Physico-Chemical Characteristics of Polyacrylamide Solutions after Mechanical Degradation through a Porous Medium

Abstract

ABSTRACT Mechanical degradation of polymer solutions is an important problem which has to be assessed before injection into a reservoir. The main consequence is a viscosity loss due to macromolecules breakage which can strongly reduce the polymer solution effectiveness in controlling the water mobility inside the reservoir. Flow experiments have been performed by recirculating hydrolyzed polyacrylamide solutions through a small pack of sand particles. Polymer characteristics determined by viscometric and light scattering measurements have been analysed before and after injection at various flow rates. A normalized rate of degradation was defined by comparing the initial and final values of the intrinsic viscosity of solutions. The parameters investigated were: polymer concentration molecular weight, concentration and nature of electrolytes. INTRODUCTION During a polymer injection in oil field operation, the highest flow rates occur near the injection wells. This high velocity range is responsible for the mechanical degradation of polymer chains which causes an important viscosity loss. [1],[2],[3]. During flow in porous media, the deformation rate is a combination of elongational and shear terms. When flexible polymer molecules flow under such complex conditions, the elongational term induces a more or less important streching of the chains in solution. Significant streching leads to an additional viscosity but during drastic streching, chain scissions are expected and consequently a viscosity loss. The purpose of this paper is to discuss the effects of parameters such as concentration, molecular weight distribution and the presence of cations on the mechanical degradation of polyacrylamide chains through porous media. The degraded polymer solutions were characterized by intrinsic viscosity and molecular weight.