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Reservoir Characterization and Sequence Stratigraphy of the Permian San Andres Platform Carbonates, Permian Basin, West Texas

Helbert, Dana 1; Ruppel, Stephen C.1
1 Jackson School of Geosciences, University of Texas at Austin, Austin, TX.

The San Andres Formation is the most prolific oil reservoir in the Permian basin. However, despite more than 60 years of production, an estimated 70% of the original oil in place remains. Recovery of this huge resource requires a better understanding of facies and reservoir framework. High resolution correlation and facies categorization is thus essential for understanding the complex heterogeneities found in these shallow water platform carbonates. In Fullerton Field, the San Andres Formation comprises high frequency cycles of upward shoaling shallow-marine carbonates. Post depositionally these rocks have undergone widespread dolomitization and sulfate emplacement that in part mask some textural features.

Studies of nine cores (1730 ft) in Fullerton field reveal five primary facies based on depositional texture, fossil assemblages, and sedimentary structures. Three subtidal facies were defined: skeletal packstone, containing dominantly molluscs, cross-laminated pellet wackestone-packstone, and burrowed pellet mollusc wackestone. Near the base of the section the burrowed wackestone often contains angular lignite clasts and shaley interbeds. Peritidal facies include silty mudstone with wispy laminations and planar-laminated mudstone, commonly with fenestral pores and occasional teepee structures. Both are interpreted as deposited in a tidal flat setting and are associated with exposure surfaces. A trend of upward decreasing accommodation is apparent through the section, as lower cycles are thicker and thin upward. All cycles contain subtidal burrowed wackestone at the base and are capped by peritidal facies. Skeletal packstones and cross-bedded wackestone-packstones are rare, but are present in some higher-accommodation cycles. Cycles tops can be tied to their respective wireline logs enabling in the construction of a cycle-based reservoir framework.

Large-scale lateral trends across the platform may reflect primary controls such as regional subsidence rate or changes in water depth. Integration of core, petrophysical, and seismic data from surrounding fields, such as Fuhrman-Mascho, to the southeast, and West Seminole, to the north, will increase the understanding of the larger sequence stratigraphic framework for the Central Basin Platform.

 

AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009