Investigation of Enhanced Oil Recovery and CO₂ Sequestration in Low Permeability Reservoirs Through Carbonated Water Alternating CO₂ Injection

Low-permeability reservoirs exhibit pronounced heterogeneity, making them susceptible to gas channeling during gas flooding. Although water-alternating-gas (WAG) injection can suppress gas channeling, its overall development performance still requires further improvement. Through core displacement experiments combined with nuclear magnetic resonance scanning, the oil recovery and CO₂ storage efficiencies of water flooding, CO₂ flooding, WAG, and carbonated water-alternating-CO₂ (CWAG) flooding were compared, thereby evaluating the feasibility of CWAG for improving oil recovery and achieving CO₂ storage. Furthermore, reservoir numerical simulation was employed to analyze the effects of injection rate, water-gas ratio, and slug size on these outcomes. The results indicate that: (1) The oil recovery of 74.62% was achieved with CWAG, surpassing those of CO₂ flooding and WAG by 8.40% and 3.83%, respectively; the recoveries for macropores, mesopores, and micropores were 85.34%, 65.54%, and 44.06%, respectively. (2) The CO₂ storage efficiency of 51.02% was attained with CWAG, which is higher than that of CO₂ flooding however slightly lower than that of WAG. (3) Within the studied parameter range, an increase in injection rate led to higher cumulative injection volumes and improved oil recovery but reduced CO₂ storage efficiency; excessively high or low water-gas ratios were found to be detrimental to oil recovery, whereas a higher water-gas ratio favored CO₂ storage; reducing slug size was shown to enhance both oil recovery and CO₂ sto-rage efficiency. These findings demonstrate that CWAG can enhance oil recovery in low-permeability reservoirs while achieving CO₂ storage, rendering it a promising and viable development method.