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induced seismicity

Induced seismicity

Paper on analysis of sequences framing larger events at The Geysers geothermal field

The paper entitled “Analysis of Microseismicity Framing ML>2.5 Earthquakes at The Geysers Geothermal Field, California” by Stephan Bentz from our Section has been finally published in Journal of Geophysical Research: Solid Earth. This is another paper related to the analysis of seismicity at the Geysers geothermal field performed in our section.

In the paper, we statistically analyze temporal properties of seismicity utilizing
seismicity catalogs framing 20 ML>2.5 earthquakes enhanced with the template matching algorithm. We found that triggered aftershocks or larger events are mostly restricted to the northwestern part of the geothermal field and that larger events may be preceded by
isolated smaller earthquakes at approximately the same location.

Bentz, S., P. Martínez-Garzón, G. Kwiatek, G. Dresen, and M. Bohnhoff (2019). Analysis of Microseismicity Framing ML > 2.5 Earthquakes at The Geysers Geothermal Field, California, Journal of Geophysical Research: Solid Earth, DOI: 10.1029/2019JB017716.

Controlling induced seismicity during fluid injection

Finally, our new paper “Controlling fluid-induced seismicity during a 6.1-km-deep geothermal stimulation in Finland”, published on May 1st in Science Advances, is out!

In the study we report on a successful attempt to control induced seismicity during the deepest-ever hydraulic stimulation of a geothermal well in Helsinki, Finland. In a collaborative effort by a team of international researchers from commercial companies, academic institutions and universities, a safe stimulation strategy was designed and successfully applied preventing the occurrence of a project-stopping induced earthquake with a magnitude larger than 2.0, a limit imposed by local authorities for the safe continuation of the St1 Deep Heat Oy energy project. In the project, a traffic-light-style system involving near-realtime seismic monitoring allowed active feedback and guidelines to the stimulation engineers on how to adjust pumping rates and pressure at the injection. This feedback in near real-time was the key to success and allowed to deepen the understanding of the reservoir seismic response and the hydraulic energy release at depth, while ensuring promptness in the technical response to increased seismic activity. This allowed immediate adjustment of the reservoir treatment through mitigating injection-rate and duration of resting periods that were applied in the course of the months-long experiment and ensured the successful control of maximum observed magnitude of the induced seismic events.

You can download the manuscript from Science Advances website.

The reference:

Kwiatek, G., T. Saarno, T. Ader, F. Bluemle, M. Bohnhoff, M. Chendorain, G. Dresen,
P. Heikkinen, I. Kukkonen, P. Leary, M. Leonhardt, P. Malin, P. Martínez-Garzón, K. Passmore, P. Passmore, S. Valenzuela, and C. Wollin (2019). Controlling fluid-induced seismicity during a 6.1-km-deep geothermal stimulation in Finland, Sci Adv 5, no. 5, eaav7224, doi 10.1126/sciadv.aav7224. [ Article Page ]

Paper on coda-Q variability at The Geysers

Our team has published another paper related to The Geysers geothermal field. This time, Aglaja Blanke discusses peculiarities of coda-Q attenuation in the largest hydrothermal field of the world.

Reference:

Blanke, A., G. Kwiatek, P. Martínez‐Garzón, and M. Bohnhoff (2019). Sensitivity and Stability Analysis of Coda Quality Factors at The Geysers Geothermal Field, CaliforniaSensitivity and Stability Analysis of Coda Quality Factors at The Geysers Geothermal Field, California, Bulletin of the Seismological Society of America doi 10.1785/0120180219. [ Article Page ]

Paper on cyclic soft stimulation at Pohang EGS

I co-authored paper in Geophysical Journal International by Hannes Hofmann discussing the cyclic soft stimulation campaign performed in August 2017 at Pohang EGS system. The paper is available to download from journal website. The analysis performed by Hannes was a part of activities performed within DESTRESS DEmonstration of Soft Stimulations Treatments of Geothermal Reservoirs project.

Reference:
Hofmann, H. et al. (2019). First field application of cyclic soft stimulation at the Pohang Enhanced Geothermal System site in Korea, Geophys. J. Int. 217, no. 2, 926–949, doi 10.1093/gji/ggz058.

Abstract:
Large-magnitude fluid-injection induced seismic events are a potential risk for geothermal energy developments worldwide. One potential risk mitigation measure is the application of cyclic injection schemes. After validation at small (laboratory) and meso (mine) scale, the concept has now been applied for the first time at field scale at the Pohang Enhanced Geothermal System (EGS) site in Korea.From 7 August until 14 August 2017 a total of 1756 m³ of surface water was injected into Pohang well PX-1 at flow rates between 1 and 10 l s–1, with a maximum wellhead pressure (WHP) of 22.8 MPa, according to a site-specific cyclic soft stimulation schedule and traffic light system. A total of 52 induced microearthquakes were detected in real-time during and shortly after the injection, the largest of Mw 1.9. After that event a total of 1771 m³ of water was produced back from the well over roughly 1 month, during which time no larger-magnitude seismic event was observed. The hydraulic data set exhibits pressure-dependent injectivity increase with fracture opening between 15 and 17 MPa WHP, but no significant permanent transmissivity increase was observed.The maximum magnitude of the induced seismicity during the stimulation period was below the target threshold of Mw 2.0 and additional knowledge about the stimulated reservoir was gained. Additionally, the technical feasibility of cyclic injection at field scale was evaluated. The major factors that limited the maximum earthquake magnitude are believed to be: limiting the injected net fluid volume, flowback after the occurrence of the largest induced seismic event, using a cyclic injection scheme, the application of a traffic light system, and including a priori information from previous investigations and operations in the treatment design.