Stabilizing silica nanoparticles in high saline water by using ionic surfactants for wettability alteration application

Wettability alteration is one of the main methods for increasing recovery of oil-wet reservoirs. Chemical modifiers like surfactants and nanoparticles can alter the wettability of a surface from strongly oil-wet to water-wet. Small size and high surface area of nanoparticles provide these materials to permeate through micrometer-sized rock pores and to alter their surface wettability. Therefore, many studies have focused on the use of nanoparticles in enhanced oil recovery (EOR). However, instability of these particles in high saline water limits their application at practical scale. In this work, the effects of two ionic surfactants (sodium dodecyl sulfate (SDS) and N-cetyl-N,N,N-trimethyl ammonium bromide (CTAB)) on the stability of nano-silica (SiO₂) and gamma nano-alumina (γ-Al₂O₃) nanoparticles have been studied by measuring the zeta potential and the UV adsorption of some nanofluids. The effects of surfactant concentration and nanofluid salinity on the stabilizing performance of the surfactants have also been investigated. Based on surfactant head group and nanoparticle surface charges, two different mechanisms have been proposed to explain surfactant and nanoparticle adsorption behavior. Finally, the effect of stabilized silica-based nanofluids on oil-brine interfacial tension (IFT) and the wettability of a carbonate rock has been explored. According to zeta potential and contact angle measurements, SDS increased the stability of SiO₂ nanoparticles in highly concentrated electrolytes. Furthermore, it intensified the performance of nanoparticles in altering the wettability of a strongly oil-wet rock.