Low-salinity water-alternating-CO₂ EOR

Carbon dioxide flooding is currently the most technically and economically viable enhanced oil recovery (EOR) process in carbonate and sandstone reservoirs. Low-salinity waterflood is a relatively new EOR process; and our experiments in carbonate cores show significant oil recovery improvements with low-salinity waterflood. We propose a new EOR process to improve recovery, which involves low-salinity water-alternating-CO₂/gas (LS-WACO₂ or LS-WAG) injection.To evaluate the proposed idea, three core floods and several contact angle and IFT measurements were performed. The core floods include: seawater flood, followed by low-salinity waterflood, followed by CO₂ injection, which yielded fourteen, twenty-five, and thirty-eight percent additional oil recovery by CO₂ from two carbonate and one sandstone experiments.We performed contact angle measurements on several low-permeability carbonate, medium-permeability Berea sandstone, and ultra-low permeability Three Forks mudstone core discs using different salinities brine with and without CO₂ gas. The contact angle measurements confirmed that favorable wettability alteration is achievable with the proposed EOR process. In addition, visual observations suggested that the proposed EOR process could be effective for cleaning the matrix-fracture interface in conventional and unconventional reservoirs. Interfacial tension (IFT) measurements and correlation relevant to the EOR process is also included in this study.