High-Temperature-Resistant CO ₂ Foam System for Assisted Steam Flooding in Heavy Oil Recovery

The late stage of steam flooding in heavy oil reservoirs faces significant challenges, including low initial formation pressure, severe steam channeling, and substantial heat loss, which severely hampers development efficiency. To address these issues, this study investigates CO 2 and foam-assisted steam flooding for Block N of the Xinjiang Oilfield. A suitable foam system was screened through evaluations of single agents, compounding high-efficiency foaming systems, emulsification experiments, and the assessment of influencing factors. The results show that an optimized, high-temperature-resistant and efficient foaming system, composed of 0.08% APG0810 and 0.32% AOS, was developed. This system exhibits a foam expansion ratio of 5.8–6.6, withstands temperatures of 120–140 °C, and possesses both foaming and emulsifying capabilities. During propagation in porous media, foam preferentially enters the high-permeability channels. Owing to its higher viscosity compared to water or steam, foam experiences greater flow resistance, resulting in higher displacement pressure. The system effectively enhances profile control and flooding in formations with permeability below 3000 mD, increasing injection pressure by 2–3 MPa. This research refines the mechanistic understanding of CO 2 foam-assisted steam flooding.