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Efforts To Curb Earthquakes Triggered By Injection Studied
January 23, 2018

In a new study, Virginia Tech researchers have found that efforts to curb earthquakes triggered by the injection of oilfield wastewater into the ground in Oklahoma are not targeting the most dangerous tremblers, and that a larger reduction in injection volumes is needed.

Ryan Pollyea at his Computational Geofluids Laboratory. On the screen in background is a map of Oklahoma, with clusters of earthquake events displayed. Credit: Virginia Tech.

Prior to 2011, Oklahoma averaged one magnitude 3-plus earthquake per year, but in 2015 there were more than 900 such earthquakes, making Oklahoma the most seismically active state in the mainland United States. Increased seismic activity has occurred simultaneously with the increased retrieval of unconventional oil and gas, which uses hydrofracturing, commonly referred to as fracking, to unlock previously inaccessible oil and gas resources.

This rapid proliferation of unconventional oil and gas recovery has also resulted in millions of gallons of highly brackish wastewater, which comes up with the retrieved oil and gas. To dispose of this wastewater, the liquid is re-injected into geologic formations deep underground.

Such wastewater injections have been taking place for decades, but the rapid increase in oil and gas production via fracking means substantially more oilfield wastewater is now being re-injected. In Oklahoma, the injections triggering earthquakes are taking place in the Arbuckle formation, a deep and highly porous sedimentary rock layer.

The new study shows that locations that experienced earthquakes are tied in proximity and timeliness to mass waste water injection sites. Further, the study indicates that tracking annual data on the injection well locations can help predict how corresponding earthquake activity will change. This new finding builds on previous studies showing that earthquake activity increases when wastewater injections increase.

“Our results show that average annual injection well locations are a predictor of increasing earthquake activity,” said Ryan M. Pollyea, an assistant professor in the Virginia Tech College of Science, and director of the Computational Geofluids Laboratory, who spearheaded the study, published online in the journal “Geology”.

“When we compared the spatial correlation using datasets that include only magnitude 3-plus earthquakes, there was no change,” said Pollyea, adding that a larger reduction in wastewater injection volumes is needed to reduce the dangers of large magnitude earthquakes.

Pollyea and his team caution that while earthquakes cannot be predicted, the study indicates that geologists can test hypothetical wastewater injection scenarios before wells come online to estimate potential impact on earthquake activity.

The new study is part of a larger effort that Pollyea and his collaborators are pursuing to study fluid-triggered earthquakes and wastewater injection volume and their relation to population centers in Oklahoma, building codes, policy decisions, and industry regulations.

Funding for the study came from the Virginia Tech Department of Geosciences, the Georgia Tech Department of Civil and Environmental Engineering, and the National Science Foundation.

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