EFFECT OF ELASTICITY DURING VISCOELASTIC POLYMER FLOODING A POSSIBLE MECHANISM OF INCREASING THE SWEEP EFFICIENCY

Effect of Elasticity during Viscoelastic Polymer Flooding ‑ A Possible Mechanism of Increasing the Sweep Efficiency It has been long believed that the visco‑elasticity of polymer solution improves the displacement efficiency, but the individual effect of shear viscosity and the first normal stress have not been distilled for single polymer solution. In this study, the effect of visco‑elasticity of fluids on the sweep efficiency in the polymer flood operation is investigated via injection of two polymeric fluids having identical shear thinning characteristics but very different elastic characteristic. Blends of a water‑soluble resin (Polyoxyethylene) with different molecular weight distribution (MWD) and similar average molecular weight were prepared. The Polyox blends were then used to prepare aqueous polymer solutions, which had similar shear viscosity but significantly different elastic characteristics. A series of experiments were performed by injecting two blends of polymer solutions in a special core holder designed to simulate radial flow through a sand pack ‑ saturated with mineral oil. Injection was done through perforated tubing located at the center and producing through two production tubing located at the periphery. Effect of injection rate on displacement efficiency for both polymer blends was also studied within the shear rate range of field applications. Since both fluids have the same shear viscosity but different elastic properties, it was possible to see the effect of fluid elasticity on the displacement efficiency alone at various injection rates. Experimental results indicated that sweep efficiency of a polymer based fluid could be effectively improved by adjusting the MWD of the polymer at constant shear viscosity and concentration of the polymer. The fluid with higher elasticity exhibited significantly higher resistance to flow through porous media than that of the fluid with lower elasticity resulting into higher displacement efficiency and lower residual oil saturation.