Laboratory investigation of hybrid nanofluid – smart water flooding for enhanced oil recovery in carbonate reservoirs

Abstract

Purpose. Carbonate reservoirs account for more than half of global conventional oil reserves, yet their inherently oil-wet surfaces and complex pore architecture present persistent challenges to conventional waterflooding. This study investigates the combined application of smart water (SW) and SiO2 nanoparticles as a hybrid enhanced oil recovery (EOR) strategy to improve displacement efficiency in carbonate rock. Methods. Four injection scenarios were evaluated at reservoir temperature (85°C) with carbonate core samples: formation brine (FB), smart water (SW), SiO2 nanofluid (NF) at 0.05 wt.%, and a hybrid NF-SW formulation. Key measurements inclu-ded contact angle, interfacial tension (IFT), cumulative oil recovery, zeta potential, and colloidal stability over seven days. Findings. The hybrid NF-SW system produced the most pronounced wettability alteration (contact angle reduced from ~145 to ~28°), the lowest IFT (~4.2 mN/m), and the highest cumulative oil recovery (~74% OOIP), representing a 36-percentage-point improvement over formation brine flooding. A strong linear correlation (R2 = 0.92) was observed between contact angle and recovery factor across the four scenarios. Originality. This work presents the first systematic quantification of synergistic mechanisms between low-salinity smart water and SiO2 nanoparticles in carbonate cores, integrating electrokinetic, wettability, and IFT analyses within a single experimental framework. Practical implications. The hybrid NF-SW approach provides a technically viable and scalable EOR option for carbonate reservoirs, with implications for field-scale injection design and nanofluid formulation optimization.