Method and apparatus for determining particle size distribution by acoustic speckle

• US 6,698,276 B2
• Filed: 10/29/2002
• Issued: 03/02/2004
• Est. Priority Date: 10/12/1999
• Status: Expired due to Fees

• Current Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: Tong, Jie, Jones, Gregory M., Povey, Malcolm J. W., Nelson, Phillip V.
• Primary Examiner(s): NOLAND, THOMAS
• Application Number:
  US10/282,425
• Publication Number:
  US 20030061868A1
• Time in Patent Office: 490 Days
• Field of Search: 73/617.5, 736/02, 736/46, 736/45, 736/47, 736/48, 73/617.9, 73/10.2, 73/10.3, 73/18.3, 738/655, 702/29, 702/100, 702/103, 702/128, 702/190
• US Class Current: 73/61.75
• CPC Class Codes: G01N 15/02 Investigating particle size or size distribution by measuring osmotic pressure G01N7/10; investigating sedimentation of particle suspensions G01N15/04; investigating individual particles G01N15/10
• CPC Class Codes: G01N 2291/015 Attenuation, scattering
• CPC Class Codes: G01N 2291/02416 Solids in liquids
• CPC Class Codes: G01N 2291/02809 Concentration of a compound, e.g. measured by a surface mass change
• CPC Class Codes: G01N 2291/02836 Flow rate, liquid level
• CPC Class Codes: G01N 29/032 by measuring attenuation of acoustic waves
• CPC Class Codes: G01N 29/221 Arrangements for directing or focusing the acoustical waves electronic orientation or focusing G01N29/262; sound directing or focusing G10K11/26; mechanical steering of sound transducers or their beams G10K11/35
• CPC Class Codes: G01N 29/46 by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14
• CPC Class Codes: G01S 15/885 Meteorological systems

Abstract

The invention provides a method and an apparatus for measuring the size, concentration and size distribution of particles in a fluid by determining the characteristics of an acoustic speckle signal of the particles and relating these characteristics to the size and concentration characteristics of the particles. The method and the apparatus are especially useful for the measurement of the size distribution of small particles in optically opaque liquids.

Claims

1. A method for determining the size of particles in a fluid comprising the steps of obtaining an acoustic speckle signal of the particles in the fluid and deriving the size of the particles in the fluid from the acoustic speckle signal.

2. The method as set forth in claim 1, wherein the acoustic speckle signal is obtained by introducing an input signal of acoustic energy into the fluid;

sensing a portion of scattered acoustic energy resulting from interaction of the particles with the input signal;

producing an output signal corresponding to amplitude of the portion of scattered acoustic energy as a function of time;

transforming the output signal from a time domain to a frequency domain; and

identifying the acoustic speckle signal from the output signal transformed to the frequency domain.

3. The method as set forth in claim 2, wherein the input signal is focused on a focal region in the fluid and some of the input signal is scattered by particles in the focal region, and wherein the output signal is limited to the portion of acoustic energy scattered by particles in the focal region.

4. The method as set forth in claim 3, where the fluid contains particles that produce individual speckle events and wherein the size of the particles in the fluid is determined from the acoustic speckle signal by, for each of two or more individual speckle events, identifying an individual acoustic speckle signal corresponding to each individual speckle event;

measuring the duration of the individual acoustic speckle signal;

deriving the size of the particles that produced the speckle event from the duration of the individual acoustic speckle signal; and

determining the size of particles in the fluid from the particle sizes measured for the two or more speckle events.

5. The method as set forth in claim 4, wherein, for each individual speckle event, the size of the particles that produced the speckle event is derived from the duration of that individual speckle event by using a diffusion model.

6. The method as set forth in claim 5, wherein, the diffusion model is of the form

7. The method as set forth in claim 4, wherein, for each individual speckle event, the size of the particles that produced the speckle event is derived from the duration of that individual speckle event by using an autocorrelation model.

8. The method as set forth in claim 4, wherein, for each individual speckle event, the size of the particles that produced the speckle event is derived by correlating the particle size with the maximum amplitude of such acoustic speckle signal.

9. The method as set forth in claim 1 wherein the fluid is a liquid hydrocarbon.

10. The method as set forth in claim 9, wherein the fluid is crude oil and the particles are asphaltene particles.

11. The method as set forth in claim 9, wherein the particles are particles that produce individual speckle events by interaction with acoustic energy, and the method comprises the steps of (a) introducing an input signal of acoustic energy into the hydrocarbon, which input signal is focused on a focal region in the hydrocarbon such that particles in the focal region interact with the input signal to scatter the acoustic energy, producing an output signal of the acoustic energy scattered by the particles in the focal region;

(b) sensing the output signal in the form of amplitude as a function of time;

(c) transforming the sensed output signal from a time domain to a frequency domain;

(d) identifying an acoustic speckle signal from the transformed output signal in the frequency domain;

(e) carrying out each of the steps (a), (b), (c) and (d) except on a control liquid that contains no particles that produce individual speckle events by interaction with acoustic energy, instead of the hydrocarbon, and (f) determining the size of the particles in the hydrocarbon by comparing the acoustic speckle signal derived from the hydrocarbon with the acoustic speckle signal derived from the control liquid.

12. The method as set forth in claim 11, wherein the acoustic speckle signal of the hydrocarbon has a magnitude at each of a plurality of frequencies, including a selected frequency, and the acoustic speckle signal of the control liquid has a magnitude at each of the plurality of frequencies, and the comparison of the acoustic speckle derived from the hydrocarbon is compared with the acoustic speckle signal derived from the control liquid by subtracting the magnitude of the acoustic speckle signal of the hydrocarbon at the selected frequency from the magnitude of the acoustic speckle signal of the control liquid at the selected frequency to obtain a difference.

13. The method as set forth in claim 11, wherein the sensed output signal is transformed from a time domain to a frequency domain by use of a Fast Fourier Transform algorithm.