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 F-3 and F-7 and reverse fault F-5 in southern Renlou coal mine are open structures. The coal seam between faults F-7 and F-5 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 F-5 and F-7 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 F-7 and F-5, the gas pressure gradient of coal seam No. 7(2) 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. 7(2) between faults F-3 and F-2 is 0.00726 MPa/m and the maximum measured gas pressure is 1.7 MPa (-692 m). The relative methane emission (RME) of working fare 7257 located between faults F-7 and F-5 was 2.01 m(3)/t on average with a maximum value of 4.96 m(3)/t. The average RME of working face II7211 located between faults F-3 and F-2 reached 12 m(3)/t in the area of 0-600 m away from F-3 fault and increased to 30 m(3)/t in the region of >600 m away from fault F-3. (C) 2013 Elsevier B.V. All rights reserved.