Attenuation correction for distrbuted temperature sensors using antistokes to rayleigh ratio

Patent metadata

Field	Value
Publication number	US-9989425-B2
Application number	US-201514664254-A
Country	US
Kind code	B2
Filing date	Mar 20, 2015
Priority date	Apr 21, 2014
Publication date	Jun 5, 2018
Grant date	Jun 5, 2018

Abstract

A distributed temperature sensor, a method of determining temperature, and a processing system to compute temperature are described. The sensor includes an optical fiber disposed in an area where temperature is to be measured, a primary light source to inject light into the optical fiber, and a secondary light source to inject light into the optical fiber. The sensor additionally includes a photodetector to detect backscatter light energy from the optical fiber the backscatter light energy including Stokes Raman scatter or anti-Stokes Raman scatter and primary Rayleigh scatter resulting from the primary light source and secondary Rayleigh scatter resulting from the secondary light source, and a processor to determine temperature based on a ratio of the Stokes Raman scatter or the anti-Stokes Raman scatter and a combination of the primary Rayleigh scatter and the secondary Rayleigh scatter.

First claim

The invention claimed is:

1. A distributed temperature sensor, comprising:
an optical fiber disposed in an area where temperature is to be measured;
a primary light source configured to inject light into the optical fiber;
a secondary light source configured to inject light into the optical fiber, the light injected by the secondary light source as pulses always having a wavelength either equal to a Stokes Raman scatter resulting from injection of the light injected by the primary light source or a wavelength equal to an anti-Stokes Raman scatter resulting from injection of the light injected by the primary light source;
a photodetector configured to detect backscatter light energy from the optical fiber the backscatter light energy including the Stokes Raman scatter or the anti-Stokes Raman scatter resulting from the injection of the light injected by the primary light source, primary Rayleigh scatter resulting from the primary light source, and secondary Rayleigh scatter resulting from the secondary light source; and
a processor configured to calculate temperature based on a ratio of the Stokes Raman scatter to a combination of the primary Rayleigh scatter and the secondary Rayleigh scatter or the anti-Stokes Raman scatter to the combination of the primary Rayleigh scatter and the secondary Rayleigh scatter.

2. The sensor according to claim 1 , wherein the processor determines the temperature based on

S

RAp

⁢

RAs

,

where S is the Stokes Raman backscatter, RAp is the primary Rayleigh backscatter, and RAs is the secondary Rayleigh backscatter.

3. The sensor according to claim 1 , wherein the processor determines the temperature based on

AS

RAp

⁢

RAas

,

where AS is the anti-Stokes Raman backscatter, RAp is the primary Rayleigh backscatter, and RAas is the secondary Rayleigh backscatter.

4. The sensor according to claim 3 , wherein the processor determines the temperature according to

1

λ
as
4

⁢

F
⁡

(
T
)

(

1

λ
p

⁢

λ
as

)

4

·
σκ

,

where λ as is a wavelength of the anti-Stokes Raman scatter, λ p is a wavelength of the first Rayleigh scatter, σ represents all geometrical and fundamental constants associated with RAp, κ represents all the geometrical and fundamental constants associated with RAas, and F(T) includes all temperature dependent terms.

5. The sensor according to claim 1 , wherein the area is a subsurface environment to determine the temperature in a borehole.

6. The sensor according to claim 1 , wherein the photodetector detects the backscatter light energy from the optical fiber originating at a plurality of points along the optical fiber, and the processor determines the temperature at the plurality of points along the optical fiber.

7. A method of determining temperature, the method comprising:
disposing an optical fiber in an area where the temperature is to be measured;
injecting, using a primary light source, primary light into the optical fiber;
injecting, using a secondary light source, secondary light as pulses into the optical fiber, the secondary light always having a wavelength either equal to Stokes Raman scatter generated by the injecting the primary light or equal to anti-Stokes Raman scatter generated by the injecting the primary light;
detecting, using a photodetector, backscatter light energy resulting in the optical fiber from the primary light source and the secondary light source, the backscatter light energy including the anti-Stokes Raman scatter or the Stokes Raman scatter generated by the injecting the primary light, primary Rayleigh scatter resulting from the injecting the primary light, and secondary Rayleigh scatter resulting from the injecting the secondary light; and
processing the backscatter light energy to calculate the temperature based on a ratio of the anti-Stokes Raman scatter to a combination of the primary Rayleigh scatter and the secondary Rayleigh scatter or the Stokes Raman scatter to the combination of the primary Rayleigh scatter and the secondary Rayleigh scatter.

8. The method according to claim 7 , wherein the processing the light energy includes determining the temperature based on

S

RAp

⁢

RAs

,

where S is the Stokes Raman scatter, RAp is the primary Rayleigh scatter, and RAs is the secondary Rayleigh scatter.

9. The method according to claim 7 , wherein the processing the light energy includes determining the temperature based on

AS

RAp

⁢

RAas

,

where AS is the anti-Stokes Raman scatter, RAp is the primary Rayleigh scatter, and RAas is the secondary Rayleigh scatter.

10. The method according to claim 9 , wherein the determining the temperature is according to

1

λ
as
4

⁢

F
⁡

(
T
)

Assignees

• Mitchell Ian
• Johnston William
• Chandran Ashwin
• Baker Hughes A Ge Co Llc

Inventors

• Mitchell Ian
• Johnston William
• Chandran Ashwin

Classifications

• E21B47/135

  using light waves, e.g. infrared or ultraviolet waves · CPC title

• E21B47/07

  Temperature · CPC title

• G01K11/32 Primary

  using changes in transmittance, scattering or luminescence in optical fibres · CPC title

• E21B47/065

  Fixed Constructions · mapped topic

• E21B47/123

  Fixed Constructions · mapped topic