Incremental Recovery of Gas In Place: A Macro-Geologic Perspective

Thomas J. Woods

The recovery of gas in place in high-permeability gas reservoirs was traditionally thought to be quite high, about 80-90%. As a result, improved recovery of gas in place was thought to be of negligible importance for future gas reserve additions. Historical data seemed to bear out this expectation. Revisions to natural gas reserves (where improved recovery would be booked) have played a relatively small positive role in the trends in total gas reserve additions for the continental United States.

Recently, however, current production practices seem to recover less than 80-90% of the gas in place in high-permeability reservoirs. The submittals for infill drilling in Kansas for the Hugoton field imply that current production practices recover only about 55% of the gas in place. With the approval of the infill program in the Hugoton field, reserves in Kansas were revised upward in 1986 by almost 2 tcf.

If this increase is representative of a generic property of the gas resource and long-term reserve addition trends, then improvements in the recovery of gas in place for high-permeability reservoirs could play a major role in future gas reserve additions. This incremental resource will expand the gas resource expected to be recovered from known fields and will expand the total remaining resource in undiscovered fields.

While the exploitation of this resource will rely heavily on detailed geologic analyses on a play or reservoir-specific basis, many macro-geologic parameters, such as reservoir lithology, entrapment, and reservoir areal extent, when considered in light of region or basin-specific trends in reserve additions, provide an indication of the extent of this incremental resource.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.