Manmade earthquakes are on the rise and will continue to increase due to the effort to produce more energy and store waste water and carbon dioxide in
the earth.
A new report, Induced
Seismicity Potential in Energy Technologies (2012) by the Board
on Earth Sciences and Resources (BESR),
discusses in detail these “induced earthquakes.” It has been published by the
National Research Council and is available from the National
Academies Press.
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.
Since the 1920s we have recognized that pumping fluids into or out of
the Earth has the potential to cause seismic events that can be felt. Seismic
events in Basel, Switzerland between 2006 and 2008 were felt by local residents
and were related to geothermal energy development. A string of small seismic
events in Arkansas, Ohio, Oklahoma, and Texas in the past several years has
been related to waste water disposal associated with oil and gas production.
These seismic events have brought the issue of induced (human-caused)
seismicity firmly into public view.
Ensuring a reliable 21st century energy supply for the United States
presents seminal economic, environmental, and social challenges. A variety of
conventional and unconventional energy technologies are being developed to meet
this challenge including new technologies associated with shale gas production
and geothermal energy. Energy technologies may also produce wastes. “Waste”
water is often produced during oil and gas drilling and is generally managed
either by disposal through pumping the fluids back into the subsurface or by
storage, treatment, or reuse. Carbon dioxide may also be generated as a
byproduct of energy production and may be captured and similarly pumped into
the ground for storage.
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 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.
Credit: Wikipedia
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 address the potential risks associated with
induced seismicity.
National Academies Press
Induced Seismicity Potential in Energy Technologies
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