Compositional Simulation of CO2 EOR and Storage in a Low Permeability Oil Reservoir of the Jilin Oilfield

The Daqingzijing oilfield is a special type of low-permeability oil reservoir in Jilin, characterized by poor rock properties. A CO2 miscible flooding pilot employing the reverse seven-spot well pattern was conducted in the North H79 block with a well spacing of 80 m × 240 m in July 2012. It went through three stages: energy supplementation, reaching local miscibility, and achieving overall effectiveness. By 2021, the operation had injected a cumulative amount of 32.7 × 104 t of CO2 (1.05 HCPV). The EOR performance was successful, achieving the integration of CO2 EOR and storage. Building upon the geological model of the North H79 block, a full reservoir model for integrated CO2 flooding and storage was established in an equation-of-state-based compositional stimulator. Leveraging historical production data, this work facilitated an accurate production history match for the entire region, reaching an accuracy of 90%. Subsequently, production forecasting was carried out based on the finely tuned-compositional model. Sensitivity analyses were conducted for the effects of different reservoir parameters (e.g., matrix permeability) and operational parameters (e.g., injection rate, gas-to-water ratio, etc.) on the effectiveness of CO2 flooding and storage. The main controlling factors affecting the effect of CO2 flooding and storage were analyzed and evaluated. Our study also optimized the CCUS design for this block, including an injection rate of 0.105 HCPV/a, a gas-water alternating cycle of 3 months, a gas-to-water ratio of 1:1, and a liquid production rate of 7.6 × 104 m3/a.