Title: The view from the surface in recent injection experiments at Utah FORGE: Cost-efficient and permanent monitoring strategies reveal a complex reservoir response.
Abstract: n recent years, the Utah Frontier Observatory for Research in Geothermal Energy (FORGE), a large-scale experimental facility de-risking Enhanced Geothermal Systems (EGS), successfully completed the drilling of a well doublet at a depth of 2.5 km, the stimulation of reservoir and first circulation tests. Field-scale testing at Utah FORGE allows the study and development of new tools, methodologies, and strategies to improve the economic viability of EGS and mitigate induced seismic activity.
We analyzed the microseismic data recorded by permanent and temporarily enhanced surface networks at Utah FORGE during the circulation experiments in 2023 and the stimulations in 2024. We applied state-of-the-art full-waveform-based methods for microseismic event detection supported by ML-informed image functions in a complex 3D medium for both experimental phases. Subsequently, we calculated relative relocations for the detected microseismicity. With the design of the surface network and the implemented workflow, we intend to produce a high-quality data set providing detailed insights into the reservoir even in periods without active downhole monitoring (e.g. during the circulation in 2023). Our analyses reveal a complex microseismic response of the reservoir during the injections and the shut-in phases, with reservoir volumes in close vicinity showing increased seismic activity and aseismic behaviour.
For the 2023 circulations, we attributed seismic activity occurring predominantly after the shut-in of the last two circulation stages to the complex dynamics of opening, further propagating, and closing of hydraulic fractures during circulation in the absence of major conductive features that allow for substantial flow into the production well. A one-year gap between the initial stimulation and the circulation test in 2023 might have contributed to the reduced connectivity due to the resealing/closing of previously opened flow paths. Hence, microseismic activity may not guarantee the presence of stimulated fractures that can enable efficient fluid flow without repeated stimulations or the use of proppants.
After the stimulations in 2024 in both wells and the use of proppants, the connectivity between the wells was well-established via at least two main fracture zones mapped in great detail by the microseismic surface networks during the seven‐stage stimulation of the injection well and the subsequent stimulation of the production well. Also, in this experimental phase, a spatial offset between injection intervals and the onset of seismicity in later stages points towards a complex response, e.g., aseismic flow in the reservoir.
Biography: Peter Niemz obtained his Masters degree in Geophysics from University Jena, Germany. For his PhD in seismology at University of Potsdam/GFZ Potsdam, Germany, he studied the growth of hydraulic fractures in a decameter-scale hydraulic fracturing experiments in granitic rock via picoseismic activity. For his recent PostDoc at University of Utah, he shifted from small-scale to field-scale experiments, studying reservoir dynamics at Utah FORGE.
To join virtually: Zoom
Contact: pniemz.seismology@gmail.com
Utah FORGE Website: https://utahforge.com
Recording: Zoom Recording (will be available within a week after the seminar)