Device and method for generating a beam of acoustic energy from a borehole, and applications thereof
View Patent ↗In some aspects of the invention, a method of generating a beam of acoustic energy in a borehole is disclosed. The method includes generating a first broad-band acoustic pulse at a first broad-band frequency range having a first central frequency and a first bandwidth spread; generating a second broad-band acoustic pulse at a second broad-band frequency range different than the first frequency range having a second central frequency and a second bandwidth spread, wherein the first acoustic pulse and second acoustic pulse are generated by at least one transducer arranged on a tool located within the borehole; and transmitting the first and the second broad-band acoustic pulses into an acoustically non-linear medium, wherein the composition of the non-linear medium produces a collimated pulse by a non-linear mixing of the first and second acoustic pulses, wherein the collimated pulse has a frequency equal to the difference in frequencies between the first central frequency and the second central frequency and a bandwidth spread equal to the sum of the first bandwidth spread and the second bandwidth spread.
1. A method of generating a collimated pulse of acoustic energy in a borehole, the method comprising:
generating a first broad-band acoustic pulse at a first broad-band frequency range having a first central frequency and a first bandwidth spread;
generating a second broad-band acoustic pulse at a second broad-band frequency range different from the first broad-band frequency range having a second central frequency and a second bandwidth spread, wherein the first acoustic pulse and second acoustic pulse are generated by at least one transducer arranged on a tool located within the borehole; and
transmitting the first and the second broad-band acoustic pulses into an acoustically non-linear medium, wherein a composition of the non-linear medium produces a collimated pulse by a non-linear mixing of the first and second acoustic pulses,
wherein the collimated pulse has a central frequency equal to a difference in frequencies between the first central frequency and the second central frequency and a bandwidth spread equal to the sum of the first bandwidth spread and the second bandwidth spread.
2. The method in accordance with claim 1 , wherein the frequency range of the collimated acoustic pulse has a central frequency that is between 15 kHz and 120 kHz.
3. The method in accordance with claim 1 , wherein the non-linear medium is selected from the group consisting of: a mixture of liquids, a solid, a granular material, embedded microspheres, an emulsion, and a combination thereof.
4. The method in accordance with claim 1 , wherein the bandwidth spread of the collimated pulse is between 50% and 200% of the first central frequency.
5. The method in accordance with claim 1 , wherein the bandwidth spread of the collimated pulse is between 50% and 200% of the second central frequency.
6. The method in accordance with claim 1 , further comprising transmitting the collimated pulse into a material around the borehole.
7. The method in accordance with claim 6 , wherein the material is rock formation, cement, or casing, or combinations thereof.
8. The method in accordance with claim 1 , wherein the non-linear medium has a velocity of sound between 100 m/s and 800 m/s.
9. The method in accordance with claim 1 , further comprising reflecting and guiding the collimated acoustic pulse by an acoustic mirror.
10. A wireline or pipe conveyed logging tool positionable within a borehole, the tool comprising:
a housing;
at least one transducer, carried by the housing, and configured to produce a first acoustic pulse at a first frequency range having a first central frequency and a first bandwidth spread and a second acoustic pulse at a second frequency range different from the first frequency range and having a second central frequency and a second bandwidth spread; and
a non-linear medium carried by the housing, wherein a composition of the non-linear medium is configured to produce a collimated pulse by a non-linear mixing of the first and second acoustic pulses,
wherein the collimated pulse has a frequency equal to the difference in frequencies between the first central frequency and the second central frequency and a bandwidth spread equal to the sum of the first bandwidth spread and the second bandwidth spread.
11. The tool in accordance with claim 10 , wherein the frequency range of the collimated acoustic pulse has a central frequency that is between 15 kHz and 120 kHz.
12. The tool in accordance with claim 10 , wherein the non-linear medium is selected from the group consisting of: a mixture of liquids, a solid, a granular material, embedded microspheres, an emulsion, and a combination thereof.
13. The tool in accordance with claim 10 , wherein the bandwidth spread of the collimated pulse is between 50% and 200% of the first central frequency.
14. The tool in accordance with claim 10 , wherein the bandwidth spread of the collimated pulse is between 50% and 200% of the second central frequency.
15. The tool in accordance with claim 10 , wherein the tool further comprises structure constructed and arranged to direct the collimated pulse into a material around the borehole.
16. The tool in accordance with claim 15 , wherein the material is rock formation, cement, or casing, or a combination thereof.
17. The tool in accordance with claim 15 , wherein the non-linear medium has a velocity of sound between 100 m/s and 800 m/s.
18. The tool in accordance with claim 15 , wherein the structure comprises an acoustic mirror configured to reflect and guide the collimated acoustic pulse.