World Conventional Crude Oil and Natural Gas:
Identified Reserves, Undiscovered Resources and Futures

C. D. Masters, D. H. Root, and R. M. Turner

U. S. Geological Survey Open-File Report 98-468

Abstract | Introduction | Assessment | Maps | References | Appendix A | Appendix B
Table of Contents | Plate 1 | Plate 2 | Tables

ABSTRACT

This report summarizes, at the petroleum basin level, the United States Geological Survey’s World Energy Program 1993 assessment of world conventional oil and gas resources. The maps provided show boundaries of petroleum basins that are referenced by the assessment, as well as, future oil and gas potential. The "Futures" or future potential of a basin is calculated as the the sum of the Identified Reserves and the modal value assigned to the conventional Undiscovered Resources.

I. INTRODUCTION

The United States Geological Survey’s (USGS) World Energy Program 1993 conventional oil and gas resource assessment of world petroleum basins outside the United States is reported here. The assessment was initially presented on a country basis at the 14th World Petroleum Congress (see Masters and other, 1994). The assessment of each petroleum basin, however, was not published at that time. With the October 1997 publication of the Oil and Gas Journal article entitled "World Resource Statistics Geared for Electronic Access" (Masters and others, 1997) and the activation of the website:

http:/energy.er.usgs.gov/products/papers/world_oil/index.htm

the basin level assessment and the associated basin boundaries were made public. Two elements of the website, the basin level assessment of oil and gas volumes and the associated petroleum basin "Futures" maps are presented here. The "Futures" or future potential of a basin is calculated the sum of the estimate of Identified Reserves and the mode (most likely value) of the distribution of the assessed conventional Undiscovered Resource (see Table 1 and 2).

Current activities of the World Energy Project of the USGS Energy Resources Program can be found at:

http://energy.cr.usgs.gov/energy/WorldEnergy/WEnergy.html

II. ASSESSMENT

Assessments of Identified Reserves and Undiscovered Resources of the world were prepared for the 11th, 12th, 13th, and 14th World Petroleum Congresses (Masters and others, 1984, 1987, 1992, 1994). Table 1 and Table 2 provide components of the assessment of conventional undiscovered oil and gas resources, respectively, by country and basin. Conventional Undiscovered Resources (as used here) are oil and gas resources postulated to exist from geologic information and theory outside of known oil and (or) gas fields and that, if found, could be extracted using traditional development practices. Estimates are made without reference to economic profitability. Identified Reserves, also shown for each country and some basins in Table 1 and Table 2, include proved reserves and may also include additional petroleum that could be contributed by field growth through field extensions, revisions of reserve estimates, addition of new pools, and applications of new recovery techniques. Proved reserves are the identified resource whose existence, quantity, and commercial producibility are demonstrated by geologic evidence and supported by engineering measurements. This definition is more inclusive than the accepted US definition of proved reserves.

World Energy Program assessments of undiscovered oil and gas resources dealt only with areas outside the United States and Canada. The assessment of the Undiscovered Resources was prepared by applying a modified Delphi method (Masters and others, 1992). The procedure started with a compilation of the geologic framework information and geologic data associated with the petroleum basin or province to be evaluated. Geologic information and data were analyzed both qualitatively and quantitatively to reconstruct geologic events that related to petroleum generation and accumulation. Historical discovery and drilling data were used to calculate finding rates and make projections. Where data were limited, the assessment team found an analogue basin which served as a model of the area that was assessed. The petroleum geology, interpretations, and quantitative analysis of historical exploration and discovery data were presented to six to eight members of the World Energy Resources Program Team for evaluation.

After discussion, each Team member prepared estimates of the basin’s undiscovered resources. Estimates were recorded as a low, most likely, and high. The low value was interpreted to represent a 19 in 20 chance (95%) that oil (or gas) occurrence would be at least that amount and the high value reflects a 1 in 20 chance (5%) that oil (or gas) occurrence would be at least that value. The range between the 95% and 5% values reflects the belief there is a 90% probability that the actual magnitude of oil occurrence is within the endpoints of the range. If estimates showed broad disagreement, discussion of the geologic data and interpretations was continued and the estimation procedure was repeated until the group reached a consensus. Estimates were then fit using rules of thumb to a lognormal distribution to calculate a mean and other fractiles. Individual basin estimates were aggregated to the country level, then to the regional and world levels. All estimates are prepared on the basis of technically recoverable oil or gas. Estimates and basin outlines for Canada were transmitted from the Energy Board of Canada (personal communication to Charles Masters, Ken Drummond, 1993). Also, the updated assessment for the Former Soviet Union presented in Ulmishek and Masters (1993) is used here instead of the estimates presented at the 14th World Petroleum Congress.

The assessment presented to the 14th World Petroleum Congress was prepared before completion of the 1995 USGS National Assessment (USGS, 1995). In Tables 1 and 2, the United States country total estimates are based the joint 1989 USGS/ Minerals Management Service (MMS) national assessment published in Mast and others (1989). However, at the province level for US onshore and State waters areas, the province names and boundaries were based on 1995 USGS National Assessment of Oil and Gas Resources (USGS National Oil and Gas Assessment Team, 1995) and Gautier and others (1996). Estimates of the modal values of conventional undiscovered oil and gas for these provinces were formulated by C. Masters using data presented in USGS Circular 1118 (USGS National Oil and Gas Assessment Team, 1995). Province boundaries shown on the maps for Federal Offshore areas are based on the 1989 USGS/MMS National Assessment. The province level assessments of the modal values for Federal Offshore areas were also based data from the 1989 USGS/MMS National Assessment. A complete list of the US provinces with their designation as either onshore and States waters or Federal offshore is provided in Appendix A.

There is no generally accepted standard for defining reserves. The broad definition of reported reserves used by many countries is the magnitude of the technically recoverable in-place resource based on standard recovery factors or preliminary well tests. The broad definition includes developed and undeveloped reserves and makes no reference to commercial producibility. When broad definitions of reserves are used, upward revisions in estimates of field recovery are typically only moderate. Without generally accepted reporting standards, it is difficult to interpret and verify estimates of country reserves reported in trade journals.

For countries outside the United States and Canada, the initial data used in the computations of Identified Reserves were from the Petroconsultants field file issued in September of 1993 (Petroconsultants, 1993). Field data are the preferred level of data disaggregation because it allows the most thorough verification and fields are commonly classified by petroleum basin. It was also reasoned that data from a common source would be consistently estimated. Individual field estimates of ultimate oil recovery were reviewed. For some fields detailed engineering information and results of published and unpublished field studies were available. Field production histories and estimates of cumulative production were also used in the review. For example, given that the rate of production decline in large oil fields is commonly less than 7 percent per year, field reserve estimates were adjusted upward, if necessary, to obtain a 14 to 1 reserve to annual production ratio. For newly discovered fields, if no production information was available, the Petroconsultants’ estimate of ultimate recovery was used without review. For gas fields production was rarely available, so the Petroconsultants' estimates were generally used. Field estimates of ultimate producible oil and gas were aggregated by petroleum basin and country.

Identified Reserves were computed as the difference between ultimately recoverable oil and gas and the country's cumulative production of oil and gas. Cumulative oil production data were compiled from World Oil (1993) and Twentieth Century Petroleum Statistics (DeGoyer and McNaughton, 1993). Early gas production data were from the United Nations (1976). More recent gas production estimates made by Cedigaz Inc. are published annually in the Petroleum Economist (various years). The calculated Identified Reserves were then compared to reserves as of 1/1/93 published by World Oil (1993) and the Oil and Gas Journal (1992). A country by country comparison indicated, in many cases, estimates of Identified Reserves were somewhat higher than the published estimates. In all such cases, Petroconsultants listed non-producing fields which were probably omitted in the World Oil and Oil and Gas Journal compilations. The larger reserve estimates based on the field file were used.

In a few instances, published estimates of reserves in trade journals exceeded the reserve estimates derived from the field data. For oil, these countries included the Former Soviet Union(FSU), Saudi Arabia, and several small Eastern European and Asia producers. For the FSU, the Identified Reserve estimate published in Ulmishek and Masters (1993) was used. These authors note their estimate to include significantly more than proved reserves. With regard to Saudi Arabia, 66 billion barrels of oil included in the published reserve number could not be accounted for using field data. The trade journal estimates for Saudi Arabia and the smaller producers were used as the Identified Reserves.

For gas, the countries where field data were incomplete included Venezuela, Austria, Italy, Qatar, Abu Dhabi, Libya, Nigeria, Congo, Rwanda, Tanzania, Mexico, Poland, and Romania. For these countries, the reserve estimates were taken from the Cedigaz estimates published in the Petroleum Economist (1993). Together the use of the Cedigaz estimates for these countries increased the world total about 7 percent more than the total gas that could be identified using the Petroconsultants' field data. In table 2, the United Kingdom shows an Identified Reserve estimate of 72.5 trillion cubic feet (TCF); a significant increase over published estimates. The field file shows that of this 72.5 TCF, 53.3 TCF are in fields that have no production. The lower reserve estimates appear to have omitted the resources in non-producing fields. Worldwide, Petroconsultants shows 2,333 TCF in non-producing fields.

In the United States and Canada, the most commonly used definition of reserves is that of the narrow definition of Proved reserves. Proved reserves are estimated volumes of the resource which geologic and engineering data demonstrate with reasonable certainty to be recoverable in future years from known reservoirs under existing economic, operating and regulatory conditions. The narrow definition of "proved" reserves used in the United States and Canada leads to conservative estimates of the amount of oil and gas that will ultimately be produced from a field. The increase in proved field size (past production plus proved reserves) that occurs as fields are fully developed is known as field growth and represents the reclassification of 'inferred' reserves to the proved category. Methods for estimating inferred reserves have been developed Root (1981) and were applied at the country level to arrive at estimates Identified Reserves for the United States and Canada and added to proved reserves. Identified reserves for basins of Canada were obtained from the National Energy Board (Ken Drummond, National Energy Board personal communication, 1993). For the United States the province level estimates were derived from the NRG Associates Field file (NRG, 1995).

III. WORLD PETROLEUM BASIN MAPS - Plate 1 and Plate 2

The World Petroleum Basin maps that show the basins assessed are included as plate 1 and plate 2 of this report. The World Energy Program geologists initially used the series of maps by Coury, Hendricks, and Tyler (Coury, and others, 1978 and 1979, Coury and Hendricks, 1978 and 1979) as a point of departure for their studies of petroleum basins of the world. Each Program geologist studied and refined geologic interpretations of the petroleum basins in their area. Many of the refinements in boundaries were published in various Program reports that relate to specific areas or regions of the world. Masters (1994) provides a bibliography of the World Energy Program’s publications. Maps showing revised basin boundaries were used for the 1993 Assessment within the World Energy Program as geologists revised and reviewed assessments. The basin boundaries for Canada and the United States are from the respective Federal governments. The maps (plates 1 and 2 ) that accompany Table 1 and Table 2 are digitized versions of the basin maps that emerged as successive basin assessments were prepared.

The maps show, by color, the "Futures" potential assigned each basin. The Future potential is the sum of the Identified Reserves and the modal value, or most likely, value of the conventional undiscovered resources assessed. For oil the categories are (1) less than 0.1 BBO (2) 0.1 to 1 BBO, (3) 1 to 10 BBO, (4) 10 to 20 BBO (5) 20 to 100 BBO and (6) 100 BBO or greater. For gas the categories are (1) less than 0.6 TCF, (2) 0.6 to 6 TCF, (3) 6 to 60 TCF, (4) 60 to 120 TCF, (5) 120 to 600 TCF and (6) 600 TCF or greater.

When interpreting the World Petroleum Futures Maps it is important to note that a number of basin were assessed as groups, that is jointly. For those basins belonging to jointly assessed groups, the color associated with the individual basin is same as the group, that is, there was no effort to allocate the jointly assessed resources to the member basins of the group. The groups are indicated in Tables 1 and Tables 2 and also listed separately with member basins in Appendix B.

REFERENCES

Coury, A. B., Hendricks, T. A., and Tyler, T. F., 1978, Map of prospective hydrocarbon provinces of the world: North and South America: US Geological Survey Miscellaneou Field Studies Map MF-1044A.

Coury, A. B. and Hendricks, T. A., 1978, Map of prospective hydrocarbon provinces of the world: Europe, West Asia, Africa: US Geological Survey Miscellaneou Field Studies Map MF -1044B

Coury, A. B. and Hendricks, T. A., 1979, Map of prospective hydrocarbon provinces of the world: East Asia, Australia, and the Pacific: US Geological Survey Miscellaneou Field Studies Map MF-1044C.

Coury, A. B. Hendricks, T. A., and Tyler, T. F., 1979, Bibliography for map of prospective hydrocarbon provinces of the world: US Geological Survey Open-File Report 79-201. 88p.

DeGolyer and McNaughton, 1993, Twentieth Century Petroleum Statistics 1992; DeGolyer and McNaughton, Dallas, 132 p.

Gautier, D. L., Dolton, G. L., Takahashi, K. I., and Varnes, K. L., eds., 1996, 1995 National Assessment of United States Oil and Gas Resources - Results, Methodology, and Supporting data: U.S. Geological Survey Digital Data Series 30, release 2, one CD-ROM.

Mast, R. F., Dolton, G. L., Crovelli, R. A., Root, D. H., Attanasi, E. D., Martin, P. E., Cook, L. W., Carpenter, G. B., Pecora, W. C., and Rose, M. B., 1989, Estimates of Undiscovered Conventional Oil and Gas Resources in the United States; A Summary: U.S. Geological Survey/Minerals Management Service Special Publication, 56 p

Masters, C. D., 1994, Bibliography of the World Energy Resource Program, United States Geological Survey Open-File Report 94-556, 10p.

Masters, C. D., Attanasi, E. D., and Root D. H., 1994, World Petroleum Assessment and Analysis: in Preprint of Proceedings of the 14th World Petroleum Congress, Stavanger, Norway: John Wiley and Sons Ltd., p1-13..

Masters, C. D., Root, D. H., and Attanasi, E. D., 1992, World resources of crude oil and natural gas: in Proceedings of the 13th World Petroleum Congress, v.2, p. 51-64.

Masters, C. D., Attanasi, E. D., Dietzman, W. D., Meyer, R. P., Mitchell, R. W., and Root, D. H., 1987, World resources of crude oil, natural gas, natural bitumen, and shale oil: in Proceedings of the 12th World Petroleum Congress, v. 5, P.3-27.

Masters, C. D., Root, D. H., and Dietzman, W. D., 1984, Distribution and quantitative assessment of world crude-oil reserves and resources: in Proceedings of the 11th World Petroleum Congress, London, 1983, v. 2. p.229-237.

Masters, C. D., Root, D. H., and Turner, R. M., 1997, World resource statistics geared for electronic access: Oil and Gas Journal, v. 95, no. 41, pp.98-104, (October 13, 1997).

NRG Associates, 1994 and 1995, [Includes data current as of December 31, 1993 and Decmber 31, 1994, respectively], The significant oil and gas fields of the United States: Colorado Springs, Colo., NRG Associated, Inc. [database avaiable from NRG Associates, Inc., P.O. 1655, Colorado Springs, CO 80901].

Oil and Gas Journal, 1992, Worldwide look at reserves, Oil and Gas Journal v. 90, no. 52, 44-45, (Dec. 28, 1992).

Petroconsultants International Data Corporation, 1993, Petroconsultants Worldwide Oil and Gas Field Database 1993: Genva, Switzerland, Petroconsultants International Data. Digital Database available Petroconsultants International Data Corporation, P.O. Box 740619, 6600 Sands Point Drive, Houston TX 77274-0619, USA or Petroconsultants, Inc., P. O. Box 152, 24 Chemin de la Mairie, 1258 Perly, Geneva.

Petroleum Economist, 1993, World: commercial production of natural gas and proven reservers, vol 60, no.8, p.8, (August, 1993)

Root, D. H., Estimation of inferred plus indicated reserves in the United States, Appendix F. In: Dolton G. and others, Estimates of undiscovered recoverable conventional reserves of oil and gas in the United States, U.S. Gelogical Survey Circular 860, 87 p.

Ulmishek, G. and Masters, C. D., 1993, Petroleum Resources of the Former Soviet Union, US Geological Survey Open-File Report 93-316, 17p.

United Nations, 1976, World Energy Supplies 1950-1974, Statistical Paper Series J No. 19, United Nations 200p.

United States Geological Survey, National Oil and Gas Resource Assessment Team, 1995 National Assessment of United States Oil and Gas Resources: U. S. Geological Survey Circular 1118, 20 p.

World Oil, 1993, Estimated proved world reserves, 1991 vs. 1992, World Oil v.30, no. 8, (p. 3) August 1993.

APPENDIX A: List of US petroleum provinces and designation of source of data for estimates of the mode of undiscovered conventional oil and gas resources.

Onshore and State Offshore *

990 Northern Alaska

991 Central Alaska

992 Southern Alaska

995 Northern Coastal

996 Central Coastal

997 Sonoma - Livermore

1000 Salton Trough

1019 Eastern Oregon-Washington

1020 Western Oregon-Washington

1022 Sacramento

1023 San Joaquin

1025 Los Angeles

1027 Santa Maria

1028 Klamath Sierra Nevada

1029 Southern Arizona-South West New Mexico

1030 Idaho-Snake River Downwarp

1031 Western Great Basin

1032 Eastern Great Basin-Railroad Valley

1036 Northern Arizona

1044 Uinta-Piceance

1045 Paradox

1046 San Juan

1051 South-Central New Mexico - Rio Grande Rift

1052 Albuquerque-Santa Fe Rift

1033 Montana Thrust Belt

1034 Central Montana

1035 Wyoming Thrust Belt

1037 South West Montana - Crazy Mountain

1038 Big Horn

1039 Wind River

1040 Powder River

1042 Park Basins

1043 South West Wyoming- Greater Green River

1049 Denver

1050 Raton Basin - Sierra Grande Uplift

1053 Las Animas Arch

1054 Sioux Arch

1060 Williston

1065 Palo Duro

1066 Permian

1067 Bend Arch-Fort Worth

1082 Pedernal Uplift

1086 Marathon Thrust Belt

1084 Louisiana-Mississippi Salt Basins

1085 East Texas

1088 Florida Peninsula

1090 Western Gulf

1041 Superior

1055 Iowa Shelf

1056 Cambridge Arch - Central Kansas

1057 Nemaha Uplift

1058 Ozark Uplift

1059 Cherokee

1061 Salina

1062 Forest City

1063 Anadarko

1064 Arkoma

1083 Southern Oklahoma

1087 Sedgwick

1068 Michigan

1069 Illinois

1070 Appalachian

1071 Black Warrior

1074 New England

1075 Blue Ridge Trust Belt

1076 Adirondack

1077 Cincinnati Arch

1078 Atlantic Coastal Plain

1081 Piedmont

Federal Offshore**

1001 N. Aleutian/ St. George

1002 Navarin

1003 Norton

1005 Hope

1006 Chucki Sea

1008 Beaufort Shelf

1013 Cook Inlet

1014 Gulf of Alaska/Shumagin

1015 Queen Charlotte

1016 Winona

1017 Tufino

1018 Georgia

994 Pacific Northwest

998 Central California

1024 Ventura, Santa Barbara

1026 San Diego-Oceanside-Outer Banks-USA

1072 Georges Bank (North Atlantic)

1073 Baltimore Canyon (Mid-Atlantic)

1079 Carolina Trough

1080 Blake Plateau (South Atlantic)

1089 Western Gulf (Offshore)

1091 Eastern Gulf (Offshore)

1092 Florida Bahamas

* Data for estimation of modal values for undiscovered conventional oil and gas resources are from USGS National Oil and Gas Resource Assessment Team (1995).

** Data for estimation of modal values for undiscovered conventional oil and gas resources are from the joint 1989 USGS/MMS joint national oil and gas assessment published in Mast and others (1989).

APPENDIX B.

Basins Assessed Jointly in the Oil Assessment shown by group

United States
Louisiana-Mississippi Salt Basins (1084), East Texas (1085)

Canada
Western Canada Sedimentary Basin includes Anderson (1101), Alberta (1102), Williston Canada (1103)
Arctic Islands includes Sverdrup (1104), Melville (1105), Victoria Strait (1106), Jones Lancaster (1107)
Mainland Territories includes Foxe (1108), Hudson Bay (1109), Baffin Bay (1110)

Mexico
Isthmus Saline (1131), Reforma Shelf (1132), Macuspana (1133), Comalcalco (1134)

Venezuela
Maracaibo (3002), Falcon (3003)

Algeria
Northern Algeria includes Tindouf (5005), Atlas Fold (5007), Bechar (5008), Reggane (5009)
South East Algeria includes Triassic (5011), Ghadames (5100), Illizi (5013)
South West Algeria includes Erg Occidental (5010), Ahnet (5012)

Madagascar
Morondava (5061), Majunga (5062)

China
East China Sea (8010), Okinawa Trough (8011), Ryuku (8012)

Australia
Carnarvon, North (10004), Carnarvon, South (10005)

United States
Lousiana-Mississippi Salt Basins (1084), East Texas (1085)

Canada
Western Canada Sedimentary Basin includes Anderson (1101), Alberta (1102), Williston Canada (1103)
Arctic Islands includes Sverdrup (1104), Melville (1105), Victoria Strait (1106), Jones Lancaster (1107)
Mainland Territories includes Foxe (1108), Hudson Bay (1109), Baffin Bay (1110)

Mexico
Isthmus Saline (1131), Reforma Shelf (1132), Macuspana (1133), Comalcalco (1134)

Italy
Adriatic (4030), Po (4031)

Algeria
Northern Algeria includes Tindouf (5005), Atlas Fold (5007), Bechar (5008), Reggane (5009)
South East Algeria includes Triassic (5011), Ghadames (5100), Illizi (5013)
South West Algeria includes Erg Occidental (5010), Ahnet (5012)

Madagascar
Morondava (5061), Majunga (5062)

China
East China Sea (8010), Okinawa Trough (8011), Ryuku (8012)

Australia
Carnarvon, North (10004), Carnarvon, South (10005)

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