CFD modeling of the effect of polymer elasticity on residual oil saturation at the pore-scale

Polymers are used in enhanced oil recovery (EOR) to increase sweep efficiency, but recent experimental and field data suggest that viscoelastic polymers such as hydrolyzed polyacrylamide (HPAM) reduce residual oil saturation as well. The observed reduction contradicts decades of belief that polymers could not be used to reduce residual oil because the additional pressure required to overcome capillary pressure is orders of magnitude greater than provided by the more viscous polymer. However, additional forces (such as normal stress forces) may be significant for viscoelastic fluids that are ignored in analysis of purely viscous fluids.We perform computational fluid dynamics (CFDs) simulations of viscoelastic flow around static oil droplets in geometries representative of pore throats. We show that normal forces are significant for viscoelastic fluids and increase with De and the total force imposed on the droplet may be larger than an equivalent Newtonian fluid with the same viscosity. Results indicate that normal forces could dominate and the total, effective force would be enough to mobilize trapped oil.

► Viscoelastic polymers used during EOR reduce residual oil saturation.
► CFD modeling of viscoelastic fluids in pores is performed around oil droplets.
► Normal stress forces are significant for viscoelastic fluids.
► These additional forces could provide necessary force to mobilize residual oil.