Reservoir Characterization and Modeling of Upper Jurassic Smackover Carbonate Shoal Reservoirs, Womack Hill Oil Field, Choctaw and Clarke Counties, Alabama

By

MANCINI, ERNEST A., and PANETTA, BRIAN J.

Center for Sedimentary Basin Studies and Department of Geological Sciences, University of Alabama, Tuscaloosa, AL

The Womack Hill Oil Field, Choctaw and Clarke Counties, Alabama was discovered in 1970 with the drilling of the Carlisle Unit 16-4 No. 1 well. Oil was discovered in Upper Jurassic Smackover carbonate shoal lithofacies at a depth of 11,432 to 11,442 ft. A waterflood project was initiated in the western portion of the field in 1975. To date, 30.7 million barrels of oil have been produced from the field. Estimated reserves for the field are 119 million barrels of oil. An additional 12 to 24 million barrels of oil are projected to be recovered through the application of advanced technologies that optimize reservoir management.

Reservoir characterization and modeling of the Smackover carbonate shoal reservoirs are being utilized to improve field-scale reservoir management in the field. Reservoir characterization has shown that the Smackover is productive from three carbonate shoal reservoirs that occur in three vertically stacked shallowing upward cycles (A, B, and C). The cycles consist of a sequence comprised of carbonate mudstone/wackestone at the base and ooid grainstone at the top. Porosity in the grainstone has been enhanced through dissolution and dolomitization. Porosity is chiefly interparticle and dolomite intercrystalline with grain moldic, intraparticle and vuggy types. The upper shoal (shoal A) is the most productive due to increased dolomitization. Reservoir modeling has demonstrated that lateral barriers to flow are present across the field from west to east as a result of lithofacies changes in the shoal sequences. Seismic data indicate a fault in the eastern portion of the field. The reservoir pressure differential that exists between the wells in the western portion of the field and the wells in the eastern portion is attributed to the presence of this fault. The three shoal reservoirs are, in part, vertically separated by the carbonate mudstone at the base of the three shoaling upward cycles. Knowledge of the Smackover heterogeneity and potential compartmentalization of the reservoir in the field has resulted in the design of an improved hydrocarbon production strategy for the carbonate shoal reservoirs in Womack Hill Oil Field.