Simulation of Oil Recovery By Polymer Flooding
Authors: Slater G.E. , Ali S.M. Farouq 
Published: March 2010

An experimental and mathematical investigation of oil recovery and sweep efficiency obtained in a two-dimensional polymer flood, for both single and two-phase (oil and water) flow, is presented. The mathematical models developed utilize the concept 'of the polymer resistance factor, and its possible variation with throughput past any given point in the flow pattern. The models were validated on the basis of good agreement observed between the predicted and the experimental results.

Experimental displacements were conducted in both homogeneous and heterogeneous two-dimensional transparent models, representing a quadrant of a five-spot pattern. Resistance factors under two-phase flow conditions were determined and it was shown that the average mobility of the displacing phase across a linear element of the porous medium used can be calculated as a function of throughput for this element. This technique was generalized for areal elements, and was incorporated in the mathematical models.

The single-phase, two-dimensional model considered a flow system in which the mobility of the displacing liquid was changing with time behind the flood front. The two-phase, two-dimensional model involved the simultaneous solution of the basic partial differential equations for two-phase flow. The model was used to simulate experimentally observed behaviour and to investigate two-phase flow in various heterogeneous patterns.

Good agreement was observed between the predicted and the experimental polymer floods. The improvement due to the use of polymer was approximately 12 to 20 per cent for oil recovery and 10 to 20 per cent for sweep efficiency.

INTRODUCTION

IN RECENT YEARS, much attention has been focused on the use of dilute solutions of partially hydrolyzed polyacrylamide polymers as waterflooding agents. These polymers lead to an improvement in the water/oil mobility ratio, by increasing the viscosity and decreasing the effective permeability to water, as a result of which both the displacement and the sweep efficiencies (areal and vertical) are improved, so that the oil recovery is higher. It has also been shown that the use of polymer solutions produces a more uniform flood front, because flow of the displacing fluid in the more permeable zones of the reservoir is retarded, and viscous fingering and bypassing of the, less permeable sections is minimized.

A number of authors have proposed methods for predicting the performance of a polymer flood. Graue(1) proposed a calculation technique applicable to a linear system composed of noncommunicating layers, similar to the method of Dykstra and Parsons(2) for waterflood performance prediction under similar conditions. Jewett and Schurz(3), and Patton and Coats(4) proposed computational methods for linear floods, adapted for a five-spot geometry through the assumption of a system of flow channels connecting the injection and production wells.

In a recent publication, Mungan(5) presented results of an extensive investigation of the rheological characteristics, temperature stability, adsorption and oil recovery efficiency of "Dow Pusher" polymer solutions having various concentrations and salt contents. Results of polymer floods in a five-spot Hele-Shaw model were also reported, showing that, unlike linear flow systems, the oil recovery showed a considerable improvement when polymer solution, rather than water, was employed.