An In-Situ Mobility-Controllable Nanofluid for Enhanced Oil Recovery in High Temperature and High Salinity Reservoirs: Experimental Study

Abstract In order to improve the EOR efficiency of water flooding in reservoirs which are high temperature and high salinity (HT/HS), a polymer-free nanofluid based on the synthesized amphiphilic nanocarbon with In-situ mobility-controllability has been developed and evaluated. Thickening water-in-oil Pickering emulsion was produced from this amphiphilic nanocarbon. The viscosity of the emulsion was exponentially increased as the water content increased up to 90%. The dispersibility, intrinsic wettability and oil/water interfacial tension (IFT) of the amphiphilic nanocarbon were investigated. The prepared amphiphilic nanocarbon was a nanoscale emulsifier, which had an excellent colloidal dispersibility in harsh brine for 90 days at 120 °C. Low IFTs facilitated the oil external phase emulsions within a wide range of water/oil proportions. The study of morphologies and droplet size distributions of the corresponding emulsion type within various water cut region was conducted. A distinctive Maltese cross pattern around the emulsion droplet edge indicated that a protective layer was produced in a spontaneous emulsification process. Then the shear-dependency of viscosities for emulsions were tested. The apparent viscosity of the emulsions regularly increased higher than that of crude as increasing of water proportion when the water/oil proportion was below 80%. Based on the static experiments, the core displacement behaviors of the emulsifier were evaluated by flooding test to identify the in-situ intelligent mobility-controllability of this amphiphilic nanocarbon. Owing to the tunable viscosity of the in-situ emulsions together with low magnitude of IFT, and the wettability modification of rock surface produced by this unique amphiphilic nanocarbon, the oil recovery factor could be enhanced about 20% to 35% by injection of the nanoscale emulsifier when the WCT of earlier water flooding exceeded 90%.