DATA ON FIELD SIZE USEFUL TO SUPPLY PLANNERS
L.F. Ivanhoe
Novum Corp.
Santa Barbara, Calif.
George G. Leckie
Petroconsultants SA
London
Oil company and government planners of future oil and gas supplies need realistic numbers on the sizes of fields that may be expected in any region, nation, or basin.
In the past, gross published statistics were available only of the world's giant oil and gas fields but not for the smaller fields in the U.S. and in other countries. 2 3 6 9
During the last two decades, extensive computerized government and commercial field data files have been assembled for most parts of the globe, which are now being analyzed by engineers. 8 10
The new quantitative field data will significantly improve evaluations of the petroleum-potentials of different global areas by allowing realistic estimates of what sizes and numbers of fields may still be expected.
FIELD SIZES
Sizes of oil and gas fields in any geological province vary log-normally, i.e., few "whales" but many "minnows."
The larger fields are most important for global supplies; giant fields contained 75% of the world's oil reserves in 1985.
The "oily" regions stand out. Natural gas is still less economic than crude oil in most places.
Modern petroleum exploration is an efficient technical procedure. The largest fields in any basin are normally discovered early in any exploration cycle because they are the biggest targets and easiest to find, while the number of smaller fields discovered depends on the number of wells drilled and on local economics.
The numbers in the table on the sizes of oil and gas fields in the various regions are the final result of 130 years of petroleum prospecting around the world, which cover many cycles of exploration and development technologies from the simplest wildcat drilling at Titusville, Pa., in 1859 through current electronic well logging, 3D marine seismic surveys, and deepwater offshore production facilities.
The present global exploration cycle is the result of modern petroleum geochemistry and digital seismic plus marine drilling technologies that were developed in the mid-1960s; consequently, far fewer wildcat wells are required on land or at sea effectively to test a new geological concept/play or a basin's economic oil and gas potential than were needed in earlier exploration cycles. 1 2 3 4 5 7
REVIEWS IN PROGRESS
The table is the first of several major reviews being made by various authors from computerized data bases. Table figures were prepared from the largest commercially available field data base in the world for countries outside North America and is regularly used by many oil companies and government agencies. 8
Petroconsultants has given permission to publish these new data, which cover all but a few nations of the world.
Its global data base does not include information on the U.S. Lower 48, Alaska, or Canada, which is available from other North American companies, and its data are still incomplete on the Communist nations.
Petroconsultants should have comprehensive U.S.S.R. field data some time in 1992, and on China at a later date.
The distribution of Lower 48 and Alaska field sizes is being processed by the U.S. Department of Energy/Energy Information Administration and is expected to be published in late 1991.
Total U.S. oil and gas fields as of Dec. 31, 1988, numbered 45,558. 10
Canadian field data are analyzed by the Petroleum Resources Appraisal Secretariat of the Geological Survey of Canada in Calgary.
The table includes all oil and gas fields in Petroconsultants's international data base for each region, regardless of whether the fields are producing or are still undeveloped discoveries.
In the case of new discoveries, the estimated ultimate recovery (EUR) may be a guess, particularly for the smaller fields.
The EUR of each oil field includes its reported EUR (i.e., cumulative past production plus proven recoverable reserves) of crude oil and condensate; but associated natural gas is not included due to the unreliability of associated gas reserve estimates for very small oil fields.
The EUR of each natural gas field includes its reported EUR of nonassociated natural gas plus any condensate/natural gas liquids (NGL).
Natural gas was converted to barrels of oil equivalent (BOE) at the practical economic ratio of 10,000 cu ft/bbl rather than at the usual heat ratio of 5,800 cu ft/bbl. Use of 10,000 cu ft/bbl facilitates comparison with the primary author's 1976 graphs, simplifies the tables, and in many cases is as accurate as the foreign gas reserve estimates.
NGL was treated as oil equivalent. This general procedure will permit realistic comparisons with the number of very small fields in the Lower 48 when such data are published by the DOE/EIA.
Field grades A to F are from the American Association of Petroleum Geologists field size system, which has been used for many years, while the AA to AAAAA grades were added to expand the AAPG system to cover the entire range of the world's oil and gas field sizes.
Names of field size categories (giant, etc.) are per common international oil company usage.
Field sizes for each field grade are defined per EUR. These are logarithmic for the largest fields grades A to AAAAA (+50 million BOE) but are broken down per the AAPG system for fields smaller than grade A.
Geographic areas: Conventional groups of nations were followed. Latin America includes Mexico and the Caribbean; Western Europe includes what was formerly West Germany, plus Turkey and Yugoslavia; the Middle East includes Israel, Yemen, and Iran; and the Far East includes Pakistan, Burma, Viet Nam, Indonesia, Taiwan, and Japan; and Australasia includes Papua New Guinea and New Zealand.
Not included are the U.S. Lower 48 plus Alaska, Canada, China, the U.S.S.R., and Eastern Europe, which includes the former East Germany.
REFERENCES
- Baker, R.A., Gehman, H.M., James, W.R., and White, D.A., 1986; Geologic field number and size assessment of oil and gas plays; pp. 25-31, in Oil and Gas Assessment-Methods and Applications, Ed. D.D. Rice; AAPG Studies in Geology #21.
- Ivanhoe, L.F., Oil/gas potential in basins estimated; OGJ, Dec. 6, 1976, pp. 154-155.
- --, Foreign prospective basins evaluated; OGJ, Dec. 13, 1976, pp. 108-110.
- --, Petroleum prospects of non-OPEC LDCs; OGJ, Aug. 27, 1979, pp. 144-151.
- --, World's prospective petroleum areas; OGJ, Apr. 28, 1980, pp. 146-148.
- --, World's giant petroleumprovinces; OGJ, June 30, 1980, pp. 146-148.
- Leckie, George, U.S. wildcat success rate figures 1946-88 reveal disturbing trend; OGJ, July 2, 1990, pp. 69-70.
- Petroconsultants SA, (International) Petroleum Exploration Database, December 1990; Petroconsultants SA, Geneva.
- Roadifer, R.E., Size distributions of world's largest known oil, tar accumulations; OGJ, Feb. 24, 1986, pp. 93-100.
- U.S. Dept. of Energy/Energy Information Administration, U.S. oil and gas reserves by year of field discovery, DOE/EIA-0534, 1990.
Copyright 1991 Oil & Gas Journal. All Rights Reserved.