Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 3
Summary
Although the vast majority of earthquakes that occur in the world each year have natural
causes, some of these earthquakes and a number of lesser magnitude seismic events are related to
human activities and are called “induced seismic events” or “induced earthquakes.” Induced
seismic activity has been documented since at least the 1920s and has been attributed to a range
of human activities including the impoundment of large reservoirs behind dams, controlled
explosions related to mining or construction, and underground nuclear tests. In addition, energy
technologies that involve injection or withdrawal of fluids from the subsurface can also create
induced seismic events that can be measured and felt. Historically known induced seismicity has
generally been small in both magnitude and intensity of ground shaking.
Recently, several induced seismic events related to energy technology development
projects in the United States have drawn heightened public attention. Although none of these
events resulted in loss of life or significant structural damage, their effects were felt by local
residents, some of whom also experienced minor property damage. Particularly in areas where
tectonic (natural) seismic activity is uncommon and energy development is ongoing, these
induced seismic events, though small in scale, can be disturbing to the public and raise concern
about increased seismic activity and its potential consequences.
This report addresses induced seismicity that may be related to four energy development
technologies that involve fluid injection or withdrawal: geothermal energy; conventional oil and
gas development including enhanced oil recovery (EOR); shale gas recovery; and carbon capture
and storage (CCS). These broad categories of energy technologies are divided into finer
categories herein (including underground waste water disposal), to show details of induced
seismic events as they relate to specific aspects of each energy technology. The study arose
through a request by Senator Bingaman of New Mexico to Department of Energy (DOE)
Secretary Stephen Chu. The DOE was asked to engage the National Research Council (NRC) to
examine the scale, scope, and consequences of seismicity induced during the injection of fluids
related to energy production; to identify gaps in knowledge and research needed to advance the
understanding of induced seismicity; to identify gaps in induced seismic hazard assessment
methodologies and the research needed to close those gaps; and to assess options for interim
steps toward best practices with regard to energy development and induced seismicity potential.
The report responds to this charge and aims to provide an understanding of the nature and scale
of induced seismicity caused by or likely related to energy development and guidance as to how
best to proceed with safe development of these technologies while minimizing their potential to
induce earthquakes that can be felt by the public.
INDUCED SEISMICITY RELATED TO FLUID INJECTION OR WITHDRAWAL AND
CAUSAL MECHANISMS
Seismic events have been measured and felt at a limited number of energy development
sites in the United States. Seismic events caused by or likely related to energy development have
3
Prepublication version – Subject to revision
OCR for page 4
4 INDUCED SEISMICITY POTENTIAL IN ENERGY TECHNOLOGIES
been documented in Alabama, Arkansas, California, Colorado, Illinois, Louisiana, Mississippi,
Nebraska, Nevada, New Mexico, Ohio, Oklahoma, and Texas (Figure S.1). Proving that a
particular seismic event was caused by human activity is often difficult because conclusions
about the causal relationship rely on local data, prior seismicity, and the preponderance of
scientific studies. In this report we give examples of seismic events that are universally believed
to have been caused by human activities, as well as seismic events for which the evidence for
causality is credible but less solid.
Research conducted on some of these incidents has led to better understanding of the
probable physical mechanisms of inducing seismic events and allowed for the identification of
criteria that could be used to predict whether future induced seismic events might occur. The
most important criteria include the amplitude and direction of the state of stress in the Earth’s
crust in the vicinity of the fluid injection or withdrawal area; the presence, orientation, and
physical properties of nearby faults; pore fluid pressure (pressure of fluids in the pores of the
rocks at depth; hereafter simply called “pore pressure”); pore pressure change; the rates and
volumes of fluid being injected or withdrawn; and the rock properties in the subsurface.
Figure S.1 Sites in the United States and Canada with documented reports of seismicity caused by or likely related
to energy development from various energy technologies. The reporting of the occurrence of small induced seismic
events is limited by the detection and location thresholds of local surface-based seismic monitoring networks.
Prepublication version – Subject to revision
OCR for page 5
SUMMARY 5
Seismicity induced by human activity related to energy technologies is caused by change
in pore pressure and/or change in stress taking place in the presence of (1) faults with specific
properties and orientations, and (2) a critical state of stress in the rocks. In general, existing
faults and fractures are stable (or are not sliding) under the natural horizontal and vertical
stresses acting on subsurface rocks. However, the crustal stress in any given area is perpetually
in a state in which any stress change, for example through a change in subsurface pore pressure
due to injecting or extracting fluid from a well, may change the stress acting on a nearby fault.
This change in stress may result in slip or movement along that fault creating a seismic event.
Abrupt or nearly instantaneous slip along a fault releases energy in the form of energy waves
(“seismic waves”) that travel through the Earth and can be recorded and used to infer
characteristics of energy release on the fault. Magnitude “M” measures the total amount of
energy released at the seismic event source, whereas “intensity” of a seismic event is a measure
of the level of ground shaking at any location. Both the magnitude and maximum intensity of a
seismic event are directly related to the total area of the fault that undergoes movement – a larger
area of slip along the fault results in a larger seismic event.
Although the general mechanisms that create induced seismic events are well understood,
current computer modeling techniques cannot fully address the complexities of natural rock
systems in large part because the models generally lack information on local crustal stress, rock
properties, fault locations and properties, and the shape and size of the reservoir into which fluids
are injected or withdrawn. When adequate knowledge of this information is available, the
possibility exists to make accurate predictions of earthquake occurrences. Without this detailed
information, hazard and risk assessments have to be based on statistical analysis of data from
analogous regions. The ability to predict induced seismicity at a particular energy development
site will continue to rely on both theoretical modeling and available data including field
measurements, and on statistical methods.
ENERGY TECHNOLOGIES AND THEIR INDUCED SEISMICITY POTENTIAL
Geothermal energy, oil and gas production (including hydraulic fracturing for shale gas
production), and CCS technologies each involve fluid injection and/or withdrawal. Therefore,
each technology has the potential to induce seismic events that can be felt. Seismic events with
M greater than 2.0 have the possibility of being felt, particularly if they occur at shallow depths,
but smaller seismic events (M<2.0) generally are not felt. The injection rate and pressure, fluid
volumes, and injection duration vary with the technology as do the potential sizes of the seismic
events and the possible risk and hazards of the induced events (Table S.1).
Prepublication version – Subject to revision
OCR for page 6
6 INDUCED SEISMICITY POTENTIAL IN ENERGY TECHNOLOGIES
Table S.1 Summary Information about Historical Felt Seismic Events Caused by or Likely Related to
Energy Technology Development in the United Statesa
Energy Number Number of Maximum Number of Net Mechanism Location
technology of Felt Magnitude of Events Reservoir for Induced of M>2.0
d
Projects Induced Felt Events M>4.0 Pressure Seismicity Events
Events Change
Vapor- 1 300-400 per 4.6 1 to 3 per Attempt to Temperature CA (The
dominated year since year maintain change Geysers)
geothermal 2005 balance between
injectate and
reservoir
4.1b
Liquid- 23 10-40 per Possibly Attempt to Pore CA
dominated year one maintain pressure
geothermal balance increase
Enhanced ~8 pilot 2-10 per 2.6 0 Attempt to Pore CA, NV
geothermal projects year maintain pressure
systems balance increase and
cooling
Secondary oil ~108,000 One or more 4.9 3 Attempt to Pore AL, CA,
and gas (wells) events at 18 maintain pressure CO, MS,
recovery sites across balance increase OK, TX
(waterflooding) the country
Tertiary oil and ~13,000 None known None known 0 Attempt to Pore None
gas recovery maintain pressure known
(EOR) balance increase
(likely
mechanism)
Hydraulic 35,000 1 2.8 0 Initial Pore OK
fracturing for wells total positive; pressure
shale gas then increase
production withdraw
Hydrocarbon ~6,000 20 sites 6.5 5 Withdrawal Pore CA, IL, NB,
withdrawal fields pressure OK, TX
decrease
4.8c
Waste water ~30,000 8 7 Addition Pore AR, CO,
disposal wells pressure OH
increase
Carbon capture 1 None known None known 0 Addition Pore IL
and storage, pressure
small scale increase
Carbon capture 0 None None 0 Addition Pore None yet in
and storage, pressure operation
large scale increase
a
Note that that in several cases the causal relationship between the technology and the event was suspected but not
confirmed. Determining whether a particular earthquake was caused by human activity is often very difficult. The
references for the events in this table and the way in which causality may be determined are discussed in the report.
Also important is the fact that the well numbers are those wells in operation today, while the numbers of
events listed extend over a total period of decades.
b
One event of M 4.1 was recorded at Coso, but the committee did not obtain enough information to determine
whether or not the event was induced.
c
M 4.8 is a moment magnitude. Earlier studies reported magnitudes up to M 5.3 on an unspecified scale; those
magnitudes were derived from local instruments.
d
Although seismic events M>2.0 can be felt by some people in the vicinity of the event, events M>4.0 can be felt by
most people and may be accompanied by more significant ground shaking, potentially causing greater public
concern.
Prepublication version – Subject to revision
OCR for page 7
SUMMARY 7
Geothermal Energy
The three different types of geothermal energy resources are (1) “vapor-dominated”,
where primarily steam is contained in the pores or fractures of hot rock, (2) “liquid-dominated”,
where primarily hot water is contained in the rock, and (3) “Enhanced Geothermal Systems”
(EGS), where the resource is hot, dry rock that requires engineered stimulation to allow fluid
movement for commercial development. Although felt induced seismicity has been documented
with all three types of geothermal resources (Table S.1), geothermal development usually
attempts to keep a mass balance between fluid volumes produced and fluids replaced by injection
to extend the longevity of the energy resource. This fluid balance helps to maintain fairly
constant reservoir pressure—close to the initial, pre-production value—and can aid in reducing
the potential for induced seismicity. Seismic monitoring at liquid-dominated geothermal fields in
the western United States has demonstrated relatively few occurrences of felt induced seismicity.
However, in The Geysers geothermal steam field in northern California, the large temperature
difference between the injected fluid and the geothermal reservoir results in significant cooling
of the hot subsurface reservoir rocks, causing the rocks to contract, reducing confining pressures
and allowing the release of local stresses that results in a significant amount of observed induced
seismicity. EGS technology is in the early stages of development; many countries including the
United States have pilot projects to test the potential for commercial production. In each case of
active EGS development, at least some, generally minor levels of felt induced seismicity have
been recorded.
Conventional and Unconventional Oil and Gas Development, Including Enhanced Oil
Recovery (EOR) and Shale Gas
In a conventional oil or gas reservoir the hydrocarbon fluids and associated aqueous
fluids in the pore spaces of the rock are usually under significant natural pressure. Fluids in the
oil or gas reservoir flow to the surface when penetrated by a well bore, generally aided by
pumping. Oil or gas reservoirs often reach a point when insufficient pressure, even in the
presence of pumping, exists to allow sufficient hydrocarbon recovery. Various technologies,
including secondary recovery and tertiary recovery (the latter is often referred to as enhanced oil
recovery [EOR], which is the term used hereafter), can be used to extract some of the remaining
oil and gas. Secondary recovery and EOR technologies both involve injection of fluids into the
subsurface to push more of the trapped hydrocarbons out of the pore spaces in the reservoir and
to maintain reservoir pore pressure. Secondary recovery often uses water injection or
“waterflooding” and EOR technologies often inject carbon dioxide (CO2). Approximately
151,000 injection wells are currently permitted in the United States for a combination secondary
recovery, EOR, and waste water disposal with only very few documented incidents where the
injection caused or was likely related to felt seismic events (Table S.1). Secondary recovery—
through waterflooding—has been associated with very few felt induced seismic events (Table
S.1). Among the tens of thousands of wells used for EOR in the United States, the committee did
not find any documentation in the published literature of felt induced seismicity, nor were any
instances raised by experts in the field with whom the committee communicated during the
study. Oil and gas extraction (fluid withdrawal) from a reservoir may cause induced seismic
events. These events are rare relative to the large number of oil and gas fields around the world
and appear to be related to decrease in pore pressure as fluid is withdrawn (Table S.1).
Prepublication version – Subject to revision
OCR for page 8
8 INDUCED SEISMICITY POTENTIAL IN ENERGY TECHNOLOGIES
Similar to geothermal systems, conventional oil and gas projects are designed to maintain
the pore pressure within a field at its pre-production level by maintaining a balance between
fluids being removed from one part of the reservoir and fluids injected in another part of the
reservoir. The proportionally very small number of induced seismic events generated by these
technologies relative to the large number of wells is in part due to this effort to maintain the
original pore pressure of the reservoir.
Shale formations can also contain hydrocarbons—gas and/or oil. The extremely low
permeability of these rocks has trapped the hydrocarbons as they developed in the rock and
largely prevented them from migrating out of the rock over geologic time. The low permeability
also prevents the hydrocarbons from easily flowing into a well bore without production
stimulation by the operator. These types of “unconventional” reservoirs are developed by
drilling wells horizontally through the reservoir rock and using hydraulic fracturing techniques to
create new fractures in the reservoir to allow the hydrocarbons to migrate up the well bore.
About 35,000 hydraulically fractured shale gas wells exist in the United States (Table S.1); only
one case of felt seismicity (M ~2.8) in the United States has been described in which hydraulic
fracturing for shale gas development is suspected, but not confirmed, as the cause (Table S.1).
Globally only one case of felt induced seismicity in England (M 2.3) has been confirmed as
being caused by hydraulic fracturing for shale gas development. The very low number of felt
events relative to the large number of hydraulically fractured wells for shale gas is likely due to
the short duration of injection of fluids and the limited fluid volumes used in a small spatial area.
Waste Water Disposal Wells Associated with Energy Extraction
In addition to fluid injection directly related to energy development, injection wells
drilled to dispose of waste water generated during oil and gas production are very common in the
United States. Tens of thousands of waste water disposal wells are currently active throughout
the country. Although only a few induced seismic events have been linked to these disposal
wells (Table S.1), the occurrence of these events has generated considerable public concern.
Examination of these cases has suggested causal links between the injection zones and
previously unrecognized faults in the subsurface.
In contrast to wells for EOR which are sited and drilled for precise injection into well-
characterized oil and gas reservoirs, injection wells used only for the purpose of waste water
disposal normally do not have a detailed geologic review performed prior to injection and the
data are often not available to make such a detailed review. Thus, the location of possible nearby
faults is often not a standard part of siting and drilling these disposal wells. In addition, the
presence of a fault does not necessarily imply an increased potential for induced seismicity,
creating challenges for the evaluation of potential sites for disposal injection wells that will
minimize the possibility for induced seismic activity.
Carbon Capture and Storage
For several years researchers have explored various methods for reducing carbon
emissions to the atmosphere, such as by capturing CO2 and developing means for storing (or
sequestering) it permanently underground. If technically successful and economical, CCS could
become an important technology for reducing CO2 emissions to the atmosphere. The risk of
induced seismicity from CCS is currently difficult to accurately assess. With only a few small-
Prepublication version – Subject to revision
OCR for page 9
SUMMARY 9
scale commercial projects overseas and several small-scale demonstration projects underway in
the United States, few data are available to evaluate the induced seismicity potential of this
technology (Table S.1); these projects so far have involved very small injection volumes. CCS
differs from other energy technologies in that it involves continuous CO2 injection at high rates
under pressure for long periods of time, and is purposely intended for permanent storage (no
fluid withdrawal). Given that the potential magnitude of an induced seismic event correlates
strongly with the fault rupture area, which in turn relates to the magnitude of pore pressure
change and the rock volume in which it exists, large-scale CCS may have the potential for
causing significant induced seismicity. CCS projects that do not cause a significant increase in
pore pressure above its original value will likely minimize the potential for inducing seismic
events.
Energy Technology Summary
The balance of injection and withdrawal of fluids is critical to understanding the potential
for induced seismicity with respect to energy technology development projects. The factors
important for understanding the potential to generate felt seismic events are complex and
interrelated and include: the rate of injection or extraction; volume and temperature of injected or
extracted fluids; pore pressure; permeability of the relevant geologic layers; faults and fault
properties; crustal stress conditions; the distance from the injection point; and the length of time
over which injection and/or withdrawal takes place. However, the net fluid balance (total
balance of fluid introduced and removed) appears to have the most direct consequence on
changing pore pressure in the subsurface over time. Energy technology projects that are designed
to maintain a balance between the amount of fluid being injected and the amount of fluid being
withdrawn, such as geothermal and most oil and gas development, may produce fewer induced
seismic events than technologies that do not maintain fluid balance.
Of the well-documented cases of induced seismicity related to fluid injection, many are
associated with operations involving large amounts of fluid injection over significant periods of
time. Most waste water disposal wells typically involve injection at relatively low pressures into
large porous aquifers that have high natural permeability, and are specifically targeted to
accommodate large volumes of fluid. Thus, although a few occurrences of induced seismic
activity have been documented, the majority of the hazardous and nonhazardous waste water
disposal wells do not pose a hazard for induced seismicity. However, the long-term effects of
any significant increases in the number of waste water disposal wells on induced seismicity are
unknown.
The largest induced seismic events reported in the technical literature are associated with
projects that did not balance the large volumes of fluids injected into, or extracted from, the
Earth within the reservoir. This is a statistical observation; the net volume of fluid that is
injected and/or extracted may serve as a proxy for changes in subsurface stress conditions and
pore pressure, injection and extraction rates, and other factors. Coupled thermo-mechanical and
chemo-mechanical effects may also play a role in changing subsurface stress conditions.
Projects with large net volumes of injected or extracted fluids over long periods of time such as
long-term waste water disposal wells and CCS would appear to have a higher potential for larger
induced events. The magnitude and intensity of possible induced events would be dependent
upon the physical conditions in the subsurface—state of stress in the rocks, presence of existing
faults, fault properties, and pore pressure. The relationship between induced seismicity and
Prepublication version – Subject to revision
OCR for page 10
10 INDUCED SEISMICITY POTENTIAL IN ENERGY TECHNOLOGIES
projects with large volume, long-term injection, such as in large-scale CCS projects, is untested
because no large-scale projects are yet in existence.
UNDERSTANDING AND MANAGING HAZARDS AND RISKS ASSOCIATED WITH
INDUCED SEISMICITY FROM ENERGY DEVELOPMENT
The hazard of induced seismicity is the description and possible quantification of what
physical effects will be generated by human activities associated with subsurface energy
production or carbon dioxide sequestration. The risk of induced seismicity is the description and
possible quantification of how induced seismic events might cause losses including damage to
structures, and effects on humans including injuries and deaths. If seismic events occur in an area
with no structures or humans present, there is no risk. The concept of risk can also be extended
to include frequent occurrence of ground shaking that is a nuisance to humans.
Several questions can be addressed to understand and possibly quantify the hazard and
risk associated with induced seismicity associated with energy technologies. Questions
associated with understanding the hazard include whether an energy technology generates
apparent seismic events, whether such events are of M greater than 2.0, whether the events
generate ground shaking (shallower earthquakes have greater likelihood of causing felt ground
shaking than deep earthquakes), and the effects of the shaking. Risk to structures occurs only if
the shaking is minor, moderate, or larger; risk to structures does not occur if the shaking is felt by
humans but is not strong enough to damage the structures.
The quantification of hazard and risk requires probability assessments, which may be
either statistical (based on data) or analytical (based on scientific and engineering models).
These assessments can then be used to establish “best practices” or specific protocols for energy
project development. A risk analysis of an entire industry project would include the extent of the
spatial distribution of the operation and the multiple structures in the area that induced seismic
event might affect. While the risk of minor, moderate, or heavy damage from induced event
shaking may be small from an individual well, a large number of spatially distributed wells may
lead to a higher probability of such damage; a risk analysis of an industry operation thus includes
the entire spatial distribution of the operation and the structures an earthquake might affect.
Although historic data indicate that induced seismic events have not generally been very
large nor have they resulted in significant structural damage, induced seismic events are of
concern to affected communities. Practices that consider induced seismicity both before and
during the actual operation of an energy project can be employed in the development of a “best
practices” protocol specific to each energy technology. The aim of such protocols is to diminish
the possibility of a felt seismic event from occurring and to mitigate the effects of an event if one
should occur. A “traffic light” control system within a protocol can be established to respond to
an instance of induced seismicity, allowing for low levels of seismicity, but adding monitoring
and mitigation requirements, including the requirement to modify or even cease operations if
seismic events are of sufficient intensity result in a significant concern to public health and
safety. The ultimate success of such a protocol is fundamentally tied to the strength of the
collaborative relationships and dialogue among operators, regulators, the research community,
and the public.
Prepublication version – Subject to revision
OCR for page 11
SUMMARY 11
GOVERNMENT ROLES AND RESPONSIBILITIES
Four federal agencies—the Environmental Protection Agency (EPA) the Bureau of Land
Management (BLM), the U.S. Department of Agriculture Forest Service (USFS), and the U.S.
Geological Survey (USGS)—and different state agencies have regulatory oversight, research
roles and/or responsibilities related to different aspects of the underground injection activities
that are associated with energy technologies. To date, these various agencies have dealt with
induced seismic events with different and localized actions. These efforts to respond to potential
induced seismic events have been successful but have been ad hoc in nature. Many events that
scientists suspect may be induced are not labeled as such, due to lack of confirmation or
evidence that those events were in fact induced by human activity. In areas of low historical
seismicity, the national seismic network coverage tends to be sparser than more seismically
active areas, making it difficult to detect small events and to identify their locations accurately.
ADDRESSING INDUCED SEISMICITY
The primary findings, gaps in knowledge or information, proposed actions, and research
recommendations to address induced seismicity potential in energy technologies are presented
below. Details specific to each energy technology are elaborated in Chapter 7.
Overarching Issues
Findings
1. The basic mechanisms that can induce seismic events 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. Models to predict of the size and location of earthquakes 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 on the interactions among rock, faults,
and fluid as a complex system; these data are difficult and expensive to obtain.
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 have 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 a 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
Prepublication version – Subject to revision
OCR for page 12
12 INDUCED SEISMICITY POTENTIAL IN ENERGY TECHNOLOGIES
predict observations from the field.
Gaps
1. The basic data on fault locations and properties, in situ stresses, fluid 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 S.1. These recommendations also
have relevance for specific energy technologies and address gaps in present understanding of
induced seismicity.
Box S.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 microseisms1 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.
1
Microseisms designate seismic events that are not generally felt by humans, and in this report are those with M<2.
Prepublication version – Subject to revision
OCR for page 13
SUMMARY 13
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.
Energy Technologies
Findings
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
increase or decrease in net fluid volume.
2. The induced seismic responses to injection or extraction differ in cause and magnitude among
each of the three different forms of geothermal resources. Decrease of the temperature of the
subsurface rocks caused by injection of cold water in a geothermal field has the potential to
produce seismic events.
3. The potential for felt induced seismicity due to secondary recovery and EOR is low.
4. 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.
5. The United States currently has approximately 30,000 Class II2 waste water disposal wells
among a total of 151,000 Class II injection wells (which includes injection wells for both
secondary recovery and EOR). Very few felt seismic events have been reported as either caused
by or temporally associated with waste water disposal wells; these events have produced felt
earthquakes generally less than M 4.0. Reducing injection volumes, rates, and pressures have
been successful in decreasing rates of seismicity associated with waste water injection.
6. The proposed injection volumes of liquid CO2 in large-scale sequestration projects are much
larger than those associated with other energy technologies. 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 net volumes may have
the potential to impact the pore pressure over vast areas. Relative to other energy technologies,
2
Class II wells are specifically those that address injection of brines and other fluids associated with oil and gas
production and hydrocarbons for storage.
Prepublication version – Subject to revision
OCR for page 14
14 INDUCED SEISMICITY POTENTIAL IN ENERGY TECHNOLOGIES
such large spatial areas may have potential to increase both the number and magnitude of seismic
events.
Proposed Action
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 (see Box S.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.
Hazards and Risk Assessment
Finding
Risk assessments depend on methods that implement assessments of hazards, but those
methods currently do not exist. 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;
Gross statistics of induced seismicity and fluid injection or extraction.
Proposed Actions
1. A detailed methodology should be developed for quantitative, probabilistic hazard
assessments of induced seismicity risk. The goal in developing this 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 location coordinates, injection depths, injection volumes
and pressures, time frames) should be collected by state and federal regulatory authorities in a
common format and made publicly accessible (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.
Best Practices
Finding
The DOE Protocol for EGS is a reasonable model for addressing induced seismicity that
can serve as a template for protocol development for other energy technologies.
Prepublication version – Subject to revision
OCR for page 15
SUMMARY 15
Gap
No best practices protocol for addressing induced seismicity is generally in place for each
energy technology. The committee suggests that best practices protocols be adapted and tailored
to each technology to allow continued energy technology development.
Proposed Actions
Protocols for best practice should be developed for each of the energy technologies
(secondary recovery and EOR for conventional oil and gas production, shale gas production,
CCS) by experts in each field, in coordination with permitting agencies, potentially following the
model of the DOE EGS protocol. For all the technologies a “traffic light” system should be
employed for future operations. The protocols should be applied to:
the permitting of operations where state agencies have identified areas of high
potential for induced seismicity; or
an existing operation that is suspected to have caused an induced seismic event of
significant concern to public health and safety.
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.
Government Roles and Responsibilities
Findings
1. Induced seismicity may be produced by a number of different energy technologies and may
involve either injection or extraction of fluid. However, responsibility for oversight of induced
seismicity is dispersed among a number of federal and state agencies.
2. Responses to energy development-related seismic events 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 unexpected events and more events
could stress this ad hoc system.
3. Currently EPA has primary regulatory responsibility for fluid injection under the Safe
Drinking Water Act, which does not address induced seismicity. EPA is addressing the issue of
induced seismicity through its 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 its mission within the seismic hazard
assessment program is focused on large impact, natural earthquakes. Significant new resources
would be required if the USGS mission was expanded to include comprehensive monitoring and
research on induced seismicity.
Gap
No mechanisms are currently in place for efficient coordination of governmental agency
response to seismic events that may have been induced.
Prepublication version – Subject to revision
OCR for page 16
16 INDUCED SEISMICITY POTENTIAL IN ENERGY TECHNOLOGIES
Proposed Actions
1. Relevant agencies including EPA, USGS, and land management agencies, and possibly DOE,
and state agencies with authority and relevant expertise (e.g., Oil and Gas Commissions, state
geological surveys, state environmental agencies) should develop coordination mechanisms to
address induced seismic events.
2. Appropriating authorities for agencies with potential responsibility for induced seismicity
should consider resource allocations for responding to induced seismic events in the future.
Prepublication version – Subject to revision
