The National Institute for Occupational Safety and Health (NIOSH) has been evaluating longwall mining-induced strata fractures and their impacts on casing stability of Marcellus shale gas wells located in longwall pillars. To understand the extent of overburden fractures after longwall mining, NIOSH researchers drilled a post-mining corehole into the fractured strata above the Pittsburgh coal seam longwall gob. Knowing the extent of the fracture zone height will help gas operators minimize the hazards of drilling into longwall gobs. The core was retrieved from the surface down to the top of the gob void. Various fractures were encountered varying from 35 to 64°, depending on lithologic type and relative closeness to the gob. The longwall panel dimension was 457-m wide and 3657-m long, in which the total fracture zone height was found to be at 141 m and the hydraulic connected fracture zone at 87.7 m above the top of the Pittsburgh seam. In addition to core drilling through the gob, FLAC3D modeling was also used to simulate the formation of fracture zone and the orientations of longwall-induced fractures. This study provides much-needed evidence on the fracture zone of Pittsburgh seam longwall gobs to help gas operators avoid potential hazards associated with drilling through highly fractured zones in longwall gobs.

美国国家职业安全与健康研究所 (NIOSH) 一直在评估长壁开采引起的地层裂缝及其对位于长壁柱中的 Marcellus 页岩气井套管稳定性的影响。为了了解长壁开采后覆盖层裂缝的范围，NIOSH 研究人员在匹兹堡煤层长壁采空区上方的裂缝地层中钻了一个采后岩心孔。了解断裂带高度的范围将有助于天然气运营商最大限度地减少钻入长壁采空区的危险。岩芯从地表一直回收到采空区的顶部。根据岩性类型和与采空区的相对接近程度，遇到了从 35° 到 64° 不等的各种裂缝。长壁板尺寸为 457 米宽和 3657 米长，其中，Pittsburgh 煤层顶部以上的总裂缝带高度为 141 m，水力连通的裂缝带为 87.7 m。除了通过采空区进行岩心钻探外，FLAC3D 建模还用于模拟裂缝带的形成和长壁诱发裂缝的方向。这项研究为匹兹堡煤层长壁采空区的断裂带提供了急需的证据，以帮助天然气运营商避免与钻穿长壁采空区高度断裂带相关的潜在危险。