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Wednesday, August 8, 2012

Underground wastewater injection and earthquakes linked (again) by new study


It is no surprise that injecting fluids deep underground can trigger earthquakes.  A U.S. Geological Survey report released earlier this year found a connection between small temblors in the Midwest and the injection of drilling wastewater in deep disposal wells. In March, an Ohio state agency concluded that a wastewater injection well was responsible for a dozen earthquakes in the Youngstown area in 2011.  And in June, the National Academy of Science released a report concluding that while there is a low risk of earthquakes from hydraulic fracturing, underground wastewater injection wells pose a higher risk of inducing seismic activity.

A new, two-year study by a seismologist at the University of Texas at Austin echoes this previous work and takes it a step further.  UTA seismologist Cliff Frohlich has found that injection wells used to dispose of wastewater from oil and gas drilling cause relatively minor temblors – and more frequently than commonly thought.

Frohlich analyzed seismic activity in the Barnett Shale of Texas between November 2009 and September 2011.  He identified the epicenters for 67 earthquakes — more than eight times as many as reported by the National Earthquake Information Center — with magnitudes of 3.0 or less. Most were located within a few miles of one or more injection wells. All of the wells nearest the epicenters reported high rates of injection exceeding 150,000 barrels (17.6 million liters) of water per month. He also found more than 100 wells with similar injection rates that experienced no nearby earthquakes during the time of the study. He suggests that fluid injection may trigger earthquakes only if fluids reach and reduce friction on a nearby fault.

The implications of all of this are clear.  The risks of induced seismicity from wastewater injection wells are real, but manageable.  More geological and geophysical study should be required of wastewater well developers before the wells are sited and approved; and operating wells should be strictly monitored.  Ohio officials, for example, responded to the Youngstown quakes by imposing new permitting requirements on disposal well drillers. (In Pennsylvania, there are only 5 operating injection wells; but 3 more are in the planning stages.)

Perhaps the only surprise related to this new report has to do with the way it was reported.  Despite plain language used to describe the study as related specifically to wastewater injection, published reports say the study links earthquakes to fracking.  It does not.

Regulators, injection well operators, and reporters all need to do a better job.


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