Composite Transducer for Downhole Ultrasonic Imaging and Caliper Measurement

• US 20090213690A1
• Filed: 02/25/2009
• Published: 08/27/2009
• Est. Priority Date: 02/27/2008
• Status: Active Grant

• Current Assignee: Baker Hughes, a GE Company, LLC (Baker Hughes Company)
• Original Assignee: Baker Hughes Incorporated (Baker Hughes Company)
• Inventors: Patterson, Douglas J., Steinsiek, Roger R., Redding, Charles E., Achanta, Anjani R.
• Granted Patent: US 10,416,330 B2
• Time in Patent Office: Days
• US Class Current: 367/35
• CPC Class Codes: B06B 1/0629 Square array
• CPC Class Codes: G01V 1/40 specially adapted for well-logging
• CPC Class Codes: G01V 1/52 Structural details

Abstract

A transducer assembly for downhole imaging includes a 1-3 Piezoelectric composite transducer of high Q ceramic rods in a polymer matrix. The assembly also includes a Teflon® window, a fluid-filled cavity adjacent to the window, and impedance matching material between the composite transducer and the fluid. The transducer is positioned to reduce the reverberation time.

Claims

1. An apparatus configured to evaluate an earth formation, the apparatus comprising:

a rotatable transducer assembly;

a composite transducer on the rotatable transducer assembly configured to propagate an acoustic signal through an acoustically transparent window into a borehole and receive a reflection from a wall of the borehole; and

at least one processor configured to use the reflection obtained at a plurality of orientations of the transducer during rotation of the transducer assembly to provide an image of the earth formation.

2. The apparatus of claim 1 wherein the composite transducer further comprises piezoelectric transducer (PZT) rods in a polymer matrix.

3. The apparatus of claim 1 wherein the rotatable transducer assembly further comprises:

(i) a fluid in a cavity adjacent to the acoustically transparent window, and

(ii) an impedance matching material disposed between the composite transducer and the fluid.

4. The apparatus of claim 1 wherein a distance between the composite transducer and the acoustically transparent window is selected to at least one of:

(i) reduce a reverberation time of a reverberation therebetween, and (ii) improve acoustic coupling with the acoustically transparent window.

5. The apparatus of claim 1 further comprising a backing material on a side of the transducer opposite to the acoustically transparent window configured to absorb acoustic signals.

6. The apparatus of claim 1 wherein the image produced by the at least one processor is selected from:

(i) a traveltime image, and (ii) a reflectance image.

7. The apparatus of claim 1 wherein the rotatable transducer assembly is part of a logging string conveyed into the borehole on a wireline.

8. The apparatus of claim 1 wherein the PZT further comprises a ceramic having a high quality factor.

15. The method of claim 1 further comprising conveying the rotatable transducer into the borehole on a wireline.

16. The method of claim 1 further comprising using for the PZT a ceramic having a high quality factor.

9. A method of evaluating an earth formation, the method comprising:

conveying a rotatable transducer assembly into a borehole;

using a composite transducer on the rotatable transducer assembly configured to propagate an acoustic signal through an acoustically transparent window into the borehole and receive a reflection from a wall of the borehole; and

using the reflection obtained at a plurality of orientations of the transducer during rotation of the transducer assembly to provide an image of the earth formation.

10. The method of claim 9 further comprising using, as the composite transducer, a piezoelectric transducer (PZT) rods in a polymer matrix.

11. The method of claim 9 further providing in the transducer assembly:

(i) a fluid in a cavity adjacent to the acoustically transparent window, and

(ii) an impedance matching material disposed between the composite transducer and the fluid.

12. The method of claim 9 further comprising selecting a distance between the composite transducer and the acoustically transparent window to at least one of:

(i) reduce a reverberation time of a reverberation therebetween, and (ii) improve acoustic coupling with the acoustically transparent window.

13. The method of claim 9 further comprising providing a backing material on a side of the transducer opposite to the acoustically transparent window configured to absorb acoustic signals.

14. The method of claim 9 wherein the produced image produced is selected from:

(i) a traveltime image, and (ii) a reflectance image.

17. A computer-readable medium accessible to at least one processor, the computer-readable medium including instructions which enable the at least one processor to use a reflected signal from a borehole wall resulting from generation of an acoustic signal by a composite transducer on a rotatable transducer assembly in the borehole and transmission of the generated acoustic signal through an acoustically transparent window on the transducer assembly into the borehole.

18. The computer-readable medium of claim 17 further comprising at least one of:

(i) a ROM, (ii) an EPROM, (iii) an EEPROM, (iv) a flash memory, and (v) an optical disk.