Shear-thinning or shear-thickening fluid for better EOR? - A direct pore-scale study

Non-Newtonian fluids are widely applied in Enhanced Oil Recovery (EOR) techniques, and the good performances have been ascribed to the shear-thinning or shear-thickening characteristics of them. In this paper, we aim at discovering the roles of these rheological properties in non-Newtonian fluid displacement from the pore scale. A recently developed lattice Boltzmann model (LBM) for multiphase viscoplastic fluid flow [Xie et al. J Non-Newton Fluid, 2016.234: 118-128] is used. Displacements in both homogeneous and heterogeneous porous media are considered. For homogeneous cases, the performances of shear-thinning and shear-thickening fluids are almost the same when compared in favorable displacement regime; while the performance of shear-thinning fluid is poorer than that of shear-thickening fluid in unfavorable displacement regime. For heterogeneous cases, we demonstrate that the shear-thinning property does not contribute too much to the diversion effect, which clarifies the debate of understandings. Our pore-scale modeling results also indicate the significance of low viscosity ratio for diversion and EOR, which can stabilize the displacing front despite of the increased viscous resistance.