One of the concerns about hydraulic fracturing for oil and shale gas is the risk of what is known as induced seismicity, or in English, man-made earthquakes.
A new report from the National Academy of Sciences has found that hydraulic fracturing is suspected in one case of seismic activity in the U.S. and has been confirmed as the cause for small seismic events at one location in the world. However, NAS says that overall, fracking does not pose a high risk for inducing earthquakes.
Injection of wastewater for disposal – currently a major component of shale gas exploration - has been “suspected or determined a likely cause” for induced seismicity at 8 sites in the past several decades, according to the study; however, the long-term effects of increasing the number of waste water disposal wells on the potential for induced seismicity are unknown.
One of the principal authors of the report told the U.S. Senate Energy and Natural Resources Committee last week that changing the way wastewater injection wells are planned and operated can largely resolve most concerns about man-made earthquakes. Mark Zoback, professor of geology at Stanford University, told the committee that with proper planning, monitoring and response, the occurrence of seismic activity associated with waste injection can be reduced and the risks effectively managed.
Zoback said that wastewater well drillers should avoid areas with geological faults. This is a no-brainer, but current EPA guidelines do not require the consideration of seismicity in injection well approval, and there are no standard methods to implement risk assessments for induced seismicity. That clearly must change. Injection wells must be sited subject to pre-development seismic studies to thoroughly characterize the site geologically, just as oil and gas well drillers do.
In addition, Zoback said that waste well sites should be monitored for seismic activity and be drilled with a plan for what to do if there is evidence of earthquake. Additional regulation requiring these practices is a must.
The study found that four federal agencies—the U.S. Environmental Protection Agency, the Bureau of Land Management, and the U.S. Department of Agriculture Forest Service and the U.S. Geological Survey—and several different state agencies have regulatory oversight, research roles and responsibilities relating to different parts of underground injection activities, but coordination on induced seismicity issues is lacking. That, too, must change.
Current trends in the shale gas industry toward wastewater recycling and the development of innovative wastewater treatment technologies can go a long way to reducing the need for wastewater injection and have wide benefits beyond minimizing the risk of man-made earthquakes.