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or likely related to these wells. Rare cases of wastewater injection have produced
seismic events, typically less than
M
5.0.
2.
Injected fluid volume, injection rate, injection pressure, and proximity to existing
faults and fractures are factors that determine the probability to create a seismic
event. High injection volumes in the absence of corresponding extractions may
increase pore pressure and in proximity to existing faults could lead to an induced
seismic event.
3.
The area of potential influence from injection wells may extend over several square
miles, and induced seismicity may continue for months to years after injection
ceases.
4.
Reducing the injection volumes, rates, and pressures has been successful in decreas-
ing rates of felt seismicity in cases where events have been induced.
5.
Evaluating the potential for induced seismicity in the location and design of injec-
tion wells is difficult because no cost-effective way to locate unmapped faults and
measure in situ stress currently exists.
g
aps
1.
Effective and economical tools are not available to accurately predict induced seis-
mic activity prior to injection.
2.
No capability exists to predict exactly how reducing volumes, pressures, and rates
can lead to reduction in seismicity after it has begun. The models discussed in
Chapter 2 are critical to developing the capacity to make such predictions.
p
roposed
a
ctions
The actions proposed by the committee to address the potential for induced seismic-
ity related to injection wells for disposal of wastewater are similar to those suggested for
geothermal energy technologies:
1.
The adoption and use of a matrix-style “best practices” protocol as outlined in
Chapter 6 in those cases where there is a known probability of inducing seismicity
at levels that could pose a concern to the public. In those cases where the need
becomes apparent only after disposal has begun, the developer should adopt the
protocol procedures needed to complete the project in a manner that protects
public safety.
2.
When a “traffic light” system is to be adopted or imposed to control operations
that could cause unacceptable levels of induced seismicity, full disclosure and
discussion of the system at a public forum is necessary prior to the start of opera-
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