Structural and Stratigraphic Controls on Natural Gas Production from Devonian Shales of Appalachian Basin of Southeastern Ohio: ABSTRACT

Abstract

Detailed subsurface mapping and evaluation of production data from 12 Devonian shale units in southeastern Ohio indicate that the lower Huron Member of the Ohio Shale is the primary gas-producing zone. Jointed or fractured structural traps serve as the dominant reservoirs and consist of (1) regional joint or fracture systems, (2) fractures related to anticlinal or domal features, and (3) fractures related to monoclines. Evaluation of production data shows the Devonian shale reservoirs to be a multiple-porosity system. Gas is released from the reservoir in a stepwise manner: first, from the open fracture system; second, from adsorbed gas on the fracture surface; and third, from adsorbed gas within the shale matrix. Rapid decline of production typically occurs during the first year. However, release of adsorbed gas from the shale matrix has resulted in wells producing for 50 years. Stratigraphic variations in the shale units are of secondary importance. Isopach mapping is most useful in defining areas of penecontemporaneous faulting during shale deposition. These areas may serve as untested jointed or fractured reservoirs characteristic of Devonian shale reservoirs in southeastern Ohio.