Study of Viscoelastic Characteristics of Polyacrylamide Solutions in Polymer Flooding of Heterogeneous Reservoirs

This study addresses the need for enhanced oil recovery (EOR) in mature reservoirs, particularly in Russian oil fields that have undergone prolonged production and exhibit declining performance. Among EOR techniques, polymer flooding remains one of the most widely applied and effective methods following conventional waterflooding. In this work, the rheological and viscoelastic behavior of partially hydrolyzed polyacrylamide (HPAM) solutions and their impact on oil displacement efficiency in heterogeneous reservoirs were investigated. Two polymers with different molecular weights were evaluated using steady shear, oscillatory rheology, and one-dimensional core flooding experiments. The results revealed pronounced shear-thinning behavior, with viscosity increasing with polymer concentration and molecular weight. Viscoelasticity was observed only for the high-molecular-weight polymer, characterized by a well-defined linear viscoelastic region and relaxation behavior sensitive to pore size, salinity, and temperature. Core flooding experiments showed that waterflooding recovered 30–31% OOIP, while high-molecular-weight polymer injection increased recovery to ~62% OOIP. In contrast, low-molecular-weight polymer yielded only ~40% OOIP, whereas a combined injection strategy achieved up to 74–76% OOIP. These findings highlight the critical role of polymer molecular weight and viscoelasticity in improving sweep efficiency and enhancing oil recovery in heterogeneous reservoirs.