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Abstract: The Role of Diagenetic Studies in Flow-Unit Modeling: San Andres Formation, Yoakum County, Texas

Steven Henderson

The Permian San Andres Formation represents one of the most prolific hydrocarbon-producing intervals of the Permian basin. Dolostone lithofacies intercalated with thin evaporites accommodate highly compartmentalized reservoirs resulting from complex depositional and diagenetic histories. This compartmentalization often facilitates the use of these reservoirs in flow-unit studies. Perhaps more important than the relationship of productive intervals to depositional facies is the degree to which diagenetic processes have influenced reservoir properties.

Detailed petrographic evaluation of the reservoir in question, though often overlooked, should be an integral part of flow-unit studies. Once a diagenetic sequence is established, the information may be incorporated into the facies model to better understand how to subdivide the reservoir. Such an investigation has been conducted on the San Andres Formation in Reeves field of southeastern Yoakum County, Texas. Here, multistage diagenetic overprints are superimposed on depositional facies that vary in degree of lateral extent, thereby complicating the geometries of individual productive zones within the reservoir.

Analysis of the reservoir reveals that Reeves San Andres sediments were subjected to dominant diagenetic processes, including dolomitization and sulfate implacement, both of which are major factors in porosity preservation, and a variety of minor processes that have had little effect on reservoir quality. The recognition of diagenetic facies, an understanding of the processes that have created them, and identification of the implications of these processes on reservoir properties is a vital part of any flow-unit study.

AAPG Search and Discovery Article #90980©1994 AAPG Southwest Section Meeting, Ruidoso, New Mexico, April 24-26, 1994