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Rockmass Permeability Induced by Longwall Mining Under Deep Cover: Potential Gas Inflow from a Sheared Gas Well

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Abstract

The stability of shale gas wells drilled through current and future coal reserves can be compromised by ground deformations due to nearby longwall mining. Depending on the longwall-induced rockmass permeability, the high-pressure explosive gas from the damaged well may reach mine workings and overwhelm the mine ventilation systems. This study uses geomechanical models to estimate the rockmass permeability induced by mining. A two-panel longwall model of a deep, 341-m-cover mining site in southwestern Pennsylvania is constructed in 3DEC to explicitly model the rockmass by a discrete fracture network (DFN) technique. Stress-induced fracture apertures and permeabilities are calculated across the model and are validated against permeability measurements. A fracture flow code (FFC) is developed to use these results to predict potential inflow to the mine should a gas well breach occur. One hundred DFN realizations are simulated, and the results show that for a gas pressure of 2.4 MPa, the average of the predicted inflow rates to this deep-cover mine is 0.006 m3/s, significantly lower than the average inflow of 0.22 m3/s for a shallow-cover mine (145-m deep) studied in the previous work (Khademian, et al. 2021). The result can help assess the potential hazards of a shale gas well breach for mine safety and evaluate the ventilation requirements to mitigate the risk.

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Acknowledgements

Data from this manuscript have been presented at the MINEXCHANGE 2022 SME Annual Conference & Expo, February 27–March 2, 2022, Salt Lake City, UT.

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Authors and Affiliations

  1. Pittsburgh Mining Research Division, CDC NIOSH, Pittsburgh, PA, USA

    Zoheir Khademian, Kayode M. Ajayi & Steven J. Schatzel

  2. Independent Mining Engineer, Pittsburgh, PA, USA

    Gabriel S. Esterhuizen

  3. CDC NIOSH, Spokane Mining Research Division, Spokane, WA, USA

    Bo H. Kim

Authors
  1. Zoheir Khademian
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  2. Kayode M. Ajayi
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  3. Steven J. Schatzel
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  4. Gabriel S. Esterhuizen
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  5. Bo H. Kim
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Correspondence to Zoheir Khademian.

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The findings and conclusions in this report are those of the author(s) and do not necessarily represent the official position of the National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention (CDC). Mention of any company or product does not constitute endorsement by NIOSH.

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Khademian, Z., Ajayi, K.M., Schatzel, S.J. et al. Rockmass Permeability Induced by Longwall Mining Under Deep Cover: Potential Gas Inflow from a Sheared Gas Well. Mining, Metallurgy & Exploration 39, 1465–1473 (2022). https://doi.org/10.1007/s42461-022-00635-8

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  • DOI: https://doi.org/10.1007/s42461-022-00635-8

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