Marcellus Shale: Aftershocks From Ohio Earthquakes
Drew T. Bell, Lynn Kerr McKay
On New Year’s Eve, an earthquake, measuring 4.0 on the Richter scale, shook Youngstown, Ohio. This tremor was relatively minor—no one was injured, and Youngstown buildings did not suffer significant damage. Because Youngstown is near a permitted injection well used for disposing of wastewater from hydraulic fracturing operations—the Northstar well, critics of shale gas development have cited the tremor as further support for their opposition to development of shale gas reserves.
Importantly, the Northstar well is not a production well, and no hydraulic fracturing activities took place there. On January 3, 2012, the Ohio Department of Natural Resources (“Ohio DNR”) announced that D&L Energy, the Northstar’s operator, agreed to stop operations at this well and four others within five miles until the cause of the earthquakes is determined.  The Northstar well is the only Class II well in Ohio to be shut down under suspicion that its activities may have induced seismic activity. Although the potential for seismic events associated with certain oil and gas production activities has long been understood, investigation of the Northstar well may increase demands for further regulation of not only disposal wells, but also shale gas operations.
Class II Oil and Gas Related Underground Injection Wells
In light of the potential for interaction between geologic formations used for injection and drinking water aquifers, the Safe Drinking Water Act’s Underground Injection Control (“UIC”) program regulates the permitting and operation of injection wells.  Under the UIC, deep injection wells associated with oil and gas production are Class II wells,  and must meet certain construction and maintenance standards such as defining a zone of endangering influence, determining maximum injection pressure and injection rates, and testing mechanical integrity.  These standards are targeted at protecting drinking water quality.
EPA promotes the use of such injection wells as the “preferred way to dispose of this waste fluid.”  There are 150,851 Class II injection wells in the United States; 177 in Ohio. Due to geologic conditions, Pennsylvania has only six Class II wells that accept wastewater from hydraulic fracturing operations, so some Pennsylvania operators transport water to Ohio for disposal.  Although Class II wells long have been viewed by EPA and others as the preferred method of hydraulic fracturing wastewater disposal, the recent earthquakes are contributing to public anxiety about hydraulic fracturing in Ohio and in other states.
Seismic Activity Related to Oil and Gas Activities
In the 1930s, scientists determined that oil and gas production could induce seismic activity.  Early production operations, which rapidly extracted fluids without replacing them, were tied to damaging earthquakes in Wilmington, California. Based on this finding, the industry took steps to mitigate these effects.  In fact, minor, imperceptible seismic activity has been found to be common in oil and gas production. 
The Department of Energy (“DOE”) notes that more recently, injection of produced water under high pressure can “produce significant seismic activity.”  But, DOE found that these effects can be mitigated by adjusting the area or depth of injection. The agency further found that “oil and gas induced seismicity has been dealt with successfully and is well understood.” 
Critics of hydraulic fracturing have blamed recent earthquakes in Arkansas, Colorado, and Oklahoma on hydraulic fracturing and underground injection of wastewater in disposal wells.  In investigating and addressing these seismic events, it will be important to distinguish between these potential causes. Activities related to oil and gas production may have had nothing to do with these earthquakes. For example, in November 2011, there was a 5.6 magnitude earthquake near Oklahoma City. Although some critics attributed the quake to hydraulic fracturing operations, it occurred along an active fault. The United States and Oklahoma Geological Surveys concluded that it was doubtful that hydraulic fracturing caused the earthquake.  On the other hand, Cuadrilla Resources, a British gas developer, reported that it is “highly probable” that its hydraulic fracturing operations resulted in minor earthquakes in Lancashire, England.
Concerns about induced seismicity led Senator Jeff Bingaman (D-NM) to request a National Academy of Sciences study of how oil and gas production, not just disposal practices, can lead to earthquakes.  The NAS is expected to issue its report in summer 2012.
Preliminary Investigation of the Youngstown Earthquakes
In addition to the New Year’s Eve earthquake, Youngstown experienced ten minor tremors between March and December 2011. Because earthquakes are rare in the Youngstown area, Ohio DNR brought in seismologist John Armbruster from Columbia University’s Lamont-Doherty Earth Observatory to investigate the series of tremors.  He concluded that the earthquakes originated in the area of the Northstar well and were the result of slippage along a fault three kilometers below the surface, approximately the same depth as the well’s injection site.  From this, Dr. Armbruster determined that the earthquakes were related to injections at the Northstar well, noting that all of the earthquakes occurred after D&L began operating the well, and Youngstown is not normally seismically active. However, Dr. Armbruster conceded that the other 177 Class II wells in Ohio have not experienced seismic events, and Youngstown’s seismic activity has been “a matter of luck.” 
Class II wells likely will continue as the preferred method for disposal of non-recyclable wastewater from hydraulic fracturing activities regardless of the conclusion Ohio DNR reaches about the Northstar well. Earthquakes such as those near Youngstown are rare,  and most induced seismic activity from deep well injection is imperceptible.
However, concerns about earthquakes could spur new legislative and regulatory requirements for operators, such as evaluating an area for potential seismic effects as part of the UIC permitting process, or obligations for continual monitoring of seismic activity in an area. Further, concerns about seismic events could lead those opposed to shale gas development to demand additional limits on this activity, including prohibiting operations in certain areas. For that reason, we will continue to monitor how Ohio, EPA, DOE and other others respond to this event.