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In order to study the capacity of CO2 storage in coal bed and the displacement of methane CH4 in coal by CO2 injection, an experiment about the CO2 adsorption and coalbed methane ( CBM) replacement in coal under given pressure was carried out with coal specimens of large size (100 mm x100 mm x 200 mm) from the No. 3 coal seam, Qinshui Basin, China. Based on the experiment, the CO2 storage capacity difference between coal containing CH4 and coal without CH4 was contrastively analyzed. The experimental results demonstrate that, the storage of CO2 in the coal specimen can amount to 11. 03 L under the in-situ stress condition of the coal bed and injection pressure of 0. 5 MPa. CO2 permeability through the coal decreases with the increase of its adsorption amount during the experiment duration of 180 min. When the CO2 injection pressure increases to 1. 0 MPa from 0. 5 MPa under the same confining stresses, the CO2 storage amount in the coal increases by 93. 00%, the storage rate increases by 13. 50% and the amount of CH4 desorption increases by 18. 13%. It is found that the amount of CH4 desorption is larger than CO2 adsorption in the initial experimental stage. After that, the amount of CH4 desorption tends to be stable but far less than CO2 adsorption amount. Under the similar experimental condition, the CO2 storage capacity in coal containing CH4 is 59. 29% more than that of coal without CH4 and the storage rate in coal containing CH, increases by 12. 51% compared that in coal without CH4. [ABSTRACT FROM AUTHOR]

A new experimental equipment MCQ-II for supercritical CO2-ECBM recovery test with large size specimen was designed. The equipment can measure the specimen swelling during the supercritical CO2-ECBM recovery test. With the equipment, series of experiments for supercritical CO2 seepage and CH4 recovery with supercritical CO2 displacement were carried out. It is found that, under the conditions of 50 °C and constant volumetric stress, supercritical CO2 permeability is positively related to the infiltrating pressure, while it is negatively related to the confined volumetric stress. It turns out that supercritical CO2 permeability in the coal is higher than CO2 in general condition. The rise of volumetric stress and pore pressure will increase the supercritical CO2 adsorption. Under 48 MPa and 60 MPa volumetric stress, 10. 82 to 17. 52 and 16. 12 to 20. 40 units of carbon dioxide can be stored in per unit of coal, respectively. During the process of CH4 adsorption, CO2 adsorption and CH4 displacement by CO2, coal swelling volumetric percentage is recorded. In the experiment of CH4 displacement by supercritical CO2, more CH4 and CO2 were injected to specimen No. 1 (weakly caking coal) than specimen No. 2 (coking coal),but the replacement ratio of carbon dioxide to methane and the CO2 storage rate are almost equal, 4.01/4.16, 20.05%/20.09% Respectively. [ABSTRACT FROM AUTHOR]