CFD-based representation of non-Newtonian polymer injectivity for a horizontal well with coupled formation-wellbore hydraulics

Polymers are often injected into horizontal wells during enhanced oil recovery (EOR) processes. During injection of these high-viscosity, non-Newtonian polymers, a significant pressure drop may occur along the length of the well. Accurate models for pressure drop in the well and polymer leakage into the reservoir are necessary for simulation but presently do not exist. We developed new, approximate models for pressure in horizontal wells based on Computational Fluid Dynamics (CFD) modeling of coupled well/reservoir flow. Here, the polymer is shear-thinning in the wellbore and may exhibit viscoelastic effects (such as shear-thickening behavior) in the surrounding reservoir. The CFD results are used to improve existing analytical models for simple, Newtonian flows. The closed-form model accounts for fluid, well, and reservoir properties and can easily be implemented into conventional reservoir simulators.The CFD-based model was directly implemented into the reservoir simulator UTCHEM to evaluate the effect of pressure loss in the well on sweep efficiency. Early times (less than 100 days) yielded a significant loss in oil recovery when compared to the uniform-pressure assumption for the well. However, at later times the recovery loss was negligible, suggesting a uniform-pressure well may be a reasonable assumption at these time scales, even for highly-viscous polymer fluids.

Research highlights► An inclusive pressure equation (IPE) that includes application for non-Newtonian flow in horizontal wellbores and porous media was created to determine the impact of viscous pressure drop on oil recovery. The pressure equation is based on the analytical solution presented by Marshall and Trowbridge (1974) for Newtonian flow, but empirically corrected using numerical simulations of a coupled well and reservoir. The new model uses a shear-rate dependent viscosity and a ratio of the viscosity in the well and reservoir at the interface. ► The IPE can incorporate high-velocity flow of Newtonian and non-Newtonian fluids. For non-Newtonian fluids, both shear-thinning and shear-thickening rheology can be implemented in the reservoir. ► Early time (~ 10 days) recovery loss can be significant (greater than 10%); however, the magnitude of the net recovery loss diminishes with time. Over a long time span (> 1000 days) no significant recovery loss was observed. ► Heterogeneous reservoirs result in greater axial pressure drop which results in greater recovery loss. ► Low drawdowns result in the largest percentage of recovery loss.