Hydrogeochemical characteristics and significance of produced water from coalbed methane wells in Fukang Mining Area

In order to explore the hydrogeochemical characteristics of coal seam water produced in Fukang Mining Area, the recharge relationship between stagnant aquifer and coal seam water in the fire area and the water chemical evolution model, this study collected water samples from coalbed methane wells in three well areas of the mining area, and carried out the test and spread characteristics of ion concentration, mineralization, hydrogen-oxygen isotope and dissolved inorganic carbon isotope, and analyzed by comparative and analysis methods, combined with structural characteristics and hydrogeological conditions. Research shows that the produced water of coalbed methane wells in the three well areas is mainly Na-HCO₃ and Na-HCO₃·Cl type water with high salinity; the stagnant water layer in the burning area is an important source of coal seam water supply in well C, and the transition from the stagnant water layer in the burning area to Fukang inclined axis is characteristic of the recharge area to the stagnant water area; the hydrogen-oxygen isotopes in the three well areas all fell near the atmospheric precipitation line, and the hydrogen-oxygen isotopes in the C well area showed obvious ¹⁸O drift, which was mainly due to the ¹⁸O drift of groundwater in the stagnant water layer in the burning area; the value of δ¹³C_DIC in the produced water of coalbed methane wells in C well area was the largest, indicating that the microbial effect was strong and secondary biogas existed; the dissolved inorganic carbon isotopes in three well areas were negatively correlated with sulfate concentration, and the correlation with gas production was obvious, which could be used as a reference factor to identify the favorable area for secondary biological CBM enrichment.