Characterization and Quantification of Mining-Induced Fractures in Overlying Strata: Implications for Coalbed Methane Drainage

Coalbed methane (CBM) production in the overlying strata of coal reservoirs is often hampered by the unknown distribution of the mining-induced fractures. Mining-induced fractures are CBM migration pathways in the fractured overlying strata, and the excavation of coal seams within a mine causes the CBM in adjacent coal seams to flow into the overlying strata. The mining-induced fracture field in the overlying strata is the best place from which this CBM is drained. Here, to better understand the distributions of vertical and horizontal fractures caused by excavation, we propose a novel approach to quantify the dimensions of vertical and horizontal fractures in fractured zones. In addition, we demonstrate that there are negligible changes in the dimensions of horizontal fractures and great changes in the dimensions of vertical fractures when there is an increase in the height of the fractured zone. We further demonstrate that mining-induced angles mainly concentrate on 0 degrees-10 degrees, 50 degrees-70 degrees, 110 degrees-120 degrees and 170 degrees-180 degrees, and larger width fractures exist in both sides and top due to the de-stressed effect and fractures in the middle of model close under mining-induced stress. The approach described here could be used to improve the accuracy of cross-measure borehole positioning and the efficiency of CBM drainage.