Geoscience Reference
In-Depth Information
stages, before damage can occur. This type of system
would also be useful for overall well integrity monitoring,
and in the process would be able to, at a minimum, detect
and possibly localize annulus flow of fluids upward in the
well system, or the displacement of fluids by gases. In
older oil and gas wells, it may be possible to assess
the presence of microannulus and its connectivity to
protected aquifer formations. For old, reentrant oil and
gas fields, old plugged and abandoned wells may be
assessed for integrity and microannulus issues associated
with protected aquifer formations. Additionally, it may
be possible to monitor aquifer systems for potential
long-term problems by employing a continuous
aquifer monitoring based on the physical principles and
some of the measurement concepts used for these
experiments.
These results also indicate that fluid flowing in the
annulus of the well (in contact with porous media
such as concrete or natural formations) can be connected
to pore water flowing in a network of cracks. As such,
this pore water flow would produce electrical signals
similar to those observed in these experiments. This
could lead to the ability to help characterize fractured
rock systems through the movement of the fluids within
them. This opens up a new area of fractured rock
characterization through passive electrical potential
measurement and may lead to the characterization of
the fracture networks that opens up in hydraulically
fractured formations.
A number of very near-surface civil and environmen-
tal applications could also benefit from the findings
presented here. For example, injection grouting is
commonly used to fill voids in soil and rock, strengthen
weak soil, and slow water seepage, for example, in dams
and levees. One significant limitation in current practice
is the inability to track the movement of grout during
injection. Passive electrical potential measurements
could be employed to address this challenge. Further,
environmental applications involve tracking fluid flow
associated with injection and pumping gallery remedia-
tion techniques. Passive electrical potential measure-
ments could be used to check for biofouling of the
screens or ports on the relevant wells or other relevant
changes to the flow field. This can improve system effi-
ciency by detecting reduction in flow rates or changes
in the flow pattern through ports in gallery wells or
within the formation. It is also possible to apply these
techniques to water wells of a diverse variety to check
10
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Sediments and volcanic rocks
This experiment
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T
= 20-25°C
10
0
0.001
0.01
0.1
10
Electrolyte conductivity (S m
-1
)
Figure 5.37
Comparison between the coupling coefficient
inferred from the block experiment (this study) and the
experimentally measured streaming potential coupling
coefficients reported by Revil et al. (2003). The consistency
between the data indicates that the observed coupling
mechanism is likely to be electrokinetic in nature.
When the coupling process is electrokinetic in nature
(i.e., related to a relative displacement between the solid
skeleton and the pore water), the coupling coefficient
scales with the pore water conductivity (e.g., Revil
et al
.
, 2003). In the present case, the coupling coefficient
is roughly estimated to be on the order of
20 mVMPa
−
1
from the data shown in Figure 5.20b and c (typically
3
−
0.3MPa of pore fluid pressure
changes) at a pore water conductivity of 1.7 S m
−
1
.In
Figure 5.37, we plotted the data of Revil et al. (2003) with
the result of the present estimate (roughly
-
6 mV variations for 0.2
-
20 mV
MPa
−
1
). The present estimate of the coupling coefficient
matches the trend for electrokinetic data, implying that
the mechanism we observed is likely to be electrokinetic
in nature.
The results presented here have several applications. In
the oil and gas industry, the extension of these laboratory
observations to field applications can help close the
knowledge gap associated with the risks of drilling, com-
pletion, and hydraulic fracturing operations. This can be
accomplished by electrically monitoring drinking water
aquifers with an aquifer safety system designed to detect
undesirable leaks of fluids or gases in their very early
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