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The results of an experimental study of the interfacial tension and surface wettability in the nanosuspension/oil/rock system are given. The effect of the concentration and size of silicon oxide nanoparticles on the coefficient of interfacial tension and the contact angle of wetting has been systematically studied for the first time. A wide range of weight concentrations of nanoparticles (from 0 to 1 wt %) and their average sizes (from 5 to 50 nm) are considered. It is established that the use of nanosuspensions makes it possible to radically change the wettability of rocks with respect to oil. In this case, this effect depends substantially on the concentration and size of nanoparticles.

The paper presents the results of systematic experimental studies of interfacial tension (IFT) and oil wettability of three different types of rock (dolomite, metabasalt, and sandstone) in nanosuspensions. Nanoparticles of silicon and aluminum oxides were used at the concentration ranged from 0.01 to 1 wt%. It is shown that with increasing NP concentration, the contact angle of an oil droplet resting on a rock in a nanosuspension increases quite essentially (from 33 to 153°). The nanoparticle size and compositional effects on interfacial tension coefficient and contact angle (CA) within a wide range of particle concentrations were systematically studied for the first time. The contact angle oil/dolomite/nanofluid increased from 92 to 151° with decrease in the SiO2 nanoparticle size 50 nm to 5 nm. With an increase in the NP size from 5 to 50 nm, there was a decrease in interfacial tension of about 30%. The first-ever experiments were conducted to study the influence of nanoparticles in water on the oil wettability of various types of hydrophilic and hydrophobic rocks. It is shown that the wettability characteristics of various types of rocks can be controlled by adding minor amounts of nanoparticles of different sizes and compositions to influence the parameters that play a key role in the problems related to oil recovery enhancement during reservoir flooding.