4
Plenary Conclusion
Brian Anderson, co-chair of the planning committee, and Kris Nygaard, member of the planning committee captured some of the main themes from the induced seismicity session. Anderson began by reiterating what has been learned in the past three or four years since the National Academies report on induced seismicity was released (NRC, 2013). He highlighted several of the gaps in knowledge or information described in that report: 1) the capability to predict and model how reducing volumes, pressures, and rates of fluid injection can lead to a reduction in seismicity after it has begun; 2) effective and economical tools to predict induced seismicity prior to injection; 3) insufficient basic data on fault locations and properties, in situ stresses, pore pressures, and rock properties; and 4) current predictive models cannot properly quantify or estimate the seismic efficiency and mode of failure for faults. The research recommendations identified in that report were targeted toward addressing some of these gaps and included collecting basic data on features such as faults, stresses, reservoir pressures during injection, and reservoir and rock properties. Predictive, probabilistic modeling was another research area recommended by the NRC (2013) report and Zoback’s presentation captured the need for models that can be related to local seismic events and the regional geologic system and can identify rock and fault properties that can be incorporated in hazard and risk assessments.
Although many gaps still remain in our understanding of induced seismicity, Nygaard concurred with the speakers that the past five years have seen a great deal of progress. One of the major areas of progress has been in terms of collaboration among industry, researchers, and regulators and the focus and attention that is being paid by these groups, collectively, to the issue. In addition to the NRC report, Nygaard noted two other recent publications that captured the common themes between different areas experiencing induced seismicity, the current technical understanding of induced seismicity, and different approaches used across different sectors in managing risk (EPA, 2016; IOGCC-GWPC, 2016). He underscored the importance of scientific knowledge as a driver to develop response protocols that had been described from states such as Oklahoma after some of the recent, large earthquakes. Gaps continue to exist in terms of data availability and transparency; funding issues and
how to secure the funding through the different entities engaged in this issue; and finally, communicating with the public and ensuring the public that the various parties involved in fluid injection activities (industry, regulators, and researchers) are collectively responsive to the public concerns. Nygaard offered that continuing to make progress with the scientific understanding of induced seismicity will help inform regulation and that focusing on risk management associated with fluid injection could help with development of new methods, approaches, and response protocols for addressing the risk. Nygaard then sought final input from the audience.
One participant noted the need to consider the lay people in communities that have been affected by induced seismic activity and those who have not yet experienced such activity but live in areas where wastewater injection related to oil and gas development takes place. The lay public has difficulty understanding risk and the participant emphasized the idea of discussion among industry, regulators, researchers, and the lay public to describe what ‘managed seismicity’ could mean and what kinds of alternatives exist to injection (such as water reuse). Another participant offered that ‘managed seismicity’ involves addressing risk through consideration of local geology, local infrastructure, and local activities. The States First document (IOGCC-GWPC, 2016) outlines different approaches for given local situations and aims to help communities drive what is an acceptable risk and risk management strategy.
Additional discussion by several participants about how best to communicate risk and to develop strategies to manage risk included suggestions for industry, regulators, and the research community to communicate with the public 1) what the frequency and significance of these earthquakes are, so that those people have a better appreciation of what they might experience; 2) the advances made in understanding both how these earthquakes are caused and what can be done to reduce their frequency, particularly in the case of the larger induced earthquakes; and 3) the importance of ground motion and ways in which data from ground shaking can be used to enhance ground motion models.
Proactive approaches to managing risk of seismicity were discussed by a participant who cited regulatory decisions with respect to permitting injection wells as one means to implement a prudent risk management strategy. Earthquakes in Dallas-Ft. Forth in 2009 near the airport prompted officials to shut down the nearby injection wells because of the potential risk to the infrastructure there. Another example cited a permit application for a high-volume injection well near an Arkansas nuclear power plant that was rejected by officials because of the potential risk.
A participant tied together points made during the first day of the workshop (Day 1, companion volume) with those during the induced seismicity session through discussion of cumulative effects. Seismologists have a seismic network that is growing and providing more information on smaller earthquakes in various parts of the country, the participant noted. A similar network does not exist to monitor potential cumulative effects to water quality and, although water quality data exist in many places including with the USGS, EPA, and the states, the data are not readily shared. Another participant indicated the presence of a network of state data on ground water quality but said that the data are being assembled in an incremental way due to constrained resources.
Wendy Harrison, roundtable co-chair, closed the workshop.