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

Abstract 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, the special tectonic units and their influence on the accumulation and production of coalbed methane (CBM). Water composition variation, H and O isotopes, and total dissolved solids were used to indicate the type and source of the co-produced water, the connection between the CBM wells and aquifers, the flow direction of groundwater, and to characterize water-rock interactions. Coal seam No. 3 is less affected by the external water, while coal seam No. 15 has a hydraulic connection with the K2 limestone in the C3t aquifer and the O2f aquifer. The gas content of coal seam No. 15 in the Taiyuan Formation is higher than that of coal seam No. 3 in the Shanxi Formation, which was mainly caused by the hydrodynamic units, structural uplift, and faults. Hydrostratigraphic cross sections were built to characterize the CBM accumulation in coal seams No. 3 and No. 15, showing the variations of gas content, gas and water production rate of wells in different hydrodynamic units. The hydrodynamic units and the water-conducting faults or collapse columns are the main factors affecting the gas and water production rate in the Anze Block.