Although application of nanofluids in enhanced oil recovery has been reported, the dispersibility of nanoparticles in water is one of the most difficult problems to overcome in the process of application. In this research, (3-mercaptopropyl) trimethoxysilane and sodium p-styrene sulfonate were alternatively assembled on the surface of silica nanoparticles. Fourier transform infrared spectroscopy was used to identify the surface components of functional silica nanoparticles. Transmission electron microscopy was employed for observing the shape and the size of functional silica nanoparticles. The water-based nanofluid with functional silica nanoparticles was stable at pH 9. Particle size distribution of nanofluid (with a mean diameter of 20±8 nm) was investigated by dynamic light scattering. Imbibition tests of water-based nanofluid, alkaline aqueous solution (pH value equality with the water-based nanofluid) and brine into oil presaturated ultra-low permeability sandstone cores were completed. As expected, the oil recovery of the core immersed in nanofluid was significantly higher than cores immersed in alkaline water (pH 9) and 3 wt% NaCl solution. To reveal the mechanism responsible for enhanced oil recovery, contact angle measurements were performed on the oil-wet surface before and after treatment with the nanofluid. The results showed that the wettability of the oil-wet surface changed from oil-wet to water-wet after treatment with nanofluid. The crude oil displacement from anoil-wet glass surface innanofluid was also studied. The nanofluidexhibitedan excellent capability that makesoil displace from an oil-wet surface. These results aid our understanding of the role of the nanofluid in displacing crude oil from the rock. The essential results from our experiments showed that nanoparticles can be stably dispersed in water by surface-functionalized and nanofluid have more potential in enhanced oil recovery.

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