Research on the viscoelastic scCO2 foam systems synergistically stabilized by nonionic/zwitterionic mixed surfactants

It is generally believed that ionic/zwitterionic surfactants have strong interactions with each other. However, our experiments found that nonionic/ zwitterionic surfactants exhibit strong synergistic effects, which differs from the previous understanding. In this study, a scCO2 foam system stabilized by the synergistic action of alkyl glucoside (APG-10, nonionic surfactant) and erucamide propyl betaine (EAB, zwitterionic surfactant) was constructed. Through the measurement of drainage and coarsening characteristics, surface properties, bulk rheological properties, dynamic light scattering (DLS) and Cryo-scanning electron microscopy (SEM), the stabilizing mechanism of the synergistic action of APG-10 and EAB was revealed for the first time at the macro and micro levels. The results indicate that APG10 and EAB exhibit mixed adsorption at the interface, resulting in a denser molecular arrangement at the interface and enhancing the foaming ability. At 80℃ and 8MPa, compared to the EAB foam system, the drainage half-life of the EAB+APG-10 system increased by 276.9%, and the Ostwald ripening rate decreased by 62.4%. Rheological studies have shown that the zero shear viscosity of the EAB+APG-10 system is 6837.8 mPa·s, with an increase of 44.4% compared to the EAB system at 80℃. This is believed to be mainly due to the binding of APG-10 to the micellar structure to enhance the entanglement strength of the micelles, aiding in suppressing the expulsion and deformation of foam bubbles. Additionally, the mixed system exhibits larger G’ and E’, effectively suppressing the expansion and contraction of the liquid film. Finally, the sizes and distributions of micellar aggregates were measured by DLS and Cryo-SEM, confirming the presence of wormlike micelles and their distribution within the liquid film. The results of this work provide theoretical support for the development and application of the novel VES-scCO2 foam fracturing fluid system, which contributes to the efficient extraction of unconventional oil and gas.