The impact of faults on the occurrence of coal bed methane in Renlou coal mine, Huaibei coalfield, China

The fault has an important impact on coal bed methane (CBM) occurrence. The complexity of the fault exacerbates the variability of CBM occurrence, which increases the difficulty of mine gas prevention and thus threats to mining safety seriously. The coal-bearing strata in the Renlou coal mine located in the Linhuan mining area of the Huaibei coalfield have undergone three transformations caused by major tectonic movements since its formation. In addition, the large-angle tectonic stress superposition leads to structure characteristic and mechanical properties of faults transform in the area or just make it become multiplicity. The normal faults F3 and F7 and reverse fault F5 in southern Renlou coal mine are open structures. The coal seam between faults F7 and F5 is in the emission range of the two faults (partially in the superimposed range) in which a significant amount of gas escapes. The formation between faults F5 and F7 is horst, and it turns from NS to EW. The stress in the formation is large, which results in the presence of numerous fractures and cleats. Therefore, there is difference of methane occurrence between the two regions. Between faults F7 and F5, the gas pressure gradient of coal seam No. 72 is 0.00356 MPa/m with a maximum value of 0.39 MPa (−633.5 m). However, the gas pressure gradient of coal seam No. 72 between faults F3 and F2 is 0.00726 MPa/m and the maximum measured gas pressure is 1.7 MPa (−692 m). The relative methane emission (RME) of working face 7257 located between faults F7 and F5 was 2.01 m3/t on average with a maximum value of 4.96 m3/t. The average RME of working face ІІ7211 located between faults F3 and F2 reached 12 m3/t in the area of 0–600 m away from F3 fault and increased to 30 m3/t in the region of >600 m away from fault F3.