Study on the mechanism of pseudo-interpenetrating network enhancing recyclable VES-CO2 foam system and the key performance as fracturing fluid

Responsive viscoelastic surfactant (VES) stabilized CO 2 foam fracturing fluids (VES-CO 2 foam fracturing fluids) can be recycled through external stimuli, which holds significant value in the petroleum industry. However, stability issues and unclear high-pressure performance of responsive VES-CO 2 foam fracturing fluids severely impact their application. In this study, we developed a celluouse nanofibers (CNF) enhanced VES-CO 2 foam fracturing fluid that is recyclable. The stability mechanism of the CNF-enhanced responsive VES-CO 2 foam fracturing fluid was revealed through interfacial and bulk property analyses, and its performance under high pressure was investigated. The results show that CNF can entangle with worm-like micelles to form a more complex pseudo-interpenetrating network, increasing the viscosity of the foaming liquid from 2732.16 mPa·s to 3343.37 mPa·s and extending the half-life of drainage from 3720 s to 5520 s. After foam formation, the pseudo-interpenetrating network structure encapsulates the foam film, further delaying foam coarsening and enhancing foam stability. Interfacial property analysis indicates that the addition of CNF can improve the adsorption efficiency of responsive surfactant molecules at the interface. Moreover, there is a strong hydrogen bond interaction between CNF and responsive surfactant molecules. Under the effect of hydrogen bonds, CNF can enhance the lateral interaction of molecules at the interface, thereby increasing the resistance of the liquid film to external disturbances. Performance evaluations show that, under high-pressure conditions, the incorporation of CNF reduces the proppant settling rate from 2.33 to 1.75 cm/min, and in the supercritical CO 2 (scCO 2 ) environment, the settling rate is further reduced to 0.9 cm/min, primarily due to the formation of the pseudo-interpenetrating network. The foam fracturing fluid can be recycled by introducing CO 2 /N 2 , and under laboratory conditions, after 7 cycles, there was no significant change in the performance of the foam fracturing fluid. Additionally, the average formation damage rate of the VES-CO 2 recyclable foam fracturing fluid is 10.43 %, significantly lower than the damage rate of guar gum fracturing fluid (25.54 %), demonstrating favorable applicability in unconventional reservoirs. This study provides a new approach for developing a high-performance, low-damage, low-cost, and recyclable foam fracturing fluid system.