Public Access Copy DO NOT REMOVE from room 208. UNIVERSITV OF DELAWARE DELAWARE GEOLOGICAL SURVEY REPORT OF INVESTIGATIONS No" 33

EXPLORINGJ DRILLING~ AND PRODUCING PETROLEUM OFFSHORE

BY

NENAD SPOLJARIC

STATE OF DELAWARE NEWARKJ DELAWARE

December 1979 EXPLORING, DRILLING, AND PRODUCING PETROLEUM OFFSHORE

By , Nenad Spoljaric Delaware Geological Survey

December 1979 CONTENTS Page ABSTRACT. ••• ...... 1 INTRODUCTION •• 2 THE NATURE AND ORIGIN OF PETROLEUM. · . 2 MIGRATION AND ACCUMULATION OF PETROLEUM • 3 SEARCH FOR PETROLEUM. •••• . . . . . 6 Leasing of Offshore Areas. . . 6 Geological and Geophysical Investigations•• 6

Drilling Equipment and Drilling. • 11

Testing for Petroleum. ·...... • 20 Obtaining Rock Samples • • 23 PRODUCTION OF PETROLEUM ••• •• 24

Getting Petroleum Onshore•• 27 Probability of Oil Spills...... • . 28 PROBABILITY OF FINDING PETROLEUM. • • 31

SELECTED LIST OF REFERENCES •••• · ...... • 34

ILLUSTRATIONS Figure 1. Types of traps where petroleum can accumulate in large quantities • 5 2. Continental shelf areas of the U. S. considered for exploration or already being explored for petroleum • • • • • 7 EXPLORING, DRILLING, AND PRODUCING PETROLEUM OFFSHORE

A Non~Technical Review

ABSTRACT This report was prepared to provide a concise des­ cription of offshore operations related to exploration for petroleum (oil and natural gas} from the initial geologic and geophysical investigations to production. Petroleum deposits differ in their physical and chemical properties and are associated in the rocks with saline water. The origin of petroleum and its migration through rocks are not well understood. Commercial accumulations are found in certain suitable rocks or geologic structures - strati­ graphic and structural traps, respectively. Prospective areas offshore are leased to exploration companies by the federal government. Exploration begins with geological and geophysical investigations that lead to the selection of smaller, promising areas. Detailed studies and drilling are then carried out and, if petroleum is found, various tests are performed to determine the volume of oil or gas or both. If the quantities are large, production facilities are designed and located on the site. The petroleum produced is transported to refining facilities or gas companies onshore by pipelines or tankers. Experience has shown that large, damaging oil spills are very rare. The most common cause of spills is marine transportation.

I To find new, large petroleum accumulations exploration will have to be expanded into deeper waters and into less hospitable regions.

INTRODUCTION Exploration offshore for petroleum (oil and natural gas) began in the United States about 30 years ago. Since that time more than 23,000 offshore wells have been drilled and about 8.5 billion barrels of oil and more than 50 trillion cubic feet of natural gas have been produced. The need for resources and decline in production from existing oil and gas fields, both onshore and offshore, have made it necessary to intensify the search for new signifi­ cant petroleum accumulations throughout the world. In view of the fact that offshore exploration on the Atlantic Shelf off the United States' East Coast has begun, the Delaware Geological Survey has prepared this brief, generalized report. Its purpose is to provide laymen with a summary of procedures involved in offshore oil and gas exploration and development.

THE NATURE AND ORIGIN OF PETROLEUM Crude oils (unrefined or "natural") vary greatly in their physical and chemical properties. They are composed mainly of carbon and hydrogen, hence the term "hydrocarbon." Other elements, such as sulphur, nitrogen, oxygen, and heavy metals (iron, calcium, magnesium, nickel, copper, titanium, and others) are present in varying amounts ranging from a fraction of one percent to a few percent. Commercial quantities of crude oil are associated in the subsurface with natural gas. Natural gas is a mixture of gases that can contain both hydrocarbons and non-hydro­ carbons. The principal component of this mixture is methane (generally more than 90 percent) with small amounts of ethane, propane, and butane. Water is also found associated with oil and gas. It is called "interstitial water" and is saline; the total amount of solids in solution usually exceeds that in sea water. The origin of petroleum is still a subject of contro­ versy. Although a great majority of petroleum geologists

2 believe that oil and gas formed from organic matter (decay­ ing plant and animal remains) by decomposition and trans­ formation, there are some geologists who subscribe to the hypothesis of inorganic origin of petroleum. This contro­ versy in itself suggests that the process by which the ori­ ginal material, whether it be organic or inorganic, changes into oil and gas is not well known.

Nearly all petroleum is found in sedimentary rocks ranging in age from Cambrian (550 million years ago) to Quaternary (one million years ago). But there are some important oil fields found in crystalline rocks. Whether or not oil migrated into such rocks from sedimentary rocks in the vicinity is unclear.

The fact that the origin of petroleum is still not well understood is one of the difficulties encountered in the search for new, large, and economic petroleum deposits. Exploration is further complicated by problems involving the location of deposits hidden deep underground. Statis­ tical data available for the period between 1949 and 1968 show that it took to drill more than 1,000 new field wild­ cat (exploratory) wells to discover one large oil field of 50 million or more barrels of oil or the equivalent in natural gas.

MIGRATION AND ACCUMULATION OF PETROLEUM

The generation of petroleum is thought to have occurred in source rocks. The concentration of petroleum in the source rocks is generally relatively small, and such rocks are normally very fine-grained sediments, for example shales, with low porosity (small amount of open spaces between individual sediment grains). Petroleum must migrate from source rocks into reservoir rocks that are porous and permeable and allow accumulation and extraction of petroleum if sufficiently large quantities are present.

Migration is believed to take place in two phases. First, petroleum moves from the source rocks into the .reservoir rocks (primary migration), and second, it accumulates in the reservoir rocks (secondary migration). Tertiary migration refers to any subsequent migration of petroleum that may be brought about by specific geologic processes.

How migration is accomplished is not well understood. It is believed that water, moderately high temperature,

3 pressure of the overlying sediments, and buoyancy play important roles in the movement of petroleum through the rocks. In some instances petroleum migrates to the land surface or to the bottom of the ocean and can be observed in the form of natural oil and gas seeps. A study done by the National Academy of Sciences (1975) has shown that these natural seeps of petroleum in the world oceans amount to about 0.6 million metric tons, or about 4 million barrels, per year. Small seeps of natural gas can be observed in many places in Delaware marshes; this gas is mainly methane and the marsh sediments in which it develops can be considered source rocks. How do oil and gas fields develop? The consensus is that they form by primary and secondary migration. The necessary secondary migration is possible only if the reser­ voir rocks are "capped" with impervious layers to prevent seepage or flushing of petroleum. Such capped reservoir rocks are appropriately called traps. There are basically two different types of traps: stratigraphic and structural (Figure 1). Stratigraphic traps develop when the migrating petroleum encounters very fine sediments that prevent further migration. Such traps are common and can be sometimes recognized in the subsurface by the utilization of various geological and geophysical techniques. Structural traps are in fact structural obstructions, such as faults, anticlines, and domes (Fig. 11 that prevent further migration of petroleum. In case of the faults it is important, for example, that the fault plane itself is plugged with impermeable material and that the rocks on the opposite sides of the fault are also impervious so that further migration or seepage of petroleum can not occur. There are many specific types of both stratigraphic and structural traps, but their discussic,n here is not essential to this report. Interested readers may refer to Selected List of References for additional information on this subject.

4 A B SALT DOME ANTICLINE FAULT STRATIGRAPHIC

U1

Figure 1. Types of traps where petroleum can accumulate in large quantities. Petroleum shown in black. A- Structural traps; B- Stratigraphic trap. (Source: Leasing and Management of Energy Resources of the Outer continental Shelf, U.S.G.S.: NF-74-33) SEARCH FOR PETROLEUM

Leasing of Offshore Areas

Congress and the courts have determined that the federal government has jurisdiction over most of the offshore areas where oil and gas exploration is likely to be conducted. States control the area immediately offshore, three miles in the case of East Coast States, including Delaware, and may establish their own leasing procedures•. Present explora­ tory efforts are concentrated in federal waters off Delaware and the federal procedures are currently of principal interest.

Leasing of offshore areas (Fig. 2) for petroleum explora­ tion and production is conducted by the Bureau of Land Manage­ ment with the assistance from the United States Geological Survey. Selection of the areas is based on petroleum poten­ tial as estimated by both government and industry, market considerations, and environmental factors. The area to be explored is subdivided into blocks about 9 square miles in size for which leases are then auctioned to a company or group of companies offering the highest bid.

Once an area has been selected for sale, industry begins geological and geophysical studies under permits issued by the U. S. Geological Survey. At the same time government agencies begin studies to establish an environmental refer­ ence base to be used to detect any adverse effects that may result from exploration and production of petroleum, and to prepare an Environmental Impact Statement.

The Secretary of the Department of the Interior is res­ ponsible for the preparation of a leasing schedule. Figures 3 and 4 show the flow chart of steps from lease sales to lease termination in the areas under federal jurisdiction. The lease scheduling is continuously updated; the latest revised schedule is shown in Figure 5.

Geological and Geophysical Investigations

No specific guidelines exist for exploration, drilling, or development of petroleum resources offshore. Commonly used, general procedures will be described here. It should be understood that many variations in the details of all

6 SOUTH ATlANTIC

IfCJn BASIN NORTON BASIN NAVARIN BASIN ST. GEORGE~ -.-. BASIN

~~ ContkIenlal III.., 8IIolllltlfl -- fII *'tIfI pofenlJal

Figure 2. Continental shelf areas. of the U. S. considered for exploration or already being explored for petroleum. (Source: Leasing and Management of Energy Resources on the Outer Continental Shelf, U.S.G.S.: NF-74-33). aspects of offshore operations are possible and may be employed as conditions require. In principle there is no significant difference in seek­ ing petroleum-bearing rocks onshore and offshore. The geo­ logical and geophysical studies involve examination of physi­ cal characteristics, ages, and distribution of rocks. These factors are used to develop more accurate information about subsurface rock layers and to detect and map various geologi­ cal structural features such as faults, anticlines, and domes.

7 APPROXIMATE T1I~E, I'lON THS -----.

4

9

OM-OOING CJl-GOING

24

27

30

<:-::::> NON-fEDERAL DECISIONS 57 PROCESS, EYENT 011 DECISION lJOClKNTS WITlI OPPORTUNITIES fall fOllW. STATE r--- --'""'\ AND/OR LOCAl INPUT l COfIIEACIAl \ OIl-GOING PIIOGIIAK 101 , PIlOOUCT ION, ON-GOING o IIIITI AI. USE Dr PAOGIIAM '~-r-./ fOIl DECIS10ll..wlllG INDICATES LEASE SAlE SCH£WLI~ ,..-_...... APPL IES TO AlL , LEASE \ LEAS£ SAlES TEIllIIlATlON ~ \ \.!!PJ!:Jlll!!J' Figure 3. Steps preceeding commercial production. (Source: Atlantic Index, May 1979, u. S. Department of the Interior).

8 STEP

2 OII-4iOING OII-GOIIlG

OH-GOIIlG

'----, NOH-FEDERAL '----' IEtlSIOIIS PIPELINE PEMIT PROCESS. EVENT OR c::::> IlEtlS1011 c::J /lClCUIEITS ,r-··r_ \\ > I ...,...,1tt1N. \ ~ DOClIlENTS IIITH OPPORTUIlITIES .. \ PIlOIIUCT I011 / ~ fOR FOlNL STATE MIIIOR \ -"'--r---·I LOCAL IlU'ur .--~---- c::::J OII-GO ING PIlllGllMS f, LEASE \ INITIAL USE OF TEMIIlATION \ PAOGMM 4 \ OIl I IN '-~X!!~!t

9 FINAL 5-YEAR OCS OIL & GAS LEASING SCHEDULE JUNE 1980

",o·"IID 1980 1181 1982 1913 19M 1985 ••0.0$10 Salt: AUA OUE JFMA "',J 'J"A'S'OtH o J'F M A'M J'JfAS O'N 0 JIF MAIM JIJ AS 0 NO J F'M A,hI; JIJ!A'S O~N'D J FM'AMJ'J'ASOND JFMAMJJ'ASONO I, I I' I N:S~ , ~ I,I A62 Gulf or Mexico 9iSO fj I pSc'R I , I II ! , ; If; II'' :I II I I I , ·' f . t I , ' I' I' I',' ! 55 Gul or Alaska 10'50 ::F P: ~c R:N'S I , :'I : i ' I I i I I I ! ,: Ii: i : ~R,.jS! ~ ~ ~ i : ' I',. t"· ,; 62 Gulf or Mexico 11:'10 f: , : I i , ; i r I i l i I ! I II, I I', ~i!l i :I 53 Central N. &alif. :E R ,:FU ScRNSI:,: ~ I ! ! I ! ! 01 II : :,I i ; I I , RS-1 Reofferfnll $ale 6111 : I, I : I, Ie RN S; , I' I ' :'~l\.'.....~\.. ". '-. I: 'I, ~~,. A66 Gul or Mexico 1111 ! : .£ ,R if , 'eRN S' , .. I ; i I . · : ( 56 Soutll Allantic 1111 I ,E ,R f , 'cR,.,S . I: 1;~

Drilling Equipment and Drilling After an area is under lease and when geological and geophysical exploration has pinpointed a target, the pros­ pect must be drilled to determine whether or not petroleum is present.

11 r Seismic Streamer I U' ,. '000'

Figure 6. Diagram showing a marine seismic survey. Sound waves {black solid lines} are shown bouncing off different rock layers at various depths below the sea bottom. (Source: Mineral Resource Management of the Outer Continental Shelf; U.S.G.S. Circular 720, 1975).

There are three basic types of drilling equipment for offshore exploration presently in use: bottom supported, self­ elevating rig; floating, semi-submersible rig; and, ship-type drilling rig.

Once a specific drilling locat~on has been selected, a site investigation must be carried out. This includes inspec­ tion of the sea bottom topography, studies of the foundation characteristics of the bottom sediments, and observation of weather conditions. An investigation of all these, plus the water depth at the site, will determine which type of drilling equipment is most suitable.

12

If a self-elevating, bottom supported rig (Fig. 8) is selected it will have to be jacked up to its final height above the water surface. Open-ended steel pipes more than 40 inches in diameter are driven or drilled from the rig into the sea bottom to a penetration of up to 200 or 300 feet and cemented. Blow-out preventing devices and the well­ head are installed above the conductor pipe. The location of both the wellhead and the blow-out preventing valves, make them easily accessible for inspection and manual opera­ tion if required. If a floating, semi-submersible, drilling rig (Fig. 9) is selected, the setting-up of the equipment for drilling has to take into account the fact that the structure will be exposed to continuous motion- due to waves. The wellhead and the blow-out preventers (Fig. 10) are installed on the ocean floor and are remotely controlled from the unit. Auxiliary lines may be installed for underwater television cameras so that a constant observation of the wellhead and blow-out preventing devices can be maintained. Ship-type drilling rigs (Fig. II) have an advantage over the other two types in their mobility. However, the main disadvantage is their motion characteristics. High waves and wind may cause excessive rolling of the ship and the drilling operations may have to be suspended. This problem can be minimized by employing a new type of vessel with a rotary table moored to the ocean bottom. After the installation of the guide base, a hole is drilled to about 1,000 feet depth and a string of casing pipes is placed and cemented. The installed marine riser has a function of allowing the return of drilling fluid to the rig and gives access to the well. A ball-joint installed in the riser allows for angular deflection of the riser when the rig moves horizontally, and a slip-joint, also a part of the riser, allows vertical motion of the rig without causing large stresses in the riser, preventer, or wellhead. The drilling from any of the above rigs is done by rotary techniques using 90-foot long sectional drilling pipes (drilling string). The drilling bit and drilling pipes are rotated by the rotary table (Fig. 12) and gradually penetrate downward into the rocks. As the drilling progresses deeper into the subsurface the total length of the drilling pipes increases and their weight on the drilling bit also increases. To control this pressure, and thus prevent damage to the bit, the drilling string is partly suspended on the drilling tower (drilling derrick). The drilling bit

14

oil have high resistivity. Therefore, electric logs can identify a rock layer or layers containing petroleum. A drill stem test (Fig. 14) is conducted to determine the pressure of the petroleum in the rocks and to obtain samples for analysis. Special tools are used to perform this test: a perforated anchor pipe is installed with a pressure recorder and a packer assembly to open and close the tool in the hole to allow fluids to flow from the segregated section below the packer upward into the drill pipe. The test itself is performed by releasing the hydro­ static mud pressure, and thus allowing fluids to move from the rock layer being tested into the perforated anchor pipe and to rise through the packer and valve assembly into the dry drill pipe. As the column of fluid rises inside the drill pipe, its pressure is proportional to the height to which the fluid rises. A wire-line tester is used to obtain samples of fluid from rocks at any depth. The operation,of this tester is controlled electrically from the surface. Sampling pressure, formation pressure, and hydrostatic mud pressure are recorded on logging film. The device consists of a mechanical unit in the upper part, which isolates the formation to be tested, and a sample unit in the lower part, which collects and contains the sample of the formation fluid in order that it may be brought to the surface. The amounts of oil and gas recovered in the tester are good criteria for determining the nature of the petroleum that the rock layer will pro­ duce. The information obtained by such testing yields quanti­ tative data on the properties of the petroleum, on the pro­ duction potential, and on the gas-oil ratio in both low and high permeability rocks. Testing provides data valuable to production geologists in the evaluation of shows of oil or gas encountered during drilling operations. There is also available a continuous retrieval fluid sampler that allows tests to be made of a formation during drilling without removing the drill pipes from the bore hole. This is accomplished by using a packer as a part of the drill pipe string and recovering a sample of formation fluid in a container or reservoir which is retrievable by a wire line. As the formation to be sampled is penetrated by the bit, the sampler assembly is dropped into the drill pipe. When the sampler reaches its position and is seated inside the drill pipe, pump pressure is applied to inflate the packer, causing it to expand and seal out the drilling mud. A valve

21 A B ._----­ ..------._------­-----­ ------...------­ -----.------­-- Drilling mud ..------_---- .----­------­~----­ ._------­------Dry drill pipe ------:-:-:-:-:-.:=----- SHALE ...------_------­ mii[_ ---- Packer

SAND Perforated anchor pipe Bottom of the hole

Figure 14. Packer assembly for drill stem test. A the assembly is closed. B the assembly is open and the arrows indicate the flow direction of petroleum· from rock formation (sand) into the perforated anchor pipe and dry drill pipe. in the sampler assembly then opens to permit the passage of petroleum from the rocks below the packer into the sampler. A pressure recording device in the sampler assembly deter­ mines formation pressure. At the end of the test the pump pressure is released allowing the sampler valve to close and the packer to deflate. A wire line is used to retrieve the sampler assembly inside the drill pipe, and the formation fluid is brought to the surface for analysis. One of the most important pieces of information obtained with the described testing devices is probably the pressure of the petroleum in the formations. The pressure build-up

22 values can be.usEld:~~i~stimate ~ormation permeability. Sometimes it is po~~~~l~t.o estimate the actual production rates. The data a-x-e.t!lso important in determining the most suitable completion '~ndproduction techniques.

obtaining Rock Samples

Rock sampl~s.are important because they provide geologists with 'knowfedge needed to assess the potential of the area for peB~oleUrn. ~::-.,-,:-,,--~~~~~:~~{~,' ',.' - . Rock cuttifi9s"pX'oduced by the bit while penetrating through the formations are returned to the surface in the drilling mud, as des!?ribed before. This is the most economical way O£Qp.t~;j.hing samples, but there is a consider­ able delay b~tWeei'lt'h~time the bit has penetrated a given rock and the time the cuttings of the same rock arrive at the surface. Charts can be prepared to account for the time­ lag in the cutt~ngsreaching the surface and thus get an approximate depth':c':I:'9m which they came. Sometimes cuttings may be contamina:ted·~!bychipsof other rock layers.

";.~: ,,-~-

1.0>, Alamo., Scit'ntifil' Lahoratoq, Gr- 2 OF THE UNlVUSITY OF CALIFORNIA CORE NO. IS

• 910 nIl u'" " .. " •• M101121UJ4'1tH""")Q,------

Figure 15. An example of a part of a core sample obtained by drilli,ng:':i·.(Source: Energy Research and Development Agency, ERDA-76-ll.)

23 Sidewall core samples can also be taken in the uncased portion of the hole at any time. When a sampling interval is selected, the drilling pipes are removed from the hole, the sampling device lowered to the desired formation depth, and special bullet-type samplers are fired into the wall of the hole. Then they are retrieved for analysis. This type of sampling is particularly useful because it makes it possi­ ble to obtain samples of rocks at any depth after the drill­ ing is completed. Sometimes the results of electric logging or other kinds of logging techniques reveal certain forma­ tions worth further testing. Sidewall samples can then be obtained and their examination may indicate the potential of a particular formation for petroleum.

PRODUCTION OF PETROLEUM If oil and gas are encountered in test drilling, it must be decided whether results of the tests indicate an economic (profitable) amount of oil or gas, whether more or deeper test drilling is needed, or whether the results are not promising and the drilling should be abandoned. If the discovery of hydrocarbons is such that the estimated reserves justify production, a production platform(s) (Fig. 16) and wells will be designed. Production drilling is done from platforms installed on the seafloor (Fig. 17). These large structures are ordered from a platform construction company by the company or com­ panies holding the lease on the productive offshore area. Construction and installation of the production platform normally requires about two years. The offshore platform can serve many purposes; it can be used as a drilling platform, production facility, and living quarters for the crew. A platform is basically composed of a framework (jacket) pinned to the ocean bottom by pilings. The jacket extends above the ocean surface and a deck is placed on it. It is possible by directional drilling to drill 40 to 50 wells from a single platform. The deepest water in which a platform has been installed is 1,024 feet in the Gulf of Mexico. The development of an oil or gas field includes studies to determine the spacing and number of production wells to be drilled, the number and location of producing platforms (Fig. 16) to be installed, and how the oil and gas are to be stored and transported to shore. All such matters have to be resolved before the actual production starts.

24

:Undersea Drilling Platform (simplified schematic)

Drilling Derrick ------1------....

Work Deck for Drilling Equipment, and Safety and Monitoring Controls ------il------ll. Crew Quarters ------1------.... Blowout Preventer ------11------1~l::3~~

Mean Sea Level ------....·r ....'------,~n;=;i~'t---..--__J Seawater ----~

Seabed ------r!-lC::::=--.::r:::.:::::;;...,,~ ;., Platform Legs Imbedded ------1HI-~ __--:· in Seabed " ,r' '. _" • • • "" ·~:::~ly ~,~ .. ~ '.. :. ~ Well Casing Containing ++ ::-~...:.-!~ Drill Pipe Recent Sedimentary ------~••< Deposits

- Section Omitted for - - Simplification of Diagram -----1 -- Intermediate Strata of .... ~ sedimentary Rock --

Cap Rock

Porous Stratum Containing: Natural Gas ------Iiiiii Crude Oil ------­ Bottom of Well ------Salt Water ------~__=;;;;;;;;;;.::;;....;;.;.,.;,,;;;..:...:..;;..:...;:::...... :;;; _=~~

Figure 17. Simplified diagram with useful terminology. (Source: The Why and How of Undersea Drilling, 1974; with permission of American Petroleum Institute) ,

26 Production wells differ from test wells in that produc­ tion casing is installed in the well to control the flow of fluid, confine the production to the specific layers indi­ cated to contain petroleum, and permit installation of the equipment necessary to regulate pressures. Additional holes will then be drilled to delineate the producing field. As the information from each well is obtained, estimates of field production can be revised and refined. It should be stressed that such estimates early in the production phase of a field are quite unreliable. More accurate estimates are made after the field has been in production for four to six years. Such estimates will take into consideration the field's productive history and reservoir characteristics. It should be pointed out also that exploratory drilling will continue even after the development of a field has begun, and will be carried on for many years simultaneously with development work.

Getting Petroleum Onshore

While production platforms and wells are being installed the producing company will be making arrangements to transport and market the oil or gas or both. If gas is produced off­ shore by an oil company it will generally arrange with a gas company for transportation and marketing. Oil in small quanti­ ties may be transported by barges or tankers if conditions are suitable. Larger quantities are usually transported through pipelines. Natural gas transportation requires the installation of a pipeline from platform to shore.

If pipelines are used, they are laid down from the pro­ duction platforms to various gathering stations and from there to shore. The basic procedure is for barges to lay concrete-coated pipes on the sea floor (Fig. 14). The pipes may range up to more than 50 inches in diameter and each section is about 40 feet in length. The sections are welded together and the joints are examined by x-ray instruments for possible flaws. Then they are guided from the barge to "the sea floor by a special device called a stinger (Fig. 18) which also keeps the pipes from excessive bending. Before the pipes are actually positioned on the sea floor a trench may be dug to accommodate the pipeline. If trenching is used, sea currents eventually cover the pipeline with bottom sediments. These pipelines may terminate either at special gathering platforms where oil and gas are separated or they may lead to storage facilities onshore for shipment to refineries, or to tanker terminals for further transport

27 Figure 18. Pipe-laying barge with stinger shown on . the left. (Reprinted from: Lamp, Vol. 56, No.1., 1974; with permission of Exxon Corporation.) by tanker. Gas pipelines terminate at gas processing plants, generally located onshore, from which further distribution is made. As pipelines originate in offshore federal territory and lead into nearshore and onshore areas under State juris­ dictions, attempts to coordinate the actions of the several governmental units involved are conducted under a program sponsored by the Department of the Interior.

Probability of Oil Spills The best way to determine the probability of an oil spill that may result from either drilling or transportation is to study past occurrences. Table 1 gives data on oil spills in the Gulf of Mexico Outer Continental Shelf for the period 1971­ 1975. Total production during the same period of time exceeded 1.8 billion barrels. . A study conducted by the National Academy of Science (1975) concluded that petroleum in marine environments is due to: .

28 TABLE 1. Causes of Oil Spills of more than one barrel, Gulf of Mexico Outer Continental Shelf.

Spills greater than 50 barrels, Spills of 1-50 barrels, 1971-75 1971-75

Number Percent Spill Percent Number Percent Spill Percent of of vol. of of of vol. of Causes spills spills (bbls. volume spills spills (bbls. ) volume

Production-platform equip. malfunctions of misuse 6 30.0 10,925 23.6 536 61.5 2,286 58.7 P1pe11ne pump fa1!- ures, leaks and breaks 7 35.0 27,396 59.2 232 26.6 1,106 28.4

N Dr1ll1ng operat1ons \0 and workover mis- haps 0 0 0 0 20 2.3 64 1.6 Barge sp1lls (leak or oil transfer) 2 10.0 7,100 15.4 - - - - \'1or~boat spills dur1ng unloading of diesel fuel; or collision 3 15.0 506 1.1 -- - - M1SC. equ1pment failures and employee errors 2 10.0 320 0.7 84 9.6 440 11.3

TOTALS 20 100.0 46,247 100.0 872 100.0 3,896 100.0 Source: Danenberger, 1976. Million metric tons/year Percentage Marine transportation 2.13 34.9 River and Urban Runoff 1.9 31.1 Coastal Refineries & waste 0.8 13.1 Offshore Oil Production 0.08 1.3 Atmospheric Fallout 0.6 9.8 Natural Seeps 0.6 9.8 Total 6.11 100.0

A U. S. Coast Guard study (1977) of oil pollution inci­ dents in and around U. S. waters also concluded that marine transportation is the main source of pollution. What are the chances of having a large oil spill in the Mid-Atlantic region? Bureau of Land Management estimates of probable oil spills for lease areas #40 and *49 are shown in Table 2.

TABLE 2. Estimate of Probable Oil Spills for Lease Areas #40 and #49, Mid-Atlantic Region.

Size Range Expected Number l Size 2 Volume (barrels) (barrels)

< 1,000 bbl. 3,398 2.4 8,155 > 1,000 bbl. 4 37,500 150,000 Total 158,155 1 Based on Slack and Wyant, 1978. 2 Based on Devanney and Stewart, 1974.

30 PROBABILITY OF FINDING PETROLEUM To appreciate the complexity of the search for petroleum it is necessary to look back at past experience and predict future trends in the context of that experience. To fulfill the U. S. energy needs it is essential to find new large fields containing at least 50 million or more barrels of oil or the equivalent in gas. Figure 19 shows how success­ ful petroleum explorationists were in the past in discover­ ing such large fields. In the period from 1949-1968 it was necessary to drill more than 1,000 wildcat wells both on- and offshore to discover one field with 50 million barrels or more of oil or 300 billion cubic feet or more of gas. The success rate of finding such fields declined at 75 percent from 1949 to 1968. At the same time the cost of drilling has increased. It is much more costly to drill offshore than onshore. For example, on the average the 1978 drilling cost of an offshore well (9,800 feet deep) was about $2.1 million as compared to about $230,000 for the average onshore well (4,800 feet deep). In vi.ew of the trend shown -in Figure 16 it is apparent that at the present rate of petroleum con­ sumption the known resources are being rapidly depleted while the odds of finding new petroleum resources are declining.- As of January 1, 1979, proved reserves of crude oil in the United States were about 30 billion barrels and of natural gas about 209 trillion cubic feet. Worldwide, proved reserves of oil were about 642 billion barrels and of natural gas, 2,500 trillion cubic feet. Response of domestic production to increased activity resulting from higher crude oil prices will be slow initially because of a long lead time between discovery and signifi­ cant production. For example, the average worldwide time lead between intial exploration and significant production is seven years and from initial exploration to peak produc- -tion about thirteen years. In the United States only, the lead time is somewhat shorter; about six and eight years, respectively. The response time between discovery and peak production in the offshore areas ranges between five and 15 years. Exploration for petroleum is becoming more expensive, not only because of inflation, but also because it is necessary to drill deeper and to expand exploration into

31 NFW Per 37386 Discovery A 34624 2000 -

1472 B 14_43 ~

1000 w to.) 5 c 24 --20 0·10------_ 1949-53 . 1954-58 1959-63 1964-68

Figure 19. A-total number of new field wildcats (NFW) drilled within a specified year inverva1s. B-number of NFW drilled per discovery of each field with reserves of 50 million barrels of oil or 300 billion cubic feet of gas. C-number of fields discovered. (Modified from AAPG Background Paper #5, 1975). less hospitable areas, such as the Alaskan North Slope and the North Sea. In offshore areas the drilling is being conducted in deeper and deeper water. M. King Hubbert, in his presentation at the Annual Meeting of the American Association of Petroleum Geologists held in 1979 in Houston, Texas, pointed out that the united States has produced 52.4 billion barrels of crude oil. The ultimate amount of oil to be produced in the lower 48 States is believed to be 150- 200 billion barrels and about 1,000-1,100 trillion cubic feet of gas. These are the estimates made in the mid-1950's and they appear to be still valid. However, discovery rates and production have been consistently declining more than these estimates and, if this trend continues, the ultimate quantity of oil and gas may be less than estimated. Most of the principal sedimentary basins remaining to be explored lie offshore. In spite of the difficulties and higher expenses, it appears likely that exploration offshore will continue for many years. These efforts will almost certainly con­ tinue to involve the Mid-Atlantic area near Delaware and familiarity with the processes described herein should be helpful to the citizens of our State.

33 SELECTED LIST OF REFERENCES

Adams, M. V., John,C. B., Kelly, R. F., LaPointe, A. E., and . Meurer, R. W., 1976, Mineral resource management of the Outer Continental Shelf: U. S. Geological Survey Circular 720, 32 p.

American Petroleum Institute, 1974, The why and how of undersea drilling, 12 p.

AMOCO Canada Petroleum Company, Ltd., and Imperial Oil Ltd., Offshore Exploration Staff, 1974, Regional geology of Grand Banks: Special A.A.P.G. Foundation Issue, East Coast Offshore Symposium, Atlantic City, N.J. (H. H. Emmerich, Special Editor), A.A.P.G. Bulletin v. 58, no. 6, (pt. II of II), p. 1109-1123.

Anderson, J., 1975, Coring and core analysis handbook; PPC Books, Tulsa, 200 p.

Benton, J. B., Bisselle, C. A., Gilliam, R., McDowell, T. W., Slaughter, J., Tyndall, R. W., and Wik, J. D., 1979, Directory of federal, state, and local.OCS-related activities and contracts: Prepared by the MITRE Corp. for the U. S. Department of the Interior, U. S. Geological Survey in cooperation with the Council on Environmental Quality, 192 p.

Benton, J. B., Holman, R., and McDowell, T. W., 1979, Atlantic Index (January 1975-April 1979); Prepared by the MITRE Corp. for the U. S. Department of the Interior, U. S. Geological Survey, and the Bureau of Land Management in cooperation with the Council on Environmental Quality, 68 p.

Bureau of Land Management, 1979, Final environmental impact statement, proposed 1979 Outer Continental Shelf oil and gas lease sale offshore the Mid-Atlantic states, OCS Sale No. 49, v. 1 of 3, 673 p.

Danenberger, E. P., 1976, Oil spills, 1971-75, Gulf of Mexico, Outer Continental Shelf: U. S. Geological Survey Circular 741, 47 p.

34 Dobrin, M. B., 1960, Introduction to geophysical prospecting: McGraw Hill, New York, 446 p.

Dott, R. H., Sr., and Reynolds, M. J., 1979, Sourcebook for petroleum geology, semicentennial commemorative volume: Am. Assoc. Petroleum Geologists Memoir 5, 471 p.

Energy Research and Development Agency and Los Alamos Scientific Laboratory, 1976, Near-normal geothermal gradient workshop, Univ. of California in cooperation with the U. S. Geological Survey, ERDA 76-11, 310 p.

Harris, L. M., 1972, Deepwater floating drilling operations: The Petroleum Publishing Company, Tulsa, Oklahoma, p. 29-34.

Hunt, J. M., 1979, Geochemistry of petroleum: W. H. Freeman and Company, San Francisco, 617 p.

Lamp (The), Exxon Corporation; v. 56, no. 1, Spring, 1974, 37 p.

Levorsen, A. I., 1967, Geology of petroleum; (2nd Edition): W. H. Freeman and Company, San Francisco, 724 p.

Macpherson, G. S., and Bookman, C. A., 1980, Outer Continental Shelf oil and gas activities in the Mid-Atlantic and their onshore impacts: A summary report, November 1979: Prepared by Rogers & Golden, Inc. for the U. S. Department of the Interior, Geological Survey, in cooperation with the Council on Environmental Quality; U. S. Geological Survey Open-File Report 80-17, 63 p.

Mattick, R. E., and Hennessy, Jacqueline L. (eds.), 1980, Structural framework, stratigraphy, and petroleum geology of the area of oil and gas Lease Sale No. 49 on the Atlantic continental shelf and slope: U. S. Geological Survey Circular 812, 101 p.

Moore, C. A., 1963, Handbook of subsurface geology: Harper & Row, New York, Evanston, and London, 235 p.

National Academy of Sciences, Petroleum in the marine environ­ ment, Washington, D. c.,1975, 107 p.

Oil and Gas Journal, published weekly by PennWe11 Publishing Co., Tulsa, Oklahoma.

Payton, C. E., (ed.), 1978, Seismic stratigraphy - applications to hydrocarbon exploration: Am. Assoc. Petroleum Geologists Memoir 26, 520 p.

35 Reineck, H. W., and Singh, I. B., 1973, Depositional sedimentary environments: Springer-Verlag, New York, 439 p. Tissot, B., and Welte, D. H., 1978, Petroleum formation and occurrence, a new approach to oil and gas exploration: Springer-Verlag, New York, Heidelberg, Berlin, 580 p. U. S. Department of the Interior, Bureau of Land Management and U. S. Geological Survey, 1974, Leasing and manage­ ment of energy resources of the Outer Continental Shelf, U. S. Geological Survey: INF-74-33, 40 p •

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