29 / 2025-11-18 22:17:52

Investigation of CO2-CH4 hydrate replacement using continuous CO2 injection in a dual-well injection-production mode

Natural gas hydrates; CO2-CH4 replacement; CO2 sequestration; continuous CO2 injection; dual-well injection-production

CO₂ replacement is a promising method for natural gas hydrates (NGHs) exploitation and it shares the advantages of CO₂ sequestration and energy recovery. In this work, CO₂-CH₄ hydrate replacement by continuous CO₂ injection in the dual-well injection-production mode was investigated at various CO₂ injection rates. It is found that compared to the static replacement CH₄ production and CO₂ sequestration were greatly enhanced with the increase of CO₂ injection rate, peaking at 0.210 ml/min of the CO₂ injection rate. Both CO₂ hydrate formation and CH₄ hydrate dissociation during the replacement were promoted by the continuous CO₂ seepage flow, beneficial to the nondestructive and high-efficiency exploitation of NGH. However, a massive NGH decomposition was induced and the CO₂ sequestration was reduced when increasing the CO₂ injection rate to 0.420 ml/min, which was detrimental to the stratum stability. The CO₂/CH₄ fugacity difference remains larger under continuous CO₂ injection and increases with the injection rate, providing higher driving forces for the replacement. Moreover, it is found that CO₂ seepage flow simultaneously accelerated the fast and sluggish stages with the CO₂ injection rate ranging from 0.104 to 0.210 ml/min, but the promoting effect declined at 0.420 ml/min.