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Executive Summary
Earthquakes attributable to human activities are called “induced seismic events”
or “induced earthquakes.” In the past several years induced seismic events related to
energy development projects have drawn heightened public attention. Although only a
very small fraction of injection and extraction activities at hundreds of thousands of
energy development sites in the United States have induced seismicity at levels that are
noticeable to the public, seismic events caused by or likely related to energy development
have been measured and felt in Alabama, Arkansas, California, Colorado, Illinois,
Louisiana, Mississippi, Nebraska, Nevada, New Mexico, Ohio, Oklahoma, and Texas.
Anticipating public concern about the potential for energy development projects
to induce seismicity, the U.S. Congress directed the U.S. Department of Energy to
request that the National Research Council examine the scale, scope, and consequences
of seismicity induced during fluid injection and withdrawal activities related to
geothermal energy development, oil and gas development including shale gas recovery,
and carbon capture and storage (CCS). The study was also to identify gaps in knowledge
and research needed to advance the understanding of induced seismicity; identify gaps in
induced seismic hazard assessment methodologies and the research to close those gaps;
and assess options for steps toward best practices with regard to energy development and
induced seismicity potential.
Three major findings emerged from the study:
(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;
(2) injection for disposal of waste water derived from energy technologies into the
subsurface does pose some risk for induced seismicity, but very few events have
been documented over the past several decades relative to the large number of
disposal wells in operation; and
(3) CCS, due to the large net volumes of injected fluids, may have potential for
inducing larger seismic events.
Induced seismicity associated with fluid injection or withdrawal is caused in most
cases by change in pore fluid pressure and/or change in stress in the subsurface in the
presence of faults with specific properties and orientations and a critical state of stress in
the rocks. The factor that appears to have the most direct consequence in regard to
induced seismicity is the net fluid balance (total balance of fluid introduced into or
removed from the subsurface), although additional factors may influence the way fluids
affect the subsurface. While the general mechanisms that create induced seismic events
are well understood, we are currently unable to accurately predict the magnitude or
occurrence of such events due to the lack of comprehensive data on complex natural rock
systems and the lack of validated predictive models.
Energy technology projects that are designed to maintain a balance between the
amount of fluid being injected and withdrawn, such as most oil and gas development
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EXECUTIVE SUMMARY 2
projects, appear to produce fewer seismic events than projects that do not maintain fluid
balance. Hydraulic fracturing in a well for shale gas development, which involves
injection of fluids to fracture the shale and release the gas up the well, has been
confirmed as the cause for small felt seismic events at one location in the world.
Waste water disposal from oil and gas production, including shale gas recovery,
typically involves injection at relatively low pressures into large porous aquifers that are
specifically targeted to accommodate large volumes of fluid. The majority of waste
water disposal wells do not pose a hazard for induced seismicity though there have been
induced seismic events with a very limited number of wells. The long-term effects of a
significant increase in the number of waste water disposal wells for induced seismicity
are unknown.
Projects that inject or extract large net volumes of fluids over long periods of time
such as CCS may have potential for larger induced seismic events, though insufficient
information exists to understand this potential because no large-scale CCS projects are
yet in operation. Continued research is needed on the potential for induced seismicity in
large-scale CCS projects.
Induced seismicity in geothermal projects appears to be related to both net fluid
balance considerations and temperature changes produced in the subsurface. Different
forms of geothermal resource development appear to have differing potential for
producing felt seismic events. High-pressure hydraulic fracturing undertaken in some
geothermal projects has caused seismic events that are large enough to be felt.
Temperature changes associated with geothermal development of hydrothermal resources
has also induced felt seismicity.
Governmental response to induced seismic events has been undertaken by a
number of federal and state agencies in a variety of ways. However, with the potential for
increased numbers of induced seismic events due to expanding energy development,
government agencies and research institutions may not have sufficient resources to
address unexpected events. Forward-looking interagency cooperation to address potential
induced seismicity is warranted.
Methodologies can be developed for quantitative, probabilistic hazard
assessments of induced seismicity risk. Such assessments should be undertaken before
operations begin in areas with a known history of felt seismicity and updated in response
to observed, potentially induced seismicity. 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 and site
location.
Although induced seismic events have not resulted in loss of life or major damage
in the United States, their effects have been felt locally, and they raise some concern
about additional seismic activity and its consequences in areas where energy
development is ongoing or planned. Further research is required to better understand and
address the potential risks associated with induced seismicity.
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