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ABSTRACT: Potential for Additional Recovery in Restricted Platform Carbonate Reservoirs, Permian Basin, Texas

Noel Tyler, D. G. Bebout, C. Kerans, R. P. Major, S. C. Ruppell

By any standard the Permian Basin is a petroleum province of world-class proportion. As of 1985, reservoirs in this basin had produced a cumulative volume of 25.3 billion bbl of oil, or roughly 25% of the in-place resource of 105 billion bbl. Beyond proved reserves of 6 billion bbl, an unrecovered oil resource of 74 billion bbl still remains in existing reservoirs. Much of the remaining oil (40%) is concentrated in restricted platform carbonate reservoirs in the San Andres, Grayburg, and Clear Fork formations.

The unrecovered oil in these carbonate reservoirs is composed of both mobile oil (13.2 billion bbl) and residual oil (17.5 billion bbl). Increased recovery of either requires improved understanding of internal reservoir architecture and its relation to fluid flow paths. Detailed study of six San Andres and Grayburg reservoirs on university lands shows these reservoirs to be characterized by moderate degrees of lateral permeability variation and high degrees of vertical permeability variation. This variability results in moderate contact of oil saturation by well bores but poor conformance during waterflooding. Projected recovery of mobile oil at current technological levels is estimated at 52%. Location of remaining mobile oil saturations is largely governed by distribution of grainst ne. Geologically targeted infill drilling to tap these grainstones, coupled with waterflood redesign to sweep contacted reservoir intervals more efficiently, holds the promise of doubling the remaining reserves in the Permian basin.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990