Downhole EM sensing using SAGNAC interferometer for wellbore monitoring

Patent metadata

Field	Value
Publication number	US-9926778-B2
Application number	US-201315038265-A
Country	US
Kind code	B2
Filing date	Dec 20, 2013
Priority date	Dec 20, 2013
Publication date	Mar 27, 2018
Grant date	Mar 27, 2018

Abstract

Method and apparatus are disclosed for use of a fiber-optic sensor loop for use within a wellbore; with a plurality of light sources optically coupled to the fiber-optic sensor loop; at least one electromagnetically sensitized region within the fiber-optic sensor loop; and a plurality of detectors optically coupled to the fiber-optic sensor loop; and using the sensing system to detect changes in a magnetic field within the wellbore.

First claim

What is claimed is:

1. A sensing system, comprising:
a fiber-optic sensor loop disposed within a wellbore;
a plurality of light sources optically coupled to the fiber-optic sensor loop wherein the plurality of light sources comprises a first light source that emits light at a first wavelength and a second light source that emits light at a second wavelength;
a first output of the first light source coupled to a first input of a first wavelength division multiplexer;
a second output of the second light source coupled to a second input of the first wavelength division multiplexer, wherein the first wavelength division multiplexer combines the first output and the second output;
a polarizer coupled to the first wavelength division multiplexer, wherein the polarizer receives the combined first output and the second output;
a first optical coupler coupled to the polarizer, wherein the first optical coupler splits the combined first output and the second output into a clockwise path to a second wavelength divisional multiplexer and a counterclockwise path to a third divisional multiplexer, and wherein a clockwise center of the clockwise path and a counterclockwise center of the counterclockwise path are offset in opposite direction from a geometric center of the fiber-optic sensor loop;
at least one electromagnetically sensitized region within the fiber-optic sensor loop that allows the fiber-optic sensor loop to detect changes in one or more electromagnetic fields acting on the fiber-optic sensor loop based, at least in part, on a first gain modeled for the clockwise path and a second gain modeled for the counterclockwise path; and
a plurality of detectors optically coupled to the fiber-optic sensor loop.

2. The sensing system of claim 1 , wherein the plurality of light sources are broadband light sources.

3. The sensing system of claim 1 , wherein the plurality of detectors are orthogonal phase demodulators.

4. The sensing system of claim 1 , further comprising a lyot depolarizer connected to the sensor loop and located at approximately a sensor loop midpoint.

5. The sensing system of claim 1 , wherein the electromagnetically sensitized region comprises a ferromagnetic coating.

6. The sensing system of claim 1 , wherein the fiber-optic sensor loop is attached to a casing string located in the wellbore.

7. The sensing system of claim 1 , wherein the electromagnetically sensitized region is placed in a depth of interest having a waterfront.

8. A method of sensing, comprising:
providing a fiber-optic sensor loop, wherein the fiber-optic sensor loop is disposed within a wellbore;
optically coupling a plurality of light sources to the fiber-optic sensor loop, wherein the plurality of light sources comprises a first light source that emits light at a first wavelength and a second light source that emits light at a second wavelength; optically coupling a first output of the first light source to a first input of a first wavelength division multiplexer;
optically coupling a second output of the second light source to a second input of the first wavelength division multiplexer, wherein the first wavelength division multiplexer combines the first output and the second output;
optically coupling a polarizer to the first wavelength division multiplexer, wherein the polarizer receives the combined first output and the second output;
optically coupling a first optical coupler to the polarizer, wherein the first optical coupler splits the combined first output and the second output into a clockwise path to a second wavelength divisional multiplexer and a counterclockwise path to a third divisional multiplexer, and wherein a clockwise center of the clockwise path and a counterclockwise center of the counterclockwise path are offset in opposite direction from a geometric center of the fiber-optic sensor loop;
optically coupling a plurality of detectors to the fiber-optic sensor loop; sending light from the plurality of light sources through the fiber-optic sensor loop;
and detecting a disturbance that causes an optical path change at a first position on the fiber-optic sensor loop, wherein the disturbance is caused by a magnetic field based, at least in part, on a first gain modeled for the clockwise path and a second gain modeled for the counterclockwise path.

9. The method of claim 8 , wherein the fiber-optic sensor loop further comprises at least one electromagnetically sensitized region.

10. The method of claim 9 , wherein the electromagnetically sensitized region comprises a ferromagnetic coating.

11. The method of claim 8 , wherein detecting a disturbance to the fiber-optic sensor loop comprises determining a location of the disturbance to the fiber-optic sensor loop.

12. The method of claim 11 , wherein determining the location of the disturbance comprises detecting a first disturbance and a second disturbance to the fiber-optic sensor loop and determining a first location of the first disturbance and a second location of the second disturbance, wherein the first disturbance and the second disturbance occur at substantially the same time.

13. The method of claim 8 , wherein the plurality of detectors are orthogonal phase demodulators.

14. The method of claim 8 , wherein detecting a disturbance to the fiber-optic sensor loop caused by a magnetic field further comprises detecting a change to the magnetic field within a depth of interest, and wherein the change to the magnetic field is caused by a waterfront.

15. A method of sensing a magnetic field, comprising:
providing an optical sensing system, comprising:
a fiber-optic sensor loop,
a plurality of light sources optically coupled to a first end of the fiber-optic sensor loop, wherein the plurality of light sources comprises a first light source that emits light at a first wavelength and a second light source that emits light at a second wavelength;
a first output of the first light source coupled to a first input of a first wavelength division multiplexer;
a second output of the second light source coupled to a second input of the first wavelength division multiplexer, wherein the first wavelength division multiplexer combines the first output and the second output;
a polarizer coupled to the first wavelength division multiplexer, wherein the polarizer receives the combined first output and the second output;
a first optical coupler coupled to the polarizer, wherein the first optical coupler splits the combined first output and the second output into a clockwise path to a second wavelength divisional multiplexer and a counterclockwise path to a third divisional multiplexer, and wherein a clockwise center of the clockwise path and a counterclockwise center of the counterclockwise path are offset in opposite direction from a geometric center of the fiber optic sensor loop;
at least one electromagnetically sensitized region within the fiber-optic sensor loop that allows the fiber-optic sensor loop to detect changes in one or more electromagnetic fields acting on the fiber-optic sensor loop; and
a plurality of detectors optically coupled to a second end of the fiber-optic sensor loop;
placing the fiber-optic sensor loop in a wellbore;
sending at least the light at the first wavelength from the first light source and the light at the second wavelength from the second light source through the fiber-optic sensor loop; and
detecting a disturbance to the fiber-optic sensor loop caused by a magnetic field based, at least in part, on a first gain modeled for the clockwise path and a second gain modeled for the counterclockwise path.

16. The metho

Assignees

• Halliburton Energy Services Inc

Inventors

• Maida John L
• Mandviwala Tasneem A
• Cekorich Allen

Classifications

• G01V8/24

  using optical fibres · CPC title

• G01R33/032 Primary

  using magneto-optic devices, e.g. Faraday {or Cotton-Mouton effect} · CPC title

• E21B43/20 Primary

  Displacing by water · CPC title

• E21B47/113

  using electrical indications; using light radiations · CPC title

• G01C19/722

  of the mechanical construction · CPC title