Ultrasonic logging methods and apparatus for measuring cement and casing properties using acoustic echoes

Patent metadata

Field	Value
Publication number	US-10358905-B2
Application number	US-201414153174-A
Country	US
Kind code	B2
Filing date	Jan 13, 2014
Priority date	Jan 13, 2014
Publication date	Jul 23, 2019
Grant date	Jul 23, 2019

Abstract

A method and apparatus for measuring parameters of a borehole using an acoustic logging system. By transmitting a high frequency acoustic signal essentially perpendicular to the major axis of a borehole casing using a transducer, the high frequency acoustic signal may produce one or more acoustic echoes. By receiving and analyzing a first acoustic echo from an inner wall of the borehole casing and at least one second acoustic echo from a back wall of the borehole casing, borehole parameters such as the impedance of the casing cement and the thickness of thicker borehole casings, up to and greater than 1 inch, may be determined.

First claim

What is claimed is:

1. A method using an acoustic logging system in a borehole having a borehole casing filled with fluid, the borehole casing being surrounded by casing grout, having an inner wall, having a back wall, and being excitable at a resonant frequency that induces reverberation, the borehole casing having a first impedance, the method comprising:
using a transducer of the acoustic logging system to transmit a signal in the direction of the borehole casing, the signal providing a frequency different from the resonant frequency of the borehole casing that induces reverberation, the signal producing acoustic echoes;
receiving a first of the acoustic echoes with the transducer from the inner wall of the borehole casing;
receiving a second of the acoustic echoes with the transducer from the back wall of the borehole casing, and
determining a naught impedance of the fluid in the borehole casing with the acoustic logging system;
determining, with at least one processor of the acoustic logging system, at least one borehole parameter based on at least one of the first and second acoustic echoes comprising determining a second impedance (Z 2 ) of the casing grout based at least in part on the naught impedance (Z 0 ) of the fluid, the first impedance (Z 1 ) of the borehole casing, and a ratio of amplitudes of the first and second acoustic echoes.

2. The method of claim 1 , wherein using the transducer to transmit the signal in the direction of the borehole casing comprises transmitting the signal to provide the frequency of at least 3 to 5 times the resonant frequency of the borehole casing.

3. The method of claim 1 , wherein using the transducer to transmit the signal in the direction of the borehole casing includes transmitting the signal perpendicular to the major axis of the borehole casing.

4. The method of claim 1 , wherein determining the second impedance of the casing grout is determined according to the equation:

Z
⁢

⁢
2

=

Z
⁢

⁢
1
*

(

K
-
EAR

K
+
EAR

)

where
⁢

:

K
=

(

4
*
Z
⁢

⁢
1
*
Z
⁢

⁢
0

Z
⁢

⁢

1
2

-

Z
⁢

⁢

0
2

)

EAR is an Echo Amplitude Ratio related to the ratio of the amplitudes measured by the acoustic logging system,
Z 1 is the first, acoustic impedance of the borehole casing which is a known constant,
Z 0 is the naught, internal fluid impedance of the fluid measured by a mud chamber in the acoustic logging system, and
Z 2 is the second impedance of the casing grout.

5. The method of claim 4 , wherein the Echo Amplitude Ratio comprises the ratio of the amplitude of the second acoustic echo to the amplitude of the first acoustic echo.

6. The method of claim 5 , wherein the Echo Amplitude Ratio is determined by adding the amplitudes of more than one of the second acoustic echoes from the back wall of the borehole casing and dividing the sum by the amplitude of the first acoustic echo.

7. The method of claim 1 , wherein determining the at least one borehole parameter further includes determining a thickness of the borehole casing.

8. The method of claim 7 , wherein determining the thickness of the borehole casing is determined according to the equation:

Thick
=

Δ
⁢

⁢
Techo

2
*
Caslow

where,
Thick is the thickness of the borehole casing,
ΔTecho is a time difference between receiving the first acoustic echo and receiving the second acoustic echo, and where
Caslow is an amount the borehole casing slows down a penetrating wave which is a known constant.

9. A downhole tool used in a borehole having a borehole casing filled with fluid, the borehole casing surrounded by casing grout, having an inner wall, having a back wall, and being excitable at a resonant frequency that induces reverberation, the borehole casing having a first impedance, the tool comprising:
an acoustic transducer configured to measure acoustic echoes in the borehole, the acoustic transducer configured to:
transmit a signal in the direction of the borehole casing, the signal providing a frequency different from the resonant frequency of the borehole casing that induces reverberation, the signal producing acoustic echoes;
receive a first of the acoustic echoes with the transducer from the inner wall of the borehole casing;
receive a second of the acoustic echoes with the transducer from the back wall of the borehole casing, and

a processor communicatively coupled to the acoustic transducer and having one or more instructions that when executed cause the processor to:
determine a naught impedance of the fluid in the borehole casing with the downhole tool; and
determine at least one borehole parameter based on at least one of the first and second acoustic echoes, comprising determining a second impedance (Z 2 ) of the casing grout based at least in part on the naught impedance (Z 0 ) of the fluid, the first impedance (Z 1 ) of the borehole casing, and a ratio of amplitudes of the first and second acoustic echoes.

10. The downhole tool of claim 9 , wherein the acoustic transducer is configured to transmit the signal in the direction of the borehole casing to provide the f

Assignees

• Weatherford Lamb Inc
• Weatherford Tech Holdings Llc

Inventors

• Tello Lucio N
• Roberts Edwin K
• Blankinship Thomas J

Classifications

• G01V1/50

  Analysing data · CPC title

• E21B47/0005

  Fixed Constructions · mapped topic

• E21B47/00 Primary

  Survey of boreholes or wells (monitoring pressure or flow of drilling fluid E21B21/08) · CPC title

• E21B47/005 Primary

  Monitoring or checking of cementation quality or level · CPC title