The large-scale injection of wastewater from oil and gas production sites into a handful of disposal wells buried deep underground is the likely cause for a dramatic increase in the number of earthquakes in central Oklahoma since 2009, according to a new study published in the journal Science on Thursday.
The study said that the injection of wastewater -- a byproduct of the process of hydraulic fracturing, also known as fracking, which uses a pressurized liquid to free oil trapped in underground rocks -- into the ground causes fluid pressure underneath the surface to rise enough to produce tremors of magnitude 3 or higher.
“The area of increased pressure related to these wells continually expands, increasing the probability of encountering a larger fault and thus increasing the risk of triggering a higher-magnitude earthquake,” the researchers said, in a statement.
And, while the study found that areas of Oklahoma with a high rate of wastewater disposal constitute nearly half of all seismic activities in the central and eastern U.S. between 2008 and 2013, it stopped short of directly linking fracking to an increase in earthquake activity.
“Induced seismicity is one of the primary challenges for expanded shale gas and unconventional hydrocarbon development. Our results… suggest that adherence to standard best practices may substantially reduce the risk of inducing seismicity,” Katie Keranen, a professor of geophysics at Cornell University in Ithaca, New York, and the study’s lead author, said in the statement.
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“The best practices include avoiding wastewater disposal near major faults and the use of appropriate monitoring and mitigation strategies.”
Four Oklahoma wells with the greatest volume of wastewater disposal could have triggered 20 percent of recent earthquakes in the central U.S. among a swarm of smaller quakes covering nearly 2,000 square kilometers (772.2 square miles), the study said, adding that the disposal wells could be responsible for quakes up to nearly 22 miles away.
According to a report from the U.S. Geological Survey, nearly 450 earthquakes of magnitude 3 and larger occurred in the central and eastern parts of the U.S. between 2010 and 2013, and at some locations, the increase in the frequency of earthquakes coincided with the injection of wastewater into deep disposal wells.
The researchers said that the latest results from Oklahoma, where the rate of magnitude 3 earthquakes is now double that of California, are relevant for better understanding earthquakes caused by a change in fluid pressure and the rapid transmission of wastewater across great distances beneath the surface.
“Earthquake and subsurface pressure monitoring should be routinely conducted in regions of wastewater disposal and all data from those should be publicly accessible,” Keranen said. “In many states the data are more difficult to obtain than for Oklahoma; databases should be standardized nationally.”