Monitoring wettability alteration by silica nanoparticles during water flooding to heavy oils in five-spot systems: A pore-level investigation

It is well known that the displacement efficiency of EOR processes is mainly affected by wettability of porous medium; however, the role of nanoparticles on wettability alteration of pores surfaces remains a topic of debate in the literature. Furthermore, a little is known about how the dispersed silica nanoparticles affect the microscopic/macroscopic recovery efficiency of heavy oils during common immiscible EOR processes such as water flooding. In this study, a series of injection experiments was performed on five-spot glass micromodel which is initially saturated with the heavy oil. Distilled water and dispersed silica nanoparticles in water (DSNW) at different values of weight percent were used as injected fluids. The macroscopic efficiency as well as fluid distribution in the pores and throats was monitored from analysis of continuously provided pictures during the experiments. Contact angles of the glass surfaces at different conditions of wettability were measured by using sessile drop method when the glass surfaces coated by heavy oil, distilled water and the solutions of DSNW. The results revealed that the silica nanoparticles caused enhancement of sweep efficiency during water flooding and this enhancement was intensified by increasing the silica nanoparticles percent in water. And also, ultimate efficiency for DSNW (0.1 wt%) flooding increased by a factor of 8.7% in comparison to distilled water flooding. This increment in oil recovery was reached to 26% by increasing silica nanoparticles weight percent from 0.1 wt% to 3 wt%. However, beyond a specific limit of nanoparticles concentration, around 3 wt%, incremental oil recovery declines to some extent. The distribution of DSNW solution during flooding tests in pores and throats showed strong water-wet condition after flooding with high concentration of nanosolution. The results of sessile drop experiments showed that coating with heavy oil, could make an oil-wet surface. While, coating with distilled water could partially alter the wettability of surface to water-wet and coating with high concentration of DSNW could make a strongly water-wet surface. The hydrophilic nature of selected silica nanoparticles, strong hydrogen bonding between silica and water and therefore increment in surface free energy are responsible for wettability alteration of the micromodel from oil-wet to water-wet. Results of this work disclose the effect of silica nanoparticles on wettability alteration of pores surfaces as well as on enhancement of microscopic/macroscopic efficiency during DSNW flooding to heavy oils.