Optimization and mechanistic insights into SiO2 nanoparticle–CTAB surfactant pickering emulsions for water mobility control

Pickering emulsions have gained considerable attention for water mobility control because of their high kinetic stability and resistance to coalescence under harsh reservoir conditions. Here, SiO2 nanoparticles (NPs) combined with cetyltrimethylammonium bromide (CTAB) were used to stabilize emulsions for flow diversion in dual-permeability porous media. The novelty of this work lies in integrating a Box–Behnken experimental design (BBD) with quantitative analysis to evaluate the individual and interactive effects of NPs concentration, surfactant concentration, and water-to-oil (W/O) ratio on emulsion stability and to develop a predictive correlation for the stability index (SI). The model showed excellent agreement with the experimental data (R2 = 0.9849), identifying NPs concentration as the dominant factor and revealing a significant NPs–surfactant interaction, with an optimal W/O ratio near 60/40. Thermal analysis indicated that the emulsions remained stable up to 80 °C; above this temperature, droplet size increased markedly (47 μm to 149 μm), accompanied by a decrease in stability. Rheological measurements confirmed shear-thinning behavior: viscosity increased from 30 to 57 mPa.s with increasing water fraction and decreased to 15 mPa.s at 120 °C. Micromodel flooding demonstrated effective flow diversion, increasing oil recovery from 46% (50/50) to 68% (75/25) under seawater (SW) flooding, whereas high-salinity conditions reduced recovery to approximately 27–34%.