Geoscience Reference
In-Depth Information
Spatial response (mV) - top array
Spatial response (mV) - back array
Time = 1807.9844 s
0.08
4
8
12
16
20
24
28
32
270
270
0.06
Hole 10
0.04
3
7
11
15
19
23
27
31
E0
190
190
0.02
CMS
DRL
0
2
6
10
14
18
22
26
30
110
110
−0.02
Hole 9
1
5
9
13
17
21
25
29
−0.04
30
30
−0.06
30
110
190
270
20
100
180
260
X
-position (mm)
Z
-position (mm)
(a)
(b)
Spatial response (mV) - top array
Spatial response (mV) - back array
Time = 1808.8594 s
0.25
4
8
12
16
20
24
28
32
270
270
0.2
Hole 10
0.15
3
7
11
15
19
23
27
31
E1
190
190
0.1
CMS
DRL
0.05
2
6
10
14
18
22
26
30
110
110
0
Hole 9
1
5
9
13
−0.05
17
21
25
29
30
30
−0.1
30
110
190
270
20
100
180
260
X
-position (mm)
Z
-position (mm)
(c)
(d)
Figure 5.18
Self-potential spatial voltage distributions for the snapshot E0 and the Event E1. Each panel is a kriged contoured
distribution of the electrical potential on the top and back panels (ordinary kriging). The black dots denote the position of the electrode
positions.
a)
and
b)
Spatial electrical potential distribution for snapshot E0 showing the spatial variations associated with the
background noise. Note the very small color bar voltage scale (+0.08 to
0.06 mV).
c)
and
d)
Voltage distribution for Event E1
showing the burst of the electrical field associated with the first hydraulic pulse taking place during constant flow injection. Note the
voltage polarities in the spatial distributions and the much larger color bar voltage scale (+0.25 to
−
−
0.1 mV). (
See insert for color
representation of the figure
.)
Figures 5.18 and 5.19 show the spatial evolution of
the electrical potential on the monitored faces of the
test block, starting with snapshot #E0 taken prior the
occurrence of Events E1 and E3. For these snapshots,
ordinary spatial kriging was performed on each face sep-
arately. It can be seen in Figure 5.17d, 4a, and 4b that the
snapshot E0 shows random spatial electrical potential
fluctuations associated with the temporal noise that can
be seen in Figure 5.17d. In these figures, channel 13 is
noisier with respect to the rest of the channels possibly
from poor contact between the electrode and the cement
block.
Event E1 in Figure 5.18c and d shows an initial voltage
distribution with a small negative potential on the top
surface of the block and a bipolar signal on the side of
the block. This voltage distribution implies that there is
a current source density possibly near Hole 9 (see posi-
tion in Figure 5.15) that is pointing mostly downward
into the block. The time series in Figure 5.17d shows
the onset of this small peak (Event E1), followed by a
quick decay and reversal of the polarity of the current
source density as indicated by Event E2 as shown in
Figures 5.17c and 5.19a and b. We consider that the
polarity reversal may be described by a sequence of
