Experimental investigation of sophorolipids injection for enhanced oil recovery in carbonate reservoir.

Inroduction: Biosurfactants have become a topic of interest in recent years as low-cost and environmentally friendly agents. Their potential to improve oil recovery has been addressed previously, yet there are some concerns about their performance under reservoir extreme conditions. This study aims to assess Sophorolipids, an anionic biosurfactant, to enhance oil recovery in one of the Omani tight carbonate reservoirs characterized by high temperature and high salinity conditions. Methods: This was conducted by examining its effect on interfacial tension and wettability of carbonate at different concentrations, followed by core flooding experiments and ending by observing the stability of the biosurfactant at reservoir conditions. Results: Results showed that the biosurfactant solution at the determined critical micelle concentration (CMC) of 1% was able to decrease the surface tension (ST) from 65.3 ± 0.2 mN/m to 32.46 ± 0.01 mN/m, and the interfacial tension (IFT) of oil/ water from 20.45 ± 0.3 mN/m to 2.02 ± 0.22 mN/m. Similarly, the dynamic interfacial tension showed a reduction by two orders of magnitude, i.e., from 20.63 to 0.454 mN/m. Contact angle (CA) revealed that the tested solution has a good potential to modify rock wettability from oil-wet (120°) to more intermediate-wet (70.6°), which was in line with Amott test results. In addition, core flooding resulted in an additional recovery fall of 4.6 to 8.9% of the oil volume initially in place. It was found that incremental oil recovery was mainly due to wettability alteration toward intermediate wet coupled with IFT reduction. Moreover, the anionic biosurfactant exhibited good thermal stability after 6 months of aging at 70 °C, as indicated by stable surface/interfacial tension, contact angle, and recovery factors. Results of this study support the potential of this biosurfactant for EOR applications in carbonate reservoirs.