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Chapter 7
Addressing Induced Seismicity: Findings, Conclusions, Research, and
Proposed Actions
Induced seismic activity attributed to a range of human activities has been documented
since at least the 1920s. However, recent induced seismic events related to energy technology
development projects that involve fluid injection or withdrawal in the United States have drawn
heightened public attention. Although none of these events resulted in loss of life or significant
damage, their effects were felt by local residents. These induced seismic events, though usually
small in scale, can be disturbing for the public and raise concern about additional seismic activity
and its consequences in areas where energy development is ongoing or planned. The findings,
gaps, proposed actions, and research recommendations outlined in this chapter, based upon
material presented earlier in the report, address:
the types and causes of induced seismicity;
issues specific to each energy technology addressed in the study (geothermal
energy, conventional and unconventional oil and gas production, injection wells
for disposal of waste water associated with energy development, and carbon
capture and storage [CCS]);
oversight, monitoring, and coordination of underground injection activities to help
avoid felt induced seismicity;
hazards and risk assessment; and
best practices.
Although credible and viable research into possible induced seismic events has been
conducted to date by industry, the academic community, and the federal government, further
research is required because of the potential controversies surrounding such events. The
Department of Energy, the U.S. Geological Survey, and the National Science Foundation are
important organizations both for conducting and supporting this kind of research and research
partnerships with industry and academia. In addition to proposed actions to address induced
seismicity, research recommendations are specifically highlighted in Box 7.1; some of these
recommendations are specific to individual energy technologies, but most can be conducted with
a purpose to understand induced seismicity more broadly.
151
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ADDRESSING INDUCED SEISMICITY 152
TYPES AND CAUSES OF INDUCED SEISMICITY
Findings
1. The basic mechanisms that can induce seismicity related to energy-related injection and
extraction activities are not mysterious and are presently well understood.
2. Only a very small fraction of injection and extraction activities among the hundreds of
thousands of energy development wells in the United States have induced seismicity at levels
that are noticeable to the public.
3. Current models employed to understand the predictability of the size and location of
earthquakes through time in response to net fluid injection or withdrawal require calibration from
data from field observations. The success of these models is compromised in large part due to the
lack of basic data at most locations on the interactions among rock, faults, and fluid as a complex
system.
4. Increase of pore pressure above ambient value due to injection of fluids and decrease in pore
pressure below ambient value due to extraction of fluids has the potential to produce seismic
events. For such activities to cause these events, a certain combination of conditions has to exist
simultaneously:
a. significant change in net pore pressure in a reservoir;
b. a pre-existing, near-critical state of stress along a fracture or fault that is
determined by crustal stresses and the fracture or fault orientation; and
c. fault-rock properties supportive of brittle failure.
5. Independent capability exists for geomechanical modeling of pore pressure, temperature, and
rock stress changes induced by injection and extraction and for modeling of earthquake
sequences given knowledge of stress changes, pore-pressure changes, and fault characteristics.
6. The range of scales over which significant responses arise in the Earth with respect to induced
seismic events is very wide and challenges the ability of models to simulate and eventually
predict observations from the field.
Gaps
1. The basic data on fault locations and properties, in situ stresses, pore pressures, and rock
properties are insufficient to implement existing models with accuracy on a site-specific basis.
2. Current predictive models cannot properly quantify or estimate the seismic efficiency and
mode of failure; geomechanical deformation can be modeled but a challenge exists to relate this
to number and size of seismic events.
Proposed Actions
The actions proposed to advance understanding of the types and causes of induced
seismicity involve research recommendations outlined in Box 7.1. These recommendations also
have relevance for specific energy technologies and address gaps in understanding induced
seismicity.
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153 INDUCED SEISMICITY POTENTIAL IN ENERGY TECHNOLOGIES
Box 7.1
Research Recommendations
Data Collection—Field and Laboratory
1. Collect, categorize, and evaluate data on potential induced seismic events in the field. High-quality
seismic data are central to this effort. Research should identify the key types of data to be collected and
data collection protocol.
2. Conduct research to establish the means of making in situ stress measurements non-destructively.
3. Conduct additional field research on microseisms in natural fracture systems including field-scale
observations of the very small events and their native fractures.
4. Conduct focused research on the effect of temperature variations on stressed jointed rock systems.
Although of immediate relevance to geothermal energy projects, the results would benefit understanding
of induced seismicity in other energy technologies.
5. Conduct research that might clarify the in situ links among injection rate, pressure, and event size.
Instrumentation
1. Conduct research to address the gaps in current knowledge and availability of instrumentation: Such
research would allow the geothermal industry, for example, to develop this domestic renewable source
more effectively for electricity generation.
Hazard and Risk Assessment
1. Direct research to develop steps for hazard and risk assessment for single energy development
projects (as described in Chapter 5, Table 5.2).
Modeling
1. Identify ways in which simulation models can be scaled appropriately to make the required predictions
of the field observations reported.
2. Conduct focused research to advance development of linked geomechanical and earthquake
simulation models that could be utilized to better understand potential induced seismicity and relate this to
number and size of seismic events.
3. Use currently available and new geomechanical and earthquake simulation models to identify the most
critical geological characteristics, fluid injection or withdrawal parameters, and rock and fault properties
controlling induced seismicity.
4. Develop simulation capabilities that integrate existing reservoir modeling capabilities with earthquake
simulation modeling for hazard and risk assessment. These models can be refined on a probabilistic
basis as more data and observations are gathered and analyzed.
5. Continue to develop capabilities with coupled reservoir fluid flow and geomechanical simulation codes
to understand the processes underlying the occurrence of seismicity after geothermal wells have been
shut in; the results may also contribute to understanding post-shut in seismicity in relation to other energy
technologies.
Research Specific to CCS with Potential to Understand Induced Seismicity Broadly
1. Use some of the many active fields where CO2 flooding for EOR is conducted to understand more
about the apparent lack of felt induced seismic events in these fields; because CO2 is compressible in the
gaseous phase are other factors beyond pore pressure important to understand in terms of CO2
sequestration?
2. Develop models to estimate the potential earthquake magnitude that could be induced by large-scale
CCS.
3. Develop detailed physicochemical and fluid mechanical models for injection of supercritical CO2 into
potential storage aquifers.
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ADDRESSING INDUCED SEISMICITY 154
ENERGY TECHNOLOGIES: HOW THEY WORK
Overarching Findings for All Technologies
1. Injection pressures and net fluid volumes in energy technologies, such as geothermal energy
and oil and gas production, are generally controlled to avoid increasing pore pressure in the
reservoir above the initial reservoir pore pressure. These technologies thus appear less
problematic in terms of inducing felt seismic events than technologies that result in a significant
net increase or decrease in net fluid volume.
2. The basic data needed to fully evaluate the potential for induced seismicity – including fault
locations and properties, in situ stresses, fluid pressures, and rock properties – are very difficult
and expensive to obtain.
3. Existing regional seismic arrays may not be capable of precisely locating small induced
seismic events to determine causality and better establish the characteristics of induced
seismicity.
4. Temporary local seismic arrays can be installed to find faults, determine source mechanisms,
decrease error in location of seismic events, and increase resolution of future events.
Gap
Simple geometric considerations to help visualize subsurface problems and identify cases
that deserve further attention are in most cases absent. Developing these kinds of simple analyses
could, for example, be applied to understand the length scale affected by a single well or by
multiple wells relative to depth or proximity to major faults and to the surface.
Proposed Action
In locales where a causal relationship may exist between subsurface energy activities and
seismicity (even for small earthquakes of M between 3 and 4), a local seismic array should be
installed for seismic monitoring. An appropriate body to determine whether such an array is
necessary may be the permitting agency for the well(s) thought to be involved in the seismicity.
Installation of such an array may require significant resources (including instrumentation and
analysis). Existing groups, such as the U.S. Geological Survey, National Laboratories, state
geological surveys, universities, and private companies have the expertise necessary to install
arrays and conduct the necessary analyses. Full disclosure of the data and results of such
monitoring is required.
Geothermal Energy
Findings
1. The induced seismic responses to injection differ in cause and magnitude with each of the
three different forms of geothermal resources. At the vapor-dominated Geysers field hundreds of
earthquakes of M 2 or greater are produced annually with one or two of M 4, all apparently
caused principally by cooling and contraction of the reservoir rocks. The liquid-dominated field
developments generally cause little if any induced seismicity because the water injection
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155 INDUCED SEISMICITY POTENTIAL IN ENERGY TECHNOLOGIES
typically replaces similar quantities of fluid extracted at similar pressures and temperatures. The
high-pressure hydraulic fracturing associated with the stimulation operations at EGS
developments into generally impermeable fractured rock can cause hundreds of small micro-
seismic events and an occasional earthquake of up to M 3 due mainly to the imposed increased
fluid pressures.
2. The mitigation of the effects of induced seismicity is in some instances clearly necessary to
maintain or to restore public acceptance of the geothermal power generation activities. The early
use of a “best practices” protocol and a “traffic light” control system indicates that such
measures can provide an effective means to control operations so that the intensity of the induced
seismicity is within acceptable levels. Further information on implementation of a protocol and
control system is outlined under the final section below on “Best Practices.”
Gaps
1. Suitable coupled reservoir fluid flow and geomechanical simulation codes are not currently
available to understand the processes underlying the occurrence of seismicity after geothermal
wells have been shut in (ceased operation).
2. Field operators currently do not have ready access to downhole temperature and pressure
recording instruments capable of making accurate measurements where reservoir conditions
reach 750 degrees F.
Proposed Actions
1. Adopt and use of a matrix-style “best practices” protocol by developers as outlined in Chapter
6: Such a protocol is appropriate to use 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
induced seismicity occurs but was previously unanticipated, the developer should consider
adopting the protocol procedures needed to complete the project in a manner more satisfactory to
the public.
2. Fully disclose and discuss a “traffic light” system in a public forum prior to the start of
operations when such a system is to be adopted or imposed. Such disclosure and discussion will
ensure that these safeguards are clearly known and understood by all concerned.
Conventional Oil and Gas Development Including Oil and Gas Withdrawal, Secondary
Recovery, and Enhanced Oil Recovery
Findings
1. Generally, withdrawal associated with conventional oil and gas recovery has not caused
significant seismic events, however several major earthquakes have been associated with
conventional oil and gas withdrawal.
2. Relative to the large number of waterflood projects for secondary recovery, the small number
of documented instances of felt induced seismicity suggests such projects pose relatively small
risk for events that would be of concern to the public.
3. The committee has not identified any documented, felt induced seismic events associated with
EOR (tertiary recovery). The potential for induced seismicity is low in EOR operations as pore
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ADDRESSING INDUCED SEISMICITY 156
pressure is not significantly increased beyond the original levels in the reservoir because injected
fluid volumes tend to be balanced by fluid withdrawals.
Unconventional Oil and Gas: Hydraulic Fracturing for Shale Gas Development
Findings
1. The process of hydraulic fracturing a well as presently implemented for shale gas recovery
does not pose a high risk for inducing felt seismic events. Thirty-five thousand wells have been
hydraulically fractured for shale gas development to date in the United States. To date, hydraulic
fracturing for shale gas production was cited as the possible cause of one case of felt seismic
events in Oklahoma in 2011, the largest of which was M 2.8. The quality of the event locations
was not adequate to fully establish a direct causal link to the hydraulic fracture treatment.
Hydraulic fracturing for shale gas development has been confirmed as the cause of induced
seismic events in one case worldwide—in Blackpool, England (maximum M 2.3).
2. One case of induced seismicity (maximum M 1.9) was documented in Oklahoma in the late
1970s as being caused by hydraulic fracturing for oil and gas development for conventional oil
and gas extraction.
Proposed Action
When a seismic event occurs that appears to be associated with hydraulic fracturing and
is considered to be a concern to the health, safety, and welfare of the public, an assessment is
needed to understand the causes of the seismicity (see protocol below).
Injection Wells for the Disposal of Water Associated with Energy Extraction
Findings
1. The United States currently has approximately 30,000 Class II waste water disposal wells;
very few felt induced seismic events have been reported as either caused by or likely related to
these wells. Rare cases of waste water 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 have been successful in decreasing rates
of felt seismicity in cases where events have been induced.
5. Evaluating the potential for induced seismicity in the location and design of injection wells is
difficult because no cost-effective way to locate unmapped faults and measure in situ stress
currently exists.
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157 INDUCED SEISMICITY POTENTIAL IN ENERGY TECHNOLOGIES
Gaps
1. Effective and economical tools are not available to accurately predict induced seismic 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
develop the capacity to make such predictions.
Proposed Actions
The actions proposed by the committee to address the potential for induced seismicity
related to injection wells for disposal of waste water are similar to those suggested for geothermal
energy technologies, namely:
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 operations. Knowledge and understanding of these
safeguards by all concerned is of great importance. Further information is outlined under the final
section below on “Best Practices.”
Carbon Capture and Storage
Findings
1. The only long-term (~14 years) commercial CO2 sequestration project in the world at the
Sleipner field offshore Norway is of small scale relative to commercial projects proposed in the
United States. Extensive seismic monitoring at this offshore site has not indicated any significant
induced seismicity.
2. Proposed injection volumes of liquid CO2 in large-scale sequestration projects (> 1 million
metric tonnes per year) are much larger than those associated with the other energy technologies
currently being considered. There is no experience with fluid injection at these large scales and
little data on seismicity associated with CO2 pilot projects. If the reservoirs behave in a similar
manner to oil and gas fields, these large volumes have the potential to increase the pore pressure
over vast areas. Relative to other technologies, such large affected areas may have the potential
to increase both the number and magnitude of seismic events.
3. CO2 has the potential to react with the host/adjacent rock and cause mineral precipitation or
dissolution. The effects of these reactions on potential seismic events are not understood.
Gaps
1. The short- and long-term effect of supercritical CO2 in influencing rock strength and rock slip
strength are not well understood.
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ADDRESSING INDUCED SEISMICITY 158
2. The potential earthquake magnitudes that can be induced by the injection volumes being
proposed for CCS are not known.
3. The complexities of hydro-chemical-mechanical effects on CO2 injection and storage are not
thoroughly understood.
Proposed Actions
Because of the lack of experience with large-scale fluid injection for CCS, continued
research supported by the federal government is needed on the potential for induced seismicity in
large-scale CCS projects. Some specific research recommendations are outlined in Box 7.1. As
part of a continued research effort, collaboration between federal agencies and foreign operators
of CCS sites is important to understand induced seismic events and their effects on the CCS
operations.
OVERSIGHT, MONITORING, AND COORDINATION OF UNDERGROUND
INJECTION ACTIVITIES FOR MITIGATING INDUCED SEISMICITY
Findings
1. Induced seismicity may be produced by a number of different energy technologies and may
result from either injection or extraction of fluid. As such, responsibility for oversight of
activities that can cause induced seismicity is dispersed among a number of federal and state
agencies.
2. Recent, potentially induced seismic events in the United States have been addressed in a
variety of manners involving local, state, and federal agencies, and research institutions. These
agencies and research institutions may not have resources to address these unexpected events and
more events could stress this ad hoc system.
3. Currently the Environmental Protection Agency (EPA) has primary regulatory responsibility
for fluid injection under the Safe Drinking Water Act; however, this act does not address induced
seismicity. EPA appears to be addressing the issue of induced seismicity through a current study
in consultation with other federal and state agencies.
4. The USGS has the capability and expertise to address monitoring and research associated
with induced seismic events. However, the scope of their mission within the seismic hazard
assessment program is focused on large impact, natural earthquakes. Significant new resources
would be required if the USGS mission is expanded to include comprehensive monitoring and
research on induced seismicity.
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159 INDUCED SEISMICITY POTENTIAL IN ENERGY TECHNOLOGIES
Gap
Mechanisms are lacking for efficient coordination of governmental agency response to
seismic events that may have been induced.
Proposed Actions
1. In order to move beyond the current ad hoc approach for responding to induced seismicity,
relevant agencies including EPA, USGS, land management agencies, and possibly the
Department of Energy, as well as state agencies with authority and relevant expertise (e.g. Oil
and Gas Commissions, state geological surveys, state environmental agencies, etc.) should
consider developing coordination mechanisms to address induced seismic events that correlate to
established best practices (see recommendation below).
2. Appropriating authorities and agencies with potential responsibility for induced seismicity
should consider resource allocations for responding to induced seismic events in the future.
HAZARDS AND RISK ASSESSMENT
Gap
Currently, methods do not exist to implement assessments of hazards upon which risk
assessments depend. The types of information and data required to provide a robust hazard
assessment would include:
Net pore pressures, in situ stresses, information on faults,
Background seismicity, and
Gross statistics of induced seismicity and fluid injection for the proposed site
activity.
Proposed Actions
1. A detailed methodology should be developed for quantitative, probabilistic hazard
assessments of induced seismicity risk. The goals in developing the methodology would be to:
make assessments before operations begin in areas with a known history of felt
seismicity;
update assessments in response to observed induced seismicity.
2. Data related to fluid injection (well locations coordinates, injection depths, injection volumes
and pressures, time frames) should be collected by state and federal regulatory authorities in a
common format and made accessible to the public (through a coordinating body such as the
USGS).
3. In areas of high-density of structures and population, regulatory agencies should consider
requiring that data to facilitate fault identification for hazard and risk analysis be collected and
analyzed before energy operations are initiated.
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ADDRESSING INDUCED SEISMICITY 160
BEST PRACTICES
Findings
1. The DOE Protocol for EGS, which lists seven sequential steps, provides a reasonable initial
model for dealing with induced seismicity that can serve as a template for other energy
technologies.
2. Based on this initial model, the committee has proposed two matrix-style protocols as
examples to illustrate the manner in which these seven activities can ideally be undertaken
concurrently (rather than only sequentially), while also illustrating how these activities should be
adjusted as a project progresses from early planning through operations to completion.
Gap
No best practices protocol for addressing induced seismicity is generally in place for each
of these technologies, with the exception of the protocol recently developed for EGS. The
committee suggests that best practices protocols be adapted and tailored to each technology to
allow continued energy technology development. Actions toward developing these protocols are
outlined below.
Proposed Actions
1. A matrix-style “best practices” protocol should be developed in coordination with the
permitting agency or agencies by experts in the field of each energy technology, including EOR,
shale gas production, and carbon capture and sequestration.
2. The adoption and use by developers of such protocols is recommended in each case where
there is a known or substantial probability of inducing seismicity at levels that could pose a
concern to the public. In cases where induced seismicity becomes an issue at some stage in the
project, the developer can adopt the protocol procedures needed to continue the project in a
manner more satisfactory to the public.
3. Even with the adoption and use of a best practices protocol, induced seismicity of serious
concern to public health and safety may occur. The regulatory body affiliated with the
permitting of well(s) should include, as part of each project’s operation permit, a mechanism
(such as a “traffic light” mechanism) for the well operator to be able to control, reduce, or
eliminate the potential for felt seismic events.
4. When a “traffic light” system is to be adopted or imposed to control operations that may cause
unacceptable levels of induced seismicity, full disclosure and discussion of the adopted system at
a public forum prior to the start of operations is advised so that these safeguards are clearly
known and understood by all concerned. Simultaneous development of public awareness
programs by federal or state agencies in cooperation with industry and the research community
could aid the public and local officials in understanding and addressing the risks associated with
small magnitude induced seismic events.
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Appendixes
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