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 scCO 2 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 8 MPa, 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-scCO 2 foam fracturing fluid system, which contributes to the efficient extraction of unconventional oil and gas.