Characterizing and monitoring the locations, connected geometry, and hydromechanical response of subsurface fracture networks is a crucial step in efficiently developing enhanced geothermal systems (EGS). Unfortunately, EGS reservoirs, dominated by high temperatures and corrosive brines, are a hostile environment for classical point sensors most useful in these monitoring tasks; seismic sensors in particular have a poor track record during intermediate and long duration studies in geothermal reservoirs. Full characterization of fracture networks requires coupled thermal and geodetic (e.g. strain) measurements at depth to effectively understand both the creation and dynamic behavior of fractures during flow. High temperature distributed fiber optic sensing (DFOS) systems present one potential solution to these challenges in the context of EGS. We present initial results from deployment of an integrated DFOS system at the Utah FORGE facility in well 16B(78)-32, as part of the Fiber Optic Geophysical Monitoring Of Reservoir Evolution (FOGMORE@FORGE) project. This well is the production well in the Utah FORGE EGS doublet. The DFOS system was designed to measure microseismic activity (DAS), record timelapse VSP surveys (DAS), temperature during production (DTS), and fracture-associated strain (DSS and LF-DAS). The sensing cable was designed to continuously survive temperatures in excess of 265 C through use of a rugged nickel alloy sheath (A825), high-temperature polymer buffers (PFA), and polyimide-coated fibers (2xSM, 2xMM, 1 engineered fiber). The cable and interrogator units were installed during July of 2023 and the deepest section equilibrated at ~235 C; the system was utilized during the 2023 stimulation and flow test, during periods of passive recording, and during the April 2024 stimulation experiment before failing due to fluid intrusion. We will present results from the system design phase, installation, commissioning, and stimulation/circulation experiments. A variety of interesting data streams were recovered during the 2024 stimulation which, while not fully analyzed, have helped to constrain the induced fracture geometry at depth. We will conclude with a discussion of some lessons learned during development of the DFOS deployment at Utah FORGE.

Press the Back button in your browser, or search again.

Copyright 2025, Stanford Geothermal Program: Readers who download papers from this site should honor the copyright of the original authors and may not copy or distribute the work further without the permission of the original publisher.