Low interfacial tension emulsion flooding under harsh reservoir conditions: the effect of phase inversion behavior on enhanced oil recovery

Abstract

Enhancing oil recovery by chemical injection in harsh reservoirs remains a challenge due to the high temperature and high salinity conditions. The current study demonstrates a compound surfactant system for forming in situ emulsion flooding under harsh reservoir conditions. The surfactant exhibited favorable oil/water interfacial tension (IFT) reducing capability which could reduce IFT to 3.9 × 10−2 mN/m. The emulsion formed by the surfactant showed a phase inversion behavior at 7:3 water/oil volume ratio (WOR). The viscosity of the emulsion significantly increased after the phase inversed from oil-in-water type to water-in-oil type. Therefore, despite the relatively weak Jamin effect resulting from the low IFT, the phase inversion behavior endowed the emulsion with a favorable mobility control capability, which had been confirmed by visual model on macro-scale and nuclear magnetic resonance (NMR) on micro-scale. According to the results of oil flooding experiments, the low IFT in situ emulsion flooding could yield incremental oil recovery of 32.25% under high temperature (96 °C) and high salinity (203795 mg/L) conditions, demonstrating great potential for enhancing oil recovery.