Temporal changes of static stress drop as a proxy for poroelastic effects at The Geysers geothermal field, California

Staszek, Monika and Orlecka-Sikora, Beata and Lasocki, Stanislaw and Kwiatek, Grzegorz and Leptokaropoulos, Konstantinos Michail and Martinez-Garzon, Patricia (2017) Temporal changes of static stress drop as a proxy for poroelastic effects at The Geysers geothermal field, California. In: EGU General Assembly 2017, 23–28 April 2017, Vienna, Austria.

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Abstract

One of the major environmental impacts of shale gas exploitation is triggered and induced seismicity. Due to the similarity of fluid injection process data from geothermal fields can be used as a proxy for shale gas exploitation associated seismicity. Therefore, in this paper we utilize ‘The Geysers’ dataset compiled within SHale gas Exploration and Exploitation induced Risks (SHEER) project. The dependence of earthquake static stress drops on pore pressure in the medium was previously suggested by Goertz-Allmann et al. (2011), who observed an increase of the static stress drop with the distance from injection well during reservoir stimulation at Deep Heat Mining project in Basel, Switzerland. Similar observation has been done by Kwiatek et al. (2014) in Berlín geothermal field, El Salvador. In this study, we use a high-quality data from The Geysers geothermal field to determine whether the static stress drops and the stress drop distributions change statistically significantly in time or not, and how such changes are correlated with the values of hypocenter depth, water injection rate, and distance from injection well. For the analyses we use a group of 354 earthquakes, which occurred in the proximity of Prati-9 and Prati-29 injection wells. Spectral parameters of these earthquakes were determined using mesh spectral ratio technique. Our results indicate that: (1) the static stress drop variation in time is statistically significant, (2) median static stress drop is inversely related to median injection rate. Therefore, it is highly expected that static stress drop is influenced by pore pressure in underground fluid injection conditions. References: Goertz-Allmann B., Goertz A., Wiemer S. (2011), Stress drop variations of induced earthquakes at the Basel geothermal site. Geophysical Research Letters, 38, L09308, doi:10.1029/2011GL047498. Kwiatek G., Bulut F., Bohnhoff M., Dresen G. (2014), High-resolution analysis of seismicity induced at Berlin geothermal field, El Salvador. Geothermics, 52, 98-111, doi: 10.1016/j.geothermics.2013.09.008. Acknowledgements: This work was supported under SHEER: "Shale Gas Exploration and Exploitation Induced Risks" project funded from Horizon 2020 – R&I Framework Programme, call H2020-LCE-2014-1 and by the Ministry of Science and Higher Education of Poland under project no. 500-10-27.

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Item Type: Conference or Workshop Item (Speech)
Subjects: Methodology > Method and procesing > Stress field modeling > Technology induced stress field redistribution
Methodology > Method and procesing > Stress field modeling > Evolution of stress field changes
Region > USA > California > Geysers
Inducing technology > Geothermal energy production
Project: SHEER project > THE GEYSERS: geothermal energy production