Reservoir Characteristics and Depositional Environments of Upper Strawn Series (Pennsylvanian) Capps Limestone and Fry Sandstone Core, Lake Abilene Field, Taylor County, Texas

Hughbert Collier

Detailed geologic and special core analyses were conducted on cores from the McIver, Inc., Sears 9 well, Lake Abilene field, Taylor County, Texas. The total Fry-Capps primary production from the Sears lease was approximately 473,000 bbl of oil and 737 mmcf of gas. Primary recovery was 109 bbl/ac-ft. Waterflood susceptibility tests indicate a 39% residual oil saturation after flooding and a 61% original mobile oil saturation. Secondary recovery should equal or exceed primary production.

The Fry sandstone is a medium to fine-grained, well-sorted, quartz- and calcite-cemented quartzarenite, fining upward into a sublitharenite. Scanning electron microscopy and x-ray diffraction reveal 1-3% authigenic clays (kaolinite, illite, and chlorite) lining the pores. Horizontal permeability averages 473 md, and the weighted-average porosity is 14%. Pore diameters range from 0.05 to 0.3 mm and average 0.1 mm. Primary porosity of 30% or more has been greatly reduced by quartz overgrowths and poikilotopic calcite. Much of the current porosity is secondary.

The Capps Limestone is wackestone and packstone. The average horizontal permeability is 199 md, and the weighted-average porosity is 10.5%. Pore types are predominantly moldic and vuggy. Pore diameters range from 0.05 to 2 mm and average 0.1-0.3 mm.

The Fry sandstone in this core was deposited as a minor distributary channel on the distal end of a westward or northwestward prograding cratonic bayhead delta. The Capps is a thin limestone that transgressed east over the abandoned and subsiding Fry sand channel.

AAPG Search and Discovery Article #91037©1987 AAPG Southwest Section, Dallas, Texas, March 22-24, 1987.