Coalbed Methane Accumulation Indicated by Geochemical Evidences from Fracture-filling Minerals in Huaibei coalfield, East China

Fracture-filling minerals in coal-bearing strata are the product of water-rock interactions under specific geological conditions, which reflect the accumulation process and characteristics of CBM enrichment and migration. In this study, vein-bearing sedimentary rock samples from coal-bearing strata in the Huaibei coalfield were selected to reveal the fluid sources and the filling periods of CBM. The carbon source of the vein samples is a mixture of the degraded organic carbon of coal and the dissolution of carbonate minerals in coal measure. Considering the low salinity of the fluid, the infiltration of surface water will also bring some supergenic carbon supplement. Moreover, the high 87 Sr/ 86 Sr ratios might also be induced by the infiltration of surface water and the dissolution of radiogenic strontium adsorbed in coal. Based on the temperature, salinity, and Raman spectral analysis, the formation of fluid inclusions is divided into two phases: the first phase corresponded to the generation of large-scale thermogenic gas, while the second phase reflected the event of large-scale secondary biogas formation. The values of δD–CH 4 and δ 13 C–CH 4 in the group inclusions showed that no significant isotope fractionation occurred between the methane in the inclusions and that in the coal seam; the methane in the inclusions is predominantly biogas. This study further reveals the mechanism of CBM formation and accumulation process in the Huaibei coalfield, which could benefit the exploration and development of CBM in this area.