A Numerical Study on the Multiphase Newtonian and Non-Newtonian Displacement in a Porous Micromodel via Water–Surfactant–Polymer Flooding

Abstract

The multiphase displacement of Newtonian and non-Newtonian fluids in a porous media has some important applications in enhanced oil recovery (EOR) and water resources contamination. In such flows, the viscosity difference between the phases and the surface tension could destabilize the flow and cause complex patterns to occur in the interface. According to the literature, the physics of chemical flooding inside a homogeneous porous medium is not comprehensively understood. The numerical simulations are mostly restricted to the simplified volume-averaging equations for the flow inside the porous media, such as Darcy’s law and its modifications (Darcy-Brinkman, Darcy-Forchheimer, Darcy-Oldroyd, Modified-Darcy) for both cases of Newtonian and non-Newtonian fluid flows. These simplified equations might be unsuitable/inaccurate, especially in the case of non-Newtonian fluids. There are few studies in which the full nonlinear momentum equations of Newtonian and/or non-Newtonian fluids (i.e., the Navier-Stokes and Cauchy equations) are solved for the case of immiscible two-phase flows inside a pore-scale micromodel of the porous media. Here, we studied this problem for cases of both displacement of Newtonian and non-Newtonian fluids using the level-set method, which is excellent for tracking the interface between the phases. Therefore, the results of these simulations are expected to be more realistic than solving the simplified volume averaging equations. Here, the oil displacement efficiency in the micromodel is evaluated by seawater, an aqueous solution of sodium dodecyl sulfate (an anionic surfactant), and a polystyrene solution as the shear-thinning non-Newtonian fluid. The effect of displacing fluid injection rate, viscosity ratio, mobility ratio, and power-law index n of the non-Newtonian Carreau fluid model on the displacement parameters and Saffman-Taylor instability is studied in detail. The result indicates the effectiveness of shear-thinning non-Newtonian fluid within the sweeping range of the micromodel, compared to other discussed chemical factors. It was found that for the case of injected polystyrene at a flow rate of 0.5 mL/h, the breakthrough time increased to 34 s, compared to 21 s for seawater.