Computational Modelling of Wettability in Calcite-Oil-Water Systems

Abstract

Abstract The injection of low-salinity water in oil reservoirs to improve the recovery of oil is effective in sandstones but its application in carbonates is still a matter of debate. To address the wettability of rock-brine-oil systems and the recovery of oil in a porous medium, a new integrated methodology comprising Molecular Dynamics (MD), Electrohydrodynamics (EHD) and Computational Fluid Dynamics (CFD) is developed and applied to a thin brine film on a carbonate rock that is bounded by an oil phase. Microscopic classical MD allows following the trajectories of the atoms and estimating the interaction energies and key parameters of the system. The mesoscopic EDH theory is applied to model a nanometric fluid layer through hydrodynamic equations and allows to obtain linear stability diagrams and to follow the nonlinear evolution of the system. The macroscopic CFD approach allows computing the flow of a biphasic fluid in a porous medium model designed from the images of scanning electron microscopy. The modelling allows us to improve the understanding of the physicochemical mechanisms behind the wettability of carbonate rocks and the flow of brine and oil phases. The rock wettability depends on several factors such as the balance between van der Waals, electrostatic and hydration forces. At reservoir conditions, the oil-water surface bears negative electric charges resulting from the oil polar groups located in the oil-brine interface, while the net concentration of electric charges at the rock-brine surface is positive due to the adsorption of positively charged ionic species. The van der Waals disjoining pressure is negative and that arising from hydration interactions is positive. In turn, the electrostatic disjoining pressure may be negative or positive. The rock surface tends to be more water-wet if it bears lower positive surface charge concentrations and more oil-wet otherwise. The approach of the two film surfaces is also regulated by the repulsive interactions originating from the hydration disjoining pressure. Recovery factors for more water-wet and more oil-wet systems are estimated.