Effect of the SiO₂ Nanoparticle Size on Application of Enhanced Oil Recovery in Medium-Permeability Formations

Nanoparticles (NPs) have been applied in enhanced oil recovery (EOR) successfully over the last couple of decades, due to their unique property inherited by the small size (most of the studies focused on sizes smaller than 50 nm) and abundant surface functional groups. The important mechanism of EOR using a NP-based nanofluid is the change of interfacial properties. However, the effect of the nanoparticle size on the same type of oil recovery has not been systematically studied, especially the larger size. Therefore, in this research, SiO2 NPs of different sizes, namely, similar to 60, similar to 100, similar to 200, and similar to 300 nm, were synthesized using the Sto?? 30b;ber method and the properties of the NP-based nanofluids were investigated, including interfacial tension (IFT), contact angle, viscosity, capillary pressure, and the ability to extract oil. The experimental results showed that as the SiO2 NP size decreased, there was a little increase in the IFT, oil contact angle, viscosity, and capillary pressure. With a NP concentration of 0.3 wt % in 3 wt % NaCl brine, the similar to 60 nm SiO2 NP-based nanofluid was the most efficient oil-displacing agent to recover oil from the medium-permeability core sample of Daqing Oilfield. Therefore, according to the discussion of the selective preference for SiO2 NP sizes, the developed nanofluid is a promising new material in medium-permeability reservoirs for enhanced oil recovery.