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Who's at fault? High injection rates add pressure to Oklahoma's basement rock

From the ENE ongoing investigation: Who's at fault? series
  • 3 min to read

EDITOR’S NOTE: This is the second installment of a six-part series on earthquakes. The third installment of this earthquake series runs Sunday, Sept. 20, 2015.


ENID, Okla. — How much water can you put in a balloon before it pops? And, if the balloon has a hole, how quickly can you put the water in the balloon in before it pops?

That’s how new Oklahoma Geological Survey Director Jeremy Boak describes the current wastewater injection well and earthquake issue: How much and how fast can operators inject wastewater before it causes an earthquake?

‘Like a slowly leaking balloon’

Wastewater injection wells are not a new thing to Oklahoma.

Oklahoma Corporation Commission spokesman Matt Skinner said there are about 4,500 disposal wells in Oklahoma, but only 3,200 are operating at any given time.

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“We have been disposing of wastewater for decades,” said Boak, adding the increase in recent years is due to more produced water coming up with oil and gas. “The technology has evolved that we can produce more oil and gas, but we have to dispose of more water.” 

Bill Ellsworth, a geologist with the U.S. Geological Survey, said an oil drilling operation always includes a mixture of oil and water.

“Any time you’re getting oil, you don’t get pure oil,” he said. “Even in conventional oil fields, you might be five barrels of water and one barrel of oil. This isn’t new.”

The spike in produced water levels started about 10 years ago, Ellsworth said.

“A number of very clever oil men figured out there was oil to be had in formations, rocks, that had never been considered economical to obtain before,” he said. “The oil is distributed through rock with lots of water. With horizontal drilling and big pumps, it’s possible to suck everything out of these formations. You get lots of water and less oil, so you have a huge wastewater issue.”

With more wastewater, companies needed to figure out where to put it; they couldn’t re-inject it into the same formation, a former practice that would help push oil to the surface, so they decided to inject it into formations below the oil fields, he said. 

In Oklahoma, the most popular injection formation is the Arbuckle, the deepest rock formation above the crystalline basement, he said.

About 950 injection wells go into the Arbuckle formation, Skinner said.

Before the increase in wastewater production, injecting into the Arbuckle formation didn’t raise any concerns, Ellsworth said. But after a magnitude 5.6 earthquake — the largest recorded in state history — hit Prague in November 2011, things changed: Injecting high amounts of wastewater at high pressures caused problems.

“Volumes went up and rates went up,” said Todd Halihan, a geology professor at Oklahoma State University’s Boone Pickens School of Geology. “We went above rates that have caused earthquakes in other places.”

The high rates of injection have added water pressure in the Arbuckle and crystalline basement, which affects the pressure that holds fault lines together, Ellsworth said.

“That pressure can bleed into the basement, where it may encounter faults and that can be enough to tip the pressure over the edge,” he said.

The issue, Boak said, is to find the medium between injecting enough wastewater to dispose of it in an economical and timely manner, but not enough to cause an earthquake.

“It’s like a slowly leaking balloon,” he said. “Don’t exceed the volume that it can leak.”

‘Bad stuff to have on the surface’

Hydraulic fracturing wastewater is a combination of two water sources: injected water and produced water.

Injected water contains sand and chemicals, such as guar gum and hydrochloric acid, to break up rock formations that hold the oil and gas.

Produced water is old seawater that has been mixed in with the oil and gas in the rock formations, making a salty brine that comes up with the oil and gas.

“About 5 percent of the total water is actually frack water,” Boak said. “It’s a relatively small amount of water. Most of the water that comes back up was already there.”

It’s difficult and expensive to treat wastewater to a reusable state, so it has to go somewhere, Boak said; the least expensive answer is to put it back into the ground.

Wastewater injection wells are drilled deeper than the rock formations, which hold the oil, gas and wastewater, and groundwater aquifers, down to rock formations that allow the injected wastewater to distribute without the risk of contaminating groundwater or farmland.

“The real issue is, how well was that well drilled?” Boak said. “You have to drill down through the aquifers, and part of the process is showing you aren’t contaminating groundwater. But not everything works perfectly, and there are penalties that go along (with) failing.”

Other states like Colorado and Wyoming use evaporation pits to dispose of wastewater, Boak said.

Oklahoma Corporation Commission banned the use of evaporation pits for wastewater disposal, Skinner said, to protect groundwater sources.

“Our primary mandate has always been water protection,” Skinner said in reference to wastewater disposal. “We don’t want it on the surface. It’s bad stuff to have on the surface.”


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