Abstract: Assessment of, and Access to, the Natural Gas Reserve Appreciation Resource

Robert J. Finley

The reserve appreciation, or reserve growth, category of the conventional natural gas resource base in the lower 48 states is now assessed at 203 Tcf (National Petroleum Council [NPC]) to 242 Tfc (Gas Research Institute)(as of 12/31/90). The existence of this resource, much less its amenability to assessment and its magnitude, has been controversial. The 1988 U.S. Department of Energy (DOE) resource assessment first utilized an approach based on the inherent heterogeneity of depositional systems at the between-well (macroscopic) scale. That approach was an extension of the relationship between reservoir architecture and oil recovery efficiency and was developed for nonassociated gas on a play-by-play basis using a commercially available national data base.

The 1988 DOE results were seen by some as overly optimistic. Yet that estimate exceeds the 1992 NPC estimate by less than 5 percent after adjusting

for 1987-1990 conversion of resources to reserves. The NPC assessment was based on an entirely different methodology related to ultimate recovery estimates tied to year of discovery.

For producers, the opportunity exists to apply integrated geological, geophysical, engineering, and petrophysical technologies toward extraction of the reserve appreciation resource. Five years of Texas Gulf Coast reservoir studies have shown fully costed and risk-weighted development costs of $O.65-O.95/Mcf (1992 dollars) through strategic recompletion and infill drilling. Unrisked costs were half that level. Average gas reservoir completion spacing has dropped to about 90 acres in major Frio fields, such as Stratton, where production comes from complex, stacked fluvial channel and crevasse-splay facies. Effective development of reserve growth resources is dependent on understanding of reservoir heterogeneity keyed to the facies architecture of the target reservoir. Given the demonst ated moderate costs and the greater than 200 Tcf size of the resource base, such development opportunities are substantial.

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