Study of Stabilization Mechanism of CO₂ Foam Flooding System Using Gas-Soluble Nonionic Surfactant and Nano-SiO₂

CO₂ flooding is essential for enhancing oil recovery in low-permeability reservoirs; however, the large viscosity contrast between CO₂ and crude oil leads to severe gas channeling and low sweep efficiency. In this study, a binary composite system was constructed with a gas-soluble nonionic surfactant (OXO1312) as the foaming core and nano-SiO₂ as the Pickering stabilizer. The solubility of the surfactants in scCO₂ was evaluated at 60 °C and 20 MPa using a variable-volume apparatus, the foam performance was assessed by the Waring Blender method, and the foam morphology was observed by optical microscopy. The nonionic surfactants exhibited markedly higher scCO₂ solubilities (>2 wt%) than the anionic surfactants (<1 wt%), following a clear carbon-chain-length window effect. OXO1312, combining high CO₂-philicity with an appropriate EO number, was selected as the optimal foaming agent. The addition of 1.5 wt% nano-SiO₂ increased the drainage half-life of the OXO1312 system by 84% through pronounced Pickering stabilization. The binary system remained stable below 50 °C under moderate salinity, whereas the half-life declined sharply above 70 °C. These findings provide a theoretical basis for the formulation design of CO₂ foam flooding systems for CCUS-EOR.