PSI - Issue 64

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Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2023) 000 – 000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2023) 000 – 000 ScienceDirect

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

ScienceDirect

Procedia Structural Integrity 64 (2024) 1642–1648

SMAR 2024 – 7th International Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures Distributed fiber-optic temperature monitoring in boreholes of a seasonal geothermal energy storage Michael Iten a, *, Matthias Bühler a , Frank Fischli a , Falko Bethmann b and Andre El-Alfy b a Marmota Engineering AG, Technoparkstrasse 1, 8005 Zürich, Switzerland b GeoEnergie Suisse AG, Reitergasse 11, 8004 Zürich, Switzerland Abstract Monitoring the in-situ temperature is key for the characterization of a seasonal geothermal energy storage. Distributed fiber-optic temperature sensing (DTS) systems provide temporally and spatially continuous measurement data in near real-time that captures borehole temperature dynamics. In the presented project, three boreholes of a seasonal geothermal energy storage with a vertical depth of down to 500 meters were instrumented with distributed fiber-optic sensors. For this purpose, a standard armored sensor cable was modified to allow for combined DTS, distributed acoustic sensing (DAS) and distributed strain sensing (DSS) at temperatures up to 120 °C. The cable was installed in a loop configuration to allow for temperature calibration using a temperature matching approach. A “Mini - Bend” solution was selected to cope with the limited space between formation and casing and the single cable feedthrough at the wellhead of the pressurized system. Using specially designed centralizers, the fiber-optic cable was installed and hold in place successfully in the 2” annulus outside the casing. Within the present paper, the focus lies on the DTS system and the data acquired during cementation. This continuous temperature data showcases the ability of DTS systems to detect small temperature changes in high detail. During the whole cementation process, the rising level of cement as well as setting temperatures were captured by rising temperature values in the range of a few degrees Celsius. As next project steps, not part of this paper, spatiotemporally temperature data will be recorded during stimulation treatments of the seasonal geothermal energy storage. The authors believe that the experience made with this fiber-optic monitoring system can be a good demonstration of the capabilities of fiber-optic sensing in deep borehole environments. SMAR 2024 – 7th International Conference on Smart Monitoring, Assessment and Rehabilitation of Civil Structures Distributed fiber-optic temperature monitoring in boreholes of a seasonal geothermal energy storage Michael Iten a, *, Matthias Bühler a , Frank Fischli a , Falko Bethmann b and Andre El-Alfy b a Marmota Engineering AG, Technoparkstrasse 1, 8005 Zürich, Switzerland b GeoEnergie Suisse AG, Reitergasse 11, 8004 Zürich, Switzerland Abstract Monitoring the in-situ temperature is key for the characterization of a seasonal geothermal energy storage. Distributed fiber-optic temperature sensing (DTS) systems provide temporally and spatially continuous measurement data in near real-time that captures borehole temperature dynamics. In the presented project, three boreholes of a seasonal geothermal energy storage with a vertical depth of down to 500 meters were instrumented with distributed fiber-optic sensors. For this purpose, a standard armored sensor cable was modified to allow for combined DTS, distributed acoustic sensing (DAS) and distributed strain sensing (DSS) at temperatures up to 120 °C. The cable was installed in a loop configuration to allow for temperature calibration using a temperature matching approach. A “Mini - Bend” solution was selected to cope with the limited space between formation and casing and the single cable feedthrough at the wellhead of the pressurized system. Using specially designed centralizers, the fiber-optic cable was installed and hold in place successfully in the 2” annulus outside the casing. Within the present paper, the focus lies on the DTS system and the data acquired during cementation. This continuous temperature data showcases the ability of DTS systems to detect small temperature changes in high detail. During the whole cementation process, the rising level of cement as well as setting temperatures were captured by rising temperature values in the range of a few degrees Celsius. As next project steps, not part of this paper, spatiotemporally temperature data will be recorded during stimulation treatments of the seasonal geothermal energy storage. The authors believe that the experience made with this fiber-optic monitoring system can be a good demonstration of the capabilities of fiber-optic sensing in deep borehole environments. © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SMAR 2024 Organizers © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SMAR 2024 Organizers © 2024 The Authors. Published by Elsevier B.V. Peer-review under responsibility of SMAR 2024 Organizers

* Corresponding author. Tel.: +41 44 515 91 50; E-mail address: michael.iten@marmota.com * Corresponding author. Tel.: +41 44 515 91 50; E-mail address: michael.iten@marmota.com

2452-3216 © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SMAR 2024 Organizers 2452-3216 © 2024 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of SMAR 2024 Organizers

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