06 Jul 2021

06 Jul 2021

Review status: a revised version of this preprint is currently under review for the journal SE.

Dynamic motion monitoring of a 3.6 km long steel rod in a borehole during cold-water injection with distributed fiber-optic sensing

Martin P. Lipus1, Felix Schölderle2, Thomas Reinscha,1, Christopher Wollin1, Charlotte M. Krawczyk1,3, Daniela Pfrang2, and Kai Zosseder2 Martin P. Lipus et al.
  • 1GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany
  • 2Technical University Munich, Hydrogeology and Geothermal Energy, Arcisstr. 21, 80333 Munich, Germany
  • 3Technical University (TU) Berlin, Institute for Applied Geosciences, Ernst-Reuter-Platz 1, 10587 Berlin, Germany
  • apresent address: Fraunhofer IEG, Fraunhofer Research Institution for Energy Infrastructures and Geothermal Systems IEG, Am Hochschulcampus 1 IEG, 44801 Bochum, Germany

Abstract. Fiber-optic distributed acoustic sensing (DAS) data finds many applications in wellbore monitoring such as e.g. flow monitoring, formation evaluation, and well integrity studies. For horizontal or highly deviated wells, wellbore fiber-optic installations can be conducted by mounting the sensing cable to a rigid structure (casing/tubing) which allows for a controlled landing of the cable. We analyze a cold-water injection phase in a geothermal well with a 3.6 km long fiber-optic installation mounted to a ¾” sucker-rod by using both DAS and distributed temperature sensing (DTS) data. During cold-water injection, we observe distinct vibrational events (shock waves) which originate in the reservoir interval and migrate up- and downwards. We use temperature differences from the DTS data to determine the theoretical thermal contraction and integrated DAS data to estimate the actual deformation of the rod construction. The results suggest that the rod experiences thermal stresses along the installation length – partly in the compressional and partly in the extensional regime. We find strong evidence that the observed vibrational events originate from the release of the thermal stresses when the friction of the rod against the borehole wall is overcome. Within this study, we show the influence of temperature changes on the acquisition of distributed acoustic/strain sensing data along a fiber-optic cable suspended along a rigid but freely hanging rod. We show that observed vibrational events do not necessarily originate from induced seismicity in the reservoir, but instead, can originate from stick-slip behavior of the rod construction that holds the measurement equipment.

Martin P. Lipus et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on se-2021-63', Ryan Schultz, 06 Aug 2021
    • AC1: 'Reply on RC1', Martin Lipus, 20 Sep 2021
  • RC2: 'Comment on se-2021-63', Anonymous Referee #2, 14 Aug 2021
    • AC2: 'Reply on RC2', Martin Lipus, 20 Sep 2021

Martin P. Lipus et al.

Martin P. Lipus et al.


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Short summary
A fiber optic cable was installed along a sucker rod in a deep geothermal well in Munich, Germany. A cold water injection test was monitored by means of fiber-optic distributed acoustic and temperature sensing. During injection, we observe vibrational events in the lower part of the well. On the basis of a mechanical model, we conclude that the vibrational events are caused by thermal contraction of the sucker rod. The results illustrate potential artifacts when analyzing downhole seismic data.