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.