Describing mechanical degradation in polymer solution using the FENE-P bead-spring-chain non-Newtonian fluid model.

Abstract

Polymer solutions are non-Newtonian fluids used in enhanced oil recovery due to their specific properties: Adding high-molecular-weight polymers to injected water significantly increases the apparent viscosity of the latter, which leads to improved sweep efficiency and allows to recover more oil from a reservoir. Under certain flow conditions, polymer molecules can undergo mechanical degradation: rupture of polymer chains under large stresses. This effect is undesirable, since the polymer solution gradually loses its important properties when it degrades. Although the impact of degradation on shear viscosity is well understood from experiments, it is not clear how degradation affects the polymer behavior in complex flows, when non-trivial geometries and time-dependent effects are involved. The first step to understanding of the role of mechanical degradation can play in complex flows is realizing how it affects different material functions,describing the polymer dynamics at various flow regimes. To do that, use of the differential tensor FENE-P Bead-Spring-Chain model of polymeric liquids, based on kinetic theory plays important role. In this model, each polymer molecule is represented by a very long linear chain consisting of identical spherical beads connected by non linear springs. Mechanical degradation i.e.rupture of polymeric chains, can therefore be described by a simultaneous change in bead number and number density of polymer molecules. For this a simple degradation scheme is considered which is gradual erosion from the ends. The material functions for FENE-P Bead-Spring-Chain model are derived and scaled plots, through which the impact of degradation on the material functions including viscosity can be studied, are made.