Abstract: Berea (Mississippian) Sandstone Core from CSO Island Creek Coal C-7, McDowell County, West Virginia
Gary A. Flesch, William R. Almon
Depositional environment and reservoir characteristics were interpreted for a Berea Sandstone (Mississippian) core from the Cities Service Oil Co. Island Creek Coal C-7 well, McDowell County, West Virginia. The well location is 11,550 ft (3,520 m) south of 37°22^prime and 1,000 ft (305 m) west of 81°45^prime. Gas is produced from the lower Berea Sandstone in the area; however, production commonly is marginal because of low porosity and permeability and the susceptibility of the unit to reservoir damage during well completion.
The Berea Sandstone is very fine grained, consisting primarily of quartz with minor feldspar and rock fragments (i.e., a feldspathic litharenite) and originated in a nearshore (upper foreshore) marine environment, as evidenced by the abundance of slightly inclined, graded parallel laminations. Siltstone and shale units were deposited in a transitional to offshore environment. Berea sandstone bodies in this area generally are elongated in a northeast-southwest direction.
Diagenetic alteration of the original sediment strongly controls reservoir characteristics of the Berea. Diagenetic components (listed in order of occurrence) consist of first-generation quartz overgrowths, chlorite (chamosite) and minor illite clay films, second-generation quartz overgrowths and in-fillings, and carbonate-siderite cementation. Compaction and pressure solution, which resulted in grain suturing and formation of stylolites, preceded or was simultaneous with the second generation of quartz overgrowths.
There are several indications that the Berea Sandstone has been affected by moderate to high temperatures in the geologic past. The well appears to be located in a thermal-gas area. However, the reconstructed depth of burial is about the same as the present depth of approximately 4,000 ft (1,219 m). A working hypothesis to explain the higher temperatures may be tectonism which occurred during the Alleghanian (Pennsylvanian to Permian) orogeny. The well is near the structural front of the Valley and Ridge province of the Appalachian Highlands where significant tectonic activity occurred. Simultaneous with tectonism, silica and iron-rich solutions were generated locally from stylolites or from adjacent shale units. These solutions and the tectonic related heat flow appear responsible for the high degree of alteration in the Berea Sandstone.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC