Challenges and Strategies for Monitoring Induced Seismicity
October 29, 2015
Induced seismicity is potentially caused by activities such as mining, reservoir or dam impoundment, geothermal reservoir stimulation, wastewater injection, hydraulic fracturing and CO2 sequestration. Induced seismic events are rarely large enough to be felt locally or detected regionally. However, between 2013 and 2015, several events larger than M3.0 were recorded in British Columbia, Alberta, Ohio and Oklahoma. As a result, many jurisdictions now have new regulations to mitigate risks associated with induced seismicity.
Most of these regulations call for real-time seismic monitoring networks to drive operational traffic light systems. To help energy companies comply with these regulations, we address the challenges and strategies associated with monitoring for induced seismicity.
Our emphasis on deploying networks that are grounded in science, yet cost-effective, requires rigorous array design and performance modeling. How many stations are needed to meet the monitoring mandate and what should be their geographical distribution? How many stations could be inoperative before the network does not meet its monitoring mandate?
Instrumentation plays an important role in accurately characterizing events. Among the sensing technologies—seismometers, accelerometers and geophones—which one provides the best combination of self-noise, clip level and frequency response to cover the seismic event magnitude and epicentral distance range? As most current traffic light thresholds are based on magnitudes, which magnitude scale should be used?
Many recent large events showed different magnitudes reported by different organizations, depending on the scale as well as stations used. Are ground motions better suited to drive traffic light systems? Recorded ground motions carry much less error, as they are independent of event location accuracy and magnitude scale used; however, they are specific to a single geographical location and are affected by local site amplification.
These ISM networks offer benefits beyond risk management. Generated data sets can be used to assist operators in optimizing completion operations, identify or refine knowledge of geological structures, estimate the direction of in-situ stress regimes, monitor critical infrastructures and develop regional attenuation relationships for more accurate ground motion and magnitude estimates.
