Geoscience Reference
In-Depth Information
0.001
NaCl (0.01-0.1 S m
-1
)
10
-3
+
0.0001
10
-4
+
Schmutz et al. (2010)
Slater and Lesmes (2002)
+
Börner (1992)
10
-5
10
-5
Revil and Skold (2011)
Koch et al. (2012)
All data corrected at 1 S m
-1
(NaCl)
10
-6
0.001
0.01
0.1
1
10
-6
10
4
1
10
100
1000
Inverse of the grain diameter (μm
-1
)
Cation exchange capacity, CEC (C kg
-1
)
Figure 1.16
Influence of the mean grain diameter upon
the quadrature conductivity of sands. Pore water conductivity in
the range 0.01
Figure 1.17
Trends for the quadrature conductivity versus CEC
for sands and clayey materials. All the experimental data are
corrected for salinity to bring them to a pore water conductivity
of 1 S m
−
1
(NaCl) using the salinity dependence of
f
the fraction
of counterions in the Stern layer. The two different trends
between the silica sands and the clayey materials are an
indication that the mobility of the counterions in the Stern layer
is much smaller for clay minerals than for silica. This plot shows
how difficult it is to extract the petrophysical properties of
formations from the quadrature conductivity alone. Indeed,
formations with very different permeabilities and lithologies can
have the same quadrature conductivity.
0.1 S m
−
1
NaCl. The measurements are from
Schmutz et al. (2010), Slater and Lesmes (2002), Börner (1992),
Revil and Skold (2011), and Koch et al. (2012). The quadrature
conductivities in this figure are reported at the relaxation peak.
-
R
sand
≈
f
1 97
We can analyze the value of
R
for sands and clays. For
sands,
β
+
Na
+
,25 C =52×
10
−
8
m
2
s
−
1
V
−
1
,
f
= 0.50 (f depends actually on pH and
salinity; see Figure 1.6), we have
R
S
+
Na
+
,25 C =
taking
β
≈
0.50. In the case
S
+
Na
+
,25 C =15×10
−
10
symmetric couplings existing between EM and seismic
disturbances in a porous material (Frenkel, 1944; Pride,
1994). The electroseismic effects correspond to the gen-
eration of seismic waves when a porous material is sub-
mitted to a harmonic electrical field or electrical current.
The seismoelectric effects correspond to the generation of
electrical (possibly EM) disturbances when a porous
material is submitted to the passage of seismic waves.
The electroseismic and seismoelectric couplings are both
controlled by the relative displacement between the
charged solid phase (with the Stern layer attached to
it) and the pore water (with its diffuse layer and conse-
quently an excess of electrical charges per unit pore
volume).
Figure 1.18 sketches the general idea underlying the
seismoelectric theory. We consider porous media in
which seismic waves propagate. The description of the
propagation of
of clay minerals,
taking
β
β
(+)
(Na
+
,25C) = 5.2 × 10
−
8
m
2
s
−
1
V
−
1
,
f
= 0.90, yields
R
= 0.0260. In both cases, the results are
consistent with the experimental results displayed in
Figures 1.13 and 1.17.
m
2
s
−
1
V
−
1
and
1.4 Principles of the seismoelectric
method
Now that the electrical double layer has been described
and the direct consequences of the existence of this elec-
trical double layer discussed, we need to introduce the
key concepts behind the seismoelectric method.
1.4.1 Main ideas
The electroseismic (electric to seismic) and seismoelectric
(seismic to electric) phenomena correspond to two
the seismic waves depends on the
