The Cottageville, West Virginia, gas field produces from the Lower Huron Member of the Ohio Shale formation of the Upper Devonian. The production results from increased permeability caused by anomalous fracturing of the shale. A normal basement fault, which lies below the fracture zone, may control fracturing in the shales.

Seismic reflection data obtained in the area in 1977 show the fault extending up into the Ordovician. These data are also analyzed for seismic velocity and attenuation anomalies associated with the gas-producing fracture zone. Gas production occurs in an area several miles long but only about one mile wide. Increased fracture intensity and presence of gas in the shale within this limited area serve to decrease the shear strength of the rock, decreasing the seismic velocity. Similarly, greater attenuation of the high-frequency components of the seismic wave can be expected. Examples from the Cottageville data showing basement structure and seismic velocity and attenuation anomalies associated with gas production are presented.

An exploration rationale for prospecting for eastern shale gas is developed. Although the total area covered by gas-bearing shales in the eastern United States is large, individual gas fields within this area are relatively small. Reflection seismology is used to target specific exploration wells after reconnaissance by other methods has been done.

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