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Philippe Jousset

Use of distributed sensing optical fibres for parameter monitoring. Philippe Jousset. Motivation. Faults are important for exploration of structure and morphology of the Earth seismic hazard volcano eruptions Unknows within faults Detailled structure F ault motion

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Philippe Jousset

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  1. Use of distributed sensing optical fibres for parameter monitoring Philippe Jousset

  2. Motivation • Faults are important for • exploration of structure and morphology of the Earth • seismic hazard • volcano eruptions • Unknows within faults • Detailled structure • Fault motion • What triggers earthquakes? • Creeping processes?

  3. Motivation Densification of sensors - Examples: + Volcanoes iMUSH - Mount St Helens – 900 nodes VolcArray - Piton de la Fournaise – 300 sensors + Geothermal systems LABEX g-eauthermie, Strasbourg – 250 nodes + Volcanoes, calderas and geothermal systems - IMAGE network– 230 sensors - GEMEX network – 55 sensors – see poster

  4. Fibre optic sensing technologies allow • Imaging of faults • Detect 100 nanometers fault movement

  5. Fibre Optic Sensing Technologies • Single sensor – designed sensors • More accurate strain measurement – Bragg sensors • Limited spatial resolution Coutant et al., 2015 • Transmission of information in the cable with the light • Telecommunication technologies • Time transmission and delays Marra et al., 2018 • – example project Refimeve+ • Distributed sensors: the whole length of the fiber is used • Dense and accurate of strain mesaurement – DAS • Several tens km, sampled every meter Jousset et al., 2018

  6. FiberOptic Sensing Technologies Optical source PHYSICAL PHENOMENA Transmission SENSOR Analysis Spectrometer Delays in phase transmission DAS: fibre is the sensor Single sensor Jousset et al. 2018 Coutant et al. 2015 Marra et al. 2018

  7. Distributed Sensing • traditional sensors rely on discrete sensors (pre-determined points) • distributed sensing does not rely upon manufactured sensors but utilises the optical fibreas sensing principle. Telecom cables already deployed work. • continuous, real-time measurements along the entire length of a fibre optic cable. • Temperature – DTS Henninges et al., 2014 • Strain – DAS Jousset et al., 2016; VSP, borehole measurements Reinsch et al, 2016

  8. DAS – Distributed Acoustic SensingThe sensor is the fibre itself • allow for a simultaneous dense(meter-scale spacing) acquisition of strain along the entire lengthof the cable (several 10 km) • read-out unit operated remotely • -> Objective: • more detailed structural images • more acute understanding of processes

  9. Measurement Principle Optical fiber Coherent laser pulse Elastic Rayleigh scattering  Change in Intensity/Time = Change in Strain/Time (strain rate)  Integration of strain rate = Local strain

  10. VeðurstofaÍslands Hengill Reykjanes Svartsengi IMO 1 - 1.5 cm/year

  11. Geophysical Instrumental Pool of Potsdam BB sensor + cube(+GPS) Geophone + cube(+GPS)

  12. Geophysical Instrumental Pool of Potsdam BB sensor + cube(+GPS) ~ 15 km Geophone + cube(+GPS) Recording for 9 days continuously (1000 Hz)

  13. PreliminaryResults

  14. Local Earthquake P-Wave 1 s S-Wave • IMO 23.03.2015 16:07:08.53 • Depth: 3.563 km • Magnitude: 1.02Ml • Location: Beneath Cable

  15. Local Earthquake P-Wave 1 s S-Wave 3700 traces (4 m interval) • IMO 23.03.2015 16:07:08.53 • Depth: 3.563 km • Magnitude: 1.02Ml • Location: Beneath Cable

  16. Fibre optic allows fine structure exploration of faults Jousset et al., Nat. Comm, 2018

  17. Fibre optic measuresfault creeping mechanisms Jousset et al., Nat. Comm, 2018

  18. We have acquired data on a cable already deployed (1994) at the surface Acquisition of Digital Acoustic Sensing data Allows imaging of fault damage zone Detect fault creeping mechanism Compared seismometer and geophone and fiber optic data -> Broadband character of the records Summary, conclusions • High potential for applications in geoscience • Seismic source understanding (natural earthquakes, noise, ...) • New methods for imaging with dense acquisition (Helmholtz tomography, ...) • Volcanic, seismic hazard, etc. • New concept of seismic data analysis, processing and modelling Jousset P., T. Reinsch, T. Ryberg, H. Blanck, A. Clarke et al. (2018) Dynamic strain determination using fibre-optic cables allows imaging of seismological and structural features, Nature Communications, 3 July 2018.

  19. Thank you Pic Thomas Reinsch (GFZ), April 2015

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