Geoscience Reference
In-Depth Information
1.80
400
350
300
1.20
250
200
Water
h
150
0.60
100
Ref
50
0
Permeable
membrane
0
10
20
30
40
50
Core sample
Time (min)
(a)
(b)
Figure 2.9
Simple streaming potential coupling coefficient measurement setup and experimental results.
a)
The sample is packed at
the bottom of a Plexiglas tube and is maintained in the tube by a permeable membrane with a coarse mesh (the mesh is, however,
finer than the diameter of the grains). The record of the self-potential during the flow of the electrolyte through the sample is done with
Ag/AgCl
2
electrodes (
is the reference electrode) attached to the end faces of the sample. The hydraulic heads are maintained
constant at different levels as the streaming potentials are recorded at the various levels.
b)
Example of a typical run for sample S3 (grain
size of 150
“
Ref
”
m) and a water conductivity of 10
−
3
Sm
−
1
. The filled circles correspond to the measurements of the streaming
potential at the two end faces of the sample, while the gray columns correspond to themeasurement of the hydraulic heads. From this, it
can be seen that the measured streaming potentials are proportional to the imposed hydraulic heads. The results are reproducible. This
means that there is no drift of the electrical potential of the electrodes for the duration of the experiment.
-
212
μ
of the surface conductivity. We obtain
Q
V
=4×10
5
Cm
−
3
. We check that
Q
V
controlled by the pH dependence of the zeta potential of
kaolinite. This pH dependence can be therefore predicted
from the double layer theory discussed in Chapter 1.
Q
0
V
, in the case of the Berea
sandstone (porosity 0.23, permeability 450 mD, NaCl).
This is expected because the Berea sandstone has pretty
large pores (6 to 9
m), and therefore, the double layer is
very thin with respect to the size of the pores.
μ
2.3.4 Influence of the inertial effect
The previous results will be used to predict the frequency
dependence of the streaming potential coupling coeffi-
cient in the Berea sandstone. In Figure 2.13, we compare
the prediction of our model with the recent measure-
ments of the dynamic streaming potential coupling coef-
ficient from Zhu and Toksöz (2013) (the values reported
at 1 kHz are actually the static values). Our model is able
to reproduce these data very well up to 100 kHz for five
different salinities. The decrease of the coupling coeffi-
cient at high frequency is due to the effect of the inertial
term in the Navier
2.3.3 Streaming potential dependence on pH
Because the
-potential of the surface of silicates and alu-
minosilicates is pH dependent, we expect that the seismo-
electric current generated through the seismoelectric
effect should be also pH dependent. Dukhin et al.
(2010) performed seismoelectric current measurements
at different pH for three sandstones including the Berea
sandstone. Their data, shown in Figure 2.12, is showing
a clear dependence with the pH. The Berea sandstone has
some kaolinite, and the observed pH dependence seems
ζ
-
Stokes equation.
