Increasingly, wastewater from oil and gas operations is pumped into the ground for disposal, and the pressure it creates might be causing small earthquakes, says a report released by EPA.
Concern about a connection between wastewater injection and seismic activity arose following a series of earthquakes in 2011, says Peter C. Grevatt, director of EPA’s Office of Ground Water & Drinking Water. “We thought it was very timely to ask a group of experts to look into this issue.”
The report was prepared by the Underground Injection Control National Technical Workgroup, a group of regional and state experts.
Advanced oil and gas recovery techniques, which include horizontal drilling and hydraulic fracturing, bring ancient seawater to the surface along with oil and gas. At the surface, the brine and other wastes are separated from the economically valuable hydrocarbons. The water’s high salinity renders it too expensive to treat and discharge at the surface. Instead, it is often injected into deep wells for disposal. Over time, as pressure builds underground, release through ground-shaking tremors is possible, researchers say.
“Where individual cases of suspected induced earthquakes have been studied, the common denominator has been one or more high-volume injections wells,” says William L. Ellsworth, a seismologist with the U.S. Geological Survey, who is not a member of the workgroup.
The workgroup studied sites where wastewater injection is suspected of causing small to moderate earthquakes. It evaluated earthquake history, the proximity of disposal wells to these events, and the behavior of the wells.
“It’s very difficult to conclusively link any particular injection activity with a seismic event,” Grevatt says.
A series of Oklahoma quakes in 2011 with magnitudes greater than 5.0 brought attention to a possible connection between hydraulic fracturing and induced earthquakes. A recent study called one of these earthquakes, with a magnitude of 5.7, the largest yet associated with wastewater injection (J. Geophys. Res. 2014, DOI: 10.1002/2013jb010612).
The report offers guidance to state and federal officials who want to minimize and manage seismic activity that might be a result of injection, the agency says.