Timothy R. Klett¹, James W. Schmoker¹

(1) U.S. Geological Survey, Denver, CO

ABSTRACT: Changes In Observed Field-Size Estimates Of The World's Giant Oil Fields

Analysis of total recoverable oil volume (field size) of some well-known giant oil fields of the world (greater than 0.5 billion barrels of oil, BBO, and discovered prior to 1981), exclusive of the United States and Canada, demonstrates general increases in field sizes through time. Field sizes were analyzed collectively and within the categories of OPEC and non-OPEC countries.

From 1981 through 1996, the volume of oil in the 186 fields for which adequate data were available increased from 617 to 777 BBO (26 percent). Processes other than new-field discoveries added 160 BBO to known reserves in this subset of the world's oil fields. Although methods for estimating field sizes vary among countries, the sizes of the giant oil fields of the world increased in a manner similar to oil fields in the U.S.

Volumes in OPEC fields increased from a total of 550 to 668 BBO and volumes in non-OPEC fields increased from 67 to 109 BBO. In terms of percent change, non-OPEC field sizes increased more than OPEC field sizes (63 versus 22 percent).

The changes in estimated total recoverable oil volumes that occurred within three 5-year increments between 1981 and 1996 were all positive. Between 1981 and 1986, the increase in estimated total recoverable oil volume within the set of giant oil fields was 11 BBO; between 1986 and 1991, the increase was 120 BBO; and between 1991 and 1996, the increase was 29 BBO. Fields in both the OPEC and non-OPEC countries followed these trends.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado