Geoscience Reference
In-Depth Information
Offset (m)
Offset (m)
-50
Ref
-300
-200
-100
P1
0
100
200
300
-250
-200 -150
-100
0
50
100
150
200
250
0
Explosive source
Coseismic
IR1
0.1
0.2
0.3
0.4
100
RCS1
IR2
200
RCS2
0.5
Oil-illed
porous body
(reservoir)
0.6
0.7
300
0.8
400
0.9
1
(a)
500
Offset (m)
-50
-250
-200 -150 -100
0
50
100
150
200
250
600
Electrical stations
Direct P-wave
0.1
0.2
0.3
0.4
Seismic source
(a)
PPr1
P1
O
x
(1)
z
0.5
PPr2
(4)
(2)
0.6
0.7
(5)
IR1
(3)
0.8
Reservoir
0.9
1
IR2
(b)
(b)
Figure 2.4
Electrograms and seismograms.
a)
The electrograms
show the coseismic electrical potential field associated with the
direct wave and the reflections of the P-wave (labeled RCS1 and
RCS 2) and the seismoelectric conversions with a smaller
amplitude and a flat shape (labeled IR1 and IR2).
b)
The
seismograms reconstructed by the geophones show the P-wave
direct field and the reflections of the P-waves. The reflections
PPr1 and PPr2 correspond to the reflections on the top and
bottom of the reservoir, respectively.
Figure 2.3
Sketch of the geometry used for the numerical
simulation.
a)
The depth of the oil reservoir is 250 m. Its length
and thickness are 200 and 100 m, respectively. The depth of the
source is 50 m. The observation station is P
1
.
b)
Wavepaths.
There is a signal associated with the source itself that diffuses
nearly instantaneously from the seismic source to the
observation station. We decided not to model this signal. In the
early times of the electrogram, various contributions include
the seismoelectric conversions of the P-wave reaching the top of
the reservoir (2) (labeled IR1) and the bottom of the reservoir
(3) (labeled IR2). In addition, coseismic signals are associated
with the direct wave (1) (labeled
considered as a Newtonian fluid. The ground surface cor-
responds to the top surface of the system where the nor-
mal component of the electrical field vanishes. We
consider a volumetric source located 50 m below the
ground surface generating P-waves. The reservoir is
100 m thick and its top surface is located 250 m below
the ground surface (Figure 2.3a). The time dependence
of the source
S
(
t
) is a Ricker with a dominant frequency
of 30 Hz. We consider the arrival of the seismic and
) and the reflected
waves (4) and (5) (labeled RCS1 and RCS 2).
“
coseismic
”
that are generated in response to seismic stimulation of a
simple oil reservoir geometry.
Experiment #1 corresponds to the simulation of the
seismoelectric response of an oil-filled reservoir (see
Figure 2.3) in a half-space with the nonwetting oil
