Electrolyte nanofluid performance on the oil detachment from an oil-wetted carbonate surface: Water channel formation using molecular dynamics simulation

In this research, molecular dynamics simulation is used to provide a molecular-scale insight into the working mechanisms of the silica nanoparticles in oil detachment from carbonate surface in absence and presence of ionic compounds. The oil model comprises of heptane, decane and toluene mixture. The contents of aqueous phase are variated in different cases: (I) water, (II) water and ions of Na+, Cl−, Mg2+and SO42−, (III) water and silica nanoparticles and (IV) water, silica nanoparticles and individual ions. In each simulation, an oil layer with a thickness of 15°A were placed between the calcite surface and the water phase to cut the interactions between calcite surface and oil phase and form an oil-wet surface. According to the results, in the absence of nanoparticles, the aqueous layer could not change the conformation of the oil layer. However, in presence of nanoparticles, water molecules could diffuse into the oil phase and move toward calcite surface. Contact angle measurement showed oil contact angle reaching to 112.5° and 120.5° for the systems of (III) and (IV), respectively. Radial distribution function calculation showed more nanoparticles approaching the calcite surface in the presence of ions yielding to more detachment of the oil molecules and also showed the Na+ and Cl− ions more effects than Mg2+ and SO42−. •Oil phase detachment from the calcite surface was achieved when the nanoparticles were in the aqueous phase.•In presence of silica nanoparticles a channel of water molecules was formed into the oil layer toward the calcite surface.•Cation arrangement in the EDL near the calcite surface, improved detachment process due to increasing calcite zeta potential.