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.

长壁引起的变形可能会危及位于长壁矿山基台柱中的页岩气井套管的机械完整性。气井周围的原位和诱导裂缝网络可能为气体流入矿井提供通道，从而产生安全问题。因此，美国国家职业安全与健康研究所 (NIOSH) 的这项研究开发了一个离散裂缝网络 (DFN) 模型，该模型基于宾夕法尼亚州西南部一个研究地点的采矿引起的裂缝孔的地质力学分析来表征覆盖层中的裂缝。地质力学模型中的孔径用于在裂缝流代码 (FFC) 中开发场地的随机 DFN 模型。模拟了复制潜在裂缝几何形状的随机 DFN 模型的多个实现，并将裂缝渗透率与现场测量值进行比较。最大场测量为 5.03 × 10^-12 m ² (5080 mD) 和 3.82 × 10 ^-13 m ² (386 mD) 分别估计在 Sewickley 和 Uniontown 地平线处的桥台柱上。结果表明，DFN 模型的平均渗透率与现场测量值非常吻合。此外，所有现场测量和 100 个 DFN 实现的比较表明该模型具有现场条件的代表性。这些发现提供了有关覆盖层裂缝特征的关键信息，这些信息将进一步用于预测在非常规气井套管破裂的情况下可能流向矿山的页岩气。