Synergistic mechanism of CO₂-soluble surfactant dissolution and foam formation under high-pressure conditions

CO₂ foam flooding is a promising enhanced oil recovery (EOR) technique for improving sweep efficiency and mitigating gas channeling in heterogeneous reservoirs and the solubility behavior of surfactants plays a critical role in determining foam formation and stability. In this study, a representative CO₂-soluble surfactant was investigated under high-pressure conditions. Solubility tests, foam performance evaluation, and interfacial tension measurements were conducted to systematically examine the effects of surfactant solubility and dissolution rate on foam volume and stability. The results showed that at 60 °C and 22 MPa, the surfactant exhibited a CO₂-phase solubility of up to 2.4 %, which decreased to approximately 1.1 % at 90 °C under the same pressure. As the pressure increased from 8 MPa to 22 MPa, the foam half-life extended from 70 min to nearly 500 min, and the foam comprehensive index increased from 1000 mL·min to over 4000 mL·min, indicating significant performance enhancement. Additionally, as the surfactant concentration increased from 0 % to 1.2 %, interfacial tension decreased substantially, and the minimum miscibility pressure (MMP) dropped from 31.4 MPa to 27.6 MPa. Further analysis revealed that the surfactant improves foam film formation and stability through a synergistic mechanism involving “dissolution–transport–precipitation–interfacial activity regulation.” These findings provide both theoretical insights and practical guidance for the design and screening of efficient surfactants in CO₂ foam flooding applications. • Reveals a cooperative foaming mechanism for CO₂-soluble surfactants: dissolution → transport → precipitation → interfacial regulation . • At 22 MPa, 60 °C, the surfactant’s solubility in the CO₂ phase reaches 2.4 %, markedly enhancing foam stability. • By increasing pressure from 8 to 22 MPa, foam half-life extends to 500 min and foam index quadruples. • The surfactant lowers the CO₂–crude oil MMP from 31.4 → 27.6 MPa, improving displacement efficiency. • Higher temperatures reduce solubility and foam stability; 60–70 °C is the optimal operating window.