Geoscience Reference
In-Depth Information
View from above
Side view
0.3
0.3
0.25
0.25
Before voltage acquisition
During voltage acquisition
After voltage acquisition
0.2
0.2
0.15
0.15
Well #9
Well #9
0.1
0.1
0.05
0.05
0
0
0
0.05
0.1
0.15
0.2
0.25
0.3
0
-0.05
-0.1
-0.15
-0.2
-0.25
X
-position (m)
Z
-position (m)
Figure 5.36
Localization of the acoustic emissions with respect to the time window shown in Figure 5.20. The events localized
far from Well #9 are probably associated with the reactivation of small cracks. Note that only a tiny fraction of the AE hits
shown in Figure 5.20 are localizable. (
See insert for color representation of the figure
.)
from the initial solution point in the matrix. The new
point solutions are generally biased in the positive
y
direction (see Figure 5.35). The result of this noise anal-
ysis demonstrates the robustness of the solution method
by showing the volumetric clustering nature of all of the
solutions in the same general area. The bias in the com-
puted noise solutions may indicate that the true solution
for the problem resides somewhere in between the initial
solution and the noise-based solutions or that more than
one closely spaced dipoles may also be a satisfactory solu-
tion to the problem. The coarse nature of the point matrix
forces solutions that are on the point matrix grid, and
therefore, this is a significant contribution to the degree
of error in the solution misfit, as well as the simple dipole
approximation assumption.
as it expands under increased internal fluid pressure. This
type of event is highly localizable because it is associated
with clear arrivals in the AE.
The AE events associated with the seal rupture along
the Hole 9 are difficult to localize for two reasons:
(i) there may be too many overlapping events to localize
them, and (2) some events likely have a tremor-type
signature which makes localization difficult. It seems,
however, that a number of events localized close to Well
#9 progress further up over time along the well in
agreement with the localization of the source current
density associated with the burst in the electrical field.
Note that the latest AE localizations occur near the top
of the injection hole at the time where the seal failure
was confirmed through the appearance of water on the
surface of the block and indicate surface breakthrough.
This shows the possibility, in the future, to perform a joint
localization of the electrical and AE data to improve the
localization of the hydromechanical disturbances.
The second point to address concerns the nature of
the coupling mechanism. We define the sensitivity
coefficient of
5.3.7 Discussion
The AE hit count data (see Figure 5.20a) indicates nom-
inally progressive increases in breakage intensity around
the times of the pressure changes. The localization of the
AE is shown in Figure 5.36. Some of the AE hits are due
to activity far from Well #9. These AE hits could be asso-
ciated with stress changes and the reactivation of existing
fractures in the block. Indeed, because the block is
unconfined, there may be numerous surface events that
would be generated by the cracking of the block surface
the voltage with respect
to the fluid
pressure changes as
C
0
=
∂
ψ
∂
5 54
p
J
=0
