A viscoelastic model for polymer flow in reservoir rocks

In this work, steady-state flow experimental data have been analyzed for two commonly used polymers representing two generic classes: polysaccharides (xanflood), and partially hydrolyzed polyacrylamides (pusher-700) flowing inside bead packs and Berea sandstone. Oscillatory flow measurements have been used to compute the polymer solution's longest relaxation time (θ_f1). Steady-state flow experimental data for the two polymers combined with measured polymer viscous properties have been converted to average shear stress-shear rate data inside porous media. An average power-law exponent (n) is therefore obtained for the polymer flow inside the porous medium. Using θ_f1 and n, rock permeability (k) and porosity (φ) and fluid flow velocity (u), a dimensional number N_v (viscosity number) is calculated, and found to strongly correlate with the pressure gradient inside porous medium. This correlation is the basis for defining a viscoelastic model for polymer flow in porous media. The capillary-tube model is found to be adequate for only flow of viscous polymers with insignificant elasticity.