An empirical investigation of polymer flow in porous media

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 (theta(f1)), which is referred to as the characteristic relaxation time in this paper. 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) over bar) is therefore obtained for the polymer flow inside the porous medium. Using theta(f1), (n) over bar, rock perneability (k), porosity (phi), and fluid flow velocity (u), a viscoelasticity number (N-v) is calculated and found to strongly correlate with the pressure gradient inside porous media. This correlation is the basis for defining a viscoelastic model for polymer flow, analogous to Darcy's law. The proposed model asserts a nonlinear relationship between fluid velocity and pressure gradient. It accounts for polymer elasticity and for pore geometry changes due to molecular adsorption and mechanical entrapment.