In-situ rheology and mechanical degradation of EOR polyacrylamide solutions under moderate shear rates

A study of rheological behavior and mechanical degradation of hydrolyzed polyacrylamides (anionic) used in EOR/IOR applications under low-to-medium shear rates (γ<500s^-1) has been carried out. Aqueous polymer solutions have been injected into a core sample. Polymer degradation rate was evaluated from the flow induced viscosity loss of the polymer solution. Polymer degradation and mobility reduction were evaluated at different shear rates, salinities and concentrations. The effects of polymer viscosity, brine salinity and re-circulation of polymer effluent on degradation were investigated. The experiments revealed that polymer degradation in cores is low (<20%) and no further degradation was observed above a critical shear rate. Degradation due to re-injection of polymer effluents into the core was found to be very small (3-5%). Degradation increases with salinity and viscosity. An apparent shear thinning behavior is observed at low shear rates until a critical shear rate above which shear thickening behavior takes place.