Here’s Why Oklahoma May Be Having So Many Earthquakes
Turns out pumping millions of gallons of salty wastewater from oil wells deep into the bowels of the Earth can give Oklahoma the shakes.
Scientists have long suspected a link between the spate of earthquakes that have made Oklahoma the most seismically active state in the US this year and the boom in oil drilling on the prairies. Now, researchers at California’s Stanford University say they’ve figured out how it happens.
“We think we understand the physical mechanism. We think we understand the relationship in space and time between the earthquakes and the wells, and we’re trying to provide that information to the interested parties — to the companies and the regulators,” Stanford geophysicist Rall Walsh told VICE News.
A new study by Walsh and Stanford Professor Mark Zoback looked at quakes northwest of Oklahoma City, around the towns of Jones, Perry, and Cherokee — the state’s current seismic hot spot. Sucking petroleum out of the surrounding prairie brings up as much as 10 gallons of brackish water for every gallon of oil retrieved, and that water is separated out and pumped thousands of feet underground into a sedimentary rock layer known as the Arbuckle Formation, Walsh said.
The additional water — about 400 million barrels a year in 2013, according to the study — adds to the pressure on faults beneath the Arbuckle. And when the pressure gets high enough, the faults slip, setting off an earthquake that’s often centered far from any well, Walsh said.
“What you have is an area 40 or 50 miles on a side, with hundreds of wells in it and hundreds of earthquakes in it,” he said. “And often, the earthquake isn’t going to be under the well. It’ll be where the fault is, which is not necessarily where the well is.”
More than two-dozen temblors over magnitude 2.5 have hit Oklahoma in the past week, including a 4.0 that rocked the town of Perry on Wednesday. Walsh and Zoback recommended that drillers stop injecting wastewater into the Arbuckle Formation and instead pump it into other oil-rich formations, where the additional pressure can make wells more productive. But Walsh said even if the practice stopped tomorrow, it could take months or years for the earthquakes to subside.
“In the meantime, Oklahomans shouldn’t keep heavy things in high places,” he said.
The study was published Thursday in the peer-reviewed journal Science Advances. Dan McNamara, a research geophysicist at the National Earthquake Information Center in Colorado, called it “the most comprehensive study so far” of the issue.
McNamara told VICE News that drilling-related earthquakes aren’t unique to Oklahoma. But other states that have seen heavy oil and gas drilling in the recent years don’t have as many faults, “so you just don’t get as many.” And the faults beneath Oklahoma are oriented in such a way that they are more susceptible to slipping, making a quake more likely.
“The small earthquakes aren’t that big of a deal,” said McNamara, who has published other studies on the question. But a larger quake, in the magnitude five to six range, “could cause damage to sensitive areas like Cushing or Oklahoma City, where you have people and infrastructure. This study is a good step toward identifying and mitigating problems.”
The Independent Petroleum Association of America, through its website Energy in Depth, raised questions about the Stanford study Thursday afternoon. It argued that wastewater volumes were far higher in the 1980s without producing the seismic effects seen in recent years, and that other parts of the state with high-volume injection wells haven’t seen the same kind of quakes.
“Everyone can agree that no matter what is causing the spike of seismic activity in Oklahoma over the past five years, it’s an issue that all parties want to see addressed,” the website stated. It called the new study “a significant contribution to scientific knowledge,” but said the focus on wastewater volumes “does raise a number of questions to consider.”
McNamara said he expected government and industry figures to cast doubt on the findings.
“But I would challenge the industry at this point to come with an alternative theory,” he told VICE News. “There’s no other published study that shows any other mechanism.”