Hydrogeological control on the accumulation and production of coalbed methane in the Anze Block, southern Qinshui Basin, China

This study of geological and hydrogeological conditions in the coal-bearing Shanxi and Taiyuan formations in the Anze Block, southern Qinshui Basin, reveals the water-flow direction, hydrodynamic units, special tectonic units and their influence on the accumulation and production of coalbed methane. Water composition variation, hydrogen and oxygen isotopes, and total dissolved solids were used to analyze the type and source of the co-produced water, the connection between the coalbed methane wells and aquifers, the flow direction of groundwater, and to characterize water-rock interactions. Coal seam No. 3 in the Shanxi Formation is less affected by external water, while coal seam No. 15 in the Taiyuan Formation has a hydraulic connection with the roof K2 limestone aquifers. Due to the differences in the hydrodynamic units, structural uplift, and faults, the gas content of coal seam No. 15 is higher than that of coal seam No. 3. Hydrostratigraphic cross sections were built to characterize the coalbed methane accumulation in coal seams No. 3 and No. 15. The hydrodynamic units and the water-conducting faults or collapse columns are the main factors affecting the gas content, and gas and water production rates in the Anze Block.