Dual-seal drill bit pressure communication system

• US 20030019666A1
• Filed: 08/07/2002
• Published: 01/30/2003
• Est. Priority Date: 12/19/1995
• Status: Active Grant

• Current Assignee: Smith International Incorporated (Schlumberger NV)
• Original Assignee: Smith International Incorporated (Schlumberger NV)
• Inventors: Cariveau, Peter, Didericksen, Roger, Portwood, Gary Ray, Denton, Robert, Cawthorne, Chris Edward, Slaughter, Robert H. Jr.
• Granted Patent: US 6,679,342 B2
• Time in Patent Office: Days
• US Class Current: 175/371
• CPC Class Codes: E21B 10/25 characterised by sealing details
• CPC Class Codes: F16C 21/00 Combinations of sliding-contact bearings with ball or roller bearings, for exclusively rotary movement F16C17/24, F16C19/52 take precedence
• CPC Class Codes: F16C 2352/00 Apparatus for drilling in general E21
• CPC Class Codes: F16C 33/7836 floating with respect to both races
• CPC Class Codes: F16C 33/7896 with two or more discrete sealings arranged in series
• CPC Class Codes: Y10S 277/928 Seal including pressure relief or vent feature

Abstract

A drill bit for use in a borehole at least partially containing drilling fluid includes a bit body having at least two bit components, including at least one leg, the leg having a journal segment, and a roller cone rotatably mounted upon the journal segment and forming at least one bearing cavity therebetween. Also included is an annular primary seal disposed between the leg and the roller cone, an annular secondary seal disposed between the leg and the roller cone and between the annular primary seal and the borehole and an annular space disposed between the annular primary seal and the annular secondary seal, the annular space at least partially containing fluid and being in substantially absolute fluid isolation from the bearing cavity and means for permitting the flow of fluid from the annular space to the borehole. The annular secondary seal may be primarily elastomeric and the means for permitting the flow of fluid may further permit the flow of fluid from the borehole to the annular space. The annular space may at least partially include a grease possessing a water washout value of under approximately 50% per ASTM D-4049 water spray test for lubrication characteristics and the grease may include a polymer tackifier of between approximately 1% and approximately 5% by weight.

Claims

1. A drill bit for use in a borehole at least partially containing drilling fluid, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone;

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole;

an annular space disposed between said annular primary seal and said annular secondary seal, said annular space at least partially containing fluid and being in substantially absolute fluid isolation from said bearing cavity; and

means for permitting the flow of fluid from said annular space to the borehole.

2. The drill bit of claim 1 wherein said annular secondary seal is primarily elastomeric.

3. The drill bit of claim 2 wherein said means further permits the flow of fluid from the borehole to said annular space.

4. The drill bit of claim 1 wherein said means is integral with said annular secondary seal.

5. The drill bit of claim 1 wherein said means is integral with at least one of said bit components.

6. The drill bit of claim 1 wherein said annular space at least partially includes a grease possessing a water washout value of under approximately 50% per ASTM D-4049 water spray test for lubrication characteristics, said grease including a polymer tackifier of between approximately 1% and approximately 5% by weight.

7. The drill bit of claim 1 wherein said annular secondary seal is primarily radially energized.

8. The drill bit of claim 2 wherein said annular secondary seal is primarily axially energized.

9. The drill bit of claim 1 wherein said annular secondary seal is disposed in an annular groove formed in one of said bit components.

10. The drill bit of claim 2 wherein said secondary seal is disposed in an annular interstice formed between said leg and said roller cone.

11. A drill bit for use in a borehole comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone and between said bearing cavity and the borehole, said annular primary seal having a primarily dynamic sealing surface;

an annular secondary seal disposed between said annular primary seal and the borehole, said annular secondary seal having a primarily dynamic sealing surface;

wherein a first contact pressure occurs at said primarily dynamic sealing surface of said annular primary seal and a second contact pressure occurs at said primarily dynamic sealing surface of said annular secondary seal, said first contact pressure being greater than said second contact pressure; and

an annular space disposed between said annular primary seal and said annular secondary seal, said annular space at least partially containing fluid and in substantially absolute fluid isolation from said bearing cavity.

12. The drill bit of claim 11 wherein said annular secondary seal is primarily elastomeric.

13. The drill bit of claim 11 wherein said fluid in said annular space is capable of flowing past said annular secondary seal from said annular space to the borehole.

14. A drill bit for use in a borehole at least partially containing drilling fluid, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone;

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, said annular secondary seal having a primarily dynamic sealing surface and a primarily static sealing surface, wherein a first contact pressure occurs at said primarily dynamic sealing surface and a second contact pressure occurs at said primarily static sealing surface, said first contact pressure and said second contact pressure being unequal; and

an annular space disposed between said annular primary seal and said annular secondary seal, said annular space at least partially containing fluid and in substantially absolute fluid isolation from said bearing cavity.

15. The drill bit of claim 14 wherein said first contact pressure is greater than said second contact pressure.

16. The drill bit of claim 14 wherein said second contact pressure is greater than said first contact pressure.

17. A drill bit for use in a borehole at least partially containing drilling fluid, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone; and

an annular secondary seal disposed between said annular primary seal and the borehole and between said leg and said roller cone, wherein said annular secondary seal is engageable with said leg and said roller cone, said annular secondary seal including a sealing surface engageable with one of said bit components, wherein said sealing surface includes first and second regions; and

wherein a first contact pressure occurs at said first region of said sealing surface and a second contact pressure occurs at said second region of said sealing surface, said first contact pressure being greater than said second contact pressure.

18. The drill bit of claim 17 further including an annular space disposed between said annular primary seal and said annular secondary seal, said annular space at least partially containing fluid and in substantially absolute fluid isolation from said bearing cavity.

19. The drill bit of claim 18 wherein said fluid in said annular space is capable of migrating past said annular secondary seal from said annular space to the borehole.

20. The drill bit of claim 17 wherein said sealing surface is a primarily dynamic sealing surface.

21. The drill bit of claim 17 wherein said sealing surface is a primarily static sealing surface.

22. A drill bit for use in a borehole at least partially containing drilling fluid, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone;

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole; and

an annular space formed between said annular primary seal and said annular secondary seal, said annular space at least partially containing fluid and in substantially absolute fluid isolation from said bearing cavity, said annular space having a chamber pressure, wherein said chamber pressure may be altered by allowing the passage of fluid from said annular space to the borehole and from the borehole to said annular space.

23. The drill bit of claim 22 wherein the borehole includes a borehole pressure and wherein a differential pressure occurs when said chamber pressure and the borehole pressure are unequal, further wherein said chamber pressure may be altered when said differential pressure is between approximately 0 psi and approximately 100 psi.

24. The drill bit of claim 22 wherein the borehole includes a borehole pressure and wherein a differential pressure occurs when said chamber pressure and the borehole pressure are unequal, further wherein said chamber pressure may be altered when said differential pressure is between approximately 30 psi and approximately 70 psi.

25. A drill bit for use in a borehole at least partially containing fluid and having a borehole pressure, comprising:

a bit body having at least two bit components said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone;

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole; and

an annular space formed between said annular primary seal and said annular secondary seal, said annular space having a chamber pressure and at least partially containing fluid, said annular space being in substantially absolute fluid isolation from said bearing cavity, wherein said fluid migrates from said annular space to the borehole when said chamber pressure is greater than the borehole pressure and wherein fluid migrates from the borehole to said annular space when the borehole pressure is greater than said chamber pressure.

26. The drill bit of claim 25 wherein a differential pressure occurs when said chamber pressure and the borehole pressure are unequal, said fluid in said annular space migrating from said annular space to the borehole when said chamber pressure is greater than the borehole pressure by a value equal to or greater than a first differential pressure, and wherein fluid in the borehole migrates from the borehole to said annular space when the borehole pressure is greater than said chamber pressure by a value equal to or greater than a second differential pressure.

27. The drill bit of claim 26 wherein said second pressure differential is higher than said first pressure differential.

28. A drill bit for use in a borehole at least partially containing fluid and having a borehole pressure, comprising:

a bit body having at least two bit components said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone;

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole; and

an annular space formed between said annular primary seal and said annular secondary seal, said annular space having a chamber pressure and at least partially containing fluid, said annular space being in substantially absolute fluid isolation from said bearing cavity, wherein said fluid migrates from said annular space to the borehole when said chamber pressure is greater than the borehole pressure.

29. The drill bit of claim 28 wherein said annular secondary seal is primarily elastomeric.

30. The drill bit of claim 28 wherein a differential pressure occurs when said chamber pressure and the borehole pressure are unequal, said fluid in said annular space migrating from said annular space to the borehole when said chamber pressure is greater than the borehole pressure by a value equal to or greater than a first differential pressure.

31. A drill bit for use in a borehole at least partially containing drilling fluid, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone; and

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, said annular secondary seal having a sealing surface engageable with at least one said bit component, said sealing surface having first and second adjacent regions, wherein the thickness of said annular secondary seal at said first region of said sealing surface is greater than the thickness of said annular secondary seal at said second region of said sealing surface.

32. The drill bit of claim 31 wherein said sealing surface is a primarily dynamic sealing surface.

33. The drill bit of claim 31 wherein said sealing surface is a primarily static sealing surface.

34. The drill bit of claim 31 wherein said annular secondary seal includes first and second side surfaces adjacent to said sealing surface, further wherein at least one of said bit components includes at least one non-energizing surface at least partially engageable with one of said first and second side surfaces of said annular secondary seal, wherein at least one of said first and second side surfaces of said annular secondary seal and said non-energizing surface of said bit component includes first and second sections, wherein said first section is uneven with respect to said second section.

35. The drill bit of claim 34 wherein said first section includes at least one surface feature.

36. The drill bit of claim 31 wherein said annular secondary seal includes a lip, wherein said second region of said sealing surface is formed on said lip.

37. The drill bit of claim 36 wherein said lip is at least partially bellows-shaped.

38. A drill bit for use in a borehole at least partially containing drilling fluid, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone; and

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, said annular secondary seal including at least one region having a tapered cross-section.

39. The drill bit of claim 38 wherein said at least one region of said annular secondary seal includes an outer surface, said annular secondary seal including a primarily dynamic sealing surface, wherein at least a portion of said primarily dynamic sealing surface is disposed on said outer surface of said region having a tapered cross-section.

40. The drill bit of claim 38 wherein said at least one region of said annular secondary seal includes an outer surface, said annular secondary seal including a primarily static sealing surface, wherein at least a portion of said primarily static sealing surface is disposed on said outer surface of said region having a tapered cross-section.

41. The drill bit of claim 38 wherein said annular secondary seal includes first and second side surfaces adjacent to said sealing surface, further wherein at least one of said bit components includes at least one non-energizing surface at least partially engageable with one of said first and second side surfaces of said annular secondary seal, wherein at least one of said first and second side surfaces of said annular secondary seal and said non-energizing surface of said bit component includes first and second sections, wherein said first section is uneven with respect to said second section.

42. The drill bit of claim 41 wherein said first section includes at least one surface feature.

43. The drill bit of claim 38 wherein the cross-section of said annular secondary seal is tapered around the entire circumference of said annular secondary seal.

44. A drill bit for use in a borehole at least partially containing drilling fluid, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone; and

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, said annular secondary seal including at least first and second circumferentially adjacent regions, a primarily static sealing surface and a primarily dynamic sealing surface, each of said first and second circumferentially adjacent regions having a height measured between said primarily static and primarily dynamic sealing surfaces,

wherein at least one of said static and dynamic sealing surfaces is at least partially disposed on said first and second circumferentially adjacent regions, wherein the height of said first circumferentially adjacent region is greater than the height of said second circumferentially adjacent region.

45. The drill bit of claim 44 wherein said annular secondary seal includes a concave sealing surface extending at least partially across said second circumferentially adjacent region.

46. The drill bit of claim 44 wherein said primarily dynamic sealing surface is at least partially disposed on said second circumferentially adjacent region.

47. The drill bit of claim 44 wherein said primarily static sealing surface is at least partially disposed on said second circumferentially adjacent region.

48. The drill bit of claim 44 wherein said annular secondary seal includes first and second side surfaces adjacent to said sealing surface, further wherein at least one of said bit components includes at least one non-energizing surface at least partially engageable with one of said first and second side surfaces of said annular secondary seal, wherein at least one of said first and second side surfaces of said annular secondary seal and said non-energizing surface of said bit component includes first and second sections, wherein said first section is uneven with respect to said second section.

49. The drill bit of claim 48 wherein said first section includes at least one surface feature.

50. A drill bit for use in a borehole, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween, wherein at least one of said bit components includes an annular groove having first and second circumferentially adjacent regions, wherein the width of said first circumferentially adjacent region is greater than the width of said second circumferentially adjacent region;

an annular primary seal disposed between said leg and said roller cone; and

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, wherein said annular secondary seal is disposed within said annular groove.

51. The drill bit of claim 50 wherein said first circumferentially adjacent region includes at least one pocket.

52. A drill bit for use in a borehole, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween, wherein said bit components include first and second primarily non-energizing seal engagement surfaces;

an annular primary seal disposed between said leg and said roller cone;

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, said annular secondary seal having first and second sides engageable with said first and second primarily non-energizing seal engagement surfaces of said bit components, respectively; and

wherein at least one of said first and second primarily non-energizing seal engagement surfaces of said bit components includes first and second regions, said first region including at least one cut-out.

53. The drill bit of claim 52 wherein said cut out is a pocket.

54. The drill bit of claim 52 wherein said first primarily non-energizing seal engagement surface is disposed between said second primarily non-energizing seal engagement surface and said bearing cavity, further wherein said first region is disposed on said second primarily non-energizing seal engagement surface.

55. The drill bit of claim 54 wherein said first and second primarily non-energizing seal engagement surfaces are surfaces of an annular interstice.

56. The drill bit of claim 54 wherein said first and second primarily non-energizing seal engagement surfaces are surfaces of an annular groove.

57. The drill bit of claim 52 wherein each of said first and second primarily non-energizing seal engagement surfaces includes a first region having at least one cut-out.

58. A drill bit for use in a borehole, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween, wherein said bit components include first and second primarily non-energizing seal engagement surfaces;

an annular primary seal disposed between said leg and said roller cone;

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, said annular secondary seal having first and second sides engageable with said first and second primarily non-energizing seal engagement surfaces of said bit components, respectively; and

wherein at least one of said first and second primarily non-energizing seal engagement surfaces of said bit components includes first and second regions, said first region being uneven with respect to said second region.

59. The drill bit of claim 58 wherein said first region includes at least one surface feature.

60. The drill bit of claim 58 wherein said first primarily non-energizing seal engagement surface is disposed between said second primarily non-energizing seal engagement surface and said bearing cavity, further wherein said first region is disposed on said second primarily non-energizing seal engagement surface.

61. The drill bit of claim 58 wherein each of said first and second primarily non-energizing seal engagement surfaces includes first and second regions, wherein each said first region is uneven with respect to each said second region, respectively.

62. A drill bit for use in a borehole, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween, wherein at least one of said bit components includes an annular groove;

an annular primary seal disposed between said leg and said roller cone;

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, said annular secondary seal having first and second sides and being disposed within said annular groove; and

wherein said annular groove includes a first primarily non-energizing surface engageable with said first side of said annular secondary seal and a second primarily non-energizing surface engageable with said second side of said annular secondary seal, said first primarily non-energizing surface disposed between said second primarily non-energizing surface and said bearing cavity, further wherein said second primarily non-energizing surface includes at least first and second circumferentially adjacent regions, wherein said first region of said second primarily non-energizing surface includes at least one cut-out, whereby the distance from said first region of said second primarily non-energizing surface to said first primarily non-energizing surface is greater than the distance from said second region of said second primarily non-energizing surface to said first primarily non-energizing surface.

63. The drill bit of claim 62 wherein said cut out includes at least one pocket.

64. A drill bit for use in a borehole at least partially containing drilling fluid, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone; and

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, said annular secondary seal having first and second circumferentially adjacent regions and a sealing surface extending at least partially upon said first and second circumferentially adjacent regions, wherein said sealing surface of said first circumferentially adjacent region is uneven with respect to said sealing surface of said second circumferentially adjacent region.

65. The drill bit of claim 64 wherein said sealing surface of said first circumferentially adjacent region includes at least one surface feature.

66. The drill bit of claim 64 wherein said sealing surface is a primarily static sealing surface.

67. The drill bit of claim 64 wherein said sealing surface is a primarily dynamic sealing surface.

68. The drill bit of claim 64 wherein said annular secondary seal includes first and second side surfaces adjacent to said sealing surface, further wherein at least one of said bit components includes at least one non-energizing surface at least partially engageable with one of said first and second side surfaces of said annular secondary seal, wherein at least one of said first and second side surfaces of said annular secondary seal and said non-energizing surface of said bit component includes first and second sections, wherein said first section is uneven with respect to said second section.

69. The drill bit of claim 68 wherein said first section includes at least one surface feature.

70. A drill bit for use in a borehole at least partially containing drilling fluid, comprising:

a bit body having at least two bit components, a first said bit component including at least one leg, said leg having a journal segment, and a second said bit component including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone;

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole; and

wherein each of said first and second bit components includes at least one component surface engageable with said annular secondary seal, at least one said component surface including first and second adjacent regions, wherein said first region of said component surface is uneven with respect to said second region of said component surface.

71. The drill bit of claim 70 wherein said first region of said component surface includes at least one surface feature.

72. The drill bit of claim 70 wherein each said at least one component surfaces is a primarily non-energizing surface.

73. The drill bit of claim 70 wherein each said at least one component surfaces is a primarily energizing surface.

74. A drill bit for use in a borehole, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween, wherein at least one of said bit components includes an annular groove having at least first and second circumferentially adjacent regions, wherein the depth of said first circumferentially adjacent region is greater than the depth of said circumferentially adjacent second region;

an annular primary seal disposed between said leg and said roller cone; and

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, wherein said annular secondary seal is disposed within said annular groove.

75. The drill bit of claim 74 wherein said first region includes at least one pocket.

76. The drill bit of claim 74 wherein said annular groove is formed in said leg.

77. The drill bit of claim 74 wherein said annular groove is formed in said roller cone.

78. A drill bit for use in a borehole, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular interstice formed between said bit components, said annular interstice having at least one seal engagement surface, said seal engagement surface having first and second circumferentially adjacent regions, wherein the depth of said first circumferentially adjacent region of said seal engagement surface is greater than the depth of said second circumferentially adjacent region;

an annular primary seal disposed between said leg and said roller cone; and

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, wherein said annular secondary seal is disposed within said annular interstice.

79. A drill bit for use in a borehole at least partially containing drilling fluid, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone; and

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, said annular secondary seal including a primarily dynamic sealing surface and a primarily static sealing surface, each of said primarily dynamic and static sealing surfaces engageable with one of said bit components, wherein at least a portion of at least one of said primarily dynamic and static sealing surfaces includes a non-elastomeric porous inlay capable of at least partially allowing the passage of fluid past said annular secondary seal when said portion of at least one of said sealing surfaces is engaged with said bit component.

80. The drill bit of claim 79 wherein said porous inlay is constructed at least partially of wire mesh.

81. The drill bit of claim 79 wherein said porous inlay is a screen.

82. The drill bit of claim 79 wherein said porous inlay is constructed at least partially of fabric.

83. The drill bit of claim 79 wherein said porous inlay is constructed at least partially of felt.

84. A drill bit for use in a borehole at least partially containing fluid and having a borehole pressure, comprising:

a bit body having at least one leg, said leg including an exterior surface and a journal segment;

a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone;

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole;

an annular space disposed between said annular primary seal and said annular secondary seal, said annular space at least partially including fluid and being in substantially absolute fluid isolation from said bearing cavity;

an opening in said exterior surface of said leg; and

a passage disposed in said leg and extending from said opening to said annular space, said passage allowing fluid communication between said annular space and the borehole.

85. The drill bit of claim 84 further including a plurality of passages disposed in said leg and extending from said opening to said annular space.

86. The drill bit of claim 84 wherein said annular space at least partially includes a grease possessing a water washout value of under approximately 50% per ASTM D-4049 water spray test for lubrication characteristics, said grease including a polymer tackifier of between approximately 1% and approximately 5% by weight.

87. The drill bit of claim 84 wherein said passage is capable of allowing the flow of fluid from said annular space to the borehole and from the borehole to said annular space.

88. The drill bit of claim 87 wherein said annular space has a chamber pressure, said chamber pressure being substantially equal to the borehole pressure.

89. The drill bit of claim 84 further including a fluid control member disposed in said leg in fluid communication with said passage.

90. The drill bit of claim 89 wherein said fluid control member is a two-way valve.

91. The drill bit of claim 89 wherein said fluid control member is a perforated member.

92. The drill bit of claim 91 wherein said perforated member allows fluid flow from said annular space to the borehole and disallows fluid flow from the borehole into said annular space.

93. The drill bit of claim 91 wherein said perforated member is at least partially elastomeric.

94. The drill bit of claim 93 wherein said perforated member is a washer.

95. The drill bit of claim 91 wherein said perforated member is a filter.

96. The drill bit of claim 89 wherein said fluid control member is a primarily one-way fluid valve capable of allowing the flow of fluid from said annular space to the borehole.

97. The drill bit of claim 96 wherein said primarily one-way fluid valve includes a ball and a spring.

98. The drill bit of claim 84 wherein said annular space is filled with incompressible fluid through said passage.

99. A drill bit for use in a borehole at least partially containing fluid and having a borehole pressure, comprising:

a bit body having at least one leg, said leg including an exterior surface and a journal segment;

a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone and forming a substantially absolute seal therebetween;

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole;

an annular space disposed between said annular primary seal and said annular secondary seal, said annular space in substantially absolute fluid isolation from said bearing cavity;

an opening in said exterior surface of said leg;

a passage disposed in said leg and extending from said opening to said annular space, said passage being filled with incompressible fluid; and

a plug disposed in said opening.

100. A drill bit for use in a borehole at least partially containing fluid, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween, wherein at least one of said bit components includes at least two seal engagement surfaces;

an annular primary seal disposed between said leg and said roller cone; and

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, said annular secondary seal including a primarily dynamic sealing surface and a primarily static sealing surface, each said sealing surface of said annular secondary seal having a width and being engageable at said width with one of said seal engagement surfaces of said bit components, at least one of said annular primarily dynamic and primarily static sealing surfaces including first and second regions, said width of said first region being smaller than said width of said second region.

101. A drill bit for use in a borehole at least partially containing fluid, comprising:

a bit body having at least two bit components, said bit components including at least one leg, said leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone; and

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, said annular secondary seal including at least one region having an at least partially non-symmetrical cross-section.

102. The drill bit of claim 101 wherein said region of said annular secondary seal has an outer surface, further wherein said annular secondary seal includes a primarily dynamic sealing surface and a primarily static sealing surface, wherein at least a portion of at least one of said primarily dynamic and primarily static sealing surfaces is disposed on said outer surface.

103. An incompressible fluid for use to lubricate a seal in a sealed bearing drill bit, the drill bit useful in a borehole at least partially containing drilling fluid and solid particles, comprising:

a grease capable of lubricating at least one seal after said grease contacts drilling fluid.

104. The incompressible fluid of claim 103 wherein said grease is capable of trapping solid particles to assist in preventing the ingress of solid particles to the seal.

105. The incompressible fluid of claim 103 where said grease is capable of transmitting energy between first and second seals after said grease contacts drilling fluid.

106. The incompressible fluid of claim 103 wherein said grease is disposed between a primary seal and a secondary seal.

107. The incompressible fluid of claim 103 wherein said grease possesses a water washout value of under approximately 50% per ASTM D-4049 water spray test for lubrication characteristics.

108. The incompressible fluid of claim 103 wherein said grease possesses a water washout value of under approximately 30% per ASTM D-4049 water spray test for lubrication characteristics.

109. The incompressible fluid of claim 107 wherein said grease includes a polymer tackifier of between approximately 1% and approximately 5% by weight.

110. The incompressible fluid of claim 109 wherein said grease includes between approximately 10 percent and approximately 30 percent by weight of at least one mineral oil and between approximately 70 percent and approximately 90 percent by weight of at least one synthetic oil.

111. The incompressible fluid of claim 110 wherein said grease includes between approximately 1.0 percent and approximately 10.0 percent by weight of silica thickener and between approximately 1.0 percent and approximately 5.0 percent by weight of tackifier.

112. A drill it for use in a borehole at least partially containing fluid, comprising:

a bit body having at least two bit components, said bit components including at least one leg having a journal segment, said bit components further including a roller cone rotatably mounted upon said journal segment and forming at least one bearing cavity therebetween;

an annular primary seal disposed between said leg and said roller cone; and

an annular secondary seal disposed between said leg and said roller cone and between said annular primary seal and the borehole, said annular secondary seal having a primarily dynamic sealing surface and first and second side surfaces adjacent to said primarily dynamic sealing surface, wherein at least one of said bit components includes at least one non-energizing surface at least partially engageable with one of said first and second side surfaces of said annular secondary seal, at least one of said first and second side surfaces of said annular secondary seal and said non-energizing surface of said bit component including first and second sections, wherein said first section is uneven with respect to said second section.

113. The drill bit of claim 112 wherein said first section includes at least one surface feature.

114. The drill bit of claim 113 wherein said first section includes at least one protrusion.

115. A method for communicating fluid pressure between a borehole at least partially containing drilling fluid and the annular space formed between first and second annular seals in a dual-seal drill bit, the drill bit including a bit body having at least two bit components, the bit components including at least one leg having a journal segment, the bit components further including a roller cone rotatably mounted upon the journal segment and forming at least one bearing cavity therebetween, the first annular seal disposed between the leg and the roller cone, the second annular seal disposed between the leg and the roller cone and between the annular primary seal and the borehole, including:

providing an absolute seal between the first annular seal and the bit components;

fluidly isolating the annular space between the first and second annular seals from the bearing cavity;

filling the annular space between the first and second annular seals with incompressible fluid;

permitting the flow of incompressible fluid from the annular space to the borehole; and

permitting the flow of drilling fluid from the borehole to the annular space.