Method and tool for producing a formation velocity image data set

• US 6,678,616 B1
• Filed: 11/05/1999
• Issued: 01/13/2004
• Est. Priority Date: 11/05/1999
• Status: Expired due to Term

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Inventors: Winkler, Kenneth W., DʼAngelo, Ralph M.
• Primary Examiner(s): Barlow, John
• Assistant Examiner(s): Taylor, Victor J.
• Application Number:
  US09/434,694
• Time in Patent Office: 1,530 Days
• Field of Search: 702/6, 702/10, 181/105, 181/104, 181/106, 367/31, 367/75, 367/35, 367/86, 166/4, 706/49, 703/10
• US Class Current: 702/6
• CPC Class Codes: G01V 1/44 using generators and receivers in the same well G01V1/52 takes precedence
• CPC Class Codes: G01V 1/52 Structural details

Abstract

Methods and tools are provided for real time velocity imaging of a borehole wall with sufficiently high resolution to identify vugs, worm holes, thin beds, dip angles, fractures and breakouts, for both open hole logging and logging while drilling in the presence of OBM'"'"'s. A method is provided which includes transmitting an ultrasonic pulse through the borehole wall, receiving at first and second spaced-apart receivers an ultrasonic pulse refracted from the borehole wall, and producing a velocity image data value indicative of difference of arrival times at first and second spaced-apart receivers. This is repeated at a plurality of azimuths and depths to produce a velocity image data set. The method uses compressional pulses and/or pseudo-Raleigh pulses.

A tool is provided for wireline use having an ultrasonic transmitter for transmitting ultrasonic pulses into the borehole wall, and a plurality of ultrasonic receivers. A processor in the tool produces real time velocity image data values indicative of time of flight of an ultrasonic pulse in the borehole wall. A similar tool is provided for logging while drilling (LWD).

Claims

1. A method for producing a velocity image data set representing formation surrounding a borehole, the method comprising the steps of:

a) transmitting an ultrasonic pulse through the wall of said borehole such that by refraction said ultrasonic pulse travels in said formation along said borehole;

b) receiving said ultrasonic pulse at first and second receivers spaced-apart in a direction along said borehole;

c) producing a velocity image data value indicative of difference of arrival times of said ultrasonic pulse at said first and second receivers;

d) repeating steps a)-c) at a plurality of azimuths to produce a velocity image data value at each of the plurality of azimuths; and

e) repeating steps a)-d) at a plurality of depths in the borehole to produce a velocity image data set.

2. A method according to claim 1, wherein producing a velocity image data value includes dividing receiver spacing by difference of arrival times.

3. A method according to claim 1, wherein step (c) further includes the step of:

determining a compressional pulse arrival time by digitizing a signal from a receiver, determining noise level, setting a compressional amplitude threshold to be a multiple of the noise level, determining compressional amplitude threshold time as time at which an absolute value of the signal exceeds the threshold for compressional pulse, picking the first zero-crossing after threshold time, and setting compressional pulse arrival time equal to the time of first zero-crossing.

4. A method according to claim 3, further comprising the step of associating the velocity image data value derived from the compressional pulse arrival time with a compressional image data set.

5. A method according to claim 3, wherein step (c) further includes the steps of:

determining a pseudo-Raleigh pulse arrival time by setting a pseudo-Raleigh amplitude threshold to be a multiple of the larger of the first two extrema of signal following the first zero-crossing, determining pseudo-Raleigh amplitude threshold time as time at which an absolute value of the signal exceeds the threshold for pseudo-Raleigh pulse, picking the first zero-crossing after pseudo-Raleigh threshold time, and setting pseudo-Raleigh pulse arrival time equal to the time of first zero-crossing.

6. A method according to claim 5, further comprising the step of associating the velocity image data value derived from the pseudo-Raleigh pulse arrival with a pseudo-Raleigh velocity data set.

7. A method according to claim 3, further comprising the step of calculating a correction factor to correct for error in effective spacing between receivers according to critical angle and formation velocity.

8. A method for producing a velocity image data set representing formation surrounding a borehole, the method comprising the steps of:

a) measuring ultrasonic velocity in a portion of a formation surrounding the wall of said borehole at a plurality of azimuths and depths in the borehole to produce a velocity value at each of the plurality of azimuths and depths; and

b) using the velocity values as a two-dimensional velocity image data set.

9. A method according to claim 8, wherein measuring ultrasonic velocity includes dividing receiver spacing by difference of arrival times of an ultrasonic pulse refracted from the wall of said borehole at first and second spaced-apart receivers, said receivers spaced-apart in a direction along said borehole.

10. A tool for producing a velocity image data set representing formation surrounding a borehole, comprising:

a) transmitter means for transmitting an ultrasonic pulse through the wall of said borehole such that by refraction said ultrasonic pulse travels in said formation along said borehole;

b) receiver means for receiving said ultrasonic pulse at first and second locations spaced-apart in a direction along said borehole;

c) means for producing a velocity image data value indicative of difference of arrival times of said ultrasonic pulse at said first and second locations;

d) means for operating said transmitter means and said receiver means at a plurality of azimuths and depths in the borehole to produce a velocity image data set.

11. A tool according to claim 10, wherein said means for transmitting an ultrasonic pulse includes an ultrasonic transmitter attached to an elongate body that is moveable through said borehole.

12. A tool according to claim 10, wherein said means for receiving said ultrasonic pulse includes first and second receivers spaced-apart in a direction along said borehole.

13. A tool according to claim 10, wherein said means for operating said transmitter means and said receiver means includes means for operating said transmitter means and said receiver means at a plurality of azimuths, means for operating said transmitter means and said receiver means at a plurality of depths in the borehole, and processor means for compiling a velocity image data set.

14. A tool for producing a velocity image data set representing formation surrounding a borehole, comprising:

an elongate body that is moveable through the borehole;

an ultrasonic transmitter attached to said elongate body for transmitting ultrasonic pulses through the borehole wall;

at least one ultrasonic receiver, attached to said elongate body and spaced apart from said transmitter, for receiving refracted ultrasonic pulses from the borehole wall; and

a processor, coupled to said at least one ultrasonic receiver, including means for producing a velocity image data value from time of flight of an ultrasonic pulse, at a plurality of azimuths and depths in the borehole.

15. A tool for producing a velocity image data set representing formation surrounding a borehole, comprising:

an elongate body that is moveable through the borehole;

an ultrasonic transmitter attached to said elongate body for transmitting ultrasonic pulses through the borehole wall;

at least one pair of first and second spaced-apart ultrasonic receivers, attached to said elongate body and spaced apart from said transmitter, for receiving refracted ultrasonic pulses from the borehole wall; and

a processor, coupled to said receivers, including means for producing a velocity image data value from difference of arrival times at first and second spaced-apart receivers, at a plurality of azimuths and depths in the borehole.

16. A tool according to claim 15,

wherein the tool is a wireline tool adapted for suspension from a wireline;

wherein said at least one ultrasonic receiver includes a plurality of pairs of receivers located at azimuthal intervals around the elongate body, each pair of receivers including first and second spaced-apart receivers;

wherein said processor is coupled to receive signals from a pair of receivers; and

wherein said processor includes means for producing a velocity image data value indicative of difference of arrival times at first and second spaced-apart receivers.

17. A wireline tool according to claim 16, wherein said processor includes means for associating a difference of arrival times with an azimuthal position of first and second spaced-apart receivers such as to produce image data with an azimuthal position attribute.

18. A wireline tool according to claim 17, wherein said processor includes means for associating a difference of arrival times with a depth in the borehole such as to produce an image data value with an azimuthal position attribute and a depth attribute.

19. A wireline tool according to claim 18, wherein said processor includes means for adding image data values to a stored velocity image data set.

20. A wireline tool according to claim 18, wherein said processor further includes means for identifying an arrival as a compressional pulse arrival.

21. A wireline tool according to claim 18, wherein said processor further includes means for identifying an arrival as a pseudo-Raleigh pulse arrival.

22. A wireline tool according to claim 18, wherein said processor further includes means for determining a difference of arrival times at the first and second spaced-apart receivers.

23. A wireline tool according to claim 18, wherein said processor further includes means for dividing spacing between first and second receivers by difference of arrival times.

24. A wireline tool according to claim 18, wherein said processor further includes means for first motion detection.

25. A wireline tool according to claim 18, wherein said processor further includes means for first zero crossing detection.

26. A wireline tool according to claim 18, wherein said plurality of pairs of receivers comprises a plurality of azimuthally aligned pairs of receivers.

27. A wireline tool according to claim 18, wherein a first pair of receivers is axially offset from a second pairs of receivers.

28. A wireline tool according to claim 18, wherein a first receiver is azimuthally offset from a second receiver.

29. A wireline tool according to claim 16, wherein the first receiver of a first pair of receivers is also the first receiver of a second pair of receivers.

30. A wireline tool according to claim 16, wherein at least one ultrasonic transmitter includes means for transmitting a pulse of ultrasonic waves in the frequency range 50-500 kHz.

31. A wireline tool according to claim 30, wherein said at least one ultrasonic transmitter element includes a directional transducer.

32. A wireline tool according to claim 31, wherein said at least one ultrasonic transmitter element is oriented at a true angle of incidence such that ultrasonic compressional waves propagate longitudinally with respect to the borehole along a portion of the borehole wall.

33. A wireline tool according to claim 32, wherein said true angle of incidence is approximately 25 degrees.

34. A wireline tool according to claim 32, wherein said true angle of incidence is approximately 40 degrees.

35. A wireline tool according to claim 32, wherein said true angle of incidence is in the range 20-40 degrees.

36. A wireline tool according to claim 32, wherein each receiver is oriented normal to the borehole wall for greater receiver density.

37. A tool according to claim 15, wherein the transmitter has a width of approximately 12 mm.

38. A tool according to claim 15, wherein the transmitter has a selected width in the range 10-15 mm.

39. A tool according to claim 15, wherein the transmitter has a selected width in the range 30-40 mm and an angle that is optimized for the velocity range of a slow formation.

40. A tool according to claim 15,

wherein the tool is an LWD tool and the elongate body is a portion of drill string proximate to a drill bit;

wherein said at least one ultrasonic receiver is a pair of first and second spaced-apart receivers;

wherein said processor is coupled to receive signals from the pair of receivers; and

wherein said processor includes means for producing a velocity image data value from difference of arrival times at first and second spaced-apart receivers.

41. An LWD tool according to claim 40, wherein said processor includes means for associating a difference of arrival times with an azimuthal position of first and second spaced-apart receivers to produce a series of image data values with an azimuthal position attribute as the drill string rotates in the borehole.

42. An LWD tool according to claim 41, wherein said processor includes means for associating a difference of arrival times with a depth in the borehole to produce an image data value with an azimuthal position attribute and a depth attribute.

43. An LWD tool according to claim 40, wherein said processor includes means for adding image data values to a stored borehole wall image data set.

44. An LWD tool according to claim 40, wherein said processor further includes means for identifying an arrival as a compressional pulse arrival.

45. An LWD tool according to claim 40, wherein said processor further includes means for first motion detection.

46. An LWD tool according to claim 40, wherein said processor further includes means for identifying an arrival as a pseudo-Raleigh pulse arrival.

47. An LWD tool according to claim 46, wherein said processor further includes means for first zero crossing detection.

48. An LWD tool according to claim 40, wherein said processor further includes means for determining a difference of arrival times at first and second spaced-apart receivers.

49. An LWD tool according to claim 40, wherein said processor further includes means for dividing receiver spacing by difference of arrival times at first and second spaced-apart receivers.

50. An LWD tool according to claim 40, the tool further comprising mud pulse data transmitter for transmitting velocity image data values to the surface station.

51. An LWD tool according to claim 40, further comprising a transmitter/receiver mount, attached to the drill string proximate to the drill bit, having a cylindrical section portion between said transmitter and said pair of receivers, the cylindrical section portion defining at least one slot for blocking direct arrivals.

52. An LWD tool according to claim 51, wherein a slot is filled with a rubber compound for blocking direct arrivals.

53. An LWD tool according to claim 40, further comprising a sleeve-like transmitter mount for attaching said ultrasonic transmitter to said drill string;

and a sleeve-like receiver mount for attaching said pair of receivers to said drill string.

54. An LWD tool according to claim 40, wherein said receiver mount is sized to minimize standoff of a pair of receivers from the borehole wall.

55. An LWD tool according to claim 40, wherein each receiver is oriented normal to the drill string axis.

56. An LWD tool according to claim 40, wherein each receiver is a segmented cylindrical receiver.

57. An LWD tool according to claim 40, further comprising a plurality of transmitters and a plurality of groups of receivers, each transmitter associated with a group of receivers.

58. An LWD tool according to claim 57, wherein a group of receivers comprises a plurality of azimuthally spaced pairs of receivers.

59. An LWD tool according to claim 57, wherein a first pair of receivers is axially offset from a second pair of receivers.

60. An LWD tool according to claim 57, wherein a pair of receivers includes a first receiver and a second receiver, and wherein said first receiver is azimuthally offset from the second receiver.

61. An LWD tool according to claim 40, wherein the first receiver of a first pair of receivers is also the first receiver of a second pair of receivers.

62. An LWD tool according to claim 15, wherein said ultrasonic transmitter includes means for transmitting pulses of ultrasonic waves in the frequency range 50-500 kHz.

63. An LWD tool according to claim 62, wherein said transmitter comprises a directional transmitter element for generating directional pulses of ultrasonic waves.

64. An LWD tool according to claim 63, wherein said transmitter element is oriented at a true angle of incidence such that ultrasonic compressional waves propagate toward the receiver along a portion of the borehole wall longitudinally with respect to the borehole.

65. An LWD tool according to claim 64, wherein the true angle of incidence is selected to optimize for compressional waves.

66. An LWD tool according to claim 64, wherein the true angle of incidence is approximately 25°

.

67. An LWD tool according to claim 64, wherein the true angle of incidence is in the range 20°

-40°

.

68. An LWD tool according to claim 64, wherein said transmitter is oriented at true angle of incidence is selected to optimize for ultrasonic pseudo-Raleigh waves.

69. An LWD tool according to claim 15, further comprising a coupling wedge made of PEEK mounted proximate to the transmitter.

70. An LWD tool according to claim 15, further comprising a coupling wedge made of PEEK mounted proximate to the receiver.

71. An LWD tool according to claim 15, further comprising a protective plate made of titanium mounted proximate to at least one receiver.

72. A method according to claim 15, wherein producing a velocity value at each of the plurality of azimuths and depths in the borehole includes:

a) transmitting an ultrasonic pulse through the wall of said borehole such that by refraction said ultrasonic pulse travels in said formation along said borehole;

b) receiving said ultrasonic pulse at first and second receivers spaced-apart in a direction along said borehole;

c) producing a velocity image data value indicative of difference of arrival times of said ultrasonic pulse at said first and second receivers;

d) repeating steps a)-c) at a plurality of azimuths to produce a velocity image data value at each of the plurality of azimuths; and

e) repeating steps a)-d) at a plurality of depths.

73. A method according to claim 72, wherein producing a velocity image data value includes dividing receiver spacing by difference of arrival times.

74. A method according to claim 72, wherein step (c) further includes the step of:

determining a compressional pulse arrival time by digitizing a signal from a receiver, determining noise level, setting a compressional amplitude threshold to be a multiple of the noise level, determining compressional amplitude threshold time as time at which an absolute value of the signal exceeds the threshold for compressional pulse, picking the first zero-crossing after threshold time, and setting compressional pulse arrival time equal to the time of first zero-crossing.

75. A method according to claim 74, further comprising the step of associating the velocity image data value derived from the compressional pulse arrival time with a compressional image data set.

76. A method according to claim 74, wherein step (c) further includes the steps of:

determining a pseudo-Raleigh pulse arrival time by setting a pseudo-Raleigh amplitude threshold to be a multiple of the larger of the first two extrema of signal following the first zero-crossing, determining pseudo-Raleigh amplitude threshold time as time at which an absolute value of the signal exceeds the threshold for pseudo-Raleigh pulse, picking the first zero-crossing after pseudo-Raleigh threshold time, and setting pseudo-Raleigh pulse arrival time equal to the time of first zero-crossing.

77. A method according to claim 76, further comprising the step of associating the velocity image data value derived from the pseudo-Raleigh pulse arrival with a pseudo-Raleigh velocity data set.

78. A method according to claim 74, further comprising the step of calculating a correction factor to correct for error in effective spacing between receivers according to critical angle and formation velocity.