(615c) Surfactant-Induced Nanoparticle Amphiphilicity for Generation and Stabilization of Carbon Dioxide-in-Brine Foams in High Salinity at High Temperature

Whereas previous studies have examined the generation and stabilization of emulsions and foams in low salinity and low temperature with nanoparticles (NPs) with or without added surfactants, recent interest has grown in higher salinity brines and elevated temperatures relevant to subsurface oil and gas applications. Here, for the first time, we demonstrate that NPs grafted with well-defined low molecular weight ligands are colloidally stable in concentrated American Petroleum Institute (API) brine (8% NaCl + 2% CaCl₂) at temperature up to 80^oC and are interfacially active at the CO₂-brine and air-brine interface with added surfactant. These NPs form stable dispersions with various zwitterionic surfactants in API brine at ambient or at 80^oC tested for over 40 hours. The interfacial activity of NPs was tuned by either increasing the hydrophobic tail length of the added surfactants from C₁ to C₁₆ or by increasing the surfactant concentration, based on interfacial tension measurements and foam generation. Mixtures of NPs and zwitterionic solutions that formed stable dispersions in API brine were able to stabilize CO₂ in water (C/W) foams in porous media and in bulk at temperature up to 80^oC with a beadpack apparent viscosity (µ_app) up to 65 cP. The foam exhibited a well-defined foam texture and texture stability for over 20 hours, which was related to µ_app. Viscous and stable C/W foam can be used for conformance control during enhance oil recovery applications.