1. Fiber Optic Distributed Temperature Sensing:
Seafloor and Subseafloor Applications
Robert Kleinberg
Schlumberger
Ridgefield, Connecticut
July 2003

2. Methane Hydrate Stability in Ocean and Sediment
Hydrate Stability Zone
after
Suess
Hydrate Trapped
in Sediments

3. Motivation for Temperature Sensing
To understand DBSR (Double Bottom Simulating Reflector)
Which BSR represents the contemporary thermal regime?
Are hydrates forming or dissociating between the BSRs?
To understand thermal regime throughout gas hydrate stability zone
Are the temperature gradients nonlinear?
If so, are they due to dynamic processes or heterogeneous distribution of hydrate?

4. Two Fiber Optic Temperature Measurement Systems
Distributed Temperature Sensing System (DTS) for coarse measurements over entire stability zone (~500 m)
continuous profile
z = 1 m vertical resolution
T = 0.2C temperature resolution
 Bragg Grating method (FBG) for fine point measurements near base of gas hydrate stability zone
30 discrete sensors
z = 8 mm sensor, 1 m measurement interval
T = 0.01C temperature resolution

5. DTS: Raman Scattering Lower Frequency Stokes Line - Weak Temperature
Dependence
Lower Frequency
Anti-Stokes Line -
Strong Temperature
Dependence
Higher Frequency

6. Incident Raleigh Light Incident Raleigh Light Incident Raleigh Light
DTS Measurement Concept
10 ns infrared pulses
Optical Fiber
Laser
Incident Raleigh Light
Brillouin
Anti-Stokes
Raman Band
Stokes
Incident Raleigh Light
Brillouin
Anti-Stokes
Raman Band
Stokes
Incident Raleigh Light
Brillouin
Anti-Stokes
Raman Band
Stokes
Back Scattered Light
Incident Raleigh Light
Analyser
Brillouin
Anti-Stokes
Raman Band
Stokes
Raman Band
Spectra of Back
Scattered Light

7. Fiber Bragg Grating Measurement Concept
Light
Source
Detector
Temperature-Dependent
Interference Gratings
splitter
Wavelength
Broadband
Excitation
one peak from
each grating
temperature changes
peak positions slightly

8. Temperature Measurement Cable & System Deployment Nankai Trough, Offshore Honshu
Schlumberger
JNOC
AIST
JAMSTEC
~1000m

9. Seafloor Monitoring System
power/signal buoy
sea surface
1000 m
sensor packages
seafloor