Wastewater from oil and natural gas drilling that’s pumped underground for disposal is more likely to trigger earthquakes than extracting the fuel by fracking, according to a new study.
The salty byproduct of hydraulic fracturing is often injected back underground where it penetrates fault lines and triggers seismic activity, said Mark Zoback, a geophysics professor at Stanford University and lead author of the study Thursday in the journal Science Advances. Fracking, in which fluids are forced underground to shatter rock and release oil and gas, presents a much lower risk, he said.
The issue has gained attention in Oklahoma where a drilling boom has coincided with a surge in earthquakes measuring 3.0 or higher on the Richter scale. About 10 barrels of water are produced for every barrel of oil in Oklahoma where there were two dozen magnitude-4 earthquakes last year compared with one or two a decade prior to 2008, according to the study.
“It’s really important to dispel this notion that all of these earthquakes, which may be associated with the oil and gas industry, are due to fracking,” Zoback said in a telephone interview. Data from the study will benefit policy makers and drillers working to improve methods of water disposal, he said.
In March, state seismologist Austin Holland told Bloomberg News that Oklahoma was on pace to have 875 earthquakes this year of at least 3.0 in magnitude after experiencing only 62 from 1974-2009. Holland did not reply to phone or e-mail messages seeking comment on the study.
Bill Ellsworth, a U.S. Geological Survey researcher, said in April that wastewater injection “is undoubtedly responsible for the majority of these earthquakes.”
Oklahoma’s biggest recorded earthquake, a 5.7-magnitude temblor near Prague, Oklahoma, on Nov. 6, 2011, was linked to wastewater wells by researchers from the University of Oklahoma, Columbia University and the U.S. Geological Survey. The state’s geological office initially said the connection was inconclusive.
On April 21, the state-run Oklahoma Geological Survey issued a statement declaring that the oil and gas industry is “very likely” contributing to the huge rise in earthquakes in Oklahoma.
The Oklahoma Corporation Commission, which regulates drilling in the state, is taking a closer look at about 350 wells to ensure injections don’t trigger earthquakes, Matt Skinner, a spokesman for the agency, said in a telephone interview.
“This is a constantly evolving thing,” Skinner said. “Obviously, we hope for a reduction in seismicity. There’s new data every day.”
The risk of earthquakes increases when drilling wastewater injected back into rock formations seeps down to the fault line, exacerbating plate movement, Zoback said.
“The water flows very easily, spreads out, penetrates basement faults and triggers seismicity,” Zoback said. “When you’re hydraulically fracturing you’re only pressurizing a limited volume of rock for a relatively short period of time. A typical frack stage lasts a couple hours, whereas injection can go on for years or even decades.”
For more, read this QuickTake: Fracking