Low-salinity enhanced oil recovery using biosurfactant-ZnO nanoparticle-xanthan gum formulations: A comparative study of rhamnolipid and sophorolipid systems

This study investigates the synergistic effects of biosurfactant-nanoparticle systems for enhanced oil recovery (EOR) through low-salinity waterflooding (LSWF), focusing on rhamnolipid (RH) and sophorolipid (SO) biosurfactants combined with zinc oxide (ZnO) nanoparticles (NPs) in 0.3 wt% NaCl brine. The research addresses key knowledge gaps concerning the integration of biodegradable surfactants and nanomaterials for sustainable and efficient EOR formulations. A comprehensive experimental program was conducted, including Fourier Transform Infrared Spectroscopy (FTIR), Field Emission Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (FESEM-EDX) imaging, zeta potential analysis, UV–visible spectroscopy, dynamic light scattering (DLS), rheology, visual stability test, contact angle, surface tension measurements, and core flooding under elevated temperature conditions (70 °C). FTIR spectra confirmed molecular interactions between ZnO nanoparticles and biosurfactants, while FESEM-EDX analyses validated particle morphology and elemental composition. Zeta potential measurements indicated high colloidal stability for Rhamnolipid-ZnO (−36.1 mV) and Sophorolipid-ZnO (−30.9 mV) systems, supporting dispersion stability and reduced nanoparticle aggregation. The rhamnolipid-ZnO formulation demonstrated enhanced stability and superior oil recovery (83 % OOIP) compared to the sophorolipid-ZnO system (76 %), while baseline water flooding yielded only 50 % recovery. Xanthan gum (0.1 wt%) further improved viscosity control and thermal resilience. The improved EOR performance is attributed to synergistic interactions between biosurfactants and ZnO nanoparticles, effective mobility control via polymer addition, and significant wettability alteration under LS conditions. This work highlights the potential of integrating environmentally benign surfactants with nanoparticles and biopolymers for advanced, field-relevant EOR strategies in LS environment.