Earlier this year a study linked Oklahoma’s largest earthquake to disposal wells. And now a new study, released yesterday, suggests the increase Oklahoma has seen in earthquakes is linked to oil and gas disposal wells. The study was done by U.S. Geological Survey geophysicist, William Ellsworth.
The study states that microearthquakes (those below magnitude 2) are routinely produced as part of the hydraulic fracturing (“fracking”) process. However, the current process appears to pose a low risk of inducing destructive earthquakes, with the largest induced earthquake being magnitude 3.6, too small to pose a serious risk. Disposal wells are a different story.
“Yet, wastewater disposal by injection into deep wells poses a higher risk, because this practice can induce larger earthquakes. For example, several of the largest earthquakes in the U.S. midcontinent in 2011 and 2012 may have been triggered by nearby disposal wells. The largest of these was a magnitude 5.6 event in central Oklahoma that destroyed 14 homes and injured two people.”
Nicholas van der Elst of Columbia’s Lamont-Doherty Earth Observatory in Palisades, New York, who led another study on earthquakes and disposal wells, had this to says,
“The fluids (in wastewater injection wells) are driving the faults to their tipping point.”
The new study by Ellsworth states that only a small fraction of the more than 30,000 disposal wells appear to be problematic. The wells that dispose very large volumes of wastewater and/or communicate pressure perturbations directly into the basement faults, appear to the the problematic wells.
Nicholas van der Elst’s study found that distant earthquakes can trigger earthquakes at disposal wells.
“The 2010 magnitude 8.8 Chile quake, which killed more than 500 people, sent surface waves rippling across the planet, triggering a magnitude 4.1 quake near Prague 16 hours later, the study says. The activity near Prague continued until the magnitude 5.7 quake on Nov. 6, 2011 that destroyed 14 homes and injured two people. A study earlier this year led by seismologist Katie Keranen, also a coauthor of the new study, now at Cornell University, found that the first rupture occurred less than 650 feet away from active injection wells. In April 2012, a magnitude 8.6 earthquake off Sumatra triggered another swarm of earthquakes in the same place. The pumping of fluid into the field continues to this day, along with a pattern of small quakes.”
The same Chile quake also set off an earthquake swarm on the Colorado-New Mexico border, near wells where wastewater used to extract methane from coal beds had been injected. The study also found that Japan’s devastating magnitude 9.0 earthquake in 2011 trigged an earthquake swarm in west Texas.
“The idea that seismic activity can be triggered by separate earthquakes taking place faraway was once controversial. One of the first cases to be documented was the magnitude 7.3 earthquake that shook California’s Mojave Desert in 1992, near the town of Landers, setting off a series of distant events in regions with active hot springs, geysers and volcanic vents. The largest was a magnitude 5.6 quake beneath Little Skull Mountain in southern Nevada, 150 miles away; the farthest, a series of tiny earthquakes north of Yellowstone caldera, according to a 1993 study in Science led by USGS geophysicist David Hill.”
Earthquakes are not the only concern with disposal wells, the U.S. Environmental Protection Agency is currently conducting a study of the effects of fracking, particularly the disposal of wastewater. This study could be the basis of new regulations on oil and gas drilling.
Proponents of fracking reacted to the study saying,
“More fact-based research … aimed at further reducing the very rare occurrence of seismicity associated with underground injection wells is welcomed, and will certainly help enable more responsible natural gas development,” said Kathryn Klaber, chief executive of the Marcellus Shale Coalition.
Studies on fracking, disposal wells, and their ability to cause earthquakes will likely be ongoing. It has been hard for researchers to get all of the data they need to do the research and still need to do more. However, evidence is mounting.
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Map Credit: U.S. Geological Survey
Department of the Interior/USGS