Experimental study of optimized injection schemes for enhanced gas recovery and carbon sequestration

To reduce the carbon capture costs in CO2 enhanced gas recovery (EGR) process, three types of displacing fluids, pure CO2, flue gas and gas-altering gas, were used in the conventional injection mode for experimental comparison. It was found that pure CO2 had the highest recovery efficiency and the smallest dispersion coefficient at supercritical state. The dispersion coefficients of the three displacing fluids became larger with increasing water saturation. The optimized EGR injection schemes were proposed, in which the first stage was displaced by N2 or CO2 mixtures as booster gas, while the second stage was displaced by CO2 to improve CH4 recovery and CO2 sequestration efficiency as well as to reduce CO2 capture costs. Both N2 and flue gas were found to perform well as booster gas in the gaseous state. The highest CH4 recovery efficiency of 36.05% and the highest CO2 sequestration efficiency of 21.31% were obtained for N2 as booster gas in dry rock core due to the overall improved sweep efficiency and the barricade effect of N2. Whereas, the flue gas as booster gas had better performance under supercritical conditions with the highest recovery efficiency of 36.69%. In addition, it was found that the dispersion coefficients of the optimized injection schemes became larger due to the pipeline entry/exit effects. Due to the dissolution of CO2 into connate water, the optimized scheme had the best results in CH4 recovery and CO2 sequestration with flue gas as the booster gas, improving by 20.5% and 13.5%, respectively, compared to the conventional CO2 injection scheme.