Abstract: Wildcat Valley Sandstone in Southwest Virginia--Possible Reservoir Sandstone

Ralph L. Miller, William Back, Ruth G. Deike

In southeast Virginia, the Wildcat Valley Sandstone of Early Devonian age is present in several fault belts of the Valley and Ridge province and underlies the Cumberland Plateau in Wise, Dickenson, and Buchanan Counties. In the southeastern part of its depositional basin, it is predominantly a medium- and coarse-grained marine sandstone about 15 m thick. Northwestward beneath the plateau, it thickens and becomes predominantly limestone.

At the surface, carbonate cement that originally was present largely has been removed, and the sandstone is extremely porous and permeable, in some places even unconsolidated. Some or most of this solution could have taken place in the long interval of Middle Devonian time after cessation of Wildcat Valley sedimentation and before invasion of the Late Devonian seas in which the overlying Chattanooga (black) Shale was deposited.

In the Cumberland Plateau, deep cable-tool wells have penetrated the Wildcat Valley Sandstone well below the zone of recent weathering. Laboratory analysis of cuttings from several of these wells indicates that much of the carbonate rock in the Wildcat Valley Sandstone is impoverished in carbon 13, and hence resembles a freshwater carbonate more than a marine carbonate. Removal of original marine carbonate cement and replacement with freshwater carbonate is indicated. Thus, in this region, pore spaces that formed as a result of subaerial weathering in Middle Devonian time seem largely to have been refilled by freshwater carbonate. In the Valley and Ridge province, however, where the formation is almost entirely sandstone, porosity that formed in Middle Devonian time may have been reta ned. Hence, the formation could be an excellent reservoir for migrating hydrocarbons.

Three formations contain probable source beds for the generation of gas, of which the black shale of the Chattanooga is thickest and most promising. Both fault and anticlinal traps, or combinations of the two, may be present. Drilling will be needed, however, to determine whether gas has entered and been trapped in the Wildcat Valley Sandstone in the Valley and Ridge province.

AAPG Search and Discovery Article #90975©1976 GCAGS- GC Section SEPM Annual Meeting Shreveport, Louisiana