Study: Energy firms set off quakes miles from wells

Each day across the U.S., 2 billion gallons of fossil fuelindustry wastewater flies through thousands of underground tubes. The injection wells descend into porous rock, filling gaps with brine and chemicals and are the result of extracting oil and gas from the ground. The goal of the wells is for the wastewater to be out of sight, out of drinking water and out of harm’s way.

Except the wells can cause earthquakes. In some cases, the quakes begin as far as 15 miles from the wells. In a new study in the journal Science, scientists describe for the first time how earthquakes can be triggered so far away from the wells themselves. An efficient practice by the oil and gas industry is creating a ripple effect far beyond its drilling locations.

Geologists have linked injection wells to quakes based on years of observation. Humanmade earthquakes, though most are moderate in size, put 1 in 50 people in the U.S. at risk, according to a recent U.S. Geological Survey analysis. Wastewater injection wells are concentrated in Oklahoma, Texas, California and Kansas, according to the Environmental Protection Agency.

“Induced earthquakes are becoming more and more of an issue in central U.S. and the eastern U.S.,” said University of California at Santa Cruz seismologist Thomas Goebel. In 2011, an injection well in Oklahoma was responsible for a magnitude 5.6 earthquake, which damaged a highway, shook buildings and generated a dozen aftershocks.

To figure out how there could be such a distance between well and earthquake, Goebel, along with fellow University of California at Santa Cruz earthquake expert Emily Brodsky, sifted through quakes triggered by dozens of waste injection sites in several states as well as Australia and Europe.

Industrial techniques like hydraulic fracturing, or fracking, shove water underground to force oil and gas out of shale deposits. Most induced earthquakes are not a result of fracking itself but wastewater generated at the oil and gas wells. Some of that water can be reused or treated. The rest is buried in wells.

Earthquakes occur when a crack underground — a fault — pulls apart. A few decades ago, when scientists were beginning to understand that humans could generate earthquakes, the idea was “you put water directly into the fault,” said Brodsky.

The study authors were able to identify two types of earthquakes triggered by wastewater wells. One kind of earthquake formed close to the injection well, but stopped abruptly at about a half-mile from the site, Goebel said.

The other kind had a “very long-distance tail” — the quakes could appear far from the well, with the triggers petering out only after several miles. This occurred if a well dumped its wastewater into softer sedimentary rock.

But the new study suggests energy companies are injecting waste into the wrong place to avoid earthquakes.

MIT earth scientist Bradford Hager said this report convincingly described the two different ways humans trigger earthquakes, Still, he said, this kind of work is begging to find its way into “regulatory behaviors.”

Brodsky anticipates “there will be some resistance to this” research. “Multibillion dollar industries are, you know, not rapid to change,” she said.

Meanwhile, Goebel said, the scientists are running smallscale laboratory experiments to further examine how the earthquake triggering mechanism works.