Rattle and Hmm: Oil Mining Triggering Quakes in Oklahoma, Study Finds

Wastewater injection is causing stronger and more frequent “ruptures” across the eastern and central swathes of the state, a research team says.

Chad Devereaux clears bricks that fell from his in-laws' home in Sparks, Okla., following two earthquakes in November 2011. More than 500 earthquakes have shaken Oklahoma since 2009.

Chad Devereaux clears bricks that fell from his in-laws' home in Sparks, Okla., following two earthquakes in November 2011. More than 500 earthquakes have shaken Oklahoma since 2009.

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It’s the shakiest state in the nation, and now we know why.

Wastewater injection, a critical part of the Oklahoma oil boom, is behind the state’s dramatic surge in earthquakes since 2009, a new study finds.

The number of earthquakes in Oklahoma has dramatically increased since 2009.
The number of earthquakes in Oklahoma has dramatically increased since 2009.

What’s more, for earthquakes that have rattled parts of eastern and central Oklahoma, four high-volume wells may be the main culprits: “Flower Power,” “Deep Throat,” “Chambers,” and “Sweetheart” – all owned by a single Tulsa-based energy firm – may have triggered as many as 20 percent of the two regions' recent earthquakes, the study found. And if those four wells keep pumping unabated, the consequences could prove dire for years to come, experts warn.

“The number of earthquakes is growing, the area affected by the earthquakes is growing, and it’s a very different process than other earthquakes,” says Katie Keranen, the study’s lead author and a geophysics and seismology professor at Cornell University.

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Much of Oklahoma’s oil is mixed with water underground. To draw it out, energy companies pump the blend from the ground, extract the oil, then inject the leftover fluid – the “wastewater,” a kind of salty “brine” as Kernanen described it – back into the ground.

Since this process – along with hydraulic fracturing – ramped up in Oklahoma five years ago, more than 500 earthquakes have rattled the state – over 230 quakes in the past seven months alone. Before then, from 1978 to 2008, there were fewer than three quakes a year.

Researchers have long speculated whether and how fracking and wastewater injection have been triggering the quakes. Keranen’s study, harnessing 3-D computer modeling to examine dozens of wells, has apparently proven a connection – and also gone so far as to show that quakes can be set off much farther from an injection site than previously thought.

Here’s why: The ground beneath Oklahoma is permeable. As water is pumped back underground, it spreads through nooks and crannies and puts pressure on the porous surfaces of rocks – something known as “pore pressure.”

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The pore pressure acts like a wave, moving across rock as water is pumped underground, gradually subsiding as it spreads farther from the injection site. Previously, scientists believed that the pressure was only strong enough to set off an earthquake within a 5-kilometer radius. Keranen, however, found that it could happen as far as 30 kilometers away – especially with a well pumping water at high volumes.

Workers hose fluid into a holding tank, at right, at a Texas well site in June 2014. More and more earthquakes have been rumbling across parts of Oklahoma and Texas, where wastewater injection and other oil well operations are occurring.
Workers hose fluid into a holding tank, at right, at a Texas well site in June 2014. More and more earthquakes have been rumbling across parts of Oklahoma and Texas, where wastewater injection and other oil well operations are occurring.

Whereas most wells in Oklahoma inject about 400,000 to 500,000 barrels of water a month, Keranen says, the wells Flower Power, Deep Throat, Chambers and Sweetheart operate at closer to 1.5 to 2 million barrels.

They’re near an area known as the Jones swarm – a large web of faults near the town of Jones in eastern Oklahoma, population 2,800. As the wells have pumped away, the earthquakes have continued and the swarm has expanded.

“This swarm keeps getting bigger and bigger, and as it gets bigger, the size of the earthquake depends on the faults available to rupture,” Keranen says. “I’m particularly worried about the prospect of larger quakes. As we’ve seen more and more smaller quakes, there’s a greater risk of larger quakes.”

New Dominion LLC, which owns the four wells, disputed the study’s findings – and pointed to potential legal action.

“While New Dominion has not had adequate time to thoroughly review the paper, an initial review reflects it is premised on certain false assumptions,” the firm said in a release. “The company notes the author did not consult with NDL’s geologist and engineers to determine whether her premises are in any way correct. At best, these incorrect assumptions are irresponsible. NDL will make no additional statements while it consults legal counsel on this issue.”

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Asked what exactly was inaccurate in the seven-page report, media resources manager Jack Money says he “can’t provide any additional information beyond what the release says.”

A map shows earthquake activity in Oklahoma from 1882 to 2013. Earthquakes that have shaken Oklahoma communities in recent months have damaged homes, alarmed residents and prompted lawmakers and regulators to investigate what's behind the temblors — and what can be done to stop them.
A map shows earthquake activity in Oklahoma from 1882 to 2013.

Keranen has avoided making any policy prescriptions. 

“I wouldn’t be so bold to say everybody should operate below this level, but we see people operating at around 400,000 to 500,000 barrels, and they are operating probably pretty benignly,” she says.

Instead, she plans to focus her attention now on predicting tremors, "signs we can see to predict at an earlier stage if the swarms will be active," she describes.

She also plans to discuss the study's results with the Oklahoma Corporation Commission, which oversees energy production in the state.
 
"We are carefully going over it," commission spokesman Matt Skinner says of the study. "That’s about all we can say. This is a large study, it heads into new territory and it deserves careful attention."

The paper was published Thursday in the journal Science.