  The study of flow of non-Newtonian fluids in porous media is very important
and serves a wide variety of practical applications in processes such as
enhanced oil recovery from underground reservoirs, filtration of polymer
solutions and soil remediation through the removal of liquid pollutants. These
fluids occur in diverse natural and synthetic forms and can be regarded as the
rule rather than the exception. They show very complex strain and time
dependent behavior and may have initial yield-stress. Their common feature is
that they do not obey the simple Newtonian relation of proportionality between
stress and rate of deformation. Non-Newtonian fluids are generally classified
into three main categories: time-independent whose strain rate solely depends
on the instantaneous stress, time-dependent whose strain rate is a function of
both magnitude and duration of the applied stress and viscoelastic which shows
partial elastic recovery on removal of the deforming stress and usually
demonstrates both time and strain dependency. In this article the key aspects
of these fluids are reviewed with particular emphasis on single-phase flow
through porous media. The four main approaches for describing the flow in
porous media are examined and assessed. These are: continuum models, bundle of
tubes models, numerical methods and pore-scale network modeling.
