Oklahoma's Fracking Wells Behind the Spate of Earthquakes
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Scientists have, for the first time, linked hundreds of earthquakes across a broad swath of Oklahoma to a handful of wastewater wells used by the fracking industry.
The research, published in the journal Science on Thursday, said about one-fifth of the quakes that helped turn Oklahoma into the earthquake capital of America were caused by just four wells.
Oklahoma has had about 240 magnitude 3.0 or higher earthquakes just since the start of the year. The state now has twice the number of 3.0 earthquakes as California.
Before 2008, when the oil and gas boom got underway, the state averaged about one a year.
The researchers from Cornell University and other institutions traced a large number of earthquakes through 2012 to just four wells, south-east of Oklahoma city.
Those wells were pumped with significantly higher volumes of fracking wastewater and chemicals than the thousands of other disposal wells in the state.
The findings were the first to show such waste wells can trigger earthquakes up to 40kms away from the injection site.
They are bound to further deepen the controversy surrounding fracking, which has vastly expanded America's oil and natural gas production, but with rising consequences for health, safety and the environment.
Another Cornell-led team this week found that 40% of the fracked wells in north-eastern Pennsylvania were at risk of leaking methane into groundwater and air.
The researchers said faulty cement casings could be responsible.
In Thursday's study, researchers found a suite of wells around Oklahoma city, which collectively were pumped with nearly 5m barrels a month of waste, caused the swarm of earthquakes.
“These really big wells have the biggest impacts on the system,” said Geoffrey Abers, a professor at Columbia University's Lamont-Doherty Earth Observatory, and one of the authors of the study.
The biggest of the disposal wells was pumped with up to 1.6m barrels a month of fracking waste.
“The earthquakes themselves seem to occur on small discrete faults. As the pressure builds up in the sedimentary formation that they are pumped into ... They put that fault over the edge by jacking up the pore pressure.”
He ruled out a natural explanation for the spike in earthquakes. “This many earthquakes over and over again is not really something we have seen in a natural system,” he said.
Instead, the researchers found the earthquakes over the last five years were triggered by a relatively small number of the thousands of injection wells drilled across the state to dispose of the mix of water and chemicals used by drillers to flush oil and gas from layers of rock.
The researchers said the four Oklahoma city wells raised underground pressures, triggering a swarm of earthquakes across nearly 2,000 square kilometres.
In some instances, the earthquakes were more than 30km from the disposal site – much farther than researchers had expected.
The first earthquakes known to be caused by a fracking waste disposal well, occurred in Youngstown, Ohio. Scientists registered at least 109 earthquakes after the injection well came into operation in December 2010 until it was shut down a year later, following an earthquake that registered a magnitude of 3.9.
Those earthquakes were localised, however, the researched noted.
In their study, earthquakes travelled great distances from the disposal sites. There was also a time lag.“This is a situation where the pumping starts months or a couple of years before the earthquakes are observed at all,” Abers said.