Silicon dioxide nanofluids with low-salinity brines for interfacial tension and wettability control in enhanced oil recovery

Abstract

Residual oil recovery remains limited by high interfacial tension (IFT) and unfavorable wettability. This study aimed to evaluate a hybrid silicon dioxide (SiO₂) nanofluid–low-salinity water (LSW) system designed to reduce IFT, alter wettability, and enhance core-scale recovery efficiency. Twelve standardized core plugs (n=6 sandstone, n=6 carbonate) were tested using factorial flooding experiments. Treatments included baseline brine (5000 ppm NaCl), LSW (500–2000 ppm), SiO₂-only (0.01–0.05 wt%), and hybrid SiO₂–LSW. Interfacial tension was measured via pendant drop tensiometry, wettability was assessed via sessile drop/USBM index, and recovery was measured through core flooding to 98% water cut. Nanoparticle stability was evaluated using zeta potential and particle size distribution. Statistical analysis employed two-way ANOVA, regression, and Tukey post hoc tests (p<0.05). Sandstone cores exhibited higher porosity (21.3 ± 1.8%) than carbonate (16.7 ± 2.1%) and higher baseline recovery (28.7 ± 2.8% vs. 22.5 ± 3.1% original oil in place [OOIP]). Hybrid floods reduced IFT from 27.5 to 4.6 mN/m in sandstone and from 29.8 to 5.2 mN/m in carbonate, achieving >75% reduction relative to brine. Contact angles decreased from 102° to 42° in sandstone and from 110° to 50° in carbonate, with USBM (U.S. Bureau of Mines) indices shifting from negative (oil-wet) to positive (water-wet). Incremental recovery reached 18.6% OOIP in sandstone and 14.1% in carbonate, both exceeding the 10% target. Permeability loss was minimal (<2%), with stable nanoparticle retention (<0.6 mg/g rock). Hybrid SiO₂–LSW flooding achieves field-relevant thresholds in IFT reduction, wettability alteration, and recovery efficiency, supporting scalable application in enhanced oil recovery.