Simulation of Polymer Flood Processes in Heterogeneous Layered Systems with Crossflow and Adsorption

Abstract

Injection of polymer solutions has been recognized as an effective means to improve oil recovery. To provide a comparative evaluation of the influence of water-soluble polymer on the flow behavior and oil recovery, numerical simulations were performed on layered reservoirs with adsorption and crossflow. A three-dimensional numerical model for fluid flow and mass transport is used to analyze the performance of the reservoir in a five-spot pattern operating under polymer flood followed by waterflood. Results are examined for different scenarios in the degree of crossflow, reservoir adsorption parameters, and permeability reduction. For different parameters of the system, the performances of polymer flooding were compared in terms of cumulative recovery and water-oil ratio (WOR) at the production well and pressure drop at the injection well. Properties of polymer and reservoir rock such as adsorption parameter, vertical permeability heterogeneity, and permeability reduction are shown to impact the predicted recovery. With increase of polymer loss due to large value of adsorption parameter, decrease in oil recovery and increase in water-oil ratio are obtained by unfavorable mobility ratio and low the sweep efficiency. Polymer flood in reservoirs with a severe permeability contrast between horizontal strata leads to lower volumetric sweep efficiency and displacement efficiency. An increase in the degree of crossflow induced by sufficient vertical permeability is responsible for the enhanced sweep of the low permeability layers, which results in increased oil recovery and decreased WOR. The permeability reduction by polymer has a limited effect on oil recovery and WOR, particularly in reservoirs with high crossflow, but considerably on injectivity impairment. In considering the application of polymer floods, a through understanding of permeability heterogeneity of layered reservoirs, retention properties of polymer solution, and accompanying changes in reservoir properties is crucial.