Effect of supercritical CO2 on various rank coals: implications for CO2 sequestration in coal seams with enhanced coalbed methane recovery

Sequestration of CO2 in coal seams with enhanced coalbed methane recovery (CO2-ECBM) can mitigate CO2 emissions. In this work, the effects of the supercritical CO2 fluid on the physicochemical property of coals were elucidated. The results show that CO2 interaction can mobilise the volatile hydrocarbons in the coal matrix and subsequently result in the decrease of volatile matter content. The volatile matter contents of coals decrease with temperature, pressure and injection rate of CO2 interaction. The extracted volatile matters are of biological toxicity, thus CO2-ECBM process should be operated at the optimum temperature, pressure and CO2 injection rate. The moisture contents of Zhangji coal and Liulin coal after CO2 interaction increase which implies that the pore morphology of the above two coals grows up. For low rank Bulianta coal and high rank Qinshui coal, the swelling effect induced by CO2 is dominant. Thus, the moisture content after CO2 interaction decreases in comparison with the raw state.