A Model for Non-Newtonian Flow in Porous Media at Different Flow Regimes

Abstract

The EOR potential of polymer flooding is well documented in the scientific literature. However, it has remained a challenge to create good simulation tools that can be used for predictive purposes. A main limitation with the current models is the insufficient description of the transition between the different flow regimes that characterize the polymer rheology. Typically, Newtonian behaviour is observed at low shear rates, followed by shear-thinning, shear-thickening and shear-degradation regimes at increasing shear rates. Furthermore this is complicated by the fact that the apparent viscosity of the polymer is influenced by a combination of factors, such as adsorption, brine salinity, polymer concentration and molecular weight. In this work we present a core scale simulation model that is capable of describing all the aforementioned flow regimes. The novel feature of the proposed model is the inclusion of an equation to describe polymer (mechanical) degradation. The polymer degradation rate is linked to the effective pore radius (via permeability through a Kozeny-Carman type equation), wall shear stress, and polymer molecular weight, Mw. The degradation results in a lower Mw, while the polymer volumetric concentration is unaffected. The change in Mw over a time step is found using an implicit chord method at the end of each transport time step, and the solution is then used to update the effective polymer properties. The main flow field is computed using a standard sequential algorithm, where a linear pressure equation is solved first, followed by an implicit saturation equation formulated in a fractional flow approach. The model is applied to a series of laboratory experiments. Our model explains the core data very well, taking into account that several experimental factors have been varied such as synthetic polymer types, core length and permeability.