Investigation on enhanced oil recovery and CO2 storage efficiency of temperature-resistant CO2 foam flooding

Foam flooding can effectively suppress CO2 channeling, improving oil recovery and CO2 storage efficiency. However, elevated reservoir temperatures can considerably impair the effectiveness of CO2 foam. Moreover, our comprehension of the storage capacity and mechanisms involved in CO2 foam flooding remains limited. This study introduces a temperature-resistant foam system, denoted as EFS, and conducts assessments of its enhanced oil recovery (EOR) efficiency and CO2 storage ability. To begin, the polymeric surfactant (FA) was synthesized by micellar polymerization, and its temperature resistance performance was evaluated by the TGA curve, aging viscosity, and hydrodynamic size test. Following, the room- and high-temperature foaming performance of FA, foaming agent EBB, and the compound system (EBB + FA, named EF, and EBB + FA + nano-SiO2, named EFS) were compared, and the optimal foam system formula was optimized. Next, the plugging performance of EFS foam under three gas–liquid ratios and two injection rates was evaluated by core injectivity experiments. Lastly, CO2 flooding (5 MPa, 15 MPa, and 30 MPa) and CO2 foam flooding (15 MPa) were carried out to clarify the CO2 channeling law, EOR, and CO2 storage effect of CO2 foam flooding. Meanwhile, the contribution rates of different mechanisms to CO2 storage were qualitatively split. The TR-IR and 1H spectra confirm the successful synthesis of FA, whose molecular degradation temperature surpasses 230 °C and has good solution thermal stability. Upon meticulous evaluation of foam volume and half-life, the pinnacle formulation for the EFS foam system emerged as comprising 0.2 wt% EBB, 0.3 wt% FA, and 0.05 wt% nano-SiO2. Notably, the introduction of nano-SiO2 exerted a profound influence on enhancing foaming performance, particularly at elevated temperatures. In terms of plugging efficacy, the EFS foam exhibited impressive performance. Optimal results were obtained using a gas–liquid ratio of 3:1 and an injection rate of 0.4 mL/min. Supercritical CO2 flooding can slightly delay CO2 channeling, but the effect is significantly lower than near-miscible CO2 flooding. CO2 foam flooding can further increase EOR by 13.74 % based on CO2 flooding. Meanwhile, CO2 foam flooding can increase the storage rate by 3.53 % based on reducing CO2 consumption by 15.23 %. Residual storage, comprising a substantial majority at over 65 %, stands as the predominant method for CO2 storage, with oil dissolution storage following behind, which increases significantly with the remaining oil.