Induced seismicity spikes during abrupt changes in injection and production rates in geothermal reservoirs

Roshan Koirala, Emily Brodsky, Thomas H. Goebel, & Grzegorz Kwiatek

Submitted August 3, 2021, SCEC Contribution #11146, 2021 SCEC Annual Meeting Poster #129

Fluid injection in deep geothermal reservoirs can result in fluid pressure changes that are sufficiently high to induce seismicity. There are, however, some examples of seismic activity during a decrease in injection rates. Here, we analyze the strong seismic response due to abrupt maintenance shutdowns in the Blue Mountain geothermal reservoir in Nevada. We use continuous seismic monitoring data recorded by a local array of 8 stations from 2016 to 2020 for seismicity analysis. We identify episodes of coherent seismic energy excitation across the array using a network-detection algorithm and determine accurate phase-arrivals using an AIC picker applied to trimmed single-channel waveforms. The picks satisfying appropriate signal-to-noise ratios (SNR) were used for locating events with NonLinLoc and subsequent local magnitude calculation. The results show that seismicity is clustered around the geothermal reservoir with focal depths shallower than 1.5 km and magnitudes smaller than 2.5 The most striking observation is that seismicity rates spike during the operation shutdowns. Interestingly, seismic activity decreases as geothermal operations resume and reaches the background seismicity rate within a week. The sudden seismicity rate increase after shutdown may be a result of the unclamping of pre-stressed faults due to the release of poroelastic stress.

Key Words
Induced seismicity, Geothermal

Citation
Koirala, R., Brodsky, E., Goebel, T. H., & Kwiatek, G. (2021, 08). Induced seismicity spikes during abrupt changes in injection and production rates in geothermal reservoirs. Poster Presentation at 2021 SCEC Annual Meeting.


Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)