CLAIMSWhat is claimed is:
1. A process for treating a wellbore, comprising: subjecting a substantially same portion of the wellbore to vibratory waves produced by a plurality of vibratory wave generators.
2. The process of claim 1 wherein the vibratory waves have about the same frequency.
3. The process of claim 1 wherein the vibratory waves have a plurality of frequencies.
4. The process of claim 3 wherein the plurality of frequencies partially overlap.
5. The process of claim 3 wherein the plurality of frequencies do not overlap.
6. The process of claim 2 wherein the frequencies are modulated.
7. The process of claim 3 wherein the frequencies are modulated.
8. The process of claim 6 wherein the frequencies are repeatedly and simultaneous modulated via electrical summing of the oval, hoop, and flexural modes.
9. The process of claim 7 wherein the frequencies are repeatedly and simultaneous modulated via electrical summing of the oval, hoop, and flexural modes.
10. The process of claim 1 wherein the vibratory waves are produced simultaneously.
11. The process of claim 1 wherein the vibratory waves are produced sequentially.
12. The process of claim 2 wherein the vibratory waves are produced simultaneously.
13. The process of claim 2 wherein the vibratory waves are produced sequentially.
14. The process of claim 3 wherein the vibratory waves are produced simultaneously.
15. The process of claim 3 wherein the vibratory waves are produced sequentially.
16. The process of claim 1 wherein the vibratory waves are acoustically streamed from the plurality of vibratory wave generators.
17. The process of claim 16 wherein the vibratory waves are streamed in a viscous boundary layer near obstacles.
18. The process of claim 16 wherein the vibratory waves are streamed outside a viscous boundary layer near obstacles.
19. The process of claim 16 wherein the vibratory waves are streamed in a free non- uniform sound field.
20. The process of claim 1 wherein at least one vibratory wave generator is a vibrating pipe.
21. The process of claim 20 wherein the vibrating pipe comprises an inner pipe positioned within an outer pipe and forming a hermetically sealed chamber between the exterior surface of the inner pipe and the interior surface of the outer pipe, and a plurality of drivers attached to the interior surface of the outer pipe.
22. The process of claim 21 wherein at least one of the drivers is a transducer.
23. The process of claim 22 wherein the transducer comprises floating piezoelectric stacks.
24. The process of claim 1 wherein at least one vibratory wave generator is a piston pulser.
25. The process of claim 24 wherein the piston pulser comprises a hydraulically actuated control piston connected to a slave piston, the slave piston being in contact with a fluid in the wellbore.
26. The process of claim 1 wherein at least one vibratory wave generator is a valve.
27. The process of claim 26 wherein the valve is a rotary valve.
28. The process of claim 26 wherein the valve is the valve disclosed in U.S. Pat. No. 4,790,393.
29. The process of claim 29 wherein the valve has a gate and a seat, and the gate is on the high pressure side of the valve and the seat is on the low pressure side of the valve.
30. A process for treating a wellbore, comprising: subjecting a portion of the wellbore to vibratory waves having a first frequency produced by a first vibratory wave generator; and subjecting substantially the same portion of the wellbore to vibratory waves having a second frequency produced by a second vibratory wave generator.
31. The process of claim 30 wherein the first frequency about equals the second frequency.
32. The process of claim 30 wherein the first frequency about does not equal the second frequency.
33. The process of claim 30 wherein the first frequency partially overlaps the second frequency.
34. The process of claim 30 wherein the first frequency is in the range of about 2 to 100 kHz and the second frequency is in the range of about 0.2 to 5 kHz.
35. The process of claim 30 wherein the first frequency is in the range of about 2 to 50 kHz and the second frequency is in the range of about 0.5 to 2 kHz.
36. The process the claim 31 wherein the frequencies are modulated.
37. The process the claim 32 wherein the frequencies are modulated.
38. The process the claim 33 wherein the frequencies are modulated.
39. The process the claim 34 wherein the frequencies are modulated.
40. The process the claim 35 wherein the frequencies are modulated.
41. The process of claim 31 wherein the frequencies are repeatedly and simultaneous modulated via electrical summing of the oval, hoop, and flexural modes.
42. The process of claim 32 wherein the frequencies are repeatedly and simultaneous modulated via electrical summing of the oval, hoop, and flexural modes.
43. The process of claim 33 wherein the frequencies are repeatedly and simultaneous modulated via electrical summing of the oval, hoop, and flexural modes.
44. The process of claim 34 wherein the frequencies are repeatedly and simultaneous modulated via electrical summing of the oval, hoop, and flexural modes.
45. The process of claim 35 wherein the frequencies are repeatedly and simultaneous modulated via electrical summing of the oval, hoop, and flexural modes.
46. The process of claim 30 wherein the production of vibratory waves having first and second frequencies is simultaneous.
47. The process of claim 30 wherein the production of vibratory waves having first and second frequencies is sequential.
48. The process of claim 31 wherein the production of vibratory waves having first and second frequencies is simultaneous.
49. The process of claim 31 wherein the production of vibratory waves having first and second frequencies is sequential.
50. The process of claim 32 wherein the production of vibratory waves having first and second frequencies is simultaneous.
51. The process of claim 32 wherein the production of vibratory waves having first and second frequencies is sequential.
52. The process of claim 30 wherein the vibratory waves are acoustically streamed from the first and second vibratory wave generators.
53. The process of claim 52 wherein the vibratory waves are streamed in a viscous boundary layer near obstacles.
54. The process of claim 52 wherein the vibratory waves are streamed outside a viscous boundary layer near obstacles.
55. The process of claim 52 wherein the vibratory waves are streamed in a free non- uniform sound field.
56. The process of claim 30 wherein the first vibratory wave generator is a vibrating pipe.
57. The process of claim 56 wherein the vibrating pipe comprises an inner pipe positioned within an outer pipe and forming a hermetically sealed chamber between the exterior surface of the inner pipe and the interior surface of the outer pipe, and a plurality of drivers attached to the interior surface of the outer pipe.
58. The process of claim 57 wherein at least one of the drivers is a transducer.
59. The process of claim 58 wherein the transducer comprises floating piezoelectric stacks.
60. The process of claim 56 wherein the second vibratory wave generator is a piston pulser.
61. The process of claim 60 wherein the piston pulser comprises a hydraulically actuated control piston connected to a slave piston, the slave piston being in contact with a fluid in the wellbore.
62. The process of claim 56 wherein the second vibratory wave generator is a valve.
63. The process of claim 62 wherein the valve is a rotary valve.
64. The process of claim 62 wherein the valve is the valve disclosed in U.S. Pat. No. 4,790,393.
65. The process of claim 64 wherein the valve has a gate and a seat, and the gate is on the high pressure side of the valve and the seat is on the low pressure side of the valve.
66. The process of claim 30 wherein the first vibratory wave generator is a piston pulser and the second vibratory wave generator is a valve.
67. The process of claim 30 further comprising subjecting substantially the same portion of the wellbore to vibratory waves having a third frequency produced by a third vibratory wave generator.
68. The process of claim 67 wherein the first, second, and third frequencies are about equal.
69. The process of claim 67 wherein the first frequency about does not equal the second frequency and the second frequency about does not equal the third frequency.
70. The process of claim 67 wherein the first frequency is greater than the second frequency and the second frequency is greater than the third frequency.
71. The process of claim 67 wherein the first frequency partially overlaps the second frequency and the second frequency partially overlaps the third frequency.
72. The process of claim 67 wherein the first frequency is in the range of about 2 to 100 kHz, the second frequency is in the range of about 0.2 to 5 kHz, and the third frequency is in the range of about 0.05 to 0.2 kHz.
73. The process of claim 67 wherein the first frequency is in the range of about 2 to 50 kHz, the second frequency is in the range of about 0.5 to 2 kHz, and the third frequency is in the range of about 0.05 to 0.2 kHz.
74. The process the claim 68 wherein the frequencies are modulated.
75. The process the claim 69 wherein the frequencies are modulated.
76. The process the claim 70 wherein the frequencies are modulated.
77. The process the claim 71 wherein the frequencies are modulated.
78. The process the claim 72 wherein the frequencies are modulated.
79. The process the claim 73 wherein the frequencies are modulated.
80. The process of claim 74 wherein the frequencies are repeatedly and simultaneous modulated via electrical summing of the oval, hoop, and flexural modes.
81. The process of claim 75 wherein the frequencies are repeatedly and simultaneous modulated via electrical summing of the oval, hoop, and flexural modes.
82. The process of claim 76 wherein the frequencies are repeatedly and simultaneous modulated via electrical summing of the oval, hoop, and flexural modes.
83. The process of claim 77 wherein the frequencies are repeatedly and simultaneous modulated via electrical summing of the oval, hoop, and flexural modes.
84. The process of claim 78 wherein the frequencies are repeatedly and simultaneous modulated via electrical summing of the oval, hoop, and flexural modes.
85. The process of claim 79 wherein the frequencies are repeatedly and simultaneous modulated via electrical summing of the oval, hoop, and flexural modes.
86. The process of claim 67 wherein the production of vibratory waves having first, second, and third frequencies is simultaneous.
87. The process of claim 67 wherein the production of vibratory waves having first, second, and third frequencies is sequential.
88. The process of claim 68 wherein the production of vibratory waves having first, second, and third frequencies is simultaneous.
89. The process of claim 68 wherein the production of vibratory waves having first, second, and third frequencies is sequential.
90. The process of claim 69 wherein the production of vibratory waves having first, second, and third frequencies is simultaneous.
91. The process of claim 69 wherein the production of vibratory waves having first, second, and third frequencies is sequential.
92. The process of claim 70 wherein the production of vibratory waves having first, second, and third frequencies is simultaneous.
93. The process of claim 70 wherein the production of vibratory waves having first, second, and third frequencies is sequential.
94. The process of claim 67 wherein the vibratory waves are acoustically streamed from the first, second, and third vibratory wave generators.
95. The process of claim 94 wherein the vibratory waves are streamed in a viscous boundary layer near obstacles.
96. The process of claim 94 wherein the vibratory waves are streamed outside a viscous boundary layer near obstacles.
97. The process of claim 94 wherein the vibratory waves are streamed in a free non- uniform sound field.
98. The process of claim 60 further comprising subjecting substantially the same portion of the wellbore to vibratory waves having a third frequency produced by a third vibratory wave generator comprising a valve.
99. The process of claim 98 wherein the valve is a rotary valve.
100. The process of claim 98 wherein the valve is the valve disclosed in U.S. Pat. No. 4,790,393.
101. The process of claim 100 wherein the valve has a gate and a seat, and the gate is on the high pressure side of the valve and the seat is on the low pressure side of the valve.
102. A process for measuring the thickness of a mudcake on the interior surface of a wellbore, comprising:
(a) calibrating the speed of sound in a fluid in the wellbore;
(b) transmitting an ultrasonic signal from a transducer;
(c) measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the wellbore fluid and the mudcake back to the transducer;
(d) measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the mudcake and the interior surface of the wellbore back to the transducer; and (e) calculating the thickness of the mudcake according to the equation L= (T2-
Tι *c/2, where L is the thickness of the mudcake, c is the speed of sound calibrated in step
(a), Ti is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (c), and T is time of flight for an echo reflected from the boundary of the mudcake and the interior surface of the wellbore measured in step (d).
103. The process of claim 102 wherein the step of calibrating the speed of sound further comprises transmitting a tone burst signal from a second transducer and measuring the time of flight of a reflection echo across a known distance.
104. The process of claim 1 further comprising the step of measuring the thickness of a mudcake on the interior surface of a wellbore, comprising:
(a) calibrating the speed of sound in a fluid in the wellbore;
(b) transmitting an ultrasonic signal from a transducer;
(c) measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the wellbore fluid and the mudcake back to the transducer; (d) measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the mudcake and the interior surface of the wellbore back to the transducer; and
(e) calculating the thickness of the mudcake according to the equation L= (T2- Tι)*c/2, where L is the thickness of the mudcake, c is the speed of sound calibrated in step (a), T\ is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (c), and T is time of flight for an echo reflected from the boundary of the mudcake and the interior surface of the wellbore measured in step (d).
105. The process of claim 30 further comprising the step of measuring the thickness of a mudcake on the interior surface of a wellbore, comprising: (a) calibrating the speed of sound in a fluid in the wellbore;
(b) transmitting an ultrasonic signal from a transducer;
(c) measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the wellbore fluid and the mudcake back to the transducer;
(d) measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the mudcake and the interior surface of the wellbore back to the transducer; and
(e) calculating the thickness of the mudcake according to the equation L= (T2-
Tι.)*c/2, where L is the thickness of the mudcake, c is the speed of sound calibrated in step
(a), Ti is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (c), and T is time of flight for an echo reflected from the boundary of the mudcake and the interior surface of the wellbore measured in step (d).
106. The process of claim 67 further comprising the step of measuring the thickness of a mudcake on the interior surface of a wellbore, comprising: (a) calibrating the speed of sound in a fluid in the wellbore;
(b) transmitting an ultrasonic signal from a transducer;
(c) measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the wellbore fluid and the mudcake back to the transducer;
(d) measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the mudcake and the interior surface of the wellbore back to the transducer; and
(e) calculating the thickness of the mudcake according to the equation L= (T - Tι,)*c/2, where L is the thickness of the mudcake, c is the speed of sound calibrated in step (a), Ti is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (c), and T2 is time of flight for an echo reflected from the boundary of the mudcake and the interior surface of the wellbore measured in step (d).
107. The process of claim 22 further comprising the step of measuring the thickness of a mudcake on the interior surface of a wellbore, comprising:
(a) calibrating the speed of sound in a fluid in the wellbore; (b) transmitting an ultrasonic signal from the transducer;
(c) measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the wellbore fluid and the mudcake back to the transducer;
(d) measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the mudcake and the interior surface of the wellbore back to the transducer; and
(e) calculating the thickness of the mudcake according to the equation L= (T2- Tι)*c/2, where L is the thickness of the mudcake, c is the speed of sound calibrated in step (a), TΪ is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (c), and T is time of flight for an echo reflected from the boundary of the mudcake and the interior surface of the wellbore measured in step (d).
108. The process of claim 107 wherein the step of calibrating the speed of sound further comprises transmitting a tone burst signal from a second transducer on the vibrating pipe and measuring the time of flight of a reflection echo across a known distance.
109. The process of claim 58 further comprising the step of measuring the thickness of a mudcake on the interior surface of a wellbore, comprising:
(a) calibrating the speed of sound in a fluid in the wellbore;
(b) transmitting an ultrasonic signal from the transducer; (c) measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the wellbore fluid and the mudcake back to the transducer;
(d) measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the mudcake and the interior surface of the wellbore back to the transducer; and (e) calculating the thickness of the mudcake according to the equation L= (T2-
Tι)*c/2, where L is the thickness of the mudcake, c is the speed of sound calibrated in step (a), T\ is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (c), and T2 is time of flight for an echo reflected from the boundary of the mudcake and the interior surface of the wellbore measured in step (d).
110. The process of claim 109 wherein the step of calibrating the speed of sound further comprises transmitting a tone burst signal from a second transducer on the vibrating pipe and measuring the time of flight of a reflection echo across a known distance.
111. A process for measuring the change in thickness of a mudcake on the interior surface of a wellbore, comprising: (a) at a first point in time, calibrating the speed of sound in a fluid in the wellbore;
(b) at the first point in time, transmitting an ultrasonic signal from a transducer and measuring the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake back to the transducer; (c) at a second point in time after the first point in time, calibrating the speed of sound in the fluid in the wellbore;
(d) at the second point in time, transmitting an ultrasonic signal from the transducer and measuring the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake back to the transducer; and (e) calculating the change in thickness of the mudcake between the second point in time and the first point in time according to the equation ΔL = 0.5*(Tιa*ca - Tib *Cb), where ΔL is the change in thickness of the mudcake, ca is the speed of sound calibrated in step (c), C is the speed of sound calibrated in step (a), is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (d), and Tib is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (b).
112. The process of claim 1 further comprising measuring the change in thickness of a mudcake on the interior surface of a wellbore, comprising:
(a) at a first point in time, calibrating the speed of sound in a fluid in the wellbore;
(b) at the first point in time, transmitting an ultrasonic signal from a transducer and measuring the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake back to the transducer;
(c) at a second point in time after the first point in time, calibrating the speed of sound in the fluid in the wellbore;
(d) at the second point in time, transmitting an ultrasonic signal from the transducer and measuring the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake back to the transducer; and
(e) calculating the change in thickness of the mudcake between the second point in time and the first point in time according to the equation ΔL = 0.5*(Tla*ca - T^ *Cb), where ΔL is the change in thickness of the mudcake, ca is the speed of sound calibrated in step (c), Cb is the speed of sound calibrated in step (a), Tιa is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (d), and T]b is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (b).
113. The process of claim 30 further comprising measuring the change in thickness of a mudcake on the interior surface of a wellbore, comprising: (a) at a first point in time, calibrating the speed of sound in a fluid in the wellbore;
(b) at the first point in time, transmitting an ultrasonic signal from a transducer and measuring the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake back to the transducer; (c) at a second point in time after the first point in time, calibrating the speed of sound in the fluid in the wellbore; (d) at the second point in time, transmitting an ultrasonic signal from the transducer and measuring the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake back to the transducer; and
(e) calculating the change in thickness of the mudcake between the second point in time and the first point in time according to the equation ΔL = 0.5*(Tla*ca - Tib *Cb), where ΔL is the change in thickness of the mudcake, ca is the speed of sound calibrated in step (c), Cb is the speed of sound calibrated in step (a), Tιa is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (d), and
Tib is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (b).
114. The process of claim 67 further comprising measuring the change in thickness of a mudcake on the interior surface of a wellbore, comprising:
(a) at a first point in time, calibrating the speed of sound in a fluid in the wellbore; (b) at the first point in time, transmitting an ultrasonic signal from a transducer and measuring the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake back to the transducer;
(c) at a second point in time after the first point in time, calibrating the speed of sound in the fluid in the wellbore; (d) at the second point in time, transmitting an ultrasonic signal from the transducer and measuring the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake back to the transducer; and
(e) calculating the change in thickness of the mudcake between the second point in time and the first point in time according to the equation ΔL = 0.5*(Tla*ca - Tib *Cb), where ΔL is the change in thickness of the mudcake, ca is the speed of sound calibrated in step (c), Cb is the speed of sound calibrated in step (a), Tιa is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (d), and
Tib is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (b).
115. The process of claim 22 further comprising measuring the change in thickness of a mudcake on the interior surface of a wellbore, comprising:
(a) at a first point in time, calibrating the speed of sound in a fluid in the wellbore; (b) at the first point in time, transmitting an ultrasonic signal from the transducer and measuring the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake back to the transducer;
(c) at a second point in time after the first point in time, calibrating the speed of sound in the fluid in the wellbore;
(d) at the second point in time, transmitting an ultrasonic signal from the transducer and measuring the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake back to the transducer; and
(e) calculating the change in thickness of the mudcake between the second point in time and the first point in time according to the equation ΔL = 0.5*(Tιa*ca - Tib *Cb), where ΔL is the change in thickness of the mudcake, ca is the speed of sound calibrated in step (c), C is the speed of sound calibrated in step (a), Tιa is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (d), and
Tib is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (b).
116. The process of claim 58 further comprising measuring the change in thickness of a mudcake on the interior surface of a wellbore, comprising:
(a) at a first point in time, calibrating the speed of sound in a fluid in the wellbore; (b) at the first point in time, transmitting an ultrasonic signal from the transducer and measuring the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake back to the transducer;
(c) at a second point in time after the first point in time, calibrating the speed of sound in the fluid in the wellbore; (d) at the second point in time, transmitting an ultrasonic signal from the transducer and measuring the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake back to the transducer; and
(e) calculating the change in thickness of the mudcake between the second point in time and the first point in time according to the equation ΔL = 0.5*(Tιa*ca - Ti *Cb), where ΔL is the change in thickness of the mudcake, ca is the speed of sound calibrated in step (c), Cb is the speed of sound calibrated in step (a), Tιa is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (d), and Tib is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured in step (b).
117. An apparatus for treating a wellbore, comprising a tool capable of being deployed down the wellbore and a plurality of vibratory wave generators affixed to the tool.
118. The apparatus of claim 117 wherein the plurality of vibratory wave generators comprises a first vibratory wave generator for producing vibratory waves having a first frequency and a second vibratory wave generator for producing vibratory waves having a second frequency.
119. The apparatus of claim 118 wherein the first vibratory wave generator is a vibrating pipe and the second vibratory wave generator is a piston pulser.
120. The apparatus of claim 118 wherein the plurality of vibratory wave generators further comprise a third vibratory wave generator for producing vibratory waves having a third frequency.
121. The apparatus of claim 120 wherein the third vibratory wave generator is a valve.
122. An apparatus for measuring the thickness of a mudcake on the interior surface of a wellbore, comprising:
(a) a first transducer for transmitting a tone burst signal in a wellbore fluid and measuring the time of flight of a reflection echo of the tone burst signal across a known distance; (b) a second transducer for transmitting an ultrasonic signal, measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the wellbore fluid and the mudcake back to the second transducer, and measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the mudcake and the interior surface of the wellbore back to the second transducer; and (c) a calculator connected to and receiving the measurements from the transducers, the calculator calculating the thickness of the mudcake according to the equation L= (T2-Tι)*c/2, where L is the thickness of the mudcake, c is the speed of sound in the wellbore fluid calibrated from part (a), Ti is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured by part (b), and T2is time of flight for an echo reflected from the boundary of the mudcake and the interior surface of the wellbore measured by part (b).
123. An apparatus for measuring the change in thickness of a mudcake on the interior surface of a wellbore, comprising: (a) a first transducer for transmitting a tone burst signal in a wellbore fluid and measuring the time of flight of a reflection echo of the tone burst signal across a known distance at a first point in time and a subsequent second point in time;
(b) a second transducer for transmitting an ultrasonic signal at the first point in time and measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of the wellbore fluid and the mudcake back to the second transducer and for transmitting an ultrasonic signal at the second point in time and measuring the time of flight for an echo of the ultrasonic signal reflected from the boundary of wellbore fluid and the mudcake back to the second transducer; and (c) a calculator connected to and receiving the measurements from the transducers, the calculator calculating the change in thickness of the mudcake between the second point in time and the first point in time according to the equation ΔL = 0.5*(Tla*ca - Tib *Cb), where ΔL is the change in thickness of the mudcake, ca is the speed of sound calibrated from part (a) at the second point in time, Cb is the speed of sound calibrated from part (a) at the first point in time, Tιa is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured by part (b) at the second point in time, and Tib is the time of flight for an echo reflected from the boundary of the wellbore fluid and the mudcake measured by part (b) at the first point in time.