Environmental Engineering Reference
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1.0
0.8
Tailing (attenuated transport through sample)
0.6
0.4
Leading (rapid transport through sample)
0.2
Sandstone
Fractured carbonate
Burrow-mottled limestone
0.0
0
10
20
30
40
50
Pore volumes exchanged (
V
*)
FIGURE 4
Gingras et al. (2004a,b)
determined the relative dispersivities of three types of geologi-
cal media: homogeneous sandstone, fractured limestone, and burrowed dolomitic limestone. Their
results showed that the flow paths present in burrow-associated dolomite are tortuous, and that the
interaction between the flow paths and the matrix is extensive. Results from their dispersivity
experiments support this by indicating substantial leading of tracer gas through the sample (indi-
cated). Leading is associated with permeability streaks in the rock, and tailing, which is associated
with extensive matrix/flow path interactions.
3.1 Permeability Contrast
In stratified sedimentary rocks, fluid flow dominantly occurs either parallel or
perpendicular to the layers. Assuming that each layer is homogeneous, the sys-
tem as a whole can be characterized as a homogeneous, yet anisotropic medium
(
Freeze and Cherry, 1979
). An estimate of the overall bulk permeability parallel
to stratification is obtained from a simple volume-weighted arithmetic mean of
the permeability of each layer:
X
n
k
i
d
i
d
;
K
arithmetic
¼
i¼
1
where
k
i
is the permeability of each layer,
d
i
is the individual layer thickness,
and
d
the total thickness.
For fluid flow occurring perpendicular to layered media, applying a volume-
weighted harmonic mean provides an estimate of the bulk vertical permeability:
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