Abstract

This paper presents the results of an extensive study aimed at describing the viscoelastic properties of polymer solutions for enhanced oil recovery. Using natural and artificial cores and polymer solutions with different storage factors, core floods were performed to examine the influence of viscoelasticity of polymer solutions oil flow behaviour and oil recovery.

From the experimental results, it appears that beyond a critical injection rate the viscoelasticity of polymer solutions is reflected by increasing of effective viscosity. This critical injection rate is dependent on the concentration and degree of hydrolization (HPAA), molecular weight of polymers, core permeability, salinity and temperature. Therefore the viscoelastic core flow behaviour of polymer solutions can be adjusted to specific reservoir conditions by variation and optimization of these parameters.

To describe and quantify the viscoelastic effects by means of experimental results, a model based on Maxwell-Fluid-Relation is applied. Using the proposed model, the model index E can be, determined, which represents the viscoelastic behaviour of polymer solutions in porous media. It is found that not the relaxation time, but the model index E is the parameter which should used for quantifing this viscoelastic behaviour of polymer solutions in porous media.

Introduction

The flow behaviour of polymer solutions in porous media can be explained by two distinct processes: Shear flow and Strain flow. Accordingly the effective viscosity of the solution () is composed of the individual contributions of shear - () and strain () viscosity.

(1)

As long as the molecules of the polymer are able to rotate in the volume, of the, pore while flowing through it, the molecules will not be strained and the effective viscosity is caused by shear flow alone. If the period under strain during rotationless flow is long enough, a deformation of the polymer molecules is possible under certain pore geometries. This deformation will cause an increase in strain viscosity and therefore results in an overall increase in the effective viscosity.

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