Geoscience Reference
In-Depth Information
Step 2: Resistivity tomography module
Source at the scanning point Si
Electrical resistivity tomogram
Forward propagation of the P-waves
Simulate
resistivity
Record at the position of all of seismic sources Mi
Model covariance matrix computation
acquisition
Time reserval in reinjection of the seismic signals
Edge detection algorithm
Focus of the seismic wave in Si
Record of the electrical potential at Pi
Build the map of electrical voltages at Si
Summation of all
the maps
No
Yes
Last scanning point Si
End
Figure 6.13
Description of the two-step procedure for obtaining a high-definition electrical resistivity tomogram between two wells. We
scan all the points for a given region
ℜ
between the two wells. The density of points depends on the wavelength of the seismic
wave used to scan the formations. At each scanning point, we place a seismic source (e.g., a Ricker wavelet) and record the seismograms
at the positions of all the seismic sensors located in the wells. We then reinject the recorded seismograms in the formation in order
to focus at the position of the scanning point (time reversal). The voltage is recorded at the focusing time at a set of electrodes, Pi (the
reference of the voltage is considered to be at infinity). This voltage is reported at the focus position; a map of these voltages obtained
for a collection of scanning points generates a
“
seismoelectric image
”
usable as a physical constraint for electrical tomography (Step 2).
× (m)
× (m)
× (m)
0
200
400
0
200
400
0
200
400
0
0
0
200
200
200
400
400
400
600
600
600
800
800
800
1000
1000
1000
Figure 6.14
Seismic wave fields from a seismic source located at one of the scanning locations belonging to the scanning domain
ℜ
. The
seismic wave field spreads throughout the medium and reaches the seismic receivers located in the two wells. The corresponding
seismograms are recorded at these seismic receivers (see Figure 6.15).
