Scientists have linked Oklahoma’s biggest recorded earthquake to the disposal of wastewater from oil production, adding to evidence that may lead to greater regulation of hydraulic fracturing for oil and gas.
The 5.7-magnitude quake in 2011 followed an 11-fold bump in seismic activity across the central U.S. in recent years as disposal wells are created to handle increases in wastewater from hydraulic fracturing, or fracking.
Researchers at the University of Oklahoma, Columbia University and the U.S. Geological Survey, who published their findings yesterday in the journal Geology, said the results point to the long-term risks the thousands of wells pose and shows a need for better monitoring and government oversight.
“There’s not a magic bullet,” Heather Savage, assistant research director at the Lamont-Doherty Earth Observatory at Columbia University, said in an interview. “But if we have more monitoring capabilities, we can watch these things, and catch all the precursor events.”
The earthquake near Prague, Oklahoma, on Nov. 6, 2011, was the state’s biggest and may be the largest linked to the injection of water from drilling process, the researchers reported. The state’s geological office disagreed, and said it was likely “the result of natural causes.” The temblor destroyed 14 homes, damaged other buildings, injured two people and buckled pavement, according to the report.
The wastewater behind the earthquakes came from conventional wells in the Hunton formation, said Katie Keranen, assistant professor at Oklahoma and co-author of the report. The findings are a cautionary note for disposal of the millions of gallons of fluids from hydraulic fracturing, she said.
“It has little to do with where the water comes from,” Keranen said in an interview. “What really matters is how you’re getting rid of the water.”
A spate of earthquakes in the central U.S. in recent years is “almost certainly” man-made, and may be connected with wastewater disposal, U.S. Geological Survey researchers said a year ago. For the three decades until 2000, seismic events in the nation’s midsection averaged 21 a year. They jumped to 50 in 2009, 87 in 2010 and 134 in 2011.
Concerns over earthquakes prompted the U.K. to temporarily halt fracking. The ban ended late last year when the government adopted standards, including a rule that would suspend operations when unusual seismic activity is detected.
Those same worries in the U.S. have the oil and gas industry hunting for alternatives for wastewater disposal.
“It’s an important issue that is going to become a public policy issue,” Benjamin Salisbury, a senior energy policy analyst at FBR Capital Markets Corp. in Arlington, Virginia, said in an interview. “I wouldn’t expect this to be a turning point that would slow development.”
“I don’t know anybody who says that underground injection is the future of this industry,” he said. “We are going to wastewater treatment and recycling for a plethora of reasons.”
In fracking, water, sand and chemicals are injected into deep shale formations to split underground rock and free trapped gas. Much of that water comes back to the surface for disposal. Wastewater is also produced from conventional oil wells to boost production.
Fluids from conventional oil extraction in Oklahoma had been pumped into abandoned wells for 17 years before the quake, according to the study. In 2006, pressure in the underground holding areas escalated quickly, as they began to fill, Savage said.
A series of earthquakes occurred over three days near Prague, with the 5.7-magnitude temblor triggered by the initial earthquake, not the injection of drilling wastewater, according to Keranen.
Prague is between Oklahoma’s two largest cities, 50 miles east of Oklahoma City and 65 miles southwest of Tulsa.
That “cascading series of tremors” shows “the risk of humans inducing large earthquakes from even small injection activities is probably higher” than thought, Geoffrey Abers, a co-author from the Lamont-Doherty Earth Observatory at Columbia, said in a statement.
The Oklahoma Geological Survey maintains the “interpretation that best fits current data” is that the earthquakes in 2011 were naturally occurring, according to an agency statement. The U.S. Environmental Protection Agency has recently participated in studies of the pressure of the disposal reservoirs in the state, it said.
``We have not had a chance to review this study so we can't comment on its findings,'' said Dan Whitten, a spokesman for the natural gas group, who also noted the geological survey's conclusion most of the quakes were naturally occurring.
``There have been a handful of cases that may be tied to wastewater disposal out of the 150,000 disposal injection wells operating in this country, and our member companies have worked constructively with state regulators who have looked into this issue,'' Whitten said.