Deploying Coiled Tubing Conveyed Fiber Optic Cables at the Utah FORGE Enhanced Geothermal System

Abstract

Fiber optic cables offer a powerful tool for monitoring enhanced geothermal systems (EGSs), and practical deployment approaches remain under development. We designed, tested, and field-deployed coiled tubing conveyed fiber optic cables to evaluate their feasibility for long-term, retrievable monitoring. The deployment was supported by benchtop strain testing and careful planning of coiled tubing operations. Operational lessons included the importance of circulation contingencies (e.g., burst discs), optimized blowout preventer stack height, and extended coil length at surface to aid in retrieval. Distributed temperature sensing (DTS) measurements provided reliable bottomhole temperature estimates consistent with the bottomhole temperature gauge. Distributed acoustic sensing (DAS) indicated inflow zones and microseismicity. Standard single-mode fiber with RFS-DSS interrogation successfully captured thermal slug responses for production logging. The experimental strain-coupled fiber failed during installation, likely due to thermal expansion effects. Overall, this study demonstrates the feasibility of coiled tubing deployed fiber optics for retrievable monitoring in EGSs.