Geoscience Reference
In-Depth Information
Fig. 4.23
Assessment of the lithofacies REV, from
Nordahl et al. (
2005
). Comparison of porosity (
a
) and
horizontal permeability (
b
) estimated or measured from
different sources and sample volumes. The lower and
upper limits of the box indicate the 25th and the 75th
percentile while the whiskers represent the 10th and the
90th percentile. The
solid line
is the median and the
black
dots
are the outliers. The values at the REV are measured
on the bedding model at a representative scale (With the
distribution based on ten realisations) (Redrawn from
Nordahl et al.
2005
, Petrol Geoscience, v. 11
Geologi-
#
cal Society of London [2005])
Thin section
& SEM
Probe
Perm.
Core
plugs
Logging
tools
Welltests
& seismic
Sequence REV
Lithofacies REV
Lamina REV
10
-12
10
-11
10
-10
10
-9
10
-8
10
-7
10
-6
10
-5
10
-4
10
-3
10
-2
10
-1
10
0
10
1
10
2
10
3
10
4
Measurement Volume [m
3
] (log scale)
Fig. 4.24
Sketch illustrating multiple scales of REV within a geological framework and the relationship to scales of
measurement (Adapted from Nordahl and Ringrose
2008
)
measurement or model gives a representative
average of the smaller-scale natural variations
(Fig.
4.25
). At the pore-scale this volume is
typically around a few mm
3
. For heteroge-
neous rock systems the REV is of the order
of m
3
. The challenge is to find the representa-
tive volumes for the reservoir system in the
subsurface.
4.3.4 Handling Variance as a Function
of Scale
Typical practice in petroleum reservoir studies is
to assume that an average measured property for
any rock unit is valid and that small-scale
variability can be ignored. Put more simply, we
often assume that
the average log-property
