Investigation of Pore-Scale dispersion in Polymer Flooding

Abstract

Abstract Local displacement in polymer flooding is significantly affected by mixing taking place in the medium. Despite decades of research on mixing and dispersion, there remain questions about the amount of mixing occurring at pore-scale, especially for non Newtonian fluid. This study has investigated the local mixing experimentally as well as computationally. Tracer dispersion in Newtonian and shear-thinning fluids flowing through sand pack has been carried out experimentally using classical transmission dispersion. Transmission dispersion increases markedly with the shear thinning index of the fluid at all Peclet numbers. The normalized dispersivity difference has same order of magnitude for sand packs and increases with the shear thinning exponent a. Local mixing is also investigated by solving the Non-Newtonian Nervier-Stokes model and convection-diffusion equations in two dimensional packing of circular disks. The computational studies qualitatively support the experimental observations for the homogeneous sand pack and explain the mixing mechanism inside the pore body. In limit of very large fluid velocity local mixing tends to zero and core-scale mixing is entirely caused by variations in velocity. If the fluid flowing inside the porous medium has shear thinning properties, the velocity fluctuations are enhanced: in the zones of large permeability where the shear rates are large, the effective viscosity is low, and the velocity is higher than for Newtonian fluids. On the contrary, in the zones of low permeability where the shear rates are low and thus the viscosity high, the velocity is smaller.