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Understanding the interaction mechanisms between graphene nanoparticles (GNs) and oil molecules is crucial for successful oil recovery. Numerous studies have shown that nanofluids, and in particular nanofluids (NF) from the graphene family (GNF), are suitable candidates for enhanced oil recovery in various reservoirs. Increased oil recovery from nanofluid injection is attributed to changes in wettability, decreases in interfacial tension and changes in viscosity. Therefore, knowing the mechanisms that influence the viscosity of the GNF is an urgent task of modern science, both fundamental and applied. A comprehensive study of the molecular interaction between graphene nanoparticles and hydrocarbon oil molecules was carried out in order to understand the mechanisms that affect the viscosity of nanofluids. The paper presents the results of a study of the rheological properties of oil with different content of graphene nanoparticles in it. At low concentrations of graphene nanoparticles, a 10%-17% decrease in the dynamic viscosity of the base fluid was observed. It is also shown that the relative viscosity is affected not only by the concentration, but also by the temperature. Thus, for the mass fraction of graphene nanoparticles wt = 0.5 × 10-3% and temperature T = 50 °C, a maximum viscosity reduction of 17% is observed. By increasing the concentration of graphene nanoparticles from wt = 5 × 10-3% and more, the oil shows the rheological properties of nanofluid. Based on the data obtained by computer simulation and direct observation of self-assembly of graphene nanoparticles and hydrocarbon molecules of oil, a mechanism has been proposed to explain the reason for the decrease of viscosity of nanofluid at low concentrations of nanoparticles. It was also shown that this nanofluid behavior is mainly possible for hydrocarbon liquids as base fluid and planar graphene nanoparticles.

Graphene, due to its two-dimensional structure, has some unique properties. For example, the thermal conductivity and electrical conductivity of graphene are an order of magnitude higher than the thermal conductivity and electrical conductivity of copper. For this reason, graphene-based nanofluids are now used in many industries. Due to the effect of self-organization of graphene nanoparticles with hydrocarbon molecules, the use of graphene has become possible in the oil industry. Graphene-based nanofluids are used as a displacement fluid to increase the oil recovery coefficient. The displacing ability of graphene-based nanofluids is concentration dependent. An increase in the concentration of nanoparticles entails an increase in viscosity, which negatively affects the performance characteristics of the nanofluid. This problem is partially solved due to the synergistic effect, hybrid nanofluids consisting of nanoparticles of graphene and metals or carbides enhance the displacing ability. Using atomic force microscopy, scanning electron microscopy and molecular modelling methods, this work has studied the formation of supramolecular structures that form a transition region at the oil-nanofluid interface with low surface tension as a result of a synergistic effect in the interaction of graphene planar nanoparticles and silicon carbide nanoparticles covered with graphene layers (Core-shell). The model experiments on a Hele-Shaw cell have shown that in a porous medium, such hybrid nanofluids have a high displacement ability of residual oil. At the same time, the oil — nanofluid interface remains stable, without the formation of viscous fingers. During the study by scanning electron microscopy, a transition region was observed, in the structuring of which the nanoparticles were directly involved. The displacement efficiency of a hybrid nonofluid depends on the concentration of nanoparticles and their interaction.