Structural controls on coalbed methane reservoirs in Faer coal mine, Southwest China

Abstract

Guizhou (贵州) Province, Southwest China, is rich in coalbed methane (CBM) resources, wherein its geological structure is complicated. We discuss the occurrence characteristics of CBM based on CBM borehole test data and geological setting. In combination with the analysis of the regional tectonics, macro- and micro-scopic geological structures and pore size distributions, the structural controls on CBM reservoirs were further discussed from the aspects involving tectonic evolution, structural features, and deformation of coal. The results show that the CBM enrichment was mainly controlled by the regional tectonic subsidence and weak structural deformation on coal reservoirs after coal formation. The Yangmeishu (杨梅树) syncline and topography are the main controlling factors to the current distribution pattern of CBM, which is higher in the north than the south and trending toward the NE direction. Normal faults and fractures can be divided into open, closed, and occluded types. The open type reduces both gas content and methane concentration of nearby coal seams. The closed type causes the decrease of gas content, while methane concentration is still high. The occluded type fail to reduces gas content, and even results in the enrichment of CBM in small areas near fault. Moderate brittle deformation can improve the pore structure and development of structural fracture of coal reservoir. Cataclastic structural coals with well-developed fractures and relatively uniformly distributed pore structures are common in the Faer (发耳) coal mine, which are favorable for the production of CBM.