, particularly heavily treated ones containing diesel oil.
While this report was in preparation, the previously unpublished
results of several investigations became available. These studies
measured the acute toxicities and sublethal effects of 11 used drilling
fluids obtained from offshore drilling sites in the Gulf of Mexico,
which the Petroleum Equipment Suppliers Association supplied to EPA.
The mean 96-h LC50 values for bioassays performed with the liquid and
suspended particulate phases of drilling fluids and suspended whole
fluid preparations for opossum shrimp Mysidopsis bahia were 176,500,
25,145, and 649 U 1/1 respectively. The mean 96-h LC50 for suspended
whole fluid preparations of the 11 drilling fluids for 1-day old larvae
of grass shrimp Palaemonetes pugio was 14,516 ul/l. There was a
statistically significant inverse relationship between the 96-h LC50
for opossum shrimp and the concentration in the drilling fluids of
petroleum hydrocarbons identified as No. 2 fuel oil (r = -0.73, p <
0.05). Drilling-fluid toxicity was not correlated to concentration of
chromium in the fluid (r = -0.5, p > 2). The drilling fluids
contained 100 to 9,430 mg/kg (ppm) petroleum hydrocarbons, and 42 to
1,345 mg/kg total chromium.
When 1 h old embryos of hard shell clams Mercenaria mercenaria were
exposed to liquid and suspended particulate phases of the 11 drilling
fluids for 48 h, the concentration causing 50-percent inhibition of
shell formation ranged from 87 to greater than 3,000 uI /1 for the
liquid phase and 64 to greater than 3,000 Ii1/1 for the suspended
particulate phase. Liquid phase preparations at concentrations as low
as 10 to 100 ug/l interfered with fertilization or caused abnormal
embryonic development in sand dollars Echinarachnius parma and sea
urchins Lytechius variegatus, L. pictus and Strongylocentrotus
purpuratus. Reef corals exhibited several sublethal responses follow-
ing exposure for 24 h to 25 g1/1 whole drilling fluid followed by 48
h recovery. These responses included protein loss, changes in the size

and concentration ratios of tissue-free amino acids, and depressed
calcification rate. The drilling fluids eliciting sublethal responses
at the lowest exposure concentrations were those most acutely toxic
and containing the highest concentrations of diesel fuel.

Microcosm Studies

Various types of experimental microcosms have become popular in recent
years as links between laboratory experiments and field observations.
Microcosms have been used a few times to study the effects of drilling
fluids on recruitment of planktonic larvae to benthic communities. In
these experiments, drilling fluid is layered on or mixed with the
bottom sediment or injected into natural seawater flowing into aquaria
(Rubinstein et al., 1980; Tagatz et al., 1978, 1980, 1982). Most of
these experiments have tested relatively high concentrations of
drilling fluid on or in the sediments (100,000 ppm), which depressed
the recruitment of some species. Other species were found in greater
numbers in the sediments contaminated with drilling fluids. Certain
species of bacteria and microeucaryotes (ciliates, nematodes, etc.)
were more abundant in contaminated sediments than in clean ones (Smith
et al., 1982). These effects could owe to changes in sediment texture
from the presence of drilling fluid, to organic enrichment of
sediments, or to the particular chemical compositions of the fluids.
When marine aquaria were supplied with unfiltered natural seawater
containing 50 vl/l (ppm) of used chrome lignosulfonate drilling fluid
for 8 weeks, the numbers of tunicates, molluscs, and annelids settling
in the sandy substrate or on the walls of the aquaria were signifi-
cantly decreased compared to those settling in control aquaria (Tagatz
et al., 1982). Differences in community structure in control and
experimental aquaria receiving 50 ppm drilling fluid were indicated by
a decrease in species abundance by Spearman's measure of rank correla-
tion and an increase in species diversity as measured by the Shannon-
Weaver index. These differences could have owed to the physical or
chemical effects of suspended drilling fluids on survival or settlement
of planktonic larvae or to the accumulation of drilling fluids in the
sediments over time (which was noted but not quantified) altering
sediment texture.

Field Studies

Table 21 provides summary information on the few field investigations
that have been conducted of the environmental fate and effects of
drilling fluids and cuttinggs discharged to the marine environment.
These studies corroborate predictions derived from laboratory studies.
The effects of drilling-fluid discharges to marine ecosystems, where
detected, are localized to an area around and downcurrent of the dis-
charge and to the benthos.
Gettleson (1978) monitored the condition of reef corals on the East
Flower Garden Bank off the Texas-Louisiana coast before, during, and

TABLE 21 Summary of Major Field Investigations of the Environmental Fate and Effects of Drilling Fluids and Cuttings

Discharged to the Environment

Location Objectives Physical Characteristics Results References

East Flower Garden Fate of drilling fluids Drilling at 129 m water depth; coral Drill fluids and cuttings Gettleson, 1978
Bank, NW Gulf of Mexico shunted to 10 m above zone at 20-50 meters & NW of drill distributed to 1,000 m from
bottom; effects on coral site; bottom currents toward WSW discharge; no impact on
reef 2,100 meters away drill site coral zone

Palawan Island, Effects of drilling discharges Drilling directly on reef at 26 m 70-90% reduction in some spp. Hudson et al., 1982
Phillippines on coral reefs 2 wells drilled 3 m apart; 3 cm/s of living corals within 115
currents to the north x 85 m area; epifauna associated
with corals affected to 40 m

Lower Cook Inlet, AK Fate of drilling discharges Drilling at 62 m water depth, 4.6-5.3 m Little accumulation of mud & Dames & Moore, 1978
and effects on benthic tides, mean maximal tide currents cuttings on bottom; no effects Houghton et al., 1980
communities 42-104 cm/s between bottom and on benthos attributable to Lees & Houghton, 1980
surface discharges

NJ 18-3 Block 684, Fate of drilling discharges; Drilling at 120 m water depth; Visible cuttings pile 150 n EG&G Environmental
Mid-Atlantic OCS effects on benthic community; bottom currents< 10 cm/s diameter; elevated Ba in Consultants, 1982
bioaccumulation of metals 62% of time, sediments sediments to 1.6 km; abundance
20% silt/clay of predatory demersal spp.
increased; large decrease in
abundance of henthic infauna
near rig with some bioaccumu-
lation of Ba and possibly Cr
by benthic infauna

Georges Bank, Fate of drilling discharges; Rigs at 80 and 140 m monitored; Evidence of cuttings within E attelle/W.E.O.I., 1983
North-Atlantic OCS effects on benthic community; residual bottom current 3.5 cm/s; 200 m of rigs; elevated Ba in Bothner et al., 1982
bioaccumulation of metals Frequent severe storms; sediments bulk sediments to 2 km; no Payne, et al., 1982
1% silt/clay effects on benthos attributable
to drilling; no bioaccumulation

U.S. Beaufort Sea, Effects of above-ice and Water depth 5-8 m; ice cover most 0.5-6 cm fluid and cuttings Northern Technical
AX below-ice disposal of of year with bottom scour in on bottom but carried away Services, 1981
drilling mud and cuttings on shallower areas quickly; no effects attribut-
benthic communities; able to discharges on benthos;
bioavailability of metals possible uptake of Ba by macro-
algae and Cu by amphiphods

Offshore Southern Effects of drilling discharges Platform on site 2-3 years, Surfaces within 10 m of dis- senesch et al., 1980
California on fouling community on sampling in August charge had different fouling
pontoons of semisubmersible community, attributed to
rig drilling fluid accumulation

Canadian Beaufort Sea Metals from drilling dis- Drilling from artificial island; Elevated levels of Hg, Pb, Zn, Crippen et al., 1980
charges in sediments and rapid seasonal erosion and ice scour Cd, As, and Cr in sediments
benthos near discharge with elevated
Eg to 1,800 m; no correlation
between metals in sediments and
biota

NW Gulf of Mexico Distribution of metals in Shallow water, h'?h suspended sediment Decreasing concentration Tillery and Thomas, 1980
sediments and biota in oil load gradients of Ba, Cd, Cr, Cu,
production fields Pb, and Zn in sediments around
some rigs. Metals not elevated
in commercial species of shrimp
and fish

100

after the drilling of an exploratory well approximately 2,100 m south-
east of the reef. Discharges were shunted to 10 m off the bottom.
Although some of the discharged fluid and cuttings were distributed by
currents to a distance greater than 1,000 m from the rig, none could
be detected in the coral reef zone, which was shallower than the depth
of discharge.
Hudson et al. (1982) found little or no suppression of growth in the
coral Porites lutea from drilling-fluid discharges made in exploratory
drilling near a coral reef off Palawan Island, Philippines. Living
foliose, branching, and plate-like corals were reduced by 70 to 90
percent, however, in an area 115 by 85 m around the wellheads, possibly
because of the smothering or toxic effects of these discharges.
Communities of small organisms living in crevices and cavities in and
among the coral heads (coelobites) were severely disturbed within 40 m
of the wellheads (Choi, 1982). Minor changes in coelobite community
structure were observed up to 100 m from the wellhead. Animals living
on the surface of the reef were less affected.
Lees and Houghton (1980) studied benthic communities in the vicinity
of the C.O.S.T. well in Lower Cook Inlet, Alaska, before, during, and
after the drilling operation. Changes in benthic communities were seen
near the drilling platform during the course of the study. None could
be unequivocably attributed to the drilling operations, however,
because of irregularities in faunal distribution, probably owing to
differences in successional stages among the areas sampled and the
failure to resample control sites. They concluded that, in the very
high energy environment of Lower Cook Inlet, the rate of accumulation
of drilling fluids and cuttings on the bottom was not sufficient to
affect measurably benthic populations. Although populations of an
opportunistic species of polychaete, Spiophanes bombyx, may have
increased after drilling, such resistence is characteristic of dynamic
environments. In a related study of the same drilling rig, Houghton
et al. (1980) placed pink salmon fry, shrimp, and hermit crabs in live
boxes at 100, 200, and 1,000 m downcurrent from the drilling-fluid
discharge. In an observation made after 4 days, no mortalities could
be attributed to the fluid's discharge plume.
Detailed studies have been performed on the shortand long-term
effects of drilling fluids and cuttings on benthic communities around
an exploratory drilling platform in New Jersey 18-3 Block 684 on the
mid-Atlantic OCS off Atlantic City, New Jersey (EG&G Environmental
Consultants, 1982; Gillmor et al., 1981, 1982; Maurer et al., 1981;
Menzie et al., 1980). A zone approximately 150 m in diameter of
visible accumulation from drilling discharges (primarily from drill
cuttings) was observed in the immediate vicinity of the well site,
while elevated levels of clays were detected up to 800 m southwest of
the site immediately after drilling ceased (during a first post-
drilling survey 2 weeks later). A side-scan sonar survey 1 year after
drilling ceased revealed scour marks left by anchor chains and
depressions left by the anchors. Drill cuttings and debris had
accumulated heavily in an area about 40 to 50 m in diameter immediately
south of the well site. The height of the cuttings pile was estimated
to be less than 1 m. During the second postdrilling survey, elevated
levels of clay were not detected southwest of the drill site. In both
postdrilling surveys, concentrations of barium in the upper 3 cm of
sediments were elevated (up to 3,477 ppm in the first survey and 2,144
ppm in the second survey, compared to 148 to 246 ppm before drilling)

101

near the rig site and decreasing with distance from the rig. The
concentration of barium was elevated in sediments up to 1.6 km from
the drill site. Neither the concentration of chromium nor of several
other metals was elevated in sediments near the rig following drilling.
The abundance of hake (Urophycis chuss), cancer crabs (Cancer spp.),
and starfish (Astropecten americanus) increased between the predrilling
and first postdrilling surveys in the immediate vicinity and to the
south of the well site. These animals may have been attracted by the
increased microrelief of the accumulated cuttings or by clumps of
mussels Mytilus edulis that had fallen off the drilling rig or anchor
chains. Within about 150 m of the discharge, sessile benthic animals
such as sea pens Stylatula elegans were subject to burial by drill
cuttings. The second postdrilling survey found sea pens completely
absent from the main cuttings pile, although they were observed among
patches of cuttings away from it. One year after drilling, hake and
cancer crabs were no longer concentrated near the rig site, and star-
fish had a patchy distribution throughout the area.
Before drilling, the abundance of benthic macrofaunal in the
vicinity of the rig site was greater than that at a nearby BLM bench-
mark station (8,011 animals/mr versus 3,064 animals/m2). The
abundance of benthic macroinfauna at the rig site dropped to 1,729
animals/m2 immediately after drilling, and then rose to 2,638
animals/m2 one year later. These changes in abundance were the same
for the four major taxonomic groups (polychaetes, echinoderms,
crustaceans, and molluscs). Polychaetes predominated in the macroin-
fauna at the study site during all three survey periods. Their
relative abundance, however, dropped from 78 percent in the predrilling
survey to 70 percent in the first postdrilling survey and to 66 percent
in the second postdrilling survey, compared to 70 percent at the nearby
BLM benchmark station. Molluscs were the only group to return to their
original abundance at the site within 1 year after drilling.
The abundance of the brittle star Amphioplus macilentus substan-
tially decreased within 100 m of the rig site and remained decreased
at the time of the second postdrilling survey. The abundance of small
brittle stars (of disc diameter less than 1.5 mm) decreased more than
that of larger specimens. The number of polychaetes measured during
the first postdrilling survey was significantly lower at stations near
the rig site that had elevated levels of clay (from drill cuttings)
compared with nearby stations that show no elevation in sediment clay
concentration between predrilling and postdrilling surveys. The
composition of polychaete feeding guilds, however, was similar in all
three surveys (Maurer et al., 1981). With the exception of these
cases, benthic macrofauna decreased in abundance similarly between the
predrilling survey and the two postdrilling surveys for the major
species within all taxnomic groups. With the exception of a few
stations less than 100 m southwest (downcurrent) of the drill site that
had markedly reduced benthic fauna during the first postdrilling
survey, there was no relationship between direction, distance from the
rig site (out to 3.2 km), or sediment barium concentration and the
extent of decrease in abundance of any major taxonomic group or major
species.

102

Unfortunately, there were no control stations sufficiently far from
the rig site to ensure that they were not affected and thus that they
provided true reference points to evaluate the three benthic samplings.
Data from more distant stations might establish better how much changes
in benthic fauna resulted from drilling or from other factors. Sta-
tions farthest from the rig site and considered beyond the influence
of drilling discharges (Stations 55, 56, and 58) showed the same
patterns of faunal change as did stations near the rig site. The
composition and abundances of benthic fauna observed in the two post-
drilling surveys were more like those observed in the earlier BLM
benchmark program in the area, particularly from BLM Station A3
(Boesch, 1979), than like those observed in the predrilling survey.
Because of natural temporal variability, the predrilling survey may not
have provided a suitable baseline (at least as far as macrobenthos
abundance levels are concerned) to evaluate the results of the post-
drilling surveys. Natural temporal variability is the probable cause
for the large, area-wide changes in macrobenthic abundance that was
observed between surveys. This premise is supported by considering
that an exploratory well was drilled approximately 2.8 km north
(upcurrent) of the monitored well site shortly before the predrilling
survey. If area-wide impacts occurred as a result of drilling this
well, they should have influenced the stations north of the test well;
however, no differences in composition and abundance were observed
between these stations and stations south of the test well. The
previously-drilled well was drilled by the same operator using the same
drilling fluid company and program and drilled through similar forma-
tions as the test well. Water depth, bottom topography and currents
at both sites are similar. Thus similar distributions of drilling
discharges around each well would be expected. If natural variability
is ignored, pre-drilling macrofaunal abundance appears to be elevated
(with respect to BLM benchmark data) even though some of the stations
could have been exposed to impacts from the previous well. However,
data from the monitored well suggest that macrofaunal abundances
decreased upon exposure to drilling discharges. This contradiction
strengthens the arguments that, except for those stations in the
immediate well-site area, the observed decrease in macrofaunal
abundance between pre- and post-drilling surveys resulted from natural
temporal variability.
Species richness (number of species per 0.2 m2) at the rig site
dropped from 70 + 7 in the predrilling survey to 38 + 10 immediately
after drilling and then rose again to 53 + 8 one year later. Shannon
diversity (H') and evenness (J') showed only very small changes between
the predrilling and the two postdrilling surveys. Diversity decreased
slightly, probably in part because of increased evenness, which was
observed in the postdrilling surveys. These changes in species
richness, diversity, and evenness were similar at stations near the
well site and at the three stations considered to be beyond the
influence of drilling discharges.
The authors concluded that the physical and biological effects of
exploratory drilling discharges on the benthic environment of a
low-energy area of the mid-Atlantic OCS persisted for at least 1 year
after drilling activities ceased. To the extent that the decreased

103

abundance and species richness of benthic macrofauna around the rig
site immediately after drilling resulted from drilling discharges,
there was evidence of recovery during the year after drilling ceased.
A similar investigation is being performed for the Minerals
Management Service (formerly the Bureau of Land Management) on Georges
Bank, southeast of the Massachusetts coast (Battelle/Woods Hole
Oceanographic Institution, 1983; Bothner et al., 1982; Payne et al.,
1982). Small amounts of cuttings were detected in bottom sediments
within about 200 m of the exploratory rigs in Blocks 312 (94 m water
depth) and 410 (137 m water depth) following drilling (Bothner et al.,
1982). No pile of cuttings was visible in any bottom photograph.
Barium concentration increased in the top centimeter of bulk sediments
between predrilling and postdrilling surveys up to 3.5 times (from 32
to 110 ppm) within 200 m of the rig in Block 410. A smaller increment
in sediment barium concentration was observed in the upper centimeter
of sediments collected from within 200 m of the rig site in Block 312.
Elevated levels of barium, but not chromium, were detected in bulk
sediment samples up to 2 km from both drill sites. The silt-clay
fraction of the sediments, representing about 1 percent of the total,
contained elevated concentrations of barium and chromium at stations
up to 6 km downcurrent of the Block 312 drill site after 6 months of
drilling.
During the first year of the monitoring program, benthic samples
were collected four times on a seasonal basis (in July and November
1981, and in February and May 1982) from 47 sampling stations
upcurrent, in the vicinity, and downcurrent of the lease blocks.
Drilling began at the two rig sites in Blocks 312 and 410 in December
and July 1981 respectively. Drilling was observed to have little
impact on the abundant and diverse benthic macroinfauna during the
first year of monitoring (Battelle/Woods Hole Oceanographic
Institution, 1983). In Block 312, where drilling started shortly after
the second survey, there was a change in the abundance of several
species at some stations within 2 km of the rig where Bothner et al.
(1982) showed that barium (and by inference the solid components of
drilling fluids) accumulated between the first and fourth surveys. In
February, shortly after drilling started, some species increased in
abundance at stations closest to the rig and declined at stations
farther away. The abundance of the corophiid amphipod Erichthonius
rubicornis showed a marked decline in February at some stations.
Barium was not observed to accumulate at these stations until May.
Thus it is doubtful that the population changes observed resulted
directly from the accumulation of discharged drilling fluids on the
bottom, since the discharges accumulated after the amphipod population
had declined. However, the distribution and abundance of E. rubi-
cornis, an epifaunal suspension feeder, and of certain other species
around the rig may have been influenced by the accumulation on the
bottom of drill cuttings, most of which are discharged during the
drilling of the shallow portion of the hole early in drilling (Ayers
et al., 1980a). Severe winter storms in February 1982, however, caused
substantial sediment resuspension and bottom scour at these stations,
as documented by bottom photography. Changes in sediment texture
resulting from the storms probably were a major cause of the benthic

104

infaunal changes seen near the rig in February. Most of the
macrofaunal species that declined in abundance near the rig site in
February substantially increased in abundance in May. Thus, any
effects of drilling discharges were apparently of short duration.
The much milder effects of exploratory drilling on the benthos of
Georges Bank than those on the mid-Atlantic OCS probably result in
large part from the difference in the amounts of drilling fluids and
cuttings accumulating on the bottom at the two sites. The lower energy
environment of the mid-Atlantic OCS allowed more drilling fluids and
cuttings to accumulate on the bottom than did the higher energy
environment of Georges Bank.
Northern Technical Services (1981) investigated the effects of
above-ice and below-ice disposal of drilling fluids and cuttings on the
nearshore benthos of the U.S. Beaufort Sea. Approximately 2.6 x 104
1 of drilling effluents were discharged below the ice at shallow-water
(5.5-m) and deep-water (8.2-m) test locations near the Reindeer Island
Stratigraphic Test Well site approximately 15 km north of Prudhoe Bay,
Alaska. In addition, approximately 3.5 x 105 1 of drilling effluents
were discharged on the ice in 6.7 m of water. Reference sites were
located nearby in 4.9 and 7.67 m of water. Four days after the test
discharge at the deep water site, a layer of drilling fluid and
cuttings of 5 to 6 cm was observed on the bottom under the discharge
point. About 3 m east of the site the estimated depth of the layer was
about 0.5 cm. At the shallow water site the maximum accumulation of
drilling fluid and cuttings was about 1 to 2 cm.
In order of relative abundance, the benthic fauna of the study area
included polychaetes, molluscs, and crustaceans. The experimental and
reference stations in shallow water (5 m) and in deep water (8 m)
differed significantly in infaunal abundance, diversity, species rich-
ness, evenness, and biomass. The experimental discharges took place
in late April and early May 1979. Analysis indicated that the abun-
dance of some species changed at the experimental and reference sites
between May and August. The changes probably were due to seasonal
effects. At the disposal site above ice, the numbers of polychaetes
and harpacticoid copepods were significantly fewer than at the nearby
deep-water reference site in August 1979 and January 1980. Grain size
and trace metal analyses of bottom sediments from the two sites indi-
cated that drilling effluents did not remain for long at the disposal
site. The authors attributed the differences in polychaete and
harpacitcoid abundances at reference and above-ice disposal sites to
natural differences in ambient physical conditions (mainly sediment
grain size) at the two sites.
Amphipods (Onisimus species and Boeckosimus species), placed in live
boxes on the bottom or at mid-depth 3 to 12 m from the discharge points
for 4 to 89 days suffered few mortalities. Trays containing clams
(Astarte species and Liocyma fluctuosa) were deployed for up to 89 days
on the bottom at the deep-water reference site and the above-ice
experimental discharge site. After 4 days, 1 to 2 clams were dead in
both reference and experimental trays. After 87 to 89 days, 7 clams
(26 percent) were dead in the experimental tray and 9 were missing,
compared to 1 dead in the reference tray. The experimental tray had
also been disturbed, however, which could have contributed to the
mortalities observed.

105

Benech et al. (1980) studied fouling communities on submerged
pontoons of a semisubmersible drilling rig off southern California.
The horizontal pontoon surfaces within 10 m downcurrent of the dis-
charge pipe where solids accumulated had different fouling communities
than pontoon surfaces where these solids did not settle. Differences
were attributed primarily to sedimentation of the drilling fluids and
cuttings. Sediment-intolerant species disappeared and sediment-
tolerant species became more abundant on the fluid-exposed pontoons.
In summary, the effects of drilling fluids and cuttings on benthic
and fouling communities is related to the amount of material accumulat-
ing on the substrate, which in turn is related to current speed and
related hydrographic factors. In a high-energy environment, fluids and
cuttings do not accumulate and have not been observed to affect the
benthos. In low-energy environments, more material accumulates, and
in the vicinity of the drill site the abundance of certain benthic
species is reduced as a result of burial, the species' incompatibility
with clay, or the chemical toxicities of the components of drilling
fluids or cuttings.

BIOAVAILABILITY

Hydrocarbons

Highly aromatic diesel fuels (containing 30 to 40 percent aromatics)
such as No. 2 diesel fuel are among the most toxic petroleum products
to marine organisms. Most of the petroleum hydrocarbons in a used
diesel-treated drilling fluid probably will be sorbed to the bentonite
clay fraction of the fluid and be incorporated in the sediments.
Petroleum hydrocarbons sorbed to organic or inorganic particles
generally are less bioavailable to marine organisms than hydrocarbons
in solution or dispersed in the water column (Augenfeld et al., 1982;
McCain et al., 1978; Roesijadi et al., 1978a,b; Rossi, 1977; Lyes,
1979; Neff, 1979). The bioconcentration factor (concentration in
tissue/concentration in sediments) for petroleum hydrocarbon uptake
from sediments and detritus by marine animals usually falls in the
range of 1 to 2. Augenfeld et al. (1982) reported maximum bioaccumula-
tion factors of 7.9 and 11.6 for phenanthrene and chrysene respectively
by the clam Macoma inquinata from sediments. Although particle-sorbed
petroleum hydrocarbons are less bioavailable than hydrocarbons in
solution, there could be sufficient uptake of hydrocarbons from drill-
ing fluids to contribute significantly to the toxicity of those fluids
that contain diesel oil. There have been no published laboratory
investigations to date of the uptake of petroleum hydrocarbons from
diesel-treated drilling fluids.

Heavy Metals

Metals commonly found in drilling fluids are barium, chromium, cadmium,
copper, iron, mercury, lead, and zinc (Table 22). Compounds containing

TABLE 22 Trace Metal Concentrations in Drilling Fluids From Different Sourcesa

Drilling Fluid Ba Cr Cd Cu Fe Hg Pb Zn Others References

48 Canadian ND 0.1-909 ND 0.05-250 0.002- ND ND 0.06- Siferd, 1976
Arctic fluids 9,250 1,700
3 Barite CLS ND ND 0.16-54.4 6.4-307 ND 0.2-10.4 0.4- 6.6- 3.8-19.9 Ni Nelson et al., 1980
fluids 307 4,226 12,270
2 Mid-Atlantic 229,100- 1,112- 0.6-0.8 5.8-7.7 ND <0.05 102.6- 36.0- 1.8-2.3 As Ayers et al., 1980a
CLS fluids 303,700 1,159 218.5 48.4 13.5-17.0 Ni
22.7-28.0 V
3 Mid-Atlantic 823- 57-90 2 ND ND 1-2.8 10-241 101- 20-33 EG&G, 1980
CLS fluids 19,300 197
Baltimore Canyon 202,000 850 ND 20 19,000 ND ND ND Liss et al., 1980
CLS fluid
Gulf of Mexico 449,000 378 ND ND ND ND ND ND 10,800 Al Ayers et al., 1980b
CLS fluid
Gulf of Mexico 133,000 200 ND 280 16,000 ND ND ND Liss et al., 1980
CLS fluid
Gulf of Mexico ND 51 0.51 ND ND ND ND ND Page et al., 1980
Spud Fluid--
Gulf of Mexico high- ND 257 0.78 ND ND ND 1.3 ND Page et al., 1980
density CLS fluidb
Gulf of Mexico mid- ND 396 1.70 ND ND ND 5.0 ND Page et al., 1980
density CLS fluidb
Gulf of Mexico low- ND 596 1.18 ND ND ND ND ND Page et al., 1980
density CLS fluidb .
Gulf of Mexico ND 485.2 3.0 48.2 ND ND 179.4 251.4 McCulloch et al., 1980
seawater CLS fluid
Gulf of Mexico ND 10.9 3.5 30.2 ND ND 134.2 297.3 McCulloch et al., 1980
spud fluidb
Gulf of Mexico high- ND 229.9 10.9 118.8 ND ND 209.5 274.5 McCulloch et al., 1980
density CLS fluidk
2 CMC/gel fluids 4,400- 28-63 0.5-0.6 6.4-10.4 ND 0.017- 2.4-12.8 42-64 Tornberg et al., 1980
Alaskac 6,240 0.031
XC polymer fluids 720-1,120 66-176 0.5-1.5 10-16 ND 0.015- 5.6-56 49-110 Tornberg et al., 1980
Alaska (20)c 0.070
XC polymer/unical ND 56-125 ND 2.8-17.0 ND 0.028- 9-117 198-397 Tornberg et al., 1980
fluids Alaska (6)2 0.217
CLS fluids 800-7,640 121-172 0.5 10-12 ND 0.03- 16.4-56.0 49-56 Tornberg et al., 1980
Alaska (4)c 0.07
Gulf of Mexico 90,000 500 ND 43 27,000 ND 91 370 400 Mn Trefry et al., 1981
CLS fluid
Mobil Bay treated ND 5,960 ND 47 10,100 ND 22 540 290 Mn Trefry et al., 1981
CLS fluid

NOTE: ND, not determined; CLS, chrome lignosulfonate; CMC, carboxymethylcellulose.

aConcentrations are in mg/kg dry weight (ppm).
-Fluids also analyzed by Page et al. (1980) and McCulloch et al. (1980).
2Concentrations given on a wet-dry basis.

107

barium, chromium, lead, and zinc are intentionally added to drilling
fluids to serve different functions. Other metals the fluids contain
are trace contaminants of barite and bentonite clay and formation
solids (Kramer et al., 1980; MacDonald, 1982). Elevated concentrations
of barium, and occasionally chromium, zinc, cadmium, and lead, presum-
ably derived in part from discharged drilling fluids, have been
reported in the water, bottom sediments, or both in the immediate
vicinity of offshore exploratory wells (Crippen et al., 1980; Ecomar,
1978; EG&G Environmental Consultants, 1982; EG&G Environmental Con-
sultants, 1982 Gettleson and Laird, 1980; Meek and Ray, 1980; Tillery
and Thomas, 1980; Trocine et al., 1981; Wheeler et al., 1980;). The
important question relating to these metals is whether marine animals
can accumulate them in their tissues from the water or sediment to the
extent that the metals are toxic to the animals themselves or to
animals at higher trophic levels, including, for example, human
consumers of fishery products.

Laboratory Studies

There have been a number of laboratory investigations of the bio-
accumulation of some metals in drilling fluids or drilling-fluid
ingredients (Brannon and Rao, 1979; Carr et al., 1982; Espey Huston &
Associates, 1981; Gerber et al., 1981; Liss et al., 1980; McCulloch et
al., 1980; Page et al., 1980; and Rubinstein et al., 1980). They show
that some heavy metals in used drilling fluids are bioavailable to
marine animals. Statistically significant bioaccumulation of chromium
and barium may occur, despite'-the very low solubility of barium sulfate
in seawater. Liss et al. (1980) have shown that higher concentrations
of chromium and barium than predicted are present in filtrates of sea-
water suspensions of drilling fluids; this may be the fraction accumu-
lated by marine animals. Much of the lead, zinc, and possibly cadmium
is in particulate form and associated with pipe dope (usually high in
lead and zinc) and in the clay or barite fractions of the fluids
(Kramer et al., 1980; MacDonald, 1982; McCulloch et al., 1980).

Field Studies

Several metals in drilling fluids, particularly barium, tend to
accumulate in bottom sediments in the immediate vicinity and down-
current of the drilling rig, where they may persist indefinitely
(Boothe and Presley, 1983; Crippen et al., 1980; EG&G Environmental
Consultants, 1982; Gettleson and Laird, 1980; Meek and Ray, 1980;
Tillery and Thomas, 1980; Trocine et al., 1981; Wheeler et al., 1980).
The question of the bioavailability of these sedimented metals to
benthic marine animals has been explored by Crippen et al. (1980), and
Tillery and Thomas (1980).
Changes were reported in concentrations of several metals in sedi-
ments and benthic invertebrates in the vicinity of an offshore explor-
atory rig in the Baltimore Canyon off New Jersey before and after
drilling (EG&G Environmental Consultants, 1982). Only the elevations

108

in barium concentration in the postdrilling sediment samples could be
attributed to the drilling-fluid discharges. Concentrations of
chromium in sediments from the postdrilling surveys were within the
range of values obtained for sediments from the predrilling survey and
from BLM stations A2 and A3 near the drill site sampled on five surveys
prior to exploratory drilling. Other investigators have identified
barium as the metal most enriched in bottom sediments around drilling-
fluid discharges (Bothner et al., 1982; Chow and Snyder, 1980;
Gettleson and Laird, 1980; Wheeler et al., 1980). This is not
surprising given the high density and low solubility of barite and the
large amounts of it used in most fluids when drilling deep.
Some samples of mixed-species assemblages of brittle stars,
molluscs, and polychaetes collected during the first and second post-
drilling surveys, at approximately 2 weeks and 1 year after drilling
ceased, had significantly elevated concentrations of barium and
chromium compared with animals collected in the predrilling survey
nearly 1 year before drilling started (EG&G Environmental Consultants,
1982). The reported increase in mercury concentration in tissues of
animals from the first postdrilling survey (Mariani et al., 1980) was
later found to be in error (EG&G Environmental Consultants, 1982).
Recalculation of the range of mercury concentrations in molluscs,
brittle stars and polychaetes revealed no statistically significant
increase in mercury concentration between biota sampled before and
after drilling.
In both postdrilling surveys the concentrations of barium in tissues
of molluscs from the immediate vicinity of the drill site were within
the range observed during the predrilling survey. Barium concentra-
tions in tissues of polychaete worms and brittle stars from the
vicinity of the drill site were significantly higher in samples from
the first postdrilling survey than in those collected before drilling
started. Mean barium concentrations in polychaetes and brittle stars
were 24 and 15 ppm before drilling, and 88 and 218 ppm during the first
postdrilling survey. One year after drilling ceased, barium concentra-
tions in all but a few polychaete and brittle star samples had returned
to those observed prior to drilling. Concentrations of chromium were
elevated in tissues of polychaetes during the first postdrilling
survey, and in tissues of molluscs, polychaetes, and brittle stars
during the second postdrilling survey. Concentrations of barium and
chromium in the tissues of benthic organisms were not correlated with
the concentration gradients of these metals in bottom sediments.
Payne et al. (1982) could find no indication of any increase in the
concentration of barium, chromium, or several other metals in the
tissues of bivalve molluscs Arctica islandica or of demersal fish near
exploratory drilling on Georges Bank. A few mollusc samples collected
in February and May 1982 contained slightly elevated levels of
petroleum hydrocarbons, but the source of these could not be
identified.
Concentrations of several metals were measured in tissues of macro-
invertebrates and macroalgae from the bottom at a reference and above-
ice drilling-fluid disposal site in the Beaufort Sea 8 and 12 months
after an experimental discharge (Northern Technical Services, 1981).
Most metals were present in higher concentrations in organisms from the

109

reference than from the experimental site. The concentration of barium
was found to be elevated in polychaete tubes and macroalgae (Eunephyta
rubriformis) from the experimental site, but this concentration was
analyzed by atomic absorption spectrometry, so the results may not be
reliable. The macroalgae also had slightly elevated levels of chromium
(3.86 compared to 1.54 pg/g dry weight at experimental and reference
sites). Amphipods maintained in live boxes for 89 days at the experi-
mental site contained slightly elevated levels of copper (114 compared
to 89.5 pg/g dry weight at experimental and reference sites). Con-
centrations of other metals analyzed (chromium, lead and zinc) were
similar in both experimental and control groups.
Crippen et al. (1980) measured the concentrations of several metals
in sediments, drilling fluids, and benthic animals from a drilling site
in the Beaufort Sea. Mercury, lead, zinc, cadmium, and arsenic were
present at higher concentrations in the drilling fluid than in the
surface sediment. Some of these metals were associated with an impure
grade of barite used to formulate the drilling fluid and probably were
in the form of insoluble metallic sulfides (Macdonald, 1982). Metal
levels in the sediment near the discharge site were not significantly
correlated to those found in nearby benthic infaunal organisms.
Tillery and Thomas (1980) reviewed several investigations of the
distribution of heavy metals in sediments and biota in oil production
fields in the northwest Gulf of Mexico and found that the concentration
gradients of barium, cadmium, chromium, copper, lead, and zinc in sur-
ficial sediments decreased with distance from some platforms. Trace
metal concentrations in muscle tissues of four commercially important
species (brown shrimp Penaeus aztecus, Atlantic croaker Micropogon
undulatus, sheepshead Archosargus probatocephalus, and spadefish
Chaetodipterus faber) generally were not significantly higher in
animals from the vicinity of oil production fields than in animals from
other regions. They found, however, that such metal concentrations
were not determined for other tissues, some of which are more likely
than muscle to accumulate metals.
The results of the limited field studies tend to corroborate the
results of laboratory studies. The accumulation in organisms of heavy
metals from sedimented drilling fluids is low. Most of the metals of
concern are originally associated with the barite and bentonite clay
fractions of the drilling fluid (Crippen et al., 1980; Kramer et al.,
1980) and are in the form of highly insoluble imorganic sulfides or
sulfates (MacDonald, 1982), although chromium is associated initially
with lignosulfonate. In a used drilling fluid more than 75 percent of
the chrome lignosulfonate becomes bound to the clay fraction (Knox,
1978; McAtee and Smith, 1969; Skelly and Dieball, 1969). Heavy metals
in the form of insoluble sulfides, adsorbed to particulates, or in the
form of nonlabile organic complexes, have a much lower bioavailability
to marine animals than do the metal ions in solution (Breteler et al.,
1981; Bryan, 1982 Jenne and Luoma, 1977; Neff et al., 1978). Page et
al. (1980) showed that mussels Mytilus edulis accumulated more chromium
from a solution of trivalent chromium salts than from solutions of
ferrochrome lignosulfonate or aqueous fractions of chrome lignosul-
fonate drilling fluid. Capuzzo and Sasner (1977) showed that chromium
adsorbed to bentonite clay was less bioavailable to mussels Mytilus

110

edulis and clams Mya arenaria than was an equivalent amount of chromium
in a solution of CrC13. Chromium adsorbed to clay particles was much
less available to sea scallops Placopecten magellanicus than chromium
in solution (Liss et al., 1980). High levels of a metal in a sediment
or drilling-fluid sample are not by themselves an indication of bio-
logical hazard. These adsorbed metals have very limited bioavail-
ability.
Field studies conducted around offshore platforms report little to
no significant elevation of metals in sediments (EG&G, 1982; Battelle/
Woods Hole Oceanographic Institution, 1983). This same pattern was
seen around shallow and deep water, multiple well development and
production platforms (8-25 wells per platform) in the Gulf of Mexico
(Boothe and Presley, 1983). Boothe and Presley did note some slight
elevation of mercury and lead within 125 m of two deep water locations.
Based on analytical correlation, the mercury appeared to be associated
with barium concentration and probably was due to trace contamination
levels in the barite.

Toxicity and Biomagnification

Several laboratory and field studies have addressed the uptake and
retention by organisms of potentially toxic substances like trace
metals and organic compounds in drilling fluids. The goal of these
studies has been to determine whether marine organisms accumulate
toxins in their tissues to concentrations sufficient to harm the
organism or animals at higher trophic levels, including man.
Laboratory studies have been useful in indicating uptake and depuration
kinetics and, to a certain degree, the anatomical fates of accumulated
materials, but laboratory studies of accumulation and field studies
monitoring tissue are difficult to interpret because organisms may
sequester and detoxify both metal and organic contaminants (Coombs and
George, 1978; Jenkins and Brown, 1982; Stegeman, 1981). In order to
effectively estimate the biological consequence of tissue or body
burdens, it is important to examine the subcellular distributions of
the contaminants (Bayne et al., 1980; Brown et al., 1982a; Jenkins et
al., 1982). Because most bioaccumulation studies of drilling fluids
have measured only total tissue or body burdens, their usefulness in
predicting biological effects is limited. The little metal accumula-
tion observed in both laboratory and field investigations, however,
suggests that the biological effects of this accumulation are minimal.
Another issue that must be considered is the potential for the
biomagnification of accumulated contaminant body burdens through marine
food webs. This issue has not been addressed directly with regard to
drilling fluids. Phelps et al. (1975) examined the distributions of
heavy metals, however, particularly chromium, in Narragansett Bay
organisms representing several trophic levels. Their data suggest that
chromium body burdens decrease with trophic level. In similar studies
in the Southern California Bight, Brown et al. (1982b) found zinc and
copper levels decrease with higher trophic level, suggesting that
inorganic metals do not biomagnify. In these studies, however, total
mercury and DDT body burdens were found to increase significantly with

lllI

TABLE 23 Summary of Biological Effects of Drilling Fluids and
Drilling Fluid Ingredients on Marine Animals

Laboratory Studies
Acute Lethal Bioassays
Parameter (LC50 Range, ppm) Chronic and Sublethal EffectsA

Drilling fluid ingredients

Barite, bentonite, and
lignite >10,000 5-mm layer on sediment

Chrome- & Ferrochrome- 120-12,000 50 ppm
lignosulfonates

Chromium (VI) 0.5-250 12 ppb

Diesel fuel 0.1-1,000 =10 ppb water, 100
ppm sediment

Paraformaldehyde 0.07-30 10 ppb

Detergents, Surfactants 0.4-14,000

Used drilling fluids of 400 Bioassays 1-160,000 ppm in water
38% >100,000 1-12 mm Layer on bottom
41% 10,000-99,999 50-100,000 ppm affects
12% 1,000-9,999 recruitment to microcosms;
6% 100-999 some bioaccumulation
0.5% <100 of barium and chromium
3% LC50 Not Determinable demonstrated

FIELD STUDIES

Community responses Effects seen only on benthos in the vicinity of
discharge, and are most pronounced in low-energy
environments where discharges accumulate on
bottom.

Bioaccumulation of metalsb Small uptake of barium and chromium immediately
after drilling

aThe lowest concentration at which effects are observed.
kThere are no specific data available on the bioaccumulation of hydrocarbons.

112

increased trophic level. Of the total mercury measured, some 90
percent was organic (e.g., CH3Hg). A more direct examination of the
biomagnification of metals in the marine environment would be useful.

CONCLUSIONS

Based on laboratory and field studies to date, most water-based drill-
ing fluids used on the U.S. OCS have low acute and chronic toxicities
to marine organisms in light of the fluids expected or observed rates
of dilution and dispersal in the ocean after discharge. Their effects
are restricted primarily to the ocean floor in the immediate vicinity
and for a short distance downcurrent from the discharge. The bio-
accumulation of metals from drilling fluids appears to be restricted
to barium and chromium and is observed to be small in the field.
Table 23 summarizes the concentrations of drilling fluids eliciting
deleterious responses in marine organisms.

REFERENCES

Abel, P.D. 1974. Toxicity of synthetic detergents to fish and aquatic
invertebrates. J. Fish. Biol. 6:179-298.

American Petroleum Institute. 1978. Oil and gas well drilling fluid
chemicals. API. Bull. 13F. 1st ed. American Petroleum
Institute, Washington, D.C.

Anderson, J.W., R.G. Riley, and R.M. Bean. 1978. Recruitment of
benthic animals as a function of petroleum hydrocarbon concentra-
tions in the sediment. J. Fish. Res. Bd. Can. 35:776-790.

Atema, J., D.F. Leavitt, D.E. Barshaw, and M.C. Cuomo. 1982. Effects
of drilling fluids on behavior of the American lobster, Homarus
americanus in water column and substrate exposures. Can. J. Fish.
Aquat. Sci. 39:675-690.

Augenfeld, J.M. 1980. Effects of Prudhoe Bay crude oil contamination
on sediment working rates of Abarenicola pacifica. Mar. Environ.
Res. 3:307-313.

Augenfeld, J.M., J.W. Anderson, R.G. Riley, and B.L. Thomas. 1982.
The fate of polyaromatic hydrocarbons in an intertidal sediment
exposure system: bioavailability to Macoma inquinata (Mollusca:
Pelecypoda) and Abarenicola pacifica (Annelida: Polychaeta). Mar.
Environ. Res. 7:31-50.

Augenfeld, J.M., J.W. Anderson, D.L. Woodruff and J.L. Webster.
1980. Effects of Prudhoe Bay crude oil-contaminated sediments on
Protothaca staminea (Mollusca: Pelecypoda): hydrocarbon content,
condition index, free amino acid level. Mar. Environ. Res.
4:135-143.

113

Ayers, R.C., Jr., T.C. Sauer, Jr., R.P. Meek, and G. Bowers.
1980a. An environmental study to assess the impact of drilling
discharges in the Mid-Atlantic. I. Quantity and fate of discharges.
In: Proceedings of a Symposium on Research on Environmental Fate
and Effects of Drilling Fluids and Cuttings. Washington, D.C.:
Courtesy Associates. Pp. 382-418.

Ayers, R.C., Jr., T.C. Sauer, Jr., D.O. Stuebner, and R.P. Meek.
1980b. An environmental study to assess the effect of drilling
fluids on water quality parameters during high rate, high volume
discharges to the ocean. In: Proceedings of a Symposium on
Research on Environmental Fate and Effects of Drilling Fluids and
Cuttings. Washington, D.C.: Courtesy Associates. Pp. 351-381.

Baker, J.M. (ed.). 1976. Marine Ecology and Oil Pollution. New York:
Halsted Press. 566 pp.

Battelle/Woods Hole Oceanographic Institution. 1983. Georges Bank
benthic infauna monitoring program. Final report, Year 1.
Contract No. 14-12-0001-29192. Prepared for the New York OCS
Office, Minerals Management Service, U.S. Department of the
Interior.

Benech, S., R. Bowker, and B. Pimental. 1980. Chronic effects of
drilling fluids exposure to fouling community composition on a
semi-submersible exploratory drilling vessel. In: Proceedings of
a Symposium on Research on Environmental Fate and Effects of
Drilling Fluids and Cuttings. Washington, D.C.: Courtesy
Associates. Pp. 611-635.

Birdsong, C.L., and L.W. Avault. 1971. Toxicity of certain chemicals
to juvenile pompano. Prog. Fish-Cult. 33:76-80.

Boesch, D.F. 1979. Benthic ecological studies: macrobenthos. In:
Middle Atlantic Outer Continental Shelf Environmental Studies. Vol.
IIB. Chemical and Biological Benchmark Studies. Special Report in
Applied Marine Science and Ocean Engineering No. 194. Virginia
Institute of Marine Sciences, Gloucester Point, Va. New York OCS
Office, Bureau of Land Management, U.S. Department of the Interior.

Boesch, D.F., and R. Rosenberg. 1981. Response to stress in marine
benthic communities. In: G.W. Barrett and R. Rosenberg (eds.),
Stress Effects on Natural Ecosystems. New York: John Wiley &
Sons. Pp. 179-200.

Bookhout, C.G., R. Monroe, R. Forward, and J.D. Costlow, Jr. 1982.
Effects of soluble fractions of drilling fluids and hexavalent
chromium on the development of the crabs, Rhithropanopeus harrisii
and Callinectes sapidus. EPA-600/S3-82-018. Final report to U.S.
EPA Environmental Research Laboratory, Gulf Breeze, Fla.

114

Borthwick, P.W., and S.C. Schimmel. 1978. Toxicity of
pentachlorophenol and related compounds to early life stages of
selected estuarine animals. In: K.R. Rao (ed.), Pentachlorophenol:
Chemistry, Pharmacology, and Environmental Toxicology. New York:
Plenum Press. Pp. 141-146.

Bothner, M.H., R.R. Rendigs, E. Campbell, M.W. Doughton, P.J.
Aruscavage, A.F. Dorrzapf, Jr., R.G. Johnson, C.M. Parmenter, M.J.
Pikering, D.C. Brewster, and F.W. Brown. 1982. The Georges Bank
monitoring program. Analysis of trace metals in bottom sediments.
Interagency Agreement No. AA851-IA2-18. First year final report to
the New York OCS Office, Minerals Management Service, U.S.
Department of the Interior. Woods Hole, Mass: Geological Survey,
U.S. Department of the Interior.

Brannon, A.C., and K.R. Rao. 1979. Barium, strontium and calcium
levels in the exoskeleton, hepatopancreas and abdominal muscle of
the grass shrimp Palaemonetes pugio: relation to molting and
exposure to barite. Comp. Biochem. Physiol. 63A:261-274.

Breteler, R.J., I. Valiela, and J.M. Teal. 1981. Bioavailability of
mercury in several northeastern U.S. Spartina ecosystems.
Estuarine Coastal Shelf Sci. 12:155-166.

Brown, D.A., R.W. Gossett, and K.D. Jenkins. 1982a. Contaminants in
white croakers Geneyonemus lineatus (Ayres, 1855) from the Southern
California bight. II. Chlorinated hydrocarbon detoxification/
toxification. In: W.B. Vernberg, A. Calabrese, F.P. Thurberg, and
F.J. Vernberg (eds.). Physiological Mechanisms of Marine Pollution
Toxicity. New York: Academic Press. In press.

Brown, D.A., R.W. Gossett, G.P. Hershelman, K.A. Schofer, K.D. Jenkins,
and E.M. Perkins. 1982b. Bioaccumulation and detoxification of
contaminants in marine organisms from southern California coastal
waters. Proceedings of the Southern California Academy of Sciences.
In press.

Bryan, G.W. In press. The biological availability and effects of
heavy metals in marine deposits. In: Proceedings of Ocean Dumping
Symposium. New York: Wiley-Interscience.

Cantelmo, F.R., M.E. Tagatz, and K.R. Rao. 1979. Effect of barite
on meiofauna in a flow-through experimental system. Mar. Environ.
Res. 2:301-309.

Capuzzo, J.M., and J.J. Sasner, Jr. 1977. The effect of chromium on
filtration rates and metabolic activity of Mytilus edulis L. and Mya
arenaria L. In: F.J. Vernberg, A. Calabrese, F.P. Thurberg, and
W.B. Vernberg (eds.), Physiological Responses of Marine Biota to
Pollutants. New York: Academic Press. Pp. 225-240.

Carls, M.G., and S.D. Rice. 1980. Toxicity of oil well drilling
fluids to Alaskan larval shrimp and crabs. Research unit 72.
Final report. Project No. R7120822. Outer Continental Shelf
Energy Assessment Program. Bureau of Land Management, U.S.
Department of the Interior. 29 pp.

Carney, L.L., and L. Harris. 1975. Thermal degradation of drilling
mud additives. In: Proceedings, Environmental Aspects of Chemical
Use in Well-Drilling Operations, May 21-23, 1975, Houston, Tex.
Report No. EPA-5601/1-75-004. Washington, D.C.: Office of Toxic
Substances, U.S. Environmental Protection Agency. vi + 604 pp.

Carr, R.S., W.L. McCulloch, and J.M. Neff. 1982. Bioavailability
of chromium from a used chrome-lignosulfonate drilling fluids to
five species of marine invertebrates. Mar. Environ. Res. 6:189-204.

Carr, R.S., L.A. Reitsema, and J.M. Neff. 1980. Influence of used
chrome-lignosulfonate drilling fluids on the survival, respiration,
growth, and feeding activity of the opossum shrimp Mysidopsis
almyra. In: Proceedings of a Symposium on Research on
Environmental Fate and Effects of Drilling Fluids and Cuttings.
Washington, D.C.: Courtesy Associates. Pp. 944-963.

Chaffee, C., and R.B. Spies. 1982. The effects of used ferrochrome
lignosulfonate drilling fluids from a Santa Barbara Channel oil well
on the development of starfish embryos. Mar. Environ. Res.
7:265-277.

Chesser, B.G., and W.H. McKenzie. 1975. Use of a bioassay test in
evaluating the toxicity of drilling fluid additives on Galveston Bay
Shrimp. In: Proceedings, Environmental Aspects of Chemical Use in
Well-Drilling Operations, May 21-23, 1975, Houston, Tex. Report
No. EPA-560/1-75-004. Washington, D.C.: Office of Toxic
Substances, U.S. Environmental Protection Agency. Pp. 153-168.

Choi, D.R. 1982. Coelobites (reef cavity-dwellers) as indicators of
environmental effects caused by offshore drilling. Bull. Mar. Sci.
32:880-889.

Chow, T.S., and C.B. Snyder. 1980. Barium in the marine environment.
A potential indicator of drilling contamination. In: Proceedings
of a Symposium on Research on Environmental Fate and Effects of
Drilling Fluids and Cuttings. Washington, D.C.: Courtesy
Associates. Pp. 723-738.

Conklin, P.J., D.G. Doughtie, and K.R. Rao. 1980. Effects of barite
and used drilling fluids on crustaceans, with particular reference
to the grass shrimp, Palaemonetes pugio. In: Proceedings of a
Symposium on Research on Environmental Fate and Effects of Drilling
Fluids and Cuttings. Washington, D.C.: Courtesy Associates. Pp.
723-738.

116

Conklin, P.J., D. Drysdale, D.G. Doughties, K.R. Rao, J.P. Kakareka,
T.R. Gilbert, and R.F. Shokes. In press. Comparative toxicity of
drilling fluids: role of chromium and petroleum hydrocarbons.
Mar. Environ. Res.

Coombs, T.L., and S.C. George. 1978. Mechanisms of immobilization
and detoxification of metals in marine organisms. In: D.S.
McLusky and A.J. Berry (eds.). Physiology and Behavior of Marine
Organisms. Oxford: Pergamon Press. Pp. 179-187.

Craddock, D.R. 1977. Acute toxic effects of petroleum on arctic and
subarctic marine organisms. In: D.C. Malins (eds.), Effects of
Petroleum on Arctic and Subarctic Marine Environments and
Organisms. Vol. II. Biological Effects. New York: Academic
Press. Pp. 1-93.

Cranston, R.E., and J.W. Murray. 1980. Chromium species in the
Columbia River and estuary. Limnol. Oceanogr. 25:1104-1112.

Crawford, R.B., and J.D. Gates. 1981. Effects of drilling fluid on
the development of a teleost and an echinoderm. Bull. Environ.
Contam. Toxicol. 26:207-212.

Crippen, R.W., S.L. Hodd, and G. Greene. 1980. Metal levels in
sediment and benthos resulting from a drilling fluid discharge into
the Beaufort Sea. In: Proceedings of a Symposium on Research on
Environmental Fate and Effects of Drilling Fluids and Cuttings.
Washington, D.C.: Courtesy Associates. Pp. 636-669.

Dames & Moore, Inc. 1978. Drilling fluid dispersion and biological
effects study for the lower Cook Inlet C.O.S.T. well. Report sub-
mitted to Atlantic Richfield Co. Dames & Moore, Inc., Anchorage,
Alaska. 309 pp.

Daugherty, F.W. 1951. Effects of some chemicals used in oil well
drilling on marine animals. Sewage Ind. Wastes 23:1282-1287.

Derby, C.D., and J. Atema. 1981. Influence of drilling fluids on the
primary chemosensory neurons in walking legs of the lobster, Homarus
americanus. Can. J. Fish. Aquat. Sci. 38:268-274.

Dodge, R.E. 1982. Effects of drilling fluids on the reef-building
coral Montastrea annularis. Mar. Biol. 71:141-147.

Ecomar, Inc. 1978. Tanner Bank fluids and cuttings study. Conducted
for Shell Oil Company, January through March 1977. Ecomar, Inc.,
Goleta, Calif. 495 pp.

EG&G Bionomics. 1976a. Acute toxicity of two-drilling fluid
components, barite and Aquagel, to the marine alga (Skeletonema

117

costatum) and calanoid copepods (Acartia tonsa). Report submitted
to Shell Oil Co., New Orleans. EG&G Bionomics, Pensacola, Fla.

EG&G Bionomics. 1976b. Toxicity of ICMO Services No. 1 drilling
fluids to a marine algae (Skeletonema costatum) and calanoid copepod
(Acartia tonsa). Toxicity report to IMCO Services. EG&G Marine
Research Laboratory, Pensacola, Fla. 16 pp.

EG&G Bionomics. 1976c. Acute toxicity test report submitted to Shell
Oil Co., New Orleans, La.

EG&G Environmental Consultants. 1980. Monitoring program for Exxon's
block 564 Jacksonville OCS area (Lease OCS-G3705). Report submitted
to Exxon Company, U.S.A., Houston, Tex.

EG&G Environmental Consultants. 1982. A study of environmental
effects of exploratory drilling on the mid-Atlantic outer conti-
nental shelf--final report of the Block 684 Monitoring Program.
Waltham, Mass.: Available from Offshore Operators Committee,
Environmental Subcommittee, P.O. Box 50751, New Orleans, LA 70150.

Eisler, R., and R.J. Hennekey. 1977. Acute toxicitiies of Cd2+,
Cr6+, Hg2+, Ni2+, and Zn2+ to estuarine macrofauna. Arch.
Environ. Contam. Toxicol. 6:315-323.

EPA/COE. 1977. Ecological evaluation of proposed discharge of dredged
material into ocean waters. EPA/COE Technical Committee on Criteria
for Dredged and Fill Material. U.S. Army Corps of Engineers,
Waterways Experiment Station, Vicksburg, Miss.

ERCO. 1980. Results of joint bioassay monitoring program. Final
report to the Offshore Operators Committee under direction of Exxon
Production Research Co., Houston, Tex. ERCO, Inc., Cambridge, Mass.

Espey, Huston & Associates, Inc. 1981. Bioassay and depuration
studies on two types of barite. Document No. 81123. Report to
Magcobar Group, Dresser Industries, Inc., Houston, Tex. Espey,
Huston & Assoc., Inc., Houston, Tex. 256 pp.

Federal Register. 1978. 43(49). Monday, 13 March. Pp. 10474-10508.

Frank, P.M., and P.B. Robertson. 1979. The influence of salinity on
toxicity of cadmium and chromium to the blue crab, Callinectes
sapidus. Bull. Environ. Contam. Toxicol. 21:74-78.

George, S.G., B.J.S. Pirie, and T.L. Coombs. 1976. The kinetics of
accumulation and excretion of ferric hydroxide in Mytilus edulis
(L.) and its distribution in the tissues. J. Exp. Mar. Biol. Ecol.
23:71-84.

118

Gerber, R.P., E.S. Gilfillan, J.R. Hotham, L.J. Galletto, and S.A.
Hanson. 1981. Further studies on the short and long-term effect
of used drilling fluids on marine organisms. Unpublished. Final
Report, Year II to the American Petroleum Institute, Washington,
D.C. 30 pp.

Gerber, R.P., E.S. Gilfillan, B.T. Page, D.S. Page, and J.B. Hotham.
1980. Short- and long-term effects of used drilling fluids on
marine organisms. In: Proceedings of a Symposium on Research on
Environmental Fate and Effects of Drilling Fluids and Cuttings.
Washington, D.C.: Courtesy Associates. Pp. 882-911.

Gettleson, D.A. 1978. Ecological impact of exploratory drilling:
a case study. In: Energy/Environment '78. Society of Petroleum
Industry Biologists Symposium, 22-24 August, 1978, Los Angeles,
Calif. 23 pp.

Gettleson, D.A., and C.E. Laird. 1980. Benthic barium in the vicinity
of six drill sites in the Gulf of Mexico. In: Proceedings of a
Symposium on Research on Environmental Fate and Effects of Drilling
Fluids and Cuttings. Washington, D.C.: Courtesy Associates. Pp.
739-788.

Gilbert, T.R. 1981. A study of the impact of discharged drilling
fluids on the Georges Bank environment. New England Aquarium. H.
E. Edgerton Research Laboratory. Progress Rept. No. 2 to U.S. EPA,
Gulf Breeze, Fla. 98 pp.

Gillmor, R.B., C.A. Menzie, G.M. Mariani, D.R. Levin, R.C. Ayers,
Jr., and T.C. Sauer, Jr. In press. Effects of exploratory
drilling discharges on the benthic environment in the middle
Atlantic OCS: biological results of a one-year postdrilling survey.
In: Proceedings of Ocean Dumping Symposium. New York: Wiley-
Interscience.

Gillmor, R.B., C.A. Menzie, and J. Ryther, Jr. 1981. Side-scan sonar
and TV observations of the benthic environment and megabenthos in
the vicinity of an OCS exploratory well in the Middle Atlantic
Bight. In: Conference Record. Vol. 2 Oceans '81 Symposium.
Boston, Mass. IEEE Publ. No. 81CH1685-7 IEEE Service Center,
Piscataway, N.J. Pp. 727-731.

Grantham, C.K., and J.P. Sloan. 1975. Toxicity study of drilling
fluid chemicals on aquatic life. In: Environmental Aspects of
Chemical Use in Well-Drilling Operations. EPA/560/1-75-004.
Washington, D.C.: U.S. Environmental Protection Agency. Pp.
103-112.

Grassle, J.F., R.E. Imgren, and J.P. Grassle. 1980. Response of
benthic communities in MERL experimental ecosystems to low level,
chronic additions of No. 2 fuel oil. Mar. Environ. Res. 4:279-297.

119

Hollingsworth, J.W., and R.A. Lockhart. 1975. Fish toxicity of
dispersed clay drilling mud deflocculants. In: Environmental
Aspects of Chemical Use in Well-Drilling Operations. EPA-360/1-
75-004. Washington, D.C.: U.S. Environmental Protection Agency.
Pp. 113-123.

Houghton, J.P., D.L. Beyer, and E.D. Thielk. 1980. Effects of oil
well drilling fluids on several important Alaskan marine organisms.
In: Proceedings of a Symposium on Research on Environmental Fate
and Effects of Drilling Fluids and Cuttings. Washington, D.C.:
Courtesy Associates. Pp. 1017-1043.

Hudson, J.H., and D.M. Robbin. 1980. Effects of drilling fluids on
the growth rate of the reef-building coral, Montastrea annularis.
In: Proceedings of a Symposium on Research on Environmental Fate
and Effects of Drilling Fluids and Cuttings. Washington, D.C.:
Courtesy Associates. Pp. 1101-1122.

Hudson, J.H., E.A. Shinn, and D.M. Robbin. 1982. Effects of offshore
oil drilling on Philippine Reef corals. Bull. Mar. Sci. 32:890-908.

Intergovernmental Maritime Consultative Organization, et al. 1969.
Abstract of first session report of Joint Group of Experts on the
Scientific Aspects of Marine Pollution. Water Res. 3:995-1005.

Jenkins, K.D., and D.A. Brown. 1982. Determining the biological
significance of contaminant bioaccumulation. In: H. White (ed.),
Proceedings of the Workshop on Meaningful Measures of Marine
Pollution Effects. Pensacola, Fla., April 1982. College Park,
Md.: University of Maryland Sea Grant Program. In press.

Jenkins, K.D., D.A. Brown, G.P. Hershelman, and W.C. Meyer. 1982.
Contaminants in white croakers Geneyonemus lineatus (Avres, 1855)
from the Southern California bight. I. Trace metals detoxifica-
tion/toxification. In: W.B. Vernberg, A. Calabrese, F.P.
Thurberg, and F.J. Vernberg (eds.). Physiological Mechanisms of
Marine Pollutant Toxicity. New York: Academic Press. In press.

Jenne, E.A., and S.N. Luoma. 1977. Forms of trace elements in soils,
sediments, and associated waters: an overview of their determination
and biological availability. In: H. Drucker and R.E. Wildung
(eds.), Biological Implications of Metals in the Environment. NTIS
Conf.-750929. Springfield, Va. Pp. 110-143.

Jones, M., and M. Hulse. 1982. Drilling fluid bioassays and the OCS.
Oil Gas J. 80(25):241-244.

Knox, F. 1978. The behavior of ferrochrome lignosulfonate in natural
waters. Masters Thesis. Massachusetts Institute of Technology,
Cambridge, Mass. 65 pp.

120

Kramer, J.R., H.D. Grundy, and L.G. Hammer. 1980. Occurrence and
solubility of trace metals in barite for ocean drilling operations.
In: Proceedings of a Symposium on Research on Environmental Fate
and Effects of Drilling Fluids and Cuttings. Washington, D.C.:
Courtesy Associates. Pp. 789-798.

Krone, M.A., and D.C. Biggs. 1980. Sublethal metabolic responses of
the hermatypic coral Madracis decactis exposed to drilling fluids,
enriched with ferrochrome lignosulfonate. In: Proceedings of a
Symposium on Research on Environmental Fate and Effects of Drilling
Fluids and Cuttings. Washington, D.C.: Courtesy Associates. Pp.
1079-1100.

Land, B. 1974. The toxicity of drilling fluid components to aquatic
biological systems. A literature review. Tech. Rep. No. 487.
Environment Canada, Fisheries and Marine Service, Research and
Development Directorate, Freshwater Institute, Winnipeg, Manitoba,
Canada. 33 pp.

Lees, D.C., and J.P. Houghton. 1980. Effects of drilling fluids on
benthic communities at the lower Cook Inlet C.O.S T. well. In:
Proceedings of a Symposium on Research on Environmental Fate and
Effects of Drilling Fluids and Cuttings. Washington, D.C.:
Courtesy Associates. Pp. 209-350.

Liss, R.G., F. Knox, D. Wayne, and T.R. Gilbert. 1980. Availability
of trace elements in drilling fluids to the marine environment. In:
Proceedings of a Symposium on Research on Environmental Fate and
Effects of Drilling Fluids and Cuttings. Washington, D.C.:
Courtesy Associates. Pp. 691-722.

Logan, W.J., J.B. Sprague, and B.D. Hicks. 1973. Acute lethal
toxicity to trout of drilling fluids and their constituent chemicals
as used in the Northwest Territories. Appendix to M.R. Falk and
M.J. Lawrence. Acute toxicity of petrochemical drilling fluids
components and wastes to fish. Tech. Rep. Ser. No. CEN-T-73-1.
Environment Canada, Resource Management Branch, Central Region,
Winnipeg, Manitoba, Canada. Pp. 45-108.

Lyes, M.C. 1979. Bioavailability of hydrocarbon from water and
sediment to the marine worm Arenicola marina. Mar. Biol.
55:121-127.

MacDonald, R.W. 1982. An examination of metal inputs to the southern
Beaufort Sea by disposal of waste barite in drilling fluid. Ocean
Manage. 8:29-49.

Malins, D.C. (ed.). 1977. Effects of Petroleum on Arctic and
Subarctic Marine Environments and Organisms. Vol. II. Biological
Effects. New York: Academic Press. 500 pp.

121

Mariani, G.M., L.V. Sick, and C.C. Johnson. 1980. An environmental
monitoring study to assess the impact of drilling dischages in the
mid-Atlantic. III. Chemical and physical alterations in the
benthic environment. In: Proceedings of a Symposium on
Environmental Fate and Effects of Drilling Fluids and Cuttings.
Washington, D.C.: Courtesy Associates. Pp. 438-498.

Marine Bioassay Labs. 1982. Drilling fluids bioassays. Texaco
Habitat Platform Well A-1 Pitas Point Lease Sale Unit: Acanthomysis
sculpta and Macoma nasuta. Report submitted to Texaco, Inc., Los
Angeles, Calif., and IMCO Services, Houston, Tex., by Marine
Bioassay Labs., Watsonville, Calif.

Maurer, D., W. Leathem, and C. Menzie. 1981. The impact of drilling
fluid and well cuttings on polychaete feeding guilds from the U.S.
northeastern continental shelf. Mar. Pollut. Bull. 12:342-347.

McAtee, J.L., and N.R. Smith. 1969. Ferrochrome lignosulfonates.
I. X-ray absorption edge fine structure spectroscopy. II. Inter-
action with ion exchange resin and clays. J. Colloid Interface
Sci. 29:389-398.

McCain, B.B., H.O. Hodgins, W.D. Gronlund, J.W. Hawkes, D.W. Brown,
M.S. Myers, and J.J. Vandermuelen. 1978. Bioavailability of crude
oil from experimentally oiled sediments to English sole (Parophrys
vetulus), and pathological consequences. J. Fish. Res. Bd. Can.
35:657-664.

McCulloch, W.L., J.M. Neff, and R.S. Carr. 1980. Bioavailability of
heavy metals from used offshore drilling fluids to the clam Rangia
cuneata and the oyster Crassostrea gigas. In: Proceedings of a
Symposium on Research on Environmental Fate and Effects of Drilling
Fluids and Cuttings. Washington, D.C.: Courtesy Associates. Pp.
964-983.

McFarland, V.A., and R.K. Peddicord. 1980. Lethality of a suspended
clay to a diverse selection of marine and estuarine macrofauna.
Arch. Environ. Contam. Toxicol. 9:733-741.

McLeay, D.J. 1976. Marine toxicity studies on drilling fluid wastes.
In: Industry/Government Working Group in Disposal Waste Fluids
from Petroleum Exploratory Drilling in the Canadian Arctic. Vol.
10. Yellowknife, N.W.T., Canada. 17 pp.

Meek, R.P., and J.P. Ray. 1980. Induced sedimentation, accumulation,
and transport resulting from exploratory drilling discharges of
drilling fluids and cuttings. In: Proceedings of a Symposium on
Research on Environmental Fate and Effects of Drilling Fluids and
Cuttings. Washington, D.C.: Courtesy Associates. Pp. 259-284.

122

Menzie, C.A., D. Maurer, and W.A. Leathem. 1980. An environmental
monitoring study to assess the impact of drilling discharges in the
mid-Atlantic. IV. The effects of drilling discharges on the
benthic community. In: Proceedings of a Symposium on
Environmental Fate and Effects of Drilling Fluids and Cuttings.
Washington, D.C.: Courtesy Associates. Pp. 499-540.

Moraitou-Apostolopoulou, M., and G. Verriopoulos. 1982. Toxicity of
chromium to the marine planktonic copepod Acartia clausi,
Giesbrecht. Hydrobiologia 96:121-127.

Morse, M.P., W.E. Robinson, and W.E. Wehling. 1982. Effects of
sublethal concentrations of the drilling fluids components attapul-
gite and Q-Broxin on the structure and function of the gill of the
scallop, Placopecten magellanicus (Gmelin). In: W.B. Vernberg, A.
Calabrese, F.P. Thurberg and F.J. Vernberg, (eds.). Physiological
Mechanisms of Marine Pollutant Toxicity. New York: Academic
Press. Pp. 235-260.

Nakayama, E., T. Kuwamoto, S. Tsurubo, H. Tokoro, and T. Fujinaga.
1981a. Chemical speciation of chromium in seawater. Part 1.
Effect of naturally occurring organic materials on the complex
formation of chromium (III). Analy. Chim. Acta 130:289-294.

Nakayama, E., T. Kuwamoto, S. Tsurubo, and T. Fujinaga. 1981b.
Chemical speciation of chromium in seawater. Part 2. Effects of
manganese oxides and reducible organic materials on the redox
processes of chromium. Analy. Chim. Acta 130:401-404.

Nakayama, E., T. Kuwamoto, H. Tokoro, and T. Fujinaga. 1981c.
Chemical speciation of chromium in seawater. Part 3. The deter-
mination of chromium species. Analy. Chim. Acta 131:247-254.

National Research Council. 1975. Petroleum in the Marine Environment.
Washington, D.C.: National Academy of Sciences.

Neff, J.M. 1979. Polycyclic Aromatic Hydrocarbons in the Aquatic
Environment. Sources, Fates, and Biological Effects. Barking
Essex, England: Applied Science Publ. 262 pp.

Neff, J.M. 1980. Effects of used drilling fluids on benthic marine
animals. Publ. No. 4330. American Petroleum Institute, Washington,
D.C. 31 pp.

Neff, J.M., and J.W. Anderson. 1981. Response of Marine Animals to
Petroleum and Specific Petroleum Hydrocarbons. New York: Halsted
Press. 177 pp.

Neff, J.M., R.S. Carr, and W.L. McCulloch. 1981. Acute toxicity of a
used chrome lignosulfonate drilling fluids to several species of
marine invertebrate. Mar. Environ. Res. 4:251-266.

123

Neff, J.M., R.S. Foster, and J.F. Slowey. 1978. Availability of
sediment-adsorbed heavy metals to benthos with particular emphasis
on deposit-feeding infauna. Tech. Rep. D-78-42. U.S. Army
Engineer Waterways Experiment Station, Vicksburg, Miss. 286 pp.

Neff, J.M., W.L. McCulloch, R.S. Carr, and K.A. Retzer. 1980.
Comparative toxicity of four used offshore drilling fluids to
several species of marine animals from the Gulf of Mexico. In:
Proceedings of a Symposium on Research on Fate and Effects of
Drilling Fluids and Cuttings. Washington, D.C.: Courtesy
Associates. Pp. 866-881.

Nelson, D.W., S. Liu, and L.E. Sommers. 1980. Plant uptake of toxic
metals present in drilling fluids. In: Proceedings of a Symposium
on Research on Fate and Effects of Drilling Fluids and Cuttings.
Washington, D.C.: Courtesy Associates. Pp. 114-138.

Nimmo, D. et al. 1979. The long term effects of suspended
particulates on survival and reproduction of the mysid shrimp,
Mysidopsis bahia, in the laboratory. In: Proceedings of MESA
Symposium, New York, June 10-15. Rockville, Md.: National Oceanic
and Atmospheric Administration.

Norseth, T. 1981. The carcinogenicity of chromium. Environ. Health
Perspect. 40:121-130.

Northern Technical Services. 1981. Beaufort Sea drilling effluent
disposal study. Performed for the Reindeer Island stratigraphic
test well participants under the direction of Sohio Alaska Petroleum
Company. Northern Technical Services, Anchorage, Alaska. Available
from Sohio Alaska Petroleum Co., Anchorage, Alaska. 329 pp.

Oshida, P.S., L.S. Word, and A.J. Mearns. 1981. Effects of
hexavalent and trivalent chromium on the reproduction of Neanthes
arenaceodentata (Polychaeta). Mar. Environ. Res. 5:41-50.

Oviatt, C., J. Frithsen, J. Gearing, and P. Gearing. 1982. Low
chronic additions of No. 2 fuel oil: chemical behavior, biological
impact and recovery in a simulated estuarine environment. Mar.
Ecol. Prog. Ser. 9:121-136.

Paffenhofer, R. 1972. The effects of suspended "red mud" on
mortality, body weight, and growth of the marine planktonic
copepod, Calanus helgolandicus. Water Air Soil Pollut. 1:314-321.

Page, D.S., B. T. Page, J.R. Hotham, E.S. Gilfillan, and R.P. Gerber.
1980. Bioavailability of toxic constituents of used drilling
fluids. In: Proceedings of a Symposium on Research on
Environmental Fate and Effects of Drilling Fluids and Cuttings.
Washington, D.C.: Courtesy Associates. Pp. 984-996.

124

Payne, J.R., J.L. Lambach, R.E. Jordan, G.D. McNabb, Jr., R.R. Sims,
A. Abasumara, J.G. Sutton, D. Generro, S. Gagner, and R.F. Shokes.
1982. Georges Bank monitoring program. Analysis of hydrocarbons
in bottom sediments and analysis of hydrocarbons and trace metals
in benthic fauna. First year final report to the New York OCS
Office, Minerals Management Service, U.S. Department of the
Interior, by Science Applications, Inc., La Jolla, Calif.

Pearson, R.G. 1981. Recovery and recolonization of coral reefs.
Mar. Ecol. Prog. Ser. 4:105-122.

Perricone, D. 1980. Major drilling fluid additives. In:
Proceedings of a Symposium on Research on Environmental Fate and
Effects of Drilling Fluids and Cuttings. Washington, D.C.:
Courtesy Associates. Pp. 15-29.

Petrazzuolo, G. 1981. Preliminary report. An environmental
assessment of drilling fluids and cuttings released onto the Outer
Continental Shelf. Vol. 1: Technical assessment. Vol. 2: Tables,
figures and Appendix A. Draft report prepared for Industrial
Permits Branch, Office of Water Enforcement and Ocean Programs
Branch, Office of Water and Waste Management, U.S. Environmental
Protection Agency, Washington, D.C.

Phelps, D.K., G. Telek, and R.L. Lapan. 1975. Assessment of heavy
metal distribution within the food web. In: Pearson and
Frangipane (eds.). Marine Pollution and Marine Waste Disposal.
New York: Pergamon Press.

Powell, E.N., M. Kasschau, E. Che, M. Loenig, and J. Peron. 1982.
Changes in the free amino acid pool during environmental stress in
the gill tissue of the oyster, Crassostrea virginica. Comp.
Biochem. Physiol. 71A:591-598.

Reish, D.J., J.M. Martin, F.M. Piltz, and J.L. Ward. 1976. The
effect of heavy metals on laboratory populations of two polychaetes
with comparisons to the water quality conditions and standards in
Southern California marine waters. Water. Res. 10:299-302.

Rhoads, D.C., P.L. McCall, and J.Y. Yingst. 1981. Disturbance and
production of the estuarine seafloor. Am. Sci. 66:577-586.

Rice, S.D., J.W. Short, and J.F. Karinen. 1977. Comparative oil
toxicity and comparative animal sensitivity. In: D.A. Wolfe
(ed.), Fate and Effects of Petroleum Hydrocabons in Marine Organisms
and Ecosystems. New York: Pergamon Press. Pp. 78-94.

Roesijadi, G., and J.W. Anderson. 1979. Condition index and free
amino acid content of Macoma inquinata exposed to oil-contaminated
marine sediments. In: W.B. Vernberg, F.P. Thurberg, A. Calabrese
and F.J. Vernberg (eds.), Marine Pollution: Functional Responses.
New York: Academic Press. Pp. 69-83.

125

Roesijadi, G., J.W. Anderson, and J.W. Blaylock. 1978a. Uptake of
hydrocarbons from marine sediments contaminated with Prudhoe Bay
crude oil: influence of feeding type of test species and avail-
ability of polycyclic aromatic hydrocarbons. J. Fish. Res. Bd.
Can. 35:608-614.

Roesijadi, G., D.L. Woodruff, and J.W. Anderson. 1978b.
Bioavailability of naphthalenes from marine sediments artificially
contaminated with Prudhoe Bay crude oil. Environ. Pollut.
15:223-229.

Rossi, S.S. 1977. Bioavailability of petroleum hydrocarbons from
water, sediments and detritus to the marine annelid Neanthes
arenaceodentata. 1977. In: Proceedings 1977 Oil Spill Conference
(Prevention, Behavior, Control, Cleanup). Washington, D.C.:
American Petroleum Institute. Pp. 621-626.

Rubinstein, N.I., R. Rigby, and C.N. D'Asaro. 1980. Acute and
sublethal effects of whole used drilling fluids on representative
estuarine organisms. In: Proceedings of a Symposium on Research
on Environmental Fate and Effects of Drilling Fluids and Cuttings.
Washington, D.C.: Courtesy Associates. Pp. 828-846.

Sanders, H.L., J.F. Grassle, G.R. Hampson, L.S. Morse, S. Garner-Price,
and C.C. Jones. 1980. Anatomy of an oil spill: long-term effects
from the grounding of the barge Florida off west Falmouth,
Massachusetts. J. Mar. Res. 38:265-380.

Sharp, J.R., R.S. Carr, and J.M. Neff. 1982. Influence of used
chrome lignosulfonate drilling and fluids on the early life history
of the mummichog Fundulus heteroclitus. In: Proceedings of Ocean
Dumping Symposium. New York: John Wiley & Sons.

Siferd, C.A. 1976. Drilling fluids wastes characteristics from
drilling operations in the Canadian North. In: Industry/Government
Working Group "A" Program, Pollution Aspects from Waste Drilling
Fluids in the Canadian North. Vol. 5. Arctic Petroleum Operators
Association and Environment Canada, Yellowknife, N.W.T., Canada.

Skelly, W.G., and D.E. Dieball. 1969. Behavior of chromate in
drilling fluids containing chromate. In: Proceedings of the 44th
Annual Meeting of the Society of Petroleum Engineers of AIME.
Paper No. SPE 2539. 6 pp.

Smillie, R.H., K. Hunter, and M. Loutit. 1981. Reduction of chromium
(VI) by bacterially produced hydrogen sulfide in a marine environ-
ment. Water Res. 15:1351-1354.

Smith, G.A., J.S. Nickels, R.J. Bobbie, N.L. Richards, and D.C. White.
1982. Effects of oil and gas well-drilling fluids on the biomass
and community structure of microbiota that colonize sands in running
seawater. Arch. Environ. Contam. Toxicol. 11:17-24.

126

Sprague, J.B., and W.J. Logan. 1979. Separate and joint toxicity to
rainbow trout of substances used in drilling fluids for oil explor-
ation. Environ. Pollut. 19:269-281.

Stegeman, J.J. 1981. Polynuclear aromatic hydrocarbons and their
metabolism in the marine environment. In: H.V. Gelboin and P.O.P.
Ts'o (eds.), Polycyclic Hydrocarbons and Cancer. Vol. 3. New
York: Academic Press. Pp. 1-60.

Szmant-Froelich, A., V. Johnson, T. Hoen, J. Battey, G.J. Smith,
E. Fleishmann, J. Porter, and D. Dallmeyer. In press. The
physiological effects of oil-drilling fluids on the Carribbean
coral Montastrea annularis. In: Proceedings of the 4th
International Coral Reef Symposium, Manila. Vol. 1.

Tagatz, M.E., J.M. Ivey, C.E. DalBo, and J.L. Oglesby. 1982.
Responses of developing macrobenthic communities to drilling fluids.
Estuaries 5:131-137.

Tagatz, M.E., J.M. Ivey, H.K. Lehman, and J.L. Oglesby. 1978.
Effects of lignosulfonate-type drilling fluids on development of
experimental estuarine macrobenthic communities. Northeast. Gulf
Sci. 2:25-42.

Tagatz, M.E., J.M. Ivey, H.K. Lehman, M. Tobia, and J.L. Oglesby.
1980. Effects of drilling fluids on development of experimental
estuarine macrobenthic communities. In: Proceedings of a
Symposium on Research on Environmental Fate and Effects of Drilling
Fluids and Cuttings. Washington, D.C.: Courtesy Associates. Pp.
847-865.

Tagatz, M.E., J.M. Ivey, and J.L. Oglesby. 1979. Toxicity of
drilling fluids biocides to developing macrobenthic communites.
Northeast. Gulf Sci. 3:88-95.

Tagatz, M.E., and M. Tobia. 1978. Effect of barite (BaSO4) on
development of estuarine communites. Estuarine Coastal Mar. Sci.
7:401-407.

Thompson, J.H., Jr. 1978. Effects of drilling fluids on seven species
of reef building corals as measured in field and laboratory. Final
report to U.S.G.S. Grant No. 14-08-001-1627. College of
Geosciences, Texas A&M University. 54 pp.

Thompson, J.H., Jr. 1980. Responses of selected scleractinian corals
to drilling fluid used in the marine environment. Ph.D. Disserta-
tion. Texas A&M University. 130 pp.

Thompson, J.H., Jr., and T.J. Bright. 1977. Effects of drilling
fluids on sediment clearing rates of certain hermatypic corals.
In: Oil Spill Conference. Washington, D.C.: American Petroleum
Institute. Pp. 495-498.

127

Thompson J.H., Jr., and T.J. Bright. 1980. Effects of an offshore
drilling fluid on selected corals. In: Proceedings of a Symposium
on Research on Environmental Fate and Effects of Drilling Fluids
and Cuttings. Washington, D.C.: Courtesy Associates. Pp.
1044-1078.

Thompson, J.H., Jr., E.A. Shinn, and T.J. Bright. 1980. Effects of
drilling fluids on seven species of reef-building corals as measured
in the field and laboratory. In: R.A. Geyer (ed.), Marine
Environmental Pollution. Vol. 1. Hydrocarbons. Elsevier
Oceanography Series. Vol. 27A. New York: Elsevier/North-Holland.

Thorson, G. 1957. Bottom communities (sublittoral or shallow shelf).
In: J.W. Hedgepeth (ed.), Treatise on Marine Ecology and
Paleoecology. Vol. I. Geol. Soc. Am. Mem. 67. Washington, D.C.

Thorson, G. 1966. Some factors influencing the recruitment and
establishment of marine benthic communities. Neth. J. Sea. Res.
3:267-293.

Tillery, J.B., and R.E. Thomas. 1980. Heavy metal contamination from
petroleum production platforms in the Gulf of Mexico. In:
Symposium on Environental Fate and Effects of Drilling Fluids and
Cuttings. Washington, D.C.: Courtesy Associates. Pp. 562-587.

Tornberg, L.D., E.D. Thielk, R.E. Nakatoni, R.C. Miller and S.O.
Hillman. 1980. Toxicity of drilling fluids to marine organisms in
the Beaufort Sea, Alaska. In: Proceedings of a Symposium on
Research on Environmental Fate and Effects of Drilling Fluids and
Cuttings. Washington, D.C.: Courtesy Associates. Pp. 997-1006.

Trefry, J.H., R.P. Trocine, and D.B. Meyer. 1981. Tracing the fate
of petroleum drilling fluids in the northwest Gulf of Mexico. In:
Oceans '81. Available from Marine Technology Society, Washington,
D.C. Pp. 732-736.

Trocine, R.P., J.H. Trefry, and D.B. Meyer. 1981. Inorganic tracers
of petroleum drilling fluid dispersion in the northwest Gulf of
Mexico. Reprint Extended Abstract. Div. Environ. Chem. ACS
Meeting. Atlanta, Ga. March-April 1981.

Van der Weijden, C.H., and M. Reith. 1982. Chromium(III)-
Chromium(VI) interconversions in seawater. Mar. Chem. 11:565-572.

Ward, J.A. 1977. Chemoreception of heavy metals by the polychaetous
annelid Myxicola infundibulum (Sabellidae). Comp. Biochem. Physiol.
58C:103-106.

128

Wheeler, R.B., J.B. Anderson, R.R. Schwrzer, and C.L. Hokanson. 1980.
Sedimentary processes and trace metal contaminants in the Buccaneer
oil/gas field, northwesten Gulf of Mexico. Environ. Geol.
3:163-175.

White, D.C., J.S. Nickels, M.J. Gehron, J.H. Parker, R.F. Martz, and
N.L. Richards. In press. Effect of well-drilling fluids on the
physiological status and microbial infection of the reef-building
coral Monastrea annularis. Arch. Environ Contam. Toxicol.

Wilbert, T. 1971. Turbidity. In: Marine Ecology. New York: Wiley-
Interscience. Pp. 1184-1194.

Wildish, D.J. 1972. Acute toxicity of polyoxyethylene esters and
polyoxyethylene ethers to S. salar and G. oceanicus. Water Res.
6:759-762.

Zitko, V. 1975. Toxicity and environmental properties of chemicals
used in well-drilling operations. In: Environmental Aspects of
Chemical Use in Well-Drilling Operations. EPA-560/1-75-004.
Washington, D.C.: U.S. Environmental Protection Agency. Pp.
311-326.

Considerations in Using the Information Availble

on the Fates and Effects of Driling Discharges

Most information about the effects of drilling fluids on marine
organisms comes from laboratory experiments. Most of these have
studied lethal effects over a short period of time, typically in 96 hr
LC50 toxicity tests. The organisms most frequently used in these bio-
assay tests have been the coastal and estuarine species readily avail-
able for testing and easily maintained in the laboratory. Only a few
assessments of drilling-fluid effects have been made in the field, and
these field measurements are not very advanced.
The limitations of the laboratory experiments have led to some
criticisms of their adequacy and of their applicability in assessing
the effects of drilling-fluid discharges on the OCS. These criticisms
also apply to current assessments of the effects of most anthropogenic
additions to the marine environment. information on the effects of
discharged drilling fluids is generally no less substantial than that
on municipal and industrial wastes, sewage sludge, and dredged sedi-
ments and in some respects is of higher quality because of more
sophisticated research in recent years. The issue to address is what
degree of confidence is warranted by hazard assessment models that rely
on laboratory studies of toxic effects along with predicted exposure
regimes for the benthic and pelagic communities of the various conti-
nental shelf environments. In such models, testing acute toxicity is
only the first step in evaluating biological effects. More sophisti-
cated measures of environmental effects, some of which are discussed
below, are required in rigorous models. Even in sophisticated inves-
tigations, however, a fundamental dilemma remains in relying on either
prospective studies, which may be limited in their environmental
realism, or retrospective field asssessments, which may be limited in
their predictive value.

LABORATORY EVALUATIONS OF TOXICITY

In evaluating the toxic effects of substances on aquatic organisms, two
types of tests are used: (1) acute toxicity tests, which determine the
concentration that causes the mortality of some proportion of test
organisms, (for example, half in the LC50 test); and (2) chronic
toxicity tests, which determine what concentration causes some other

129

13 0

measurable effect. Acute toxicity tests are usually conducted during
a 4-day period (96 h) to provide a standard for comparing the toxici-
ties of different substances and the relative sensitivities of dif-
ferent species. Chronic toxicity tests are conducted over various time
intervals, for example, 48 h, 96 h, 10 days, or 21 days, and measure
the effects of substances ongrowth, development, reproduction, or
behavior.
Most information on toxicity is based on the results of acute
toxicity tests. Often this is the only information available on the
effects of drilling fluids on marine organisms and thus is the infor-
mation extrapolated for use in evaluating field situations in hazard
assessments. Some of the limitations in extrapolating these tests
should be recognized:

* Acute tests measure only lethality, not sublethal effects.
� They are not conducted over the course of organisms entire life
stages or life cycles.
* They may not test species that are sensitive or commercially
important.
* They require using such high concentrations of substances that
they do not simulate the actual environmental exposure condi-
tions, in which discharges may be diluted by 100 times within
a few meters of the discharge pipe (see Chapter 3).

The method used to extrapolate from acute toxicity values to proba-
ble sublethal effects for a species is by using an application or
safety factor. An application factor is the ratio of averaged acute
and chronic values. Where no chronic test values are available for a
species, a safety factor is used. For the results on drilling fluids,
the safety (or application) factors that have been used range from
>0.1-.01. In comparison, application factors for most toxicants,
range from 0.01 to >0.001. Caution must be exercised in using these
factors because the mechanism eliciting a sublethal toxic effect or an
effect through chronic exposure may not be the same one producing the
more easily measured acute toxicity. Ideally, application factors
should be used in a hazard assessment only when the toxic responses in
question result from the same mechanism; in practice this ideal is
seldom attained. When assessing the actual ratios of acute to chronic
toxicities, many being from sensitive species and life stages, the
ratios range from 0.03 to 0.33, with the majority being towards the
0.33 end. This indicates that the normal safety factor is
conservative.
Laboratory tests of the acute toxicities of drilling fluids have
been conducted on over 70 species representing 5 major phyla. More
than 36 percent of these tests have been conducted on organisms in
larval and juvenile stages. Many of the tests of more sensitive
species test were conducted on species in their early life stages: 48
percent of all shrimp tests, 43 percent of all decapod tests, 38
percent of all finfish tests, and 81 percent of all mysid tests (Neff
et al., 1981; Petrazzuolo, 1983). Since 1980, the emphasis has been
on testing the toxicities of drilling fluids on sensitive species and
those in earlier developmental stages (eggs, larvae, and juveniles).

131

A range of 96-h LC50 values covering three orders of magnitude
(102 to 105 ppm) has been reported in testing drilling fluids.
Petrazzuolo (1981) concluded that because of the distribution of these
values (92 percent are greater than 103 ppm) even sensitive oceanic
species are unlikely to exhibit lethal toxicities to fluids much below
the lowest known 96-h LC50 value, 50 to 100 ppm. This conclusion may
be challenged if the observed distribution of toxicities is a function
of variable fluid toxicity and not the result of testing with a few
extremely sensitive and many insensitive species. If it is found that
a small number of fluids are much more toxic than others, then the
factors contributing to their toxicity must be identified.
It has been argued that the results of bioassays with intertidal,
estuarine, and nearshore organisms should not be extrapolated to
predict the effects of fluids on offshore species. The first groups
of organisms often survive better any rapid changes in temperature and
salinity, as well as the rigors of collection, transport, and being
held in aquaria. It has been argued that these characteristics reflect
these species' insensitivity to chemical pollutants. Recent studies
indicate, however, that at least some nearshore species are as sensi-
tive as those of similar morphology found offshore. For example, LC50
values for two copepods, estuarine Acartia tonsa and oceanic Centro-
pages typicus, were similar in tests with several drilling fluids, even
though the second species was much more difficult to keep in the
laboratory (New England Aquarium, 1981). Moreover, a number of the
species listed in Table 20 are found both near shore and on the outer
continental shelf. These include the ocean scallop Placopecten
magellanicus wich constitutes a commercial fishery on Georges Bank but
which is also found along the coast of Maine. Other species with a
similar range of habitat that have been the subject of bioassays
include the bat star fish Patiria miniata (Chaffee and Spies, 1982),
the cancer crab Cancer borealis (Gerber et al., 1981), and various
species of echinoderms (embryos) (Crawford and Gates, 1981).
The design of some laboratory toxicity tests has also been criti-
cized. For example, the EPA/COE method for assessing the toxicity of
liquid, suspended particulate, and solid phases of drilling fluids at
1:4 dilution does not realistically separate the components of treated
drilling fluids. The high ratio of fluid to seawater in this dilution
(as compared to that in field conditions) results in a suspended par-
ticulate phase that is frequently unsuitable for testing the toxicity
of the fluid. Thus, this method of preparing the bioassay mixture may
confuse the estimated toxicity value of the drilling fluid or drilling-
fluid fraction. Other problems with current bioassay techniques
include their difficulty in filtering the suspended particulate phase
(excess solids stay in suspension) and the opaqueness of their test
solutions (especially of chrome lignosulfonate fluids), which makes
conducting bioassay observations difficult. Small copepods have even
been observed mired in layers of settled drilling-fluid solids (New
England Aquarium, 1981), a situation unlikely to occur in nature.
The sophistication of toxicity tests of drilling fluids has
improved in recent years. A growing body of data describes the sub-
lethal effects of drilling fluids, effects including the abnormal

132

development of mollusc larvae and embryos (Neff, 1980; New England
Aquarium, 1981), decreased growth rates in mysid shrimp (Carr et al.,
1980) and sea scallops (Gerber et al., 1981), and depressed feeding in
adult lobsters Homarus americanus (Derby and Atema, 1981). Sublethal
tests often examine organisms in critical life stages, and when they
are properly designed their results allow a more realistic evaluation
of the hazards posed by drilling fluids. In spite of the improvement
that the tests here cited represent, the range of concentrations and
the exposure durations they use may result in longer exposures than
thoseoccurring in the field.
The biological effects of discharged materials may also be assessed
through microcosm studies of benthic larval recruitment (see Chapter
4). The resettlement of natural larval populations to defaunated
sediment that has been mixed with or covered with drilling fluid in
these microcosms may to some degree simulate the development of benthic
communities following a drilling operation. Still, two factors limit
the extrapolation of results from these tests to other regions. First,
the effects on organisms of grain size, sediment chemistry, and other
physical, chemical, and microbiological factors in the sediments have
not always been isolated in experimental designs. Second, the results
of these experiments are limited in that they apply only to larval
populations.
In summary, laboratory toxicity testing has been useful in gauging
the relative toxicities of drilling-fluid suspensions and will continue
to be useful in screening drilling-fluid additives and in attempting
to understand the mechanisms of toxicity and sublethal effects and the
effects of short-term exposures. Given the data on the fates of
drilling fluids in the field, expecially on rapid plume dispersion, and
the available results of acute toxicity tests, as well as the inherent
limitations in extrapolating from laboratory results, additional acute
toxicity testing is unlikely to improve predictions of drilling fluids'
effects on organisms in the water column. Laboratory tests have not
realistically simulated the exposure conditions experienced by benthic
organisms.

BIOACCUMULATION

The bioaccumulation of metals from drilling fluids and cuttings has
been addressed by both laboratory and field studies. In laboratory
exposures to drilling-fluid components and in field situations both
barium and chromium have been found to accumulate beyond levels in
control organisms. Chronic ingestion of drilling-fluid solids by
deposit-feeding organisms should be investigated further, since parti-
culate metals may be accumulated under these circumstances (Liss et
al., 1980). Such studies should consider that undigested solids would
be eliminated from the digestive tract and should attempt to distin-
guish between metals that are nonspecifically bound to macromolecules
(e.g., to enzymes and nucleic acids) and those associated with intra-
cellular ligands, like metallothionein, or sequestered in membrane-
bound vesicles and thus effectively detoxified (Jenkins and Brown,

133

1982). Bioaccumulation by organisms in the water column has not been
examined directly. Their exposure to water-soluble phases is usually
of short duration, as the fluid plume disperses rapidly, and thus
bioaccumulation in these circumstances is unlikely.

THE VARIABILITY OF DRILLING FLUIDS

It is important that a wide range of drilling fluids be evaluated in a
comprehensive testing program. The cooperative program between the
Petroleum Equipment Suppliers Association (PESA) and EPA to obtain
samples of used drilling fluids for toxicity testing, which relied on
random samples, gave some much-needed breadth to the data base on
drilling-fluid composition and toxicity. Random sampling is essential
in such a program if the results are to be credible. Complete docu-
mentation of the samples, detailing their source, the method used to
obtain them, and their components and components concentrations are
also needed to allow informed interpretation of chemical and toxico-
logical testing.
It is clear from a review of the literature (Table 20, Chapter 4,)
that the toxicities of drilling fluids to marine fauna vary up to three
orders of magnitude even though the major constituents do not vary
greatly. Toxic substances are added to some drilling fluids.
Hexavalent chromium may be added to aid deflocculation, which it
accomplishes mainly by extending the thinning ability of chrome ligno-
sulfonate (Knox, 1978). Lubricants, such as diesel fuel, may be added
to reduce torque along the drill string, particularly when drilling
deviated (inclined) holes. The drilling fluids found to be relatively
toxic include those from a well drilled in Mobile Bay in 1979 under a
"1no discharge" stipulation (Rubinstein et al., 1980) to which both
hexavalent chromium and diesel fuel were added. These additives and
their degradation products are probably the principal toxic agents in
drilling fluids.
The purity of unrefined barite varies substantially; barite mined
from vein displacement deposits may contain concentrations of lead and
zinc sulf ides in excess of I g/kg (Kramer et al., 1980). Because the
concentrations of lead and zinc in deep ocean water are below 10-7
g/kg (Bruland, 1980; Patterson, 1974), discharges of drilling fluid
weighted with barite will cause a temporary increase of these metals
in the water column. These sulfide minerals dissolve slowly, however,
so increases in their dissolved concentrations are difficult to detect.

FIELD STUDIES OF THE FATES AND EFFECTS OF DRILLING FLUIDS

Direct measurement of the fates and effects of drilling fluids in the
field is inherently more rigorous than a hazard assessment that relies
on models to predict such fates along with laboratory measures of
toxicity. On the other hand, field studies suffer the problem of site-
specificity and that of distinguishing genuine effects from natural
variability. Furthermore, even when effects are documented in the

134

field, it is generally difficult to determine the significance of their
geographic extent or duration for the ecosystem or for man. Final
appraisals thus become highly subjective. Finally, field assessments
suffer the inherent limitations of retrospective studies.
Field determinations of environmental fates have been of two types:
monitoring dissolved and particulate concentrations of drilling-fluid
constituents during discharge, and monitoring the concentrations of
drilling-fluid constituents in bottom sediments and organisms after
discharge.
In studies of the water column, the visible or detectable plume of
suspended particulate matter has sometimes been sampled for potential
toxicants. Several recent studies of plume dispersion employed in situ
transmissometry techniques (Ayers et al., 1980; Ray and Meek, 19780) or
acoustical techniques (Proni and Trefry, 1981) to sample areas where
concentrations of suspended matter were highest. In near-field disper-
sion, the advection and dispersion of dissolved and suspended phases
in the surface plume should be qualitatively similar; greatly under-
estimating dissolved concentrations in the water column seems unlikely.
Plume dispersion studies have been conducted using dye releases,
transmissometer profiling, or discrete water grabs for a variety of
discharge rates (bulk and continuous), water depths (23 to 120 in), and
current speeds (16 to 120 cm/s). The results of these empirical
studies support the theoretical models (see Chapter 3) and indicate
that the soluble phase is diluted by at least 104 within Ilb after
discharge. Of course, the distance from the discharge point at which
a particular dilution is reached will vary depending on current
velocity, and time from discharge is generally a better predictor of
dilution. Apparent dispersion of the suspended particulate phase is
at least an order of magnitude greater, because most of the discharged
drilling fluids (probably more than 90 percent, especially of bulk
discharges) and essentially all of the cuttings sink to the seabed
within a short distance of the discharge (in depths less than about
125 m--at greater depths the discharges reach neutral buoyancy before
encountering the seafloor).
With the dispersion of potentially soluble toxicants by a factor
of 104 within 1 h of discharge (corresponding usually to a spatial
extent of about 1,000 in), toxic responses in this zone should be
anticipated only if short-term exposures of several hours to the
substance discharged produced EC50 values in the 100 ppm, (v/v) range.
This conclusion is strongly supported by the plume effects model of the
EPA Adaptive Environmental Assessment Workshop (Auble et al., 1982) and
by Petrazzuolo's (1981) dispersion toxicity models. The results of
recent analyses of sublethal effects in organisms at critical life
stages indicate that discharges of drilling fluids would usually not
approach such values. This conclusion cannot yet be extrapolated with
confidence to shallow-water environments (<10 m) and embayments where
dispersion may not be as rapid, although recent dispersion measurements
from the Beaufort Sea (Nortec, 1983) suggest similar dispersion in
shallow water.
Direct field surveys of the effects an planktonic or nektonic
organisms have not been attempted and are probably not feasible given

135

natural and sampling variability and the turbulent mixing of poten-
tially affected and unaffected populations, and in light of some of the
conclusions of prior hazard assessments.
A significant shortcoming in understanding the long-term effects
of drilling discharges concerns the fate of particulate components once
they reach the seabed. An important factor in determining the fate of
pollutants is the resuspensive transport of sediments that tends to
dilute and disperse particulate contaminants. Transport depends on
the hydrodynamic regime of an environment. While most of the fluids
discharged on Tanner Bank (Meek and Ray, 1980) and in Lower Cook Inlet
(Dames and Moore, 1978) settled to the seabed rapidly, no accumulation
of contaminants in bottom sediments was observed because strong
currents resuspended and dispersed the discharged material. On the
other hand, gradients in barium concentration persisted in the more
quiescent benthic environments of the Gulf of Mexico (Boothe and
Presley, 1983; Gettleson and Laird, 1980; Trocine et al., 1981) and the
shelf break of the Middle Atlantic Bight (EG&G Environmental Con-
sultants, 1982). Within the Gulf of Mexico, Boothe and Presley (1983)
also found that the degree to which they could account for the total
barium discharged in sediments surrounding an exploratory rig was
directly related to water depth. In 13 m of the water, only 5.4
percent of the barium discharged could be accounted for in sediments
within 3 km of the rig. At another exploratory well in 13 m depth 84
percent of the barium could be accounted for within a similar radius
and 9.6 percent within a radius of 500 m. At a production platform
where 25 wells had been drilled in 79 m of water, only 11.6 percent of
the barium was found within 500 m as compared to 1.5 percent at a
production platform in 34 m of water (see Table 16).
In most reports, elevated levels of major drilling-fluid components
like barium were confined to an area within 1 km of the discharge
point. Care must be taken in interpreting such results because con-
centrations of drilling fluids can be diluted beyond detection in
samples that include the upper two cm of surficial sediments. In one
study that sampled only the top 1 cm of sediment, barium concentrations
were three times ambient concentrations 1.9 km from the well (Trocine
et al., 1981). Surface layer contamination may pose elevated exposure
conditions to those benthic organisms that feed at the sediment-water
interface. With time, sediment contaminants will disperse horizontally
and also be vertically mixed in sediments. Boothe and Presley (1983)
found incorporation of barium to at least 15 cm near a production
platform more than 5 years after drilling had ceased.
Few studies have attempted to measure the temporal extent of
benthic changes. The effects of discharges on the benthos depends
greatly on how quickly the community recovers, not only in total
density and biomass, but also in the composition and structure of the
community. Populations of larger, deeper burrowing benthic organisms,
which contribute to the geochemical structure of sediments and to other
features of the benthos by their feeding, burrowing, and respiration,
recover more slowly than small surface dwellers (Boesch and Rosenberg,
1981; Rhoads et al., 1978). Particularly in outer shelf habitats,
important species may have populations dominated by individuals several

136

years old, so substantial time is required to reestablish the natural
age structure in the community, even given rapid recolonization.
Gillmor et al. (1981), in the only study sampling the benthos 1 year
after drilling-fluid discharges ceased, found reduction in the density
of the ophiuroid Amphioplus macilentus at the site of an exploratory
well on the outer middle Atlantic shelf. Amnphioplus is an important
burrower in the benthic community in this habitat and is probably long
lived, as indicated by its persistent populat~ions and community
structure. Amphioplus also showed depressed recruitment in affected
areas.
Drilling-fluid discharges may more greatly damage the ecosystem if
the spatial extent of their effects transcends those observed through
chemical analyses of sediments, or if their effects are long lasting,
because of slow recovery of communities or habitat modification (or
both). The postdepositional fates of drilling fluids and the recovery
of altered communities are the processes for which data are most
limited and predictions most tenuous. Hydrodynamic regimes, including
tidal and nontidal currents and wave-induced orbital water movements,
obviously vary from one region to another and across the continental
shelf. Furthermore, information on the resilience of benthic communi-
ties suggests that recovery rates from complete annihilation vary from
weeks in shallow-water communities (that are frequently disturbed by
nature), to several months or years for continental shelf communities,
and to many years on the continental slope and in the deep sea (Boesch
and Rosenberg, 1981). The variability in dispersion in the benthic
boundary layer, the resistance of biota to physical and toxic effects,
and the resilience of communities in different continental shelf
environments all need to be taken into account in assessing benthic
effects (Auble et. al., 1982; Petrazzuolo, 1981).
Concern about the sensitivity of hard-substrate epibiota to the
physical and toxic effects of drilling fluids has prompted special
studies and regulatory restrictions, such as those on the Flower Garden
reefs and Tanner Bank. This concern is often translated into treating
all areas where hard-substrate epibiota exist (such as reefs, rocky
outcrops, and canyon heads) as "biologically sensitive areas" in
environmental impact statements and when applying lease stipulations
or permit requirements. A characteristic feature of hard-substrate
communities is a lack of sediment cover. The absence of sediments
allows the colonization and proliferation of colonial or solitary
epibiota on the hard substrate, which enhances the structure of the
habitat and affords habitation to a variety of motile animals seeking
refuge or food. The lack of sediment cover may result from a dynamic
physical regime that sweeps sediments away or from the lack of a source
of fine sediments for deposition. In the first case, drilling fluids
dumped or advected into the habitat may not be deposited or accumulate.
Thus, despite the sensitivity of its biota, the habitat is not very
susceptible to harmful accumulation of drilling fluids. Concern should
be directed to hard-substrate communities in more quiescent habitats.
Organisms in these communities may be sensitive to nearby discharges
of drilling fluids if the fluids' rate of accumulation exceeds the
organisms' ability to remove settling material or if the material is

137

toxic. The sensitivity of hard-substrate communities should be evalu-
ated in light of their potential exposure to drilling fluids and
cuttings rather than through assuming categorically that hard-substrate
habitats are "ibiologically sensitive."

EXTRAPOLATION OF RESULTS

A common concern in using research results is whether they can be
extrapolated to a particular case. Such extrapolation includes that
from laboratory and other experimental results to the natural environ-
ment and also that from one environment or geographic area to another.
Marine ecosystems on the OCS clearly vary in their sensitivities to
anthropogenic stress, and caution is therefore advisable in extrapo-
lating observations from one region to another. On the other hand, to
dismiss all research results not obtained directly from the environment
analyzed may amount to ignoring valuable data. Most important in
extrapolating results are considering the kind of physicochemical
processes affecting the fates of contaminants and the resistance and
resilience of affected communities.
There are generally adequate data to predict the fates of dissolved
and suspended drilling-fluid components in the water column in dif-
ferent OCS environments. Such data are not necessary available on the
long-term fates of deposited materials. The general model of a
continuum of marine environments from those relatively dynamic (for
example, in Cook Inlet or on the inner continental shelf) to those
quiescent (for example, in the Gulf of Mexico or on the outer shelf)
is adequate to conceptualize these differences but not to quantify
them. The emerging theories of the dynamics of the bottom boundary
layer, including their treatment of the effects of surface roughness,
biological processes, and heterogeneity of grain size, will be required
in making sound quantitative extrapolations.
Laboratory experiments have shown no clear differences in the
relative sensitivities of organisms from different geographic regions
to drilling fluids. Given that drilling fluids' most profound effects
will likely be on the benthos, this suggests that relative biological
susceptibility will be determined primarily by the fates of deposited
materials and by a biological community's ability to recover (resil-
ience). The resilience of benthic communities varies significantly.
It can be predicted approximately (Boesch and Rosenberg, 1981), but not
precisely, for most hard- and soft-substrate communities.
In summary, because of the lack of quantitative models of the fates
of deposited materials and biological resistance and resilience, the
extrapolation of results from one environment or geographic area to
another can presently be only qualitative.

LONG-TERM FATES AND EFFECTS

Most information available on the fates and effects of drilling fluids
and cuttings comes from studies of single exploratory wells. The long-
term effects of drilling discharges clearly may be greater when the

138

discharges are made during oil and gas field development, when scares
of wells may be drilled from a single platform or within a lease block.
In drilling multiple development wells from a single platform (see
Chapter 2) the volume of drilling fluids discharged per well is sub-
stantially less, but the mass loading within an area and the duration
of discharges are greater. For example, extensive drilling in the Gulf
of Mexico OCS has gone on for 30 years, with an estimated current
annual discharge of drilling-fluid solids of 1.6 million t (Gianessi
and Arnold, 1982), while in the first few years of exploring a frontier
area between 10,000 and 100,000 t of drilling-fluid solids may be
discharged.
Several studies have addressed the long-term effects of oil and gas
development and production in the Gulf of Mexico, notably, the Offshore
Ecology Investigation (Ward et al., 1979), the Buccaneer Field Study
(Middleditch, 1981), and the Central Gulf Platform Study (Bedinger,
1981). The Offshore Ecology Investigation conducted in 1972 to 1973
contributed little to understanding the fates of contaminants resulting
from petroleum development because it failed to measure the contamin-
ants in bottom sediments adequately. The other studies examined the
distribution of potential sediment contaminants (trace metals and
hydrocarbons) along gradients from discharge points and compared these
data to those obtained from presumably uncontaminated areas. Of
course, there are many sources of contaminants other than drilling
fluids and cuttings related to the platform and its operation. These
include corrosion of materials, produced water discharges, sacrificial
anodes, domestic wastes, vessel discharges, and chemicals used in
operating the platform. At most of the platforms studied, many trace
metals were elevated (including mercury, lead, copper, and zinc) in
surface sediments compared to areas removed from development and sub-
surface sediments, and were found in gradients around the platform
(Tillery, 1980a,b; Tillery et al., 1981; Boothe and Presley, 1983).
Interestingly, Boothe and Presley (1983) found no evidence of elevated
concentrations of chromium, the only other metal for which drilling
fluids are a likely source. Barium was the only trace metal elevated
around development and production platforms whose most likely source
is drilling fluids, although it can also be present in formation waters
at higher concentrations than in seawater.
Barium concentrations in surface sediments within 100 to 200 m of
Buccaneer Field platforms (17-22 m water depth) were higher than those
in subsurface sediments and surface sediments in undeveloped areas of
the south Texas continental shelf (Anderson et al., 1981). Decreasing
barium concentration gradients were also observed with increasing
distance from the Buccaneer Field platforms (Tillery, 1980a,b), from
many of those off Louisiana sampled during the Central Gulf Platform
Study (Tillery et al., 1981), and from all of the six rigs considered
in Boothe and Presley's recent study (1983) of exploration, develop-
ment, and production sites. Near Buccaneer Field plataforms, Anderson
et al. (1981) also noted the presence of bentonite clay, atypical of
local marine sediments and possibly originating from drilling fluids.
On the other hand, Boothe and Presley (1983) were unable to distinguish
any bentonite clay that could have come from drilling fluids from the
similar montmorillonite clays naturally present in Gulf of Mexico

139

sediment using simple bulk x-ray diffraction. It is also noteworthy
that one study found barium concentration gradients around several
platforms in the Mississippi delta region (Tillery et al., 1981),
despite the authors' assertion that the influence of the Mississippi
River masks platform-related contamination.
The localized effects (within 100 m) on benthic communities
observed in the Buccaneer Field (Harper et al., 1981) cannot be related
unequivocably to drilling discharges because of the other contaminant
sources and physical effects associated with the platforms (for
example, seabed scour). However, the barium tracer data are signifi-
cant in that 10 or more years had elapsed since active drilling to the
time of sampling at some of these platforms. With regard to the fates
of drilling fluids these data suggest that detectable contamination of
bottom sediments, which may or may not have biological effects, may
persist under some OCS sedimentary regimes for years and perhaps
decades. The results of these Gulf of Mexico studies are, at present,
insufficient to quantify the long-term effects of drilling discharges
from large-scale offshore oil and gas development in the Gulf of Mexico
and to extrapolate elsewhere. This is in part because of the paucity
of long-term observations and because of the difficulties in separating
the effects of drilling discharges from those of other activities.
Given the limitations of these Gulf of Mexico studies, what do the
assessments of single exploratory wells suggest about the long-term
effects of more massive drilling discharges during field development?
Are the operative transport processes for the two kinds of discharges
quantitatively similar? Do greater discharges result in greater, more
extensive or more persistent contamination? Are the effects of greater
discharges simply additive or are they different from those of dis-
charges from single wells?
These questions cannot be answered with absolute certainty. Even
so, the results of studies of exploratory wells should be pertinent to
the assessment of long-term effects. In the water column, the elevated
concentrations of contaminants and their effects should be very small
and transient. Documented effects of long-term discharges on the
benthos are areally limited and transient. The fates of deposited
materials are more strongly influenced by the dispersal regime (for
example, as determined by water depth) than by any other factor. Con-
tamination of bottom sediments from multiple wells appears to be less
than simply additive (Boothe and Presley, 1983). Despite these condi-
tions, the existence of subtle effects caused by contamination over
broad areas in heavily developed environments cannot be ruled out.

OTHER INFORMATION

Information available on the fates and effects of drilling fluids and
cuttings shows that the effects of an individual discharge are likely
to be limited in extent and primarily confined to the benthos. Research
to date indicates that the environmental risks of discharges from
exploratory drilling to most OCS communities are small. No additional
research is needed on the fates and effects of drilling fluids in the
water column in open water where rapid mixing is likely.

140

These conclusions do not hold for shallow-water, low-energy
environments like estuaries or embayments or for some areas under ice
in the Arctic. If additional information on these topics is sought,
it should be on the fates and effects of materials discharged in the
development of production wells and on particularly susceptible
environments.
The above issues are general ones applying to the fates and effects
of all human inputs into the coastal ocean. Better understanding of
the potential contamination of nearshore environments would probably
best be attained by generic studies of the processes that determine the
ecological effects of foreign substances in these environments.

Transport and Transformation

There is little information on the dispersion of drilling fluids and
cuttings in the bottom boundary layer. The vast majority of drilling
fluids and cuttings discharged into the water column settle in little
time near the discharged point. Resuspension and tractive (bed load)
transport determine the persistence, dispersion, and ultimate fates of
contaminants associated with this particulate material. The tidal and
mean currents and wave climates that affect these sediment transport
processes vary widely among OCS areas. Such differences in physical
regimes can be clearly seen in comparisons of sediment contamination
in Cook Inlet, Tanner Bank, the Middle Atlantic Bight, and the Gulf of
Mexico (see Chapter 3). Significant advances have been made recently
in measuring sediment transport in the bottom boundary layer and in
modeling the interactive effects of waves and currents (Grant and
Madsen, 1982). This emerging technology and theory should be applied
in any development of predictive models an the fates of the sedimentary
fractions of drilling fluids and cuttings, if the models are to be
relevant to the variety of erosional and depositional OCS environments.
Such understanding is important in assessing the fate of contaminants
from long-term oil and gas development. Predicting the physical fates
of contaminants is also important in judging the susceptibility of
sensitive or valuable environments, such as hard-bottom banks and the
estuaries adjacent to nearshore discharges.
The bioaccumulation as well as the transport of trace metals in
marine discharges has been extensively studied. The data on the
subject suggest that bioavailability is related to the chemical
activity of the metal ions. The bioaccumulation of barium in marine
bivalves, however, appears to be related to the loading of particulate
BaSO4 and not just to the concentration of barium ions in the
environment. The mechanism of the uptake of barite particles is not
well understood, nor are the composition, transformation, and bioavail-
ability of some of the organic additives in used drilling fluids.
Petroleum hydrocarbons are included in this category since they are
often found in water-based drilling fluids.

141

Effects

The biological effects of drilling discharges are restricted primarily
to the benthos. The conditions of benthic exposure and toxicity are
only partially understood. These conditions include the rates and
routes of bioavailability in benthic organisms to contaminants in
resuspended particles and interstitial waters. Documenting these
conditions would require coordinated laboratory and experimental field
approaches because of the difficulty in duplicating exposure conditions
in conventional bioassays and the need to assess "sublethal" effects
in light of their significance for the organism's life and for the
survival of populations. Another part of the analysis would describe
the relative resistance of benthic communities to the physical and
chemical effects of sediment contamination from anthropogenic inputs,
and the resilience (or speed of recovery) of affected communities.
The development of sensitive and reproducible methods for testing
toxicity is required to standardize assessments of drilling-fluid
components and additives.

Resource Management

Like most environmental research, that on drilling-fluid discharges in
the marine environment should be closely coordinated with resource
management. Particular regulatory needs in this field include specify-
ing operational alternatives for the composition and discharge of
drilling fluids (especially with regard to additives, including diesel
fuel) and standardizing toxicity tests to screen drilling fluids and
their components.

REFERENCES

Anderson, J.B., R.B. Wheeler, and R.S. Schwarzer. 1981. Sedimentology
and geochemistry of recent sediments. In: B.S. Middleditch
(ed.), Environmental Effects of Offshore Oil Production. New
York: Plenum Press. Pp. 59-67.

Armstrong, R.S. 1981. Transport and dispersion of potential
contaminants. In: B.S. Middleditch (ed.), Environmental Effects
of Offshore Oil Production. New York: Plenum Press. Pp. 403-420.

Auble, G.T., A.K. Andrews, R.A. Ellison, D.B. Hamilton, R.A. Johnson,
J.E. Roelle, and D.R. Marmorek. 1982. Results of an adaptive
environmental assessment modeling workshop concerning potential
impacts of drilling muds and cuttings on the marine environment.
Office of Biological Services, U.S. Fish and Wildlife Service, Fort
Collins, Colo.

Ayers, R.C., Jr., T.C. Sauer, Jr., D.O. Steubner, and R.P. Meek.
1980. An environmental study to assess the effect of drilling
fluids on water quality parameters during high rate, high volume

142

discharges to the ocean. In: Proceedings of a Symposium on
Research on Environmental Fate and Effects of Drilling Fluids and
Cuttings. Washington, D.C.: Courtesy Associates. Pp. 351-391.

Bayne, B.L. , D.A. Brown, F.L. Harrison, and P.P. Yevich. 1980.
Mussel health. In: E. Goldberg (ed.), International Mussel
Watch, Report on a Workshop at Barcelona, Spain, December 1978.
Washington, D.C.: National Academy of Sciences. Pp. 196-235.

Bedinger, C.A., Jr. (ed.). 1981. Ecological investigations of
petroleum production platforms in the central Gulf of Mexico.
Report to Bureau of Land Management. Contract AA551-CT8-17.
Southwest Research Institute, San Antonio, Tex.

Boothe, P.N., and B.J. Presley. 1983. Distribution and behavior
of drilling fluid and cuttings around Gulf of Mexico drill sites.
Draft final report. API Project No. 243. American Petroleum
Institute, Washington, D.C.

Bruland, K.W. 1980. Oceanographic distributions of cadmium, zinc,
nickel and copper in the north Pacific. Earth Planet. Sci. Lett.
47:176-198.

Carls, M.G., and S.D. Rice. 1980. Toxicity of oil well drilling muds
to Alaskan larval shrimp and crabs. Research unit 72. Final
report. Project No. R7120822. Outer Continental Shelf Energy
Assessment Program, Bureau of Land Management, U.S. Department of
the Interior. 29 pp.

Carr, R.S., L.A. Reitsema, and J.M. Neff. 1980. Influence of a used
chrome-lignosulfonate drilling mud on the survival, respiration,
growth, and feeding activity of the opossum shrimp Mysidopsis
almyra. In: Proceedings of a Symposium on Research on
Environmental Fate and Effects of Drilling Fluids and Cuttings.
Washington, D.C.: Courtesy Associates. Pp. 944-963.

Dames & Moore, Inc. 1981. Fate and effects of drilling fluids and
cuttings discharges in lower Cook Inlet, Alaska and on Georges
Bank. Final report to National Oceanic and Atmospheric Adminis-
tration and Bureau of Land Management. 336 pp., 3 appendixes.

143

Derby, C.D., and J. Atema. 1981. Influence of drilling muds on the
primary chemosensory neurons in walking legs of the lobster,
Homarus americanus. Can. J. Fish. Aquat. Sci. 38:268-274.

EG&G Environmental Consultants. 1982. A study of environmental
effects of exploratory drilling on the mid-Atlantic Outer
Continental Shelf--final report of the Block 684 Monitoring
Program. EG&G Environmental Consultants, Waltham, Mass. Available
from Offshore Operators Committee, Environmental Subcommittee, P.O.
Box 50751, New Orleans, LA 70150.

Gettleson, D.A., and C.E. Laird. 1980. Benthic barium in the
vicinity of six drill sites in the Gulf of Mexico. In:
Proceedings of a Symposium on Research on Environmental Fate and
Effects of Drilling Fluids and Cuttings. Washington, D.C.:
Courtesy Associates. Pp. 739-788.

Gianessi, L.P., and F.D. Arnold. 1982. The discharges of water
pollutants from oil and gas exploration and production activities
in the Gulf of Mexico region. Draft report to National Oceanic
and Atmospheric Administration, Contract NA-80-SAC-00793.
Resources for the Future, Washington, D.C.

Gilfillan, E.S., R.P. Gerber, S.A. Hanson, and D.S. Page. 1981.
Effects of various admixtures of used drilling mud on the develop-
ment of a boreal soft bottom community (unpublished manuscript).
American Petroleum Institute, Washington, D.C. 17 pp.

Gillmor, R.B., C.A. Menzie, G.M. Mariani, D.R. Levin, R.C. Ayers, Jr.,
and T.C. Sauer, Jr. 1981. Effects of exploratory drilling
discharges on the benthic environment in the middle Atlantic OCS:
biological results of a one-year post-drilling survey. In:
Proceedings, 3rd International Ocean Disposal Symposium, October
12-16, Woods Hole, Mass.

Grant, W.D., and O.S. Madsen. 1982. Combined wave and current
interaction with a rough bottom. J. Geophys. Res. 84:1797-1808.

Harper, D.E., Jr., D.L. Potts, R.R. Salzer, R.J. Case, R.L. Jaschek,
and C.M. Walker. 1981. Distribution and abundance of macrobenthic
and merobenthic organisms. In: B.S. Middleditch (ed.), Environ-
mental Effects of Offshore Oil Production. New York: Plenum
Press. Pp. 133-177.

Jenkins, K.D., and D.A. Brown. In press. Determining the biological
significance of contaminant bioaccumulation. In: H. White (ed.),
Proceedings of the Workshop on Meaningful Measures of Marine
Pollution Effects. Pensacola, Fla., April 1982. College Park,
Md.: University of Maryland Sea Grant Program.

144

Knox, F. 1978. The behavior of ferrochrome lignosulfonate in natural
waters. Masters Thesis. Massachusetts Institute of Technology,
Cambridge, Mass. 65 pp.

Koh, R.C.Y., and Y.C. Chan. 1973. Mathematical model for barged ocean
disposal wastes. EPA-660/2-73-029. Pacific Northwest
Environmental Research Laboratory, Environmental Protection
Agency. Corvallis, Oreg.

Liss, R.G., F. Knox, D. Wayne, and T.R. Gilbert. 1980. Availability
of trace elements in drilling fluids discharged to the marine
environment. In: Proceedings of a Symposium on Research on
Environmental Fate and Effects of Drilling Fluids and Cuttings.
Washington, D.C.: Courtesy Associates. Pp. 691-722.

Middleditch, B.S. (ed.). 1981. Environmental Effects of Offshore Oil
Production. New York: Plenum Press. 446 pp.

Neff, J.M. 1980. Effects of used drilling muds on benthic marine
animals. Publ. No. 4330. American Petroleum Institute,
Washington, D.C. 31 pp.

Neff, J.M. 1981. Fate and biological effects of oil well drilling
fluids in the marine environment: a literature review. Final
technical report to U.S. Environmental Agency, Gulf Breeze, Fla.
151 pp., 2 appendices.

Neff, J.M., R.S. Carr, and W.L. McCulloch. 1981. Acute toxicity of a
used chrome lignosulfonate drilling mud to several species of
marine invertebrates. Mar. Environ. Res. 4:251-266.

New England Aquarium. H.E. Edgerton Research Laboratory. 1981. A
study of the impact of discharged drilling fluids on the Georges
Bank environment. Progress Report No. 2 to the U.S. Environmental
Protection Agency, Gulf Breeze, Fla. 98 pp.

Page, D.S., B.T. Page, J.R. Hotham, E.S. Gilfillan, and R.P. Gerber.
1980. Bioavailability of toxic constituents of used drilling muds.
In: Proceedings of a Symposium on Research on Environmental Fate

145

and Effects of Drilling Fluids and Cuttings. Washington, D.C.:
Courtesy Associates. Pp. 984-996.

Patterson, C.C. 1974. Lead in seawater. Science 183:553-554.

Petrazzuolo, G. 1981. Preliminary report: an environmental
assessment of drilling fluids and cuttings released onto the Outer
Continental Shelf from the Gulf of Mexico. Vol. I: Technical
assessment. Vol. II: Tables, figures and Appendix A. Draft
report prepared for Industrial Permits Branch, Office of Water
Enforcement and Ocean Programs Branch, Office of Waster and Waste
Management, U.S. Environmental Protection Agency, Washington, D.C.

Petrazzuolo, G. 1983. Environmental assesment: drilling fluids and
cuttings released onto the OCS. Draft final technical support
document. Submitted to the Office of Water Enforcement and
Permits, U.S. Environmental Protection Agency, Washington, D.C.

Proni, J., and J.A. Trefry. 1981. Drilling fluid discharge in the
Gulf of Mexico. Paper presented at Third International Ocean
Disposal Symposium, Woods Hole, Mass. October 12-16.

Rhoads, D.C., P.L. McCall, and J.Y. Yingst. 1978. Disturbance and
production of the estuarine sea Ffoor. Am Sci. 66:577-586.

Rubinstein, N.I., R. Rigby, and C.N. D'Asaro. 1980. Acute and
sublethal effects of whole used drilling fluids on representative
estuarine organisms. In: Proceedings of a Symposium on Research
on Environmental Fate and Effects of Drilling Fluids and
Cuttings. Washington, D.C.: Courtesy Associates. Pp. 828-846.

Tagatz, M.E., J.M. Ivey, H.K. Lehman, and J.L. Oglesby. 1978.
Effects of lignosulfonate-type drilling mud on development of
experimental estuarine macrobenthic communities. Northeast. Gulf
Sci. 2:25-42.

Tillery, J.B. 1980a. Trace metals. Vol. VIII in W.B. Jackson and
E.P. Wilkens (eds.), Environmental assessment of Buccaneer gas and
oil field in the northwest Gulf of Mexico, 1978-1979. NOAA/NMFS
Annual Report to EPA. NOAA Tech. Memorandum NMFS-SEFC-42. 93 pp.

Tillery, J.B. 1980b. Trace metals. Vol. VI in W.B. Jackson and E.P.
Wilkens (eds.), Environmental assessment of Buccaneer gas and oil
field in the northwestern Gulf of Mexico, 1978-1979. NOAA/NMFS
Annual Report to EPA. NOAA Tech. Memorandum NMFS-SEFC-52. 39 pp.

Tillery, J.B., R.E. Thomas, and H.L. Windom. 1981. Trace metal
studies in sediment and fauna. In: C.A. Bedinger (ed.),
Ecological Investigations of Petroleum Production Platforms in the
Central Gulf of Mexico. Vol. I, Part 4. Report to Bureau of Land
Management, Contract AA551-CT8-17. San Antonio, Tex.: Southwest
Research Institute. Pp. 1-122.

146

Trocine, R.P., J.H. Trefry, and D.B. Meyer. 1981. Inorganic tracers
of petroleum drilling fluid dispersion in the northwest Gulf of
Mexico. Reprint extended abstract. Div. Environ. Chem. ACS
Meeting, Atlanta, Ga. March-April 1981.

Ward, C.H., M.E. Bender and D.J. Reish (eds.). 1979. The offshore
ecology investigation. Rice Univ. Stud. 65(4&5). 589 pp.

Alternative Operating Practices

in response to federal and state statutory requirements and concerns,
a number of alternatives to simple overboard discharge have been
employed or developed. Table 24 describes alternatives that have been
required, and also others that have been developed or considered. This
chapter briefly discusses these alternatives with regard to operations,
cost, and risk.

SHUNTING

Shunting refers to the discharge of drilling fluids and cuttings
through a down pipe (shunt pipe) to a predetermined water depth.
Shunting has been required for some OCS wells to reduce the exposure
of organisms in the water column or to transport discharged material
to the bottom boundary layer to reduce the exposure of sensitive
communities on topographic rises. Shunting to the water column
probably has little effect on dispersion. Where the bottom boundary
layer is slower circulating than other water masses, shunting to the
bottom can reduce the rate of dispersion.
While shunting systems can be designed for and operated in water
of any depth, their costs and operating problems increase with the
depth of the system, and also with the severity of the weather. Shunts
have been used in the Gulf of Mexico in 100 m of water. The addition
of a shunt system adds equipment and weight to the already-crowded
drilling rig and another appendage below the water line in proximity
to the marine riser and blowout control systems. If the shunt pipe
were to swing loose because of heavy weather or damage it could collide
with and damage subsea connections.
Shunting operations for one well in the Gulf of Mexico employing
a 100-in shunt system on a jackup rig were estimated to cost about
$107,000 (1982).' With proper care, such a system can be used

'James Gonders, Cities Service , July 1982, personal
communication.

147

148

TABLE 24 Discharge Alternatives

Examples of Examples of
Alternative Objective Where Used How Required

Shunting near Minimize exposure North Atlantic, EPA permit,
surface of plankton mid-Atlantic MMS stipulations

Shunting near Minimize exposure Flower Garden EPA permit,
bottom of coral reefs Banks Region VI

Dilution re- Reach greater Lower Cook Inlet, EPA permits,
quirements, dilution to limit Georges Bank regions X and I
rate of dis- harm to biota in
charge the water column
limitations

Barging to Avoid ocean Alabama and State regulation
land discharge California State
Offshore Lands

Barging to Avoid discharge --(Requires EPA-
ocean in coastal designated ocean
dump site environment dump site)

Disposal Take advantage of Beaufort Sea Lease stipulation
on ice seasonal ice
breakup to
dissipate
effluents

Generic muds Limit toxicity North Atlantic, EPA permits,
and approved of fluid mid-Atlantic, regions I, II,
additives California, IX, X
Alaska

Alternate Remove undesired
processing/ components, mini-
recycling/ mize discharge
reuse

incineration Remove oil-
contaminated
cuttings

injection Reduce open-ocean
discharge

149

on several wells. Shunting is considered a relatively inexpensive dis-
charge option.

DILUTION REQUIREMENTS AND LIMITATIONS ON RATES OF DISCHARGE

Drilling fluids and cuttings can be (and normally are) discharged at
or near the water surface. This practice results in a visible plume
that may extend over several kilometers. The extent and duration of
the plume depends on the energy of the ocean environment. In certain
areas, notably Lower Cook Inlet, Alaska, predilution or certain dis-
charge rates have been required in response to seasonal conditions.
The methods of predilution and maintaining certain discharge rates
may require additional equipment, such as pumps and special pit gauges
to monitor discharge rates. These special methods can affect cost and
operations by affecting the duration of operations. Drilling must
occasionally be stopped to complete a bulk discharge that is prolonged
because of the high volumes of water required for predilution and the
slow discharge rates allowed. This added time translates directly into
cost for the operator. At other times, the necessity of completing a
prolonged discharge may restrict the time available to move mobile rigs
with respect to weather conditions and sea states. The failure to take
advantage of good conditions for these activities can increase the risk
of the operation. The data on dispersion presented in Chapter 3 indi-
cates that such requirements for predilution and restrictive discharge
rates are not justified in most 005 areas.

OFFLOADING AND TRANSPORT FOR DISTANT DISCHARGE

Drilling discharges can be transported by barge or supply boat to an
ocean or land disposal site. Ocean disposal requires the designation
of a site in accordance with EPA ocean dumping regulations (40 CFR
220-230). Release at an ocean dump site would presumably take the
discharge from a coastal environment for dispersal in deep water.
Ocean disposal sites in the mid-Atlantic have been used for industrial
wastes and could be used for drilling discharges as well, but no ocean
dump sites have yet been used for these discharges. Land disposal also
requires a suitable site, but disposal areas for industrial wastes on
land are increasingly at a premium. Obtaining ocean dumping permits
.or disposing of drilling discharges on land adds to the cost of
drilling operations.~
The ability to off load discharges for transport is directly
related to sea states and weather conditions. Adverse conditions will
prevent offloading as shown in Table 25.

2For example, one offshore operator paid $390,000 to barge drill-
ing discharges from a well to shore (W. D. Fritz, Mobil Oil, personal
communication, 1980) The landfill operator who received the wastes
promptly sold them for fill dirt.

150

TABLE 25 Percentage of Time That Drilling Discharges Cannot Be
Transferred to Barges or Supply Boats

Gulf of Mexico Georges Bank

Offloading to barges
(when seas exceed 1 m) 20 not feasibleaa

Offloading to supply boats 2.2 12.4
(when seas exceed 3 m)

.a-Seas exceed 1 m too much of the time to plan such operations.

SOURCE: Adapted from OOC, 1981.

During adverse weather or sea states that prevent the off loading of
drilling discharges, drilling operations might have to be curtailed
due to a lack of on-rig storage space, resulting in substantial addi-
tional costs.
Some units, such as small jack-up drilling rigs, have very little
holding capacity, while other units, such as large semisubmersibles,
have a greater holding capacity. Adequate holding capacity can lessen
rig downtime in adverse conditions.
Offloading and transport increase the hazards of offshore drilling
operations. Care must be taken to moor the receiving vessel to prevent
damage to the drilling unit. The approach and mooring of the barge or
vessel are constrained by weather and by the mooring arrangements of
the drilling unit. The position of crane facilities on the drilling
unit dictates the available loading points. The addition of anchoring
systems required on a disposal barge further compounds the hazards.
Once the transfer of the discharge has been made, additional risk is
entailed in the transit of the transfer vessel to other areas for dis-
posal and in the additional handling of the drilling discharges in
disposal.
The cost of offloading and transport operations varies with the
circumstances. For an 18,000-ft (5,490-m) well in the Gulf of Mexico,
the cost of these operations has been estimated at $917,000 (OOC,
1981). Transport of discharges to shore from a comparable well drilled
off Georges Bank would cost about $3.29 million; to an ocean dump site
$3.02 million (OOC, 1981). Such costs range from 10 to 20 percent of
the cost of the well.

151

OTHER TRANSPORT TECHNIQUES

Other techniques suggested for transporting discharges include a pipe-
line to an ocean dump site and the use of a monobuoy for loading dis-
charges onto a barge or vessel at a distance from the drilling unit.
These arrangements have been reviewed (OOC, 1981), but are not con-
sidered here because of their limited applications and higher costs.

DISPOSAL ON ICE

One discharge alternative has been suggested for use in the Beaufort
Sea and other areas where sea ice is present for parts of the year.
This relatively simple and potentially inexpensive method is to deposit
spent fluids and cuttings directly on the ice. The method has recently
been tested (Miller et al., 1982). As in ocean discharges, the fates
of drilling fluids and cuttings disposed of on ice depend on site-
specific conditions. Discharges deposited on ice in nearshore areas
subject to overflow flooding from rivers would be widely dispersed
during the annual breakup of the ice. Without such flooding, the dis-
charges are dispersed more gradually. Liquid fractions are removed
during initial surface melting. Depending on the movement of the ice,
solids may be either deposited near the disposal site or carried with
the ice and widely deposited over the seafloor.

SUBSTITUTIONS

Altered Composition

Just as special fluids are formulated for special downhole conditions,
the composition of drilling fluids can be altered to include less toxic
compounds for environmental reasons. For example, paraformaldehyde, a
nonpersistent biocide, is used instead of chlorinated phenols on the
OCS. Comparable substitutions have been developed for lubricants (for
example, paraffinic oils for diesel fuel). In replacing diesel fuel,
which is toxic, the use of other additives, such as emulsifiers, can
also be minimized. (An important purpose of emulsifiers is to inte-
grate diesel fuel with other components of the drilling fluids.)
A variety of mineral and vegetable oil-based products have been
developed as alternatives to petroleum hydrocarbons as drilling fluid
additives. While these products are in limited use in the U.S., they
are used more extensively elsewhere. Field and laboratory tests of
operating characteristics and environmental acceptability have been
conducted. Tests and trial introductions continue as experience is
gained concerning the alternatives' operating characteristics and
environmental acceptability.
In substituting other oils for diesel fuel (and at other times),
it may be desirable to monitor the composition of drilling fluid to
quantify and distinguish between various types of hydrocarbons. Gas
chromatographic methods, such as those developed by ASTMA Committee

152

D-19 can be used. Methods given in part 31, ASTM Standards (1982) can
possibly be applied to whole oils, waterborne oils, and marine sedi-
ments to examine the composition, quantities and origin of hydro-
carbons.

Processing Drilling Fluids Prior to their Discharge

Drilling fluids are processed while they are used to separate cuttings
(see Chapter 2). Better use of solids control equipment can in some
instances reduce the total volume discharged. So-called 'closed mud
sytm", available commercially, accomplish this. Drilling fluids
cannot be reused more extensively than they are in current practice
because of the need to condition them for desired functions. It is
always in the operator's economic interest to conserve and reuse drill-
ing fluids when possible, but the operator must occasionally dispose
of a fluid to use another with more appropriate characteristics for a
given operating condition.
Each of these alternatives is characterized by different costs and
risks than those of common practice. The costs of such alternative
practices tend to be higher, although in some instances only slightly
SO.
A more serious concern about such alternatives is their risk. The
environmental fates and effects of some alternative fluids and addi-
tives may be less well known than those of fluids commonly used. From
an operational standpoint, the alternatives may require different
operating techniques and handling than commonly used fluids. When
using alternatives, operators cannot rely on the training and
experience they have had with commonly used fluids.
Alternative additives and processes may offer advantages in
special situations, but until more experience with them is acquired,
their operating and environmental benefits and risks will not be
established.

OTHER ALTERNATIVES

The remaining alternatives (in Table 24), incineration and injection,
are not considered practicable. Incineration is not because large
amounts of the discharge are incombustible (QOC, 1981). Injection of
other than the liquid fraction of drilling discharges into porous for-
mations is not technically feasible, since one property of drilling
fluid is to consolidate loose formations encountered while drilling,
thus clogging the pores and preventing the formation from accepting new
material. To inject under these conditions would require high
pressures, and even then the formations would resist accepting the
material.

153

THE "NO DISCHARGE" ALTERNATIVE--A CASE STUDY

Alabama's regulations for offshore exploratory drilling in Mobile Bay
prohibit the discharge of solid and liquid wastes like drilling fluids,
drill cuttings, sand, contaminated deck drainage, and effluents from
sewage treatment units. Only uncontaminated rainwater and water from
the bay used to preload rig legs or to test fire-fighting equipment can
be discharged. A major oil company recently accepted these conditions
and proceeded with a drilling program using the "no discharge" alterna-
tive.3 In the course of planning, alternatives and costs were
considered in detail. Collection and disposal of waste materials while
drilling in shallow Mobile Bay present unique and costly problems. An
obvious solution is to collect all wastes in barges and transport them
to shore for disposal. However, other methods appeared feasible to the
company and were investigated.
Since the wastes this drilling generated might be discharged to
the sea under an NPDES permit if the drilling occurred on the OCS,
barging these wastes to federal waters for ocean disposal was one
alternative considered. However, long lead times were anticipated in
obtaining the required designation of an ocean dump site. The delay
was sufficient to rule out ocean dumping for the initial well, but
there were also questions to address about the ocean dumping equipment.
Could barges used in other ocean dumping contain the liquids without
seeping as these liquids were collected at the drill site? If not,
could an adequate sealing system be developed? Could more appropriate
barges be developed in the time available? These questions were never
answered.
Since most drilling wastes would be liquid, another form of
disposal considered was the subsurface injection of liquid wastes at
the drilling site and solids disposal onshore. Alabama regulatory
agencies indicated that a permit could be obtained for an onsite
disposal well for well fluids and contaminated deck drainage, but that
injection of sewage treatment effluents would require a permit that the
state would not issue. Specifying an additional onsite injection well
in the plans that were already under review by regulatory agencies
would have delayed obtaining needed permits. Since this option only
partly solved the problems of liquids disposal, the anticipated delay
was unacceptable.
Disposal of all wastes, liquid and solid, at onshore disposal
sites was carefully evaluated, with potential sites inspected by two
company teams. In this as in similar cases a problem was posed by the
* ~~limited number of acceptable active facilities. Some sites considered
were only in the planning stage. Permits had not been obtained in some
cases, and some operators had little or no experience in managing waste
facilities. Some active sites were judged unsuitable because of oper-
* ~~ational practices.

'Floyd Garrot, Exxon, personal communication, January 1983.

154

The only active disposal facilities that met all company criteria
were sites for hazardous wastes. The main disadvantage for the company
of using these sites was a much higher disposal cost. A second dis-
advantage in using these facilities may be the use of limited disposal
space that might be needed for hazardous materials.
The plan finally adopted by the company for its first well speci-
fies disposal of solids by landfill and of liquids by subsurface
injection. Both services are provided at a hazardous waste disposal
facility located in Port Arthur, Texas, approximately 740 km from the
drilling site. waste solids are buried in clay-lined pits. Waste
liquids, containing up to 10 percent suspended solids by volume and
less than 200 ppm, oil and grease, are first filtered to remove the
suspended solids for burial. The filtered liquids are then injected
into a disposal well 2,200 m deep. Other liquids require solidifica-
tion and landfill burial. The wastes are transferred from barges to
trucks at dock facilities about 30 km from the disposal facility.
Backup disposal capability is available at a hazardous waste disposal
landfill in Alabama approximately 390 km north of the drill site.
While closer to the drill site, this facility does not have an injec-
tion well. Disposal costs would be much higher at this site because
of the need to solidify all liquids for burial.
The jackup drilling rig used was specially designed and built for
the "no discharge" operation. This increased the contractor's con-
struction cost by about $635,000 to add features not normally required
for drilling in the Gulf of Mexico. The cost of retrofitting a rig not
specially designed and built for the operation would be a minimum of
$1 million. The cost of bringing an active rig in for modification,
including standby and transportation charges, could be as much as $3
to $4 million. Special rig features for this operation include exten-
sive use of coaming, drip pans, and drains to capture and collect
liquids from all equipment areas and drainage surfaces and manifolding
the drain lines of the shale-shaker tank and the cuttings chutes.
Piping to divide the solid and liquid wastes for separate barges was
installed at the well site. Uncontaminated rainwater is kept separate
from other liquids to be used in the drilling fluid. Temporary onboard
storage space for liquid wastes was also provided to handle anticipated
short periods when barges might not be available for immediate dis-
charge of the wastes. Five tank barges, three hopper barges, and one
tug are used full time to handle waste collection and transportation.
When drilling a large-diameter hole, an additional tug is needed. The
barges required modifications to prevent pollution. Coaming (raised
framing for capturing and directing runoff or spills) was installed
around the pump and discharge lines on the tank barges, and the hopper
barges had to be compartmentalized to stabilize their cargoes. In
addition, mooring anchors and piling were required to maintain the
barges in position at the rig.
Waste drilling fluids, cement, contaminated drill-floor deck
drainage, and formation cuttings are collected in an open-top, com-
partmentalized hopper barge. When filled, the receiving barge is
replaced by another. The full barge is towed to Port Arthur, Texas.
The wastes are transferred to trucks for transportation to the disposal
site.

Contaminated rainwater and deck drainage (other than from the
drill floor), effluents from the sewage treatment unit, wash water and
other liquid wastes are collected at the well site in a permanently
moored, compartmentalized tank barge. The liquids are periodically
transferred to other tank barges for transportation to Port Arthur, and
then trucked to the disposal site.
Table 26 gives the estimated additional costs of this special
disposal operation.

TABLE 26 Estimated Costs of the "No Discharge" Alternative

Estimated Costs
(Thousands of Dollars)
Minimum-a Maximum-

Rig modifications -

Barge modifications 500 500

Tug and barge rental (including fuel) 720 1,000

Barge mooring (pilings and anchor systems) 535 535

Barge rig-up on location 250 250

Extra supervision and technical support 250 360

Waste facility charges
for disposal

Liquids 430 780

Solids 380 570

Total 810 1,350

TOTALSC- 3,065 3,995

a-Assuming: 250 drilling days and a disposal volume of 110,000 bbl
(sewage treatment, 35 bbl; contaminated deck drainage and rainwater, 55
bbl; solids from drilling fluids and cuttings 30,000 bbl.

bAssuming 350 drilling days and a disposal volume of 190,000 bbl
(sewage treatment, 35 bbl; contaminated deck drainage and rainwater,
110,000 bbl; solids from drilling fluids and cuttings, 45,000 bbl).

2The estimated total cost of the well is greater than $20 million.

156

REFERENCES

Ayers, R.C., Jr., T.C. Sauer, Jr., D.O. Stuebner, and R.P. Meek. 1980.
An environmental study to assess the effect of drilling fluids on
water quality parameters during high rate, high volume discharges
to the ocean. In: Proceedings of a Symposium on Research on
Environmental Fate and Effects of Drilling Fluids and Cuttings.
Washington, D.C.: Courtesy Associates. Pp. 351-381.

Grant, W.D., and O.S. Madsen. 1982. Moveable bed roughness in
unsteady oscillatory flow. J. Geophys. Res. 87. Pp. 469-481.

Miller, R.C., R.C. Britch, R.V. Shafer, and S.O. Hillman. 1982. How
offshore arctic conditions affect drilling mud disposal. Pet.
Eng. Int.:68-88.

Offshore Operators Committee (OOC). 1981. Alternate disposal methods
for muds and cuttings Gulf of Mexico and Georges Bank. Available
from Hubert Clotworthy, Chairman, Environmental Subcommittee,
Texaco Inc., P.O.B. 60252, New Orleans, LA 70160.

Appendix A

Composition of Drilling Fluids

DENSITY MATERIALS

Materials used in drilling fluids in the greatest quantities are those
added to increase the density in order to control subsurface pressures,
which increase with depth as the well is drilled. The dense column of
fluid exerts considerable pressure on the bottom of the borehole to
keep formation fluids and gases from entering the borehole in an uncon-
trolled fashion. Several characteristics of these density materials
are common among the various compounds and are essential for optimal
performance. These materials should be (1) of high specific gravity,
(2) nonreactive with the liquid phase of the fluid, (3) nonabrasive,
and (4) of optimal particle size.
High specific gravity is required in order to maximize the weight
or density in the smallest volume possible for logistical and economic
reasons. Nonreactivity is essential because the weighting agent must
be added oftentimes in increasing amounts as the well deepens and yet
fluid properties (e.g., rheology or fluid behavior) must not be signi-
ficantly affected by the influx of weighting materials. In the same
sense, it is important that the weighting agent not be abrasive in
pumps or to drill stages, particularly at higher concentrations, in
order to reduce wear. Optimal particle size is essential for several
reasons. This includes a minimal value (>2p~) below which the par-
ticles affect mud properties easily (e.g., viscosity) and an upper
value (<44ij) beyond which the particles are hard to keep in sus-
pension and also tend to become abrasive. By balancing these various
needs, one can obtain an optimal product. Some products, such as lead
or galena, are only used in special cases (e.g., to "kill" an uncon-
trolled well) while others are used primarily only in certain fluid
systems (e.g., calcium carbonate in low density oil base or emulsion
drilling fluids).
Of all of the materials, barite is by far the most commonly used
weighting product worldwide. Indeed, it accounts for the largest pro-
portion of all components which are in drilling fluids. Bar ite has
fairly high specific gravity (4.3-4.5) but is also fairly soft and
nonabrasive. It is inert in both oil and water.
The amount of bar ite used annually depends on the general drilling
activity and particularly on drilling activity in high pressure zones.

157

In 1942, the domestic use of barite barely exceeded 100,000 tons per
year, but it increased to 1,900,000 in 1978 (API, 1978b) and may well
reach 3,000,000 tons by the year 2000 (Morse, 1981). The United States
is the world's largest producer and consumer of barite. Mining of
barite takes place in nine states with Nevada, Arkansas, and Missouri
accounting for most of the production. Additional sources outside of
the U.S.A. include Peru, Ireland, China, India, Mexico, Morocco, and
Thailand.
Barite is barium sulfate ore. Most of the barite used in drilling
fluids contains 80-90 percent BaSO4. it is known as barytes, heavy
spar, tiff, and cawk throughout the world and is surface or shaft mined
mainly from vein, residual, or bedded deposits. The barite ranges in
color from white to black and may be interspersed with a variety of
other minerals (e.g., quartz, clay, pyrite) that may constitute from
10-15% of barite. The barite is separated from these materials at the
mine, if necessary, by a series of devices which collectively enrich
the amount of pure barite. The final product is dried and ground at
the mine or at separate grinding plants throughout the world and
packaged or sold in bulk.
Barite that is used in oil well drilling is required to conform
to a set of specifications established by API (1981) in order to ensure
consistent material. These specifications stipulate a minimum specific
gravity, pore size range and alkalinity.
Other than barite, few other compounds are used to any extent in
the domestic market as density materials. Iron oxide or hematite
(Fe2O3) was one of the first materials used but its use has been
largely discontinued because of its characteristic staining of skin and
clothes of the drilling crews. It is currently seeing some revived
interest as a product or as an additive to barite.

VISCOSIFIERS

In order for the drilling fluid to remove the formation solids and
cuttings from the bit at the bottom of the hole and carry them up the
annulus to the surface, the fluid must have a certain thickness or
viscosity. Only the smallest of particles could be carried up the long
column with just pure water, even under pressure. More importantly,
pressure or flow must be interrupted during the drilling process (for
example, to change the drill bit) and pure water alone would allow the
solids to fall back to the bottom during these static periods. It is
essential, therefore, that the drilling fluid be viscous enough to
suspend the cuttings during these periods..
As discussed in the 'Drilling Discharges" chapter, drilling fluid
ingredients often have several functions. Viscosifiers also help seal
the wellbore and prevent loss of liquids to the formation, an essential
function because an uncontrolled fluid loss would require constant
monitoring and addition of water to correct for the loss. More
importantly, critical fluid properties would be in a state of constant
flux and would make it difficult to drill. It is difficult to separate
ingredients in these two groups because of their functional overlap.

159

Clays, however, will be discussed under viscosifiers and polymers will
be discussed as fluid loss agents event though both can functional
dually.
The primary viscosifiers are the various clays that are added.
Gray et al., (1980: 536) indicates that the term clay has several
meanings; however, it is best defined to be those natural earth
materials of fine grain size which are primarily composed of hydrous
aluminum silicates. The definition becomes less precise as one reviews
the clays; however, it is more important to understand their function
and chemistry rather than find an exact definition.
In the mineralogical sense, Joseph (1978) indicates that drilling
fluid clays fall into two groups--the smectite group (layered) and the
hormite group (fibrous). The mineralogical nomenclature is confused
by a number of regional and historical names. Since the most important
characteristics of the clays are their bonding with other components,
which is largely dictated by the polyvalent ion, the clays are often
listed within each mineralogical group by cation where appropriate.
A variety of other classification schemes are available (Brindley,
1955; Degens, 1965; Warshaw and Roy, 1961), which use a compositional
basis for classification, and may be referred to for more detailed
information on clay structure. Since clays are natural minerals, the
clay composition and the presence of impurities are variable due to
geological differences. Silica, shale, calcite, mica, and feldspar are
the most common impurities (Perricone, 1980).
The primary clay in drilling fluids and one of the earliest ones
to be used is bentonite, composed mostly of sodium montmorillonite.
It is still the most commonly used clay with domestic use in excess of
650,000 tons (API, 1978). Most of the domestically used bentonite is
mined in Wyoming, South Dakota, and Montana. There mines are shallow,
surface mines where the bedded clays are typically lenses between shale
layers. The lenses are of variable thickness (e.g., 1-60 ft.) and
under fairly shallow overburdens. The bentonite is mined, weathered,
and then sized and dried before grinding. As with barite, the American
Petroleum Institute maintains industrial specifications concerning
manufacture and operating properties. These include moisture content,
maximum particle size, and viscosity and plasticity criteria. Ben-
tonite may be treated with a variety of polymers to produce viscosities
equal to or greater than API specifications (Perricone, 1980).
Another bentonite, calcium montmorillonite (also called sub-
bentonite) is used, but in far less quantities, due to its poorer per-
formance than sodium montmorillonite. Often, sub-bentonite is added
to bentonite when larger particle sizes are required. Other clays,
such as attapulgite and sepeolite, are used as viscosifiers in salt
water fluids. These clays are mined domestically also (Georgia,
Florida, and Nevada, respectively). Due to their fibrous nature, these
clays are not suitable for fluid loss reduction and serve also exclu-
sively for viscosity.

160

FLUID LOSS ADDITIVES

As discussed in the section on viscosifiers, clays and various polymers
act as both viscosifiers and as fluid loss additives. Any dissociation
of the two is spurious; however, this discussion separates the two
purely for clarity. A properly designed drilling fluid should deposit
a filter cake on the wall of the well bore during drilling to retard
the continuous liquid phase in the drilling fluid from entering the
formation. Bentonite and drilled clays are the prime builders of this
cake, but in some instances, they are inadequate to stop the flow. The
addition of fluid loss control additives may be necessary. Polymers
are particularly well suited to this task and both natural and syn-
thetic polymers are used. Starch was the first natural polymer used
(Gray et al, 1942). Corn and potatoes are the principal source of
starch for drilling fluids. Starch is prepared by treating the raw
materials with heat and chemical agents to gelatinize the starch and
then dried and ground for bagging. Modified starches have also been
developed to include cyanoethylated starch, amino starch ether,
hydroxypropyl starch ether, and quatenary ammonium salts of starch.
Additionally, preserved or nonfermenting starches are available which
may include a biocide such as paraformaldehyde.
Several natural gums have been used. Guar gum from the guar
plant, a Texas legume, is one of the most prevalent. Semi-synthetic
gums produced from the chemical modification of cellulose comprise
another prevalent group. Sodium carboxymethylcellulose (CMC) is widely
used as well as hydroxyethylcellulose (HEC). These compounds all
function by adsorbing to the omnipresent clays. Cellullosic polymers
can be further treated to produce polyanionic forms usually with
specific molecular weight ranges that function in the presence of salt
when CMC is less effective. Synthetic polymers that are water dis-
persible have been developed in recent years that function very well
in drilling fluids. Polymerization of acrylic polymers and acrylates
has resulted in the development of a number of different additives that
counter fluid loss, or function as flocculants, viscosifiers, or
bentonite extenders. The chemistry, concentration, temperature, and
original source material of the polymer additives are all variable, as
well as critical to operating characteristics.

THINNERS AND DISPERSANTS

The next largest group of products after viscosifiers are those
products which act to reduce viscosity. As drilling proceeds, the
drilling fluid has a tendency to thicken naturally from the addition
of very fine formation solids and native clays. This tendency
increases with depth as temperature rises due to the geothermal
gradient and causes the mud to undergo high temperature gellation or
thickening. Other chemical reactions may also create thickening of the
mud. A change in the clay's surface chemistry is usually the cause of
gelling and creates the need for a material to disperse the clay par-
ticles. Thinners typically have a relatively large anionic component

161

which is adsorbed on the positive sites of the clay particles, thereby
reducing the attractive forces between the particles. See Gray et al,
(1980:164) for a more complete discussion of the thinning mechanism.
Materials commonly used as thinners in water-based muds are broadly
classified as plant tannins, polyphosphates, lignitic materials, and
lignosulfonates. Tannins occur in many plants and are extracted from
bark, wood, or fruit. Most of the tannins used in drilling fluids are
from the extract of quebracho wood, one of the first thinners ever used
in the United States (Lawton et al, 1933, 1935). Chemically, tannins
are esters of one or more polyphenolic acids.
Polyphosphates are those phosphates in which two or more phos-
phorus atoms are joined together by oxygen atoms, such as sodium tetra-
phosphate. Polyphosphates may be of varying chain lengths and the
formula is usually expressed as the ratio of Na2O/P20S.
Phosphonic acids and pyrophosphates are two other general types
occasionally used. Both the tannins and phosphate compounds have
temperature limitations. The phosphates become nonfunctional above
250�F and the tannins degrade between 250-3500F (Carney and
Harris, 1975).
Lignitic materials include a variety of materials which chemically
differ due to source and preparation. Variously called lignite,
leonardite, mined lignin, brown coal, and slack, these materials became
popular as thinners after World War II when quebracho exports were
diminshed. Lignite and brown coal are actually low heat value coals
while leonardite is a naturally oxidized lignite from prolonged
weathering. Leonardite has a high content of humic acid; several
grades are available with varying humic acid contents. North Dakota
is the principal source with South Dakota, Montana, New Mexico, and
Texas as secondary sources. The material is usually strip mined, dried
to 15-20% moisture content, crushed and bagged. Modified lignites were
found to be excellent thinners after treatment with caustic soda,
chrome or potassium salts to produce a more temperature stable com-
pound. Lignitic thinners can perform satisfactorily at high tempera-
tures (3500F) and are often used in geothermal drilling fluids.
The lignosulfonates are waste byproducts of the sulfite process
for pulping wood to make paper. The chemistry in making lignosul-
fonates and the chemical structure of lignosulfonates are complex but
covered in a number of books and articles (Browning and Perriane, 1962;
Carney, 1970; and Sarkanen and Ludwig, 1971). In simplest terms, lig-
nosulfonates are polymeric salts of lignosulfonic acids with various
functional compounds attached. The functionality of the lignosulfon-
ates are enhanced by the functional compounds. These are usually added
during the sulfite pulping process and reacted, then recovered by spray
drying. Calcium, chrome, and iron compounds are the predominant
materials added to form calcium chromium, ferrochromium, or ferrolig-
nosulfonates. The mechanism of thinning by lignosulfonates is
discussed in Jessen and Johnson (1963) and more completely in Gray et
al (1980: Chapter 4), but also relies on the lignosulfonate micell
attaching to the edge surface of the clay particles to break the
electrokinetic attraction between the clays. As the clays disperse,
the viscosity of the fluid decreases and the fluid is "thinned".

1 62

pH AND ION CONTROL

The PR of most water based drilling fluids is kept alkaline for a
variety of reasons. Corrosion control and the control of poisonous
H2S gas are two of the prime reasons; however, other fluid properties
are also affected (e.g., solubility of additives). For these reasons,
an alkaline pH is maintained by adding caustic soda (sodium hydroxide)
to the system as needed. Ionic balance is also commonly affected by
contamination of the fluid system by cement, salt, or anhydrite. These
inputs can affect the rheology (fluid behavior) of the system and
require treatment. Soda ash (sodium carbonate) and baking soda (sodium
bicarbonate) are the most common additives. A number of additional
materials may be used for specialized fluids or very specialized
problems, but their relative usage frequency is rather small in compar-
ison to the above three materials: barium carbonate, potassium
hydroxide, calcium sulfate, calcium hydroxide, sodium chloride, and
potassium chloride.

LUBRICANTS

under normal drilling, the drilling fluid alone is sufficient for
adequate lubrication of the drill pipe and bit. However, because no
hole is truly vertical and the drill pipe is flexible, there are likely
to be some points of contact between the side of the hole and the drill
pipe. This creates a frictional resistance thereby increasing the
torque required to turn (as well as raise and lower) the drill pipe and
bit. Lubricants are added to drilling fluids when friction is
encountered. The addition of lubricants is generally required for
highly deviated holes, holes with frequent direction changes, under-
gauge holes, or holes with poor drill string dynamics.
Oil base drilling fluids are excellent lubricants, however, due
to higher costs and government regulations, oil fluids are generally
not used where the only advantage is lubrication. A common historical
practice concerning lubricants has been to add diesel fuel (No. 2 fuel
oil) to a water base fluid. Fluids with high diesel fuel content (as
much as 50 percent) may be used to counter friction. Prior to dis-
charge, these fluids will be worked to separate the diesel fuel from
the discharge, or the fluid may be diluted to lower the relative diesel
fuel content. These practices are within existing regulations, so long
as the drilling discharges do not cause a sheen on the surface of the
ocean or a sludge on the seafloor. Moreover, with detergents and/or
emulsifiers in the system, fluids containing as much as several percent
diesel can sometimes be discharged without a sheen. More importantly,
laboratory testing has demonstrated that emulsified oil in a water
based fluid is not as effective a lubricant as non diesel substitutes
currently available. Also, these substitutes may have less effect on
the fluids' rheology than does emulsified oil. A list of chemicals
used as lubricants is in Table A-1.

163

LOST CIRCULATION MATERIAL S

Circulating drilling fluids can be lost to downhole formations through
induced fractures, preexisting open fractures, caverns, pores, and
solution channels. Lost circulation is one of the most common problems
encountered during rotary drilling. Lost circulation materials are
added to the mix either as an additive or in some cases as a premixed
slurry slug. Whatever the means employed to add the material to the
fluid, the end result is the same--that of actually plugging the frac-
tures or openings. These additives are either fibrous, filamentous,
granular, or flaked and are almost always naturally occurring. Common
lost circulation materials include ground nut shells, mica, and ground
cellophane.

CORROS ION INHIBITORS

Corrosion of downhole tubular pipe is a very serious problem. The
simplest and most common means to control corrosion is to use a highly
alkaline drilling fluid, but this practice has limitations--hydroxyl
ions degrade clay minerals at temperatures above 200�F and a pH above
10. There are three major forms of corrosion:

* Carbon Dioxide. CO2 dissolves in water resulting in a
lowering of pH values through the production of carbonic acid. This
can be controlled using sodium hydroxide to a pH of 9-10. In some
cases excessive acids may be produced; these can be neutralized with
calcium hydroxide, but this can precipitate scale deposits which set
up corrosion cells. Scales can be controlled by the addition of a
scale inhibitor such as sodium phosphonate.
* Oxygen. 02 is almost always present in drilling fluids
where only a minimal amount is sufficient to cause significant corro-
sion pitting under rust or scale patches. This form of corrosion is
controlled using oxygen scavengers such as sodium sulfite or ammonium
bisulfite. Filming amines and morpholines can also mitigate corrosion
by deposition of a film on metal surfaces. Chromates can also be used
to incorporate a film (a complex of oxygen, iron, and chromium) on
downhole metal surfaces. Hexavalent chrome is reduced to trivalent
chromium in the fluid system.
� Hydrogen Sulfite. H2S may contaminate the drilling fluid
by an influx of sour gas or by the degradation of lignosulfonates by
sulfate-reducing bacteria or by high temperatures (3300F). Hydrogen
sulfide is both a deadly poison and a severe source of corrosion,
through the mechanism of hydrogen embrittlement. It can be removed
from the drilling fluid system through the use of sulfide scavengers
such as zinc carbonate, zinc oxide, or organically chelated zinc
compounds which prevent mud flocculation by reducing the amount of free
zinc ions. Iron oxides are also used and do not affect the theological
or filtration properties of the mud.

164

TABLE A-1 Chemicals Commonly Used in Drilling Fluid Lubricants

Acetophenones Lanolin

Alcohol Ester Low Paraffinic Solvents

Aluminum Stearate Mineral Oil

Asphalts Organic Phosphate Ester

Calcium Oleate Rosin Soap

Coconut Diethanolamides Sodium Alkylsulfates

Coconut Oil Alkanolamide Sodium Asphalt Sulfonate

Diesel Fuel Sodium Phosphates

Diphenyl Oxide Sulfonate Sorbitan Ester Sulfonate

Ethoxylates Stearates

Ethoxylated Alcohol Sulfonated Alcohol Ether

Fatty Acid Soaps Sulfonated Tall Oil

Gilsonite Sulfonated Vegetable

Glycerol Dioleate Triethanolamine

Glycerol Monoleate Vegetable Oils

Glass Beads Wool Greases

Graphite

BACTERICIDES

Three mechanisms can be used to prevent or mitigate fermentation of
drilling muds by microorganisms. Saturated salt muds and highly
alkaline muds (ph > 12) are resistant to bacteriological activity.
If these options are not available, then the addition of a bactericide
may be necessary. Bactericides are most common in drilling fluids
containing starch or polymers which are rapidly degraded by heat,

165

agitation, or microorganisms. Paraformaldehyde is the most common
bactericide used in drilling fluids as well as workover and completion
fluids.
Paraformaldehyde will depolymerize in acidic or basic solutions
to form its monomer, formaldehyde. Neglecting any loss due to absorp-
tion, there are several means by which it will be depleted from the
drilling fluid system. Reactions with bacterial mucoproteins with
activated aromatic rings found in lignosulfonates and tannins reduce
the paraformaldehyde. Also, destruction by air oxidation forms either
a formate or CO2 by the Cannizaro reaction. Due to these mechanisms,
paraformaldehyde must be routinely added to the system to maintain
adequate treatment levels. Several non-fermenting starch additives are
in use today. In these additives the bactericide has been incorporated
into the starch, eliminating the need to add additional bactericide.
Under the current regulatory scheme, all bactericides used in
drilling fluids are regulated by the Environmental Protection Agency
under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA)
as well as discharge permits. Also, the Minerals Management Service
has banned chlorinated phenols from use on the OCS. Under FIFRA
registration, end-use, labeling, chemical identification, and applica-
tion rates are tightly regulated. Of the many available bactericides,
relatively few bactericides have oilfield registrations. Those without
proper registrations are not used. Robichaux (1975) and Jones et al.,
(1980) listed eight different chemical groups that have been used
(quartenary amines, paraformaldehyde, cupric sulfate, chlorinated
thiophene chloride, glutareldehyde, carbonates, triaza chlorides, and
chlorine dioxide). Additional materials (e.g., isothiazoline) have
received approval since that time.

SURFACTANTS

Surface active agents are adsorbed on surfaces and at interfaces
resulting in a decreased surface tension. These are used in drilling
fluids for several different purposes such as emulsifiers, wetting
agents, foamers, defoamers, and agents to decrease the hydration of
clay particle surfaces.
There are three main forms of surfactants. Cationic surfactants
dissociate into large organic cations and simple inorganic anions.
These are usually salts of a fatty amine or polyamine such as trimethyl
dodecyl ammonium chloride. Anionic surfactants dissociate into large
organic anions and simple inorganic cations. Soaps are the most common
form such as sodium oleate. Nonionic surfactants are long chain
polymers and do not dissociate. The most common nonionic surfactant
is phenol reacted with 30-mol ethylene oxide. Cationic surfactants are
strongly adsorbed on to negatively charged clay and rock surfaces,
whereas anionic surfactants are adsorbed at the positively charged ends
of clay crystal lattices resulting in a retardation of the hydration
of bentonite. Other chemicals used as drilling fluid surfactants are
found in Table A-2.

166

TABLE A-2 Chemicals Commonly Used in Drilling Fluid Surfactants

Coconut Diethanolamides
Coconut Oil Alkanolamide
Calcium Oleate
Fatty Acid Derivatives
Polycyclic Alcohol Anhydrides
Polyoxyethylenes

Emulsifiers

The relationship between emulsifiers and surfactants is direct. Inter-
facial tension between oil and water is very high but can be lowered
through the use of a surfactant, which decreases the surface tension
resulting in an emulsion--a stable dispersion of fine droplets of one
liquid into another liquid. In addition, emulsifiers stabilize
emulsions due to their molecules adsorbing at the oil/water interfaces
forming a protective "skin" around dispersed droplets which prevents
coalescing when these droplets collide.
Emulsifiers are generally used in oil-base fluids, however, they
can be used in water-based systems to emulsify oil into the water
phase. They can either act to emulsify oil into water or water into
oil. Stable mechanical emulsions can be formed without using a
chemical emulsifier (surfactants) by the adsorption of colloidal solids
in the fluid at the oil-water interfaces. Dispersed clays and ligno-
sulfontates can act as mechanical emulsifiers in alkaline fluids.
Representative chemicals used as emulsifiers are found in Table A-3,
as well as those listed under surfactants, Table A-2.

TABLE A-3 Chemicals Commonly Used in Drilling Fluid Emulsifiers

Alkyl Aryl sulfonates and sulfates
Polyoxyethylene fatty acids, esters, and ethers
Nonylphenol reacted with ethylene oxide
Fatty acid soaps, polyamines, and amides blends
Calcium Dodecylbenzene Sulfonates

167

FOAMERS AND DEFOAMERS

Foaming agents (surfactants) are added to remove borehole water while
air drilling, to create a low-density fluid to remove drill solids when
performing workover and/or completions in depleted reservoirs, or as
an insulating medium in arctic wells. Very few wells drilled on the
OCS use air or foam drilling due to the depth and pressures. Chemicals
normally used are found listed under surfactants, Table A-2.
Defoamers are used to break foams used in drilling or those formed
in gas-cut drill fluids. By far the most common chemicals used as
defoamers are 2-ethyl hexanol, aluminum stearate, and ester alcohols
such as the monoisobutyrates.

FLOCCULANTS

Flocculants are used to remove small cuttings when clear water drilling
of hard rock is required. These flocculants can be injected in the
fluid return after the shale shaker allowing solids to flocculate in
the reserve pit. Flocculants are also used to clarify reserve fluid
pits prior to disposal. They are rarely used offshore.
Acrylic polymers are excellent flocculants at a concentration of
0.01 lbs/bbl, but can perform a dual function as a filtration control
agent at concentrations of 3 lbs/bbl. Chemicals currently used as
flocculants include alum, calcium sulfate, polyacrylamides, sodium
polyacrylate, copolymers of vinyl acetate and maleic anhydride, and
calcium oxide.

REFERENCES

American Petroleum Institute. 1978. Oil and gas well drilling fluid
chemicals. Bulletin 13F, first ed. American Petroleum
Institute, Washington, D.C. 9 pp.

American Petroleum Institute. 1981. API specifications for oil-well
drilling-fluid materials. Bulletin 13A, eighth ed. American
Petroleum Institute, Washington, D.C. 14 pp.

Brindley, G.W. 1955. Identification of clay minerals by x-ray
diffraction analyses. Clays and Clay Technol. Bull. 169:119-129.

Browning, W.C., and A.C. Perricone. 1962. Lignosulfonate drilling
mud conditioning agents. SPE Paper 432, Full Meeting, Society of
Petroleum Engineers, October 7-10, 1962, Los Angeles, Calif. 13
PP.

Carney, L.L. 1970. Preparation and use of chromium lignosulfonates in
drilling mud. Presentation to Spring Meeting, Production
Department, American Petroleum Institute, March 4-6, 1970,
Dallas, Tex. 9 pp.

168

Carney, L.L., and L. Harris. 1975. Thermal degradation of drilling
mud additives. In: Proceedings, Environmental Aspects of
Chemical Use in Well-Drilling Operations, May 21-23, 1975,
Houston, Tex. EPA-560/1-75-004. Office of Toxic Substances,
U.S. Environmental Protection Agency, Washington, D.C. vi + 604
PP.

Degens, E.T. 1965. Geochemistry of Sediments. Englewood Cliffs,
N.J.: Prentice-Hall. 342 pp.

Gray, G.R., J.L. Foster, and T.S. Chapman. 1942. Control of
filtration characteristics of salt water muds. Trans. AIME
146:117-125.

IMCO Services. 1980. Know your drilling mud components. Drilling
Contractor 36(3):92-110.

Jessen, F.W., and C.A. Johnson. 1963. The mechanism of adsorption of
lignosulfonates or clay suspensions. Soc. Pet. Engi. J.
3(3):267-273.

Joseph, J.H. 1978. Bentonite, sepiolite, and attapulgite. In: Raw
Materials for the Oil Well Drilling Industry. P.W. Harben (ed.),
Metal Bulletin LTD. London, England. Pp. 51-74.

Lawton, H.C., H.A. Ambrose, and A.G. Loomis. 1932. Chemical
treatment of rotary drilling fluids. In: Physics. Pp. 365-375.

Lawton, H. C., A. G. Loomis, and H. A. Ambrose. 1935. Drilling wells
and drilling fluid. U.S. Patent No. 1, 999, 766, April 30, 1935.
U.S. Patent Office, Washington, D.C.

Morse, D. E. 1981. Barite. In: Mineral Facts and Problems.
Bulletin 671. Bureau of Mines, U.S. Department of the Interior.
Washington, D.C. 12 pp.

Perricone, C. 1980. Major drilling fluids additives. In:
Proceedings of a Symposium on Research on Environmental Fate and
Effect of Drilling Fluids and Cuttings. Courtesy Associates:
Washington, D.C. Pp. 15-29.

Robichaux, T.J. 1975. Bactericides used in drilling and completion
operations. In: Proceedings, Environmental Aspects of Chemical
Use in Well-Drilling Operations, May 21-23, 1975, Houston, Tex.
EPA-560/1-775-004. Washington, D.C.: Office of Toxic
Substances, U.S. Environmental Protection Agency. vi + 604 pp.

169

Sarkanen, K.V., and C.H. Ludwig. 1971. Lignins: Occurrence,
Formation, Structure and Reactions. New York: Wiley-
Interscience. 451 pp.

Warsaw, C.M., and R. Roy. 1961. Classification and scheme for the
identification of layer silicates. Geol. Soc. Am. Bull.
72:1455-1492.

Appendix B

Functionally Equivalent Drilling Fluid Products

The extent of redundancy of drilling fluid products is difficult to
measure; neverth~eless it would be useful information, for reviewing
well histories for the purpose of permit compliance, for example. The
drilling fluid products offered by each of the four major drilling
fluid supplier companies is listed in Table B-l. While this list is
for only a segment of the industry, it is a useful comparison of
product equivalency because most of the offshore wells, and especially
wells on the OCS, are serviced by the major supplier companies. Some
areas (e.g., Georges Bank) have been exclusively serviced by majors.
Of the 86 different drilling fluid components listed, 66% were avail-
able from all 4 companies, 7% from 3 of 4, 6% from 2 of 4, and only 6%
were totally unique to one company. Products which are listed as
functional equivalents may be different chemically, although a quick
review of the table suggests that this is not often the case. It
should also be noted that chemically equivalent products may be
slightly different due to varying percentage of active ingredients,
particle sizes, processing technique, relative proportion of compo-
nents, or quality of materials. Nevertheless, this analysis suggests
a rather substantial redundancy factor among the four largest
companies. The inclusion in the table of the smaller companies which
may not devote as much effort as the majors to product development,
would likely not change the overall picture of redundancy provided by
the table.

171

TABLE B-1 Comparable Drilling Fluid Products by Tradenames

DESCRIPTION
OR PRINCIPAL IMCO
COMPONENT SERVICES BAROID MAGCOBAR MILCHEM PRIMARY APPLICATION

WEIGHTING AGENTS - VISCOSIFIERS

Barite IMCO BAR" Baroid Magcobar Mil-Bar For increasing mud weight up to 20
PPg

Barite/Hematite IMCO Bar-Gain For increasing mud weight up to
Blend BAR-PLUS 22 ppg

IMCO To increase density of a drilling
Hematite NU-DENSE and kill fluid up to 25 ppg

Calcium IMCO WATE Baracarb Lo-Wate W.O. 35 For increasing density to 11 ppg
Carbonate W.O. 50 with acid soluble material

Bentonite IMCO GEL Aquagel Magcogel Milgel Viscosity and filtration control
in water-base muds

Sub-Bentonite IMCO KLAY Baroco High Yield Green Band For viscosity and filtration
Blended Clay Clay control in water-base muds

Attapulgite IMCO Zeogel Salt Gel Salt Water Viscosifier in saltwater muds
BRINEGEL Gel

Beneficiated IMCO HYB Quick-Gel Kiwk-Thik Super-Col Quick viscosifier for freshwater,
Bentonite upper-hole muds with minimum
chemical treatment

Asbestos Fibers IMCO Flosal Visquick Flosal Viscosifier for fresh-water or
SHURLIFT salt-water muds

Bacterially Produced IMCO XC XC Polymer Duovis XC Polymer Viscosifier and fluid loss control
Polymer additive for low-solids muds

Sepiolite IMCO Geo-Gel Viscosifier in all water-base
DUROGEL muds, especially high temperature
drilling fluids

Multipurpose IMCO Mil-Polymer Polymer for fluid loss control
Polymer POLYSAF91 305 and viscosity

DISPERSANTS

Sodium IMCO PHOS Barofos Magco-Phos Oil Fos Thinner for low pH fresh-water
Tetraphosphate (STP) muds where temperatures do not
exceed 180�F

Sodium Acid IMCO SAPP SAPP SAPP SAPP For treating cement
Pyrophosphate contamination

Quebracho IMCO Q-B-T Tannex M-C Mil- Thinner for fresh-water and
Compound Quebracho Quebracho lime muds

Modified Tannin DESCO Desco Desco Desco Thinner for fresh-water and
salt-water muds alkalized for pH
control

Processed IMCO LIG Carbonox Tann A Thin Ligco Dispersant, emulsifier and
Lignite supplementary additive for fluid
loss control

Causticized IMCO THIN CC-16 Caustilig Ligcon Dispersant, emulsifier and
Lignite supplementary additive for fluid
loss control

TABLE B-1 (continued)

DESCRIPTION
OR PRINCIPAL IMCO
COMPONENT SERVICES BAROID MAGCOBAR MILCHEM PRIMARY APPLICATION

Chrome IMCO-VC-10 Q-Broxin Spersene Uni-Cal Dispersant and fluid loss
Lignosulfonate control additive for water-base
muds

Blended IMCO RD-111 Blended multi-purpose dispersant,
Lignosulfonate fluid loss agent and inhibitor
Compound for IMCO RD-111 mud systems

Chrome-Free IMCO Magco CFL X-KB Thin Dispersant and fluid loss
Lignosulfonate RD-200oo control additive for water-base
muds

FLUID LOSS REDUCERS

Organic IMCO DEXTRID Magco Control fluid loss in
Polymer PERMALOID Poly Sal water-base muds

Pregelatinized IMCO LOID Impermex My-Lo-Gel Milstarch Controls fluid loss in
Starch saturated saltwater and lime muds

Sodium Carboxy- IMCO CMC Cellex Magco CMC Milchem CMC For fluid loss control and barite
methylcellulose (Regular) (Regular) (Regular) (Med-Vis) suspension in water-base muds

Sodium Carboxy- IMCO CMC Cellex Magco CMC Milchem CMC For fluid loss control and
methylcellulose (High Vis) (High Vis) (High Vis) (High Vis) viscosity building in low-solids
muds

Polyanionic DRISPAC Drispac Drispac Drispac Fluid loss control additive and
Cellulosic Polymer viscosifier in salt muds

Polyanionic DRISPAC Drispac Drispac Drispac Primary fluid loss additive,
Cellulosic Polymer SUPERLO Superlo Superlo Superlo secondary viscosifier in
water-based muds

3odium IMCO Cypan Cypan Cypan Fluid loss control in calcium
Polyacrylate SP-101 WL-100 WL-100 WL-100 free muds

LUBRICANTS - DETERGENTS - EMULSIFIERS

Specially prepared IMCO A water dispersable, non-
blend of organic LUBE-106" foaming, nontoxic additive
liquid compounds designed to impart lubricity and
reduce torque, drag and friction
in all water-base drilling fluids

Blend of Organic IMCO Torq DOS-3 Mil-Plate 2 Supplies the lubricating pro-
Esters LUBRIKLEEN Trim II perties of oils without their
environmental pollution

Extreme Pressure IMCO EP Lube Bit Lubri-Film Used in water-base muds to
Lubricant EP LUBE Mudlube Lube impart extreme pressure lubricity

Oil Soluble IMCO Skot-Free Pipe Lax Petrocote Nonweighted fluid for
Surfactants FREEPIPE spotting to free differentially
stuck pipe H

Blend of Fatty Acids, IMCO SF-100 Carbo-Free Invert emulsion that may be
Sulfonates and SPOt" weighted to desired density
Asphaltic Materials for placement to free
differentially stuck pipe

Water Dispersible IMCO STABIL- ITI-WD Lubricant and fluid loss
Asphalts HOLECOAT II HOLE reducer for water-base muds that
contain no diesel or crude oil

TABLE B-1 (continued)

DESCRIPTION
OR PRINCIPAL IMCO
COMPONENT SERVICES BAROID MAGCOBAR MILCHEM PRIMARY APPLICATION

Processed SOLTEX Soltex Soltex Soltex Used in water-base muds to
Hydrocarbons lower downhole fluid loss and
minimize heaving shale

Oil Dispersible IMCO Baroid Pave-A Carbo-Seal Lubricant and fluid-loss
Asphalts MUD OIL Asphalt Hole reducer for water-base muds that
contain diesel or crude oil

Detergent IMCO MD Con Det D-D Milchem MD Used in water-base muds to aid in
dropping sand. Emulsifies oil,
reduces torque and minimizes bit
balling

Blend of Anionic IMCO SWS Trimulso Salinex Atiosol and Emulsifier for salt-water and
Surfactants Atiosol S fresh-water muds

DEFOAMERS - FLOCCULANTS - BACTERICIDES

Aluminum Aluminum Aluminum Aluminum Aluminum Defoamer for lignosulfonate
Stearate Stearate Stearate Stearate Stearate muds

Liquid Surface IMCO Defoamer for all water-base
Active Agent DEFOAM-LM muds

Surface-Active IMCO Bara- Magconol LD-7 All-purpose defoamer
Dispersible Liquid FOAMBAN Defoam 1 LD-8
Defoamer W300

Flocculating IMCO FLOd" Barafloc Floxit Separan Used to drop drilled solids
Agent where clear water is desirable for
a drilling fluid

Blended Carbonate IMCO CIDE Bara-B33 Magco Poly Bactericide used to prevent
Solutions Defoamer fermentation

Paraformaldehyde Para- Aldacide Paraformal- Paraformal- Bactericide used to prevent
formaldehyde dehyde dehyde fermentation

LOST CIRCULATION MATERIALS

Fibrous IMCO FYBER Fibertex Mud Fiber Mil-Fiber Filler as well as matting
Material material to restore lost
circulation

Nut Shells: IMCO PLUG Wall-Nut Nut-Plug Mil-Plug Most often used to prevent
Fine lost circulation

Nut Shells: IMCO PLUG Wall-Nut Nut-Plug Mil-Plug Used in conjunction with
Medium fibers or flakes to regain lost
circulation

Nut Shells: IMCO PLUG Wall-Nut Nut-Plug Mil-Plug Used where large crevices
Coarse or fractures are encountered

Ground Mica: IMCO MYCA Micatex Magco-Mica Milmica Used for prevention of lost
Fine circulation

Ground Mica: IMCO MYCA Milcatex Magco-Mica Milmica Used for prevention and
Coarse regaining of lost circulation

Cellophane IMCO FLAKES Jel Flake Cell-O-Seal Milflake Used to regain lost circulation

TABLE B-1 (continued)

DESCRIPTION
OR PRINCIPAL IMCO
COMPONENT SERVICES BAROID MAGCOBAR MILCHEM PRIMARY APPLICATION

Combination of KWIK SEAL Kwik Seal Kwik Seal Kwik Seal Used where severe lost
granules, flakes and circulation is encountered
fibrous materials of
various sizes in one
sack

High-water loss slurry Diaseal M Diaseal M Diaseal M Diaseal M Forms a high-solids plug to
for lost circulation cure severe lost circulation

SPECIALTY PRODUCTS

Bentonite Extender IMCO GELEX Benex Benex Benex Increases yield of bentonite H
to form low-solids drilling fluid C

Inhibiting Agent IMCO IE PAC K-Plus Imparts inhibition, fluid loss and
rheology control in potassium muds

Synergistic Polymer IMCO Durenex Resinex High-temperature rheological
Blend POLY Rx stabilization and filtration
control

Biodegradable IMCO Quick Magco Gel-Air Foaming agent in air or mist
Surfactant FOAMANT" Foam Foamer 76 drilling

CORROSION INHIBITORS

Zinc Compound IMCO Mil-Gard For use as a hydrogen sulfide
SULF-X II scavenger in water-base and
oil-base muds

Liquid Corrosion IMCO Prevent stress cracking of
Inhibitor CRACK-CHEK drill strings in an H2S
environment

A Catalyzed Ammonium IMCO XO2'" Coat 777 OS-1L Noxygen For use an an oxygen
Bisulfite scavenger

Filming Amine IMCO Bara Cora Magco Aqua-Tec All-purpose corrosion
X-CORR Inhibitor inhibitor

Filming Amine IMCO Coat 415 Magco Ami-Tec Corrosion inhibitor
PERMAFILM" Inhibitor Inhibitor

Organic Polymer IMCO Surflo-H35 SL-1000 Scale-Ban Scale inhibitor
SCALECHEK

COMMERCIAL CHEMICALS

Sodium Hydroxide Caustic Caustic Caustic Caustic For pH control in water-base
Soda Soda Soda Soda muds

Potassium Hydroxide Caustic Potassium Potassium Potassium Used to control pH in
Potash Hydroxide Hydroxide Hydroxide potassium system

Sodium Carbonate Soda Ash Soda Ash Soda Ash Soda Ash For treating-out calcium in
low pH muds

Sodium Bicarbonate Sodium Sodium Sodium Sodium For treating-out calcium or
Bicarbonate Bicarbonate Bicarbonate Bicarboniate cement in high pH muds

Barium Carbonate Barium Anhydrox Barium Barium For treating-out calcium
Carbonate Carbonate Carbonate sulfate (pH should be above
10 for best results)

Sodium Chromate Sodium Sodium Sodium Sodium Used in water-base muds to
Chromate Chromate Chromate Chromate prevent high-temperature
gelation

TABLE B-1 (continued)

DESCRIPTION
OR PRINCIPAL IMCO
COMPONENT SERVICES BAROID MAGCOBAR MILCHEM PRIMARY APPLICATION

Chrome Alum Chrome Alum Chrome Chrome Chrome For use in cross-linking XC
(chromic chloride) Alum Alum Alum Polymer systems

Calcium Sulfate Gypsum Gypsum Gypsum Gypsum Source of calcium for
formulating gyp muds

Calcium Hydroxide Lime Lime Lime Lime Source of calcium for
formulating lime muds

Sodium Chloride Salt Salt Salt Salt For saturated salt muds and
resistivity control

Calcium Chloride Calcium Calcium Magcobrine Calcium For weighting solids-free
Chloride Chloride C.C. Chloride brines and to control salinity
in invert oil muds

Potassium Chloride Potassium Potassium Magcobrine Potassium Potassium salt use in KC1
Chloride Chloride P.C. Chloride inhibitive systems