One year ago this month I was sitting in AAPG’s GEO-DC office at the American Geosciences Institute in Alexandria, Va., when a 5.8 magnitude earthquake rocked the state. It was the strongest earthquake I had ever experienced. And in a region unaccustomed to feeling such tremors many wondered if hydraulic fracturing, which was dominating headlines at the time, may have been responsible for the quake.
Fast-forward to earlier this year when I experience several earthquakes and aftershocks in Tulsa. These, too, triggered a lively debate in the media about whether they were related to hydraulic fracturing or other oil and natural gas activities.
Getting to the heart of whether energy production triggers seismic activity is the subject of a new study, titled “Induced Seismicity Potential in Energy Technologies,” released in June by the National Research Council.
The report focuses on four technologies:
- Geothermal energy.
- Carbon capture and storage (CCS).
- Conventional oil and gas, including enhanced oil recovery.
- Unconventional oil and gas development, such as shale gas, requiring hydraulic fracturing.
The National Research Council is the operating arm of the U.S. National Academies of Science and Engineering, and the Institute of Medicine. And it was commissioned to conduct this study by the U.S. Department of Energy (DOE) after a request from Sen. Jeff Bingaman (D-N.M), chair of the Senate Energy and Natural Resources Committee.
In his letter to Energy Secretary Steven Chu, Bingaman noted that “much public opposition to the deployment of advanced energy technologies in the United States stems from a lack of clear, trusted information regarding the safety of those new energy facilities for the local communities that are their neighbors. A National Academies study can provide information to these concerned communities …”
The NRC assembled a diverse group of talented and experienced scientists and engineers chaired by Murray Hitzman of the Colorado School of Mines, an AAPG member. Other AAPG members on the committee were Don Clarke and Julie Schmeta.
As the study noted, “Since the 1920s we have recognized that pumping fluids into or out of the Earth has the potential to cause seismic events that can be felt.”
Thus, the study committee’s charge was to look at geothermal, carbon storage, and oil and natural gas technologies to determine the likelihood of these inducing seismic events – but also to identify knowledge gaps and areas of additional scientific research that would be helpful in managing any risks associated with these activities.
The report lists three major findings:
- The process of hydraulic fracturing a well as presently implemented for shale gas recovery does not pose a high risk for inducing felt seismic events.
- Injection for disposal of waste water derived from energy technologies into the subsurface does pose some risk for induced seismicity, but very few events have been documented over the past several decades relative to the large number of disposal wells in operation.
- CCS, due to the large volumes of injected fluids, may have potential for inducing larger seismic events.
According to the report a principal driver of induced seismicity is the volume of fluid extracted or injected into the subsurface and the resulting effect on pore fluid pressure and/or changes in stress regimes in the rocks and around fault zones. When these volumes are roughly balanced the likelihood of triggering seismic activity appears to be lower.
Waste water disposal wells are typically designed to inject into formations with porosity and permeability sufficient to accept large volumes of fluid. So, while there have been several documented cases of induced seismicity related to waste water disposal, the probability of occurrence is low.
Fluid balance is important in geothermal wells, as well. Another factor affecting these wells is the potential for the difference in temperature between the injected fluids and rock to cause contraction and triggering seismic activity. As an example, this has been documented in The Geysers geothermal field in California.
Large-scale injection of super critical CO2 over an extended period has not occurred in either the research CCS projects conducted in the United States or the commercial CCS projects overseas. As a result there is insufficient knowledge of its potential to induce seismicity.
The difficulty in predicting induced seismicity is twofold:
- First, we are dealing with complex natural geological systems and, frequently, a lack of fundamental geological data needed to adequately understand these systems.
- Second, we do not have risk assessment models that have been sufficiently validated to be useful tools.
But these models and methodologies can be developed. And the committee urges both increased government cooperation at the federal and state level, as well as an ongoing learning process as energy development progresses resulting in a “best practices protocol” for each energy technology. In fact, they point to a protocol developed by DOE for engineered geothermal systems as a useful template.
Our understanding of the natural systems where we find and produce the energy needed to power modern life improves as we explore and produce. And as the NRC report indicates, the risks of inducing seismic activity, particularly from oil and natural gas activities, are low and manageable.
The complete report is available for download at the National Academies website.