The chair of the Induced Seismicity committee, Dr. Murray W. Hitzman of the Colorado School of Mines, advised the Senators that, since the 1920s, it has been recognized that pumping fluids into or out of the ground has the potential to cause seismic events that can be felt.
These induced seismic events, though small in scale, concern the public and raise questions about increased seismic activity and its potential consequences. Dr. Hitzman reported the following findings:
- Induced seismicity associated with fluid injection or withdrawal in energy development is “caused in most cases by change in pore fluid pressure and/or change in stress in the subsurface in the presence of faults with specific properties and orientations and a critical state of stress in the rocks.”
- The total balance of fluid introduced into or removed from the subsurface is the factor that has the most direct consequence in regard to induced seismicity.
- The very low number of felt seismic events (one unconfirmed in the U.S. and one confirmed in England) relative to the large number of hydraulically fractured wells for shale gas (more than 35,000 in the U.S.) is “ likely due to the short duration of injection of fluids and the limited fluid volumes used in a small spatial area.”
- “The majority of…waste water disposal wells do not pose a hazard for induced seismicity.” The few induced seismic events that have been attributed to disposal injection wells are causally linked between the injection zones and previously unrecognized faults in the subsurface.
- avoid injections into brittle rock faults;
- select formations to minimize pore pressure changes;
- install local seismic monitoring arrays;
- establish protocols “to define how operations would be modified if seismicity were to be triggered;” and
- reduce injection rates or abandon injection wells if triggered seismicity poses any hazard.
This article was prepared by Barclay Nicholson (firstname.lastname@example.org / 713 651 3662) from Fulbright's Energy Law Practice.