Upscaling Flow Properties - Reservoir Model Design - page 133

Fig. 4.20 The
Representative Elementary
Volume (REV) concept,
after Bear 1972

Pore

Mainly pores

The REV
A representative
average of
grains and pores

Mainly grains

Grain

Sample Volume

Fig. 4.21 The pore-scale REV illustrated for an example thin section (The whole image is assumed to be the pore-scale
REV) (Photo K. Nordahl/Statoil Statoil ASA, reproduced with permission)

#

nor treat the medium as a continuum in terms of
the physics of flow. The original concept
(Fig. 4.20 ) refers to the scale at which pore-
scale fluctuations in flow properties approach a
constant value both as a function of changing
scale and position in the porous medium, such
that a statistically valid macroscopic flow prop-
erty can be defined, as illustrated in Fig. 4.21 .
The pore-scale REV is thus an essential
assumption for all reservoir flow properties.
However, rock media have several such scales
where smaller-scale variations approach a more
constant value.

develop a multi-scale approach to the REV con-
cept. It is not at first clear how many averaging
length-scales exist in a rock medium, or indeed if
a REV can be established at the scale necessary
for reservoir flow simulation. Despite the
challenges, some degree of representativity of
estimated flow properties is necessary for flow
modelling within geological media, and a multi-
scale REV framework is required.
Several workers (e.g. Jackson et al. 2003 ;
Nordahl et al. 2005 ) have shown that an REV
can be established at the lithofacies scale - e.g. at
around a length-scale of 0.3 m for It is therefore necessary to tidal