Pipeline quality gas production from the highly fractured methane-bearing strata above longwall coal mine panels is predicted to be many times that of the gas-in-place estimate for the minable coalbed. This production is thought to come from relatively shallow gas-bearing coals, organic shales, and sandstones. In the mining process, permeability of shallower strata is increased significantly because of the fractured zone generated during longwall mining activity and, hence, gas could be produced at volumes many times that of an average conventional gas well. This paper assesses the potential production and the influence of well spacing on the drainage of gas from the strata above mining operations in southern Appalachia. In this assessment, gas reserves were quantified for a typical failure zone, formation gas content, and geologic cross section present in the Appalachian Basin. A finite element method was used to determine the size and shape of the affected stratigraphic areas for which gas contents were estimated (based on prior knowledge). A two-phase reservoir model was used to compute increased production rates from methane wells that penetrate the multiple strata and coalbed. Production data from actual wells above a longwall panel were history matched to characterize flow mechanisms and reservoir properties. These properties were then evaluated in parametric studies to determine the influence of well location on gas production. Results indicate that cumulative gas production can be increased by placing wells farther apart than 1,000 ft (304.8 m). The model appears to make reasonable predictions of the size of the multi-reservoir area in complex geologic conditions. The study considered the influence of an advancing mine face on gas production. Thus, the methodology presented in this paper is applicable to the location of gas wells in highly fractured reservoirs to optimize long-term gas production.

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