Assessing gas leakage potential into coal mines from shale gas well failures: Inference from field determination of strata permeability responses to longwall-induced deformations

This paper summarizes the changes in permeability at three boreholes located above an abutment pillar at a longwall coal mine in southwestern Pennsylvania. The motivation of this study was to better characterize the potential interaction between shale gas wells and the mine environment, through measurement of permeability changes in the coal mine overburden caused by mining-induced deformations. Measuring permeability changes around boreholes affected by longwall mining is an effective method to indicate changes in the fracture network above longwall abutment pillars and estimate the capacity for gas flow from shale gas wells to the mine environment. This study measured permeability through falling-head slug tests at different longwall face positions during the mining of two longwall panels on either side of the test abutment pillar where the test boreholes were located. Three test boreholes were drilled to different depths above the active mining level, and they had screened intervals to evaluate the response of different stratigraphic zones to mining-induced stresses. The results showed that the permeability around the slotted intervals of each borehole increased pre-mining to post-mining, and the permeability increased from mining of the first longwall panel to mining of the second one, adjacent to the pillar.