Experimental simulation of replacing and displacing CH4 by injecting supercritical CO2 and its geological significance

The technology for the replacement and displacement of CH4 by supercritical CO2 (Sc-CO2-ECBM) injection is still in its infancy, so experimental simulation and theoretical studies on this Sc-CO2-ECBM technology should be perfected. First, experimental simulations of the Sc-CO2-ECBM process were carried out under different temperatures, injected pressures and confining pressures. Then, the differences in replacement and displacement efficiency and the equivalent percentage of replacement and displacement time between samples were analyzed. Last, the influences of the pore network model on the difference in the replacement and displacement effects, the stage division and its difference of the replacement and displacement effects, and the project design of collaborative optimization of Sc-CO2 storage and ECBM were discussed. The results show the following: (1) The injected pressure, confining pressure and temperature were the key factors affecting the replacement and displacement efficiency. The equivalent percentage of replacement and displacement time negatively correlated with the differential pressure and temperature was positively correlated with the confining pressure, but the replacement and displacement efficiencies were the opposite. (2) The pore network model and its characteristic parameters explain that the replacement and displacement effects were more successful in the SH sample than that in the YW sample. (3) According to the gas condition at the outlet of the sample chamber, the replacement and displacement process can be divided into 3 stages. (9 Sc-CO2 was not detected, and the replacement effect was dominant (9 Sc-CO2 and CH4 were detected simultaneously, and the gas concentration was constantly changing, as the process changed from replacement to displacement (9 Sc-CO2 and CH4 were detected simultaneously, the gas concentration tended to be stable, and the displacement effect was dominant (4) The geological significance of this experimental simulation is that the Sc-CO2-ECBM process can be embodied by the optimization design of the Sc-CO2 project, ECBM project and Sc-CO2 and ECBM project. This research into experimental simulation of the Sc-CO2-ECBM process can further promote the implementation of the CO2-ECBM project in deep coal seams.