The Enid News and Eagle, Enid, OK

Local and State News

July 3, 2014

Study finds that quakes tied to drilling

A new study explains how just four wells forcing massive amounts of drilling wastewater into the ground probably are shaking up Oklahoma.

Those wells seem to have triggered more than 100 small to medium earthquakes in the past five years, according to a study published Thursday by the journal Science. Many of the quakes were much farther away from the wells than expected.

Combined, those wells daily pour more than 5 million gallons of water a mile or two underground into rock formations, the study found. That buildup of fluid creates more pressure that “has to go somewhere,” said study lead author Cornell University seismologist Katie Keranen.

Researchers originally figured the water diffused through underground rocks slowly. But instead, it is moving faster and farther and triggers quake fault lines that already were likely ready to move, she said.

“You really don’t need to raise the pressure a great deal,” she added.

The study shows the likely way in which the pressure can trigger fault lines — which already existed yet were not too active— but researchers need more detail on the liquid injections themselves to absolutely prove the case, Keranen said.

The wastewater is leftover from unconventional wells that drill for oil and gas with help of high pressure liquids — nicknamed fracking — and from the removal of water from diluted oil. These new methods mean much more wastewater has to be discarded. While there are about 8,000 deep injection wells in the region, the amount of water injected at the four wells — named Chambers, Deep Throat, Flower Power and Sweetheart — has more than doubled since the drilling boom started about a decade ago.

From 1976 to 2007, Oklahoma each year averaged about one quake of magnitude 3 or more — strong enough to feel locally but too weak to cause damage. But from 2008 to 2013, the state averaged 44 earthquakes of that size every year. So far this year there have been another 233, Keranen said, getting her earthquake figures from the U.S. Geological Survey database.

Northwest Oklahoma has seen an increase in the number of earthquakes felt, along with the rest of the state. Four earthquakes were recorded Tuesday between Enid and Medford. The largest measured magnitude 3.3. A magnitude 3.0 was recorded Thursday three miles east of Cherokee.

The rattling has led some Oklahomans to push for restrictions on the use of injection wells.

A previous study said the largest earthquake in recorded Oklahoma history may have been human-induced.

Researchers with U.S. Geological Survey said in March the magnitude 5.7 earthquake of Nov. 6, 2011, which was felt in Enid, may have been triggered by wastewater injection. If that is true, it would be the largest human-caused earthquake associated with wastewater injection. The quake’s epicenter was 21 miles north-northeast of Shawnee at a depth of about 1.7 miles.

The quake damaged 14 homes, injured two people and buckled a highway.

According to the USGS study, researchers said a human-induced magnitude 5.0 earthquake near Prague on Nov. 5, 2011, may have triggered the larger earthquake the next day. That earthquake occurred near an active wastewater disposal well.

While past research has shown more quakes in Oklahoma, Texas, Arkansas and Kansas and correlated it statistically to injection wells, the latest study used computer simulations to identify the mechanism of how massive amounts of water travel as much as 20 miles from the well. The pressure then triggers existing small faults — or previously unknown ones. In the past, scientists thought wells could only jump-start quakes within three miles or so.

Austin Holland, a seismologist at the Oklahoma Geological Survey said Keranen’s study confirms what he is seeing in the field and will help better understand what’s happening in Oklahoma.

“It’s a study that needed to be done,” said U.S. Geological Survey seismologist Elizabeth Cochran. “That changes how we might look at the hazard for a particular well.”

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