Flow Monitoring

• US 20140216151A1
• Filed: 09/28/2012
• Published: 08/07/2014
• Est. Priority Date: 09/29/2011
• Status: Active Grant

• Current Assignee: Optasense Holdings Limited (Luna Innovations, Inc.)
• Original Assignee: Optasense Holdings Limited (Luna Innovations, Inc.)
• Inventors: Godfrey, Alastair, Crickmore, Roger Ian
• Granted Patent: US 9,828,849 B2
• Time in Patent Office: Days
• US Class Current: 73/152.32
• CPC Class Codes: E21B 47/10 Locating fluid leaks, intrusions or movements
• CPC Class Codes: E21B 47/107 using acoustic means
• CPC Class Codes: G01F 1/663 by measuring Doppler frequency shift
• CPC Class Codes: G01F 1/704 using marked regions or existing inhomogeneities within the fluid stream, e.g. statistically occurring variations in a fluid parameter G01F1/76, G01F25/00 take precedence

Abstract

This application describes methods and apparatus for monitoring flow of fluids within conduits using fibre optic Distributed Acoustic Sensing (DAS). The method can determine flow rate and/or flow regime within a conduit such as within a production well or a pipeline. Embodiments involve introducing an acoustic stimulus (802) into the fluid within the conduit (801); interrogating an optical fibre (104) deployed along the path of the conduit to provide a DAS sensor; and analysing the acoustic signals detected by a plurality of channels of the DAS sensor to determine at least one flow characteristic. Analysing the acoustic signal comprises identifying reflections (804) of said acoustic stimulus caused by the fluid within the conduit and analysing said reflections to determine any Doppler shift (Δf).

Claims

1. A method of monitoring fluid flow along a conduit comprising:

introducing an acoustic stimulus into the fluid within the conduit;

interrogating an optical fibre deployed along the path of the conduit to provide a distributed acoustic sensor having a plurality of sensing portions of fibre; and

analysing the acoustic signals detected by said plurality of sensing portions of fibre in response to said acoustic stimulus to determine at least one flow characteristic,

wherein analysing the acoustic signal comprises identifying reflections of said acoustic stimulus caused by the fluid within the conduit and analysing said reflections to determine any Doppler shift.

2. A method as claimed in claim 1 wherein said at least one flow characteristic comprises a flow regime.

3. A method as claimed in claim 1 wherein said at least one flow characteristic comprises a flow rate.

4. A method as claimed in claim 3 comprising determining the speed of flow of the fluid from any Doppler shift.

5. A method as claimed in claim 1 comprising determining any variation in the speed of flow of the fluid within the conduit from any Doppler shift.

6. A method as claimed in claim 1 wherein the acoustic stimulus comprises at least one acoustic pulse of a defined acoustic frequency.

7. A method as claimed in claim 1 comprising analysing the frequency spread of the detected reflected signal to determine a flow regime.

8. A method as claimed in claim 1 comprising transmitting at least one additional acoustic stimulus into the fluid in the conduit to mix with the reflected signal to improve signal to noise ratio.

9. A method as claimed in claim 1 further comprising determining the rate of propagation of the acoustic stimulus along the conduit.

10. A method as claimed in claim 9 comprising analysing the detected acoustic signals to detect any change in propagation speed along the conduit.

11. A method as claimed in claim 1 comprising determining the attenuation of the acoustic stimulus as it travels along the conduit.

12. A method as claimed in claim 11 comprising analysing the detected acoustic signals to detect any change in the rate of attenuation.

13. A method as claimed in claim 11 comprising correlating change in attenuation rate with any change in Doppler shift along the conduit.

14. A method as claimed in claim 1 wherein the acoustic stimulus comprises at least one acoustic pulse having a time varying frequency and/or at least one pulse having a broadband frequency spectrum.

15. A method as claimed in claim 1 wherein analysing the detected acoustic signals comprises applying spectral analysis.

16. A method as claimed in claim 15 comprising determining the frequency dependence of the attenuation of the acoustic signals.

17. A method as claimed in claim 1 comprising inducing the acoustic stimulus using an acoustic transducer.

19. A method as claimed in claim 1 comprising using a separate flow conduit running along the same path as said conduit to introduce said acoustic stimulus into said conduit and/or further comprising introducing an additional acoustic stimulus into the material forming the conduit.

21. A method as claimed in claim 1 wherein the conduit is a flow pipe within a wellbore, and the method is a method of monitoring flow within a wellbore.

18. (canceled)

20. (canceled)

22. (canceled)

23. A method of processing data from a fibre optic distributed acoustic sensor having an optical fibre deployed along the path of a conduit so as to determine at least one flow characteristic of fluid flow in the conduit, the method comprising taking the detected acoustic signals from a plurality of sensing portions of the optical fibre and analysing the detected acoustic signals detected by said plurality of sensing portions of fibre in response to said acoustic stimulus propagating along the conduit to determine at least one flow characteristic, wherein analysing the acoustic signal comprises identifying reflections of said acoustic stimulus caused by the fluid within the conduit and analysing said reflections to determine any Doppler shift.

24. A computer program product on a non-transitory storage medium that, when run on a suitable computing device, performs the method of claim 23.

25. An apparatus for monitoring fluid flow along a conduit comprising:

an interrogator unit for interrogating an optical fibre deployed along the path of the conduit to provide a distributed acoustic sensor having a plurality of sensing portions of fibre; and

a processor configured to analysing the acoustic signals detected by said plurality of sensing portions of fibre with an acoustic stimulus propagating in the fluid within the conduit to determine at least one flow characteristic,

wherein said processor is configured to analyse the acoustic signal to identify reflections of said acoustic stimulus caused by the fluid within the conduit and analyse said reflections to determine any Doppler shift.

26. An apparatus as claimed in claim 25 wherein said processor is configured to determine the speed of flow of the fluid from any Doppler shift.

27. An apparatus as claimed in claim 25 wherein said processor is configured to determine any variation in the speed of flow of the fluid within the conduit from any Doppler shift.

28. An apparatus as claimed in claim 25 wherein said processor is further configured to determine the attenuation of the acoustic stimulus as it travels along the conduit.

31. An apparatus as claimed in claim 25 further comprising at least one acoustic transducer for generating a propagating acoustic stimulus in said conduit.

29-30. -30. (canceled)

32-34. -34. (canceled)