Enhanced oil recovery mechanism by surfactant-silica nanoparticles imbibition in ultra-low permeability reservoirs

Due to the low permeability, small pore throat and poor pore connectivity of ultra-low permeability reservoirs, the development technology of ultra-low permeability reservoirs is different from the stimulation techniques of conventional oil reservoirs, making development more difficult. In recent years, nanoparticles have been widely used in the oil industry and have shown great potential in oil exploitation. However, the application of nanofluids in high temperature and high salinity formation is still facing great challenges. In this work, a new type of nanofluid was prepared by mixing silica nanoparticles with anionic surfactant. The nanofluids were stored at high salinity (30,000 mg/L) and high temperature (80 °C) for 3 weeks without any aggregates. The particle size and zeta potential of nanofluids with different concentrations and ratios were measured. The microscopic structure of nanofluids was characterized by transmission electron microscope (TEM). By measuring and comparing the oil–water interfacial tensions between different concentrations and ratios of nanofluids and crude oil, as well as the contact angles between high salinity simulated water (30,000 mg/L) and nanofluids, the application potential of nanofluids in oil exploitation is discussed. Compared with high salinity (30,000 mg/L) simulated water, the interfacial tension decreases by 99.98% after adding nanofluids. The contact angle increases by 20° with the addition of nanofluids comparing with single surfactant, and the rock surface changes from oil wet to water wet. The recovery of nanofluids with different concentrations and ratios was measured by spontaneous imbibition experiment. The imbibition recovery of high salinity (30,000 mg/L) simulated water was only 8.9%, and that of surfactant was 14.33%. With the addition of nanofluids, the imbibition recovery is significantly improved, up to 29%. The possible mechanism of nanofluids for enhanced oil recovery (EOR) is proposed and analyzed, which proves that nanofluids have great potential in EOR. The findings of this study can be helpful for better understanding of the flooding mechanism of nanoparticles and the mechanism of enhanced oil recovery by nanofluid imbibition.