Three Dimensional Numerical Simulation of Polymer Flooding in Homogeneous and Heterogeneous Systems
Authors: Zeito G.A. 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.
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Abstract
The purpose of this study is to determine the order and magnitude of waterflood pattern recoveries as affected by slug injection of viscous polymer.
The 3-dimensional simultaneous flow of oil, water and polymer solution is treated as 2-phase incompressible flow, with the oil being the nonwetting phase and water and polymer together being the wetting phase — the latter two flow miscibly with each other. The 2-phase flow takes into account effects of gravity, capillary pressure and sand heterogeneity, and appropriate finite difference analogs are solved by standard iterative ADI technique. Propagation of polymer within the wetting phase is Propagation of polymer within the wetting phase is accomplished purely by mass transport with the assumption of negligible dispersion, and is evaluated explicitly using a moving reference technique.
Results show that injection of polymer at a watered-out stage in the flood history has no effect on the 5-spot recoveries for the homogeneous cases but has a slightly favorable effect in the layered cases with thief zones. When injected earlier, however, incremental oil recoveries of 5 to 26% over the base floods are obtained at the time of oil bank production. At polymer flood termination at production. At polymer flood termination at WOR of 25:1, the homogeneous cases show slight increase in ultimate recoveries. Consequently for these cases injection of polymer only speeds up recoveries. The layered cases, on the other hand, show that ultimate recoveries were not only somewhat speeded up but also increased by about 5 to 20%. In general, it is shown that with a combination of a more unfavorable oil-water viscosity ratio and a greater permeability contrast between the communicating layers, the polymer slug acts more favorably on the 5-spot recoveries.

Introduction
The influence of injected polymer solutions on waterflood recoveries is being studied extensively in many laboratories. Much of this study is devoted to the understanding of basic flow mechanisms of polymers in porous media. Through such studies several aspects concerning the dynamic behavior of polymer solutions have been uncovered. From rheological studies it became apparent that the viscosity of polymer solutions undergo change due to change in polymer solutions undergo change due to change in flow velocities; at high rates of flow polymer solutions appear more viscous than at low rates, but at even higher rates the viscosity decreases due to shear degradation. Salinity, pH and temperature were also found to affect pH and temperature were also found to affect polymer solution viscosities. Another important polymer solution viscosities. Another important aspect is that adsorption and attendant loss of polymer was found to be greatly influenced by polymer was found to be greatly influenced by the type of fluids rock environment, which meant that polymer flooding would have to be tailored to each specific field application.