Stratigraphy and Production Characteristics of Upper Devonian Black Shales and Siltstones, West Virginia

Douglas G. Patchen, Michael Ed. Hohn

Prior to 1979, drilling for oil and gas from Upper Devonian clastic reservoirs in West Virginia was separated into two main trends; (1) oil and gas reservoirs in thin nearshore sandstones, or bundles of discontinuous marine sandstones and siltstones, associated with the Catskill delta and (2) gas reservoirs in organic-rich black shales in the finer clastic, more offshore facies farther to the southwest. Recent exploration and development drilling in the area between these two productive trends has provided sufficient control to carefully document key facies changes and intertonguing relationships. Fine-grained sandstones and siltstone bundles that extend into the area from the east are replaced by gray shales to the west. Black, organic-rich shales interfinger with, and a e replaced by, nonorganic, gray marine shales to the east.

Oil and gas production have been developed in these distal tongues of sandstones and siltstones and in the thin black shales that thicken to the west. Although exceptional wells have been drilled, the typical well in this area of recent drilling is marginally economic. Initial decline rates are high, and most wells will be short-lived, in contrast to the low-volume, long-term wells characteristic of the black shale reservoirs farther to the southwest. In general, productivity from black shale reservoirs increases progressively to the southwest, from fields associated with the detached Burning Springs anticline to fields that overlie the Rome trough in eastern Kentucky. The difference between opposite ends of this productive trend is significant. The average shale well to the southwest produces more gas in its thirtieth year than the average shale well to the northeast produces during second year on line.

Current research funded by the Gas Research Institute has allowed us to conclude that the presence and thickness of black shales, laminated fabric types, natural fractures, local structure, amount and type of kerogen content, and thermal maturity of the shales are important factors that determine the locations of commercial reservoirs.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.