Real-time calibration for downhole spectrometer

• US 20070109537A1
• Filed: 11/14/2005
• Published: 05/17/2007
• Est. Priority Date: 11/14/2005
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Inventors: Vannuffelen, Stephane, Otsuka, Akira, Yamate, Tsutomu, Indo, Kentaro, Nakayama, Takeaki, Terabayashi, Toru
• Granted Patent: US 7,609,380 B2
• Time in Patent Office: Days
• US Class Current: 356/326
• CPC Class Codes: G01J 2001/4242 Modulated light, e.g. for synchronizing source and detector circuit
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0232 using shutters
• CPC Class Codes: G01J 3/433 Modulation spectrometry; Derivative spectrometry
• CPC Class Codes: G01N 2021/317 Special constructive features
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 21/31 Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry G01N21/72 takes precedence
• CPC Class Codes: G01N 2201/0218 Submersible, submarine
• CPC Class Codes: G01N 2201/1211 for temperature
• CPC Class Codes: G01N 2201/12723 Self check capacity; automatic, periodic step of checking
• CPC Class Codes: G01N 2201/12792 Compensating own radiation in apparatus
• 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

An apparatus for performing real-time analysis of a subterranean formation fluid includes a light source configured to transmit at least a sample signal through a sample of the subterranean formation fluid and a reference signal, at least one photodetector configured to continuously detect the sample and reference signals, and an electronics assembly configured to compensate for drift in the detected sample signal in real-time based on the value of the detected reference signal.

Claims

1. An apparatus for performing real-time analysis of a subterranean formation fluid, comprising:

a light source configured to transmit at least a sample signal through a sample of the subterranean formation fluid and a reference signal;

at least one photodetector configured to continuously detect the sample and reference signals;

an electronics assembly configured to compensate for drift in the detected sample signal in real-time based on the value of the detected reference signal.

2. The apparatus according to claim 1, further comprising a modulator for modulating the sample and reference signals.

3. The apparatus according to claim 2, further comprising a signal separation assembly for separating the modulated sample signal from the modulated reference signal.

4. The apparatus according to claim 3, wherein the signal separation assembly comprises a spectrometer.

5. The apparatus according to claim 4, wherein the spectrometer is a fixed wavelength spectrometer or a tunable spectrometer.

6. The apparatus according to claim 2, wherein the modulator modulates the sample signal and the reference signal at different frequencies.

7. The apparatus according to claim 2, wherein the modulator generates a phase shift between the sample signal and the reference signal.

8. The apparatus according to claim 6, wherein the modulator comprises:

a first optical chopper configured to modulate the sample signal at a first frequency;

a second optical chopper configured to modulate the reference signal at a second frequency differing from the first frequency.

9. The apparatus according to claim 6, wherein the modulator comprises a single optical chopper, the single optical chopper comprising:

a first circular row of apertures configured to modulate the sample signal;

a second circular row of apertures configured to modulate the reference signal;

wherein the number of apertures in the first circular row differs from the number of apertures in the second circular row.

10. The apparatus according to claim 7, wherein the modulator comprises a single optical chopper;

the sample signal is positioned to contact the single optical chopper at a first position;

the reference signal is positioned to contact the single optical chopper at a second position;

the second position is separated from the first position by a desired phase shift angle.

11. The apparatus according to claim 10, further comprising:

a sample photodetector positioned to detect the phase of the sample signal;

a reference photodetector positioned to detect the phase of the reference signal.

12. The apparatus according to claim 10, wherein the single optical chopper comprises a single aperture for modulating the sample and reference signals.

13. The apparatus according to claim 12, wherein the electronics assembly is configured to compensate for drift in the detected sample signal based on the value of the detected reference signal and an offset voltage generated by the electronics assembly.

14. The apparatus according to claim 1, wherein the light source is a wavelength tunable light source or a broad-spectrum light source.

15. The apparatus according to claim 14, wherein the light source is an incandescent lamp, a light-emitting diode (LED), a monochromator, or a tunable laser diode.

16. The apparatus according to claim 2, wherein the modulator comprises a digital modulator.

17. A method for analyzing a subterranean formation fluid, comprising:

transmitting a sample signal through a sample of the subterranean formation fluid;

continuously transmitting a reference signal;

continuously detecting the sample and reference signals using at least one photodetector;

correcting drift in the detected sample signal in real-time based on the value of the detected reference signal.

18. The method according to claim 17, further comprising:

inserting a downhole sampling tool into a borehole;

drawing down the sample of the subterranean formation fluid.

19. The method according to claim 17, further comprising modulating the sample and reference signals.

20. The method according to claim 19, further comprising separating the modulated sample signal from the modulated reference signal using a signal separation assembly.

21. The method according to claim 19, wherein modulating the sample and reference signals comprises modulating the sample signal and the reference signal at different frequencies.

22. The method according to claim 19, wherein modulating the sample and reference signals comprises generating a phase shift between the sample signal and the reference signal.

23. The method according to claim 21, wherein modulating the sample and reference signals comprises:

modulating the sample signal at a first frequency using a first optical chopper;

modulating the reference signal at a second frequency differing from the first frequency using a second optical chopper.

24. The method according to claim 21, wherein modulating the sample and reference signals comprises:

providing a first circular row of apertures in the modulator to modulate the sample signal;

providing a second circular row of apertures in the modulator to modulate the reference signal;

wherein the number of apertures in the first circular row differs from the number of apertures in the second circular row.

25. The method according to claim 22, further comprising:

positioning the sample signal to contact the modulator at a first position;

positioning the reference signal to contact the modulator at a second position;

wherein the second position is separated from the first position by a desired phase shift angle.

26. The method according to claim 25, further comprising:

positioning a sample photodetector to detect the phase of the sample signal;

positioning a reference photodetector to detect the phase of the reference signal.

27. The method according to claim 26, further comprising:

correcting drift in the detected sample signal by compensating for drift in the detected sample signal based on the value of the detected reference signal and an offset voltage generated by the electronics assembly.

28. The method according to claim 19, wherein modulating the sample and reference signals comprises digitally modulating the sample and reference signals.

29. A method for analyzing a downhole fluid, comprising:

transmitting a sample signal through a sample of the downhole fluid using a light source;

transmitting a reference signal using the light source;

continuously measuring the reference signal to compensate for drift in the sample signal in real-time.

30. The method of claim 29, further comprising communicating the measurements uphole to surface electronics.

31. An apparatus for performing real-time analysis of a subterranean formation fluid, comprising:

a light source;

a reference signal continuously transmitted by the light source;

a sample signal transmitted by the light source through a sample of the subterranean formation fluid;

a modulator for modulating the sample and reference signals at different frequencies;

at least one photodetector configured to continuously detect the sample and reference signals;

an electronics assembly configured to demodulate the sample signal and the reference and to compensate for drift in the detected sample signal in real-time based on the value of the detected reference signal.

32. An apparatus for performing real-time analysis of a subterranean formation fluid, comprising:

a downhole tool, the downhole tool comprising a fluid analysis module, the fluid analysis module comprising;

a light source configured to transmit at least a sample signal through a sample of the subterranean formation fluid and a reference signal;

at least one photodetector configured to continuously detect the sample and reference signals;

an electronics assembly configured to compensate for drift in the detected sample signal in real-time based on the value of the detected reference signal.