Experimental Study on the Stabilization Mechanisms of CO2 Foams by Hydrophilic Silica Nanoparticles

The use of nanoparticles (NPs) for foam stabilization to enhance oil recovery has shown great promise in oil and gas development. It has been proven that NPs-based foam stabilizers achieve good foam stability. We chose four kinds of surfactants, including a cationic surfactant (CTAB), an anionic surfactant (SDBS), a nonionic surfactant (TX-100), and a zwitterionic surfactant (OA-12), to investigate the influences of hydrophilic NPs on the stability of the CO2 foam. We determined the effects of the surfactant concentration, NPs concentrations, temperature, and salinity on the stability of the CO2 foam. According to previous investigation, a better synergistic effect was assumed to generate between NPs and OA-12 because of opposite charge and shorter molecular chain. The experimental results showed a synergistic effect between the hydrophilic SiO2 NPs and the zwitterionic surfactant. When CO2 was dissolved in an aqueous solution, the solution turned acidic and the zwitterionic surfactant exhibited cationic surfactant characteristics, suggesting that different mechanisms occurred due to the different interaction between the NPs and the surfactant. An investigation of the surface characteristics demonstrated a division of labor between the NPs and the surfactants; the NPs resulted in a high elasticity modulus with the zwitterionic surfactant in aqueous solution, and the surfactant caused a low surface tension. These mechanisms resulted in the stability of the NPs-surfactant CO2 foam. The results of this research provide insights into the selection of stabilized CO2 foam and broaden its potential application in enhanced oil recovery.