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A Discrete Fracture Network Model for Prediction of Longwall-Induced Permeability

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Abstract

Longwall-induced deformations could jeopardize the mechanical integrity of shale gas well casings positioned in the abutment pillar of a longwall mine. The in situ and induced fracture networks surrounding the gas well could provide pathways for gas flow into the mine creating safety concerns. Hence, this study by the National Institute for Occupational Safety and Health (NIOSH) develops a discrete fracture network (DFN) model to characterize the fractures in the overburden based on geomechanical analyses of mining-induced fracture apertures at a study site in southwestern Pennsylvania. The apertures from the geomechanical model are used to develop a stochastic DFN model of the site in fracture flow code (FFC). Multiple realizations of the stochastic DFN model that replicate potential fracture geometries are simulated, and the fracture permeability is compared with field measurements. A maximum field measurement of 5.03 × 10−12 m2 (5080 mD) and 3.82 × 10−13 m2 (386 mD) was estimated over the abutment pillar at the Sewickley and Uniontown horizon, respectively. The results show that the average permeabilities from the DFN model agree closely with the field measurements. In addition, the comparison of all the field measurements and 100 DFN realizations show the model is representative of field conditions. These findings provide critical information regarding fracture characteristics in the overburden, which will further be used to predict potential shale gas flow to the mine in the event of a casing breach for an unconventional gas well.

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Acknowledgements

The authors acknowledge the contributions of Dr. C. Ӧzgen Karacan during the review of the modeling approach. Data from this manuscript had been presented at the North American Mine Ventilation Symposium, June 2021, Rapid City, SD [12].

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  1. Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Pittsburgh, PA, USA

    K. M. Ajayi, Z. Khademian, S. J. Schatzel, E. Watkins & V. Gangrade

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  1. K. M. Ajayi
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  2. Z. Khademian
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  3. S. J. Schatzel
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  4. E. Watkins
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  5. V. Gangrade
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Correspondence to K. M. Ajayi.

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

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Ajayi, K.M., Khademian, Z., Schatzel, S.J. et al. A Discrete Fracture Network Model for Prediction of Longwall-Induced Permeability. Mining, Metallurgy & Exploration 39, 1793–1800 (2022). https://doi.org/10.1007/s42461-022-00637-6

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  • DOI: https://doi.org/10.1007/s42461-022-00637-6

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