Study on the Synergistic Stabilization Mechanism and Performance of CO₂-Responsive Viscoelastic Foam: A Leap Forward in Sustainable Fracturing Fluids

CO2 foam fracturing technology is an advantageous method for extracting unconventional resources. However, foam fracturing faces challenges, such as high costs, difficulty in handling surfactants, and potential environmental risks. To address these issues, this study combines CO2-responsive surfactants with zwitterionic surfactants to construct a reusable CO2-responsive viscoelastic foam fracturing fluid system. The mechanism of foam stabilization is revealed through the examination of interfacial characteristics, bulk properties, and microstructural features. Furthermore, the study systematically investigates the drainage kinetics of the CO2-responsive viscoelastic foam fracturing fluid under high-temperature and high-pressure conditions, uncovering its unique properties under high-pressure environments and the synergistic enhancement effects of OAB+DOAPA-CO2 (olefinic amine betaine + oleyl amide propyl dimethylamine) at high temperatures. Finally, the performance of the fracturing fluid is tested. It was found that adding DOAPA-CO2 into OAB increases the base-fluid viscosity by 491.64% and extends the drainage half-life by 281.65%. This is primarily due to the formation of pseudogemini surfactants between OAB and DOAPA-CO2, enhancing the foaming ability of the foam fracturing fluid. Additionally, the mixed wormlike micelles formed are stronger, and the network structure is denser, significantly improving foam stability. Interestingly, as pressure increases, the foam stability of this system improves, owing mainly to the swelling of the wormlike micelles; such exceptional stability under high pressure is highly beneficial during fracturing operations. Meanwhile, the activation energies (Ea) for the OAB and OAB+DOAPA-CO2 systems are 579.47 and 1009.73 J/mol, respectively, indicating that pseudogemini surfactants enhance foam thermal resistance. Performance evaluations show that the damage rate of this fracturing fluid is only 6.15%, making it reservoir-friendly. Moreover, by controlling the introduction of CO2/N2, the base fluid can switch between high- and low-viscosity modes, facilitating the recovery of the fracturing fluid. This study provides technical support for reducing costs associated with CO2 utilization (CO2 foam fracturing) and mitigating the environmental risks posed by surfactant discharge.