Managing Potential Injection-Induced Seismicity through Monitoring and Mitigation

Abstract

With the continued public and regulatory concerns regarding the potential for induced seismicity associated with Class II disposal wells, the development of a monitoring and mitigation plan is becoming a critical consideration for Class II disposal operations. Even though the practical risk of injection-induced seismicity is minimal, it is perceived as a real risk by the public and the media and therefore cannot be ignored. A plan, which includes both monitoring and mitigation elements, would be built upon hazard identification, risk assessment, and data evaluation that will provide for a technology-based process for assessing and addressing actual and perceived risks. Hazard identification and risk assessment involves evaluation and determination of site-specific subsurface geology, hydrologic conditions, injection reservoir analysis, injection history, and assessment of historical seismicity in the area. Additional risk considerations would include assessment of the population density, structures, infrastructure, human health, safety, and the environment. In many parts of the United States, existing regional seismic networks are limited in their ability to accurately locate hypocenters or even detect microseismic events. For optimal constraints on the location of any seismic event, seismic monitoring would need to include deployment of a multi-sensor passive seismic local network along with a strong motion accelerometer to record peak ground acceleration. Installation of four seismometers evenly distributed around the disposal well and a fifth unit installed at a distance equal to the depth of the well would provide for: 1) Increased accuracy of both the hypocenter and epicenter locations, 2) Real-time monitoring, and 3) Automated e-mail alerts of any seismic events. Mitigation should be proactive in its approach and based on local conditions such as existing infrastructure, population density, and risk level, with considerations to public sensitivity and tolerance. Key mitigation strategies, which would likely involve a phased approach such as a traffic light system, would include operational changes such as injection rate and/or pressure reductions that allows for regulatory agencies and stakeholders to work together to develop real world solutions to induced seismicity.

AAPG Datapages/Search and Discovery Article #90373 © 2019 AAPG Eastern Section Meeting, Energy from the Heartland, Columbus, Ohio, October 12-16, 2019