By Greg Rumbaugh, supervisory engineer, MSHA Roof Control Division
The proliferation of unconventional gas well development in the Northern Appalachian coalfields has raised a number of mine safety concerns. Unconventional wells, which extract gas from deep shale formations, are characterized by gas volumes and pressures that are significantly higher than those observed at many conventional wells. Hundreds of planned and actively producing wells penetrate protective coal pillars or barriers within active longwall mine boundaries, including chain pillars located between longwall panels. The mining-induced ground movements that may cause well damage include conventional subsidence, non-conventional subsidence (e.g. bedding plane slip), pillar failure, and floor instability. This presentation describes the known risk factors for each of the four failure mechanisms. It includes a framework that can guide the risk assessment process when mining takes place near gas or oil wells.
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