Interfacial Synergistic Stabilization of CO2 Foams by Surface-Modified SiO2 Nanoparticles and Surfactants.

The CO2 channeling issue has long plagued many oilfields implementing CO2 flooding. Foam flooding serves as an important method for controlling gas channeling, and developing an efficient foam-stabilizing system for CO2 is thus of great significance. In this study, silica nanoparticles (NPs) with a diameter of 20 nm were surface-modified to produce NP3-P4 by grafting a hydrophilic group, (γ-glycidoxypropyl)trimethoxysilane, at a density of 3.0 μmol/m2 and a hydrophobic long-chain alkyl group, propyltrimethoxysilane, at a density of 0.4 μmol/m2. The resulting NP3-P4 exhibited a contact angle of 60.2° and retained excellent stability for more than 30 days in 0.25 API brine at 80 °C. When combined with AOS31, the hybrid system produced CO2 foam with a half-life extended to 24 h under harsh conditions (0.25 API brine, 80 °C, and 8 MPa), demonstrating outstanding foam stabilization. In sand-packed tube flow experiments, the composite of AOS31 and NP3-P4 achieved a resistance factor exceeding 70, indicating strong plugging performance. Furthermore, measurements of surface tension and surface dilational modulus revealed that NP3-P4 imparted high expansion elasticity to the interfacial film. Observations via confocal laser scanning microscopy (CLSM) and cryogenic scanning electron microscopy (Cryo-SEM) confirmed a pronounced synergy between NP3-P4 and AOS31. Specifically, in a CO2-saturated environment, the adsorption of betaine surfactants from AOS31 promoted the migration of NP3-P4 to the gas-liquid interface, inducing synergistic interactions and forming a thicker mixed interfacial film in the composite system. This study not only provides deep insights into the underlying stabilization mechanism but also holds considerable potential for broad foam-based applications, particularly demonstrating significant value in carbon dioxide sequestration and enhanced oil recovery (EOR).