Abstract: U.S. Geological Survey Methodology for the 1995 National Assessment

Donald L. Gautier, Richard F. Mast, Gordon L. Dolton, James W. Schmoker

The 1995 National Assessment is broader in scope than previous USGS assessments. Three categories of resources are considered: (1) undiscovered, conventional oil and gas; (2) reserve growth; and (3) "unconventional" resources.

Undiscovered resources are evaluated at a play scale. Two categories of conventional plays are recognized. Confirmed plays can be evaluated, in part, by geologists who estimate size and number of undiscovered accumulations based upon information from discovered accumulations. Hypothetical plays generally entail significant risks and can be evaluated using analogues or simulation. Accumulations smaller than 1 million barrels of oil or 6 billion cubic feet of gas are evaluated by extrapolation from the known and estimated larger accumulations.

Unconventional resources, including most tight gas sands, autosourced shale reservoirs, and coal-bed gas are also being evaluated at a play scale. Previous assessments have relied upon estimation of in-place resources and application of estimated recovery factors. The new assessment relies upon evaluation of productive wells within a play and extrapolation to undrilled portions of the play.

Reserve growth is being evaluated using data from the Energy Information Administration and the NRG Associates field and reservoir database. In addition to interpretation of historical reserves data, the growth of selected individual fields is being evaluated in certain areas of the country.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994