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Coal Geology & Exploration

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.

Keywords

coalbed methane, CO2-ECBM, CO2 displacing CH4, CO2 synchronous storage, adsorption/desorption

DOI

10.12363/issn.1001-1986.22.11.0873

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