A New Multiscale Computational Model for Low Salinity Alkaline Waterflooding in Clay-Bearing Sandstones

摘要

We develop a new multiscale model to compute effective properties such as relative permeabilities in low salinity EOR processes in sandstones containing reactive surfaces of kaolinite clays. The approach proposed herein considers the local nanoscale description ruled by the electro-chemistry of an aqueous electrolyte solution containing Na~+, Ca~(2+), H+ and OH~- ions lying between a crude-oil droplet and clay substrate. By considering concomitant surface complexation geochemical reactions between the ionic species in the invading water and the electrically charged kaolinite surface and oilwater interface we build-up the local electric double layer problem for the electric potential based on a generalized Poisson-Boltzmann equation with nonlinear boundary conditions ruled by the geochemical reactions. By considering the local mechanical equilibrium of the electrolyte solution and solving numerically the Poisson Boltzmann problem by finite elements we compute the disjoining pressure for a wide range of brine compositions. Moreover by invoking the Frumkin/Derjaguin wetting equation, the balance between the local disjoining and capillary pressures provides highly accurate computations of the contact angle along with its dependence on pH and salinity. Such methodology allows to compute wettability alteration of the rock surface from preferential oil to water wetness. The upscaling of this result allows to compute precisely the additional dependency of relative permeability on brine composition. Computational simulations illustrate the potential of the model proposed herein in bridging the pore-scale description, ruled by the local electro-chemistry of the thin liquid film, and the constitutive law for the relative permeabilities in low salinity alkaline waterflooding.