EXPLORINGJ DRILLING~ AND PRODUCING PETROLEUM OFFSHORE · universitv of delaware delaware geological survey report of investigations no" 33 exploringj drilling~ and producing petroleum

UNIVERSITV OF DELAWARE

DELAWARE GEOLOGICAL SURVEY

REPORT OF INVESTIGATIONS No" 33

EXPLORINGJ DRILLING~ AND PRODUCINGPETROLEUM OFFSHORE

BY

NENAD SPOLJARIC

STATE OF DELAWARE

NEWARKJ DELAWARE

December 1979

Public Access CopyDO NOT REMOVEfrom room 208.

EXPLORING, DRILLING, AND PRODUCING

PETROLEUM OFFSHORE

By

, Nenad Spoljaric

Delaware Geological Survey

December 1979

CONTENTS

Page

ABSTRACT. • • •

INTRODUCTION••

. . . . . . . . . . . . . . . . . . 1

2

THE NATURE AND ORIGIN OF PETROLEUM. · . 2

MIGRATION AND ACCUMULATION OF PETROLEUM • 3

SEARCH FOR PETROLEUM. • • • •

Leasing of Offshore Areas.

. . . . .. .

6

6

Geological and Geophysical Investigations ••

Drilling Equipment and Drilling.

6

• 11

Testing for Petroleum.

Obtaining Rock Samples •

· . . . . . . . . • 20

• 23

. . .

PRODUCTION OF PETROLEUM • • •

Getting Petroleum Onshore ••

Probability of Oil Spills.

PROBABILITY OF FINDING PETROLEUM. •

• • 24

27

. . . • . 28

• 31

SELECTED LIST OF REFERENCES • • • •

ILLUSTRATIONS

· . . . . . . . . • 34

Figure 1. Types of traps where petroleum canaccumulate in large quantities • 5

2. Continental shelf areas of the U. S.considered for exploration or alreadybeing explored for petroleum • • • • • 7

EXPLORING, DRILLING, AND PRODUCING

PETROLEUM OFFSHORE

A Non~Technical Review

ABSTRACT

This report was prepared to provide a concise description of offshore operations related to explorationfor petroleum (oil and natural gas} from the initialgeologic and geophysical investigations to production.

Petroleum deposits differ in their physical and chemicalproperties and are associated in the rocks with saline water.The origin of petroleum and its migration through rocks arenot well understood. Commercial accumulations are found incertain suitable rocks or geologic structures - stratigraphic and structural traps, respectively.

Prospective areas offshore are leased to explorationcompanies by the federal government. Exploration beginswith geological and geophysical investigations that lead tothe selection of smaller, promising areas. Detailed studiesand drilling are then carried out and, if petroleum is found,various tests are performed to determine the volume of oilor gas or both. If the quantities are large, productionfacilities are designed and located on the site. Thepetroleum produced is transported to refining facilitiesor gas companies onshore by pipelines or tankers.

Experience has shown that large, damaging oil spillsare very rare. The most common cause of spills is marinetransportation.

I

To find new, large petroleum accumulations explorationwill have to be expanded into deeper waters and into lesshospitable regions.

INTRODUCTION

Exploration offshore for petroleum (oil and naturalgas) began in the United States about 30 years ago. Sincethat time more than 23,000 offshore wells have been drilledand about 8.5 billion barrels of oil and more than 50trillion cubic feet of natural gas have been produced.

The need for resources and decline in production fromexisting oil and gas fields, both onshore and offshore, havemade it necessary to intensify the search for new significant petroleum accumulations throughout the world. In viewof the fact that offshore exploration on the Atlantic Shelfoff the United States' East Coast has begun, the DelawareGeological Survey has prepared this brief, generalized report.Its purpose is to provide laymen with a summary of proceduresinvolved in offshore oil and gas exploration and development.

THE NATURE AND ORIGIN OF PETROLEUM

Crude oils (unrefined or "natural") vary greatly intheir physical and chemical properties. They are composedmainly of carbon and hydrogen, hence the term "hydrocarbon."Other elements, such as sulphur, nitrogen, oxygen, andheavy metals (iron, calcium, magnesium, nickel, copper,titanium, and others) are present in varying amounts rangingfrom a fraction of one percent to a few percent.

Commercial quantities of crude oil are associated in thesubsurface with natural gas. Natural gas is a mixture ofgases that can contain both hydrocarbons and non-hydrocarbons. 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 iscalled "interstitial water" and is saline; the total amountof solids in solution usually exceeds that in sea water.

The origin of petroleum is still a subject of controversy. Although a great majority of petroleum geologists

2

believe that oil and gas formed from organic matter (decaying plant and animal remains) by decomposition and transformation, there are some geologists who subscribe to thehypothesis of inorganic origin of petroleum. This controversy in itself suggests that the process by which the original material, whether it be organic or inorganic, changesinto oil and gas is not well known.

Nearly all petroleum is found in sedimentary rocksranging in age from Cambrian (550 million years ago) toQuaternary (one million years ago). But there are someimportant oil fields found in crystalline rocks. Whether ornot oil migrated into such rocks from sedimentary rocks inthe vicinity is unclear.

The fact that the origin of petroleum is still notwell understood is one of the difficulties encountered inthe search for new, large, and economic petroleum deposits.Exploration is further complicated by problems involvingthe location of deposits hidden deep underground. Statistical data available for the period between 1949 and 1968show that it took to drill more than 1,000 new field wildcat (exploratory) wells to discover one large oil field of50 million or more barrels of oil or the equivalent innatural gas.

MIGRATION AND ACCUMULATION OF PETROLEUM

The generation of petroleum is thought to have occurredin source rocks. The concentration of petroleum in thesource rocks is generally relatively small, and such rocksare normally very fine-grained sediments, for exampleshales, with low porosity (small amount of open spacesbetween individual sediment grains). Petroleum must migratefrom source rocks into reservoir rocks that are porous andpermeable and allow accumulation and extraction of petroleumif sufficiently large quantities are present.

Migration is believed to take place in two phases. First,petroleum moves from the source rocks into the .reservoirrocks (primary migration), and second, it accumulates in thereservoir rocks (secondary migration). Tertiary migrationrefers to any subsequent migration of petroleum that may bebrought 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 playimportant roles in the movement of petroleum through therocks.

In some instances petroleum migrates to the land surfaceor to the bottom of the ocean and can be observed in the formof natural oil and gas seeps. A study done by the NationalAcademy of Sciences (1975) has shown that these naturalseeps of petroleum in the world oceans amount to about 0.6million metric tons, or about 4 million barrels, per year.Small seeps of natural gas can be observed in many places inDelaware marshes; this gas is mainly methane and the marshsediments in which it develops can be considered sourcerocks.

How do oil and gas fields develop? The consensus isthat they form by primary and secondary migration. Thenecessary secondary migration is possible only if the reservoir rocks are "capped" with impervious layers to preventseepage or flushing of petroleum. Such capped reservoirrocks are appropriately called traps. There are basicallytwo different types of traps: stratigraphic and structural(Figure 1).

Stratigraphic traps develop when the migrating petroleumencounters very fine sediments that prevent further migration.Such traps are common and can be sometimes recognized in thesubsurface by the utilization of various geological andgeophysical techniques.

Structural traps are in fact structural obstructions,such as faults, anticlines, and domes (Fig. 11 that preventfurther migration of petroleum. In case of the faults it isimportant, for example, that the fault plane itself isplugged with impermeable material and that the rocks on theopposite sides of the fault are also impervious so thatfurther migration or seepage of petroleum can not occur.

There are many specific types of both stratigraphic andstructural traps, but their discussic,n here is not essentialto this report. Interested readers may refer to SelectedList of References for additional information on this subject.

4

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SEARCH FOR PETROLEUM

Leasing of Offshore Areas

Congress and the courts have determined that the federalgovernment has jurisdiction over most of the offshore areaswhere oil and gas exploration is likely to be conducted.States control the area immediately offshore, three miles inthe case of East Coast States, including Delaware, and mayestablish their own leasing procedures •. Present exploratory efforts are concentrated in federal waters off Delawareand the federal procedures are currently of principalinterest.

Leasing of offshore areas (Fig. 2) for petroleum exploration and production is conducted by the Bureau of Land Management with the assistance from the United States GeologicalSurvey. Selection of the areas is based on petroleum potential as estimated by both government and industry, marketconsiderations, and environmental factors. The area to beexplored is subdivided into blocks about 9 square miles insize for which leases are then auctioned to a company orgroup of companies offering the highest bid.

Once an area has been selected for sale, industry beginsgeological and geophysical studies under permits issued bythe U. S. Geological Survey. At the same time governmentagencies begin studies to establish an environmental reference base to be used to detect any adverse effects that mayresult from exploration and production of petroleum, and toprepare an Environmental Impact Statement.

The Secretary of the Department of the Interior is responsible for the preparation of a leasing schedule. Figures3 and 4 show the flow chart of steps from lease sales tolease termination in the areas under federal jurisdiction.The lease scheduling is continuously updated; the latestrevised schedule is shown in Figure 5.

Geological and Geophysical Investigations

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

6

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Figure 2. Continental shelf areas. of the U. S. consideredfor exploration or already being explored forpetroleum. (Source: Leasing and Management ofEnergy Resources on the Outer ContinentalShelf, U.S.G.S.: NF-74-33).

aspects of offshore operations are possible and may be employedas conditions require.

In principle there is no significant difference in seeking petroleum-bearing rocks onshore and offshore. The geological and geophysical studies involve examination of physical characteristics, ages, and distribution of rocks. Thesefactors are used to develop more accurate information aboutsubsurface rock layers and to detect and map various geological structural features such as faults, anticlines, and domes.

7

OIl-GOING PIIOGIIAK

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Figure 3. Steps preceeding commercialproduction.(Source: Atlantic Index, May 1979,u. S. Department of the Interior).

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In a frontier area, where not much is known about thegeology of the region, the search for petroleum usuallybegins with an aeromagnetic survey and the mapping of rocktypes and geologic structures using all available information. The aeromagnetic survey, together with the regionalgeologic framework developed by field mapping, are likelyto determine an area where more detailed geophysical andgeological study should be undertaken. In an offshore areathe field mapping is done by taking samples from the seabottom and holes and analyzing them in the laboratory; inaddition a survey of the adjacent land is conducted.This is necessary to establish the geologic framework ofthe offshore area in relationship to the adjacent land.

When a promising smaller area is determined, a moredetailed geophysical survey is carried out. The mostcommon geophysical technique currently in use is thereflection seismic method (Fig. 6). Sound waves are sentthrough the rocks and measurements are made of the traveltime necessary for the sound waves to return to the surface.The deeper the reflecting rock layer the longer it will takefor the sound to return. Taking into consideration thespeed of sound through different rocks, it is possible todevelop a picture of the rock formations in the subsurfaceshowing any anomalies such as faults, reefs, and domes(Fig. 7).

On the basis of this detailed investigation a locationfor a stratigraphic test well is determined. A major purposeof stratigraphic test wells is to provide rock samples.These are then studied carefully to determine their physicalproperties, mineralogical composition, and fossils. Fossilsare utilized to determine the ages of the rocks; this isvery important if accurate subsurface correlation ofindividual rock layers and rock formations is to be made.Such correlations are important because they may revealstructural traps, for example. Stratigraphic test wellsare not used directly to find petroleum, but are essentiallinks in the chain of research pointing to prospectivelocations.

Drilling Equipment and Drilling

After an area is under lease and when geological andgeophysical exploration has pinpointed a target, the prospect must be drilled to determine whether or not petroleumis present.

11

r Seismic StreamerI U' ,. '000'

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

There are three basic types of drilling equipment foroffshore exploration presently in use: bottom supported, selfelevating rig; floating, semi-submersible rig; and, ship-typedrilling rig.

Once a specific drilling locat~on has been selected, asite investigation must be carried out. This includes inspection of the sea bottom topography, studies of the foundationcharacteristics of the bottom sediments, and observation ofweather conditions. An investigation of all these, plus thewater depth at the site, will determine which type of drillingequipment 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 heightabove the water surface. Open-ended steel pipes more than40 inches in diameter are driven or drilled from the riginto the sea bottom to a penetration of up to 200 or 300feet and cemented. Blow-out preventing devices and the wellhead are installed above the conductor pipe. The locationof both the wellhead and the blow-out preventing valves,make them easily accessible for inspection and manual operation if required.

If a floating, semi-submersible, drilling rig (Fig. 9)is selected, the setting-up of the equipment for drillinghas to take into account the fact that the structure willbe exposed to continuous motion- due to waves. The wellheadand the blow-out preventers (Fig. 10) are installed on theocean floor and are remotely controlled from the unit.Auxiliary lines may be installed for underwater televisioncameras so that a constant observation of the wellhead andblow-out preventing devices can be maintained.

Ship-type drilling rigs (Fig. II) have an advantageover the other two types in their mobility. However, themain disadvantage is their motion characteristics. Highwaves and wind may cause excessive rolling of the ship andthe drilling operations may have to be suspended. Thisproblem can be minimized by employing a new type of vesselwith a rotary table moored to the ocean bottom. After theinstallation of the guide base, a hole is drilled to about1,000 feet depth and a string of casing pipes is placedand cemented. The installed marine riser has a function ofallowing the return of drilling fluid to the rig and givesaccess to the well. A ball-joint installed in the riserallows for angular deflection of the riser when the rig moveshorizontally, and a slip-joint, also a part of the riser,allows vertical motion of the rig without causing largestresses in the riser, preventer, or wellhead.

The drilling from any of the above rigs is done byrotary techniques using 90-foot long sectional drillingpipes (drilling string). The drilling bit and drilling pipesare rotated by the rotary table (Fig. 12) and graduallypenetrate downward into the rocks. As the drilling progressesdeeper into the subsurface the total length of the drillingpipes increases and their weight on the drilling bit alsoincreases. To control this pressure, and thus prevent damageto the bit, the drilling string is partly suspended on thedrilling tower (drilling derrick). The drilling bit

14

oil have high resistivity. Therefore, electric logs canidentify a rock layer or layers containing petroleum.

A drill stem test (Fig. 14) is conducted to determinethe pressure of the petroleum in the rocks and to obtainsamples for analysis. Special tools are used to performthis test: a perforated anchor pipe is installed with apressure recorder and a packer assembly to open and closethe tool in the hole to allow fluids to flow from thesegregated section below the packer upward into the drillpipe. The test itself is performed by releasing the hydrostatic mud pressure, and thus allowing fluids to move fromthe rock layer being tested into the perforated anchor pipeand to rise through the packer and valve assembly into thedry drill pipe. As the column of fluid rises inside thedrill pipe, its pressure is proportional to the height towhich the fluid rises.

A wire-line tester is used to obtain samples of fluidfrom rocks at any depth. The operation,of this tester iscontrolled electrically from the surface. Sampling pressure,formation pressure, and hydrostatic mud pressure are recordedon logging film. The device consists of a mechanical unitin the upper part, which isolates the formation to be tested,and a sample unit in the lower part, which collects andcontains the sample of the formation fluid in order that itmay be brought to the surface. The amounts of oil and gasrecovered in the tester are good criteria for determiningthe nature of the petroleum that the rock layer will produce.

The information obtained by such testing yields quantitative data on the properties of the petroleum, on the production potential, and on the gas-oil ratio in both low andhigh permeability rocks. Testing provides data valuable toproduction geologists in the evaluation of shows of oil orgas encountered during drilling operations.

There is also available a continuous retrieval fluidsampler that allows tests to be made of a formation duringdrilling without removing the drill pipes from the bore hole.This is accomplished by using a packer as a part of the drillpipe string and recovering a sample of formation fluid in acontainer 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. Whenthe sampler reaches its position and is seated inside thedrill pipe, pump pressure is applied to inflate the packer,causing it to expand and seal out the drilling mud. A valve

21

A B._-----------.. -----------._------ ---------------------------------- ------- ----------... --- ------------- --------.- ----------.. _--------------- ------ -.---------~---------._--------------------------------------------- -------------------------- --------------- --------:-:-:-:-:-.:=- - ---... _---------

mii[_ ----

Drilling mud

Dry drill pipe

SHALE

Packer

SAND

Perforated anchor pipe

Bottom of the hole

Figure 14. Packer assembly for drill stem test. A theassembly is closed. B the assembly is openand the arrows indicate the flow direction ofpetroleum· from rock formation (sand) into theperforated anchor pipe and dry drill pipe.

in the sampler assembly then opens to permit the passage ofpetroleum from the rocks below the packer into the sampler.A pressure recording device in the sampler assembly determines formation pressure. At the end of the test the pumppressure is released allowing the sampler valve to close andthe packer to deflate. A wire line is used to retrieve thesampler assembly inside the drill pipe, and the formationfluid is brought to the surface for analysis.

One of the most important pieces of information obtainedwith the described testing devices is probably the pressureof 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 productionrates. The data a-x-e.t!lso important in determining the mostsuitable completion '~ndproduction techniques.

obtaining Rock Samples

Rock sampl~s.are important because they providegeologists with 'knowfedge needed to assess the potentialof the area for peB~oleUrn.

~::-.,-,:-,,--~~~~~:~~{~,'',.' - .

Rock cuttifi9s"pX'oduced by the bit while penetratingthrough the formations are returned to the surface in thedrilling mud, as des!?ribed before. This is the mosteconomical way O£Qp.t~;j.hing samples, but there is a considerable delay b~tWeei'lt'h~time the bit has penetrated a givenrock and the time the cuttings of the same rock arrive atthe surface. Charts can be prepared to account for the timelag in the cutt~ngsreaching the surface and thus get anapproximate depth':c':I:'9m which they came. Sometimes cuttingsmay be contamina:ted·~!bychipsof other rock layers.

";.~: ,,-~-

1.0>, Alamo., Scit'ntifil' Lahoratoq, Gr- 2OF 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 bydrilli,ng :':i·.(Source: Energy Research and DevelopmentAgency, ERDA-76-ll.)

23

Sidewall core samples can also be taken in the uncasedportion of the hole at any time. When a sampling intervalis 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 ofthe hole. Then they are retrieved for analysis. This typeof sampling is particularly useful because it makes it possible to obtain samples of rocks at any depth after the drilling is completed. Sometimes the results of electric loggingor other kinds of logging techniques reveal certain formations worth further testing. Sidewall samples can then beobtained and their examination may indicate the potential ofa particular formation for petroleum.

PRODUCTION OF PETROLEUM

If oil and gas are encountered in test drilling, it mustbe decided whether results of the tests indicate an economic(profitable) amount of oil or gas, whether more or deepertest drilling is needed, or whether the results are notpromising and the drilling should be abandoned. If thediscovery of hydrocarbons is such that the estimated reservesjustify production, a production platform(s) (Fig. 16) andwells will be designed.

Production drilling is done from platforms installedon the seafloor (Fig. 17). These large structures are orderedfrom a platform construction company by the company or companies holding the lease on the productive offshore area.Construction and installation of the production platformnormally requires about two years.

The offshore platform can serve many purposes; it can beused as a drilling platform, production facility, and livingquarters for the crew. A platform is basically composed ofa framework (jacket) pinned to the ocean bottom by pilings.The jacket extends above the ocean surface and a deck isplaced on it. It is possible by directional drilling to drill40 to 50 wells from a single platform. The deepest water inwhich a platform has been installed is 1,024 feet in the Gulfof Mexico.

The development of an oil or gas field includes studiesto determine the spacing and number of production wells tobe drilled, the number and location of producing platforms(Fig. 16) to be installed, and how the oil and gas are to bestored and transported to shore. All such matters have to beresolved before the actual production starts.

24

:Undersea Drilling Platform(simplified schematic)

-

• • •

--

--- -

Cap Rock

Seabed ---------r!-lC::::=--.::r:::.:::::;;...,,~ ;.,Platform Legs Imbedded --------1HI-~__--:·in Seabed " ,r' '. _ "

"" ·~:::~ly ~,~ .. ~ '.. :. ~Well Casing Containing ++ ::-~...:.-!~

Drill Pipe

Recent Sedimentary------~••<Deposits

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

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

Porous Stratum Containing:

Natural Gas ----------IiiiiiCrude Oil ---------

Bottom of Well ---------

Salt Water ---------- ~__=;;;;;;;;;;.::;;....;;.;.,.;,,;;;..:...:..;;..:...;:::.......:;;; _=~~

Drilling Derrick -----------1--------....Work Deck for DrillingEquipment, and Safetyand Monitoring Controls ---------il------ ll.

Crew Quarters -----------1------....Blowout Preventer --------11------1~l::3~~

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

26

Production wells differ from test wells in that production casing is installed in the well to control the flow offluid, confine the production to the specific layers indicated to contain petroleum, and permit installation of theequipment necessary to regulate pressures. Additional holeswill then be drilled to delineate the producing field. Asthe information from each well is obtained, estimates offield production can be revised and refined. It should bestressed that such estimates early in the production phase ofa field are quite unreliable. More accurate estimates aremade after the field has been in production for four to sixyears. Such estimates will take into consideration thefield's productive history and reservoir characteristics.It should be pointed out also that exploratory drilling willcontinue even after the development of a field has begun,and will be carried on for many years simultaneously withdevelopment work.

Getting Petroleum Onshore

While production platforms and wells are being installedthe producing company will be making arrangements to transportand market the oil or gas or both. If gas is produced offshore by an oil company it will generally arrange with a gascompany for transportation and marketing. Oil in small quantities may be transported by barges or tankers if conditionsare suitable. Larger quantities are usually transportedthrough pipelines. Natural gas transportation requires theinstallation of a pipeline from platform to shore.

If pipelines are used, they are laid down from the production platforms to various gathering stations and fromthere to shore. The basic procedure is for barges to layconcrete-coated pipes on the sea floor (Fig. 14). The pipesmay range up to more than 50 inches in diameter and eachsection is about 40 feet in length. The sections are weldedtogether and the joints are examined by x-ray instrumentsfor 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. Beforethe pipes are actually positioned on the sea floor a trenchmay be dug to accommodate the pipeline. If trenching isused, sea currents eventually cover the pipeline with bottomsediments. These pipelines may terminate either at specialgathering platforms where oil and gas are separated or theymay lead to storage facilities onshore for shipment torefineries, or to tanker terminals for further transport

27

Figure 18.. Pipe-laying barge with stinger shown onthe left. (Reprinted from: Lamp, Vol. 56,No.1., 1974; with permission of ExxonCorporation.)

by tanker. Gas pipelines terminate at gas processing plants,generally located onshore, from which further distributionis made.

As pipelines originate in offshore federal territoryand lead into nearshore and onshore areas under State jurisdictions, attempts to coordinate the actions of the severalgovernmental units involved are conducted under a programsponsored by the Department of the Interior.

Probability of Oil Spills

The best way to determine the probability of an oil spillthat may result from either drilling or transportation is tostudy past occurrences. Table 1 gives data on oil spills inthe Gulf of Mexico Outer Continental Shelf for the period 19711975. Total production during the same period of timeexceeded 1.8 billion barrels. .

A study conducted by the National Academy of Science (1975)concluded that petroleum in marine environments is due to: .

28

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Million metrictons/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 9.8Total 6.11 100.0

A U. S. Coast Guard study (1977) of oil pollution incidents in and around U. S. waters also concluded that marinetransportation is the main source of pollution.

What are the chances of having a large oil spill in theMid-Atlantic region? Bureau of Land Management estimates ofprobable oil spills for lease areas #40 and *49 are shown inTable 2.

TABLE 2. Estimate of Probable Oil Spills forLease Areas #40 and #49, Mid-AtlanticRegion.

Size Range

< 1,000 bbl.> 1,000 bbl.

Expected Number l

3,3984

Size 2

(barrels)

2.437,500

Total

Volume(barrels)

8,155150,000158,155

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 petroleumit is necessary to look back at past experience and predictfuture trends in the context of that experience. To fulfillthe U. S. energy needs it is essential to find new largefields containing at least 50 million or more barrels ofoil or the equivalent in gas. Figure 19 shows how successful petroleum explorationists were in the past in discovering such large fields. In the period from 1949-1968 it wasnecessary to drill more than 1,000 wildcat wells both on- andoffshore to discover one field with 50 million barrels ormore of oil or 300 billion cubic feet or more of gas. Thesuccess rate of finding such fields declined at 75 percentfrom 1949 to 1968. At the same time the cost of drillinghas increased.

It is much more costly to drill offshore than onshore.For example, on the average the 1978 drilling cost of anoffshore well (9,800 feet deep) was about $2.1 million ascompared to about $230,000 for the average onshore well(4,800 feet deep). In vi.ew of the trend shown -in Figure 16it is apparent that at the present rate of petroleum consumption the known resources are being rapidly depletedwhile the odds of finding new petroleum resources aredeclining.-

As of January 1, 1979, proved reserves of crude oil inthe United States were about 30 billion barrels and ofnatural gas about 209 trillion cubic feet. Worldwide,proved reserves of oil were about 642 billion barrels andof natural gas, 2,500 trillion cubic feet.

Response of domestic production to increased activityresulting from higher crude oil prices will be slow initiallybecause of a long lead time between discovery and significant production. For example, the average worldwide timelead between intial exploration and significant productionis seven years and from initial exploration to peak produc-

-tion about thirteen years. In the United States only, thelead time is somewhat shorter; about six and eight years,respectively. The response time between discovery and peakproduction in the offshore areas ranges between five and15 years.

Exploration for petroleum is becoming more expensive,not only because of inflation, but also because it isnecessary to drill deeper and to expand exploration into

31

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less hospitable areas, such as the Alaskan North Slope andthe North Sea. In offshore areas the drilling is beingconducted in deeper and deeper water. M. King Hubbert, inhis presentation at the Annual Meeting of the AmericanAssociation of Petroleum Geologists held in 1979 in Houston,Texas, pointed out that the united States has produced 52.4billion barrels of crude oil. The ultimate amount of oil tobe produced in the lower 48 States is believed to be 150-200 billion barrels and about 1,000-1,100 trillion cubic feetof gas. These are the estimates made in the mid-1950's andthey appear to be still valid. However, discovery rates andproduction have been consistently declining more than theseestimates and, if this trend continues, the ultimate quantityof oil and gas may be less than estimated. Most of theprincipal sedimentary basins remaining to be explored lieoffshore. In spite of the difficulties and higher expenses,it appears likely that exploration offshore will continuefor many years. These efforts will almost certainly continue to involve the Mid-Atlantic area near Delaware andfamiliarity with the processes described herein should behelpful 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 SurveyCircular 720, 32 p.

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

AMOCO Canada Petroleum Company, Ltd., and Imperial Oil Ltd.,Offshore Exploration Staff, 1974, Regional geology ofGrand Banks: Special A.A.P.G. Foundation Issue, EastCoast Offshore Symposium, Atlantic City, N.J.(H. H. Emmerich, Special Editor), A.A.P.G. Bulletinv. 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-relatedactivities and contracts: Prepared by the MITRE Corp.for the U. S. Department of the Interior, U. S.Geological Survey in cooperation with the Council onEnvironmental Quality, 192 p.

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

Bureau of Land Management, 1979, Final environmental impactstatement, proposed 1979 Outer Continental Shelf oiland 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 ofMexico, Outer Continental Shelf: U. S. Geological SurveyCircular 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 forpetroleum geology, semicentennial commemorative volume:Am. Assoc. Petroleum Geologists Memoir 5, 471 p.

Energy Research and Development Agency and Los AlamosScientific Laboratory, 1976, Near-normal geothermalgradient workshop, Univ. of California in cooperationwith 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. Freemanand 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 ContinentalShelf oil and gas activities in the Mid-Atlantic andtheir onshore impacts: A summary report, November 1979:Prepared by Rogers & Golden, Inc. for the U. S. Departmentof the Interior, Geological Survey, in cooperation withthe Council on Environmental Quality; U. S. GeologicalSurvey Open-File Report 80-17, 63 p.

Mattick, R. E., and Hennessy, Jacqueline L. (eds.), 1980,Structural framework, stratigraphy, and petroleum geologyof the area of oil and gas Lease Sale No. 49 on theAtlantic continental shelf and slope: U. S. GeologicalSurvey 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 environment, Washington, D. c.,1975, 107 p.

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

Payton, C. E., (ed.), 1978, Seismic stratigraphy - applicationsto hydrocarbon exploration: Am. Assoc. PetroleumGeologists Memoir 26, 520 p.

35

Reineck, H. W., and Singh, I. B., 1973, Depositionalsedimentary environments: Springer-Verlag, New York,439 p.

Tissot, B., and Welte, D. H., 1978, Petroleum formation andoccurrence, 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 Managementand U. S. Geological Survey, 1974, Leasing and management of energy resources of the Outer Continental Shelf,U. S. Geological Survey: INF-74-33, 40 p •

•

36

EXPLORINGJ DRILLING~ AND PRODUCING PETROLEUM OFFSHORE · universitv of delaware delaware geological survey report of investigations no" 33 exploringj drilling~ and producing petroleum

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