Viscoelastic flow simulations in random porous media

Abstract

Polymer liquids are used in the oil industry to improve the volumetric sweep efficiency and displacement efficiency of the oil from a reservoir. Surprisingly, it is not only the viscosity but also the elastic properties of the displacing fluid that determine the displacement efficiency. This may be caused by the ability of a viscoelastic fluid to pull oil out of dead-ends. The aim of our work is to obtain a fundamental understanding of the effect of fluid elasticity, by developing an advanced computer simulation methodology for the flow of non-Newtonian fluids through porous media.We simulate a 3D unsteady viscoelastic flow through a model porous medium using computational fluid dynamics. The primitive variables velocity, pressure and stresses are used in the formulation. The physical and rheological properties of actual polymer solutions used in polymer flooding have been incorporated, where the viscoelastic stress part is formulated using a FENE-P type of constitutive equation. The simulations are performed using a finite volume methodology with a staggered grid. The solid-fluid interfaces of the porous structure are modeled with a second ordered immersed boundary method.The porous medium is generated by placing stationary spherical particles of equal size in random positions using a Monte Carlo method. By means of 3D periodic boundary conditions we model the flow behavior for Newtonian and viscoelastic fluids through such a porous structure. The effect of porosity and different Deborah numbers (De) is studied in detail. The simulations provide insight on how flow structure and viscoelastic stresses change with increasing De number. To our surprise we observe completely different flow structures at high De through various pore configurations. The simulations provide a detailed understanding of the strong interplay between fluid rheology and flow topology in a random porous medium. This work has a significant importance for applications in oil recovery, polymer and food processing, and other industries.