Low-salinity surfactant nanofluid formulations for wettability alteration of sandstone: role of the SiO 2 nanoparticle concentration and divalent cation/SO 4 2- ratio
American Chemical Society
School of Engineering
Low-salinity water injection emerges to be a cost-effective and environmentally friendly enhanced oil recovery technique. Furthermore, additives, such as the surfactant and nanoparticles in combination with low-salinity water, appear to be promising formulations for rock wettability modification and surfactant adsorption control. The detailed interaction of these novel formulations and the rock surface is, however, not well understood. Thus, an experimental study was conducted here, and results show that the anionic surfactant (AOT, 11.247 mM) augmented the effect of silica nanoparticles (1000-3000 mg/L concentration) at low-salinity conditions as effective surfactant adsorption control agents when used at appropriate divalent cation/sulfate ion ratios. Low-salinity surfactant nanofluids may thus be applied for wettability alteration of oil-bearing sandstone reservoirs for recovering residual oil. Here, we demonstrate that the ratio of divalent cations to sulfate ions (0 ≤ M 2+ /SO 4 2- ≤ 4.427) has a significant role in surfactant adsorption, irrespective of the divalent/monovalent cation ratio or the presence of nanoparticles when sulfate ions are present in the solution. We further show using USBM wettability measurements that initial water-wet Berea sandstone can be rendered more water-wet when 1000 mg/L silica nanoparticles are used in the low-salinity formulation, although a further incremental nanoparticle concentration has no significant effect on the wettability. Wettability controls the capillary pressure and relative permeability behavior and, thus, influences the rate of hydrocarbon displacement and ultimate recovery. © 2019 American Chemical Society.