Efect of the surface charge of silica nanoparticles on oil recovery: wettability alteration of sandstone cores and imbibition experiments

Recently, inorganic nanomaterials have emerged as promising wettability modifers to improve oil recovery. Among them, silica nanoparticles (SNPs) have gained a privileged place due to their outstanding properties. Several studies have reported the efectiveness of SNPs on this particular application. However, there is an increasing interest of understanding the parameters that may play an important role on oil recovery using nanofuids. The impact of particle size, particle concentration and types of nanoparticles on oil recovery have been reported. Nevertheless, to our knowledge, the infuence of the surface charge has not been investigated. In this work, the efect of the surface charge of SNPs on oil recovery was studied. Silica nanoparticles with diferent charge profles (negative, positive and slightly negative) were synthesized and characterized using transmission electron microscopy, FT-IR, dynamic light scattering and ζ-potential. Negatively charged nanoparticles (Neg-SNPs; −33.45±2.75) were obtained by following the Stöber process. The silanol groups present on the surface of the Neg-SNPs are responsible for the negative surface charge. Positively charged nanoparticles (AP-SNPs; +42.25±1.9) and slightly negatively charged nanoparticles (MeO-PEG-SNPs; −12.20±0.42) were obtained by grafting (3-aminopropyl) triethoxysilane and methoxy polyethylene glycol (MeO-PEG2K) onto the surface of Neg-SNPs, respectively. The impact of silica materials with diferent charge profles on wettability alteration and oil displacement at diferent concentrations (100 or 200 mg/L) was evaluated by contact angle estimation and spontaneous imbibition experiments. The results demonstrated that the surface charge of SNPs transformed the wettability of the sandstone cores and impacted oil recovery in a diferent extent. While MeO-PEG-SNPs showed the best performance at a low concentration, Neg-SNPs were the most efective in changing the rock wettability and removing oil from sandstone cores at a higher concentration. Overall, our results not only allowed to identify the impact of surface charge on oil recovery but also the efect of SNPs concentration on the suitability of the treatment for enhancing the oil recovery process.