Experimental study on the desorption behavior of high-volatile bituminous coals following CO2 and CH4 injection at various compositional ratios

CO2-ECBM 2-ECBM (Enhanced Coalbed Methane recovery) offers the dual benefits of increasing methane production and reducing carbon emissions through sequestration. Previous studies have primarily focused on the competitive adsorption effects of different gas compositions during the CO2-ECBM. 2-ECBM. However, the dynamic changes in desorption volume, desorption strain, and gas composition for different compositional ratios of CO2/CH4 2 /CH 4 after injecting CO2 2 remain unclear. Therefore, high-volatile bituminous coals from the southern margin of the Junggar Basin are chosen for desorption experiments with five different compositional ratios of CO2/CH4. 2 /CH 4 . Desorption volume, desorption strain, and gas composition of the coal samples are monitored during the desorption process. Finally, the mechanism influencing the dynamic changes in gas composition during desorption is analyzed. The results indicate that as CO2 2 concentration increases, both desorption volume and desorption strain correspondingly increase. At the same desorption volume, a higher CO2 2 concentration results in greater desorption strain. For different compositional ratios of CO2/CH4, 2 /CH 4 , CH4 4 concentration gradually decreases while CO2 2 concentration gradually increases over desorption time. The concentration of the desorption gas is influenced by the initial CO2 2 concentration and the pore structure. Specifically, higher initial CO2 2 concentrations, better pore opening, and more developed mesopores and macropores lead to greater changes in composition concentrations during desorption. Different concentrations of CO2 2 all promote CH4 4 production, with higher CO2 2 concentrations enhancing CH4 4 production efficiency more significantly, especially for samples that are more difficult to produce. The research findings can provide guidance for the efficient production of CBM after CO2 2 injection.