Method and apparatus for drilling and enlarging a borehole

Abstract

A reaming apparatus for enlarging a borehole, including a tubular body having one or more longitudinally and generally radially extending blades circumferentially spaced thereabout. Each of the blades carries highly exposed cutting elements, on the order of fifty percent exposure, on its profile substantially all the way to the gage. At least one of the blades is a primary blade for cutting the full or drill diameter of the borehole, while one or more others of the blades may be secondary blades which extend a lesser radial distance from the body than the primary blade. A secondary blade initially shares a large portion of the cutting load with the primary blade while the borehole size is in transition between a smaller, pass through diameter and drill diameter. It functions to enhance the rapidity of the transition while balancing side reaction forces, and reduces vibration and borehole eccentricity. After drill diameter is reached, cutting elements on the secondary blade continue to share the cutting load over the radial distance they extend from the body.

What is claimed is: 
     
       1. A reaming apparatus for expanding a borehole in a subterranean formation to a larger diameter, comprising: a body .[.have.]. .Iadd.having .Iaddend.a longitudinal bore extending therethrough, a longitudinally extending rotational axis, and means at the top and bottom thereof for securing said body within a bottom hole assembly;   at least one primary blade for cutting said enlarged borehole diameter upon rotation of said apparatus about said rotational axis, said at least one primary blade having a longitudinal extent, protruding generally radially from said body a fixed distance and defining a cutting profile on an exterior edge thereof; and   a plurality of cutting elements disposed along said primary blade cutting profile from proximate said body for cutting into said formation to expand said borehole to said larger diameter, at least some of said cutting elements being exposed beyond said cutting profile throughout substantially the entire extent of said primary blade cutting profile.   
     
     
       2. The apparatus of claim 1, wherein said primary blade cutting profile is arcuate at the bottom thereof, and extends outward and upward into a substantially linear gage segment which defines said larger diameter. 
     
     
       3. The apparatus of claim 2, wherein said at least one primary blade extends inwardly toward said body immediately above said gage segment thereof. 
     
     
       4. The apparatus of claim .[.1.]. .Iadd.2.Iaddend., wherein at least some of said cutting elements along said primary blade cutting profile gage segment include flat cutting edges oriented substantially parallel thereto. 
     
     
       5. The apparatus of claim 1, wherein said cutting elements comprise PDC cutting elements. 
     
     
       6. The apparatus of claim 5, wherein at least one of said cutting elements is set at a back rake of about 20 degrees or less. 
     
     
       7. The apparatus of claim 5, wherein at least one of said cutting elements is set at a neutral back rake. 
     
     
       8. The apparatus of claim 5, wherein at least one of said cutting elements is set at a positive back rake. 
     
     
       9. The apparatus of claim 5, wherein at least one of said cutting elements is set at a positive side rake. 
     
     
       10. The apparatus of claim 1, wherein said body is substantially tubular with a longitudinal extent substantially greater than that of said at least one primary blade, and said at least one primary blade is secured to said body along the midportion thereof. 
     
     
       11. The apparatus of claim 1, wherein said at least one primary blade is oriented with its longitudinal extent substantially parallel to said rotational axis. 
     
     
       12. The apparatus of claim 1, further including at least one longitudinally extending secondary blade protruding generally radially from said body to a lesser distance, as measured from said rotational axis, than said at least one primary blade, said at least one secondary blade being circumferentially spaced from said .Iadd.at least one .Iaddend.primary blade about said body and defining a cutting profile, said at least one secondary blade including a plurality of cutting elements disposed along said cutting profile, at least some of said cutting elements being exposed beyond said secondary blade cutting profile. 
     
     
       13. The apparatus of claim 12, wherein said cutting profile of said at least one secondary blade is arcuate at the bottom thereof, and extends outward and upward into a substantially linear gage segment. 
     
     
       14. The apparatus of claim 13, wherein said at least one primary blade comprises a plurality of primary blades circumferentially spaced about said body. 
     
     
       15. The apparatus of claim 14, wherein said at least one secondary blade comprises a plurality of secondary blades circumferentially spaced about said body. 
     
     
       16. The apparatus of claim 14, wherein said plurality of primary blades .[.define.]. .Iadd.defines .Iaddend.substantially the same cutting profile. 
     
     
       17. The apparatus of claim 15, wherein said body is substantially tubular with a longitudinal extent substantially greater than that of said primary blades, and said primary and secondary blades are secured about said body in spaced circumferential relationship along the mid-portion thereof. .Iadd. 
     
     
       18.  A reaming apparatus for expanding a borehole in a subterranean formation to a larger diameter, comprising: a longitudinally extending body;   at least one primary blade protruding generally radially from said body, having a longitudinal extent and defining a profile on an exterior edge thereof; and   at least one cutting element disposed on said primary blade profile for cutting into said formation to expand said borehole to said larger diameter upon rotation of said body, said at least one cutting element being exposed beyond said profile. .Iaddend..Iadd.19. The apparatus of claim 18, wherein said primary blade profile is arcuate proximate the bottom thereof, and extends outward and upward into a gage segment which defines said larger diameter. .Iaddend..Iadd.20. The apparatus of claim 19, wherein said at least one primary blade extends inwardly toward said body immediately above said gage segment thereof. .Iaddend..Iadd.21. The apparatus of claim 19, wherein said at least one cutting element comprises a plurality of cutting elements, and at least another of said plurality of cutting elements is disposed on said primary blade profile gage segment and includes a flat cutting edge oriented substantially parallel to a longitudinal extent of said body. .Iaddend..Iadd.22. The apparatus of claim 18, wherein said at least one cutting element comprises a PDC cutting element. .Iaddend..Iadd.23. The apparatus of claim 22, wherein said at least one cutting element is set at a back rake of about 20° or less. .Iaddend..Iadd.24. The apparatus of claim 22, wherein said at least one cutting element is set at a neutral back rake.   
     
     
        .Iaddend..Iadd.25.  The apparatus of claim 22, wherein said at least one cutting element is set at a positive back rake. .Iaddend..Iadd.26. The apparatus of claim 22, wherein said at least one cutting element is set at a positive side rake. .Iaddend..Iadd.27. The apparatus of claim 18, wherein said body is substantially tubular, and said at least one primary blade is secured to said body proximate a mid-portion thereof. .Iaddend..Iadd.28. The apparatus of claim 18, wherein said at least one primary blade is oriented with its longitudinal extent substantially parallel to the longitudinal extent of said body. .Iaddend..Iadd.29. The apparatus of claim 18, further including at least one longitudinally extending secondary blade protruding generally radially from said body to a lesser distance than said at least one primary blade, said at least one secondary blade being circumferentially spaced from said at least one primary blade on said body, defining a profile and bearing at least one cutting element disposed on said profile thereof, said at least one cutting element of said at least one secondary blade being exposed beyond said profile thereof. .Iaddend..Iadd.30. The apparatus of claim 29, wherein said profile of said at least one secondary blade is arcuate proximate the bottom thereof. .Iaddend..Iadd.31. The apparatus of claim 29, wherein said at least one primary blade comprises a plurality of primary blades circumferentially spaced about said body. .Iaddend..Iadd.32. The apparatus of claim 31, wherein each of said plurality of primary blades defines substantially the same profile. 
     
     
        .Iaddend..Iadd.33.  The apparatus of claim 31, wherein said at least one secondary blade comprises a plurality of secondary blades circumferentially spaced about said body. .Iaddend..Iadd.34. The apparatus of claim 33, wherein said body is substantially tubular and said primary and secondary blades are secured about said body in spaced circumferential relationship. .Iaddend..Iadd.35. The apparatus of claim 29, wherein said at least one secondary blade comprises a plurality of secondary blades circumferentially spaced about said body. .Iaddend..Iadd.36. The apparatus of claim 18, wherein said at least one primary blade comprises a plurality of primary blades circumferentially spaced about said body. .Iaddend..Iadd.37. An apparatus for drilling and enlarging a borehole in a subterranean formation, comprising: a pilot bit defining a first diameter;   a longitudinally extending body located above said pilot bit;   at least one primary blade protruding generally radially from said body, having a longitudinal extent, defining a profile on an exterior edge thereof and extending beyond a radius of said first diameter; and   at least one cutting element disposed on said primary blade profile at a location radially outward of said first diameter for cutting into said formation to enlarge said borehole from said first diameter to a second, larger diameter upon rotation of said body, said at least one cutting element being exposed beyond said profile. .Iaddend..Iadd.38. The apparatus of claim 37, wherein said primary blade profile is arcuate   
     
     
        proximate a lower portion thereof. .Iaddend..Iadd.39.  The apparatus of claim 37, wherein said at least one cutting element comprises a plurality of cutting elements, at least one of said plurality of cutting elements being disposed on a radially outermost portion of said primary blade profile and including a flat cutting edge oriented substantially parallel to a longitudinal extent of said body. .Iaddend..Iadd.40. The apparatus of claim 37, wherein said at least one cutting element comprises a PDC cutting element. .Iaddend..Iadd.41. The apparatus of claim 40, wherein said at least one cutting element is set at a back rake of about 20° or less. .Iaddend..Iadd.42. The apparatus of claim 40, wherein said at least one cutting element is set at a neutral back rake. .Iaddend..Iadd.43. The apparatus of claim 40, wherein said at least one cutting element is set at a positive back rake. .Iaddend..Iadd.44. The apparatus of claim 40, wherein said at least one cutting element is set at a positive side rake. .Iaddend..Iadd.45. The apparatus of claim 37, wherein said body is substantially tubular and said at least one primary blade is secured to said body proximate a mid-portion thereof. .Iaddend..Iadd.46. The apparatus of claim 37, wherein said at least one primary blade is oriented with its longitudinal extent substantially parallel to the longitudinal extent of said body. .Iaddend..Iadd.47. The apparatus of claim 37, further including at least one longitudinally extending secondary blade protruding generally radially from said body to a lesser distance than said at least one primary blade, said at least on secondary blade being circumferentially spaced from said at least one primary blade about said body, defining a profile and bearing at least one cutting element on said profile thereof, said at least one cutting element of said at least one secondary blade being exposed beyond said profile thereof. .Iaddend..Iadd.48. The apparatus of claim 47, wherein said profile of said at least one secondary blade is arcuate proximate the bottom thereof. .Iaddend..Iadd.49. The apparatus of claim 46, wherein said at least one primary blade comprises a plurality of primary blades circumferentially spaced about said body. .Iaddend..Iadd.50. The apparatus of claim 49, wherein said at least one secondary blade comprises a plurality of secondary blades circumferentially spaced about said body. .Iaddend..Iadd.51. The apparatus of claim 50, wherein said plurality of primary blades are mutually circumferentially adjacent, and at least one of said plurality of secondary blades rotationally leads said plurality of primary blades. .Iaddend..Iadd.52. The apparatus of claim 51, wherein at least another of said plurality of secondary blades rotationally trails said plurality of primary blades. .Iaddend..Iadd.53. The apparatus of claim 49, wherein said plurality of primary blades are mutually circumferentially adjacent, and said at least one secondary blade rotationally leads said plurality of primary blades. .Iaddend..Iadd.54. The apparatus of claim 53, further including at least another secondary blade rotationally trailing said plurality of primary blades. 
     
     
        .Iaddend..Iadd.55.  The apparatus of claim 49, wherein each of said plurality of primary blades defines substantially the same profile. .Iaddend..Iadd.56. The apparatus of claim 50, wherein said body is substantially tubular, and said primary and secondary blades are secured about said body in spaced circumferential relationship proximate a mid-portion thereof. .Iaddend..Iadd.57. The apparatus of claim 47, wherein said at least one secondary blade comprises a plurality of secondary blades circumferentially spaced about said body. .Iaddend..Iadd.58. The apparatus of claim 37, wherein said at least one primary blade comprises a plurality of primary blades circumferentially spaced about said body. .Iaddend..Iadd.59. An apparatus for drilling and enlarging a borehole in a subterranean formation, comprising: a pilot bit defining a first diameter;   a longitudinally extending body located above said pilot bit;   a first plurality of blades above said pilot bit protruding generally radially from said body beyond said first diameter, each of said first plurality of blades having a longitudinal extent and defining a profile on an exterior edge thereof; and   at least one cutting element disposed on a profile of each of said plurality of primary blades at a location radially outward of said first diameter for cutting into said formation to enlarge said borehole from said first diameter to a second, larger diameter upon rotation of said body, said at least one cutting element on each primary blade being exposed beyond said profile. .Iaddend..Iadd.60. The apparatus of claim 59, further including at least one longitudinally extending secondary blade protruding generally radially from said body to a lesser distance than said plurality of primary blades, said at least one secondary blade being circumferentially spaced from said plurality of primary blades about said body, defining a profile and bearing at least one cutting element disposed on said profile thereof, said at least one cutting element of said at least one secondary blade being exposed beyond said profile thereof. .Iaddend..Iadd.61. The apparatus of claim 60, wherein said plurality of primary blades are mutually circumferentially adjacent, and said at least one secondary blade rotationally leads said plurality of primary blades. .Iaddend..Iadd.62. The apparatus of claim 61, further including at least another secondary blade rotationally trailing said plurality of primary blades. .Iaddend..Iadd.63. An apparatus for drilling and enlarging a borehole in a subterranean formation, comprising:   a pilot bit defining a first diameter;   a longitudinally extending body located above said pilot bit;   at least one primary blade above said pilot bit protruding generally radially from said body beyond said first diameter to a second diameter, said at least one primary blade having a longitudinal extent and defining a profile on an exterior edge thereof; and   at least one secondary blade above said pilot bit protruding generally radially from said body to a diameter intermediate said first diameter and said second diameter, said at least one secondary blade having a longitudinal extent and defining a profile on an exterior edge thereof. .Iaddend..Iadd.64. The apparatus of claim 63, wherein said at least one secondary blade rotationally leads said at least one primary blade. .Iaddend..Iadd.65. The apparatus of claim 63, wherein said at least one secondary blade rotationally trails said at least one primary blade.   
     
     
        .Iaddend..Iadd.66.  The apparatus of claim 63, wherein said at least one primary blade comprises a plurality of circumferentially-spaced, mutually adjacent primary blades. .Iaddend..Iadd.67. The apparatus of claim 66, wherein said at least one secondary blade rotationally leads said plurality of primary blades. .Iaddend..Iadd.68. The apparatus of claim 67, further including at least another secondary blade rotationally trailing said plurality of primary blades. .Iaddend..Iadd.69. The apparatus of claim 63, further including at least one cutting element disposed on a profile of each of said blades at a location radially outward of said first diameter for cutting into said formation to enlarge said borehole from said first diameter to a second, larger diameter upon rotation of said body, said cutting elements being exposed beyond said profiles. .Iaddend..Iadd.70. An apparatus for drilling and enlarging a borehole in a subterranean formation, comprising: a pilot bit defining a first diameter;   a longitudinally extending body located above said pilot bit;   at least one primary blade above said pilot bit protruding generally radially from said body beyond said first diameter to a second diameter; and   at least one secondary blade above said pilot bit protruding generally radially from said body to a diameter intermediate said first diameter and said second diameter;   wherein said body and said protrusions of said at least one primary blade and said at least one secondary blade therefrom lie within a pass-through diameter larger than said first diameter and smaller than said second diameter. .Iaddend..Iadd.71. The apparatus of claim 70, wherein said first   
     
     
        diameter lies within said pass-through diameter. .Iaddend..Iadd.72.  An apparatus for enlarging a borehole of a first diameter in subterranean formation, comprising: a longitudinally extending body;   at least one primary blade protruding generally radially from said body beyond said first diameter to a second diameter; and   at least one secondary blade protruding generally radially from said body to a diameter intermediate said first diameter and said second diameter;   wherein said body and protrusions of said at least one primary blade and said at least one secondary blade therefrom lie within a pass-through diameter larger than said first diameter and smaller than said second diameter. .Iaddend..Iadd.73. A method for enlarging a borehole of a first diameter to a second diameter in a subterranean formation, comprising:   rotating a first cutting structure about a center of said second diameter to cut formation material adjacent said borehole to enlarge said borehole to a diameter larger than said first diameter and smaller than said second diameter; and   rotating a second cutting structure about said center of said second diameter to cut formation material adjacent said borehole to enlarge said borehole to said second diameter. .Iaddend..Iadd.74. The method of claim 73, further including drilling said borehole to said first diameter prior to said enlarging employing a third cutting structure simultaneously rotated with said first and second cutting structures. .Iaddend..Iadd.75. The method of claim 73, further including drilling a longitudinal segment of said enlarged, second diameter borehole using said first and second cutting structures, while only contacting formation material laterally adjacent said borehole near said second diameter with said second cutting structure. .Iaddend.