Molecular simulation study of interfacial tension reduction and oil detachment in nanochannels by Surface-modified silica nanoparticles

With the increasing worldwide energy demand, enhanced oil recovery (EOR) is becoming more critical for oil fields. Recent studies have reported various types of nanoparticles (NPs) for improving oil recovery either alone or in combination with surfactants. In this work, molecular dynamics simulations were carried out to study the mechanisms of surface-modified silica (SiO2) NPs in improving oil recovery. Interfacial tensions (IFTs) of octane (C8H18)/water systems in the presence of different NPs were calculated. Quartz nanochannels were constructed to study the effect of NPs on oil transport through nanopores in rocks. Both water-wet and oil-wet surfaces were considered. Simulation results indicate that IFT reduction depends strongly on the distribution and the interface concentration of NPs. Surface-modified NPs with both hydrophilic and hydrophobic functional groups can reduce the IFT between oil and water. However, the IFT reduction is not significant in terms of EOR application. The alkanes/water/NPs transport in confined nanochannels shows that the initial rock wettability affects the water flooding performance and the final oil recovery. The surface-modified NPs hold higher capacity in detaching oil droplets from the oil-wet mineral surface regardless of their abilities to change interfacial tension. Surface modification is crucial to improve the surface properties of SiO2 NPs. The strong interactions between NPs and oil/rock lead to oil detachment and incremental oil recovery. The ratio and distribution of the hydrophilic/hydrophobic functional groups on NPs should be carefully tuned to achieve the highest oil recovery rate.