A new insight into coalbed methane occurrence and accumulation in the Qinshui Basin, China

Abstract

Coalbed methane (CBM) recovery from coal seams can benefit low-carbon energy utilization and reduce greenhouse gas emissions. The Qinshui Basin, which evolved from the North China Craton Basin in the Late Paleozoic, provides abundant coal-bearing rocks and relatively stable geological conditions for CBM occurrence. To better understand CBM accumulation characteristics, various aspects of geological structure, magmatic activity, hydrodynamics, coal seam thickness, burial depth, and sedimentary characteristics of coal measures within the basin were comprehensively investigated, along with the CBM reservoir aspects of coal components, mechanical properties, pore-fracture characteristics, and gas contents. The results show that the coal-forming environment in the northern Qinshui Basin is dominated by river flood and delta plains, while the central Qinshui Basin mainly consists of delta front, inter-delta bay, and lacustrine facies. The southern part is primarily lacustrine facies with scarce delta front subfacies. In terms of ash yield, that of coal seam 3# in the center of the study area is significantly higher than that in the north and south because the center is closer to the provenance and carries a large amount of detritus during the flood season. The primary coal structure is well preserved, and the facies cleats are largely filled with dolomite and kaolinite, suggesting mineralized fluid activity after the development of the major fracture. The gas content is mainly controlled by geological structure and hydrogeological conditions. Interestingly, for the coal seams > 1000 m away from the fault, the nature of the fault has no significant effect on the gas content. This study provides insights into the efficient exploration and exploitation of CBM in Qinshui Basin.