EVALUATING RISK OF INDUCED SEISMICITY IN PENNSYLVANIA FROM DISPOSAL WELL OPERATIONS

Concern over potential for earthquakes associated with disposal well operations has increased over recent years as earthquakes in parts of Oklahoma, Texas, Ohio and other states have been linked to saltwater disposal well operations associated with shale plays. While there have been certain documented cases of strong relationships between disposal well operations and noticeable seismic activity, these cases are rare among the roughly 30,000 saltwater disposal wells operating in the United States. Research studies published by USEPA and others have found that in most cases where significant induced seismicity occurred as a result of injection well operations, that there was likely movement along Precambrian basement faults. The 4.0 magnitude earthquake in the Youngstown, Ohio area on December 31, 2011, which Ohio DNR attributed to the operation of the Northstar #1 disposal well and associated movement along a previously unidentified Precambrian basement fault, resulted in heightened concern over potential for induced seismicity from disposal wells operating in the Appalachian Basin.

There are currently only eight operating saltwater disposal wells in Pennsylvania. To date, there has been no earthquake activity linked to operation of these wells. Considering the structural geology of Pennsylvania, stratigraphic positions of candidate injection intervals, likely injection rates and overall low seismic risk (according to the USGS) for most of the state, the likelihood of significant induced seismicity resulting from disposal well operation in Pennsylvania is considered to be very low. This risk can be managed through use of the “traffic light” approach which is being utilized by certain states. PADEP has been revising their injection well approval procedures to include monitoring for induced seismicity. This presentation will evaluate the risk of significant induced seismicity associated with disposal well operation in Pennsylvania and approaches to manage the risk.