Downhole fiber optic sensors with downhole optical interrogator

Patent metadata

Field	Value
Publication number	US-2016266265-A1
Application number	US-201514645122-A
Country	US
Kind code	A1
Filing date	Mar 11, 2015
Priority date	Mar 11, 2015
Publication date	Sep 15, 2016
Grant date	—

Abstract

An apparatus for sensing a parameter beneath a surface of the earth includes an optical fiber disposed beneath a surface of the earth and comprising at least one fiber Bragg grating sensor configured to sense the parameter and a wide-band light source disposed beneath the surface of the earth and configured to emit light in a wide band of wavelengths to illuminate the at least one fiber Bragg grating. An optical interrogator is disposed beneath the surface of the earth and configured to receive light reflected by the at least one fiber Bragg grating sensor and to transform a shift in wavelength of the reflected light into a variation of light intensity. A photo-sensor is configured to measure intensity of light received from the optical interrogator. Electronics are coupled to the photo-sensor and configured to measure a voltage representing the light intensity at the photo-sensor to sense the parameter.

First claim

1 . An apparatus for sensing a parameter beneath a surface of the earth, the apparatus comprising:
an optical fiber disposed beneath a surface of the earth and comprising at least one fiber Bragg grating sensor configured to sense the parameter, wherein the at least one fiber Bragg grating is pressure compensated and the at least one fiber Bragg grating is immersed in a compressible fluid for the pressure compensation; a flexible membrane coupled to the optical fiber and configured to sense acoustic wave amplitude; a wide-band light source disposed beneath the surface of the earth and configured to emit light in a wide band of wavelengths, the light source being in optical communication with the optical fiber in order to illuminate the at least one fiber Bragg grating; an optical interrogator disposed beneath the surface of the earth and configured to receive light reflected by the at least one fiber Bragg grating sensor and to transform a shift in wavelength of the reflected light into a variation of light intensity, a photo-sensor disposed beneath the surface of the earth and configured to measure intensity of light received from the optical interrogator; and electronics coupled to the photo-sensor and configured to measure a voltage representing the light intensity at the photo-sensor to sense the parameter.

2 . The apparatus according to claim 1 , wherein the at least one fiber Bragg grating sensor comprises a series of fiber Bragg grating sensors that are configured to sense acoustic wave amplitude.

3 . (canceled)

4 . (canceled)

5 . The apparatus according to claim 1 , further comprising a capillary tube configured to communicate hydrostatic pressure at a location the at least one fiber Bragg grating to the compressible fluid.

6 . The apparatus according to claim 1 , wherein the optical interrogator comprises an arrayed waveguide grating.

7 . The apparatus according to claim 1 , wherein the optical interrogator comprises at least one matched fiber Bragg grating forming an intersecting wavelength with the at least one fiber Bragg grating sensor.

8 . The apparatus according to claim 1 , wherein the wide-band light source is configured to emit light within a range of wavelengths from 5 nm to 100 nm.

9 . The apparatus according to claim 1 , wherein the wide-band light source comprises a super luminescent diode.

10 . The apparatus according to claim 1 , wherein the wide-band light source comprises a wide-band laser diode.

11 . The apparatus according to claim 1 , wherein the photo-sensor comprises a photodiode.

12 . The apparatus according to claim 11 , wherein the photodiode comprises a plurality of photodiodes with each photodiode in the plurality of photodiodes corresponding to a unique output channel in the optical interrogator.

13 . The apparatus according to claim 1 , wherein the photo-sensor comprises a pyroelectric sensor.

14 . The apparatus according to claim 1 , wherein the optical fiber comprises a plurality of optical fibers with each optical fiber in the plurality of optical fibers comprising a series of fiber Bragg grating sensors configured to sense the parameter.

15 . The apparatus according to claim 1 , wherein the optical fiber is affixed to a downhole structure and the sensed parameter is temperature or strain.

16 . The apparatus according to claim 1 , wherein the optical interrogator comprises an acousto-optic tunable filter.

17 . The apparatus according to claim 1 , wherein the optical interrogator comprises at least one fiber Bragg grating matched to optical characteristics of the at least one fiber Bragg grating sensor.

18 . A method for sensing a parameter beneath a surface of the earth, the method comprising:
disposing an optical fiber beneath a surface of the earth, the optical fiber comprising at least one fiber Bragg grating sensor configured to sense the parameter; compensating for hydrostatic pressure by: immersing the at least one fiber Bragg grating sensor in a compressible fluid; communicating outside pressure with the compressible fluid using a capillary tube; and sensing the acoustic wave amplitude using a flexible membrane affixed to the optical fiber; illuminating the at least one fiber Bragg grating sensor using a wide-band light source disposed beneath the surface of the earth, the light source being configured to emit light in a wide band of wavelengths; receiving light reflected by the at least one fiber Bragg grating sensor using an optical interrogator disposed beneath the surface of the earth, the optical interrogator being configured to transform a shift in wavelength of the reflected light into a variation of light intensity; measuring intensity of light received from the optical interrogator using a photo-sensor disposed beneath the surface of the earth; measuring a voltage representing the light intensity at the photo-sensor to sense the parameter using electronics coupled to the photo-sensor.

19 . The method according to claim 18 , wherein the at least one fiber Bragg grating sensor is configured to sense acoustic wave amplitude.

20 . (canceled)

21 . The method according to claim 19 , wherein the acoustic wave amplitude comprises acoustic sounds and the method further comprises broadcasting the acoustic sounds sensed by the at least one of the fiber Bragg grating sensor to a user using a loudspeaker.

22 . The method according to claim 18 , further comprising affixing the optical fiber to a downhole structure and wherein the parameter is temperature or strain.

Assignees

• Kruspe Thomas
• Jung Sebastian
• Csutak Sebastian
• Baker Hughes Inc

Inventors

• Kruspe Thomas
• Jung Sebastian
• Csutak Sebastian

Classifications

• E21B47/00

  Survey of boreholes or wells (monitoring pressure or flow of drilling fluid E21B21/08) · CPC title

• G01H9/004 Primary

  using fibre optic sensors (light guides per se G02B6/00, acousto-optical devices specially adapted for gating or modulating in optical wave guides G02F1/125) · CPC title

• G02B6/02076

  Refractive index modulation gratings, e.g. Bragg gratings · CPC title

• G01V8/16

  using optical fibres · CPC title

• G01V1/186 Primary

  Hydrophones · CPC title