EGU2020-7759, updated on 12 Jun 2020
https://doi.org/10.5194/egusphere-egu2020-7759
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Deployment recommendation for Distributed Acoustic Sensing at the surface

Pascal Edme1, Patrick Paitz1, Ana Nap1, Francois Martin3, Valentin Metraux4, Luca Guglielmetti2, Cedric Schmelzbach1, Vincent Perron1, Daniel Bowden1, David Dupuy4, Andrea Moscariello2, Andreas Fichtner1, and Johan O. A. Robertsson1
Pascal Edme et al.
  • 1ETH-Zurich, Earth Sciences, Zurich, Switzerland (pascal.edme@erdw.ethz.ch)
  • 2University of Geneva, Geneva, Switzerland
  • 3Services Industriels de Geneve, Geneva, Switzerland
  • 4GEO2X SA, Yverdon-les-bains, Switzerland

Distributed Acoustic Sensing (DAS) is an optical interferometry based ground motion sensing technology which has the potential to revolutionize the field of seismological data acquisition. It offers the possibility to replace very large numbers of cost-intensive conventional point sensors (seismometers or geophones) by interrogating a single low-cost optic-fibre cable. Being unaffected by spatial aliasing, DAS is emerging as a potential next-generation broad-band geo-hazard (e.g. earthquakes, landslides) and reservoir (e.g. geothermal, oil and gas) seismic monitoring tool.

For borehole applications, with the cable appropriately coupled with the casing, the reliability and benefit of DAS-based VSP acquisition is now widely recognized. At the surface however, for reflection seismic for example, the adequate deployment procedure is less well documented, and experiments are performed with cables sometimes directly deployed on the surface, or sometimes buried quite deep (e.g. one meter) in the ground. Especially for non-permanent monitoring, the trenching effort can be substantial or unaffordable due to logistic or permitting issues. One may wonder if such an effort with its associated cost is actually beneficial.

We present here the results of a surface-based active seismic experiment conducted in Switzerland in the context of a geothermal reservoir characterization project with “co-located” stretches of cable deployed at different depths. The repeatability of the DAS measurements is quantified and compared to a dense array of conventional multi-component geophones. The study shows that deeply (50 cm) deployed cables offers only marginal data quality improvements compared to very shallow (2 cm) cables. In contrast, the parts of the cable directly laid down at the surface exhibit much larger noise levels and very poor repeatability (approximately one order of magnitude larger NRMS). Our study suggests that only a minor amount of elastic material covering the cable is enough to provide a good coupling and that a modest machine to conveniently perform such a shallow deployment would greatly benefit the growing DAS user community.

How to cite: Edme, P., Paitz, P., Nap, A., Martin, F., Metraux, V., Guglielmetti, L., Schmelzbach, C., Perron, V., Bowden, D., Dupuy, D., Moscariello, A., Fichtner, A., and Robertsson, J. O. A.: Deployment recommendation for Distributed Acoustic Sensing at the surface, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7759, https://doi.org/10.5194/egusphere-egu2020-7759, 2020

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Presentation version 3 – uploaded on 06 May 2020
With logos
  • CC1: Comment on EGU2020-7759, Tsunehisa Kimura, 06 May 2020

    Hello,

    Thank you very much for your interesting study & presentation. It encouraged us to use DAS with surface fiber cable if 2cm depth is enough to cover the fiber cable. As I asked over the chat at the end of your session, please provide answers for following questions:

    - What is the diameter of the fiber cable used for the experiment?

    - Is it special cable such as armoured cable or normal telecom cable?

    We also have DAS system called "hDVS", mainly used for VSP, flow measurement and pipeline monitoring in Oil & Gas business, but we are expanding application to others.

    Best regards,

    Tsune Kimura (tsune@slb.com)

    • AC1: Reply to CC1, Pascal Edme, 06 May 2020

      Hello Tsune

      Sorry I overlooked your message during the live chat.

      I have been exposed to hDVS as an ex SLB employe in Cambridge UK (for more than 10 years together with Hartur Hartog et al.)

      The diameter of the cable was 6.5mm with 2x SMF and 4x MMF,  tight buffered and Aramid Yarn Strength member.

      This cable (recommended by Silixa) is DAS oriented, however the fiber itself has nothing special, as used in telecom (not silixa's constellation)

      Do you think the structure of the cable itself could have a significant impact on coupling and SNR?

      Best regards

      Pascal

       

Presentation version 2 – uploaded on 04 May 2020 , no comments
Final version with GIFs
Presentation version 1 – uploaded on 01 May 2020 , no comments