Pilot test of CO2-EOR and Storage in Extra-Low-Permeability Reservoirs in the Liaohe Oilfield, Northeast China

Geological storage of carbon dioxide (CO2) is an important way to mitigate global warming, making CO2 enhanced oil recovery (CO2-EOR) and storage technology with sequestration and economic benefits a hot research topic and making positive progress in medium- to high-permeability reservoirs. However, the research on extra-low-permeability reservoirs is still poorly understand, facing the dual challenges of high cost and low efficiency. In order to clarify the potential of CO2-EOR and storage in extra-low-permeability reservoirs, this study takes the extra-low-permeability reservoir in Liaohe Oilfield, Northeast China, as an example, and integrates experimental analyzes, numerical simulations, and on-site trial injections to carry out a pilot test study of CO2-EOR and storage. The results show that the production capacity of natural energy development decreases rapidly and the recovery rate is low (similar to 7.5%); The start-up and displacement pressure gradient of water injection is high, making it impossible to achieve continuous and effective injection; Gas injection can effectively displace replacement, with a reservoir gas absorption index of 3.67 m(3)/MPa is 4-6 times the water. At 41 MPa, compared to the injection of air, nitrogen, natural gas, and CO2, the crude oil expansion was 2.7%, 2.4%, 10.7%, and 25.2%, respectively. The viscosity decreased from 0.42 to 0.35 mPa<middle dot>s, 0.35 mPa<middle dot>s, 0.30 mPa<middle dot>s, and 0.22 mPa<middle dot>s, respectively. Meanwhile, the minimum miscible replacement pressure of CO2 (31.8 MPa) is closest to the reservoir pressure (37.1-44.5 MPa), and the efficiency of oil repulsion is also the highest (79.5%). Therefore, CO2 is the optimal miscible replacement medium with high swelling and strong viscosity reduction. Accordingly, the W-128 well area was preferred for the experiment, and the injection and recovery analysis revealed that the cumulative CO2 burial and oil production were 216.44 x 10(4) t and 143.28 x 10(4) t, respectively, and the final recovery rate (40%) was 32.5% higher than that of the natural energy, demonstrating the good potential of the CO2-EOR and storage technology for large-scale application in the extra-low-permeability reservoirs. This study is expected to further expand the application of CO2 storage and provide an important scientific basis for efficient CO2-EOR in extra-low-permeability reservoirs.