Application of a Multistage Plugging System in a Fractured Reservoir of CO₂ Flooding

CO₂ flooding has been successfully used in numerous oil fields as a strategy to improve oil recovery. However, several issues, including gas channeling, profile control, CO₂ sweep efficiency, oil displacement efficiency, etc., have been revealed in the development of CO₂ flooding, particularly in a fractured reservoir. In this paper, in view of the focus issues, a novel multistage plugging system is investigated, mainly including the polymer-gel system. The static and dynamic polymer-gel system performances are comprehensively evaluated. Based on the features of a fractured reservoir, a multiscale fracture model is built, and the applicable limits of the polymer-gel system are proposed. When the fracture width is greater than 0.65 mm, the plugging effect of the polymer gel becomes worse. However, the plugging effect is clearly strengthened by the use of polymer gel, foam, and bulk particles, which also significantly improves the injection-production profile. The experimental results show that CO₂ flooding could increase the ultimate recovery by 7.67%.