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 (~ 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 m3/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·s, 0.35 mPa·s, 0.30 mPa·s, and 0.22 mPa·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 × 104 t and 143.28 × 104 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. [ABSTRACT FROM AUTHOR]