For any possible application of hard nanoparticles as an improved oil recovery agent, it is necessary to have a stable wettability modifier with improved mobility properties under broader oil reservoir conditions. Typical oil reservoir conditions with high temperature, pH and electrolytes concentration modifies the way that nanoparticles interact with the solution. In this work, the wettability and fluid diffusivity at the molecular level were studied through Molecular Dynamics simulation. We have studied the stability and mobility of functionalized (hydroxylated, PEG and sulfonic acid) silica nanoparticles for enhanced oil recovery applications, particularly at high salt concentration and high temperature. In order to stabilize the interfacial energy in the nanoparticle-brine interface, ions tend to modify the transport properties of the nanoparticle itself. We have observed an increasing in the diffusion coefficients for nanoparticles with increasing salt concentration at 300K and 0.1 MPa pressure. Our calculations also indicate that adsorption properties and salt solutions greatly influence the interfacial tension in an order of CaCl2 > NaCl. This effect was found to be due to the difference in distribution of ions in solution, which modifies the hydration and electrostatic potential of those ions near the nanoparticle. The brine/oil interfacial tension variation due to functionalized silica nanoparticles was also determined as a function of the terminal group hydrophobicity at 1% salt concentration (CaCl2 and NaCl), 300K and 0.1 MPa pressure.

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