Hydraulic fracturing, not just wastewater injection wells, has likely caused small earthquakes in Oklahoma, a research scientist with the state said Wednesday.
Austin Holland, speaking at the American Geophysical Union annual meeting in San Francisco, said his studies suggest that about 2 percent of the oil and gas wells hydraulically fractured in that state in the past 21/2 years were followed within 21 days by a quake within about five miles of the well.While some likely were coincidental, not all were, said Holland, of the Oklahoma Geological Survey.Holland's finding of quakes triggered by hydraulic fracturing itself -- the technique that pumps water, sand and chemicals at high pressure to fracture rock and release oil and gas -- goes beyond the more common conclusion that high-volume injection wells are the most likely culprits of increased earthquakes in areas with oil and gas development. Injection wells continually pump fluid into deep formations below oil and gas-producing layers, while fracturing, or "fracking," is a process that lasts only several days.He spoke at a session focused on the likelihood of quakes being induced by oil and gas activities.Fellow panelists Art McGarr, of the Earthquake Science Center at the U.S. Geological Survey, and Cliff Frohlich, associate director of the Institute for Geophysics at the University of Texas at Austin, both said injection wells, rather than fracturing, can likely trigger quakes. McGarr said that the size of quakes seems related to the volume of fluid injected.Ed Ireland, director of the Barnett Shale Energy Education Council, an industry group, said he hasn't seen Holland's research but said, "It's interesting because it would be contrary to everything that's come along so far that I'm aware of." Ireland said injection wells have garnered the most attention, "and even then it would have to be located directly over a fault."Quakes have become more frequent in Oklahoma, mostly in the center of the state, which has a history of seismic activity, Holland said. That included a 5.7-magnitude quake in November 2011, the largest in the state's history. He did not attribute that quake to oil and gas activity.But other areas of the state with a long history of oil and gas activity haven't seen an increase in earthquakes, he said. The largest quake Holland said he could connect with hydraulic fracturing registered magnitude 2.9, barely enough to be felt. Most were less than a 2. The average time between a quake and hydraulic fracturing was 11 days.Frohlich said he has not seen a connection between fracturing and earthquakes in his studies. But longtime production of oil and gas possibly can produce quakes, and so can injection wells, he said."It's almost impossible to say with certainty an earthquake is manmade," he said. "But statistically, you can say injection wells have caused earthquakes," although there are many injection wells in areas that haven't had earthquakes, he said.Frohlich, who showed a map with clusters of small quakes around high-volume injection wells in Denton, Northeast Tarrant and Johnson counties, said there is no evidence that small quakes can build into a large one.Jim Fuquay, 817-390-7552Twitter: @jimfuquayHave more to add? News tip? Tell us
