New insights into the synergism between silica nanoparticles and surfactants on interfacial properties: Implications for spontaneous imbibition in tight oil reservoirs

Nanofluids, a new cost-effective chemical additive for enhanced oil recovery (EOR) applications, have attracted increasing attention in the development of tight oil reservoirs. However, the underlying role of nanofluids in the EOR processes has yet to be identified. In this work, the synergistic effects between various surfactant molecules and silica NPs at oil/water, solid/liquid, or oil/water/solid three-phase system were systematically studied, and their effects on EOR in the tight sandstone reservoir were explored. Several silica-based nanofluids were prepared by dispersing silica nanoparticles (NPs) and surface-modifying chemical agents (i.e., anionic, nonionic, anion-nonionic, and amphoteric surfactants) in deionized (DI) water, and the properties of these nanofluids were further evaluated via dispersion stability, interfacial tension (IFT), wettability, spontaneous imbibition and nuclear magnetic resonance (NMR) tests at 60 degrees C. The experimental results showed that the imbibition efficiency potentials of stable nanofluids modified by different surfactants was: anionic-nonionic > anionic > nonionic > amphoteric. Micropores and mesopores contributed to majority of the imbibition recovery. The appropriate IFTs and oil contact angles for EOR potential were more than 1 mN/m and 140 degrees, respectively. Anionic-nonionic and anionic surfactant nanofluids were suggested as better fracturing additives or EOR agents for sandstone reservoirs. In addition, it was proven that the IFT reduction and wettability alteration were mainly attributed to the synergistic effects of silica NPs and surfactant micelles. This research provides new insights into the underlying mechanism between surfactant nanofluids to interfacial interactions and EOR applications.