PSI - Issue 64

Michael Iten et al. / Procedia Structural Integrity 64 (2024) 1642–1648 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 5. Temperature measurements during the setting of the cement of the surface casing of GES-F-1 on string “A” (left) and “B” (right) of the looped fiber-optic cable.

4. Discussion The good quality of the acquired data is proven by the congruence between the two respective strings of the looped cables as well as the high temperature resolution. Even though the temperature change induced by the injected material is limited to a few degrees, the fiber-optic temperature measurements show a clear picture of the cementation progress. In both boreholes, GES-F-1 and GES-F-2, the rising grout level inside the annulus of the surface casing is well detectable which allows to determine the height of the cement at every instant. Short interruptions in the grouting operations are as visible as the wellhead getting pressure washed with warm water from the excess cement. The high level resolution in both spatial and temporal domain combined with the availability of the acquired data in near real time allows to monitor the cementation process and the setting of the cement in detail. Protecting the fibers posed a major challenge in this project. Despite a long and detailed planning as well as the several cable reinforcement layers and the centralizers specially designed to hold the wires as close to the casings as possible, the cables got crushed repeatedly at a similar depth assumingly due to the curvatures of the directionally drilled boreholes. Thus, the concepts of positioning and protecting of the sensitive fiber-optic sensor cables will have to be revised for possible additional b oreholes in the “Forsthaus” geothermal energy storage project considering the enormous forces acting on the inclined casings of this size.