Study finds correlation between seismic activity in North Texas, hydraulic fracturing

You Texans should pay attention. BBB

Aug. 06, 2012
Study finds correlation between seismic activity in North Texas, hydraulic fracturing
Asher Price | Austin American-Statesman

AUSTIN, Texas -- ]

Using newly available technology, a University of Texas seismologist tracking small earthquakes in the Barnett Shale play area of North Texas has found a correlation between geological disturbances and the sort of injection wells that are associated with hydraulic fracturing, according to research appearing this week in the journal Proceedings of the National Academy of Sciences.

Cliff Frohlich, associate director of UT's Institute for Geophysics, looked at quakes magnitude 3.0 or smaller December 2009 to August 2011. Earthquake seismologists have identified a relationship between certain human activity - the construction of massive lakes, for instance - and seismic activity since at least the 1940s.

"Occasionally, people say to me, 'It's impossible that humans can cause earthquakes,'" Frohlich told the American-Statesman. "In my community, that's long-established." Frohlich found that the most reliably located earthquakes - those accurate to within roughly a mile - occurred in eight groups, all within 2 miles of one or more of high-production injection wells.

In hydraulic fracturing, or fracking, millions of gallons of water, mixed with sand and chemicals, are injected into rock thousands of feet underground to extract natural gas. Frohlich said the most likely explanation for the quakes is that once injected, the fluids apply pressure to faults in the area and unstick them.

Imagine, Frohlich said, a slightly inclined air hockey table, with the power turned off. A puck placed on the table will slip until friction stops it. Power up the table, introduce air and the puck will begin to slide again.

"You can't prove any one of these (quakes) is related to injection," he said in an interview, but taken all together, there's a strong correlation.

Previously, the National Earthquake Information Center had identified only two earthquake groups in the area as strongly associated with specific injection wells. Frohlich said his research suggests injection-triggered earthquakes are far more common than is generally recognized.

"These small earthquakes aren't hurting anybody," Frohlich said. "People hear about a little earthquake and think you're going to have Haiti or Japan. It's like a storm: A magnitude 2.5 or 3 earthquake is fun. Maybe something falls off a shelf. It's just that Texans are not used to earthquakes." Only now, Frohlich said, new more sophisticated equipment has picked them up. "There's almost no history of earthquakes in Johnson County," he said. "But that's partly because of the instrumentation." Frohlich also found that many high-injection wells have no earthquakes nearby.

A National Academies of Science report published this year found that "hydraulic fracturing a well as presently implemented for shale gas recovery does not pose a high risk for inducing felt seismic events."

"Although only a very small fraction of injection and extraction activities at hundreds of thousands of energy development sites in the United States have induced seismicity at levels that are noticeable to the public, seismic events caused by or likely related to energy development have been measured and felt" in 13 states, including Texas, according to the report. These "induced seismic events" have not led to deaths or major damage.

Still, the report said: "Their effects have been felt locally, and they raise some concern about additional seismic activity and its consequences in areas where energy development is ongoing or planned." The prescription: "Further research is required."