Study on the key performance and stabilization mechanism of viscoelastic scCO2 foams: The formation of pseudo-gemini surfactants

Abstract

Worm-like micelles have been recognized as “living polymers,” and their outstanding physicochemical properties provide unique advantages in improving foam stability. Recently, the use of pseudo-Gemini surfactants to create worm-like micelles has garnered substantial attention because of their cost-effectiveness and high performance. However, there is a dearth of research on the key properties of scCO2 foam stabilized by pseudo-Gemini surfactants and the mechanism behind their stabilizing effect. To address this gap, a scCO2 foam system stabilized by worm-like micelles was constructed using pseudo-Gemini surfactants. Through a combination of surface properties, bulk rheology, dynamic light scattering (DLS), and cryo-scanning electron microscopy (Cryo-SEM) measurements, the synergistic effect and foam stabilization mechanism of oleic amidopropyl betaine (OAB) and alpha-olefin sulfonate sodium (AOS) were investigated. The results confirmed the formation of pseudo-Gemini surfactants in the mixed system (OAB + AOS), with superior surface activity compared with individual surfactants. Furthermore, the assembly parameter P = 0.498, determined through interfacial parameter analysis, indicated the self-assembly of worm-like micelles in the mixed system. The rheological properties of the foam liquid, as well as foam drainage, and coarsening experiments showed that the presence of worm-like micelles increased the elasticity of the liquid film, impeding the contraction and expansion of the foam. This resulted in a 145 % increase in the liquid drainage half-life of the scCO2 foam and a 19.3 % reduction in the diffusion rate of scCO2 in the liquid film. Further evidence from DLS and Cryo-SEM confirmed the formation of robust worm-like micelle structures in the OAB + AOS mixed system, enhancing the ability of the liquid film to withstand external disturbances. This study is crucial for advancing the existing understanding of pseudo-Gemini surfactants in terms of improving foam performance and designing effective small-molecule foam fracturing fluids.