Effects of structural deformation on formation of coalbed methane reservoirs in Huaibei coalfield, China

Tectonically deformed coal is defined as coal formed by superimposed reformations from tectonic stress. The Huaibei coalfield is typically composed of various tectonically deformed coals containing rich coalbed methane resources. However, the occurrence of coal seam in this area is complicated largely by the structural deformation, which has not yet been evaluated systematically for exploration and exploitation of coalbed methane. In this study, tectonism in Huaibei coalfield is discussed by combining systematic analyses on the occurrence of coal seams and the formation of coalbed methane reservoirs. The study shows that, with structural deformation in the study area, the coal seams in Huaibei coalfield are distributed in north–south tectonic blocks and east–west tectonic zones. North tectonic block of Huaibei coalfield is not favourable for exploitation of coalbed methane because of low gas content or disadvantageous structural conditions. Within the south tectonic block, the east Suzhou syncline contains high gas content but coal permeability is very low. This area is generally not suitable for exploitation of coalbed methane and is a dangerous mining area due to gas outburst because of the widely developed mylonitic coals. South Suzhou and Nanping synclines in the middle part of the south tectonic block are exposed to relatively weak structural deformations. These synclines contain coals with high gas content and moderate permeability, which are beneficial for exploration and exploitation of coalbed methane. Linhuan mining area in the south tectonic block is generally not suitable for exploitation of coalbed methane, mainly because of well developed normal faults and interlayer slip structure, and presence of mylonitic coal, resulting in low gas content and poor structural conditions for mining coalbed methane. In contrast, Guoyang mining area in the west part of the south tectonic block, where tectonically deformed coal was generally underdeveloped, is a potential area for exploration and exploitation of coalbed methane because of moderate gas content and possibly higher permeability of its coal