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?

Abstract

Pshigoda-Desmoinesian field, located in north-central Ochiltree County, Texas panhandle, has produce 1.94 MMBO and 5 bcf of gas from a stratigraphic trap in the Middle Pennsylvanian, Desmoinesian, Marmaton Group. The Marmaton reservoir interval 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, secondarily, 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. 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. 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 in 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. Naturalmore » 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 fields is a poor candidate for a horizontal well.« less