Energy Development Related Seismicity Scrutinized
The State Journal
19 June 2012
By Taylor Kuykendall, Reporter
A new study offers some relief and proposes some questions for
natural gas extraction, but also has some bad news for fossil
fuels in general. The study, released last Friday, prompted a
Senate Energy hearing Tuesday.
The study confirmed what industry and others have been saying
regarding gas extraction. Pushing water into the ground to
fracture shale beneath has a "low risk" of inducing
Wastewater injection, a popular disposal method of water returned
from hydraulic fracturing, has a higher risk of causing
human-detectable earthquakes the report says.
The worse news for not only natural gas, but particularly coal, is
that carbon capture and storage, the study says, may have
potential for inducing seismic events as well.
Under current Environmental Protection Agency rules, new
coal-fired plants could not be built without carbon capture or
other carbon dioxide-mitigating technology. Carbon capture storage
would be necessary for natural gas plants if emissions were
restricted further, but current policy is not as burdensome for
The new study comes from the National Academy of Sciences and was
sponsored by the U.S. Department of Energy.
"Although induced seismic events associated with these energy
technologies have not resulted in loss of life or significant
damage in the United States, some effects have been felt by local
residents and have raised concern about additional seismic
activity and its consequences in areas where energy development is
ongoing or planned," NAS states.
Fracking off the hook?
As pointed out in the Senate Energy hearing regarding the
matter on Tuesday, hydraulic fracturing has a relatively small
seismic disturbance risk.
The study correlated induced earthquakes most closely with total
balance of fluid pumped in and out of the ground. All the
technologies the group examined -- oil and gas development, carbon
capture and storage and geothermal energy production -- showed
potential to induce earthquakes.
The key, authors of the report write, is to maintain a balance
between the fluid injected and withdrawn. Hydraulic fracturing and
geothermal development involve relatively smaller amounts of
liquid imbalance and thus present a smaller risk of seismic
Murray Hitzman, a professor of in the department of geology and
geological engineering at the Colorado School of Mines, said it
has been known since the 1920s that pumping fluid underground can
cause seismic activity.
"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," Hitzman said. "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
The public, as evidenced by media reports in unconventional shale
gas fields, is often disturbed when even small-scale seismic
activity crops up in areas where earthquakes are not the norm.
In his testimony before the Senate, Hitzman said that of more than
35,000 hydraulically fractured shale gas wells in the U.S., only
one case has been suspected but not confirmed of causing felt
seismicity. Globally, one case was confirmed, "likely due to the
short duration of injection of fluids and the limited fluid
volumes used in a small spatial area" in fracturing operations.
Compared to other fluid injection activities examined by the
group, relatively little fluid is injected during hydraulic
"While the chemicals that comprise the fracturing fluid are
relatively benign, the flow-back water can be contaminated with
brine, metals and potentially dangerous chemicals picked up from
the shale and must be disposed of properly," said Mark Zoback,
professor of geophysics at Stanford University.
Geological challenges of waste disposal
The real risk of earthquakes, the report states, comes from the
injection of wastewater in disposal wells.
"The occurrence of induced seismicity associated with wastewater
disposal from natural gas production, in particular, has increased
significantly since the development of technologies to facilitate
production of gas from shale and tight sand formations," said
William Leith, senior science advisor for earthquake and geologic
hazards at the U.S. Geological Survey. "While there appears to be
little seismic hazard associated with the hydraulic fracturing
process that prepares the shale for production, the disposal of
waters produced with the gas does appear to be linked to increased
A few cases of induced activity from waste water disposal have
been recently documented.
"Although only a few induced seismic events have been linked to
these disposal wells, the occurrence of these events has generated
considerable public concern," Hitzman said. "Examination of these
cases suggests causal links between the injection zones and
previously unrecognized faults in the subsurface."
A part of the problem, Hitzman said, is that geological structure
where wastewater is to be injected is not as closely scrutinized
as similar activity such as enhanced oil recovery processes.
"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," Hitzman said.
Hitzman added presence of a geologic fault does not always mean
increased potential for seismic activity. He stressed that while
there have been documented cases of earthquakes from waste water
injection, the majority of disposal sites do not present such a
What he worries about, he said, is the unknown potential
consequences of increasing these injection activities.
Fossil fuel savior or earthquake generator?
Carbon dioxide emitters are increasingly pressured to reduce or
capture emissions. Many view carbon capture and storage as the
only hope for coal under increasingly progressive emissions caps.
The problem, the NAS study suggests, is that carbon capture and
storage could have potential to induce seismic activity.
"Carbon capture and storage may have the potential for inducing
seismic events, because significant volumes of fluids are injected
underground over long periods of time," the NAS stated.
Hitzman said that all of the current CCS projects involve small
injection amounts and do not provide a full study of the problem.
"CCS differs from other energy technologies in that it involves
continuous injection of carbon dioxide fluid at high rates under
pressure for long periods of time," Hitzman said. "It is purposely
intended for permanent storage – meaning that there is no fluid
Leith said there would be two major problems associated with CCS
technology and seismic activity.
"The first type of risk is due to the possibility of a large
magnitude earthquake that causes damage to structures in the
environs of the project," Leith said. "More importantly, there is
the possibility that an induced earthquake rupture would breach
the cap rock allowing the (carbon dioxide) to escape."
Zoback was particularly concerned about the geological and
atmospheric consequences of relying on carbon capture and storage
technology to reduce carbon dioxide emissions.
"Not only would large-scale CCS be an extremely costly endeavor,
there is a high probability that earthquakes will be triggered by
injection of the enormous volumes (carbon dioxide) associated with
large-scale CCS," Zoback said.
Zoback said triggering large earthquakes is not his principal
concern regarding carbon capture and storage. He said the large
faults necessary to produce large earthquakes would presumably be
detected and avoided during site selection.
"Our concern is that even small-to-moderate size earthquakes would
threaten the seal integrity of the formations being used to store
CO2 for long periods without leakage," Zoback said.
He said studies suggest a leak rate from underground CO2 storage
reservoirs of less than 1 percent per thousand years is required
for CCS to achieve the same benefits as switching to renewable
Zoback said due to limitations on suitable sites for CCS, he's
skeptical there is even enough capacity to store the levels of
carbon dioxide scientists hope to contain.
"In this context, it must be recognized that large-scale CCS will
be an extremely expensive and risky strategy for achieving
significant reductions in greenhouse gas emissions," Zoback said.
One solution for hydraulic fracturing operations is to recycle
fluid instead of injecting it into waste water fluid repositories.
Already, Zoback said, this is becoming increasingly common.
"This is a very welcome development," Zoback said. "Re-use of
flowback avoids potential problems associated with transport and
injection flowback water or the expense and difficulty of
extensive water treatment operations."
Hitzman said it would be imperative for multiple agencies and
institutions to work together in examining seismicity risks ahead
"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," Hitzman said. "Further research is required
to better understand and address the potential risks associated
with induced seismicity."