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In the Appalachian basin, the Middle Devonian organic-rich shale interval, including the Marcellus Shale, is an important target for exploration. This unconventional gas reservoir is widespread across the basin and has the potential to produce large volumes of gas (estimated to have up to 1,307 trillion cubic feet of recoverable gas). Although the Middle Devonian organic-rich shale interval has significant economic potential, stratigraphic distribution, depositional patterns and petrophysical characteristics have not been adequately characterized in the subsurface. Based on log characteristics, tied to core information, the lithostratigraphic boundaries of the Marcellus and associated units were established and correlated throughout West Virginia and southwestern Pennsylvania. Digital well logs (LAS files) were used to generate estimates of lithology and to identify zones of higher gas content across the study area. In addition, a lithologic solution was calibrated to X-ray Diffraction (XRD) data. Using previous studies on organic shale, relationships between the natural radioactivity (as measured by the gamma-ray log) were incorporated with techniques to identify gas-prone intervals. The comparison between the Uranium content and the measured bulk density identified intervals in the Marcellus having high gas saturations and were used to generate an approach to correct water saturations. These techniques of identifying lithology and potential gas in the Marcellus are useful to identify areas of higher exploration potential and to target zones for fracture stimulation or to land a horizontal leg.

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