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First Insights into Seismic Behavior at Cape Station

February 28, 2024
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Fervo Energy continues to make tremendous strides in developing the United State’s first commercial next-generation geothermal project at Cape Station in Utah, and we have just reached a major milestone – successfully completing the first well stimulation at the project on the Frisco 1-I well. The stimulation of Frisco 1-I occurred over an 8-day period in mid-February 2024 and has achieved the key permeability enhancement characteristics required for commercial viability of the project.

In our commitment to transparent communication with the local public and our partners, it is important to recognize that, as expected, low levels of seismic activity occurred throughout the stimulation period. Following the Department of Energy’s Induced Seismicity Mitigation Protocol (ISMP), Fervo installed a local seismic monitoring system and followed a rigorous “Traffic Light System” to actively manage and mitigate seismic risk throughout the entire project. The seismic monitoring system is anchored by 17 seismometers operated by University of Utah Seismograph Stations (UUSS) and is bolstered by 6 additional stations that Fervo installed to enhance the accuracy of the system directly within our project area.

The ISMP Traffic Light System is a proven, effective method for managing seismicity, and has been used successfully by Fervo in the past at our Project Red site (as referenced here in our white paper) and by the Utah FORGE project. Fervo has partnered with leading research institutions such as the US Geological Survey, Lawrence Berkeley National Laboratory, Stanford University, and University of Utah to thoroughly vet our ISMP procedures. You can find a more detailed description of the seismic monitoring network capabilities and Fervo’s ISMP procedures at the Cape Station website.

During the stimulation of the Frisco 1-I well, the monitoring network detected seismic activity well within the expected range. The data is publicly accessible on the UUSS website. Notably, our seismic network detected two events with magnitudes that were classified as “Yellow” events (magnitude greater than 2 but less than 3). Following our approved ISMP protocol, pumping operations were paused for 6 hours in each case, in order to allow pressures to dissipate and ensure seismicity levels did not grow.

A recent UUSS blog post highlighted a magnitude ML 2.2 event and a noteworthy “swarm” of activity in the project area (a “swarm” is just a technical term that seismologists call a group of seismic events with no clear main shock). Importantly, these events fall below the threshold of human perception. Moreover, seismic events of this magnitude are routine throughout the state of Utah (see Figure below). Based on analysis performed prior to the stimulation activities, this level of seismic response is within the expected range and fully within the protocols under Fervo’s ISMP.

Seismicity measurements are a powerful tool that can be used by scientists to improve our understanding of the subsurface. In addition to allowing us to manage our operations safely, Fervo has been able to leverage detailed seismic monitoring to characterize the performance of our geothermal system. We are excited to share the data that we have generated with research groups around the world to further enhance our understanding of geothermal energy.

As Fervo looks ahead, we remain committed to collaboration, safe and responsible development, and pursuit of knowledge, ensuring that we are able to continue delivering 24/7 carbon-free geothermal energy projects.

Figure: Seismicity detected within the last 30-days throughout the western US.

Some useful definitions:

Seismic event: This is a generic term for an earthquake. It can refer to an earthquake of any magnitude. Seismic events can be detected using seismometers installed on the ground surface.

Magnitude: This is a measure of the energy released during a seismic event and is used to compare the relative size of events. Because earthquakes cannot be measured directly at the source location in the subsurface, but rather indirectly by seismometers on the ground surface, there is always some uncertainty in the precise magnitude.

Earthquake location: An estimate of the depth and geographic coordinates of an event. Typically an event must be detected by multiple seismometers in order to triangulate the event location.

Ground motion: Earthquakes radiate seismic energy that travels away from the event location, through the earth, and along the ground surface, which can result in shaking. The intensity of the shaking at any given location depends on the distance from the event, the depth of the event, and the magnitude. Ground motions can be measured with seismometers on the ground surface.

Induced seismicity: Earthquake events that are related to human activity, such as mining, oil and gas drilling, or geothermal drilling.

Seismic swarm: A sequence of earthquake events that have no distinguishable main shock event. Natural and induced earthquake swarms are fairly common throughout Utah and many states throughout the western US.