A recent study from Cornell University has determined that pumping wastewater from natural gas drilling sites into wells buried deep underground is probably why Oklahoma is experiencing more small earthquakes than California. The study says hydraulic fracturing for gas cannot be directly linked to increased seismic activity, but the injection of wastewater from drilling at disposal sites creates fluid pressure below the surface that can trigger earthquakes. The lead author of the study is Katie Keranen, an assistant professor of seismology at Corfnell University in New York.
The research, published Thursday in the journal Science, underscores earlier findings by the U.S. Geological Survey and agencies that study seismic activity in several states. State geologists have suspended or halted wastewater injection in several states, including Colorado and Ohio, after earthquakes rocked areas near wells.
Hydraulic fracturing, known as fracking, is a process in which high-pressure blasts of water mixed with a chemicals are injected into wells to fracture rock and unlock trapped natural gas. The practice creates millions of gallons of wastewater. Some fracking wastewater is trucked away, and some is pumped into disposal wells drilled into porous rock below the surface layer. According to Oklahoma state records, 10,000 wastewater wells were active in the state last year.
Much of the research centered on a sprawling natural gas drilling operation in the small town of Jones, the site of one of the state’s highest-volume disposal wells, about 15 miles north of Oklahoma City. Jones often experiences seismic swarms, a sequence of earthquakes that strike in a short time period, the study says. “Seismic swarms within Oklahoma dominate the recent seismicity in the central and eastern United States, contributing 45 percent of magnitude 3 and larger earthquakes between 2008 and 2013. No other state contributed more than 11 percent,” the study says. The study advises regulators to adhere to best practices that “include avoiding wastewater disposal near major faults,” followed by close monitoring, Keranen said.
Keranen said her research found that earthquakes do not happen near the disposal wells; they often rumble eight to nine miles away. A former professor at the University of Oklahoma, she said she felt a magnitude-5.7 earthquake, one of the strongest in the state’s recorded history, in 2011. The researchers embarked on the study in October because “it was likely induced,” she said, and “we wanted to be sure what was happening over this broader region. “I think it intrigues people,” Keranen said. “Any time that there’s an area of the world that has low seismic activity and now has an eruption is very puzzling.”
In spite of a rising number of studies pointing to the role of wastewater injection in producing earthquakes, the oil and gas industry has pushed back against the findings, saying hydraulic fracturing and the disposal of wastewater have been proved safe. Energy in Depth, a research group started by the Independent Petroleum Association of America, says that “hydraulic fracturing has been catching some unmerited headlines lately” as a result of questions about seismic activity. “Despite what you may have heard, hydraulic fracturing has been a safe and proven technology for decades and does not pose a major risk of inducing felt seismic events,” the statement says.