Revealing the Synergistic Effect of Chemically Modified SiO2 Nanoparticles and Surfactants in Enhancing CO2 Foam Stability

Summary Foaming is a crucial method for regulating the mobility of CO2 gas during injection, relying primarily on high-performance CO2 foaming agents. In this study, to develop a stable foaming agent suitable for conditions of 80°C and 2.5×104 mg/L salinity, we reacted SiO2 nanoparticles with (γ-glycidoxypropyl) trimethoxysilane and dimethyldimethoxysilane at doses of 3.0 µmol/m² and 2.0–2.2 µmol/m², respectively, producing stable nanoparticles (NP3020) in brine under these conditions with a water contact angle of 57°. Bulk foam and core flow experiments revealed that individual modified nanoparticles NP3020 had poor foaming performance; however, when combined with AOS31 [a mixture of α-olefin sulfonate and caprylamidopropyl betaine (CAPB) with a mass ratio of 3:1], the foam decaying half-life and apparent viscosity nearly doubled compared with AOS31 alone. Measurements of surface tension and surface dilatational modulus along with confocal laser scanning microscopy (CLSM) and cryogenic scanning electron microscopy (Cryo-SEM) analysis showed the adsorption of betaine surfactant onto negatively charged modified nanoparticles in saturated CO2 solution, increasing their water contact angle while reducing their negative charge. This resulted a mixed interface film between modified nanoparticles, α-olefin sulfonate, and CAPB at the interface, leading to synergistic foam stabilization effects.