FIBER OPTIC REFRACTOMETER

• US 20090153845A1
• Filed: 12/14/2007
• Published: 06/18/2009
• Est. Priority Date: 12/14/2007
• Status: Active Grant

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: DiFoggio, Rocco
• Granted Patent: US 7,852,468 B2
• Time in Patent Office: Days
• US Class Current: 356/133
• CPC Class Codes: G01D 5/268 using optical fibres G01D5/28 - G01D5/38 take precedence
• CPC Class Codes: G01N 2021/8528 Immerged light conductor
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/41 Refractivity; Phase-affecting properties, e.g. optical path length G01N21/21 takes precedence
• CPC Class Codes: G01N 21/552 Attenuated total reflection
• CPC Class Codes: G01N 33/2823 raw oil, drilling fluid or polyphasic mixtures hydrocarbon content of earth materials G01N33/241; prospecting G01V; drilling per se E21B

Abstract

A downhole refractometer apparatus and method include a light source, an optical fiber that receives light emitted from the light source and a fluid cell that receives a downhole fluid. A metalloid interface member is disposed to provide an interface with the downhole fluid in the fluid cell, and a light detecting device detects a light reaction at the metalloid interface member, the downhole fluid property being estimable at least in part based on the light reaction.

Claims

1. An apparatus for estimating a downhole fluid property comprising:

a light source;

an optical fiber that receives light emitted from the light source;

a fluid cell that receives a downhole fluid;

a metalloid interface member disposed to provide an interface with the downhole fluid in the fluid cell; and

a light detecting device that detects a light reaction at the metalloid interface member, the downhole fluid property being estimable at least in part based on the light reaction.

2. An apparatus according to claim 1, wherein the metalloid interface member comprises one or more of Si and Ge.

3. An apparatus according to claim 1, wherein the metalloid interface member comprises a metalloid material disposed on a distal end of the optical fiber.

4. An apparatus according to claim 3, wherein the distal end of the optical fiber is disposed within the fluid cell and immersed in the downhole fluid to a selected depth.

5. An apparatus according to claim 1, wherein the fluid cell comprises a window, the metalloid interface member comprising a metalloid material forming at least a portion of the window.

6. An apparatus according to claim 1, wherein the light source includes a broad-band light source and a filter for providing a source light having a selected wavelength.

7. An apparatus according to claim 1, wherein the light source includes a narrow-band light source for providing a source light having a selected wavelength.

8. An apparatus according to claim 1, wherein the light detecting device comprises a dual-layer photodetector responsive to at least two wavelengths of light, wherein a first detected wavelength is indicative of light emitted from the light source and a second detected wavelength is indicative of light interaction with the downhole fluid at the metalloid interface member.

9. An apparatus according to claim 1, wherein the optical fiber includes a first section of optical fiber and a second section of optical fiber coupled to the first section in a Y-coupling arrangement, the first section being longer than the second section and wherein the light detecting device detects light traveling in the second section of optical fiber before detecting light traveling in the first section of optical fiber.

10. An apparatus according to claim 9, wherein one of the first section of the optical fiber and the second section of the optical fiber conveys source light toward the metalloid interface member and the other of the first section of the optical fiber and the second section of the optical fiber conveys source light toward the light detecting device.

11. An apparatus according to claim 10 further comprising a processor that receives a first output signal from the light detecting device indicative of source light intensity and a second output signal indicative of reflected light intensity, the source light intensity and the reflected light intensity being detected by the light detecting device at different times.

12. A method for estimating a downhole fluid property comprising:

emitting a light from a light source;

conveying the emitted light in an optical fiber toward a metalloid interface member disposed to provide an interface with a downhole fluid in a fluid cell;

detecting a light reaction at the metalloid interface member using a light detecting device; and

estimating the downhole fluid property at least in part using the detected light reaction.

13. A method according to claim 12, wherein the metalloid interface member comprises one or more of Si and Ge and detecting a light reaction comprises detecting a light reflection intensity.

14. A method according to claim 12, wherein the metalloid interface member comprises a metalloid material disposed on a distal end of the optical fiber, the method further comprising immersing the distal end of the optical fiber in the downhole fluid to a selected depth.

15. A method according to claim 12, wherein conveying the emitted light includes conveying the emitted light to a window in the fluid cell, the metalloid interface member comprising a metalloid material forming at least a portion of the window.

16. A method according to claim 12, wherein emitting a light includes emitting a broadband light and filtering the broadband light with a filter to provide a source light having a selected wavelength.

17. A method according to claim 12, wherein emitting a light includes emitting a narrow-band light to provide a source light having a selected wavelength.

18. A method according to claim 12, wherein emitting a light includes emitting at least two wavelengths of light, the light detecting device including a dual-layer photodetector responsive to the at least two wavelengths of light and wherein a first detected wavelength is indicative of light emitted from the light source and a second detected wavelength is indicative of light interaction with the downhole fluid at the metalloid interface member.

19. A method according to claim 12, wherein conveying the emitted light includes conveying the emitted light in a first section of optical fiber and conveying the emitted light in a second section of optical fiber coupled to the first section of optical fiber in a Y-coupling arrangement, the method further comprising:

delaying detecting the light conveyed in the first section by using an optical fiber in the first section that is longer than the second section optical fiber; and

detecting light traveling in the second section of optical fiber before detecting light traveling in the first section of optical fiber.

20. A method according to claim 19, wherein one of the first section and the second section conveys source light toward the metalloid interface member and the other of the first section and the section conveys source light toward the light detecting device.

21. A method according to claim 20 further comprising transmitting a first output signal from the light detecting device indicative of source light intensity to a processor and transmitting a second output signal from the light detecting device indicative of reflected light intensity to the processor.

22. A refractometer with downhole calibration, comprising:

a light source that emits at least two wavelengths of light to an optical fiber;

a fluid cell that receives a downhole fluid;

a metalloid interface member disposed to provide an interface with the downhole fluid in the fluid cell, the metalloid interface member reflecting a first wavelength of the at least two wavelengths to a return optical fiber and transmitting a second wavelength of the at least two wavelengths to the downhole fluid, at least a fraction of the second wavelength being reflected by the downhole fluid and to the return optical fiber; and

a light detecting device that detects the first wavelength and the reflected fraction of the second wavelength, the detected first wavelength being indicative of a light source characteristic and the detected fraction of the second wavelength being indicative of a downhole fluid characteristic.

23. A refractometer according to claim 22, wherein the light detecting device includes a dual-layer photodetector comprising a first layer responsive to the first wavelength and a second layer responsive to the second wavelength.

24. A method for calibrating a refractometer downhole, comprising:

emitting at least two wavelengths of light from a light source to an optical fiber;

receiving a downhole fluid in a fluid cell, a metalloid interface member being disposed to provide an interface with the downhole fluid in the fluid cell;

reflecting a first wavelength of the at least two wavelengths to a return optical fiber;

transmitting a second wavelength of the at least two wavelengths to the downhole fluid;

reflecting at least a fraction of the second wavelength at the downhole fluid and to the return optical fiber;

detecting the first wavelength and the reflected fraction of the second wavelength with a light detecting device, the detected first wavelength being indicative of a light source characteristic and the detected fraction of the second wavelength being indicative of a downhole fluid characteristic; and

calibrating the refractometer in-situ using the light source characteristic and the downhole fluid characteristic.