Downhole densitometer

• US 6,378,364 B1
• Filed: 01/13/2000
• Issued: 04/30/2002
• Est. Priority Date: 01/13/2000
• Status: Expired due to Term

• Current Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Original Assignee: Halliburton Energy Services Incorporated (Halliburton Company)
• Inventors: Pelletier, Michael T., Proett, Mark A., Storm, Bruce H. Jr., Ritter, Thomas Edward, Birchak, James Robert
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): Politzer, Jay L.
• Application Number:
  US09/482,793
• Time in Patent Office: 838 Days
• Field of Search: 738/613.55, 738/613.56, 738/613.57, 731/524.7
• US Class Current: 73/152.47
• CPC Class Codes: E21B 47/06 Measuring temperature or pressure
• CPC Class Codes: E21B 47/107 using acoustic means
• CPC Class Codes: E21B 49/08 Obtaining fluid samples or testing fluids, in boreholes or wells
• CPC Class Codes: E21B 49/0875 determining specific fluid parameters
• CPC Class Codes: G01F 1/8413 means for influencing the flowmeter's motional or vibrational behaviour, e.g., conduit support or fixing means, or conduit attachments
• CPC Class Codes: G01F 1/8436 signal processing
• CPC Class Codes: G01F 1/8495 with multiple measuring conduits
• CPC Class Codes: G01H 11/02 by magnetic means, e.g. reluctance
• CPC Class Codes: G01N 11/167 Sample holder oscillates, e.g. rotating crucible
• CPC Class Codes: G01N 2009/006 vibrating tube, tuning fork

Abstract

A measurement device is provided that determines fluid properties from vibration frequencies of a sample cavity and a reference cavity. In one embodiment, the measurement device includes a sample flow tube, a reference flow tube, vibration sources and detectors mounted on the tubes, and a measurement module. The sample flow tube receives a flow of sample fluid for characterization. The reference flow tube is filled with a reference fluid having well-characterized properties. The measurement module employs the vibration sources to generate vibrations in both tubes. The measurement module combines the signals from the vibration detectors on the tubes to determine properties of the sample fluid, such as density, viscosity, compressibility, water fraction, and bubble size. The measurement module may further detect certain flow patterns such as slug flow, for example. To measure the sample fluid density, the measurement module determines the difference between resonance frequencies of the sample flow tube and the reference flow tube. The density can then be calculated according to a formula. Other fluid properties may be determined from the sample tube'"'"'s resonance peak amplitude, peak width and/or peak shape. Variation of the density measurements may be used to detect and characterize multiple phase fluid flow. The use of a reference tube in the disclosed measurement device is expected to greatly enhance the accuracy and reliability of the measurement device over a range of temperatures, pressures, and shock accelerations such as those that may be found downhole in a well.

Claims

1. A device for determining a property of a sample fluid, wherein the device comprises:

a sample tube having a bore that receives a fluid sample, wherein the tube vibrates at a frequency characteristic of one or more properties of the fluid sample;

a vibration sensor that converts vibrations of the sample tube into a measurement signal;

a reference standard that provides a reference frequency signal; and

a measurement module that receives the measurement signal and the reference frequency signal, and that determines a beat frequency of the measurement and reference signals to determine a property of the sample fluid.

2. The device of claim 1, wherein the fluid sample includes a liquid.

3. The device of claim 1, wherein the fluid sample includes a gas.

4. The device of claim 1, wherein the fluid sample includes suspended solids.

5. The device of claim 1, wherein the reference standard includes a solid cylinder having a length and diameter equal to those of the sample tube.

6. The device of claim 1, wherein the vibration sensor is mechanically coupled to the sample tube.

7. The device of claim 1, wherein the vibration sensor is further configured to generate vibration of the sample tube.

8. The device of claim 1, wherein multiple vibration sensors are coupled to the sample tube.

9. The device of claim 1, wherein the measurement module is configured to determine the vibration frequency response of the sample tube.

10. The device of claim 1, wherein the measurement module is configured to determine the vibration amplitude of the sample tube.

11. The device of claim 1, wherein the property of the sample fluid is density.

12. The device of claim 1, wherein the property of the ample fluid is viscosity.

13. The device of claim 1, wherein the property of the sample fluid is bubble point.

14. The device of claim 1, wherein the property of the sample fluid is thermodynamic phase.

15. The device of claim 1, wherein the reference standard includes a reference tube having a bore.

16. The device of claim 15, wherein the bore of the reference tube contains a vacuum.

17. The device of claim 15, wherein the bore of the reference tube contains a reference solid.

18. The device of claim 15, further comprising:

a second reference tube having a bore having contents different from the first reference tube, wherein the second reference tube is configured to provide a second reference signal to the measurement module.

19. The device of claim 15, further comprising:

an excitation source mounted on the reference tube to generate vibration of the reference tube, wherein vibration of the reference tube also induces vibration of the sample tube.

20. The device of claim 15, wherein the bore of the reference tube contains a reference fluid.

21. The device of claim 20, wherein the reference fluid is a gas.

22. The device of claim 20, wherein the reference fluid is subjected to substantially the same pressure and temperature as the sample fluid.

23. The device of claim 1, wherein the vibration sensor is an electromechanical sensor.

24. The device of claim 23, wherein the vibration sensor includes a piezoelectric transducer.

25. The device of claim 23, wherein the vibration sensor includes an induction coil.

26. The device of claim 1, further comprising:

an excitation source configured to generate vibration of the sample tube.

27. The device of claim 26, wherein the excitation source includes a piezoelectric transducer.

28. The device of claim 26, wherein the excitation source includes a magnetorestrictive transducer.

29. The device of claim 26, wherein the excitation source includes an induction coil.

30. The device of claim 26, wherein the excitation source includes a mechanical striker.

31. The device of claim 26, wherein the excitation source is driven by an impulse.

32. The device of claim 26, wherein the excitation source is frequency-swept.

33. The device of claim 26, wherein the excitation source is driven by a phase-lock loop.

34. The device of claim 26, wherein multiple excitation sources are coupled to the sample tube.

35. The device of claim 26, wherein the measurement module is configured to determine the drive power of the excitation source.

36. A method for measuring a property of a fluid, where the method comprises:

receiving a sample fluid into a sample cavity;

vibrating the sample cavity to obtain a vibration signal having a sample cavity vibration frequency;

producing a resonant signal from a vibratory standard independent of the sample cavity, wherein the resonant signal has a resonant frequency;

determining a frequency difference between the resonant frequency and the sample cavity vibration frequency; and

converting the frequency difference in to a density measurement of the sample fluid,

wherein the determining a frequency difference includes;

combining the vibration signal with the resonant signal to produce a beat-frequency signal; and

measuring a beat-frequency in the beat-frequency signal.

37. The method of claim 36, further comprising:

adjusting the sample cavity vibration frequency to determine the frequency differences for a sample cavity resonance frequency and at least one sample cavity half-amplitude frequency; and

calculating the density and a second fluid property from the resonance frequency difference and the half-amplitude frequency difference.

38. A method for measuring a property of a fluid, where the method comprises:

receiving a sample fluid into a sample cavity;

vibrating the sample cavity to obtain a vibration signal having a sample cavity vibration frequency;

producing a resonant signal from a vibratory standard independent of the sample cavity, wherein the resonant signal has a resonant frequency;

determining a frequency difference between the resonant frequency and the sample cavity vibration frequency;

varying the sample cavity vibration frequency to determine a sample cavity resonance peak shape; and

determining fluid properties from the peak shape.