Predicting the Impact of Non-Newtonian Rheology on Relative Permeability Using Pore-Scale Modeling

Abstract

Abstract Polymers are frequently used in waterflooding to ensure stable displacement and to control excessive water production. The viscosity of the polymer is a function of shear rate. Typically they are shear-thinning fluids whose apparent viscosity in a porous medium decreases with increasing flow rate. We use pore-scale network modeling to predict the single-and multi-phase properties of shear thinning fluids in porous media. The model uses networks that represent the disordered topology of real rocks. For single-phase flow we can accurately predict experimentally measured relationships between apparent viscosity and flow rate. We simulate two-phase primary drainage and secondary imbibition in a water-wet system, where the wetting phase (polymer in aqueous solution) is non-Newtonian (shearthinning) while the non-wetting phase (oil) remains Newtonian. We can predict the relative permeabilities for Newtonian fluids in Berea sandstone accurately. We then use the pore-scale model to predict trends in relative permeability as a function of flow rate in Berea sandstone for a non-Newtonian wetting phase. The relative permeability is defined as the ratio of the flow rate in multi-phase flow to the corresponding flow rate in single-phase flow with the same pressure gradient with the same shear-thinning fluid. The non-Newtonian phase relative permeability initially decreases with increasing pressure gradient before increasing again, while always remaining below the Newtonian values. This effect is most pronounced at low wetting phase saturation. When the wetting phase is confined to layers in the pore space, the shear rate is less than that experienced in single-phase flow when the pore is completely filled with fluid. This leads to higher effective viscosities and an apparent decrease in relative permeability.