Fracking is connected to the ongoing spike in Oklahoma earthquakes, but how the two are related hasn't been known exactly. Now researchers may have figured out the link.
Scientists at Stanford University have found that earthquakes near oil drilling operations are not caused by the drilling or fracking process itself, but by those operations' disposal of waste water in deep rock formations. (Tweet This)
"It is not caused by the hydraulic fracturing process at all," said Mark Zoback, a professor of geophysics at Stanford and the study's co-author. Zoback said quakes are being caused by "what they call 'produced water'—water that comes out of the ground with the oil and gas."
Drilling operations expose natural, brackish underground water that is mixed in with petroleum. It comes up with the drilled oil or gas, and is then injected back into the earth as waste.
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"What happened was, in the days before oil was $100 a barrel, when drillers found this underground water reserves along with the oil, they simply just shut down the well," Zoback told CNBC. "But when oil became expensive enough, it made sense to figure out how to separate the oil from the water."
The ground where drillers are working in Oklahoma has large amounts of this brackish water, and drillers have been separating it from the oil and gas reserves and then pumping the saltwater back into a deeper formation of rock known as the Arbuckle Group.
The waste water, in turn, is causing the faults in the formation to slip, which causes earthquakes. That waste water is separate from the water that drillers pump into the ground to push out oil and gas reserves, the study said.
The study was published Thursday in the journal Science Advances.
Oklahoma once averaged fewer than two earthquakes of magnitude 3.0 or greater each year, according to recent findings from the Oklahoma Geological Survey. In 2013, the OGS was observing two 3.0 or greater quakes per week, and that number increased further through 2014.
Now, roughly two earthquakes of magnitude 3.0 or greater occur each day.
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Most are strong enough to feel, but not intense enough to pose any real danger to people or property. However, much stronger earthquakes have occurred—notably a magnitude 5.7 quake that shook the town of Prague, Oklahoma in 2011.
The Stanford study said there's still a danger of a more severe earthquake occurring in the future.
"Basically I am really optimistic," Zoback said. "I think the scientists are making progress in understanding what is going on, they are making their findings known to regulators, and I think regulators will work with the oil and gas industry to figure out a solution."