Streamline-Based Simulation of Non-Newtonian Polymer Flooding

摘要

Current commercial simulators for polymer flooding often make physical assumptions that are not consistent with available experimental data and pore-scale modeling predictions. This may lead to overly optimistic recovery predictions for shear-thinning polymers, while the potential advantages of reducing flow rate or using shear-thickening agents are overlooked. We develop a streamline-based simulator that overcomes these limitations and demonstrate how it can be used to design polymer-flooding projects. The simulator implements an iterative approach to solve the pressure field because the pressure depends on the aqueous-phase viscosity, which, in turn for non-Newtonian fluids, depends on shear stress and, hence, the pressure gradients. This is in contrast to the common approach in commercial simulators where this viscosity/pressure interdependence is ignored, leading to overestimation of sweep efficiency. Furthermore, in the simulator, non-Newtonian viscosities are defined to be cell-centered while current simulators use a face-centered approach, thereby overpredicting viscosities and the stability of the displacing fronts. In addition, we use a physically based rheological model where non-Newtonian viscosities in two-phase flow are taken at actual effective stresses instead of single-phase equivalents. To validate the simulator, we construct 1D analytical solutions for waterflooding with a non-Newtonian fluid. We then compare our results to those from commercial simulators. We discuss the significance of current assumptions to demonstrate the effect of non-Newtonian behavior on sweep efficiency and recovery.