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Passive fiber-optic sensing for monitoring shallow geothermal systems

par Pätzel, Jonas ;Caudron, Corentin ;Gerard, Pierre ;Yates, Alexander ;Govoorts, Julien ;Fontaine, Olivier
Référence European Geothermal PhD Days 2024 (Delft)
Publication Publié, 2024

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Résumé :

Fiber-optic sensing has become an increasingly popular tool in bothgeoscientific research and industries over the last years, including fordownhole applications.Unlike conventional borehole instruments, distributed strain sensing (DSS)offers high spatial and temporal resolution, while Fiber Bragg gratings (FBG)allow to take precise point measurements of temperature or strain at specificdepths. Both technologies are relatively easy to deploy and do not interferewith operations, making this type of sensors highly attractive for themonitoring of geothermal operations across scales and in different geologicsettings.Here we present a first analysis from both DSS and quasi-distributed FBGmeasurements in a future shallow low-enthalpy geothermal heating systemin Brussels, Belgium. Throughout this project, we aim to estimate thepotential of passive, noise-based seismic methods to monitor all stages ofgeothermal production in space and time. For this, fourteen 120m deepgeothermal probes were equipped with different combinations oftemperature and strain sensing FBG arrays and DSS cables.Preliminary results show the possibility of a purely noise-based boreholelogging by calculating the seismic noise amplitude over depth. Regularlyobtaining temperature profiles allows to estimate the local geothermalgradient and its variability after wellbore completion. Both is essential tobetter characterize and understand geothermal systems.