The Effectiveness of the Continuous and Cyclic Method on CO₂-ECBM

This study examines the impact of different CO2 injection methods on coalbed methane recovery. Specifically, this study investigated the effectiveness of continuously injecting CO2 versus injecting CO2 that had been soaked for two weeks. The objective was to ascertain which approach was more successful in enhancing CO2 Enhanced coalbed Methane (CO2-ECBM). The experiment involved injecting 3 MPa of CH4 into dry coal samples, allowing it to adsorb until reaching equilibrium, and then injecting 5 MPa of CO2 to recover adsorbed CH4. The continuous method recovered CH4 without detectable effluent concentration for 5 hours, but desorption efficiency was only 26% due to fast flow. On the other hand, the desorption efficiency of the cyclic method was only 12%, indicating trapped CH4. A comparison of desorption efficiency per unit of time shows the continuous method is more effective than the cyclic method. The results of this study demonstrate the continuous method is more effective for the desorption of CH4, and its efficiency can be improved by briefly soaking CO2 on coal and then reinjecting it to maximize CH4 recovery. It is advisable to limit the soaking time to prevent excessive swelling of the coal matrix, which can hinder seam flow and harm long-term gas production.