The Appleton Oil Field in Escambia County, Alabama, has been producing sweet and light oil under primary recovery since 1983. Production is from two upper Jurassic Smackover carbonate reservoir units located over localized Paleozoic basement ridge anticlinal structures. Total reservoir thickness ranges from 6 to 20 m. The lower reservoir is a microbial (algal) boundstone/bindstone reef facies exhibiting a combination of primary shelter and secondary intercrystalline dolomite porosity. Reservoir grade porosity ranges from 9.5 to 25.3% (average 16.9%) with a permeability of 1.1 to 4106 md (average 356 md). The upper reservoir is a ooid-oncoidal-peloidal grainstone/packstone shoal facies with a mixture of primary interparticulate and secondary grain moldic and intercrystalline dolomite porosity. Reservoir grade porosity ranges from 7.2 to 21.5% (average 14.2%) with a permeability of 0.4 to 618 md (average 56 md). More than 90% of the production is from the more permeable reef reservoir. The shoal reservoir is more heterogeneous. less permeable and includes tight zones which act as barriers to flow. Upper Jurassic Buckner anhydrites serve as a seal rock over the basement ridges.

To date, 2.6 million stock tank barrels of oil or 68% of the original oil in place has been produced from the field. The excellent primary recovery is due to a strong bottom water drive and exceptional continuity and connectivity in the reef facies above and below the oil-water contact. However, the rising water level serves to isolate the oil which is trapped in each of the localized structural highs. Because of structural elevation differences, a well draining oil from one paleohigh cannot effectively drain attic oil from the other paleohighs. Therefore, strategic infill drilling of each of the localized paleohighs is necessary to efficiently recover the field reserves. Utilizing this improved recovery method, an additional 8% recovery is estimated.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah