GEOLOGICAL SURVEY CIRCULAR 741

Oil Spills, 1971-75,

Gulf of Mexico

Outer Continental Shelf
Oil Spills, 1971-75,

Gulf of Mexico

Outer Continental Shelf

By Elmer P. Danenberger

GEOLOGICAL SURVEY CIRCULAR 741

Statistics and discussion of oil spills 

resulting from offshore operations on 

Federal oil and gas leases in the 

Gulf of Mexico

1976
United States Department of the Interior

THOMAS S. KLEPPE, Secretary

Geological Survey

V. E. McKelvey, Director

Free on application to the Branch of Distribution, Eastern Region, U.S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304
CONTENTS

Page

System of measurement units ................. IV

Abstract..................................... 1

Introduction................................. 2

Sources and reliability of data.............. 5

Major spills................................. 7

Minor spills................................. 10

Production-platform spills.............. 12

Pipeline and pump spills................ 15

Spills of less than 1 barrel............ 16

Production incidents, by operator....... 17

Production incidents, by platform....... 18

Other sources of spillage.................... 19

Conclusions.................................. 20

Selected references.......................... 22

ILLUSTRATIONS

Page

Figure 1. Index map showing Outer Continental Shelf leasing areas

in the Gulf of Mexico off Texas and Louisiana........ 27

2. Bar graph showing number and volume of 1- to 50-barrel

spills, by year, 1971-75............................. 28

3. Schematic diagram showing casing program and production 

safety system of a typical 12,000*-foot-deep well, 

Gulf of Mexico....................................... 33

4. Simplified flow diagram for offshore oil and gas

production........................................... 34

5-10. Bar graphs showing:

5. Number and volume of 1- to 50-barrel spills, by 

year, 1971-75, for production platforms and 

for pipelines and pumps....................... 35

6. Principal causes of production-platform spills

of 1-50 barrels, by year, 1971-75............. 37

7. Principal causes of sump-system spills of 1-50 

barrels on production platforms, by year, 

1971-75....................................... 38

8. Number of 1- to 50-barrel spills involving 

failure of high-low level controls on 

production platforms, by year, 1971-75........ 39

9. Principal causes of pipeline and pump spills of 

1-50 barrels, by year and volume of spills, 

1971-75....................................... 40

10. Principal causes of pipeline and pump spills of 

1-50 barrels, by year and number of spills, 

1971-75....................................... 43

III
Page

Figure 11. Graph showing comparison, by year, of the number of 

structures having spills with the total number of 

fixed and major structures........................... 44

12. Bar graph showing estimated volumes of petroleum

hydrocarbons introduced annually into the world's 

oceans, in millions of metric tons................... 46

TABLES

Page

Table 1. Annual production of oil and condensate from all operations on the Outer Continental Shelf, 1971-75........ 27

2. Number and volume of spills each year, 1971-75, Gulf

of Mexico Outer Continental Shelf.................... 29

3. Causes of oil spills of more than 50 barrels, 1971-75.. 30

4. Causes of oil spills of 1-50 barrels, 1971-75.......... 30

5. Oil spills of more than 1,000 barrels, 1971-75......... 31

6. Blowouts resulting in pollution, casualties, or

property damage, 1971-75............................. 32

7. Causes of 1- to 50-barrel spills on production

platforms, 1971-75................................... 33

8. Causes of 1- to 50-barrel spills on production

platforms, 1971-75, grouped according to system

that failed.......................................... 36

9. Causes of 1- to 50 barrel spills from pipelines and

pumps, 1971-75....................................... 41

10. Frequency of spills among production platforms having

at least one 1- to 50-barrel spill during 1971-75.... 42

11. Production-platform spills of 1-50 barrels,

identified by operator, 1971-75...................... 45

12. Budget of petroleum hydrocarbons into the oceans....... 47

SYSTEM OF MEASUREMENT UNITS

[The following report uses the English system of units. The English 

units can be converted to metric units by multiplying 

by the factors given in the following list]

To convert 

English unit

Acres........

Barrels (oil)

Barrels (36° API oil) 

Cubic feet...........

Feet..............................

Miles, statute....................

geographical or nautical... 

Square miles, statute.............

Multiply by

0.4047 

4.047x10- 3 

0.159 

1.590xl0 2 

0.1342 

2.832x10- 2 

28.32 

0.3048

609

852

2.590

To obtain 

Metric unit

Hectares (ha). 

Square kilometers (km 2 ) 

Cubic meters (m 3 ). 

Liters (1). 

Metric tons. 

Cubic meters (m 3 ). 

Liters (1). 

Meters (m). 

Kilometers (km). 

Kilometers (km). 

Square kilometers (km2 )

IV
Oil Spills, 1971-75, Gulf of Mexico 

Outer Continental Shelf

By Elmer P. Danenberger

ABSTRACT

Oil spillage connected with federally supervised drilling and production activities has been a matter of wide public concern. In its 

supervision of mineral-resource development on the Outer Continental Shelf 

(OCS), the U.S. Geological Survey is responsible for the day-to-day 

inspection and monitoring of OCS oil and gas operations. During these 

activities, the U.S. Geological Survey records and investigates hydrocarbon discharges resulting from such operations. Beginning in 1971, all 

spills have been recorded, and a computer file has been maintained on all 

spills of 1 barrel or more.

The total Gulf of Mexico OCS oil spillage recorded during January 1, 

1971-December 31, 1975, amounted to 51,421 barrels. Production during that 

period amounted to 35,219 barrels per barrel spilled. In all, 5,857 spills 

were recorded, but 85.5 percent of the total spill volume was contributed 

by just 5 incidents. The environmental effect of these incidents apparently was minimal and of short duration. No spills of more than 50 barrels 

resulted from drilling operations during the period. The only spillage 

resulting from blowouts was caused by nondrilling incidents, including 

completion, production, and workover.

The amount of oil discharged from spills of less than 50 barrels 

decreased by more than half between 1971 and 1975. The improvement 

reflects changes in the operating philosophy of the offshore industry, 

tightening of U.S. Geological Survey operating orders, and substantial 

increases in the inspection force. Most production-platform spills involve
failures in the sump system, the separator system, or other hydrocarbonhandling equipment; improved sump-system designs and better high-low-level 

controls have reduced both the number and the volume of spills. Pipeline 

and pump spills also declined significantly, although the decline appears 

less attributable to revisions in OCS operating requirements. No operator 

consistently contributed a disproportionate amount of spillage. Most of 

the platforms having production spills had only one spill during the 

period. Of the 304 platforms having incidents, 255 had 2 spills or less 

and 188 had only 1 spill.

Comparison of the volume spilled with the volume produced for Gulf of 

Mexico OCS operations during 1971-75 results in a spillage rate of 0.0028 

percent. Spillage from tankers is estimated to be greater. The OCS 

drilling and production spillage rate is not expected to increase during 

exploration and development of the frontier areas.

INTRODUCTION

The Department of the Interior is authorized by the Outer Continental 

Shelf Lands Act of August 7, 1953, to grant mineral leases on Outer 

Continental Shelf (OCS) lands and to prescribe such regulations as might be 

necessary to carry out the provision of the act. After the 1973 oil 

embargo, in response to calls for "energy self-sufficiency," the Department expanded its Outer Continental Shelf oil and gas leasing program. The 

Bureau of Land Management has tentatively scheduled lease sales for 17 

areas before 1979. Thirteen of these areas have not yet been evaluated by 

exploratory drilling and are considered "frontier" (unexplored) areas. 

Public opinion toward these leasing programs ranges from expectation to 

apprehension and distrust; the concern arises from such matters as the 

likelihood of oil spills and the impact of these spills on the marine 

environment, valuable estuaries, commercial fishing, and tourism. This 

report summarizes statistics on oil spills during 1971-75 in the Gulf of 

Mexico and discusses the causes of these incidents and the damage that 

resulted.

The Gulf of Mexico (fig. 1) is now and has been for 30 years the 

world's most active offshore oil and gas area; since 1947, almost 13,000
wells have been drilled in Federal waters. During 1971-75, more than 1.8 

billion barrels of oil and condensate were produced from Federal lands in 

the Gulf (table 1); this was more than 10 percent of the nation's domestic 

crude oil production and approximately 15 percent of the natural gas 

production. At the end of 1975, approximately 65 mobile drilling units 

were operating in the Gulf in water depths as great as 1,775 feet. Oil and 

gas are currently being produced from 2,079 platforms in waters up to 373 

feet, and a steel tower is being constructed for a Gulf of Mexico site in 

water deeper than 1,000 feet. Subsea production systems, deepwater guyed 

towers designed to yield slightly to environmental forces, and other 

prototype equipment that are now being tested in the Gulf will greatly 

increase the capability of offshore development.

Although both onshore and offshore oil and gas operations were 

pioneered and developed in this country, few Americans are acquainted with 

actual oil and gas development practices, and some have misconceptions 

about the conduct of such operations. Oil spillage is a particularly 

emotional topic and can readily be misunderstood or distorted. The errors 

can arise from numerous sources. Study teams, though lacking sufficient 

statistical data, may seek to apply historical data to projections of spill 

estimates for "frontier areas." Definitions and statistics can intentionally be presented so as to generate an intended result. Oil-spill 

forecasts for frontier areas especially difficult to make may be 

influenced more by the forecaster's prejudices and understanding of the 

statistics than by the historical record. Interchanging statistical 

information from many different sources can lead to unreasonable conclusions. In some instances, frontier-area oil-spill forecasts have been 

expressed as high and low estimates for spills of several categories (such 

as drilling, production, and transportation). Addition of the high 

(maximum) estimates for each category gives unrealistically high estimates 

for total spillage. Other annual spillage forecasts are based on peak 

annual production for the oil field under consideration; multiplication of 

this maximum annual estimate by the anticipated years of production from 

the field gives an inordinately high estimate for total spillage. Similarly, some projected studies do not take into consideration technical
innovations that will be introduced, and other studies overcompensate for 

future improvements.

The absence of universally recognized definitions for such terms as 

"major spill," "minor spill," and "blowout," allows considerable latitude 

in categorizing incidents. One observer could justifiably say that there 

has only been 1 major pollution incident in the history of OCS operations, 

whereas another might with equal validity cite 30 incidents.

In its capacity as manager of leased lands on the OCS, the U.S. 

Geological Survey issued, effective August 28, 1969, OCS Order No. 7. This 

Order establishes pollution-prevention and waste-disposal requirements and 

requires that all spills, regardless of size, be reported to the U.S. 

Geological Survey. After issuance of this Order, the Survey significantly 

increased its field inspection staff and its contracted helicopter fleet, 

which enables regular, frequent inspection flights. The reporting 

requirements and the staffing increases were essential to establishing 

complete data on oil spills.

The first full year, 1970, of applicability of OCS Order No. 7, which 

established the requirements for reporting and recording spills, disclosed 

various shortcomings of the procedures. Reports on some spills were 

expressed in general terms such as "minor spill," rather than as the "best 

estimate" of the quantity spilled, which is essential for statistical 

analysis. The cause of the spill was not always identified or accurately 

recorded. Spill data for periods prior to 1971 are, therefore, of limited 

value, especially for minor spills. By the end of 1970, most of the spillreporting problems had been resolved.

The historical record on oil spills is utilized to forecast discharges 

in frontier areas, despite the questionable applicability, and such statistics provide one means of evaluating offshore oil and gas operations. 

Complete statistics on hydrocarbon discharges are maintained by the U.S. 

Geological Survey, in its role of supervising OCS oil and gas operations. 

Because of the public interest, these data are presented here for the years 

1971-75, for which statistics are complete.
SOURCES AND RELIABILITY OP DATA

Safety and pollution prevention are two major objectives of the U.S. 

Geological Survey OCS Lease Management Program. Meeting the objectives 

required establishing an effective oil-spill and accident-report data 

base. At the request of the Survey's Director, the Water Resources 

Division reviewed the Conservation Division's Lease Management Program; 

this study (U.S. Geological Survey, 1972) led to development of an OCS 

Events File, which utilizes the General Information Processing System 

(GIPSY), an information-handling tool developed at the University of 

Oklahoma. This computer file, which is updated monthly, encompasses 

information on all spills of 1 barrel or more, blowouts, fires and 

explosions, fatalities, and miscellaneous accidents; the data for each 

incident consist of date, location, type of operation, probable causes, and 

a brief description of the event.

The compilation of spill data, by cause, presented in tables 3,4, and 

7-9, is derived from the OCS Events File. The annual breakdown of oil 

spills by size (table 2) was compiled from the monthly reports on Gulf of 

Mexico OCS operations. For spills of 50 barrels or more, the total number 

and volume of spills as compiled from the Events File (table 3) correlates 

precisely with the more-than-50-barrel-spill totals from table 2.

Table 4, derived from the OCS Events File, shows 872 spills of 1-50 

barrels. Fifteen of those incidents are in both the pipeline and 

production-platform categories. Another seven spills were each 50 

barrels, resulting in an actual Events File count of 850 incidents 

involving 1-49 barrels. These compare with 887 such incidents compiled 

manually from the operations reports. The two data sources agree within 1 

percent on a volume-spilled basis. '

The above figures indicate that the two data sources agree and that 

virtually every incident has been recorded in the Events File. How well 

are oil-spill incidents being reported? The reporting depends to a large 

degree on the cooperation of the operators. This reporting is supplemented
by U.S. Geological Survey inspection and surveillance. At least 10 

inspection teams operate daily offshore, weather permitting; for example, 

during 1975, 3,388 pollution-surveillance flights were made. Any slicks or 

other indications of pollution are reported immediately by the inspection 

team, and an attempt is made to identify the source of such discharge. If 

the pollution is emanating from an offshore production facility, the faulty 

piece of equipment or the entire platform is shut-in at once. Any willful 

violators of regulations regarding discharge are subject to criminal 

prosecution by the Department of Justice.

U.S. Geological Survey field engineers and technicians believe that 

the offshore operators have been diligent in adhering to the spillreporting requirements of DCS Order No. 7. Although some minor spills may 

go unreported, an operator has, from a regulatory standpoint, little 

incentive not to comply with reporting requirements. The enforcement 

action resulting from a reported minor oil spill is if there are no 

aggravating circumstances an order to shut-in, whereas failure to report 

an incident could lead to criminal prosecution. The sustained increase in 

the number of less-than-1-barrel spills reported during 1971-75, in contrast to the declining number of larger spills, supports the contention 

that spill reporting became more complete during the 5 years.

Many of the oil slicks detected in the Gulf of Mexico are not related 

to oil and gas operations but result from discharges from tankers, commercial fleets, natural seeps, and other unrelated sources (table 12).

Determining the amount of oil spilled can be difficult. In many 

instances, the volume of the spill can be accurately determined, by 

measuring the differentials between successive meters, measuring the 

volume changes in production-equipment contents, knowing the flow rate's 

into the various pieces of platform equipment and the overflow period, and 

other means of detecting losses.from the closed-production system. Volumes 

discharged from blowouts commonly can be estimated from production history 

(if available), well tests, and other reservoir data. If no precise means 

of measuring is available, the quantity discharged can be estimated from 

the size and appearance of the slick. For example, a barely discernible 

slick might contain only 25 gallons of oil per square mile, whereas a dark6
brown slick could amount to more than 1,300 gallons per square mile. The 

estimate must also take into consideration natural processes acting upon 

the spill, such as weathering, solubility, emulsification, and biodegradation. Therefore, the reliability of visual estimates is low, and 

estimates on 1 spill can vary by 100 percent or more. In the past, no 

effort has been made to evaluate the precision of the discharge estimate. 

A means of rating the objectivity of an estimate on a scale of 1 to 10 is 

being considered, whereby a precise volume determined from meter differentials would receive an accuracy rating of 10, and a rough estimate based on 

the size and appearance of the slick would be rated as 1. This scale would 

provide a clearer picture of the accuracy of the volumetric determinations 

and would allow maximum- and minimum-discharge calculations based on the 

best estimates of spillage.

MAJOR SPILLS

The total Gulf of Mexico OCS oil spillage recorded during 1971-75 was 

51,421 barrels (table 2). Gulf of Mexico OCS oil and condensate production 

during the 5 years totaled 1.811 billion barrels (table 1); 1971, 1972, and 

1973 were the 3 highest production years in the history of Gulf of Mexico 

OCS operations. During the 5 years 35,219 barrels were produced per barrel 

spilled. l The total value of the oil and gas produced from both the Gulf of 

Mexico and the Pacific OCS during 1971-75 was $14.3 billion; in that time, 

the Federal Government received $13.9 billion in rentals, royalties, and 

bonuses a large share of the revenues generated by OCS operations. The 

bonuses paid to the Government for the right to explore and develop OCS

This spill figure applies only to the Gulf of Mexico OCS. At present 

the only other offshore production in Federal waters is in the Santa 

Barbara Channel, where 104.7 million barrels of oil were produced during 

1971-75. No spills of more than 50 barrels occurred in the Channel during 

the period. The only chronic discharges are related to oil seeps. Seepage 

around platform A in the Channel, triggered by the 1969 blowout, continues 

at a rate of 4-5 barrels per day. Hundreds of natural oil and gas seeps 

exist in the Channel and discharge an estimated 200-250 barrels per day 

(Fisher, 1975) . The Coal Oil Point area is the most active seep area, 

venting an average of about 50-70 barrels per day (Alien and Schlueter, 

1969).
tracts amounted to $11.5 billion, resulting in Government revenues equal to 

97 percent of production value.

Of the 5,857 spills recorded during the 1971-75 period, just 5 spills 

contributed 85.5 percent of the total volume spilled (table 5). A 

single incident the Bonita pipeline break in April 1974 accounts for 

38.6 percent of the total volume. Success in oil-spill prevention during a 

particular year, from a volumetric standpoint, depends almost entirely on 

preventing big spills. Of course, the oil-spill record cannot be evaluated 

merely from the total volumes discharged. The number of events, the cause 

and severity, and the intermediate- and long-term trends must be examined. 

For example, 1974 was the worst of the 5 years in terms of total volume 

spilled (table 2). However, only 667 barrels was spilled during the year 

as a result of less-than-50-barrel incidents, the best record of the 5 

years. These small spills (discussed later in this report) provide a much 

better yardstick of the effectiveness of operating requirements, of the 

equipment that is prone to failure, and of changes in offshore "housekeeping" and spill-prevention programs.

Furthermore, the effect of equivalent-volume spills varies widely, 

depending on the physical and chemical composition of the petroleum, the 

physiography of the area, weather conditions at the time of the spill, the 

biota of the area, the time of year, previous exposure of the area to oil, 

exposure to other pollutants, and the treatment of the spill (Straughan, 

1972).

Petroleum is a complicated mixture of compounds which contain hydrogen and carbon as the principal elements. Crude oils and their byproducts 

have amazingly complex physical and chemical properties that influence the 

manner in which they interact with the environment. Recent investigations 

by Anderson (1975) and the Battelle Pacific Northwest Laboratories (1973) 

show crude oils to be significantly less toxic than are refined products. 

This difference accounts in part for the minimal environmental damage 

recorded from OCS operations spills. Significant damage resulted from only 

one incident on the Outer Continental Shelf, the January 1969 blowout at 

platform A in the Santa Barbara Channel, and, apparently, the impacts were 

short lived. A study conducted by the Allan Hancock Foundation, University

8
of Southern California (Straughan, 1971), found that flora and fauna in the 

Channel were damaged much less than had been predicted, and that the area 

is recovering well. The only environmental damage recorded as a result of 

the 5 largest spills in the Gulf of Mexico (table 5) during the 5 years 

occurred when minor amounts of oil intermittently reached approximately 

1,000 feet of beach on the Chandeleur Islands after the September 9, 1974, 

Cobia pipeline break. On only two occasions prior to 1971, both in 1970, 

did minor amounts of oil reach the coastline after Gulf of Mexico DCS oil 

spills. Few bird deaths or other obvious forms of environmental damage 

have been attributed to DCS oil and gas operations in the Gulf.

Four of the five spills in 1971-75 which exceeded 1,000 barrels were 

related to transportation of oil from OCS production facilities (table 5). 

Of the 20 spills of more than 50 barrels (table 3), 9 were transportation 

incidents, and 6 were caused by failures in production-platform equipment. 

Of course, production-platform operations and transportation activities 

span the entire range of regular offshore-production activities and can, 

logically, be expected to account for most of the spillage. Spills of 50 

barrels or more yielded 90.6 percent of the total volume discharged during 

1971-75, and 96.0 and 97.1 percent, respectively, for 1973 and 1974. In 

1971, 1972, and 1975, when no spill exceeded 500 barrels, the more-than-50- 

barrel spills account, respectively, for only 46.3, 12.7, and 27.2 percent 

of the total volume spilled.

Particularly noteworthy is that no spills of more than 50 barrels 

resulted from drilling operations during 1971-75, even though 4,105 new 

wells were started. No such spill has occurred since July 19, 1965, when 

1,688 barrels of crude oil was discharged into the Gulf during a blowout in 

the Ship Shoal area off the coast of Louisiana. (An oil blowout which 

began on March 16, 1969, though technically a nondrilling incident, could 

be classified with the drilling events. The well had been drilled to total 

depth, and control was lost during completion operations when the rig 

shifted during a storm; 2,500 barrels was discharged through the tubing.) 

Furthermore, no spill in excess of 50 barrels has been recorded during 

exploratory drilling either on the Federal OCS or, to our knowledge, in any 

other offshore area throughout the world. Nevertheless, exploratory
drilling is often labeled as environmentally the most hazardous aspect of 

offshore operations. The record does not support such contentions.

Some analyses of offshore accidents combine all blowouts into one 

category and assume that they are related to drilling operations. Then the 

total number of wells drilled during a given period is simply divided by 

the total number of blowouts, to derive a figure showing wells drilled per 

blowout. In similar manner, the oil discharged from these blowouts is 

divided by the number of wells drilled, to obtain a figure showing barrels 

spilled per well drilled. The resulting figures are misleading, because 

many of the blowouts and much of the resulting spillage did not result from 

drilling operations. It is therefore incorrect to use these figures to 

predict, from a forecast of the number of wells to be drilled, the number 

of blowouts and the amount of spillage which will result from offshore 

activity. For frontier areas, where operations may never advance past the 

exploratory drilling stage, the system of projection is particularly 

unsatisfactory.

During 1971-75, 22 blowouts occurred during drilling, workover, or 

production. Nine of the 22 caused significant pollution or property 

damage. Of the nine (table 6) , five were associated with drilling 

operations. However, the 4 nondrilling incidents were responsible for all 

725 barrels of "blowout spillage." According to OCS blowout records, which 

go back to 1956, only two drilling-related blowouts caused significant oil 

spills the Santa Barbara blowout, during which at least 25,000 barrels of 

oil was discharged, and the previously mentioned July 1965 Gulf of Mexico 

blowout. The two most serious blowouts in the Gulf of Mexico OCS occurred 

in 1970 on production platforms and discharged more than 83,000 barrels.

MINOR SPILLS

The aggregate volume of less-than-50-barrel spills accounts for only 

9.4 percent of the total spillage; numerically, 99.5 percent of the spills 

are in this quantity category. The great number of such spills 5,830 

during the 5 years allows a more detailed statistical analysis and a more 

reliable observation of trends. The amount of oil discharged from these 

spills was reduced by 52 percent between 1971 and 1975. Discharges from 1-

10
to 14-barrel incidents decreased by 66 percent during that time. If all 

spills of 1-50 barrels are considered (fig. 2), the reduction in discharge 

volume between 1971 and 1975 is 70 percent. (Seven spills discharged 50 

barrels each.)

Although 1975 Gulf of Mexico OCS oil and condensate production was 19 

percent less than in 1971, production facilities have steadily increased. 

Therefore, reduced production is unlikely to have contributed to the 

improved oil-spill picture. The number of OCS platforms in the Gulf of 

Mexico increased from approximately 1,800 at the end of 1970 to 2,079 on 

December 31, 1975; the total number of completions jumped from 8,667 to 

10,274. Despite the production decrease, the increases in surface equipment would increase the failure probability.

The reduction in minor spills is largely attributable to changes in 

operating and regulatory philosophy as industry and Government responded 

to public concerns about the environment. Three serious incidents the 

Santa Barbara blowout and two major fires in the Gulf of Mexico occurred 

sequentially during 1969 and 1970 and drastically affected the conduct of 

OCS operations. The offshore industry was under the constant scrutiny of 

legislators, scientists, and other concerned citizens who formerly had 

given little thought to offshore oil and gas operations. Industry reacted 

quickly to improve its public image, examining its offshore operating 

procedures and initiating safety programs to prevent the recurrence of 

Santa Barbara-type pollution spectaculars.

The abruptly heightened public interest also affected the regulatory 

role of the U.S. Geological Survey. New operating requirements in the 

form of OCS Orders pertaining to drilling procedures, subsurface safety 

devices, platform safety and production equipment, and oil and gas pipelines were instituted. The inspection force of 7 technicians was 

increased approximately 700 percent between 1969 and 1975. The total 

inspection staff including technicians, engineers, and other support personnel increased tenfold. Numerous additional changes were made in U.S. 

Geological Survey regulatory programs.

OCS Order No. 8, which outlines platform safety and pollution-control 

requirements, and OCS Order No. 9, which deals with OCS pipelines, were,

11
when combined with industry's own efforts, very effective in reducing tht 

number of spills. As shown in table 4, almost 60 percent of the spillage 

from 1- to 50-barrel incidents is related to production-platform events. 

The largest number of spills were caused by failures in the sump system, 

separator system, and other hydrocarbon-handling equipment (table 7).

OCS Order No. 8 reflects the results of a study of all safety systems 

then in effect and selection of those devices that seemed least susceptible 

to failure. Redundant systems are required, in many instances. If one 

piece of equipment fails, all connected equipment is shut-in. Earlier 

regulations governing OCS production had been general in nature, allowing 

operators considerable latitude in judgment factors; each company had its 

own philosophy concerning safety practices and clean operations. Standardization of antipollution and safety procedures has had a leveling effect 

on all operators. Now each facility must meet the same requirements, 

regardless of size, distance from shore, value, or other criteria. Figures 

3 and 4 show some of the safety equipment which is required on an OCS 

production platform.

Production-Platform Spills

Minor production-platform discharges declined during 1971-75; the 

particularly sharp drop in 1972 corresponds with the implementation of OCS 

Order No. 8, which became effective on October 30, 1970, and allowed 1 year 

(until October 30, 1971) for full compliance. The number and volume of 1- 

to 50-barrel platform spills decreased by 45.9 percent and 49.3 percent, 

respectively, during 1972 (fig. 5). Each platform-spills category, 

including sump and separator systems, well and header system, and other 

hydrocarbon-handling equipment, showed significant declines in 1972 (fig. 

6). The "other hydrocarbon-handling equipment" category primarily comprises surge-tank and production-tank incidents. The spill-volume decline 

continued through 1975; the number of spills tended to level off in 1975. 

Between 1971 and 1975, the number and volume of production-platform spills 

declined by 75.9 percent and 81.6 percent, respectively (fig. 5). The 

larger reduction in spill volume, as compared with the reduction in number 

of spills, indicates that the spills which are occurring are smaller and

12
possibly that the 1- and 2-barrel incidents are being more diligently 

reported. This trend is particularly noticeable in 1975 as the number of 

production-platform and pipeline and pump spills increased slightly, while 

the volumes continued to decrease.

Most of the production-platform spills are related to failures in the 

sump system, the separator system, or other hydrocarbon-handling equipment 

(tables 7, 8). Both closed sumps and open-ended sump piles are utilized in 

the Gulf of Mexico to collect the deck drainage and the produced water. 

From an environmental standpoint, the closed tanks are generally considered to be preferable. The oil is skimmed from the closed tank and 

recycled through the low-pressure-separation system, and the water is 

discharged into the Gulf. Nevertheless, these systems are not problemfree; and if the tanks and sump pumps are too small, heavy rains can cause 

hydrocarbons to overflow.

The sump piles are generally long pipes or tanks, open at the bottom, 

that extend well beneath the water surface. Hydrocarbons are skimmed from 

the tank and rerouted through the production system, while clarified water 

is discharged into the Gulf. Problems result when a surge of oil from an 

overflowing piece of production equipment overloads the sump, when sump 

pumps fail to operate, when heavy rains overload the sump allowing oil to 

flow from the open end, and when high-level controls fail, allowing the 

sump to overfill. The open-ended sumps can be particularly troublesome in 

shallow water because of the reduced hydrostatic head and the increased 

effect of wave action.

The number of sump-related spills decreased substantially between 

1971 and 1974 and increased slightly in 1975 (figs. 6, 7). This improvement is largely a result of operator initiatives stemming from OCS Order 

No. 8 and company policy changes. New closed-tank sumps and combination 

sump tank-sump pile systems were installed on certain platforms. Effluents 

containing significant oil concentrations are routed to separate oil 

sumps. The decline in the "carry under or overfill" incidents reflects 

these changes. The newer production platforms incorporate more elaborate 

treatment schemes. On certain large platforms, an oil sump tank collects 

oil from all pressure drains and pumps it to the production surge tanks.

13
The water drains carry fluids to another closed sump tank. The effluent 

from the drain sump tank is pumped to a dirty-water surge tank. Oil 

skimmed from this tank is routed to the oil sump. The water is piped to a 

gas flotation unit, which lowers the oil content below 50 parts per 

million, and is then pumped to a clean-water surge tank. Oil is skimmed 

from the flotation unit and from the clean-water surge tank and is piped to 

the oil sump. Water from the clean-water surge tank is finally discharged 

into the receiving waters through a disposal tube. Obviously, this is an 

effective and elaborate sump system. Nevertheless, for old platforms which 

have been using open-ended sumps for years and are producing from fields in 

their twilight years, requiring installation of such an elaborate system is 

difficult to justify. Inasmuch as these platforms have been producing for 

years with no apparent adverse environmental impact and, further, the costs 

of installing elaborate drainage-treatment systems could significantly 

reduce ultimate resource recovery, the U.S. Geological Survey has not 

required extreme changes in these systems. Proposed Environmental Protection Agency regulations pursuant to the Federal Water Pollution Control Act 

do, however, specify that deck-drainage discharges meet the same oil 

limitations which apply to produced waters.

The major single cause of spills in the separator system and other 

hydrocarbon-handling equipment is the failure of high-level controls 

(table 8). The internal float devices required by OCS Order No. 8 are 

designed to automatically shut-in production when the tank fills to a 

specified level. During 1971-75, 126 spills in the 1- to 50-barrel 

category involved high-low level control failures. However, the number of 

these spills has declined sharply (fig. 8). Order No. 8 requires operators 

to submit to the U.S. Geological Survey semiannual records showing the 

present status and past history of each device including dates and details 

of inspection, testing, repairs, adjustment, and reinstallation. Testing 

of high-level controls may be difficult; in many separators and production 

vessels, filling the tank is required to activate and test the high-level 

controls, a time-consuming procedure. Because of the number of items which 

must be inspected, conducting this test may be impractical for operators 

and inspectors, and the test is often bypassed. In recent years, many

14
operators have been installing high- and low-level sensors in external 

columns that can be isolated from the vessel. This isolation permits the 

devices to be tested without interrupting production. The increase in 

these external controls probably contributed significantly to the decline 

in spills resulting from high-low level control failures. The revised 

version of OCS Order No. 8 requires that operators install the sensors in 

external columns unless solids deposition or foaming hinders activation of 

the device.

Much of the reduction in production-equipment incidents is attributed 

to the implementation schedule of OCS Order No. 8. Operators were given 

only 3 months from the October 30, 1970, effective date to comply with most 

of the provisions regarding automatic shut-in valves, pressure- and 

liquid-level sensors, and sump systems. Because of the short time allowed, 

much of the equipment was installed hastily and unsatisfactorily. Once the 

facilities were equipped to meet the Order's requirements, many of the 

systems were redesigned, and neater, more effective components were 

installed. The spill statistics reflect these improvements.

Pipeline And Pump Spills

The decline in pipeline and pump incidents (fig. 5) is not so clearly 

attributable to revisions in the OCS Orders. Although OCS Order No. 9, 

"Oil and Gas Pipelines," which became fully effective in early 1971, 

undoubtedly contributed to the sharp decline in incidents during 1972, most 

of the improvement appears to be related to better platform management. In 

1972 the total number and volume of these incidents dropped 30.6 and 40.0 

percent, respectively, from 1971 levels. The respective declines between 

1971 and 1975 were 56.9 and 64.6 percent. The major causes of pipeline and 

pump spills (table 9; fig. 9) are (1) pipeline ruptures and breaks, (2) 

pipeline pump failures, (3) discharge or transfer line ruptures or coupling 

failures, and (4) miscellaneous incidents. Improvement in the latter two 

categories (figs. 9, 10) is primarily responsible for the sharp reduction 

in pipeline and pump spills between 1971 and 1975. Improvements in these 

two categories are probably more directly related to "good housekeeping" 

than to OCS Order No. 9. Because many of the pipelines in the Gulf of

15
Mexico are old, a significant reduction in minor pipeline leaks could not 

be expected to result from implementation of Order No. 9. Improvement is 

expected as inspection programs improve and as advanced cathodic protection and monitoring systems are used.

There is also no indication of a consistent decline in events related 

to pump failures. Half the 42 pump spills (table 9) resulted from 

mechanical failures (seal, housing , packing, or piston head burst; union or 

plunger failed). One-fourth the pump spills also involved high-level 

control failures. When a pump is deactivated, the production vessel which 

precedes the pump in the flow scheme normally a surge or storage tank may 

begin to overfill. When the fluid in the tank exceeds a specified level, 

the high-level float required by OCS Order No. 8 should automatically shutin the incoming production. Therefore, 10 of the pump spills could have 

been prevented had the high-level control operated properly. In three 

other instances, the high-level control was activated, but a surface safety 

valve on one of the wells failed, allowing production to continue.

Even though the number of pump spills has not steadily declined (fig. 

10), the low number of these spills 2 in 1974 and 4 in 1975 relative to 

the tremendous volumes of hydrocarbons being handled indicates the general 

success of the equipment. Three of the 1975 incidents occurred because 

hydrocarbons continued to flow through damaged pumps when a plate loosened, 

when a plunger broke, or when a face gasket blew. Only 1 of-the 1975 pump 

spills involved the failure of a high-level control.

Spills Of Less Than 1 Barrel

The less-than-1-barrel spills were the only group to steadily 

increase during 1971-75 (table 2). These spills increased by 15 percent 

between 1971 and 1974 and decreased slightly in 1975. Much of this 

increase can probably be traced to more conscientious interpretation of OCS 

Order No. 7, which requires that operators report all spills. Operators 

are now very diligent in their observance of this requirement, sometimes 

reporting spills as small as 1 pint. Statistics are not maintained on the 

total volume discharged in spills of less than 1 barrel. For record16
keeping purposes, it is assumed that one-fourth barrel (10.5 gallons) is 

discharged in each incident. Inasmuch as many of the incidents involve 

several gallons or less, this volumetric approximation probably represents 

a maximum figure for these spills.

Production Incidents, By Operator

table 11 identifies, by operator, production-platform spills of 1-50 

barrels. This limited analysis is one means of evaluating the effectiveness of regulatory changes and modifications in platform-management. The 

column showing each operator's oil production for fiscal year 1975 (July 1, 

1974-June 30, 1975) indicates the magnitude of that operator's activities. 

The amount of oil production is only one factor in contrasting oil spills 

by operator. A complete analysis would, of course, consider many other 

factors, such as the amount of condensate production, the number of oil and 

condensate production platforms and the production per platform, the age of 

the fields and their production facilities, the types of spills, and the 

sources of spills (whether clustered at one field or scattered).

The 1- to 50-barrel production-platform incidents were tabulated 

(table 11) because these are the most frequent type of spill and the type 

which OCS Order No. 8 was designed to curtail. They also give same 

indication of the success of each operator's housekeeping programs. The 

individual trends for most operators correspond to the general trend (fig. 

5) for production-platform spills. The number of spills generally declined 

between 1971 and 1975, with a consistent sharp decline in spills between 

1971 and 1972. As expected, more spills are attributable to the large 

producers. No operator consistently contributed a disproportionate amount 

of spillage. The 1975 statistics are particularly encouraging: no single 

operator discharged more than 50 barrels.

The only 2 spills of more than 50 barrels in 1975 were related not to 

faulty operating practices on the platform but to workboat mishaps. In 

March a workboat bumped a platform and spilled 166 barrels of diesel fuel; 

and in September an anchor ship pulled an anchor too close to the drillship 

and ruptured a diesel fuel tank, spilling 100 barrels.

17
Production Incidents, By Platform

The 536 chronic (1-50 barrels) production-platform incidents during 

1971-75 were divided among 304 platforms (table 10) . Figure 11 relates the 

number of structures having spills to the total number of fixed structures 

and the number of major structures. A major structure is defined as 

having two or more pieces of production equipment (vessels other than test 

separators) and (or) more than five producible completions. Nearly all the 

production incidents occurred at major platforms. In 1971 structures 

having spills represented 19 percent of the estimated number of major 

structures. That figure declined to 3.6 percent in 1974 and 4.2 percent in 

1975.

To determine what percentage of the major platforms were actually 

producing or handling production from other platforms, the Gulf of Mexico 

platform file was examined. At the end of 1975 there were no producing 

wells on 117 of the 1,020 major platforms; 67 of these 117 nonproducing 

platforms were, however, being utilized for hydrocarbon separation and 

handling. Therefore, all but 50 (4.9 percent) of the major platforms were 

"candidates" for oil spillage at that time. The remaining 50 major 

platforms were in development-drilling or abandonment stages or were 

temporarily shut-in for mechanical reasons.

At the end of 1975, 1,202 structure complexes had at least 1 producing 

completion. The term "structure complex" is used because at some sites 

production equipment, personnel living quarters, and other facilities are 

separated onto several platforms attached by walkways. At the end of 1975 

there were 1,786 complexes comprising 2,079 platforms. The ratio of the 

number of platforms with 1975 production spills (43) to the number of 

producing complexes at the end of 1975 was 0.036 (fig. 11).

Of the 304 platforms having production spills during 1971-75, 188 

platforms had only 1 spill (table 10). Thirteen platforms had at least 5 

spills, with the maximum being 12. Of these 13 platforms, only 2 had more 

than 1 spill during 1974-75. Eight of the 13 had all their spills in 1971- 

73 and none in 1974-75.

18
OTHER SOURCES OF SPILLAGE

Comparison of volume spilled to volume produced for Gulf of Mexico DCS 

Operations (drilling, production, and transportation) during 1971-75 discloses a spillage rate of 0.0028 percent. According to the Council on 

Environmental Quality (1974) the historical spillage rate for tankers is 

0.016 percent, more than 5 times the rate for Gulf of Mexico OCS operations. This estimate is for tankers of international registry, and it is 

generally accepted that U.S.-registration vessels have a better record. 

Furthermore, the development of deepwater ports, the application of new 

regulations restricting tanker discharges, and the application of new 

technology should significantly reduce the tanker-spillage rate.

The National Academy of Sciences (NAS) has estimated the sources of 

petroleum hydrocarbons entering the oceans (table 12; fig. 12). Only 1.3 

percent of these hydrocarbons are attributed to offshore production. The 

NAS best estimate for annual discharges from offshore production is 0.08 

million metric tons, or approximately 600,000 barrels. This estimate is 25 

to 600 times the annual spillage for the Gulf of Mexico OCS in 1971-75. 

Almost two-thirds of the world's offshore production platforms, almost 

one-half of the world's offshore drilling activity, and approximately oneeighth of the offshore production occurred on the Gulf of Mexico OCS (1974 

figures); thus, the NAS spillage estimate for offshore operations is by no 

means conservative and is probably somewhat too high. The NAS estimates 

that tanker discharges account for almost 2.13 million metric tons annually, or almost 16 million barrels. At present production rates, this 

equals the total oil and condensate production from the Gulf of Mexico OCS 

for 17 days.

The NAS also estimates that 0.6 million metric tons, or 4.5 million 

barrels, is discharged annually from natural seeps, more than 7 times the 

spillage attributed to offshore production. According to Fisher (1975), an 

estimated 70 thousand to 90 thousand barrels the equivalent of the 1969 

Santa Barbara spill and several times the maximum annual Gulf of Mexico 

spillage seeps annually into Santa Barbara Channel waters.

19
These figures give perspective to the broad problem of spills. They 

are not intended to minimize the potential for localized environmental 

disturbances from OCS activities or to excuse operations-related spillage 

or careless drilling and production practices; nonetheless, they do 

indicate that even if the hydrocarbon-discharge rate from operation 

activities approaches zero, tremendous volumes of hydrocarbons still will 

enter the oceans.

CONCLUSIONS

The spill statistics serve as a means of evaluating the effectiveness 

of U.S. Geological Survey regulatory programs and pinpointing problem 

areas and research needs. Also, the public should be informed on the 

nature of offshore oil and gas operations, including the potential for oil 

spills and other environmental impacts. The more detailed oil-spill data, 

together with the growing body of information on the biological impacts of 

crude discharges, will allow better cost-benefit analyses and a more 

rational evaluation of offshore oil and gas leasing programs.

The assumption is often made that the more severe oceanographic and 

meteorological conditions in frontier areas, such as the Gulf of Alaska and 

the North Atlantic, will cause more oil-spill incidents than have occurred 

in the Gulf of Mexico. This probably will not happen. Operators in these 

frontier areas will, from the outset, assess the resource potential by 

means of exploratory drilling. Very few spills have occurred during 

drilling and even fewer during exploratory drilling. No significant 

spillage has resulted from oil and gas operations in the harsh environment 

of the North Sea, where approximately 800 wells have already been drilled.

Development and production operations in the frontier areas will 

differ somewhat from those in the Gulf of Mexico. Owing to the tremendous 

costs of development, only major fields will be commercially exploited. 

Production facilities will more closely resemble those utilized in the 

North Sea than those operating in the Gulf Of Mexico. In the Gulf of 

Mexico, more than 2,000 structures (many of which are single-well "satellites") are producing from over 1,600 oil reservoirs and approximately 

1,200 gas reservoirs. Most of these reservoirs are small and have an

20
average of less than two completed wells. Only 4 Gulf of Mexico fields 

produced an average of more than 50,000 BOPD (barrels of oil per day) 

during 1974 the Bay Marchand Block 2 Field (in State and Federal waters. 

South Timbalier area), West Delta Block 30 Field, Eugene Island Block 330 

Field, and Grand Isle Block 43 Field. By contrast, fields in the North Sea 

are far fewer and much larger. At least 10 fields in just the British 

sector of the North Sea will have peak daily productions in excess of 

50,000 barrels, 6 will exceed 100,000 BOPD, and at least 4 will ultimately 

produce more than 200,000 BOPD. North Sea steel and concrete towers are 

designed to accommodate a large number of wells and high production 

volumes. The $330 million Brent B platform is expected to produce as much 

as 160,000 BOPD. Although the Gulf of Alaska and the Atlantic Coast areas 

probably will be less productive, large fields and North Sea-type structures will be necessary for commercial exploitation. The enormous size and 

expense of the facilities dictate that only the best production and safety 

equipment and operations personnel be used. The chance of failure is 

believed to be less because more production will be processed by less 

equipment. All safety and pollution-control equipment will be designed as 

an integral part of those platforms, rather than being added after many 

years of production. The redundancy which has been added to Gulf of Mexico 

systems will be original equipment for the frontier areas. Platform 

drainage systems will be fitted to the requirements of the structure, and 

no open sumps will be permitted. Pipeline systems will be protected by the 

latest cathodic protection systems and automatic volumetric sensors. New 

equipment is being developed for detecting pipeline corrosion by pumping 

special ultrasonic tools through the line. Reductions in the relative 

number and severity of oil spills in the frontier areas can reasonably be 

expected, should these areas prove productive.

Though continuing to seek a reduction in unnecessary discharges of oil 

and other liquid and solid waste materials from OCS structures, we must 

acknowledge the practical limitations to these discharge reductions. For 

example, there have been no indications of biological impacts from discharges of produced waters with an oil content of approximately 50 parts 

per million from OCS platforms. Such discharges quickly disperse to

21
nontoxic levels in the low parts per billion range. Hydrocarbons present 

in these concentrations feed microbial oxidizers and may be beneficial. 

Some researchers determined, in laboratory experiments, that hydrocarbons 

present in seawater in concentrations less than 30 parts per billion 

actually stimulated phytoplankton growth (Gordon and Prouse, 1973). 

Lowering the hydrocarbon levels in formation-water discharges is technically feasible, but the resulting increase in costs and the loss in energy 

output are difficult to reconcile.

Although a cost-benefit approach may be both difficult and publicly 

unacceptable when the issues involve ocean-floor disturbances to sea life, 

conflicts with commercial fishing, and disturbances to onshore species and 

migratory fish and mammals, application of expensive restrictions should 

be preceded by demonstrable evidence that some benefit will indeed result. 

Efforts to protect valuable environmental resources have at times imposed 

restrictions based more on emotions than on scientific thought. Admittedly, restrictions against needless discharges must be diligently 

enforced, and additional environmental research and protection funds 

should be directed toward solving specific problems. In conjunction with 

the National Research Council Marine Board, Straughan (1975) outlined such 

a problem-oriented approach.

This report has presented statistics on one important problem associated with offshore oil and gas production. Similar statistical files will 

be developed to monitor operations in frontier areas. The frequency of 

inspections will be increased for initial exploratory operations in these 

areas. The causes of oil spillage in all offshore areas will be constantly 

examined, and efforts made to reduce them. Further modifications in the 

data system will better identify trouble areas.

SELECTED REFERENCES

Adams, M. V., John, C. B., Kelly, R. F., LaPointe, A. E., and Meurer, 

R. W., 1975, Mineral resource management of the Outer Continental 

Shelf: U.S. Geol. Survey Circ. 720, 32 p. [reprinted 1976].

Alien, A. A., and Schlueter, R. S., 1969, Estimates of surface pollution 

resulting from submarine oil seeps at Platform A and Coal Oil Point: 

Santa Barbara, Calif., General Research Corp. Tech. Memo. 1230, 43 p.

22
Anderson, J. W., 1975, Laboratory studies on the effects of oil on marine 

organisms An overview: Am. Petroleum Inst. Pub. 4249, 70 p.

Battelle Pacific Northwest Laboratories, 1973, Effects of oil and

chemically dispersed oil on selected marine biota A laboratory

study: Am. Petroleum Inst. Pub. 4191, 104 p.

Fisher, P. J., 1975, Natural gas and oil seeps, Santa Barbara Basin, 

California: California State Univ. at Northridge, Dept. Geosciences, 

spec. rept. prepared for Natl. Oceanic and Atmospheric Admin., Sea 

Grants 04-3-158-45, 04-5-158-20, 37 p.

Fisher, P. J., and Stevenson, A. J., 1973, Natural hydrocarbon seeps along 

the northern shelf of the Santa Barbara Basin, California: Offshore 

Technology Conf., 5th Ann., Houston, Tex., 1973, Paper 1738, 10 p.

Garvey, Gerald, 1972, Energy, ecology, economy: New York, W. W. Norton and 

Co., 235 p.

Gordon, D. C., Jr., and Prouse, N. J., 1973, The effects of three different 

oils on marine phytoplankton photosynthesis: Dartmouth, Nova Scotia, 

Bedford Inst. Oceanography.

Harris, W. M., Piper, S. K., and McFarlane, B. E., compilers, 1976, Outer 

Continental Shelf statistics Oil, gas, sulfur, salt, leasing, 

drilling, production, income, 1953 through 1975, calendar year 1975: 

U.S. Geol. Survey Conservation Div. Spec. Rept., 91 p.

McCulloh, T. H., 1969, Geologic characteristics of the Dos Cuadras offshore 

oil field [California], in Geology, petroleum development, and 

seismicity of the Santa Barbara Channel region, California: U.S. 

Geol. Survey Prof. Paper 679-C, p. 29-46.

National Academy of Sciences, 1975, Petroleum in the marine environment A 

report by the Ocean Affairs Board on the inputs, fates, and the 

effects of petroleum in the marine environment (Conf. at Airlie, Va., 

May 21-25, 1973): Natl. Acad. Sci., 107 p.

Sharp, J. M., and Tyson, J. W., compilers, 1974, The offshore ecology 

investigation Final project planning council consensus report: 

Galveston, Tex., Gulf Universities Research Consortium (GURC) Rept. 

138, 39 p.

Smith, R. A., Slack, J. R., and Davis, R. K., 1976, An oilspill risk 

analysis for the Mid-Atlantic Outer Continental Shelf lease area: 

U.S. Geol. Survey Open-File Rept. 76-451, 24 p.

Staff, Offshore (Magazine), 1975, Worldwide drilling and production 

report: v. 35, no. 7, p. 71-93.

23
Straughan, Dale, 1971, Summary of biological effects of oil pollution in 

the Santa Barbara Channel, Part I: Allan Hancock Foundation, Southern 

California Univ., News Release, 9 p.

1972, Factors causing environmental changes after an oil spill:

Jour. Petroleum Technology, v. 24, p. 250-254.

______1975, Environmental studies as they relate to offshore petroleum 

operations, Appendix I, Fourth report of the review committee on 

safety of OCS petroleum operations: Natl. Research Council, Marine 

Board, p. 9-25.

(U.S.) Council on Environmental Quality, 1974, OCS oil and gas An 

environmental assessment: Washington, Council Environmental Quality 

Rept. to the President, v. 1, 214 p.

U.S. Geological Survey, 1972, Outer Continental Shelf lease management 

study Safety and pollution control: Washington, U.S. Geol. Survey 

Water Resources Div. Systems Lab. Group Rept., 116 p.

24
FIGURES AND TABLES

Table 1. Annual production (barrels) of oil and condensate

from all operations on the Outer Continental Shelf (PCS) , 

1971-75

Calendar 

year

1971.....

1972

1973.....

1974.....

1975.....

Gulf of Mexico OCS

Louisiana

385,760,351 

387,590,662 

374,196,856 

342,435,496 

313,592,559

Texas

1,685,047 

1,733,018 

1,617,829 

1,381,825 

1,340,136

Pacific OCS

Santa Barbara Channel

31,103,548 

22,562,213 

18,915,314 

16,776,744 

15,304,757

Total. 1,803,575,924 7,757,855 104,662,576

TEXAS

San Antonio

VALABAMA

!

100 MILES

I 

50

i r

100 150 KILOMETERS

1. Padre Island

2. Mustang Island

3. Matagorda

4. Brazos

5. Galveston

6. High Island

7. West Cameron

AREAS

8. East Cameron

9. Vermilion

10. South Marsh Island

11. Eugene Island

12. Ship Shoal

13. South Timbalier

14. South Pelto

15. Grand Isle

16. West Delta

17. South Pass

18. Main Pass

19. Breton 

Sound

20. Chandeleur

Figure 1. Index map showing Outer Continental Shelf leasing areas off 

Texas and Louisiana. Line indicates 600-foot water depth.

27
1600

1400

1200

1000

111 

DC 

DC

< 800

HI

0 600

400

200

1515

I

Volume of spills 

Number of spills

847

337

670

207

454 456

166

I

105

I

1600

1400

1200

1000

800

600

400

200

1971 1972 1973 1974 1975

Figure 2. Number and volume of 1- to 50-barrel spills by year, 1971-75, 

Gulf of Mexico Outer Continental Shelf.

28
Table 2. Number and volume of spills each year, 1971-75 ,

to 

vo

Gulf of Mexico Outer

Spills of less than 50 barrels

Year

1971.....

1972.....

1973.....

1974.....

1975.....

1971.....

1972.....

1973.....

1974.....

1975.....

Less than 

1 bbl

913 

953 

1,005 

1,051 

1,021

228 

238 

251 

263 

255

1-14 

bbl

321 

202 

162 

75 

100

1,008 

703 

585 

329 

344

15-49 

bbl

11 

4 

4 

3 

5

257 

91 

85 

75 

112

Total

1,245 

1,159 

1,171 

1,129 

1,126

Total

1,493 

1,032 

921 

667 

711

50-499 

bbl

Number of

11 

2 

1 

6 

2

Continental Shelf

Spills

500-999 

bbl

spills

0 

0 

0 

0 

0

volume (barrels) of

1,285 

150 

240 

675 

266

0 

0 

0 

0 

0

of 50 barrels or more 

1,000- 

9,999 bbl

0 

0 

3

1 

0

spills

0 

0 

21,935 

2,213 

0

10,000 bb

or more

0 

0 

0

1 

0

0 

0 

0 

19,833 

0

I/ Includes seven spills of 50 barrels each: 5 spills in 1971, and 1 spill each in 
Table 3. Causes of oil spills of more than 50 barrels, 1971-75, 

Gulf of Mexico Outer Continental Shelf

Cause Number 

of spills

Total 

volume (bbl)

Volume (bbl) per spill 

Maximum Minimum

Production-platform equipment

malfunction or misuse............

Pipeline leaks and breaks..........

Drilling and workover mishaps......

Barge spill (leak; or

oil transfer)....................

Workboat spillage during unloading 

of diesel fuel; or collision 

with platform....................

Other causes.......................

10,925

27,396

0

7,100

9,935

19,833

0

7,000

506

320

240

200

75

70

0

100

100

120

Table 4. Causes of oil spills of 1-50 barrels, 1971-75, 

Gulf of Mexico Outer Continental Shelf

Cause Number Total Volume (bbl) per spill 

of spills volume (bbl) Average Maximum Minimum

Production-platform equipment 

malfunction or misuse..........

Pipeline and pump failure........

Drilling and workover mishaps....

Miscellaneous-equipment failures 

and employee errors............

536

232

20

84

2,286

1,105.5

64.5

440

4.26

4.75

3.23

5.24

50

35

10

36

30
Table 5. Oil spills of more than 1,000 barrels, 197

Gulf of Mexico Outer Continental Shelf

[Note: No spills of this magnitude occurred in 1971, 19

Date

Jan. 9........

Jan. 26.......

May 12. .......

Volume (bbl) 

Location . , , , 

spilled

1973

West Delta Block 79, 9,935

OCS-G 1449, platform A. 

South Pelto Block 23, 7,000

OCS-G 1238. 

West Delta Block 73, 5,000

16- inch pipeline to 

Grand Isle Block 16.

Struc

sto

rup

Barge 

hea

tia

oil

Inter

num

lea

1974

April 17, 

Sept. 9.

Eugene Island Block 317, 19,833

Bonita pipeline. 

Main Pass Block 73, 2,213

Cobia pipeline.

Dragg

and 

Pipel

cau
Table 6. Blowouts resulting in pollution, casualties, or property damage,

1971-75, Gulf of Mexico Outer Continental Shelf

Date Location

 _ ^ Volume

^P* °f (bbl) accident ^^

Casualties, property 

damage

Blowouts during drilling

March 3-6,

1971

Dec. 3-5,

1972

May 5-26,

1973

Oct. 1-2,

1973

March 19,

1975

West Came r on

Block 639,

OCS-G 2027,

well 1.

South Pass

Block 78,

OCS-G 2185,

well 2.

South Marsh Island

Block 268,

OCS-G 2310,

well 2.

West Came r on

Block 543,

OCS-G 2010,

platform A,

well A-4.

High Island

Block A-471,

OCS-G 2690,

well 1.

Gas blowout, at well 0

depth 3,956 ft.

Gas blowout, 3,850 ft.; 0

last string of

casing set at

1,018 ft.

Gas blowout during 0

drilling, depth

11,393 ft.

Blowout, explosion, 0

and fire; gas; well

depth 8,540 ft.

Gas blowout, 1,150 ft. 0

Blowout-preventer

assembly and drill

pipe lost; well

lost.

Rig collapsed and was

lost in crater.

Well lost.

Three men injured

slightly; all

platform equipment

destroyed or badly

damaged.

Well and rig lost.

Blowouts during nondrilling operations

Oct. 16-

Dec. 10,

1971

June 10,

1974

Dec. 22-

31, 1974

June 12,

1975

Eugene Island

Block 215,

OCS-0678,

platform B.

South Pelto

Block 20,

OCS 073,

platform 13,

well 13.

South Pelto

Block 19,

OCS 073,

platform 12,

well 12.

South Marsh Island

Block 50,

OCS 0788,

platform B.

Explosion and fire at 450

oil pump.

Casing valve broke 75

off wellhead

during hurricane.

Casing and tubing 200

sheared at mudline

during hurricanedamage repair.

Well blew out during (I/)

completion operations.

Gas burned for 2 days.

Production platform

and equipment

lost.

None.

None.

Platform drilling deck

and equipment

damaged by fire.

I/ Some condensate was discharged as a result of this incident. When 

the platform is repaired, production is begun, and more reservoir data are 

obtained, spillage will be estimated.

32
MANUAL EMERGENCY 

SHUT-IN VALVE ON 

HELICOPTER DECK

SEPARATOR

PLATFORM 

DECK \

MANUAL EMERGENCY SHUT-IN

VALVE ON RIG FLOOR

RELIEF VALVE 

REGULATOR 

QUICK EXHAUST VALVE 3-WAY VALVE

PRESSURESENSOR

SURFAC 

SAFETY 

VALVES

HIGH/LOW PRESSURE

LOW-PRESSURE 

CONTROL LINES

STRUCTURAL CASING (DRIVE PIPE) 

100'+ DEPTHS BELOW OCEAN FLOOR

CONDUCTOR CASING 500'-1000'

MANUAL EMERGENCY

SHUT-IN VALVE 

AT BOAT LANDING /

PRODUCTION CASING J

SUBSURFACE SAFETY

VALVE

HIGH/LOW PRESSURE SENSOR

-SURFACE CASING 1500'-4500'

-INTERMEDIATE CASING 8000'- 10,000'

Figure 3. Schematic diagram showing casing program and production safety 

system of a typical 12,000-foot-deep well, Gulf of Mexico.

Table 7. Causes of 1- to 50-barrel spills on production platforms, 

1971-75, Gulf of Mexico Outer Continental Shelf

[Note: Some incidents fall in more than one category, and therefore the total shown 

here exceeds the total number of production-platform spills shown in table 4. 

Also, the individual totals for the first three categories shown here are less 

than the sums of the itemized entries in table 8]

System that failed

Number

of 

spills

Total

volume

(bbl)

Volume (bbl) per spill

Maxi- Mini- Average

Sump system..........................

Other hydrocarbon-handling equipment. 

Separator system.....................

Well and header system...............

Flare line system....................

Heater treater system................

159

139

113

85

54

24

627.5

695

407

473

188.5

92.5

95

00

60

56

49

3.85

50

50

50

50

30

10

1

1

1

1

1

1.5

33
SEPARATOR

SAFETY DEVICES

1. SUBSURFACE SAFETY DEVICE

2. HIGH/LOW PRESSURE SENSORS

3. HIGH/LOW LEVEL SENSORS

4. PRESSURE RELIEF VALVES

5. FLOW CHECK VALVES

6. AUTOMATIC VALVES

7. COMBUSTIBLE GAS SENSORS

B. MANUAL EMERGENCY SHUTDOWNS

FREE WATER 

KNOCKOUT

WATER

: OIL THEATER

SHORE

WATER TREATING

Figure 4. Simplified flow diagram for offshore oil and gas production.

34
1000

900

800

700

600

DC 

DC 

< 500

400

O 300

200

100

927

Volume of spills 

Number of spills

470 471

1971

119

247

103

171

41

1972 1973 1974 

PRODUCTION-PLATFORM SPILLS

1975

1000

900

800

700

600

500

400

300

200

100

1971

 ' «tUU

CL 

CO

LL

o

_ 300 to

LU 

DC

§ 200

LU

^

D

o 100

J

<

0 n

373

-

-

224

72

\-\^

v^

\\N

50

i

223

52

^

$$;

150 4 « »-"»

IO-C

27

\\>l

 3-1

O 1

\>^|

«tuu

300 w

_i

o. to

Li200 o

DC

LU

CD

100 i

n

1972 1973 1974 

PIPELINE AND PUMP SPILLS

1975

Figure 5. Number and volume of 1- to 50-barrel spills, by year, 1971-75, 

for production platforms and for pipelines and pumps, Gulf of Mexico 

Outer Continental Shelf.

35
Table 8. Causes of 1- to 50-barrel spills on production platforms, 1971-75, 

Gulf of Mexico Outer Continental Shelf, grouped according to system that failed

Specific cause

Number Total

of volume

spills (bbl)

Volume (bbl) per spill 

Maxi- Minimum mum

Average

Sump system

Sump carried under or overfilled........ 58 233 4.02 50 1

Sump pump failed........................ 54 192 3.56 30 1

High-level control failed............... 22 144.5 6.57 5 1.5

Skimmer tank high-level control failed.. 13 42 3.23 10 1

Pump intake clogged..................... 5 32 6.40 25 1

Sump system leaked...................... 3 14.5 4.83 10 1.5

Miscellaneous........................... 23 72.5 3.15 5 1

Separator system

High-low level control failed........... 29 81 2.79 10 1

Dump valve failed....................... 27 118.5 4.39 20 1.5

High-low pressure sensor failed......... 19 40.5 2.13 5 1

Separation vessel or lines leaked....... 12 30 2.50 4 1

Relief valve failed..................... 8 18 2.25 4 1

Inlet valve failed...................... 3 12 4.00 91

Miscellaneous........................... 32 151 4.72 50 1

Other hydrocarbon-handling equipment

High-low level control failed........... 62 378 6.10 50 1

Dump valve failed....................... 21 93 4.43 12 2

Tank or line leaked..................... 9 32 3.56 6 2

Relief valve failed..................... 4 10 2.50 3 2

Discharge line ruptured................. 3 14 4.67 10 2

Discharge line plugged.................. 2 3 1.50 2 1

Tank ruptured........................... 2 8 4.00 53

Valve leaked or cut out................. 2 28 14.00 25 3

High-low pressure sensor failed......... 2 14 7.00 95

Sight tube loosened..................... 2 29 14.50 20 9

Bull plug broke......................... 1 1 1.00 1 1

Miscellaneous........................... 34 114 3.35 22 1

36
250

200

150

100

50

207

1

66

49

49

43

110

20

17

34

39

Separator system

Well and header system

Sump system

Other hydrocarbon-handling equipment

95

I

20

30

36

39

1

1

20

10

45

26

11

1971 1972 1973 1974 1975

Figure 6. Principal causes of production-platform spills of 1-50 barrels, 

by year and number of spills, 1971-75, Gulf of Mexico Outer Continental 

Shelf.

37
50

40

30

20

10

44

27

1971

29

14

10

1972

27

17

Sump carried under or overfilled

Sump tank high-level control failed

Sump pump failed

1973

15

1974

19

1975

Figure 7. Principal causes of sump-system spills of 1-50 barrels on 

production platforms, by year and number of spills, 1971-75, Gulf of 

Mexico Outer Continental Shelf.

38
50

40

30

20

10

48

23

16

Sump system

Separator system

Other hydrocarbon-handling equipment

26

21

15

17

11

1971 1972 1973 1974 1975

Figure 8. Number of 1- to 50-barrel spills involving failures of high-low 

level controls on production platforms, by year, 1971-75, Gulf of Mexico 

Outer Continental Shelf.

39
400

300

CO

LU 

DC 

DC 

< 200

LU

100

363

99

46

114

104

215

34

43

70

68

1971 1972

Miscellaneous pipeline and 

 pump incidents

Pipeline pump failed

Discharge or transfer line ruptured, 

or coupling failed

Pipeline ruptures and leaks

219

I

i

15

75

42

87

1973

140

1

i

I

117

1974

128

1

1

37

89

1975

Figure 9. Principal causes of pipeline and pump spills of 1-50 barrels, by 

year and volume of spills, 1971-75, Gulf of Mexico Outer Continental 

Shelf.

40
Table 9. Causes of 1- to 50-barrel spills from pipelines and 

1971-75, Gulf of Mexico Outer Continental Shelf

Cause

Number Total

of volume

spills (bbl)

Volume (bb

Average

Pipeline leaked.....................

Pipeline ruptured...................

Discharge or transfer line ruptured 

or coupling failed................

Pipeline pump failed................

Pig trap leaked.....................

High-low pressure sensor failed.....

Fuel line leaked....................

Pump capacity exceeded..............

Miscellaneous.......................

63

20

54

42

12

3

2

1

39

303.5

161

237

211

35

18

3

2

152

4.82

8.05

39

02

2.92

6.00

50

00

3.90
Table 10. Frequency of spills among production platforms

Number of 

spills per 

platform

1.....

2.....

3.....

4.....

5.....

6.....

having at least one 1- to 50-barrel spill,

Gulf of Mexico Outer Continental Shelf

Number of 

platforms having 

spills

188

67

23

13

4

3

Number of 

spills per 

platform

7......

8......

9......

10......

11......

12......

Total.

1971-75,

Number of 

platforms having 

spills

4 

0

1

0 

0

1

.... 304

42
70

60

50

w 40

30

20

10

67

22

11

22

12

46

12

14

12

ill Miscellaneous pipeline and

Liiij pump incidents

I

Pipeline pump failed

I.V.Y.J Discharge or transfer line ruptured. 

L-i-1 or coupling failed

i

Pipeline ruptures and leaks

50

17

13

17

25

1

1

17

30

1

1

25

1971 1972 1973 1974 1975

Figure 10. Principal causes of pipeline and pump spills of 1-50 barrels, 

by year and number of spills, 1971-75, Gulf of Mexico Outer Continental 

Shelf.

43
3000

2000

1000

900

800

700

600

500

400

300

200

100 

90 

SO 

70 

60

50

40

30

20

10

Number of fixed structures 

at end of year

2001 2079

1800

Number of complexes with one 

or more producing wells

(est J^^ ____

900 (est.) 930 (est.) 

Number of major structures 

at end of year

J74 Number of structures having 

production spills during 

year

85

1970 1971 1972 1973 1974 1975

Figure 11. Comparison, by year, of the number of structures having spills 

with the total number of fixed and major structures. A major structure 

is defined as having two or more pieces of production equipment and (or) 

more than five producible completions.

44
Table 11. Production-platform spills of 1-50 barrels f identified by o

1971-75,

[All lessees contributing such spills 

fiscal year 1975 (ending June 30, 

are expressed in barrels]

1971

Operator

ATnfirn

A fr^r\

Chevron. ..............

Cities Service. .......

Continental. ..........

Forest. ...............

General American. .....

Gulf..................

Kerr-McGee. ...........

Marathon. .............

Mobil.............. ...

Ocean Production. .....

Oil and Gas Futures...

Shell.................

Sun. ..................

fpo y s\ ff^

Number

16 

4 

8 

28 

0

22 

23

1 

1 

11

2 

0 

12 

8 

0

0 

6 

40 

0 

0

0 

7 

4 

0 

25

Volume

48 

11 

15 

69 

0

127 

72 

2 

2 

53

4 

0 

32 

29 

0

0 

68 

138 

0 

0

0 

22 

23 

0 

163

Gulf of Mexico Outer Continental Shelf

or having production in excess of 1 million b

1975) . Number represents number of spills; v

1972

Number

12 

4 

4 

8 

0

15 

20

1 

1 

10

1 

0 

3 

2 

0

0 

6 

18 

0 

0

0 

5 

3 

0 

6

Volume

49 

12 

8 

32 

0

92 

59 

5 

6 

32

2 

0 

9 

5 

0

0 

27 

65 

0 

0

0 

18 

7 

0 

42

1973

Number

19 

5 

4 

3 

0

12 

14 

0 

0 

4

3 

0

1 

7 

0

2

1 

11 

2 

0

0 

2 

7 

0 

5

Volume

99

11 

8 

7 

0

90 

55 

0 

0 

16

8 

0 

2 

31 

0

7 

6 

46 

8 

0

0 

4 

20 

0 

33

1974

Number

2 

0 

0

1 

0

7 

0

1 

0 

2

2 

2 

2

1 

2

1 

1 

9 

0

1

1 

1 

1 

0 

4

Volume

6 

0 

0 

2 

0

94 

0 

3 

0 

6

35 

5 

5 

5 

6

4 

5 

30 

0 

2

2 

10 

2 

0 

25

Nu

be

1
2.4

2.0

1.6

1.2

0.8

0.4

Figure 12. Estimated volumes of petroleum hydrocarbons introduced 

annually into the world's oceans, in millions of metric tons. Numerical 

breakdown of categories is shown in table 12.

46
Table 12. Budget of petroleum hydrocarbons into the 

[Data from National Academy of Sciences (1975) ; LOT, lo

Input rate (millions of metric tons an

Source

Transportation 

LOT tankers. .............

Non-LOT tankers. .........

Dry docking. .............

Terminal operations. .....

Tni^^oi'" n f*f* \ A An ^G

Woi1^ ^antckK n^oi/^on^c

f"*^nc^a1 ** dkf "i no TT i ac

Atmospheric rainout I/. ....

Coastal municipal wastes... 

Coastal, nonrefining,

Urban runoff. ..............

River runoff. ..............

SUBTOTAL............

VI n ^ M i** n 1 <3 £k AT^ <S

TOTAL...............

Probable

0.08-0

0.15-0 

0.65-1 

0.2-0 

0.00015-0 

0.4-0 

0.12-0 

0.02-0

0.2-0 

0.4-0

0.1-0

0.2-1

Best 

range 

3 estimate

.15 0.08

.4 .31 

.0 .77 

.3 .25 

.005 .003 

.7 .5 

.25 .2 

.15 .1

.3 .2 

.8 .6

 . 3 

 . 3

.5 .3 

 1.6

5.513 

.0 .6

 6.113

I/ Based upon 10 percent return from the atmosphere.