Geoscience Reference
In-Depth Information
0.018
0.1
0.016
0.08
Direct P-wave
0.014
0.06
0.012
0.04
PPr1
PPr2
0.01
0.02
0.008
0
0.006
-0.02
0.004
-0.04
0.002
-0.06
0
0.1
0.2
0.3
0.4
0.5
0.6
0
0
20
40
60
80
100
Time (s)
Frequency (Hz)
0.08
3.5
Coseismic
0.06
3
0.04
IR1 IR2
RCS1
RCS2
2.5
0.02
0
2
-0.02
1.5
-0.04
1
-0.06
-0.08
0.5
-0.1
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0
20
40
60
80
100
Time (s)
Figure 2.5
Seismogram and electrogram at an electrode (receiver
P1 in Figure 2.3). The strongest signal on the electrogram
corresponds to the coseismic disturbance associated with the
direct wave (see Figure 2.3). RCS1 and RCS2 stand for the
coseismic disturbances associated with the reflected P-waves
(see Figure 2.3). IR1 and IR2 stand for the two seismoelectric
disturbances associated with the seismoelectric conversions at
the top and bottom of the reservoir.
Frequency (Hz)
Figure 2.6
Results of the second numerical experiment
use the same geometry as in Figure 2.3. The fluid of the
reservoir is viscoelastic. The source function is a Dirac and
we investigate the electrical response in the frequency band
(1
100 Hz). The dynamic permeability versus frequency shows
the relaxation peak associated with the resonance of the
viscoelastic fluid. The peak of the vertical component of
the electrical field
E
at a remote self-potential station located
at
x
= 150 m and
y
=0m.
-
seismoelectric signals at a station P
1
(
50 m, 0 m) corre-
sponding to a single electrode. The reference for the elec-
trical potential recorded at this electrode is located at
position Ref(
−
Chapter 4. We only provide numerical results in this
section.
In Experiment #1, both seismoelectric conversion and
coseismic electrical signals are generated at the reservoir
boundaries (Figures 2.3b, 2.4, and 2.5). Figure 2.5 shows
two electrograms for station P1. The first type of signals
corresponds to the coseismic electrical signal associated
with the propagation of the P-wave. It is labeled
300 m, 0 m) (see Figure 2.3). The four
edges are absorbing boundaries for which we use PML
boundary conditions (see Jardani et al., 2010, for more
details). To solve numerically the problem, we use the
finite element modeling COMSOL Multiphysics 3.5 to
simulate both seismograms and electrograms at the
ground surface. Much more information regarding the
implementation of the partial differential equations in a
commercial finite element package will be discussed in
-
“
Coseis-
mic
in Figures 2.4a and 2.5. Other coseismic signals are
associated with the reflected P-waves at the top and
”
