Numerical modeling of polymer-augmented waterflooding in heterogeneous reservoirs

Waterflooding is by far the most widely used method to increase oil recovery. All petroleum reservoirs are heterogeneous with varying degree of heterogeneity. Waterflooding could be less effective in heterogonous, channeled reservoirs as injected water moves easily through the channels leaving most oil behind in unswept regions. The reservoir fractures and high permeability channels can create expeditious breakthrough pathways from injectors to producers. Polymer-augmented waterflooding can enhance oil recovery in channel-dominated reservoirs. Polymer helps to reduce high conductivity in the channels, thus diverting injection fluid to the unswept regions of the reservoir. Proper design of polymer flood should be inclusive of the entire drainage volume of the selected well clusters in order to enhance oil recovery while minimizing water cut at the producing wells. In this study, a finite difference numerical model was formulated and implemented, using implicit pressure-explicit saturation (IMPES) and explicit calculations for polymer concentrations and adsorption effects. The implemented approach was used to study the performance of polymer-augmented waterflooding by varying relevant reservoir parameters. Both homogenous and heterogonous variations of reservoir permeability were considered with more emphasis on channeling. A Langmuir adsorption as a function of polymer concentration was used to account for the irreversible adsorption of polymer during flooding. The effect of polymer adsorption on mobility and permeability was accounted for by a viscosity adjustment and residual resistance factor formulae. With the model's help, the proper time, to switch back from polymer injection to waterflooding, was determined by analyzing the water cut profile.