Polymer formulations with binary biosurfactants and zinc oxide nanoparticles for enhanced oil recovery

Enhancing oil recovery from mature reservoirs while minimizing environmental impact remains a critical challenge for the petroleum industry. This study presents a novel nanofluid formulation that integrates zinc oxide nanoparticles (ZnO NPs) with biodegradable binary biosurfactants and xanthan gum (XG) for enhanced oil recovery (EOR). Core flooding tests at 70 °C showed that the optimized formulation (2000 ppm ZnO + 4000 ppm biosurfactant blend) achieved 95.14 % oil recovery, outperforming the base fluid (80.94 %) and brine flooding (58.34 %). The innovation lies in the synergistic interaction between ZnO nanoparticles and a biosurfactant blend of rhamnolipid (RH) and sophorolipid (SO), forming a high-performance, environmentally friendly alternative to synthetic surfactant systems. Fourier-transform infrared spectroscopy (FTIR) confirmed successful nanoparticle functionalization. Surface tension (ST) analysis revealed up to 11.19 % additional reduction with ZnO, while contact angle (CA) decreased from 43.2° to 27.3°, confirming progressive wettability alteration. Rheological analysis at 70 °C showed improved viscosity (0.8 to 1.2 mPa·s) and preserved shear-thinning behavior. Colloidal stability over 7 days was confirmed through visual observation, turbidity, dynamic light scattering (DLS), and UV–vis spectroscopy. These tests showed size distribution convergence around 150–200 nm, sustained turbidity (∼200 FNU), and spectral stabilization, indicating the formation of well-dispersed, thermodynamically stable assemblies. Zeta potential values (−27.3 mV to − 22.0 mV) confirmed good colloidal stability due to electrostatic repulsion and biosurfactant effects. SEM revealed agglomerated spherical ZnO particles with varied sizes, and EDS verified high-purity Zn and O, confirming successful synthesis for EOR use. The amphiphilic biosurfactants adsorbed onto ZnO surfaces provided electrosteric stabilization, while xanthan gum enhanced the matrix via polymer bridging. This biodegradable, low-toxicity formulation demonstrates significant EOR potential through three complementary mechanisms: interfacial tension reduction, wettability alteration, and improved mobility control via nanoparticle–polymer cross-linking. The findings support the development of sustainable nanofluid-based strategies for high-temperature reservoir applications.