Experimental study on CO₂-enhanced coalbed methane production and its simultaneous storage

Abstract: Experimental study on CO₂-enhanced coalbed methane production and its simultaneous storage Abstract: For a long time, a lot of work has been done on CO₂-enhanced coalbed methane (CO₂-ECBM), but the limited industrial trials failed to achieve the expected purpose, which prevented the promotion and application of CBM enhancement technology. In recent years, with the establishment of carbon neutrality routes in different countries, CO₂ geological storage has gradually gained attention, and the questions of whether coal reservoirs can be treated as CO₂ storage space and whether simultaneous CO₂ displacing CH₄ and storage can be achieved have returned to the spotlight. In this study, using the coal samples from Xinjiang Zhunnan coal region, the adsorption/desorption experiments of coal were carried out with different mixture ratios of CO₂ and CH₄ to explore the effects of gas composition on CO₂-ECBM, as well as CO₂ adsorptive storage potential. The results show that, the CH₄ displacement effect decreases as the CO₂ ratio of the mixed gas decreasing, among which the CO₂ residual volume of 40% CH₄+60% CO₂ mixture is the highest, corresponding to 83.05% CH₄ production and 83.62% CO₂ storage by adsorption as the experimental pressure drops to 0.7 MPa during desorption processes. This indicates that its CO₂ adsorptive storage potential is the best. The desorption volume and rate of each mixed gas during different depressurization and desorption stages were calculated according to the Dalton’s law for partial pressure and partial volume, as well as the Langmuir’s equation. The results indicate that, as the CO₂ ratio of the mixed gas decreases, the CO₂ residual rate and volume, as well as the final CH₄ desorption rate, were decrease. The predicted trends of CH₄ desorption rate and CO₂ residual volume with gas mixture composition are generally consistent with those obtained by the experiments, indicating that high proportion of CO₂ in the gas mixture enhances CH₄ recovery, as well as CO₂ adsorptive storage potential of the coal reservoir. This study can provide not only theoretical basis for the field application of CO₂-ECBM and CO₂ storage, but also experimental supports for the promotion of this technology.