U.S. patent number RE36,817 [Application Number 09/041,519] was granted by the patent office on 2000-08-15 for method and apparatus for drilling and enlarging a borehole.
This patent grant is currently assigned to Baker Hughes Incorporated. Invention is credited to Paul E. Pastusek, Corey S. Thayn.
United States Patent |
RE36,817 |
Pastusek , et al. |
August 15, 2000 |
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.
Inventors: |
Pastusek; Paul E. (The
Woodlands, TX), Thayn; Corey S. (Lehi, UT) |
Assignee: |
Baker Hughes Incorporated
(Houston, TX)
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Family
ID: |
26718232 |
Appl.
No.: |
09/041,519 |
Filed: |
March 12, 1998 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
431510 |
Apr 28, 1995 |
05497842 |
Mar 12, 1996 |
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Current U.S.
Class: |
175/334; 175/391;
175/398 |
Current CPC
Class: |
E21B
10/26 (20130101) |
Current International
Class: |
E21B
10/26 (20060101); E21B 009/24 () |
Field of
Search: |
;175/385,391,398,399,408,334 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Hughes Christensen Company drawings (3 pages) for a bi-center bit,
Sep. 22, 1992..
|
Primary Examiner: Tsay; Frank
Attorney, Agent or Firm: Trask, Britt & Rossa
Claims
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.degree. 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.degree. 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.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to enlarging the diameter
of a subterranean borehole, and more specifically to enlarging the
borehole below a portion thereof which remains at a lesser
diameter.
2. State of the Art
It is known to employ both eccentric and bi-center bits to enlarge
a borehole below a tight or undersized portion thereof.
An eccentric bit includes an extended or enlarged cutting portion
which, when the bit is rotated about its axis, produces an enlarged
borehole. An example of an eccentric bit is disclosed in U.S. Pat.
No. 4,635,738.
A bi-center bit assembly employs two longitudinally-superimposed
bit sections with laterally offset axes. The first axis is the
center of the pass through diameter, that is, the diameter of the
smallest borehole the bit will pass through. This axis may be
referred to as the pass through axis. The second axis is the axis
of the hole cut as the bit is rotated. This axis may be referred to
as the drilling axis. There is usually a first, lower and smaller
diameter pilot section employed to commence the drilling, and
rotation of the bit is centered about the drilling axis as the
second, upper and larger diameter main bit section engages the
formation to enlarge the borehole, the rotational axis of the bit
assembly rapidly transitioning from the pass through axis to the
drilling axis when the full diameter, enlarged borehole is
drilled.
Rather than employing a one-piece drilling structure such as an
eccentric bit or a bi-center bit to enlarge a borehole below a
constricted or reduced-diameter segment, it is also known to employ
an extended bottomhole assembly (extended bi-center assembly) with
a pilot bit at the distal end thereof and a reamer assembly some
distance above. This arrangement permits the use of any standard
bit type, be it a rock bit or a drag bit, as the pilot bit, and the
extended nature of the assembly permits greater flexibility when
passing through tight spots in the borehole as well as the
opportunity to effectively stabilize the pilot bit so that the
pilot hole and the following reamer will traverse the path intended
for the borehole. This aspect of an extended bottomhole assembly is
particularly significant in directional drilling.
While all of the foregoing alternative approaches can be employed
to enlarge a borehole below a reduced-diameter segment, the pilot
bit with reamer assembly has proven to be the most effective
overall. The assignee of the present invention has, to this end,
designed as reaming structures so-called "reamer wings" in the very
recent past, which reamer wings generally comprise a tubular body
having a fishing neck with a threaded connection at the top
thereof, and a tong die surface at the bottom thereof, also with a
threaded connection. The upper mid-portion of the reamer wing
includes one or more longitudinally-extending blades projecting
generally radially outwardly from the tubular body, the outer edges
of the blades carrying superabrasive (also termed superhard)
cutting elements, commonly termed PDC's (for Polycrystalline
Diamond Compact). The lower mid-portion of the reamer wing may
include a stabilizing pad having an arcuate exterior surface of the
same or slightly smaller radius than the radius of the pilot hole
on the exterior of the tubular body and longitudinally below the
blades. The stabilizer pad is characteristically placed on the
opposite side of the body with respect to the reamer blades so that
the reamer wing will ride on the pad due to the resultant force
vector generated by the cutting of the blade or blades as the
enlarged borehole is cut. The aforementioned reamer wing as
described and as depicted herein is not acknowledged or admitted to
constitute prior art to the invention described and claimed
herein.
While the aforementioned reamer wing design has enjoyed some
success, it has been recognized by the invention herein that the
device, as presently constructed, may not effectively and
efficiently address the problem or task of achieving a rapid
transition from pass through to full hole or "drill" diameter which
closely tracks the path of the pilot bit and which does not unduly
load the blades or bottomhole assembly during the transition. Since
the reamer wing may have to re-establish a full diameter borehole
multiple times during its drilling life in a single borehole, due
to washouts and doglegs of the pilot hole, rapid transitioning
ability when reaming is restarted as well as a robust design which
can accommodate multiple transitions without significant damage is
desirable.
SUMMARY OF THE INVENTION
The present invention comprises a reamer wing having one or more
blades, at least one of which comprises a primary blade for cutting
the full diameter of an enlarged borehole and another of which may
comprise a secondary blade for enhancing the transition from the
pass through diameter to the enlarged full diameter cut by the
primary blade.
More specifically, the invention includes at least a body having a
longitudinally-extending primary blade extending generally radially
therefrom, the radial extent of the primary blade substantially
defining the gage of the enlarged borehole to be cut by the reamer
wing, and an optional, longitudinally-extending secondary blade
circumferentially spaced from the primary blade and having a radial
extent of less than that of the primary blade as measured from the
drilling axis. The blades carry cutting elements along the outer
edges or profiles thereof, the cutting elements extending from
proximate the body to the outermost extent of the
blade. Moreover, the cutting elements are substantially exposed on
the order of one-half of their cutting face height all the way up
the flank of the blades to, and optionally including, the gage. At
least some of the cutting elements are also aggressively raked
relative to conventional, prior art rakes, to promote engagement
with the formation. Thus, the cutting elements as positioned and
exposed cut away the formation to an extent that the gage pads on
the main blade or blades do not have to cut laterally.
Alternatively, contentional gage pads without cutting elements may
be completely eliminated and cutting elements may be placed along
the entire gage extent of one or more blades.
In such a manner, when multiple blades are employed, the loading of
certain cutting elements on the blades can be shared, and the
cutting elements at the flank and shoulder of the secondary blade
accelerate the removal of formation material while minimizing side
reaction forces, to speed the transition of the primary blade to
its full-diameter reaming task in rotating about the drilling axis
of the reamer wing.
The invention also contemplates a method of enlarging a borehole by
rotating a body carrying first and second radially-extending
cutting means thereon, and engaging the borehole with the first
cutting means extending to a first radius from a rotational center
for the diameter of the enlarged borehole and subsequently engaging
the borehole with the second cutting means extending to a second
radius from the drilling axis substantially equal to one-half of
drill diameter.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 through 3 comprise schematic partial sectional elevations
of a bottomhole assembly including a reamer wing as employed in one
aspect of the present invention, the bottomhole assembly being
shown in pass through condition (FIG. 1), in start up condition
(FIG. 2) and in a normal drilling mode for enlarging the borehole
(FIG. 3);
FIG. 4 comprises a side elevation of an exemplary reamer wing in
accordance with the present invention;
FIG. 5 comprises an enlarged bottom elevation of the reamer wing of
FIG. 4;
FIG. 6 comprises an enlarged schematic of the profile of the
primary and secondary reamer blades of the reamer of FIG. 4,
rotated into a single plane about the drilling axis to illustrate
cutting element position, exposure and coverage; and
FIG. 7 comprises an enlarged schematic of an alternative blade
profile and cutting element disposition according to the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIGS. 1 through 3 depict an exemplary bi-center bottomhole assembly
10 in which the reamer wing of the present invention may be
employed.
Commencing with FIG. 1 and moving from the top to the bottom of the
assembly 10, one or more drill collars 12 are suspended from the
distal end of a drill string extending to the rig floor at the
surface. Pass through stabilizer (optional) 14 is secured to drill
collar 12, stabilizer 14 being sized equal to or slightly smaller
than the pass through diameter of the bottomhole assembly 10, which
may be defined as the smallest diameter borehole through which the
assembly may move longitudinally. Another drill collar 16 (or other
drill string element such as an MWD tool housing or pony collar) is
secured to the bottom of stabilizer 14, below which reamer wing 100
according to the present invention is secured via tool joint 18,
which may be a 65/8inch API joint. Another API joint 22, for
example a 41/2inch API joint, is located at the bottom of the
reamer wing 100. Upper pilot stabilizer 24, secured to reamer wing
100, is of an O.D. equal to or slightly smaller than that of the
pilot bit 30 at the bottom of the assembly 10. Yet another, smaller
diameter drill collar 26 is secured to the lower end of pilot
stabilizer 24, followed by a lower pilot stabilizer 28 to which is
secured pilot bit 30. Pilot bit 30 may be either a rotary drag bit
or a tri-cone, so-called "rock bit". The bottomhole assembly 10 as
described is exemplary only, it being appreciated by those of
ordinary skill in the art that many other assemblies and variations
may be employed.
It should be noted that there is an upper lateral displacement 32
between the axis of pass through stabilizer 14 and that of reamer
wing 100, which displacement is provided by the presence of drill
collar 16 therebetween and which promotes passage of the assembly
10, and particularly the reamer wing 100, through a borehole
segment of the design pass through diameter.
For purposes of discussion, the following exemplary dimensions may
be helpful in understanding the relative sizing of the components
of the assembly for a particular pass through diameter, pilot
diameter and drill diameter. For a pass through diameter of 10.625
inches, a pilot diameter of 8.500 inches and a maximum drill
diameter of 12.250 inches (the full bore diameter drilled by reamer
wing 100) would normally be specified. In the bottomhole assembly
10, for the above parameters:
(a) drill collar 12 may be an eight inch drill collar;
(b) drill collar 16 may be a thirty foot, eight inch drill
collar;
(c) drill collar 26 may be a fifteen foot, 63/4inch drill collar;
and
(d) pilot bit 30 may be an 81/2inch bit.
In pass through condition, shown in FIG. 1, the assembly 10 is
always in either tension or compression, depending upon the
direction of travel, as shown by arrow 34. Contact of the assembly
10 with the borehole wall 50 is primarily through pass through
stabilizer 14 and reamer wing 100. The assembly 10 is not normally
rotated while in pass through condition.
FIG. 2 depicts the start-up condition of assembly 10, wherein
assembly 10 is rotated by application of torque as shown by arrow
36 as weight-on-bit (WOB) is also applied to the string, as shown
by arrow 38. As shown, pilot bit 30 has drilled ahead into the
uncut formation to a depth approximating the position of upper
pilot stabilizer 24, but reamer wing 100 has yet to commence
enlarging the borehole to drill diameter. As shown at 32 and at 40,
the axis of reamer wing 100 is laterally displaced from those of
both pass through stabilizer 14 and upper pilot stabilizer 24. In
this condition, the reamer wing 100 has not yet begun its
transition from being centered about a pass through center line to
its drilling mode center line which is aligned with that of pilot
bit 30.
FIG. 3 depicts the normal drilling mode of bottomhole assembly 10,
wherein torque 36 and WOB 38 are applied and, upper displacement 32
may remain as shown, but generally is eliminated under all but the
most severe drilling conditions. Lower displacement 40 has been
eliminated as reamer wing 100 is rotating about the same axis as
pilot bit 30 in cutting the borehole to full drill diameter.
It is the rapidity and efficiency of the transition from start up
as shown in FIG. 2 to normal drilling as shown in FIG. 3 to which
the present invention primarily pertains.
FIGS. 4, 5 and 6 illustrate exemplary reamer wing 100 according to
the present invention in greater detail. Reamer wing 100 comprises
a tubular body 102 having an axial bore 104 therethrough. Tubular
body 102 includes a fishing neck portion 106 at the upper exterior
thereof, and a tong die surface 108 at the lower exterior thereof.
Reamer wing 100 is secured in a bottom hole assembly such as 10,
described above, via API threaded connections of the type
indicated.
Circumferentially-spaced primary blades 110 and 112 and secondary
blades 114 and 116 extend longitudinally and generally radially
from body 102 on the upper mid-portion thereof. Body 102 and blades
110-116 are preferably formed of steel, and the blades may be
integral or welded to the body. It should be noted that the number
of blades depicted is exemplary only, and that as many as five or
more blades may be employed on a reamer wing according to the
invention. The larger the required diameter of the enlarged
borehole, the larger number of blades being generally dictated.
Depending on the number of blades used, one or more passages (not
shown) may extend from bore 104 to the surface of body 102 to
direct drilling fluid to the blades and cutting elements thereon
via nozzles (not shown), such technology being well known in the
drilling art.
Optional stabilizer pad 118 is located on the lower mid-portion of
body 102 generally diametrically opposite in location to primary
blades 110 and 112 and closely therebelow, as shown in FIG. 4 and
5. Stabilizer pad 118 is provided with an arcuate exterior surface
which is of the same or slightly less radius than the radius of the
pilot hole drilled by the pilot bit, the radius being measured from
the centerline 120 of tubular body 102. Placement of stabilizer pad
118 is dictated by the resultant lateral force vector generated by
the blades during transition from start-up condition to and during
drilling of the drill diameter hole so that the pad rides on the
borehole wall as the blades cut the transition and ultimate drill
diameter. If reamer wing 100 is employed with a steerable
bottomhole assembly, it is likely that stabilizer pad 118 would be
omitted. The exterior of stabilizer pad 118 may be faced with
tungsten carbide bricks and/or diamond wear surfaces, as known in
the art for conventional stabilizers.
As shown in FIGS. 4-6, primary blades 110 and 112 extend radially
outward from drilling axis or centerline 120 a greater distance
than secondary blades 114 and 116. Referring to FIG. 6, it can be
seen that primary blades 110 and 112 define one profile, and that
secondary blade 114 defines a second, more slender profile. Blade
116 is a main blade which has been cut back in lateral extent (see
FIG. 5) to fit the pass through diameter. Looking at FIG. 5, it can
be seen that both primary and secondary blades carry cutting
elements 122 at their lower and radially inner extents which will
continue to actively cut after full drill diameter is reached.
However, due to the radially smaller extent of the secondary
blades, cutting elements 124 and 126 on the flank of secondary
blade 114 will only cut during the transition from start up to full
drill diameter, after which they will no longer contact the
borehole sidewall, at which time cutting elements 128 and 130 on
primary blades 110 and 112 will still be active. In other words, a
major function of secondary blade 114 and cutting elements 124 and
126 is to effectuate as rapid and smooth transition as possible to
full drill diameter by permitting reamer wing 100 to remove more
formation material per revolution and with lower side reaction
forces and thus less lateral disruption of assembly rotation than
if only primary blades were employed.
Referring to FIG. 6, the large degree of exposure of cutting
elements 122, 124, 126, 128 and 130 beyond the blade profiles is
readily visible, the exposure approximating one-half or 50% of
cutting element height. This is in contrast to the prior art,
wherein extremely small cutting element exposures were generally
employed, and gage-position cutting elements such as 124, 126 and
130, if employed at all, were not exposed above or beyond the blade
profile. As shown in FIG. 6, cutting elements 130 along the gage
segment of a blade may employ flat cutting edges parallel to the
gage. Moreover, the cutting elements of the reamer wing of the
invention are set at a reduced negative back rake, such as
20.degree. or even 10.degree., as opposed to the prior art practice
of using a 30.degree. design negative back rake. It is also
contemplated that neutral rake cutting elements may be employed, or
combinations of positive and negative back rake cutting
elements.
Looking specifically to FIG. 5, the various operational stages of
reamer wing 100 can be related to pass through and drill diameters,
pass through and drill centerlines, and the transition
therebetween. Pass through centerline 130 is the centerline of the
pass through diameter 132, the smallest diameter through which
reamer wing 100 may pass longitudinally. As the bottomhole assembly
(such as 10) is placed in operation, with torque and WOB applied,
reamer wing 100 is rotated about a centerline which begins to shift
from 130 to 120 along transition line 134, which is not stationary
but obviously rotates as reamer wing 100 itself rotates. As can
readily be seen from FIG. 5, at commencement of rotation the
presence of secondary blade 114 provides a balance to the cutting
forces acting on reamer wing 100 and thus reduces vibration
tendencies and impact on the cutting elements. Circles 136 and 138
illustrate the progression from pass through to drill diameter at
the half and three-quarters open stages. Circle 140 illustrates
full drill diameter, which is drilled about centerline 120 by
primary blades 110 and 112. As can be seen in FIG. 3, during
drilling of the drill diameter, stabilizer pad 118 rides against
the pilot bit-sized borehole wall below the enlarged borehole
segment 142 drilled by primary blades 110 and 112. Also as shown in
FIG. 3, while the face and lower flank cutting elements of all the
blades are in continuous engagement with the formation, neither of
the secondary blades 114 and 116 or any other portion of reamer
wing 100, except for the primary blades, 110 and 112 on the same
radial plane as the primary blades will normally contact the
borehole sidewall during drilling after the borehole is enlarged to
drill diameter. While not so readily apparent, it will also be
appreciated that trailing primary blade 112 will not be engaged
with the formation until drill diameter is reached and the reamer
wing 100 is rotating about center-line 120.
It is contemplated that other modifications may be made to reamer
wing 100 to enhance its effectiveness. For example, neutral or even
slightly positive back rake cutting elements may be employed on one
or both secondary blades to more rapidly pull the blades into the
formation to open the borehole, back rake angle being determined
with respect to a line perpendicular to the blade profile at a
particular cutting element radial location. Side rake of the
cutting elements, being the angle thereof tangent to the profile or
the angle thereof with respect to the radial line extending from
the drilling axis through the cutting element location, may also be
altered to aggressively engage the formation. The gage pad on both
primary and secondary blades may be eliminated altogether, as shown
on exemplary alternative primary blade 160 in FIG. 7, and cutting
elements employed over the entire outer extent of the blades
intended for contact with the borehole during the reaming
operation. Alternatively, a very short gage pad may be employed to
protect the uppermost cutting element while tripping into and out
of the borehole. Material may be removed from the trailing edges of
all the blades as shown at 150 on FIG. 5 to enhance clearance at
pass through diameter and transition to drill diameter.
Many other additions, deletions and modifications of the invention
as described and illustrated herein may be made without departing
from the scope of the invention as hereinafter claimed.
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