Formation measurements using nonlinear guided waves

Patent metadata

Field	Value
Publication number	US-10094945-B2
Application number	US-201414223416-A
Country	US
Kind code	B2
Filing date	Mar 24, 2014
Priority date	Mar 24, 2014
Publication date	Oct 9, 2018
Grant date	Oct 9, 2018

Abstract

An embodiment of a method of estimating a property of an earth formation includes: disposing an acoustic tool in a borehole in an earth formation, the acoustic tool including an acoustic source and at least one acoustic receiver; transmitting acoustic signals into the borehole by the acoustic source, the acoustic signals having at least one linear guided wave mode that propagates along a surface of the borehole; receiving the acoustic signals by at least one receiver; analyzing, by a processor, the acoustic signals to measure non-linear harmonic waves generated by the formation is response to the at least one linear guided wave mode; and estimating a property of the formation based on the measured non-linear harmonic waves.

First claim

What is claimed is:

1. A method of estimating a property of an earth formation, comprising:
disposing an acoustic tool in a borehole in an earth formation, the acoustic tool including an acoustic source and at least one acoustic receiver;
selecting a linear guided wave mode having a mode and frequency that are configured to induce non-linear harmonic guided waves that propagate along the borehole, the mode and the frequency selected based on dispersion characteristics of the formations;
transmitting acoustic signals into the borehole by the acoustic source, the acoustic signals having the linear guided wave mode that propagates along a surface of the borehole;
receiving the acoustic signals by at least one receiver, the acoustic signals including a harmonic of the linear guided wave mode, the harmonic generated by the formation in response to the linear guided wave mode and propagating along the borehole as the non-linear harmonic guided waves;
analyzing, by a processor, the acoustic signals to measure the non-linear harmonic guided waves; and
estimating a property of the formation based on the measured non-linear harmonic waves.

2. The method of claim 1 , wherein the mode and the frequency are selected based on a power flux from the linear guided wave mode to a harmonic mode being above a selected threshold.

3. The method of claim 1 , wherein estimating includes estimating at least one of a non-linear property and a mechanical property of the formation based on an increase in amplitude of the non-linear harmonic waves relative to propagation distance.

4. The method of claim 3 , wherein analyzing includes calculating an amplitude of the non-linear harmonic guided waves, and estimating one or more nonlinear elastic constants based on the amplitude.

5. The method of claim 4 , wherein analyzing includes calculating the amplitude of the non-linear harmonic guided waves at a plurality of distances from the acoustic source, and calculating an increase in the amplitude as a function of distance from the acoustic source.

6. The method of claim 3 , wherein the non-linear property of the formation includes at least one of porosity, fluid saturation and micro-structure of the formation.

7. The method of claim 1 , wherein the wave mode and the frequency are configured to generate the non-linear harmonic guided waves having an amplitude sufficient for detection by the at least one receiver, the non-linear harmonic guided waves resulting from interaction between the acoustic wave pulse and the formation as the acoustic wave pulse propagates along a surface of the borehole.

8. The method of claim 7 , wherein the wave mode and the frequency are selected based on dispersion curves for multiple wave modes, the dispersion curves based on a geometry of the borehole.

9. The method of claim 1 , wherein the property of the formation is estimated based on amplitudes of the non-linear harmonic guided waves.

10. The method of claim 1 , wherein the acoustic source includes an inter-digit transducer disposed in the borehole.

11. A system for estimating a property of an earth formation, comprising:
an acoustic tool configured to be disposed in a borehole in an earth formation, the acoustic tool including an acoustic source configured to generate a linear guided wave mode that propagates along a surface of the borehole, the linear guided wave mode having a mode and frequency selected to induce non-linear harmonic guided waves that propagate along the borehole, the mode and the frequency selected based on dispersion characteristics of the formation;
a receiver configured to receive acoustic signals including a harmonic of the linear guided wave mode, the harmonic generated by the formation in response to the linear guided wave mode and propagating along the borehole as the non-linear harmonic guided waves; and
a processor configured to analyze acoustic signals received at the acoustic receiver, measure the non-linear harmonic guided waves, and estimate a property of the formation based on the measured non-linear harmonic waves.

12. The system of claim 11 , wherein the mode and the frequency are selected based on a power flux from the linear guided wave mode to a harmonic mode being above a selected threshold.

13. The system of claim 11 , wherein the processor is configured to estimate a non-linear property of the formation.

14. The system of claim 13 , wherein the processor is configured to calculate an amplitude of the non-linear harmonic guided waves, and estimate one or more nonlinear elastic constants based on the amplitude.

15. The system of claim 14 , wherein the processor is configured to calculate the amplitude of the non-linear harmonic guided waves at a plurality of distances from the acoustic source, and calculate an increase in the amplitude as a function of distance from the acoustic source.

16. The system of claim 13 , wherein the non-linear property of the formation includes at least one of porosity, fluid saturation and micro-structure of the formation.

17. The system of claim 11 , wherein the wave mode and the frequency are configured to generate the non-linear harmonic guided waves having an amplitude sufficient for detection by the at least one acoustic receiver, the non-linear harmonic guided waves resulting from interaction between the acoustic wave pulse and the formation as the acoustic wave pulse propagates along a surface of the borehole.

18. The system of claim 17 , wherein the wave mode and the frequency are selected based on dispersion curves for multiple wave modes, the dispersion curves based on a geometry of the borehole.

19. The system of claim 17 , wherein the property of the formation is estimated based on amplitudes of the non-linear harmonic guided waves.

20. The system of claim 11 , wherein the acoustic source includes an inter-digit transducer disposed in the borehole.

Assignees

• Khajeh Ehsan
• Liu Yang
• Baker Hughes A Ge Co Llc

Inventors

• Khajeh Ehsan
• Liu Yang

Classifications

• G01V1/46 Primary

  Data acquisition · CPC title

• G01V1/50 Primary

  Analysing data · CPC title