Experimental Study on a Nanoemulsion for EOR in High-Temperature, High-Salinity, Low-Permeability Reservoirs and Its Performance

Nanoemulsion has significant application potential in enhancing oil recovery in low-permeability reservoirs due to its unique nanoscale size and excellent interfacial properties. In this paper, a novel nanoemulsion flooding system was prepared by a microemulsion dilution method, using nonionic surfactant fatty alcohol polyoxyethylene ether (AEO-9), zwitterionic surfactant cocoamidopropyl hydroxy sulfobetaine (CHSB), liquid paraffin, oleic acid, n-butanol, and aqueous sodium tosylate. The key performance parameters, such as droplet size, interfacial tension (IFT), and wettability, were evaluated in the laboratory, and the oil displacement performance of the nanoemulsion was assessed through an oil-washing ability experiment and a displacement experiment. The results showed that the droplet size of the nanoemulsion system was 30-50 nm. It has ultralow IFT (<1 × 10^-2 mN/m) and could change the core surface from hydrophobic to hydrophilic, maintaining emulsion stability even at a high temperature of 100 °C. Through the displacement experiment, the nanoemulsion demonstrated the characteristics of "rapid breakthrough-high-efficiency transport" (diffusion coefficient of 5.086 × 10^-4 cm²/s). Finally, an additional oil recovery of 17.71% was achieved when the nanoemulsion injection concentration was 0.30 wt % and the injection volume was 0.4 PV. The nanoemulsion system using aqueous sodium tosylate (NaOTs) as the continuous phase exhibits both high-salt tolerance and high-temperature hydrolysis resistance, making it suitable for nanoemulsion flooding in high-temperature, high-salt reservoirs. This paper aids in selecting the optimal nano-oil displacement agent for enhanced oil recovery (EOR) projects in high-temperature, high-salinity, low-permeability reservoirs and promotes the application of nanoemulsions in oil fields.