T. R. Klett1,
Ronald R. Charpentier1,
James W. Schmoker1,
Emil D. Attanasi2
(1) U.S. Geological Survey, Denver, CO
(2) U. S. Geological Survey, Reston, VA
Abstract: Predicting changes in world oil and gas field sizes
Estimates of the total recoverable petroleum (field sizes) of discovered oil and gas fields change through time. These changes must be accounted for when assessing future potential. Although some reported field sizes decrease or remain constant, reported field sizes are observed to generally increase. Reported field sizes are typically conservative because of geologic uncertainty, economic incentives, and political constraints, and because they are based on current economic and operating conditions. Field sizes increase upon application of improved recovery techniques, discovery of new reservoirs in a field, extension of old reservoirs, and re-estimation of parameters upon which reserve calculations are based.
Changes in field sizes within the U.S.A. from 1977 through 1991 have been modeled by the U.S. Geological Survey. Analytical functions were developed for calculating the future sizes of oil or gas fields based on years since discovery. Older fields have less expectation of size increase than younger fields. The analytical functions incorporate changes with economic conditions, but show only slight differences between oil and gas fields.
World field-size data have also been analyzed for the period 1981 to 1996. The initial expectation for fields outside the U.S.A. and Canada was that size changes would be moderate because proven plus probable reserves are usually reported, rather than just proven reserves. Also, field development is often not as intense as in the U.S.A. Preliminary analysis of historical data, however, shows greater increases in field sizes than expected, for both OPEC and non-OPEC countries.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana