In a recent webinar, Craig Hartline (Calpine Corp) and Adrien Caudron (Emerson) presented a case study of geothermal production and reservoir management at The Geysers field, Northern California. Calpine has been using Emerson’s Skua-Gocad software to build and view 3D models and perform induced seismicity analysis and mitigation efforts at The Geysers since 2011. Calpine combines Gocad structural models with fluid flow simulations using Berkeley Labs’ Tough/Tough2 suite of ‘simulators for non-isothermal multiphase flow in fractured rocks’. The Geysers, the largest producing geothermal field in the world, produces 725 MW of electricity from over 300 wells. Wellhead steam temperature is around 180°C.
Hartline began with a plate-tectonic introduction to the highly active geological setting before presenting the comprehensive models and use cases that Gocad has supported. The models blend ArcGIS surface geological maps, well log-derived lithologies, steam production and public domain seismicity data. Induced seismicity is generated as cooled, re-injected produced water meets and reactivates existing faults and fractures. This is monitored in collaboration with LLNL and the USGS with an extensive permanent seismic monitoring network. Following some early hikes in seismicity as ‘too many operators were fishing out of the same pond,’ mitigation measures have been brought in and seismic activity is now essentially decoupled from steam production.
Gocad is used to combine and animate production data and seismicity. This has led to a better understanding of the spatio-temporal relationships between water injection, induced seismicity and faults and fractures. Animations span some 36 years of product and seismometry. Gocad is also used to estimate microseismic-stimulated reservoir volumes. These studies have led to better water injection distribution and reduced seismicity, further optimized by careful placement of new wells. The Geysers’ field-wide structural model is also used in public outreach exercises to assuage concerns over seismicity.
More on the Calpine/Emerson work from the Geothermal Library and the Emerson flyer. You may also like to visit The Geysers. Guided tours are available but the center is fully booked for 2022. The 2023 schedule opens on November 15, 2022.
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