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.
Graphical Abstract
Acknowledgments
The authors thank the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University for supporting this research.