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CALDWELL, CRAIG D., and HELEN E. FERRELL, Phillips Petroleum Company, Bartlesville, OK, and MARK W. BOWMAN, Phillips Petroleum Company, Borger, TX

ABSTRACT: Application of Petrology and Fracture Analysis to Characterize Reservoir Heterogeneity of the Middle Pennsylvanian Marmaton Reservoir at Pshigoda-Desmoinesian Field, Ochiltree County, Texas Panhandle: Is a Horizontal Well Appropriate?

Pshigoda-Desmoinesian field, located in north-central Ochiltree County, Texas panhandle, has produced 1.94 MMBO and 5 bcf of gas from a stratigraphic trap in the Middle Pennsylvanian, Desmoinesian, Marmaton Group. The Marmaton reservoir interval, cored in the Phillips Petroleum Blasingame #6 well, is composed of complexly interlayered, fine- to medium-grained arkosic sandstones, calcareous bioclastic sandstones, and sandy

bioclastic limestones. Sandstone and limestone layers typically are 2.5-60 cm thick.

Arkosic sandstones in the reservoir interval have core analysis porosities of 5.5-15% and horizontal permeabilities ranging from 0.06 to 1.78 md. Porosity is mainly intergranular and less common, secondary, leached feldspar. Intergranular porosity has been occluded partly by mechanical/chemical compaction, calcite cementation, and precipitation of authigenic clay minerals and quartz and feldspar overgrowths. The feldspar and clay mineral content of the arkosic sandstones results in relatively high gamma-ray log values. Calcareous, bioclastic sandstones and sandy, bioclastic limestones of the reservoir interval average 4.9 and 3.9% porosity, respectively. Horizontal permeabilities to air range from 0.003 to 0.02 md. Generally, as calcite content increases porosity decreases due to calc te cementation of intergranular pores. An increase in total carbonate, predominantly ferroan calcite, correlates with a decrease in detrital feldspar and clay mineral content and lower gamma-ray log values.

Low porosity and permeability, sandy bioclastic limestone, and calcareous bioclastic sandstone layers in the Marmaton reservoir interval at Pshigoda-Desmoinesian field may act as partial barriers to the vertical migration of fluids and gases in the reservoir. Natural fractures in the reservoir interval are relatively rare, short in length, poorly connected, restricted to sandy limestone layers, and partly calcite cemented, suggesting they do not enhance significantly the vertical movement of fluids or gases through the reservoir. Thus, the strongly layered and weakly fractured Marmaton reservoir at Pshigoda-Desmoinesian field is a poor candidate for a horizontal well.

AAPG Search and Discovery Article #90991©1993 AAPG Mid-Continent Section Meeting, Amarillo, Texas, October 10-12, 1993.