Study on the Impact of CO2-Water-Oil-Rock Interactions on Oil Recovery and Storage in Low-Permeability Reservoirs.

The reserves of low-permeability oil reservoirs are huge, but the oil recovery with conventional development technologies is low, usually below 20%. CO2 injection into low-permeability reservoirs can enhance oil recovery (EOR) while achieving a certain amount of CO2 sequestration. However, the current study of the impact of CO2-water-oil-rock interaction induced by CO2 injection into low-permeability reservoirs on reservoir properties, EOR, and CO2 storage laws is not clear, resulting in low oil recovery and CO2 storage efficiency in low-permeability reservoirs. By conducting indoor experiments of CO2 displacement and CO2-water-oil-rock interaction in high-temperature and high-pressure reaction vessels, the impact of CO2 injection on reservoir properties, oil recovery, and CO2 storage in low-permeability oil reservoirs was clarified. The long-term reaction induced by CO2 injection into low-permeability reservoirs leads to the dissolution of dolomite and feldspar minerals in reservoirs, generating quartz mineral precipitation and improving the permeability and pore volume of reservoirs. However, the contact between CO2 and oil also leads to the precipitation of asphaltene in the crude oil, damaging the physical properties, such as the porosity and permeability of the reservoirs. Nevertheless, we found that the oil recovery of 1# and 7# core samples with repeated oil saturation increased by 2.1% and 0.8%, respectively, after the second cycle of CO2 injection. This indicates that the CO2-water-oil-rock reaction induced by CO2 injection into low-permeability reservoirs has a greater effect on improving reservoir properties than the negative impact of asphaltene precipitation and overall enhances the CO2 EOR and storage efficiency.