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U.S. GEOLOGICAL SURVEY CIRCULAR 922-A

Assessment of Undiscovered Conventionally Recoverable Petroleum Resources of the Northwest European Region

Assessment of Undiscovered Conventionally Recoverable Petroleum Resources of the North\Nest European Region

By Charles D. Masters and H. Douglas Klemme

U. S. G E 0 L 0 G I CAL SURVEY CIRCULAR 9 2 2- A

Prepared in cooperation with Weeks Exploration Company under contract to the U.S. Geological Survey

A resource assessment and a brief description of the petroleum geology, including play distribution, that accounts for the petroleum accumulation in the and adjoining areas

1984 Department of the Interior WILLIAM P. CLARK, Secretary

U.S. Geological Survey Dallas L. Peck, Director

Free on application to Distribution Branch, Text Products Section, U. S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 CONTENTS

Page Pref~------v Absttact------1 Inbuduction ------1 Regional geology ------2 Pettoleum geology ------6 Resource assessment------14 COmmen~ ------15 References cited ------22

ILLUSTRATIONS

Page FIGURE 1. Map showing northwest European assessment region, including the North Sea------3 2. Sttatigraphic diagrams of selected pettoleum provinces ------5 3. Map of Play I, centtal North Sea region ------7 4. Map of Play I, southern and southwest North Sea region ------8 5. Map showing potential pettoleum basins, dismbution of Kimmeridgian source rocks in the North Sea between latitudes 59° N. and 69° N., inferred degree of maturity of source rock, and oil and gas fields------10 6. Interpreted seismic sttatigraphy and sttucture ------11 7. Map showing potential pettoleum basins, dismbution of Jurassic Kimmeridgian source rock in the North Sea between latitudes 69° N. and 76 o N., as well as the inferred degree of maturity of source rock------12 8. Interpreted seismic sttatigraphy and skucture ------13 9. Map showing Play II, southern North Sea region ------14 10. Listing by size of fields atmbuted to Play I, further division of the occurrence of pettoleum into four ttap types, and a listing of fields atmbutable to each ------16 11. Listing by size of fields atmbuted to Play II, a generalized diagram of ttap type, and a listing of certain characteristics of the play ------17 12. Discovery history by year of discovery and by field size according to time-lapse increment from year of award of concession ------18 13-26. Graphs of northwest European region, aggregate recoverable: 13. Oil, A+ B+C+D+ E ------18 14. Total gas, subregions A+ B +C+ D+ E ------18 15. Oil, subregions A+ B+ E, south of 62° N. ------19 16. Total gas, subregions A+ B+ E, south of 62° N. ------19 17. Oil, subregions C+D, north of 62° N. ------20 18. Total gas, subregions C+ D, north of 62° N. ------20 19. Oil, A, Southern North Sea Basin ------20 20. Total gas, subregion A, Southern North Sea Basin ------20 21. Oil, subregions B+E, Viking and Centtal Grabens------20 22. Total gas, subregions B+ E, Viking and Centtal Grabens ------20 23. Oil, subregion C, north of 62° N., southern sector------21 24. Total gas, subregion C, north of 62° N., southern sector------21 25. Oil, subregion D, north of 62° N., northern sector------21 26. Total gas, subregion D, north of 62° N., northern sector------21

iii TABLES

Page TABLE 1. Assessment of undiscovered conventionally recoverable petroleum resources of the northwest European assessmentregion------15 2. Supplemental and comparative data relative to the resource assessment of the northwest European assess- ment region------15 3. Distribution by country and by subregion of undiscovered recoverable petroleum resources in the northwest European assessment region ------19 PREFACE

The World Energy Resources Program of the U.S. Geological Survey (USGS) is designed to develop reliable and credible estimates of undiscovered petroleum resources throughout the world. Initial program efforts have focused on the ma­ jor producing areas of the world in order to gain a broad geological understand­ ing of the characteristics of petroleum occurrence for purposes of resource assessment as well as for analysis of production potential. Investigations of pro­ duction potential are carried out in cooperation with other U.S. Government agencies. Specifically, studies of the main exporting nations of the free world, of which this study is a part, are carried out in cooperation with the Foreign Energy Supply Assessment Program of the Department of Energy. The estimates represent the views of a U.S. Geological Survey study team and should not be regarded as an official position of the U.S. Government. The program seeks to investigate resource potential at the basin level, primarily through analogy with other petroleum regions, and thus does not necessarily require current exploration information commonly held to be pro­ prietary. In conducting the investigations, we intend to build a support base of publicly available data and geologic synthesis against which to measure the progress of exploration and thereby validate the assessment. Most of these investigations will lead directly to quantitative resource assessments. To be ef­ fective, resource assessment, like exploration, must be an ongoing process that takes advantage of changing ideas and data availability-the results produced are but progress reports reflecting on a state of knowledge at a point in time. Because the program is coordinated with the Geological Survey's domestic assessment program and uses similar assessment techniques, the user can be assured that a thread of consistency will permit comparisons between the various petroleum basins of the world, including those in the United States, that have been assessed in the overall Survey program. In addition to resource estimates, the program provides a regional base of understanding for in-country exploration analysis and for analysis of media reports regarding the exploratory success or failure of ventures in studied areas. Other USGS publications relating to the assessment of undiscovered conven­ tionally recoverable petroleum resources include the following:

Open-File Report 81-0986-Assessment of conventionally recoverable petroleum resources of Persian Gulf basin and Zagros belt (Arabian­ Iranian basin) Open-File Report 81-1027-Assessment of conventionally recoverable petroleum resources, Volga-Urals basin, U.S.S.R. Open-File Report 81-1142-Assessment of conventionally recoverable petroleum resources of Indonesia Open-File Report 81-1143-Assessment of conventionally recoverable petroleum resources of northeast Mexico Open-File Report 81-1144-Assessment of conventionally recoverable petroleum resources of southeastern Mexico, northern Guatemala, and Belize

v Open-File Report 81-1145-Assessment of conventionally recoverable petroleum resources of Trinidad Open-File Report 81-1146-Assessment of conventionally recoverable petroleum resources of Venezuela Open-File Report 81-1147- Assessment of conventionally recoverable petroleum resources of the West Siberian basin and Kara Sea basin, U.S.S.R. Open-File Report 82-0296-Assessment of undiscovered conventionally recoverable petroleum resources of the Middle Caspian basin, U.S.S.R. Open-File Report 82-1027-Assessment of undiscovered conventionally recoverable petroleum resources of the East Siberian basin, U.S.S.R. Open-File Report 82-1056-Assessment of undiscovered conventionally recoverable petroleum resources of North Open-File Report 82-1057-Assessment of undiscovered conventionally recoverable petroleum resources of the Timan-Pechora basin, U.S.S.R., and Barents-northern Kara shelf Open-File Report 83-0598-Assessment of undiscovered conventionally recoverable petroleum resources of Northwestern, Central, and Northeastern Africa Open-File Report 83-0801-Assessment of undiscovered conventionally recoverable petroleum resources of onshore China

These reports are available from Open File Services Section, Branch of Distribution, USGS, Box 25425, Federal Center, Denver, CO 80225.

vi Assessment of Undiscovered Conventionally Recoverable Petroleum Resources of the Northwest European Region

By Charles D. Masters1 and H. Douglas Klemme2

ABSTRACT The history of discovery in the North Sea would appear to deny the commonly held maxim that large fields are found first The estimates of undiscovered conventionally recoverable and early in the exploration process. However, if the discovery petroleum resources in the northwest European region at prob­ data are examined from the perspective of the award date of ability levels of 95 percent, 5 percent, statistical mean, and each exploration license, then it is clear that the largest fields mode are for oil (in billions of barrels): 9, 34, 20, and 15; and for and most of the reserves have indeed been found early in the gas (in trillions of cubic feet): 92, 258, 167, and 162. exploration process of a particular license. Discoveries made The occurrence of petroleum can be accounted for in two within 1 year of granting the license are on average large distinct geological plays located in the various subbasins of the giants, and they account for slightly less than tw~thirds of the region. Play I is associated with the distribution of mature original reserves. Discoveries made within 2 to 5 years of the source rocks of Late Jurassic age relative to four distinct trap­ granting of the license are on average less than giant size and ping conditions. The play has been demonstrated productive smaller than increment-1-year discoveries by a factor of 4; mostly in the Viking and Central Grabens of the North Sea, these fields account for a little less than one-third of the where the shale has been buried to optimum depths for the reserves. Those fields found 6 or more years after the granting generation of both oil and gas. To the north of 62° N. latitude of the license are relatively small and account for 20 percent of up to the Barents Sea, source rocks become increasingly deeply all discoveries but only 4 percent of total original reserves. buried and are interpreted to be dominantly gas prone; a nar­ These data suggest that a measure of an area's exploration row band of potentially oil-prone shales tracks most of the maturity is the length of time elapsed since the award of the coast of Norway, but water depths in favorable localities com­ concession. monly range from 600 to 1,200 feet. To the south of the Central Graben, the Jurassic source rocks are either immature or minimally productive because of a change in facies. Undrilled INTRODUCTION traps remain within the favorable source-rock area, and expl~ ration will continue to challenge the boundaries of conventional Investigation of the petroleum resource poten­ wisdom, especially on the Norwegian side where little has been tial of the northwest European region was per­ reported on the geology of the adjoining Bergen High or Horda formed under contract to Weeks Exploration Com­ Basin, though, reportedly, the Jurassic source rocks are missing on the high and are immature in the southern part of the pany (Contract No. 4-08-001-17919) by Dr. H. basin. Douglas Klemme. Sources of data include Petro­ Play II is associated with the distribution of a coal facies of consultants S.A. and published literature. The in­ Carboniferous age that is mature for the generation of gas and tent of this report is to provide a geologie setting locally underlies favorable reservoir and sealing rocks. The for the assessment and to describe our working play is limited largely by facies development to the present area of discovery and production but is limited as well to the concept of the reasons for the oil occurrence and southeast into onshore Netherlands and Germany by the factors we believe will be responsible for additional unfavorable economics of an increasing nitrogen content in the discoveries, as well as those we believe will limit gas. This increase is apparently caused by excessive tempera­ them. The petroleum geology of the North Sea tures associated with increasing depth of burial of the source region is well reported in many publications by rock. private and government sources alike; among 'U.S. Geological Survey these, notable compilations and regional syntheses 'Weeks Exploration Company

1 by Ziegler (1980), Woodland (1975), Illing and The results of the final estimates are averaged, Hobson (1981), and Hallam (1980) provided most and those numbers are fitted to a log-normal of the basic data and interpretation leading to this distribution and further computer processed by assessment report. An unpublished interpretation using probabilistic methodology (Crovelli, 1981) to of the geology by H. Douglas Klemme has been show graphically the resource values associated only slightly modified for suitability to publication with a full range of probabilities and to determine format in displaying the geologic features respon­ the 95th fractile, the 5th fractile, the mode, and the sible for the petroleum occurrences. mean, as well as other statistical parameters. The resource assessment was conducted by the All assessments are made conditional upon the Resource Appraisal Group (RAG) of the USGS, occurrence of commercial petroleum in the assess­ Branch of Oil and Gas Resources, following the ment region, but the probability of that occurrence standard procedures developed since 197 4 for do­ differs between regions. To aggregate various mestic petroleum resource analysis. The tech­ assessment regions, varying probabilities of com­ nique, briefly, requires that a given area is studied mercial petroleum occurrence must be allowed for with particular attention paid to the geologic fac­ by adjusting the assessments in accordance with tors controlling the occurrence, quality, and quan­ the marginal probability of the occurrence, thereby tity of the petroleum resource. Standardization of producing an unconditional (sometimes referred to critical elements of the investigations is achieved as "risked") probability distribution. If commer­ by the preparation of data forms for each basin, cial petroleum is known, the marginal probability which call for specific volumetric, areal, and rock­ is 1, and the conditional and unconditional prob­ quality measurements, as well as the determina­ ability distributions are identical. If, however, no tion of basin analogs for comparison purposes. In commercial petroleum has been heretofore discov­ addition, finding-rate histories and projections are ered in the region, the marginal probability (a frac­ constructed, when possible. From these data and tion of 1) of that occurrence is estimated subjec­ analyses, various analytical techniques are used to tively, and the conditional probability distribution calculate a set of resource numbers. is adjusted downward (reflecting the marginal The assessment process itself is subjective; the probability limit) to an unconditional probability results of the geological investigation and of the distribution. Aggregated assessments reflect the resource calculations derived from volumetric adjustments derived from marginal probability analog comparisons, finding-rate projections, and and are unconditional. other techniques of resource calculation are pre­ sented to a team of USGS assessment specialists who make their personal estimates conditional ACKNOWLEDGMENTS upon recoverable resources being present. Initial assessments are made for each of the assessed The resource assessment for this report was provinces as follows: prepared in collaboration with the Resource (a) A low resource estimate corresponding to a Appraisal Group of the Branch of Oil and Gas 95 percent probability of more than that Resources. amount; this estimate is the 95th fractile (F9s); (b) A high resource estimate corresponding to a REGIONAL GEOLOGY 5 percent probability of more than that amount; this estimate is the 5th fractile The northwest European region of this report (Fs); (fig. 1) is a mostly submerged part of the western (c) A modal ("most likely") estimate of the quan­ European continental margin bounded and tra­ tity of resource associated with the great­ versed by tectonic elements of widely varying est likelihood of occurrence. ages, which are largely responsible for the The individual estimates are then posted and petroleum geology as we can interpret it today. averaged, and the results debated from the per­ The region includes the Northwest European spective of the personal experiences of the individ­ Basin as well as the Atlantic Shelf basins (Ziegler, ual assessors; a second and third iteration of the 1980), the latter of which occur generally to the procedure may follow, depending on consensus. west of the British Isles and to the northwest of

2 73°N 40"1/V 35"W 30"1/V 25"W 20"W 15"W 10"1/V 5"W oo 5°E 10°E 15°E 20°E 25°E 30"E 35oE 40"E

50 100 150 200 MILES I I ! ! I I I I 0 50 100 150 200 KILOMETERS

FIGURE I.-Northwest European assessment region, including the North Sea.

3 Norway north of about 62° N. latitude. To the In Carboniferous time, the southern seaway and west and northwest lies the Atlantic Ocean Basin; associated geosynclinal development were dis­ to the east is the Precambrian of the Baltic placed by Variscan tectonic activity that metamor­ ; and to the south the bounding element is phosed and uplifted central and produced a the Variscan metamorphic belt now partly covered concomitant downwarp across the southern North by younger sediments (Ziegler, 1981). The geologic Sea area through the Netherlands, Germany, and history and processes involved in the evolution of into Poland. Lower Carboniferous sediments were this region are complex and highly varied and have fed into a deep seaway (culm flysch facies), but with resulted in many different locales for the occur­ continuing uplift and erosion, the increased rence of petroleum, but in only a few areas did all sedimentation filled the seaway, and eventually a of the factors necessary to that occurrence come balance of sedimentation and subsidence produced together in an optimum manner so as to result in a long-lived, paralic depositional environment. Up economically significant deposits. The principal to 3,500 m of coal facies rock (intra-Westphalian areas in the region with respect to reserves, as well age), which provides the source for the gas in this as undiscovered resources, are the Viking and Cen­ area, were deposited in the southern North Sea tral Grabens and the Southern North Sea Basin area (fig. 1). The Atlantic Shelf basins, which lie Variscan orogeny culminated ·in pre-Permian generally to the west of the United Kingdom and time with overthrusting in the south, but compres­ of Norway, north of 62° N. latitude, are character­ sion continued to subtly affect the foreland and ized by somewhat different geology and do not produced the Mid North Sea High and adjoining presently have commercial occurrences of petro­ basin downwarps to the north and to the south leum, but their potential for undiscovered (fig. 1). Aeolian sediments of the Rotliegendes resources must be recognized. (eventually to become the reservoir rock for the Sedimentary rocks of interest span the entire southern North Sea gas) accumulated predomi­ Phanerozoic (fig. 2), but the principal soUrce-rock nantly in the Southern Permian Basin (south of ages are Carboniferous and Jurassic; reservoir­ the Mid North Sea High, fig. 1); time-equivalent rock ages vary somewhat, but Permian and Juras­ nonmarine muds, conglomerates, and some evapo­ sic rocks dominate with significant contributions rites were deposited elsewhere in the Southern Per­ from the rocks of Cretaceous and Tertiary age. mian Basin and in the lesser subsiding Northern Early Paleozoic platform shelf carbonates and Permian Basin (Ziegler, 1980). shales ringed the main craton elements of the Marine depositional conditions returned to the Canadian and Baltic Shields. The collision of the area in Late Permian time owing to continued shields and associated rocks in Middle basin subsidence in excess of deposition and produced the Caledonide orogeny and a metamor­ presumably also to an extensional opening to the phic mountain belt extending mainly up the west­ Zechstein Sea via the Arctic region. Evaporite em side of Great Britain, across Scotland and the deposition (rocks which later were to provide a seal North Sea, and along the coastal regions of Nor­ for the gas deposits) ensued throughout the north­ way. Caledonide tectonism also occurred locally in western European region, except on the basin various parts of central Europe, but in the Baltic margins where freshwater influxes lowered salin­ Sea region Caledonide tectonism did not prevail, ity sufficiently to permit carbonate bank and reef and unmetamorphosed lower Paleozoic sediments growth locally. These reefs are productive explora­ provide targets for petroleum exploration. tion targets in onshore Netherlands and Germany. A postorogenic period of tensional basin devel­ Nonmarine depositional conditions, owing to opment south of the Caledonides and west of the broad area uplift, accompanied the onset of rifting occurred in time. Clastic in Triassic time; this rifting led eventually to the nonmarine sediments of the Old Red Sandstone tectonic opening of the Atlantic seaway. Thick Formation were eroded from the Caledonide high­ sedimentary sections of red beds and conglomer­ lands and deposited into an adjoining subsiding ates developed in the newly formed graben basins basin that was open to the ocean to the south. The and in the continually subsiding Permian basins; ocean waters, into which shallow-marine platform the widespread basal Bunter sandstone provides a deposits, typical of the rest of southern Europe at reservoir in some areas. The rift systems having a that time, were deposited, extended locally into general north-south orientation bisected the early the Southern North Sea Basin (Ziegler, 1980). east-west Variscan lineaments and resulted in an

4 Lithology, main reservoirs, oil and gas, source rock, thickness in meters AGE VIKING GRABEN CENTRAL GRABEN SO. NORTH SEA BASIN W. NETHERLANDS AND SAXONY r---- ·­ 1--_-_-_:­ 1- - _____, --- 1------.-----l---- '=---=--=-­ --- PLIO 1---- r----r--=--=--= --- 600-1500 ------MIO ·~ , .... - .;.... ·:..·:···· >-a:: 1000-3300 ~...... ,..,.,..,---+-----1 ~-=--=--= <( OLIGO 1----- 0-1000 i= --- ~---==-~ a:: w 1- EO ~~~ Y-< 300-900 =---=-.E ---.., 0-1200 ~ :.:..:.~ ~------j-~-PALEO ~~; ~--20-0--6-0-0--i~,! ~---0--6-00-----~IE~~~:;::-r=....=-!;:::s;:-----t------J~:~··_~··~&~···~·· __r~-=-l

(/) ::::J UPR r-...=-- 600-1200 I L _l 500-1100 0-1400 300-1200 0 5 w u <( 1-w a:: u t------1-~LOW ·S~~~;E 0-1200 c::_~,'OURC£ 0-700 ~ 0-1200 ~ t 250-1500 1-----+------F...._=--+-.._,~=,+--.--+-0--7-0-0----11-~-~~-,~r-/_R_O~_K+-----+t.,;.;....;...~./-----11------i ~ • 50-1500 S2 UPR (/) 1------i+....:L~ 0-1700 ~--c;;;_~ (/) <( MID 0-300 -- 500-1000 a:: ----~:~_,_~'....,.::,:·'·::!.<'::y"- 1------1 ....._.-__]~ SOURCE ::::J 1-- * ~ ~ --, LOW •. •••• -:- ••• ·.~\ . I . 0-500 0-500 ---- ROCK 500-1000 t------'------+__..... :::_.....,_.;..;,_. _= __,...~_\r--= ...... :;JI!,~----1 ~::1----+-----i ~~----_--_,~.,...... _---+------1~--=-=--=LL-e_g_e_n.l....d-----l

TRIASSIC 0-2000 ~§~ 0-1200 0-1800 r-- - :--:·.-.· .... :;d 4 1- ~ Shale =----1 f::=-'== ~--=! ~--=-=-~~---nHEffiHJ~;-1-:-~-=----!~'1>. _ ~:;;~...... =-1----+------i ~;:_·;~:~.:;J Sandstone PERMIAN * 0 1500 ------e~~-:'~.·~;;;:-.';-;;;.::~""">,....~::)'-.---r--o_-1_o_o____, 1--:·=·'·>.::.....::-·=-:~-~·,';):...... --+------1 w:::.:: V "'*"" o-1800 ~ t- "' r=-_ _ .· ..-., .. -.:: · lt::.l:::::r::: Limestone CARBONIFEROUS ;~:·:~D. 0-600 ~~;~E 2000-3200 ~ Salt }::;-~-:-,;·: I -I Coal 1---D-E-VO-N-IA_N__ -~.:·.,.~·:~~:~""':~)----+--o--1-00_0___..,~ • 0-600 1-=t::l Organic shale

CALEDONIAN BASEMENT Modified from Ziegler, P. (1980)

FIGURE 2.-Stratigraphic diagrams of selected petroleum provinces.

early access to southern seaways (Tethyan) and 1,000 km long: the Viking and Central Grabens, later (in Jurassic time) to Arctic seas. One arm of and the Danish-Polish Trough. North of 62° N. the rift development followed the Variscan basin latitude, the rift zone grades into the Atlantic rift development to the southeast through Germany system, and hence the northern Norway coastal and Poland. Seawater influx along this rift ex­ region becomes part of an open-ocean, pull-apart tended only into the Southern North Sea Basin system that worldwide is not as favorable an en­ and resulted in the deposition, distally, of evapo­ vironment for petroleum occurrence as is the two­ rites (Rot formation) and, in the open seaways, sided rift basin (Klemme, 1981 ). Marine waters Muschelkalk carbonates. Triassic time closed with from both the north and the south had access to a regression to the south and accompanied deposi­ the region through the rift basins. tion of the dominantly red-colored, generally fine­ Tectonic events throughout the Jurassic con­ grained, and somewhat evaporitic Keuper series. tinued to activate faulting in these zones and af­ The Triassic rocks have minimal petroleum reser­ fected depositional environments and types and voir potential and no source-rock potential; their localities of clastic availability. Statfjord sands, presence, however, affects burial depths to under­ for example, were deposited in association with an lying source rocks in the Carboniferous of the Early Jurassic tectonic event. Also in Early Juras­ Southern North Sea Basin. sic, a bituminous source-rock facies that supplied The generally widespread phenomenon of rifting petroleum to the overlying Jurassic-Cretaceous in Triassic time was consolidated in Early Jurassic reservoir developed in the Southern North Sea time into two long, sinuous rift zones, each over Basin area; time-equivalent sediments, however, in 5 the central and northern grabens, as well as in still earlier Jurassic processes, produce reservoir eastern Germany and Poland, are not of source­ rocks of significance to the occurrence of petroleum. rock quality. In Middle Jurassic, a volcanic dom­ ing in the central North Sea produced a triple junc­ tion between the Viking, Central, and Moray Firth PETROLEUM GEOLOGY (Witchground) Grabens; erosion from this central high fed reservoir sands mostly northward into the Possibly never before in the history of petroleum Brent area, with a lesser amount being shed to the exploration has a major basin been developed so south. Subsidence in the Late Jurassic followed systematically by utilizing at every stage state-of­ the doming episode and resulted in deep-water, the-art exploration and development tools. Key to restricted depositional conditions in the Viking, the development, also, has been the extraordinary Central, and Moray Firth Grabens, as well as in public availability of data that permitted a rapid selected parts of the Norwegian Atlantic Shelf evolution of the collective thinking and led to the north of 62° N. latitude. These conditions pro­ present extant petroleum geology synthesis. duced the Kimmeridgian ''hot shale'' source rock; Two distinct geologic situations are responsible marginally, the Sole Pit and Norwegian-Danish for almost all of the oil and gas in the North Sea Basin areas subsided less rapidly, and depositional region. The first, and most prolific of the two, is environments were such as to produce a different the dominantly Mesozoic oil and gas play (Play I) nonsource-rock facies. In the most southerly part in the Viking, Central, and Moray Firth Grabens, of the Central Graben area, the hot-shale facies in the small basins south and southwest of Ireland changes to the nonsource-rock Weald facies, and (figs. 3 and 4), and in the basins north of 62° N. likewise farther to the south into the Netherlands latitude (figs. 5, 6, 7 and 8). The second is the and Germany and to the southeast into eastern Paleozoic gas play (Play II) in the Southern North Germany and Poland, a nonsource-rock facies also Sea Basin and in the Irish Basin (figs. 1 and 9). obtains. The general transgression of the seas in Play 1-The Mesozoic play is closely controlled the Late Jurassic produced shoreline sand by the distribution of the Upper Jurassic, Kim­ deposits marginal to the Moray Firth and to the meridgian source shale, which is in tum controlled west side of the Viking Graben; some of these by the geometry and location of the grabens (figs. sands were swept out to the rift edge and tumbled 3, 4, 5, and 7). South of the Mid North Sea High in into the deep-water slope and ocean-basin environ­ the Central Graben, facies · changes destroy the ment. Both the shelf and deep-ocean sandstones source-rock character of the Jurassic, and depth of are potential reservoir rocks. burial is such as to limit maturity. Likewise, in the By Cretaceous time, the North Sea region was no Horda Basin and in the Norwegian-Danish Basin, longer significantly affected by Atlantic rifting ac­ chances for good Jurassic source rock develop­ tion. Continued subsidence associated with general ment appear limited. Farther to the southeast in transgression produced a carbonate/shale deposi­ the Danish-Polish Trough and outside of the tional system; the pure chalks that accumulated assessment area, Upper Jurassic rocks have clear­ suggest the remoteness of positive tectonic ly changed facies so as to be less suitable for elements capable of supplying clastic materials. source rock. To the southwest of the main North , Alpine compressional stresses af­ Sea graben development, Upper Jurassic rocks ap­ fected the general northwest European basin pear to vary from suitable to nonsuitable facies system in such a way as to produce continued but commonly are not buried deeply enough for downwarping in some areas but inversions in maturation (fig. 4). We assume that the Lower others; the uplifted blocks remained positive Jurassic rocks, which provide a source for modest throughout the subsequent Cenozoic. Cenozoic sedi­ oil generation in part of northwest Europe and, as mentation was concentrated in Mesozoic depo­ well, some pockets of Kimmeridgian "hot shales" centers and served to further bury the underlying (fig. 2), are also present in the rifted portions of the rocks; thus the Mesozoic source rocks were sub­ English Channel Basin, the Celtic Sea Basin, and jected to their maximum depths of burial and in the Porcupine Basin (fig. 1). Though the possible maturity levels. Only in the vicinity of the East presence of Kimmeridgian source rock is encourag­ Shetland Platform did early Cenozoic delta develop­ ing, we have little evidence to suggest that ment and deep-water sand deposition, similar to petroleum occurrences should be different from

6 40 30 20 1'W oo 1oE 20 30 80 go 10'

LEGEND

N62° ---1.1..- ----l..L...__ ---1.1...­ PARALIC-DELTAIC FACIES "o MIDDLE JURASSIC o'f ----500' ---­ 61° ISOPACH OF JURASSIC KIMMERIDGIAN ; "HOT SHALE" MATURATION 61° J) STAGE f' ~~EARLY75 1 1 B 00'- 0 ,000' UPPER JURASSIC MATURE "HOT SHALE" I • 10,000'-13,000' 60' ~ Fi':'' ;::; LATE STAGE (KIMMERIDGIAN) I (!) :;:;;:;:;:;:;:::: 1 13,000' ll~~DIS. I z / FIELDS (GIANTS ARE NAMED) 11' /'"" ~ \ GAS VIKING GRABEN Cl) \ OIL b DOMINANT PLAY TYPE (SEE FIG.10 AND 1 59' \ /~-;\[;;\ ~{;) 59° \ 'e) " \ 58° ~ ~ 58°

57°

ABERDEEN IMMATURE

57" U.K. _J r-'---._ \, \ !'--- 56° \ o_ q \ \ EDINBURGH

0 30 60 MILES N55°

Modified from unpublished maps prepared under contract to USGS by H. D. Klemme of Geo Basin Ltd.

FIGURE 3.-Play I, central North Sea region. Shows the location of potential petroleum basins between latitudes 55° N. and 62° N., isopach distribution of Jurassic Kimmeridgian source rock, interpretation of source-rock maturity,location of associated oil and gas fields, and the distribution of dominant play types as described in fig. 10.

7 3' 2' 1' E 2' 3' 4' 5' 6' I \ IMMATURE _ N54' 0 \o_ JURAS SIC KIMMERIDGIAN " HOT SHALE" MATURATI ON OIL {~ EARLY STAG E 7500'-10,000' 53' ~ MATURE 10,000'-13,000' GA S{~ LATE STAGE 13,000' FIELDS UNITED KINGDOM . OIL

52' ROTTERDAM ®

ANTWERP 51'

BELGIUM ~~~ 50' 50' FRANCE tJ ...'Z. 30 60 MILES ' \ BOUNDARY REPRESENTATIONS AR E NOT NECESSARILY AUTHORITATIVE

8' 6' 5' 4' 1' E 2' 3' 4' 5'

Modified from unpublished maps prepared under contract to USGS by H. D. Klemme of Geo Basm Ltd .

FIGURE 4.-Play I, southern and southwest North Sea region. Shows the location of potential petroleum basins between latitudes 49 ° N. and 54 ° N., isopach distribution of Jurassic Kimmeridgian source rock, interpretation of source-rock maturity, and location of associated oil and gas fields.

those discovered elsewhere in northwest Europe of burial, over a large portion of the area, suggests but outside of the North Sea proper; we assume that gas will be dominant. Discoveries by the in­ therefore only modest potential. A further area of itial wells in the Tromso Basin (fig. 7) and in the significant interest is the Rona Ridge west of the Helgeland Basin (fig. 5), which have favorable tw

8 clearly shows trap relationship to certain tectonic Exploration maturity.-By standards of other and stratigraphic conditions (fig. 3). We have no large producing areas, the northwest European evidence of significant lateral migration of oil; in region has not been tested by a large number of ex­ this assessment we assume only minimal lateral oil ploratory wells; still it is possible to argue that the migration and, hence, a geographical proximity exploration has been very thorough, and most between the traps and the areas of oil generation. areas south of 62° N. latitude are in an advanced Play 11.-The Paleozoic play, dominantly in the stage of exploration. This is so not only because of Southern North Sea Basin, is closely constrained the technical competence of the explorationists by the geographic distribution of the necessary but also because economic conditions are such that juxtaposition of the source rock, the reservoir only relatively large fields are presently economic. rock, and the seal (fig. 9). All of those, including To date, approximately 2,000 exploratory wells the related sedimentary rocks, are delimited in have been drilled in the North Sea region and, in turn by the geometry of the Caledonide and V ari­ our judgment, most of the important blocks, par­ scan events. The source rocks are the Westphalian ticularly in the United Kingdom, have been tested coal measures, the major reservoir rock is the by one or more wells. Because we can infer certain Rotliegendes aeolian sandstone, and the seal is geologic conditions that limit the favorable area, provided by the regionally distributed Zechstein we would contend that an advanced stage of ex­ salts. Locally, in the Irish Basin, the Zechstein seal ploration and development has been achieved in is not present. Gas leaked up into Triassic sands every area except offshore Norway, but we would that were in tum sealed by local Triassic suggest that water depth and absence of infra­ evaporites and produced the giant Morecambe gas structure, especially north of 62 o N. latitude, will field; the basin is small, however, and we do not ex­ significantly hamper future development. pect other such surprises. To the east into onshore The discovery history of the well-explored region Netherlands and Germany, most of the critical would appear to support this interpretation. Com­ geologic factors remain positive. However, with monly in a new region, we expect the large fields to respect to depth of burial, and hence temperature, be discovered early in the exploration process, of the Westphalian coal source rocks, they ex­ primarily because they are geographically large. In perience an increase such that resultant nitrogen the North Sea, however, large discoveries are generation reduces the heating quality of the gas distributed throughout the exploration history to an even greater degree than in Groningen; as a (fig. 12), with the largest yet, the Troll gas field, result, the gas is economically unacceptable. The found in Norwegian waters in 1978, rivaling the complexly block-faulted traps are typical across giant gas field at Groningen, which was the cause the area, and the field-size distribution is generally of all of the North Sea excitement about 20 years expectable (fig. 11 ). Groningen, however, is so ago. This unique discovery pattern is true in this large, as compared to the next largest Leman field, region only because of the systematic exploration that statistically one might expect the existence of plan controlled by governmental, area-specific fields of intermediate sizes, but the density of drill­ licensing. When one examines the discovery his­ ing is such as to give reason to argue strongly tory in relation to the year of the award of the con­ against this possibility. cession, one finds that the fields discovered within Barents Sea.-Though not a part of this assess­ the first year after the award account for 64 per­ ment area, the Barents Sea basins, east and north­ cent of the reserves discovered and an average east of Bjornoy and Tromso, would appear to pre­ field size several times larger than those fields sent mostly a lower Paleozoic play (figs. 7 and 8), discovered after greater time lapses since the con­ unless it can be demonstrated that, in fact, cession award. Those fields found several years Jurassic or some other age of rock is in proper after the concession award account for only a small facies and suitably buried for maturation. Though percent of total discovered reserves and are notably little is known of the Paleozoic section, we do not smaller. These data suggest that discovery anticipate favorable Devonian source rock as patterns are comparable to other regions and that found in the Volga Urals section of the USSR; most of the North Sea region is in a mature stage rather, we would anticipate an Old Red Sandstone of exploration, at least with respect to the extant facies similar to that in the North Sea and on exploration concepts. Spitzbergen (Ulmishek, 1982).

9 0 100 KILOMETERS

0 60 NAUTICAL MILES LOFOTEN BASIN SCALE (Approx.)

LEGEND

----600ft---­ WATER DEPTH

MAJOR FAULT OR FLEXURE

I I I I II II II I II II I I II II fl II 1! 1! I II JURASSIC ABSENT ON HACHURE SIDE

JURASSIC "HOT SHALE" SOURCE

~ POSSIBLY MATURE OIL

-MATURE OIL /1) p::::;:::;:J MATURE GAS

o (-~), /"SHETLAND 60 OIL AND GAS FIELDS I I ISLANDS '\\) - )NORTH ) I

Modified from unpublished maps prepared under contract to USGS by H. D. Klemme of Geo Basin Ltd.

FIGURE 5.-Potential petroleum basins, distribution of Jurassic Kimmeridgian source rocks in the North Sea be­ tween latitudes 59° N. and 69° N., inferred degree of maturity of source rock, and oil and gas fields. Section lines refer to interpreted seismic sections of fig. 6.

10 -sE ® CONTINUATION VESTFJORD 0 OF LOFOTEN BASIN SEA BOTIOM -sE

u ~ 1.0 1.0 ~ 2.o :;:;E E 2.0 3.0 :;:;" ~ 3.0 E 4.o ~ ~ ~ 4.0 ~ 5.0 ~ ~ 5.0 l 6.0 0 l: 6.0

(j) - SE ® HELGELAND BASIN ~sE TRAEN BASIN f NORDLAND RIDGE SEA BOTIOM --~ 1.0 ~ 1.0 ...,E 2.0 E 2.0 :;:; ~ 3.0 ~ 3.9 l" :4.0 ~ 4.0 ~ ~ ~ 5.0 l 5.0 0 l: 6.0

(j) I -sE GENERALIZED STRATIGRAPHIC SECTION TRAEN BASIN ® NORDLAND RIDGE HELGELAND BASIN VORING HELGELAND ~ FEET TERTIARY

u (PROGRADING CLASTICS) 1.0 ~ 10,000' + IN WESTERN E 2.0 5000 MORE BASIN, PINCH OUT :;:; 30 TO 40 MILES OFFSHORE. 3.0 ~ ~ 4.0 10,000 ~ ~ 5.0 CRETACEOUS 0 20 Km 15,000 (PROGRADING CLASTICS?) l: 6.0

20,000 KIMMERIDG IAN (INVERSION 25,000 TECTONIC PHASE TECTO NICS) -sE JURASSIC VORING NORDLAND ® (SS & SH 'l BASIN RIDGE HELGELAND BASIN VEGA RIDGE WEST ? EAST I

LEGEND ~ 4.0 ~ ~ 20 Km ~ 6.0 l TERTIARY

CRETACEOUS _® il -sE JURASSIC

~ ~ {:: ~~ l BASEMENT ;< r 0 25 Km l Modified from Jorgensen and Navrestad, 1981

FIGURE 6.-Interpret.ed seismic stratigraphy and structure. Locations of sections shown on fig. 5. Modified from Jorgen­ sen and Navrestad, 1981.

11 15° 20° 25°

LEGEND f ----600ft------JURASSIC A / (__ WATER DEPTH "HOT SHALE" \ SOURCE r-==. -' \ SPITZBERGEN MAJOR' FAULT OR FLEXURE' ' ~POSSIB LY MATURE BANKEN \ O \) Ill Ill Ill ~O IL DEPRESSION ~ (j 181 MATURE OIL ~ 75° \'J SALT.. DIAPIRS 75' 1: .·.::-::-::-l MATURE GAS c/'-s-- I I !I I I I I I I I I II I 1! II I I II II I! I ___, JURASSIC ABSENT H I'------""' HACHURE SIDE \ ( BARENTS SEA '-.._ .-> 'b ) 0

..

70' O NAUTICAL MILES 60

Modified from unpublished maps prepared under contract to USGS by H. D. Klemme of Gee Basin Ltd.

FIGURE 7.-Potential petroleum basins, distribution of Jurassic Kimmeridgian source rock in the North Sea between latitudes 69° N. and 76° N., as well as inferred degrees of maturity of source rock. Section lines refer to interpreted seismic sections on fig. 8.

12 0 SPITZBERGEN ® BANK EN 12" 13' 14' 15' 16' 17'

18' 19' 20' 21' ~ E ~ I ~ ~ ~ 3 l 4 Ocean•c I Continental l Crust Crust 50 Km

® WESTERN BASIN SENJA RIDGE 15' 17' ®

© WESTERN BASIN SENJA RIDGE

~~ 13" 14" 15" 16" 17" 18" 19' lEGEND CJ TERTIARY E] CRETACEOUS ll~Ocean•c IContmental Crust Crust

JURASSIC [I;] ®N TRIASSIC- l2J2J ~ PALEOZOIC ~

~ SALT l 50 Km -

© BJORNOY LOPPA HAMMERFEST 21 ' 23' 24' GENERALIZED STRATIGRAPHIC SECTION SENJA RIDGE ARCTIC SEA NOROKAPP-HAMMERFEST BASINS

TERTIARY 50 Km (PROGRADING CLASTICS-THIN VEN EER )

CRETACEOUS (CLASTI CS ? ?) CRATONIC

20.000 RIFT AND ® JURASSIC (SS AND SH) CRATONIC 71' 72' 73' 74' 75' 25,000 CRATONIC TRIASSIC (CLASTICS ?l PERMIAN ~ 30,000 I CRATONIC (CARBONATES, CLASTICS, SALT?) ! 2. CARBONIFEROUS 3 35,000 CRATONIC (? CLASTICS, CARBONATES, EVAPORITES ?) ~ 4 DEVONIAN CRATONIC (? CLASTICS, CARBONATES, EVAPORITES ?l l WEST EAST

A-E and H modified from Ronnevik. 1981

FIGURE B.-Interpreted seismic stratigraphy and structure. Locations of sections shown on fig. 7. Modified from Ronnevik, 1981.

13 60 ao go

54°N

UNITED KINGDOM 52°

LONDON ® LEGEND SO URCE WESTPHALIAN ~ 51° A AND B COAL MEASURES UNDER ROTLIEGENDES ,, --·-- RE SERVOIR --·-- ROTLIEGENDES CAP _L..L...L...L ZECHSTEIN SALT

HIGH 50° 50° PRE-PERMIAN BASEMENT BOUNDARY REPRESENTATIONS ARE GAS FIELDS ~ GIANTS ARE NAMED NOT NECESSARILY I .. 40 30 40 60 ao

Modified from unpublished maps prepa red under contract to USGS by H. D. Klemme of Geo Basin Ltd.

FIGURE 9.-Play II, southern North Sea region. Shows potential petroleum basins between latitudes 50° N. and 54° N., the distribution of principal source, reservoir, and sealing facies, and the distribution of oil and gas fields.

RESOURCE ASSESSMENT to determine the resource values associated with a full range of probabilities for each country. From The location of the northwest European assess­ this, we calculated and selected for reporting a 95 ment region is shown in figure 1. Estimates by the percent to 5 percent probability range, a mode, and U.S. Geological Survey of oil and gas resources in a statistical mean. The numbers are reported to this region are given in table 1 and figures 13 several significant figures, which represent only the through 26. These probabilistic distributions of precision of the arithmetic process, not the accuracy the assessment are arranged to first show the ag­ of the assessment. gregate amounts assessed for the entire northwest In utilizing these numbers, the reader should be European region, followed by aggregates of the aware that no single number represents the esti­ area north of 62 ° N.latitude and the area south of mate; rather, we are saying that there is a 90 per­ 62° N. latitude, and finally showing the cent probability that the correct value lies between assessments for individual play areas. Supplemen­ the 95 percent and 5 percent reported values. The tary data of interest in analyzing these estimates mean is singled out only as a convenient measure are supplied in table 2. of central tendency that can be added arithmetical­ At the time of the assessment, the country-by­ ly to other mean values. The mean value actually country allocation of resources was estimated on represents the assessment only at a single prob­ the basis of play distribution by country and on the ability value; the measure of central tendency that proportion of total estimated resources assigned to expresses the greatest range of probability values, each play (table 3). This estimate was considered to and hence the most satisfactory single number ex­ be an allocation of the mean quantity of resources, pression of the assessment, is the mode. If the and a curve was fitted by using the mean estimate distribution of the values of an assessment were

14 normal, the mean and the mode would be equal; in TABLE 1.-Assessment of undiscovered conventionally recov­ fact the distribution of the estimate tends toward erable petroleum resources of the northwest European assess­ log normal. This tendency produces an asymmetry ment region in the distribution that causes the mean values, [Resource assessment by USGS as of July 20, 1982; see also figs. 13 through 26) which in effect represent the center of gravity of the estimate, to move out toward the higher Crude oil, in billions ofbarrels1 Natural gas, in trillions of cubic feett estimated values and the lower probabilities. This Low High Mean Mode Low High Mean Mode 2 difference between the mean and the mode in a F95 F5 F95 F5 lognormally distributed estimate is especially 9 34 20 15 92 258 167 162 prominent in estimation situations that have (Fig. 13) (Fig. 14) significant unknowns. In such situations, the 1For gas, billions of barrels of oil equivalent (BBOE)@ 6,000 ft3/bbl=27; oil plus gas tendency has been to allow for favorable condi­ modal value BBOE=42. 2F denotes the 95th fractile; the probability of more than the amount F is 95 per­ tions at the low probability, which shifts the 95 95 cent. F is defined similarly. center of gravity of the assessment, or the mean, 5 to a greater degree than would be expectable in an assessment under conditions of greater geologic certainty. TABLE 2.-Supplemental and comparative data relative to the Because the use of resource estimates involves resource assessment of the northwest European assessment dealing with the unknown, we believe it prudent region 1 for the analyst to consider the reality of any point [A * indicates quantity positive but data not available ) on the curve and to actively consider a range of Crude oil, Natural gas, probability values. Commonly, we can assume in billions of in trillions of that if the low probability assessment proves ac­ barrels cubic feet curate, we are better off than planned and may have delayed only temporarily an investment op­ Cumulative production to Dec. 31, 1981 ------3.8 40 portunity. If the high probability assessment, Identified reserves to Jan. 1, 2 however, proves accurate and we have gambled on 1982 : the mean or mode, or even on other less-probable Demonstrated ------23.6 222 high values, the decisions deriving therefrom may Inferred ------* * Undiscovered recoverable resources prove to be calamitous. (mode) ------15 162 The analyst should recognize that if he is con­ TotaP ------42.4 424 sidering a single frontier basin with a marginal 1Cumulative production and reserves are composited estimates from various probability of less than 1, he may want to consider sources. the conditional assessment while taking note of 2Following terminology outlined in USGS Circular 860. "Demonstrated" is equiva­ lent to API "Proved and Indicated Additional." (For natural gas, "indicated addi­ the marginal probability (one element of risk) of tional" is zero.) "Inferred" represents anticipated field growth in existing fields. there being any commercial petroleum at all. 30riginal recoverable resources (ultimate); BBOE for gas=72; total oil and gas Resource categories assessed-Based on the (mode)=114 BBOE. assumption that present economic and technologic conditions will continue, the assessment of un­ discovered conventionally recoverable petroleum resources includes those resources that can be ex­ tracted by using conventional methods (Dolton, COMMENTS and others, 1981). The assessment does not include inferred resources that may yet be found in new • The dominant analog used in volumetric pay zones or in extensions of existing fields. Also calculations was the Klemme type 3 rift basin excluded from the assessment, even if present, are (Klemme, 1981). Some basins to the west of the unconventional resources such as extra-heavy oil British Isles and to the northwest of Norway deposits, tar deposits, oil shales, as well as gas in north of 62° N. latitude did not possess the low permeability (tight) reservoirs, gas occ;luded in two-sided rift characteristic and were classified coal, gas in geopressured reservoirs and brines, as Klemme type 5 pull-apart basins (see text and natural gas hydrates. for discussion).

15 PLAY I

UPPER JURASSIC (KIMMERIDGIAN) "HOT SHALE" FACIES SOURCE Showing field size and play type

LEGEND

g ~ ;; g ~ g 5 ..... g - ~ ~ ~ ~ ::: N g ~ ~ --' "' g "' "' "'z ~ "' g g ~~ ~ g N ~ g en i 117 "' "' "" 0 z ..... :::> ~ :::>"' z z"' (/) "' z "' u ~ "' "' J: "' 0 "' ::;; :::> ~~ .. "" ~ 9 "" ~ "' z u"" ~ :::> <( ~ <"" :::> "' "'::;; "" (!)-i:o ;:: "' "'u "'<( "" "' ~ d z ~ ~ ~ !J:l ~ ~ ~ ~~ ~ i3 "' ~ ~ ~

JURASSIC SOURCE (GENERAL) PLAY TYPE lA RESERVOIRS, TIME OF MATURATION: DEVONIAN, TRIASSIC, JURASSIC, CRETACEOUS, LATE CRETACEOUS TO MID-TERTIARY (DEPENDENT PALEOCENE AND EOCENE (MAINLY JURASSIC UPON BURIAL RATES~NTINUING TO PRESENT. s~ ~A AND LOWER TERTIARY). TIME OF TRAP FORMATION: LEVEL LEVEL MAJOR TECTONIC MOVEMENT OUTLINED TRAPS IN RESERVES (1981) OIL-(109 BBU GAS TCF LATE JURASSIC TO EARLY CRETACEOUS, SUB­ PRODUCED 2.4 ' SEQUENT LOCAL SALT FLOWAGE AND COMPAC­ PROVEN AND PRODUCED 25.0 95 TION RESHAPED SOME TRAPS IN POST­ SOURCE, PALEOCENE. SHALE~ CURRENT EVIDENCE INDICATES THE MAJOR TIME OF MIGRATION: SOURCE SHALE SOURCE IS FROM UPPER JURASSIC (KIMMERID­ FROM MATURATION TO PRESENT. AND CAP SOURCE GIAN) "HOT RADIOACTIVE BITUMINOUS SHALE" EXPULSION EFFICIENCY: POSSIBLY ±4% OF RESERVES FROM OTHER 6% OVERALL (TO DATE)- JURASSIC SHALES BELOW (KIMMERIDGIAN). ASSUME: AVERAGE TOC 7.5%, 3640 CUBIC MILES. CAP, (LOCALLY; 9% BETWEEN 600 AND 62', 4% VIKING SHALE AND IMPERVIOUS CARBONATES, JURASSIC, GRABEN BETWEEN 5B'30' AND 60", 4% CENTRAL CRETACEOUS, AND LOWER TERTIARY. GRABEN BETWEEN 55' AND 58'30'). ROTATED FAULT BLOCK TRAP-HIGH RE­ LIEF-LATE JURASSIC TO EARLY CRE­ TACEOUS GROWTH-PRIMARILY JURASSIC SOURCE AND RESERVOIRS. HYDROCAR­ BON WINDOW CONTAINS• OIL-{;ONDEN­ SATE-GAS ACCUMULATION 71% OF TYPE 1 PLAY AND 50% OF N. SEA OIL AND 10 GAS RESERVES. APPROXIMATELY 30 PLAY TYPE IB FIELDS TO DATE. 25 DISCOVERIES UNDER EVALUATION. MAJOR (GRABEN) FAULT ZONE. ANTITHE­ "TROLL GAS APPEARS TO BE UPDIP-MIG­ L~~~L ------L~~~L TIC FAULTING, VARIABLE AMOUNTS OF RATION FROM GAS "WINDOW" SOURCE. STRATIGRAPHIC CONTROL. LATE JURAS­ SIC-EARLY CRETACEOUS FAULT GROWTH AND EARLY TERTIARY CONTINUED GRA­ BEN DOWNWARP. JURASSIC SOURCE AND PLUS 25 DISCOVERIES 1974 TO PRESENT BOTH JURASSIC AND PALEOCENE-EOCENE EITHER NON COMMERCIAL OR ~S RESERVOIR RESERVOIRS. UNDER EVALUATION

~

"?~~~~ TWO POSSIBLE DISCOVERIES ~g~~~ 1 m~umu. GIANT h-.==------

lA JURASSIC SOURCE-ROTATED FAULT BLOCKS IB JURASSIC SOURCE-FAULT ZONE/STRATIGRAPHIC RESERVOIRS, RESERVES (1981), RESERVOIRS: TIME OF TRAP FORMATION: IN VIKING GRABEN AREA' OIL 1109 BBL) GAS (TCF) UPPER JURASSIC-LOCALLY BRAE FORMATION I) JURASSIC RESERVOIRS-LATE JURASSIC-EARLY UPPER JURASSIC, MIDDLE JURASSIC AND LOWER PRODUCED 2.1 ? (SUBMARINE DELTA FAN SAND). CRETACEOUS ' JURASSIC SANDSTONES, PROVEN AND PRODUCED 1B.7 64.2 PALEOCENE-DISTAL UP-DIP PINCHOUT OF 2) PALEOCENE RESERVOIRS-MIDDLE TERTIARY UPPER JURASSIC-LOCALLY PIPER FORMATION, SOURCE, SUBMARINE DELTA FAN SAND. (CONSIDERABLE STRATIGRAPHIC CONTROL). RESERVES (1981), TIME OF MIGRATION: BRUCE FORMATION, MAGNUS MEMBER; (MARGI· UPPER JURASSIC (KIMMERIDGIAN) "HOT SHALE" 9 NAL MARINE SHELF SANDS TO SUBMARINE FANS)­ (ONE FIELD-BEATRICE- 1/z% OF ABOVE RESERVES OIL (10 BBU GAS (TCF) EARLY TERTIARY TO HOLOCENE MIOOLE JURASSIC-LOCALLY BRENT FORMATION, FROM MIDDLE OR LOWER JURASSIC SHALE). PRODUCED MIDDLE AND UPPER BERYL FORMATION; (OR TAlC CAP, PROVEN AND PRODUCED l.B ± 1.0? SANDS~ UPPER AND LOWER CRETACEOUS SHALES, UPPER SOURCE: LOWER JURASSIC-STATFJORD FORMATION; (FLU­ JURASSIC SHALES. UPPER JURASSIC-(KIMMERIDGIANJ "HOT SHALE" VIAL TO COASTAL MARINE SANDS). TIME OF MATURATION, CAP: SHALE AND CLAY-UPPER ;IURASSIC-LOWER TER­ IN CENTRAL GRABEN AREA MID TERTIARY (N. VIKING AREA), LOWER TERTIARY (MORAY FIRTH AREA). TIARY JURASSIC SANDSTONES AND MINOR RESERVOIRS TIME OF TRAP FORMATION, TIME OF MATURATION: IN PERMIAN ZECHSTEIN CARBONATES. LATE JURASSIC-EARLY CRETACEOUS. EARLY TO MIDDLE TERTIARY TIME OF MIGRATION, EARLY TO MIDDLE TERTIARY TO HOLOCENE

FIGURE 10.-Listing by size of fields attributed to Play I, further division of the occurrence of petroleum into four different diagrammed trap types, and a listing of fields attributable to each. Certain characteristics of the play and of each trap type are also listed.

16 PLAY TYPE IC PLAY TYPE ID SALT DIAPIR WITH DRAPE, HIGH RELIEF, HORST (OFTEN BALD WITH COMPACTION, SEA SEA PRE-AND POST-PALEOCENE GROWTH. VARIABLE RELIEF, LATE MESOZOIC GROWTH, TERTIARY COMPACTION AND LEVEL LEVEL PRIMARILY JURASSIC SOURCE AND L~~L------L~~~L PALEOCENE RESERVOIR, 11% OF PLAY I DRAPE. 12% OF PLAY I BOE RESERVES, OIL AND GAS RESERVES (BOE). GAS TO 9 FIELDS (54% GAS TO 46 % OIL) AND OIL 44%156% RATIO. 4 DISCOVERIES UNDER EVALUATION. ~ SSRE~ :t DISCOVERIES-EITHER ~ :t4 DISCOVERIES-EITHER NONCOMMERCIAL OR OR SS RESERVOIR "!' NONCOMMERCIAL OR UNDER EVALUATION 4 0 ~ ~ SOURCE :;~~~~~\;; I GIANT H--FI=:------t------0 ~~~LL~~~-~------

IC JURASSIC SOURCE-DRAPE OVER DIAPIR ID JURASSIC SOURCE-HORST WITH COMPACTION RESERVOIRS, TIME OF TRAP FORMATION, RESERVOIRS, CAP, PALEOCENEICRETACEOUS-EKOFISK AND TOR CONTINUED SALT FLOWAGE OF DIAPIRS AFTER DE­ 1) DRAPE RESERVOIRS LOWER TERTIARY AND JURASSICICRETACEOUS FORMATIONS (CHALK) AND MONTROSE GROUP POSITION OF PALEOCENE. POST-PALEOCENE PALEOCENE/EOCENE-LOCALLY FORTIES FORMA­ SHALE. {DEEP-WATER SANDS). DRAPE. TION, FRIGG SAND; (SUBMARINE FAN TIME OF MATURATION, RESERVES (1981), TIME OF MIGRATION, SANDSTONE) LATE CRETACEOUS-EARLY TERTIARY TO HOLOCENE PRODUCED OIL (10; BBU GAS ycf) LATE CRETACEOUS TO HOLOCENE-PRESENT TRAP 2) HORST RESERVOIRS (DEPTH DEPENDENT!. FILL MID-TERTIARY TO RECENT JURASSIC (COALY DELTAIC SANDSTONES) TIME OF TRAP FORMATION, PROVEN AND PRODUCED 5.0 13.0 DEVONIAN ("OLD RED" SANDSTONE) HORST RESERVOIRS-LATE JURASSIC TO LATE SOURCE, RESERVES (1981), 9 CRETACEOUS MOST PROBABLY UPPER JURASSIC (KIMMERID­ (10 BBU GAS (TCF) DRAPE RESERVOIRS-POST -PALEOCENE (LOCAL GIAN) "HOT SHALE". PRODUCED 0.88 1 STRATIGRAPHIC CONTROL). CAP, PROVEN AND PRODUCED 2.4 16.8 TIME OF MIGRATION, SHALE AND CLAY PALEOCENE AND EOCENE (LOC­ SOURCE, MAJOR RESERVES-POST -PALEOCENE ALLY IMPERVIOUS CHALK) MOST PROBABLY UPPER JURASSIC (KIMMERID­ TIME OF MATURATION, GIAN) "HOT SHALES". LOCALLY POSSIBLE GAS LATE CRETACEOUS (PRESENTLY IN "GAS WIN­ FROM MIDDLE JURASSIC COAL SAND "WAAY KERO­ DOW") GEN" SHALE FACIES.

Modified from unpublished maps prepared under contract to USGS by H. D. Klemme of Geo Basin Ltd.

FIGURE 10. -Continued.

PLAY II II CARBONIFEROUS COAL SOURCE­ UPPER CARBONIFEROUS (WESTPHALIAN) COMPLEX, BLOCK-FAULTED TRAPS COAL SOURCE RESERVOIR, PERMIAN-{PRIMARILY) ROTLIEGEND-DUNE AND SABKA SEA LEVEL SEA LEVEL SANDS, {MINOR) ZECHSTEIN CARBONATES, HAUPTOOLOMITE­ CARBONATES, PLATIENOOLOMITE CARBONATES, TRIASSIC­ UPPER BUNTER-DESERT SANDSTONES.

RESERVES: OIL (109 BBLl GAS (TCFl PRODUCED ? 40 PROVEN AND PRODUCED ? 145 {100 TCF ONSHORE- 45 TCF OFFSHORE)

SOURCE, CARBONIFEROUS-WESTPHALIAN COAL MEASURES THERMAL METAMORPHISM TO GAS

CAP, PERMIAN-{PRIMARILYI ZECHSTEIN SALT, TRIASSIC-{MINORI SALT AND SHALE. I; TIME OF (!) MATURATION, EARLY TO MIDDLE MESOZOIC {lATE CRETACEOUS INTERRUP­ z TION IN INVERTED AREAS). 0 TIME OF TRAP 84 ffi FORMATION, LATE PALEOZOIC-MESOZOIC {TERTIARY RESHAPING OF TRAPS 77 * ONSHORE IN INVERTED AREAS). 70 TIME OF 63 MIGRATION, MESOZOIC TO PRESENT {INVERTED AREAS TERTIARY REMIG­ RATION). 56 "-(.) 1- 49 42 (f) • IRISH SEA <( (.!) ~ 35 "'z ..... 28 ...... : ~ m z -' I]) 1- PLUS SMALLER ONSHORE AND ::;; ..: (.) 0 ~ ..: 21 ~ z ~ ..: ± Modified from unpublished maps prepared ~ ~ 0 ~ "- ..: ~ ~ 3 ,<: ~ ..: ~ GIANT 3.5 "' "' 0 ± 45 DISCOVERIES {OFFSHORE! 1966 TO PRESENT-EITHER NON COMMERCIAL OR UNDER EVALUATION

FIGURE 11.-Listing by size of fields attributed to Play U. a generalized diagram of trap type, and a listing of certain characteristics of the play.

17 DISCOVERY HISTORY by year of discovery LEGEND

-' -' 0 0:: 1- 10 w 0 Ill ::c ..c "' "'?i 8 6 "" 1974 1975

DISCOVERY HISTORY By field size according to time-lapse increment from year of award of concession

FIELD DISCOVERY Fl ELD DISCOVERY FIELD DISCOVERY FIELD DISCOVERY WITHIN ONE YEAR OF WITHIN TWO TO WITHIN FOUR TO SIX YEARS OR AWARD OF CONCESSION THREE YEARS AFTER FIVE YEARS AFTER MORE AFTER AWARD OF CONCESSION AWARD OF CONCESSION AWARD OF CONCESSION

10 w 0 Ill 6 "'8 4

GIANTtt±±±i33~=ccc~~==~~LeEE~~~~====cc~~~~~~~===I~~~====~== 24.1 BOE 6.1 BOE 6.2 BOE 1.97 BOE AVG. FIELD SIZE 1.627 AVG. FIELD SIZE 0.435 AVG. FIELD SIZE 0.452 AVG. FIELD SIZE 0.196 64% OF RESERVES 16% OF RESERVES 16% OF RESERVES 4% OF RESERVES 28% OF FIELDS 26% OF FIELDS 26% OF Fl ELDS 20% OF FIELDS

FIGURE 12.-Discovery history by year of discovery and by field size according to time-lapse increment from year of award of concession. Note that discovery history relative to concession date confirms concept of large discoveries coming early in the exploration process.

~ z z ~ <{ <{ .....:::c :I: ~ ESTIMATES ...... q ESTIMATES w Mean 19.91 w Mean 167.37 a: 00 0 Median 19.20 a: 00 Median 164.02 ci 95 percent 8.66 o.ci 95 percent 91.66 ~ 75 percent 14.53 ~ 75 percent 132.45 LL co ci 50 percent 19.20 LL co 50 percent 164.02 0 25 percent 24.55 0 ci 25 percent 199.31 o:t 5 percent 34.37 5 percent 257.71 ~ ci Mode 15.41 ~ o:t Mode 162.01 ::::i Standard 7.70 ::::i ci Standard 50.98 Ci5 N deviation Ci5 deviation <{ ci <{ N m m ci 0 0 a: 0 0 ~ a: 0 ~ ci 0.0 12.0 24.0 36.0 48.0 60.0 0.0 80.0 160.0 240.0 320.0 400.0 BILLION BARRELS RECOVERABLE OIL TRILLION CUBIC FEET RECOVERABLE GAS

FIGURE 13.-Northwest European region, subregions FIGURE 14.-Northwest European region, subregions A+B+C+C+E, aggregate recoverable oil. (Unconditional A+B+C+D+E, aggregate recoverable total gas. (Uncondi­ assessment; date-7/13/82.) tional assessment; date-7/13/82.)

18 TABLE 3.-Distribution by country and by subregion of undiscovered recoverable petroleum resources in the northwest European assessment region

Crude oil (BB) Natural Gas (Tcf) Low High Mean Low High Mean

South of 62° N.latitude (assessment date March 10, 1982)

Viking and Central Grabens, Moray Firth Basin, and Ireland area (Play I): All countries ------3.7 23.2 11.9 (fig. 4) 25.4 145.7 78.6 (fig. 5) United Kingdom ----- 0.7 4.2 2.2 2.3 13.1 7.0 Norway ------2.8 17.6 9.0 21.6 123.8 66.8 Denmark ------0.1 0.7 0.4 0.8 4.4 2.4 Germany ------< 0.1 0.2 0.1 0.2 1.5 0.8 Ireland ------0.1 0.5 0.2 0.5 2.9 1.6 Southern North Sea Basin and Ireland area (Play II): All countries ------0.2 2.0 0.9 (fig. 6) 8.4 44.1 23.8 (fig. 7) United Kingdom ----- 0.0 0.5 0.0 4.2 19.8 11.9 Netherlands ------0.2 1.5 0.9 4.2 22.5 11.9 Ireland ------0.0 0.0 0.0 0.0 1.8 0.0 Total South of 62° N. latitude (Play I and Play II): All countries ------4.4 23.8 12.8 (fig. 8) 47.3 174.0 102.4 (fig. 9) United Kingdom ----- 0.8 4.3 2.3 7.6 27.8 16.4 Norway ------3.0 17.1 9.2 32.2 118.3 69.6 Denmark ------0.2 0.5 0.3 0.9 3.5 2.0 Germany------<0.1 0.2 0.1 0.5 1.8 1.0 Netherlands ------0.3 1.2 0.6 5.2 19.1 11.4 Ireland ------0.1 0.5 0.3 0.9 3.5 2.0

North of 62° N. latitude (assessment date July 30, 1982)

Southern sector (More, Helgeland, Voring, etc.) ------0.0 8.9 3.3 (fig. 10) 0.0 80.2 34.0 (fig. 11) Northern sector (Tromso, Hammerfest, etc.) ------0.0 10.3 3.8 (fig. 12) 0.0 69.9 31.0 (fig. 13) Total North of 62° N.latitude: Norway ------0.0 15.7 7.1 (fig. 14) 17.9 127.6 65.0 (fig. 15)

"! z ... z "!... ~ ~ :J: :J: 1- q ESTIMATES 1- q ... Mean 12.81 w ... ESTIMATES w Mean a: co Median 11.72 a: co 102.36 0 ci 95 percent 4.37 0 ci Median 98.72 ~ 75 percent 8.29 ~ 95 percent 47.27 75 percent 75.48 LL tO 50 percent 11.72 LL tO 0 ci 25 percent 15.97 0 ci 50 percent 98.72 5 percent 23.77 25 percent 126.31 ~ '<:I' Mode 9.78 ~ '<:I' 5 percent 173.98 ::; ci Standard 6.13 ::; ci Mode 93.52 deviation Standard 38.76 iii N iii N ~ deviation m~ ci m ci 0 0 a: 0 a: 0 a.. ci a.. ci 0.0 8.0 16.0 24.0 32.0 40.0 0.0 60.0 120.0 180.0 240.0 300.0 BILLION BARRELS RECOVERABLE OIL TRILLION CUBIC FEET RECOVERABLE GAS

FIGURE 15.-Northwest European region, south of 62° N., FIGURE 16.-Northwest European region, south of 62° N., subregions A+ B+ E, aggregate recoverable oil. (Uncondi­ subregions A+B+E, aggregate recoverable total gas. (Un­ tional assessment; date-7/13/82.) conditional assessment; date-7/13/82.)

19 z C'! < :I:.,_ ESTIMATES ~ COND UNCOND ESTIMATES w Mean COND UNCOND a: 7.55 7.10 65.66 65.00 0 00 Median 6.87 6.53 Mean d 95 percent 1.60 0.00 Median 61.80 61.47 ~ 95 percent 19.43 17.86 co 75 percent 4.25 3.68 u. 50 percent 6.87 6.53 u. co 75 percent 42.25 41.72 0 0 0 d 50 percent 61.80 61.47 25 percent 10.12 9.87 84.31 83.97 5 percent 15.90 15.70 25 percent ~ 5 percent 127.41 127.61 ~ d Mode 4.91 4.91 ~ ~ ::J ::J d Mode 55.94 55.94 4.45 4.67 Standard 32.63 33.12 m N m < c:)

FIGURE 17.-Northwest European region, north of 62° N., FIGURE 18.-Northwest European region, north of 62° N., subregions C+ D, aggregate recoverable oil. (Conditional subregions C+D, aggregate recoverable total gas. (Condi­ assessment-solid line; unconditional assessment-dashed tional assessment-solid line; unconditional assess­ line; date-7/13/82.) ment-dashed line; date-7/13/82.)

z C'! C'! < ... z :I: < .,_ :I:.,_ ESTIMATES ~... ESTIMATES ~ w w Mean 23.79 a: Mean 0.86 a: Median 22.34 0 00 Median 0.73 00 95 percent 8.40 c:i 95 percent 0.20 0 c:i ~ ~ 75 percent 15.87 u. 75 percent 0.45 50 percent 22.34 co 50 percent 0.73 u. co 0 c:i 0 c:i 25 percent 30.11 25 percent 1.12 5 percent 44.10 ~ 5 percent 2.00 ~ ~ Mode 19.60 ::J c:i Mode 0.50 ~ c:) Standard 11.10 m Standard 0.60 ::J deviation N deviation m < N c:a c:i < c:i 0 c:a a: 0 0 D.. c:) a: 0 0.00 0.90 1.80 2.70 3.60 4.50 D.. c:) 0.0 12.0 24.0 36.0 48.0 60.0 BILLION BARRELS RECOVERABLE OIL TRILLION CUBIC FEET RECOVERABLE {lAS

FIGURE 19.-Northwest European region, Southern North Sea FIGURE 20.-Northwest European region, Southern North Sea Basin, subregion A, recoverable oil. (Unconditional assess­ Basin, subregion A, recoverable total gas. (Unconditional ment; date-2/23/82.) assessment; date-2/23/82.)

z C'!... z C'! < < .,_:I: .,_:I: ESTIMATES ~ ESTIMATES ~ Mean 78.58 w w Median 74.48 a: Mean 11.94 a: 95 percent 25.40 0 00 Median 11.06 0 00 c:i c:i 75 percent 52.13 ~ 95 perce11t 3.70 ~ 50 percent 74.48 u. 75 percent 7.59 u. 25 percent 100.52 co 50 percent 11.06 co 0 c:) 0 c:i 5 percent 145.70 25 percent 15.31 Mode 66.60 5 percent 23.20 ~ ~ ~ ~ Standard 37.14 c:) Mode 9.40 ::J c:i deviation ·::J Standard 6.10 m deviation m N < N

FIGURE 21.-Northwest European region, subregions B+E, FIGURE 22.-Northwest European region, subregions B+E, Viking and Central Grabens, recoverable oil. (Unconditional Viking and Central Grabens, recoverable total gas. (Uncondi­ assessment; date-2/23/82.) tional assessment; date-2/23/82.)

20 z C'! z C'!... <( ... <( J: ESTIMATES J: ESTIMATES ..... ~ ..... ~ ... COND UNCOND ... COND UNCOND w Mean 4.21 3.33 w Mean 36.56 34.00 a: a: (lO (lO Median 3.65 2.89 Median 31.70 29.80 0 c:i 95 percent 0.80 0.00 0 c:i ~ ~ 95 percent 7.92 0.00 75 percent 2.23 0.81 75 percent 19.79 17.02 u.. <0 50 percent 3.65 2.89 u.. <0 0 c:i 50 percent 31.70 29.80 0 c:i .25 percent 5.56 4.95 25 percent 47.84 46.28 5 percent 9.50 8.94 80.19 'o:t 'o:t 5 percent 81.67 ~ c:i Mode 2.69 2.69 ~ c:i Mode 23.33 23.33 ::J Standard 2.80 3.03 ::J 23.89 24.85 m deviation m N <( N m< c:i m c:i 0 0 a: 0 a: 0 a.. a.. c:i c:i 90.0 120.0 150.0 • 0.0 3.6 7.2 10.8 14.4 .18.0 0.0 30.0 60.0 BILLION BARRELS RECOVERABLE OIL TRILLION CUBIC FEET RECOVERABLE GAS

FIGURE 23.-Northwest European region, subregion C, north FIGURE 24.-Northwest European region, subregion C, north of 62° N., southern sector, recoverable oil. (Conditional of 62° N., southern sector, recoverable total gas. (Conditional assessment-solid line; unconditional assessment-dashed assessment-solid line; unconditional assessment-dashed line; date-7/13/82.) line; date-7/13/82.) z C'! z C'! <( <( ... J: ESTIMATES J: ESTIMATES ..... ~ ..... ~ COND UNCOND ... COND IJNCOND w Mean 5.32 3.78 w Mean 36.04 31.00 a: (lO Median 4.83 3.43 a: 0 0 (lO Median 32.84 29.34 c:i 95 percent 1.23 0.00 c:i 95 percent 10.79 0.00 ~ 75 percent 3.11 0.00 ~ 75 percent 22.24 16.29 u.. <0 50 percent 4.83 3.43 u.. <0 50 percent 32.84 29.34 0 c:i 25 percent 6.99 5.99 0 c:i 25 percent 46.28 43.61 5 percent 11.10 10.28 5 percent 72.17 69.92 'o:t Mode 3.92 3.92 'o:t ~ c:i ~ Mode 27.00 27.00 ::J Standard 3.11 3.56 ::J c:i Standard 19.38 21.89 m deviation m deviation <( N <( N m c:i m c:i 0 0 a: 0 a: 0 a.. c:i a.. c:i 0.0 3.6 7.2 10.8 14.4 18.0 0.0 30.0 60.0 90.0 120.0 150.0 BILLION BARRELS RECOVERABLE OIL TRILLION CUBIC FEET RECOVERABLE GAS

FIGURE 25.-Northwest European region, subregion D, north FIGURE 26.-Northwest European region, subregion D, north of 62° N., northern sector, recoverable oil. (Conditional of 62° N., northern sector, recoverable total gas. (Conditional assessment-solid line; unconditional assessment-dashed assessment-solid line; unconditional assessment-dashed line; date-7/13/82.) line; date-7/13/82.)

• The Southern North Sea Basin geologically is • Broad areas for which there are little data, ly­ completely different from the rest of the North ing between and west of the British Isles, are Sea and appears to be a Klemme type 2A com­ included in the assessment, but regional plex basin; specific basin analogs include the analysis suggests that those regions have Ergs Oriental and Occidental in Algeria and lesser potential as compared with the heart of the West Siberian Basin in the U.S.S.R. the North Sea To the south, this would appear • In both the Viking and Central Grabens and in to be owing to facies changes in the prime the Southern North Sea Basin, a number of Jurassic source rock and possibly to inade­ discoveries are under evaluation-some 36 in quate burial depth. To the northwest, however, the former and 45 in the latter. In the assess­ due west of the Shetland Islands, a giant field ment, we assume that most of these discoveries has been discovered on the Rona Ridge (ap­ represent a marginal economic field-size poten­ proximately 4 X 109 bbl in place), but the oil is tial, and their exclusion from the discovered heavy, 22°-25° API, the result of which is that reserves does not significantly affect the recovery percent is limited, and the relatively estimate of undi~covered resource potential. shallow depth of burial poses difficult produc-

21 tion problems. Exploration undoubtedly will Dolton, G. L., and others, 1981, Estimates of undiscovered continue in this area, however. recoverable conventional resources of oil and gas in the • The assessment area extends marginally into United States: U.S. Geological Survey Circular 860, 87 p. Hallam, A., 1980, Sedimentation and tectonics in relation to oil the area that probably belongs geographically occurrence in the North Sea, in Mason, John F., ed. to the Barents Sea The geological characteris­ Petroleum geology in China, PennWell Books, Penwell tics that make the North Sea proper a produc­ Publishing Co., Tulsa, Okla, p. 171-179. tive area do not extend significantly into the Illing, L. V., and Hobson, G. D., 1981, eds., Petroleum geology of the Continental Shelf of North-West Europe, Pro­ Barents Sea; hence, the assessed potential for ceedings of the second conference: March 4-6, 1980, Insti­ that area is minimal. tute of Petroleum, London: Heyden and Son, Ltd., 539 p. • Prime areas thought to have undiscovered Jorgensen, F., and Navrestad, T., 1981, The geology of the potential appear to heavily favor Norway, con­ Norwegian shelf between 62° N. and the Lofoten Islands, sidering the as yet modest exploratory effort in in Illing, L. V., and Hobson, G. D., eds., Petroleum geology of the Continental Shelf of North-West Europe, Proceed­ the northeast Viking Graben area, the Bergen ings of the second conference: March 4-6, 1980, Institute High, and the Horda Basin. The very large off­ of Petroleum, London: Heyden and Son, Ltd., p. 407-413. shore region to the north of 62° N.latitude suf­ Klemme, H. D., 1981, Types of petroliferous basins, in fers from increasing water depth (optimum Mason, John F., ed., Petroleum geology in China, Penn­ geology would appear to lie between 600 and Well Books, Tulsa, Okla, p. 101-115. Ronnevik, H. C., 1981, Geology of the Barents Sea, in Illing, 1,200 ft of water depth) and excessive source L. V., and Hobson, G. D., eds., Petroleum geology of the rock depth of burial. Both factors decrease Continental Shelf of North-West Europe, Proceedings of economic potential, the former because of in­ the second conference: March 4-6, 1980, Institute of creasing costs and the latter because the area is Petroleum, London: Heyden and Son, Ltd., p. 395-406. rendered gas prone. The two discoveries to date Ulmishek, G. F., 1982, Petroleum geology and resource assess­ ment of the Timan-Pechora basin, USSR, and the adjacent have been gas and gas condensates. The Barents-Northern Kara shelf: Argonne National Labora­ Bergen High and Horda Basin may suffer from tory, ANL/EES-TM-199, 197 p. either absence or immaturity of source rock. Woodland, A. W., 1975, ed., Petroleum geology of the Con­ • Areas of petroleum potential were estimated tinental Shelf of Northwest Europe, v. 1: Applied Science under the assumption of normal to slightly Publishers. Ziegler, P. A., 1980, Hydrocarbon provinces of the Northwest above-normal temperature gradients. Because European Basin, in Miall, A. D., ed., Facts and principles we think the temperature gradient may in fact of world petroleum occurrence, Canadian Society of have been higher, we consider that assumption Petroleum Geologists Memoir No.6., p. 653-703. to have biased the estimate slightly toward oil. __1981, Evolution of sedimentary basins in North-West Europe, in Illing, L. V., and Hobson, G. D., eds., Petroleum REFERENCES CITED geology of the Continental Shelf of North-West Europe, Proceedings of the second conference: March 4-6, 1980, Crovelli, R. A., 1981, Probabilistic methodology for oil Institute of Petroleum, London: Heyden and Son, Ltd., and gas resource appraisal: U.S. Geological Survey Open­ p. 3-39. File Report 81-1151, 77 p.

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