Nano-scale simulation of oil-water-nanosilica-rock system: Wettability and rheological properties alteration using charged nanoparticles

Abstract

The real mechanisms beyond the effect of nanoparticles on oil phase displacement by water are still not completely understood. So, in this research, the simultaneous effects of charge and concentration of silica nanoparticles on the oil droplet detachment from calcite surface has been investigated for the first time. For this aim, the parameters of oil droplet contact angle, oil Center Of Mass, Mean Square Displacement and viscosity of water phase have been studied by using molecular dynamics simulation. The thickness of 15°A is selected for all simulations after checking the thickness effect on contact angle results. It was declared that initial shape of oil droplet affected on final contact angle slightly with the relative error of 0.7%. According to the results, silica nanoparticles can lift the oil droplet from the edges because of their interactions with rock surface and water viscosity enhancement which leads to intensify viscous forces and wettability alteration toward more water wet state. In addition, and there is an optimum concentration which decreases with nanoparticle charge rising. In neutral system, the most contact angle alteration occurs in presence of 14 nanoparticles. While the amount of optimum concentration decreased with the growth of nanoparticle's charge and reached to 4 nanoparticles at charge of 0.4 electrons. In addition, there is an optimum charge and it is 0.4e for nanoparticles. The state of rock wettability depends on nanoparticle properties such as charge, size and concentration and this lets us to design a nanoparticle with best performance and least cost.