U.S. patent application number 12/608832 was filed with the patent office on 2011-05-05 for backup cutting elements on non-concentric earth-boring tools and related methods.
Invention is credited to Mark E. Anderson, William A. Moss, David L. Rickabaugh.
Application Number | 20110100714 12/608832 |
Document ID | / |
Family ID | 43924198 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110100714 |
Kind Code |
A1 |
Moss; William A. ; et
al. |
May 5, 2011 |
BACKUP CUTTING ELEMENTS ON NON-CONCENTRIC EARTH-BORING TOOLS AND
RELATED METHODS
Abstract
An apparatus for engaging a subterranean borehole includes a
bi-center bit having backup cutting elements thereon. The bi-center
bit includes a pilot bit section and a reamer bit section adjacent
to the pilot bit section. The pilot bit section includes at least
one primary cutting element and at least one backup cutting element
rotationally trailing and laterally offset from the at least one
primary cutting element. Methods of drilling a subterranean
borehole include engaging a first portion of a borehole with a
reamer bit section of a drill bit and simultaneously engaging a
second, opposing portion of the borehole with a pilot bit section
adjacent to the reamer bit section.
Inventors: |
Moss; William A.; (Conroe,
TX) ; Rickabaugh; David L.; (Spring, TX) ;
Anderson; Mark E.; (The Woodlands, TX) |
Family ID: |
43924198 |
Appl. No.: |
12/608832 |
Filed: |
October 29, 2009 |
Current U.S.
Class: |
175/57 ;
175/385 |
Current CPC
Class: |
E21B 10/26 20130101;
E21B 10/43 20130101 |
Class at
Publication: |
175/57 ;
175/385 |
International
Class: |
E21B 10/26 20060101
E21B010/26; E21B 10/62 20060101 E21B010/62; E21B 7/00 20060101
E21B007/00 |
Claims
1. A bi-center bit for drilling subterranean formations,
comprising: a pilot bit section having a first gage diameter and
including at least one primary cutting element and at least one
backup cutting element rotationally trailing the at least one
primary cutting element disposed thereon for engaging a
subterranean formation, wherein the at least one backup cutting
element is offset from the at least one primary cutting element in
a direction substantially transverse to an intended rotational path
of the at least one primary cutting element during rotational
operation of the bi-center bit; and a reamer bit section adjacent
to the pilot bit section, the reamer bit section comprising at
least one blade extending radially beyond the first gage diameter
for rotationally engaging a subterranean formation.
2. The bi-center bit of claim 1, wherein the pilot bit section
comprises a plurality of blades, each blade of the plurality of
blades having a plurality of primary cutting elements and a
plurality of backup cutting elements rotationally trailing at least
one primary cutting element of the plurality of primary cutting
elements.
3. The bi-center bit of claim 2, wherein at least one backup
cutting element of the plurality of backup cutting elements on at
least one blade of the plurality of blades is offset from at least
one primary cutting element of the plurality of primary cutting
elements on at least another blade of the plurality of blades.
4. The bi-center bit of claim 1, wherein the reamer bit section
comprises a reamer wing and wherein the pilot bit section comprises
a fixed-cutting element drill bit, the reamer wing and the
fixed-cutting element drill bit being coupled to form the bi-center
bit.
5. The bi-center bit of claim 1, wherein the at least one blade of
the reamer bit section comprises two blades extending radially
beyond the first gage diameter.
6. The bi-center bit of claim 5, wherein the at least one backup
cutting element comprises a plurality of backup cutting elements
and wherein at least one backup cutting element of the plurality of
backup cutting elements is positioned to substantially laterally
oppose at least one blade of the two blades of the reamer bit
section.
7. The bi-center bit of claim 6, wherein at least one backup
cutting element of the plurality of backup cutting elements is
positioned on a shoulder region of the pilot bit section, wherein
at least another backup cutting element of the plurality of backup
cutting elements is positioned on a cone region of the pilot bit
section, and wherein the at least one backup cutting element of the
plurality of backup cutting elements has an exposure greater than
the exposure of the at least another backup cutting element of the
plurality of backup cutting elements.
8. The bi-center bit of claim 1, further comprising at least one
additional backup cutting element rotationally trailing the at
least one backup cutting element.
9. The bi-center bit of claim 1, wherein the at least one backup
cutting element is oriented at a back rake angle of about ninety
(90) degrees.
10. The bi-center bit of claim 9, wherein the at least one backup
cutting element comprises an ovoid shape.
11. A bi-center bit for drilling subterranean formations,
comprising: an eccentric reamer comprising at least one radially
extending blade, the at least one radially extending blade
including at least one reamer cutting element disposed thereon for
rotationally engaging a first portion of a subterranean borehole;
and a pilot bit coupled to the eccentric reamer comprising: at
least two primary cutting elements disposed on the pilot bit for
engaging a subterranean borehole; and at least one backup cutting
element rotationally trailing the at least two primary cutting
elements and disposed at least partially laterally intermediate the
at least two primary cutting elements.
12. The bi-center bit of claim 11, wherein the at least one reamer
cutting element of the eccentric reamer is configured to
rotationally engage a first portion of a subterranean borehole
while the at least one backup cutting element of the pilot bit is
configured to rotationally engage a second, opposing portion of a
subterranean borehole.
13. The bi-center bit of claim 11, wherein the at least one backup
cutting element is disposed laterally intermediate the at least two
primary cutting elements at an equal lateral distance from each of
the at least two primary cutting elements.
14. The bi-center bit of claim 11, wherein at least one radially
extending blade of the eccentric reamer comprises two radially
extending, circumferentially spaced blades.
15. The bi-center bit of claim 14, wherein the at least one backup
cutting element comprises a plurality of backup cutting elements
and wherein at least one backup cutting element of the plurality of
backup cutting elements is positioned to substantially laterally
oppose at least one radially extending blade of the two radially
extending, circumferentially spaced blades.
16. A method of drilling a subterranean borehole, the method
comprising: engaging a first portion of a borehole with a portion
of a reamer bit section of a drill bit; and simultaneously engaging
a second, opposing portion of the borehole with a portion of a
pilot bit section adjacent to the reamer bit section, comprising:
engaging the second, opposing portion of the borehole with at least
two primary cutting elements; and engaging the second, opposing
portion of the borehole with at least one backup cutting element
rotationally trailing and disposed laterally intermediate the at
least two primary cutting elements.
17. The method of claim 16, further comprising positioning at least
two backup cutting elements on a shoulder region of the pilot bit
section.
18. The method of claim 17, wherein positioning at least two backup
cutting elements on a shoulder region of the drill bit comprises at
least partially preventing wear of a matrix portion of the pilot
bit by locating the at least two backup cutting elements on a
shoulder region of the pilot bit section.
19. The method of claim 16, further comprising positioning a
plurality of backup cutting elements on a portion of the pilot bit
section.
20. The method of claim 19, wherein positioning a plurality of
backup cutting elements on a portion of the pilot bit section
comprises positioning at least one backup cutting elements of the
plurality of backup cutting elements on a shoulder region of the
pilot bit section to exhibit an exposure greater than an exposure
of at least one backup cutting elements of the plurality of backup
cutting elements on a cone region of the pilot bit section.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is related to U.S. patent application Ser.
No. 12/498,516, filed Jul. 7, 2009, pending, titled "BACKUP CUTTING
ELEMENTS ON NON-CONCENTRIC REAMING TOOLS."
TECHNICAL FIELD
[0002] Embodiments of the invention relate to drill bits and tools
for subterranean drilling and, more particularly, embodiments
relate to drill bits for enlarging the diameter of a subterranean
borehole employing primary and backup cutting elements.
BACKGROUND
[0003] Boreholes are formed in subterranean formations for various
purposes including, for example, extraction of oil and gas from
subterranean formations and extraction of geothermal heat from
subterranean formations. Boreholes may be formed in subterranean
formations using earth-boring tools such as, for example, drill
bits and reamer devices.
[0004] To drill a borehole with a drill bit, the drill bit is
rotated and advanced into the subterranean formation under an
applied axial force, commonly known as "weight on bit," or WOB. As
the drill bit rotates, the cutting elements or abrasive structures
thereof cut, crush, shear, and/or abrade away the formation
material to form the borehole, depending on the type of bit and the
formation to be drilled. A diameter of the borehole drilled by the
drill bit may be defined by the cutting structures disposed at the
largest outer diameter of the drill bit.
[0005] The drill bit is coupled, either directly or indirectly, to
an end of what is referred to in the art as a "drill string," which
comprises a series of elongated tubular segments connected
end-to-end that extends into the borehole from the surface of the
formation. Often various subs and other components, such as a
downhole motor, a steering sub or other assembly, a measuring while
drilling (MWD) assembly, a ream while drilling (RWD) assembly, one
or more stabilizers, or a combination of some or all of the
foregoing, as well as the drill bit, may be coupled together at the
distal end of the drill string at the bottom of the borehole being
drilled. This assembly of components is referred to in the art as a
"bottom hole assembly" (BHA).
[0006] The drill bit may be rotated within the borehole by rotating
the drill string from the surface of the formation, or the drill
bit may be rotated by coupling the drill bit to a down-hole motor,
which is also coupled to the drill string and disposed proximate
the bottom of the borehole. The downhole motor may comprise, for
example, a hydraulic Moineau-type motor having a shaft, to which
the drill bit is mounted, that may be caused to rotate by pumping
fluid (e.g., drilling fluid or "mud") from the surface of the
formation down through the center of the drill string, through the
hydraulic motor, out from nozzles in the drill bit, and back up to
the surface of the formation through the annulus between the outer
surface of the drill string and the exposed surface of the
formation within the borehole. As noted above, when a borehole is
being drilled in a formation, axial force or "weight" is applied to
the drill bit (and reamer device, if used) to cause the drill bit
to advance into the formation as the drill bit drills the borehole
therein.
[0007] Boreholes may be enlarged by using a non-concentric drilling
tool such as an eccentric bit or a bi-center bit. Eccentric bits or
bi-center bits may be particularly useful in enlarging a borehole
below a "tight" or undersized portion thereof. Eccentric bits or
bi-center bits may also be particularly useful when performing a
RWD process. Examples of eccentric bits and bi-center bits are
disclosed in U.S. Pat. Nos. 4,635,738 and 5,957,223.
[0008] A bi-center bit generally includes a pilot bit section,
which may be similar in configuration to the drill bits discussed
previously. The bi-center bit also includes an eccentrically
laterally extended or enlarged reamer bit portion that, when the
bit is rotated about its drilling axis, produces an enlarged
borehole. The smaller diameter pilot section is employed to
commence the drilling and establish the drilling axis. Rotation of
the bit remains centered about the drilling axis as the second,
upper and larger radius, reamer bit section extending beyond the
pilot bit section diameter to one side of the bit engages the
formation to enlarge the borehole.
[0009] Rather than employing a one-piece drilling structure, such
as an eccentric bit or a bi-center bit, to enlarge a borehole, an
extended bottom hole assembly (extended bi-center assembly) with a
pilot bit at the distal end thereof and a reamer assembly some
distance above may also be employed to enlarge a borehole. This
arrangement permits the use of any standard bit type (e.g., a rock
bit or a drag bit) as the pilot bit, and the extended nature of the
assembly permits greater drill string 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 take the path intended for the borehole. The
assignee of the present invention has designed reaming structures
(so-called "reamer wings") which 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. Such reamer wings are disclosed in, for
example, U.S. Pat. No. RE 36,817 to Pastusek et al. and U.S. Pat.
No. 5,765,653 to Doster et al. both of which are assigned to the
assignee of the present invention and the disclosure of each of
which is incorporated in its entirety by this reference. 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
cutting elements (e.g., polycrystalline diamond compacts (PDC)).
The lower mid-portion of the reamer wing may include a stabilizing
pad having an arcuate exterior surface the same or slightly smaller
than the radius of the pilot hole on the exterior of the tubular
body and longitudinally below the blades. The stabilizing pad may
also be sized so that the rotational diameter traversed by the
stabilizing pad may be the same as, or even greater than, the
physical diameter of the pilot bit to enhance the stabilization
provided by the stabilizing pad when engaging a pilot borehole of
greater diameter than a physical diameter of the pilot bit. The
stabilizer pad is characteristically placed on the opposite side of
the tubular body with respect to the reamer wing 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.
BRIEF SUMMARY
[0010] In some embodiments, the present invention includes a
bi-center bit for drilling subterranean formations. The bi-center
bit includes a pilot bit section having a first gage diameter and a
reamer bit section adjacent to the pilot bit section. The pilot bit
section includes at least one primary cutting element and at least
one backup cutting element rotationally trailing the at least one
primary cutting element disposed thereon for engaging a
subterranean formation. The at least one backup cutting element is
offset from the at least one primary cutting element in a direction
substantially transverse to an intended rotational path of the at
least one primary cutting element during rotational operation of
the bi-center bit. The reamer bit section includes at least one
blade extending radially beyond the first gage diameter for
rotationally engaging a subterranean formation.
[0011] In additional embodiments, a bi-center bit for drilling
subterranean formations includes an eccentric reamer comprising at
least one radially extending blade. The at least one radially
extending blade includes at least one reamer cutting element
disposed thereon for rotationally engaging a first portion of a
subterranean borehole. A pilot bit coupled to the eccentric reamer
includes at least two laterally adjacent primary cutting elements
disposed on the pilot bit for engaging a subterranean borehole and
at least one backup cutting element rotationally trailing the at
least two primary cutting elements and disposed at least partially
laterally intermediate the at least two primary cutting
elements.
[0012] In yet additional embodiments, the present invention
includes a method of drilling a subterranean borehole. The method
includes engaging a first portion of a borehole with a portion of a
reamer bit section of a drill bit and simultaneously engaging a
second, opposing portion of the borehole with a portion of a pilot
bit section adjacent to the reamer bit section. The second,
opposing portion of the borehole may be engaged with at least two
laterally adjacent primary cutting elements and with at least one
backup cutting element rotationally trailing and disposed laterally
intermediate the at least two primary cutting elements.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a side view of a bi-center bit in accordance with
an embodiment of the present invention;
[0014] FIG. 2 is a face view, or view looking up from the bottom of
a borehole, of the bi-center bit depicted in FIG. 1;
[0015] FIG. 3 is a face view, or view looking up from the bottom of
a borehole, of a bi-center bit having primary cutting elements and
backup cutting elements in accordance with another embodiment of
the present invention; and
[0016] FIG. 4 is a face view, or view looking up from the bottom of
a borehole, of a bi-center bit having primary cutting elements and
multiple rows of backup cutting elements in accordance with another
embodiment of the present invention.
DETAILED DESCRIPTION
[0017] Illustrations presented herein are not meant to be actual
views of any particular drill bit or other earth-boring tool, but
are merely idealized representations that are employed to describe
the present invention. Additionally, elements common between
figures may retain the same numerical designation.
[0018] The various drawings depict embodiments of the invention as
will be understood by the use of ordinary skill in the art and are
not necessarily drawn to scale.
[0019] FIG. 1 comprises a side view of a bi-center bit in
accordance with an embodiment of the present invention. As shown in
FIG. 1, the depicted bit is illustrated in its normal drilling
orientation for clarity. In an embodiment of the invention, a
non-concentric earth-boring tool such as, for example, a bi-center
bit 100 may include a pilot bit section 112. The pilot bit section
112 may comprise a fixed-cutting element drill bit include blades
118 having superabrasive cutting structures such as, for example,
primary polycrystalline diamond compact (PDC) cutting elements 120
and backup PDC cutting elements 121 mounted thereto. Fluid courses
122 extending between blades 118 carry drilling fluid laden with
cuttings sheared by primary cutting elements 120 and backup cutting
elements 121 of the blades 118 drilling the pilot borehole into
junk slots 124, which extend longitudinally on gage 126 of the
bi-center bit 100 between gage pads 128. The gage pads 128 may be
provided with a wear-resistant gage surface in the form of tungsten
carbide bricks, natural diamonds, diamond-grit impregnated carbide,
thermally stable diamond (TSP), or a combination thereof, as known
in the art. Drilling fluid is introduced into fluid courses 122
from ports 132 on the bit face 130, which may include a nozzle 134
disposed therein.
[0020] The bi-center bit 100 also includes reamer bit section 114
(e.g., an eccentric reamer). The reamer bit section 114 may include
radially extending blades 140 that may have primary PDC cutting
elements 120 mounted thereto. As shown in FIG. 1, the blades 140
comprise any suitable number of blades 140 based on the size of the
bi-center bit 100. In some embodiments, the blades 140 may be
circumferentially spaced about 90.degree. from each other about the
reamer bit section 114. Ports 142 (which, again, may include a
nozzle 134 disposed therein), located intermediate blades 140, feed
drilling fluid into fluid courses 144 located rotationally in front
of (in the direction of bit rotation) blades 140, to carry away
formation cuttings sheared by the primary cutting elements 120 of
blades 140 when enlarging the pilot borehole to full gage diameter.
Blades 140 include truncated gage pads 146, which may also include
a wear resistant surface of the types previously mentioned. The
blades 140 may include an elongated gage pad 147 thereon. A bit
shank 152, having a threaded pin connection, may be used to connect
bi-center bit 100 to a drill collar or to an output shaft of a
downhole motor, as known in the art. It is noted that while the
embodiment of FIG. 1 illustrates a bi-center bit 100 having a pilot
bit section 112 and a reamer bit section 114, the bi-center bit 100
may comprise any suitable drill bit attached to a reaming
apparatus. For example, the bi-center bit 100 may comprise an
assembly of a drag bit coupled to a reaming apparatus such as, for
example, the reamer tool described in U.S. Pat. No. 6,695,080 to
Presley et al., which is assigned to the assignee of the present
invention and the disclosure of which is incorporated in its
entirety by this reference.
[0021] FIG. 2 comprises a face view, or view looking up from the
bottom of a borehole, of the bi-center bit 100 depicted in FIG. 1.
As shown in FIG. 2, the pilot bit section 112 includes blades 118
thereon. The primary cutting elements 120 may be disposed along the
blades 118 proximate to the leading edge of the blades 118 (taken
in the direction of rotational travel of blades 118). The primary
cutting elements 120 and backup cutting elements 121 may be placed
and oriented on the blades 118 with the backup cutting element 121
located behind (i.e., rotationally trailing) the primary cutting
elements 120. The bi-center bit 100 may include backup cutting
elements 121 secured to the blades 118 in the shoulder region 138
of the pilot bit section 112 of the bi-center bit 100. The
bi-center bit 100 may also include backup cutting elements 121
secured to the blades 118 in the cone region 136 of the pilot bit
section 112 of the bi-center bit 100. The backup cutting elements
121 may be offset from the primary cutting elements 120, taken in a
direction transverse to an intended rotational path 160 of the
primary cutting elements 120 during rotational operation of the
bi-center bit 100. For example, each of the backup cutting elements
121 may be mounted in pockets 110 rotationally trailing the primary
cutting elements 120 and at a location on the bit profile at least
partially laterally intermediate two associated, rotationally
leading primary cutting elements 120 laterally spaced from one
another, taken transverse to a direction of intended bit rotation.
In other words, the primary cutting elements 120 and the backup
cutting elements 121 each have a longitudinal axis extending at a
tangent to the intended rotational path 160 of the primary and
backup cutting elements 120, 121 during rotational operation of the
bi-center bit 100. The longitudinal axes of the primary cutting
elements 120 and the longitudinal axes of backup cutting elements
121 may be laterally offset such that the longitudinal axes of the
primary cutting elements 120 and the backup cutting elements 121
are not coplanar.
[0022] In some embodiments, the backup cutting elements 121 may be
disposed in a position rotationally trailing the primary cutting
elements 120 and the longitudinal axis of each of the backup
cutting elements 121 may extend substantially between and, in some
embodiments, parallel to, the longitudinal axes of the primary
cutting elements 120. It is noted that while the embodiment of FIG.
2 illustrates the backup cutting elements 121 laterally
intermediate two laterally adjacent primary cutting elements 120 on
the same blade 118, in some embodiments, the backup cutting
elements 121 may be disposed laterally intermediate two primary
cutting elements 120 on a different blade 118. For example, the
backup cutting elements 121 on one rotationally trailing blade 118
may be disposed such that the rotational path 160 of the backup
cutting elements 121 is at least partially laterally intermediate
two laterally adjacent primary cutting elements 120 located on
another rotationally leading blade 118. In other words, the backup
cutting elements 121 on one blade 118 may travel in a rotational
path between the kerfs made by the laterally adjacent primary
cutting elements 120 on another blade 118 (i.e., the width of the
cut made by the primary cutting elements 120 as they are rotated
against a subterranean formation).
[0023] Referring to FIGS. 1 and 2, it will be appreciated by those
of ordinary skill in the art that, at some locations along the bit
profile, which extends from the centerline C/L (drilling axis) of
the bit along the outer face surface or profile of blades 118 to
gage pads 128, the at least partially intermediate location of the
backup cutting elements 121 will be somewhat more radially than
longitudinally (in the direction of centerline C/L) intermediate
the locations of associated primary cutting elements 120. On the
other hand, when adjacent or near gage pads 128 as on the shoulder
region 138 of the pilot bit section 112, the at least partially
intermediate location of a backup cutting elements 121 may
approximate the radial locations of its associated primary cutting
elements 120 while being somewhat more longitudinally intermediate
primary cutting elements 120.
[0024] Referring to FIG. 2, to form the backup cutting element
pockets 110 in the primary portion of the bi-center bit 100 a flat
bottom milling tool cuts the drill bit body by plunging directly
into the blade 118, 140 and travels along the center line of the
cutting element 120 located in front thereof. In some embodiments,
the bi-center bit 100 or a portion thereof (e.g., the pilot bit
section 112) may be fabricated to comprise a particle-matrix
composite material. A so-called "infiltration" bit includes a bit
body comprising a particle-matrix composite material and is
fabricated in a mold using an infiltration process. Recently,
pressing and sintering processes have been used to form bit bodies
of drill bits and other tools comprising particle-matrix composite
materials. Such pressed and sintered bit bodies may be fabricated
by pressing (e.g., compacting) and sintering a powder mixture that
includes hard particles (e.g., tungsten carbide) and particles of a
metal matrix material (e.g., a cobalt-based alloy, an iron-based
alloy, or a nickel-based alloy). It should be understood, however,
that the invention is not limited to steel body or particle-matrix
composite-type bits, and bits of other manufacture may also be
configured according to embodiments of the invention.
[0025] If the bi-center bit 100 or portions thereof is a
particle-matrix type bit formed of sintered tungsten carbide
particles in a suitable matrix, the backup cutting element pockets
110 in the bi-center bit 100 are formed by casing the backup
cutting element pockets 110 in the bi-center bit 100. Methods of
manufacturing the bi-center bit 100 as a particle-matrix composite
bit are described in, for example, pending U.S. patent application
Ser. No. 11/271,153, filed Nov. 10, 2005 and entitled "Earth-Boring
Rotary Drill Bits and Methods of Forming Earth-Boring Rotary Drill
Bits," and pending U.S. patent application Ser. No. 11/272,439,
filed Nov. 10, 2005 and entitled "Earth-Boring Rotary Drill Bits
and Methods of Manufacturing Earth-Boring Rotary Drill Bits Having
Particle-Matrix Composite Bit Bodies," each of which is assigned to
the assignee of the present invention and the disclosure of each of
which application is incorporated herein in its entirety by this
reference.
[0026] Referring still to FIG. 2, the intermediate placement of the
backup cutting elements 121 may afford wear protection to the
bi-center bit 100. For example, a matrix portion 158 of the blades
118 (e.g., a portion of the blades 118 surrounding the pockets 110
for receiving the cutting elements 120, 121 that may comprise
steel, a cemented material, etc., depending on the type of drill
bit materials selected) have been observed to wear unduly in
certain drilling situations involving imbalance forces of the bit,
bit vibration, and precession, including bit whirl. Such situations
may occur frequently when drilling with a bi-center bit 100 having
an eccentric portion (e.g., the reamer bit section 114). When
drilling with a bi-center bit 100 having an eccentric portion, the
centerline of a bit may be canted or tilted, or offset, with
respect to the axis of the borehole, and side loading of the bit is
of substantial magnitude due to the presence of the reamer bit
section 114. Positioning the backup cutting elements 121
intermediate the primary cutting elements 120 may provide
protection of the bi-center bit 100 by preventing undue matrix wear
at a matrix portion 158 of the bi-center bit 100 by reducing the
amount of wear on a matrix portion 158 of the blades 118 as the
backup cutting elements 121 may tend to contact the subterranean
borehole rather than a matrix portion 158 of the bi-center bit 100.
Further, the backup cutting elements 121 may prevent failure of the
cutting elements 120, 121 due to wear of the surrounding blade
material (e.g., the matrix portion 158).
[0027] In some embodiments, the backup cutting elements 121 may be
placed to substantially oppose the blades 140 of the reamer bit
section 114. For example, the backup cutting elements 121 may be
placed on blades 118 of the pilot bit section 112, which are
opposite to (i.e., on opposing lateral sides of the bi-center bit
100) the blades 140 of the reamer bit section 114. As discussed
above, the backup cutting elements 121 may be located laterally
intermediate the primary cutting elements 120 and may at least
partially prevent matrix wear of a matrix portion 158 of the blades
118 between the laterally adjacent primary cutting elements 120.
Such wear may be at least partially caused by imbalance forces
(e.g., a resultant force vector generated by the eccentric blades
140 of the reamer bit section 114) due to the cutting forces
created by the primary cutting elements 120 generated as the
enlarged borehole is cut. Such imbalance forces may cause a matrix
portion 158 of the blades 118 to contact (e.g., rub against)
portions of the subterranean borehole during a drilling operation.
Excessive contact between the matrix portion 158 of the blades 118
and the subterranean borehole may result in wear and, ultimately,
failure of the bi-center bit 100. Locating the backup cutting
elements 121 laterally intermediate the primary cutting elements
120 may reduce the amount of wear on a matrix portion 158 of the
blades 118 as the backup cutting elements 121 may tend to contact
the subterranean borehole rather than a matrix portion 158 of the
bi-center bit 100.
[0028] The exposure of the backup cutting elements 121 (i.e., the
distance the cutting elements 120, 121 extend away from the surface
of the bi-center bit 100) may vary from the primary cutting
elements 120 or may vary between the backup cutting elements 121.
For example, the backup cutting elements 121 may be underexposed
relative to the primary cutting elements 120 along the cutting
element profile for a blade 118. In some embodiments, the exposure
of the backup cutting elements 121 may vary depending on the
location of the backup cutting elements 121. For example, the
backup cutting elements 121 located in a cone region 136 of the
pilot bit section 112 may exhibit relatively less exposure as
compared to the backup cutting elements 121 located in the shoulder
region 138 of the pilot bit section 112. For example, the backup
cutting elements 121 located in the cone region 136 may be
underexposed (e.g., by approximately 0.025 inch (0.635 millimeter))
from the primary cutting elements 120 while the backup cutting
elements 121 located in the shoulder region 138 may have a exposure
substantially equal to or only slightly less than the exposure of
the primary cutting elements 120 (e.g., by approximately 0.01 inch
(0.254 millimeter)).
[0029] In some embodiments, the primary cutting elements 120 and
the backup cutting elements 121 of the bi-center bit 100 may each
have similar or differing back rake and side rake angles such as
the cutting elements described in, for example, U.S. patent
application Ser. No. 12/498,516, which was filed Jul. 7, 2009 and
entitled "Backup Cutting Elements on Non-Concentric Reaming Tools,"
which is assigned to the assignee of the present invention and the
disclosure of which is incorporated herein in its entirety by this
reference.
[0030] As shown in FIG. 3, in some embodiments, backup cutting
elements 221, 222 may have a differing orientation, geometry, or
material composition than that of the primary cutting elements 120.
A bi-center bit 200 may be substantially similar to the bi-center
bit 100 shown and described with reference to FIGS. 1 and 2. As
shown in FIG. 3, the backup cutting elements 221 may be positioned
on a pilot bit section 212 in a similar manner and the backup
cutting elements 121 shown and described with reference to FIGS. 1
and 2. However, the backup cutting elements 221 may have a
relatively larger back rack angle than the primary cutting elements
120. For example, the backup cutting elements 221 may be positioned
to have approximately a 90.degree. back rake angle. Such a backup
cutting element 221 is described in, for example, U.S. Pat. No.
6,408,958 to Isbell et al., which is assigned to the assignee of
the present invention and the disclosure of which is incorporated
in its entirety by this reference. The backup cutting elements 221
may be oriented substantially transverse to the bit face with the
sides of superabrasive tables 223 of the backup cutting elements
221 facing in an intended rotational path 160 of the bi-center bit
200. The substantially transverse orientation of the backup cutting
elements 221 may provide support to the pilot bit section 212 as
the backup cutting elements 221 are a substantially radially
unaggressive structure to a formation (e.g., a subterranean
borehole). In some embodiments, the backup cutting element 221 may
comprise a bearing block. In such an embodiment, the backup cutting
element 221 may provide a designed bearing or rubbing area
affording a surface area specifically tailored to provide support
for the bi-center bit 200 under a force (e.g., an imbalance force,
an axial WOB, etc.) on a selected formation being drilled without
exceeding the compressive strength thereof.
[0031] As further shown in FIG. 3, in some embodiments, backup
cutting elements 222 may have a differing geometry than that of the
primary cutting elements 120. For example, the backup cutting
elements 222 may have a substantially ovoid shape and may extend
between the longitudinal axes of the primary cutting elements 120.
It is noted that while the embodiment of FIG. 3 illustrates the
backup cutting elements 221, 222 having a circular or ovoid shape,
the backup cutting elements 221, 222 may comprise any suitable
shape such as, for example, semi-circular, rectangular, tombstone,
triangular, etc. In additional embodiments, the backup cutting
elements 221, 222 may have a differing material composition than
that of the primary cutting elements 120. For example, the backup
cutting elements 221, 222 may comprise another type of synthetic
diamond such as TSP. As also shown in FIG. 3, in some embodiments,
the backup cutting elements 221, 222 may only be disposed on blades
218 of the pilot bit section 212 which are opposite to (i.e., on
opposing lateral sides of the bi-center bit 200) the blades 140 of
the reamer bit section 214.
[0032] FIG. 4 is a face view, or view looking up from the bottom of
a borehole, of a bi-center bit 300 having a row of primary cutting
elements 120 and multiple rows of backup cutting elements 321, 322
thereon, as may be desired or required. As shown in FIG. 4, the
pilot bit section 312 have a first row of backup cutting elements
321 that may rotationally trail the primary cutting elements 120
and may be at a location on the bit profile at least partially
laterally offset from rotationally leading primary cutting elements
120. As shown on blade 318, in some embodiments, a second row of
backup cutting elements 322 may rotationally trail the first row of
backup cutting elements 321 and may be at a location on the bit
profile at least partially laterally offset from the rotationally
leading first row of backup cutting elements 321. As shown on blade
319, in other embodiments, the second row of backup cutting
elements 322 may rotationally trail the first row of backup cutting
elements 321 and may be located rotationally behind the
rotationally leading first row of backup cutting elements 321.
[0033] While the present invention has been disclosed herein with
reference to illustrated embodiments, those of ordinary skill in
the art will understand and appreciate that the invention is not so
limited, and that additions, deletions and modifications to the
disclosed embodiments may be made without departing from the scope
of the invention. The present invention is limited only by the
appended claims and their legal equivalents, which include within
their scope all equivalent devices and methods according to
principles of the invention as described.
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