Distributed Fiber Optic Sensing from GeoLaB1 well: cementation and drilling monitoring

The Geothermal Laboratory in the Crystalline Basement (GeoLaB) is a joint research initiative designed to investigate key scientific and technical aspects of deep geothermal energy extraction in crystalline rock.
As part of the project's initial phase, two exploration wells – GeoLaB1 (vertical) and GeoLaB2 (deviated) – were drilled to characterize the geological environment, test monitoring technologies and prepare for future in-situ experiments. Following the drilling and coring of the vertical well GeoLaB1, a fiber optic cable was clamped behind the casing, in a U-loop configuration, and permanently cemented in place. This cable contains several fibers, enabling simultaneous use of different fiber optic sensing technologies. A first dataset was acquired during and after the cementation job of GeoLaB1 using Brillouin Optical Time-Domain Reflectometry and Distributed Acoustic Sensing (DAS). This dual approach allowed joint monitoring of strain (static response) and seismic activity (dynamic response) during cement injection and hardening process. The same infrastructure was subsequently used for continuous DAS monitoring during the drilling of the nearby deviated GeoLaB2 well.
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Following the presentation of the technical aspects of the measurements, we analyze the response to the cement job of the fiber optic sensing data, with support of the logging data. Additionally, we present the drilling monitoring conducted via DAS at a short-offset distance. This study highlights the contribution of distributed fiber optic sensing to gaining valuable insights into well integrity, seismicity, and the broader potential of such systems for high-resolution, multi-parameter monitoring in geothermal environments.