U.S. patent application number 12/766988 was filed with the patent office on 2010-11-04 for bearing blocks for drill bits, drill bit assemblies including bearing blocks and related methods.
This patent application is currently assigned to BAKER HUGHES INCORPORATED. Invention is credited to Chad J. Beuershausen, Michael S. Damschen, Thorsten Schwefe.
Application Number | 20100276200 12/766988 |
Document ID | / |
Family ID | 43029563 |
Filed Date | 2010-11-04 |
United States Patent
Application |
20100276200 |
Kind Code |
A1 |
Schwefe; Thorsten ; et
al. |
November 4, 2010 |
BEARING BLOCKS FOR DRILL BITS, DRILL BIT ASSEMBLIES INCLUDING
BEARING BLOCKS AND RELATED METHODS
Abstract
Methods of drilling subterranean formations include coupling at
least one bearing block having an initial thickness to a drill bit,
engaging a formation with the drill bit within an initial depth of
cut range, and reducing the initial thickness of the bearing block
by contacting the formation to cause the initial depth of cut range
to be at least partially increased. Methods of forming drill bits
for drilling subterranean formations include forming at least one
rubbing surface of at least one bearing block from at least one
material exhibiting a reduced coefficient of friction and coupling
the at least one bearing block to the drill bit. Drill bit
assemblies include at least one bearing block having a distal
portion configured to provide an initial depth of cut range and a
base portion configured to provide an increased depth of cut range
greater than the initial depth of cut range.
Inventors: |
Schwefe; Thorsten; (Spring,
TX) ; Beuershausen; Chad J.; (Magnolia, TX) ;
Damschen; Michael S.; (Houston, TX) |
Correspondence
Address: |
Traskbritt, P.C. / Baker Hughes, Inc.;Baker Hughes, Inc.
P.O. Box 2550
Salt Lake City
UT
84110
US
|
Assignee: |
BAKER HUGHES INCORPORATED
Houston
TX
|
Family ID: |
43029563 |
Appl. No.: |
12/766988 |
Filed: |
April 26, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61174412 |
Apr 30, 2009 |
|
|
|
Current U.S.
Class: |
175/57 ; 175/428;
175/430; 175/432; 76/108.1 |
Current CPC
Class: |
E21B 10/43 20130101;
E21B 10/55 20130101 |
Class at
Publication: |
175/57 ; 175/428;
175/430; 175/432; 76/108.1 |
International
Class: |
E21B 10/46 20060101
E21B010/46; E21B 7/00 20060101 E21B007/00; E21B 10/42 20060101
E21B010/42; E21B 10/54 20060101 E21B010/54; E21B 10/55 20060101
E21B010/55; B21K 5/04 20060101 B21K005/04 |
Claims
1. A method of drilling a subterranean formation, the method
comprising: coupling at least one bearing block having at least one
rubbing surface and an initial thickness to a drill bit; engaging a
formation with at least one cutter of the drill bit within an
initial depth of cut range; drilling the formation with the drill
bit; and reducing the initial thickness of the bearing block by
contacting the formation with the at least one rubbing surface to
cause the initial depth of cut range to be at least partially
increased.
2. The method of claim 1, further comprising forming the at least
one bearing block at least partially from a material selected for
wear.
3. The method of claim 2, wherein forming the at least one bearing
block at least partially from a material selected for wear
comprises forming the at least one bearing block at least partially
from at least one of a relatively soft carbide material, a steel
material, an alloy material, and a particle-matrix composite
material.
4. The method of claim 1, further comprising forming the at least
one bearing block from a first material selected for wear and a
second material selected to exhibit a wear resistance greater than
the first material.
5. The method of claim 4, wherein forming the at least one bearing
block from a first material selected for wear and a second material
selected to exhibit a wear resistance greater than the first
material comprises forming a rubbing surface of the at least one
bearing block with the first material and forming a base portion of
the at least one bearing block with the second material.
6. The method of claim 4, wherein forming the at least one bearing
block from a first material selected for wear and a second material
selected to exhibit a wear resistance greater than the first
material comprises forming a rubbing surface of the at least one
bearing block with the second material and forming a base portion
of the at least one bearing block with the first material.
7. The method of claim 4, wherein forming the at least one bearing
block from a first material selected for wear and a second material
selected to exhibit a wear resistance greater than the first
material comprises: selecting the first material from at least one
of a relatively soft carbide material, a steel material, a metal
alloy material, and a particle-matrix composite material; and
selecting the second material from at least one of a diamond
material, a thermally stable polycrystalline material, a ceramic
material, and a tungsten carbide material.
8. The method of claim 1, wherein drilling the formation with the
drill bit comprises drilling a first formation using the drill bit
with a first average depth of cut and further comprising drilling a
second, subsequent formation using the drill bit with a second,
substantially greater average depth of cut.
9. A method of forming a drill bit for drilling a subterranean
formation, the method comprising: forming at least one rubbing
surface of at least one bearing block from at least one material
exhibiting a reduced coefficient of friction as compared to another
rubbing surface of the drill bit when the at least one rubbing
surface is rotated by the drill bit in contact with the
subterranean formation; and coupling the at least one bearing block
having the at least one rubbing surface to the drill bit.
10. The method of claim 9, wherein forming at least one rubbing
surface of at least one bearing block from at least one material
exhibiting a reduced coefficient of friction comprises selecting
the at least one material from at least one of a diamond material,
a ceramic material, a hardened steel material, an alloy material,
and a material having a polished surface.
11. The method of claim 9, wherein forming at least one rubbing
surface of at least one bearing block from at least one material
exhibiting a reduced coefficient of friction comprises selecting
the at least one material to exhibit a coefficient of friction of
less than 0.2.
12. A drill bit assembly for subterranean drilling, comprising: a
drill bit comprising a plurality of blades, a plurality of cutting
elements disposed on the plurality of blades, and at least one
receptacle located in at least one blade of the plurality of
blades; and at least one bearing block disposed in the at least one
receptacle, the at least one bearing block comprising: a distal
portion configured to provide at least one cutting element of the
plurality of cutting elements with an initial depth of cut range;
and a base portion configured to provide the at least one cutting
element of the plurality of cutting elements with an increased
depth of cut range greater than the initial depth of cut range.
13. The drill bit assembly for subterranean drilling of claim 12,
wherein the at least one bearing block further comprises at least
one of a tapered shape and a concave shape.
14. The drill bit assembly for subterranean drilling of claim 12,
wherein the distal portion of the at least one bearing block
extends laterally outward from the base portion of the at least one
bearing block.
15. The drill bit assembly for subterranean drilling of claim 14,
wherein the distal portion of the at least one bearing block
comprises a convex shape.
16. The drill bit assembly for subterranean drilling of claim 12,
wherein the distal portion of the at least one bearing block
comprises a first material selected for wear and the base portion
of the at least one bearing block comprises a second material
exhibiting a wear resistance greater than the first material.
17. The drill bit assembly for subterranean drilling of claim 16,
wherein the distal portion of the at least one bearing block
comprises at least one of a relatively soft carbide material, a
steel material, an alloy material, and a particle-matrix composite
material and the base portion of the at least one bearing block
comprises at least one of a diamond material, a thermally stable
polycrystalline material, a ceramic material, and a tungsten
carbide material.
18. The drill bit assembly for subterranean drilling of claim 12,
wherein the distal portion of the at least one bearing block
comprises a first material comprising a wear resistant material and
the base portion of the at least one bearing block comprises a
second material exhibiting a wear resistance less than the first
material.
19. The drill bit assembly for subterranean drilling of claim 18,
wherein the distal portion of the at least one bearing block
comprises at least one of a diamond material, a thermally stable
polycrystalline material, a ceramic material, and a tungsten
carbide material and the base portion of the at least one bearing
block comprises at least one of a relatively soft carbide material,
a steel material, an alloy material, and a particle-matrix
composite material.
20. The drill bit assembly for subterranean drilling of claim 12,
wherein at least one of the distal portion of the at least one
bearing block and the base portion of the at least one bearing
block comprise a material exhibiting a coefficient of friction
between 0.01 and 0.20.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 61/174,412, filed Apr. 30, 2009, the
disclosure of which is hereby incorporated herein by this reference
in its entirety.
[0002] The application is also related to, but does not claim
priority to, copending U.S. patent application Ser. No. 11/818,820,
filed Jun. 14, 2007, the disclosure of which is hereby incorporated
herein by this reference in its entirety.
TECHNICAL FIELD
[0003] The present invention, in several embodiments, relates
generally to a rotary fixed cutter or "drag" drill bit employing
superabrasive cutters for drilling subterranean formations and,
more particularly, to use of bearing blocks in association with
superabrasive cutters to provide improved accuracy for obtaining
one or more target depths of cut for the cutters, a controlled
bearing area on the face of the drill bit, or both. Methods of
drilling are also encompassed by embodiments of the invention.
BACKGROUND
[0004] Rotary drag bits employing superabrasive cutting elements in
the form of polycrystalline diamond compact (PDC) cutters have been
employed for several decades. PDC cutters are typically comprised
of a disc-shaped diamond "table" formed on and bonded under
high-pressure and high-temperature conditions to a supporting
substrate such as cemented tungsten carbide (WC), although other
configurations are known. Bits carrying PDC cutters, which for
example, may be brazed into pockets in the bit face, pockets in
blades extending from the face, or mounted to studs inserted into
the bit body, have proven very effective in achieving high rates of
penetration (ROP) in drilling subterranean formations exhibiting
low to medium compressive strengths. Recent improvements in the
design of hydraulic flow regimes about the face of bits, cutter
design, and drilling fluid formulation have reduced prior, notable
tendencies of such bits to "ball" by increasing the volume of
formation material which may be cut before exceeding the ability of
the bit and its associated drilling fluid flow to clear the
formation cuttings from the bit face.
[0005] Even in view of such improvements, however, PDC cutters
still suffer from what might simply be termed "overloading" even at
low weight-on-bit (WOB) applied to the drill string to which the
bit carrying such cutters is mounted, especially if aggressive
cutting structures are employed. The relationship of torque to WOB
may be employed as an indicator of aggressivity for cutters, so the
higher the torque to WOB ratio, the more aggressive the bit. The
problem of excessive bit aggressiveness is particularly significant
in low compressive strength formations where an unduly great depth
of cut (DOC) may be achieved at extremely low WOB. The problem may
also be aggravated by drill string bounce or torque and drag,
wherein the elasticity of the drill string may cause erratic
application of WOB to the drill bit or the drill pipe dragging on
the wall of the borehole, with consequent overloading. Moreover,
operating PDC cutters at an excessively high DOC may generate more
formation cuttings than can be consistently cleared from the bit
face and back up the bore hole via the junk slots on the face of
the bit by even the aforementioned improved, state-of-the-art bit
hydraulics, leading to the aforementioned bit balling
phenomenon.
[0006] Another, separate problem involves drilling from a zone or
stratum of higher formation compressive strength to a "softer" zone
of lower compressive strength. As the bit drills into the softer
formation without changing the applied WOB (or before the WOB can
be reduced by the driller), the penetration of the PDC cutters, and
thus the resulting torque on the bit (TOB), increase almost
instantaneously and by a substantial magnitude. The abruptly higher
torque, in turn, may cause damage to the cutters and/or the bit
body itself In directional drilling, such a change causes the tool
face orientation of the directional (measuring-while-drilling, or
MWD, or a steering tool) assembly to fluctuate, making it more
difficult for the directional driller to follow the planned
directional path for the bit. Thus, it may be necessary for the
directional driller to back off the bit from the bottom of the
borehole to reset or reorient the tool face. In addition, a
downhole motor, such as drilling fluid-driven Moineau-type motors
commonly employed in directional drilling operations in combination
with a steerable bottomhole assembly, may completely stall under a
sudden torque increase. That is, the bit may stop rotating, thereby
stopping the drilling operation and again necessitating backing off
the bit from the borehole bottom to re-establish drilling fluid
flow and motor output. Such interruptions in the drilling of a well
can be time consuming and quite costly.
[0007] Numerous attempts using varying approaches have been made
over the years to protect the integrity of diamond cutters and
their mounting structures and to limit cutter penetration into a
formation being drilled. For example, from a period even before the
advent of commercial use of PDC cutters, U.S. Pat. No. 3,709,308
discloses the use of trailing, round natural diamonds on the bit
body to limit the penetration of cubic diamonds employed to cut a
formation. U.S. Pat. No. 4,351,401 discloses the use of surface set
natural diamonds at or near the gage of the bit as penetration
limiters to control the depth-of-cut of PDC cutters on the bit
face. The following other patents disclose the use of a variety of
structures immediately trailing PDC cutters (with respect to the
intended direction of bit rotation) to protect the cutters or their
mounting structures: U.S. Pat. Nos. 4,889,017; 4,991,670; 5,244,039
and 5,303,785. U.S. Pat. No. 5,314,033 discloses, inter alia, the
use of cooperating positive and negative or neutral backrake
cutters to limit penetration of the positive rake cutters into the
formation. Another approach to limiting cutting element penetration
is to employ structures or features on the bit body rotationally
preceding (rather than trailing) PDC cutters, as disclosed in U.S.
Pat. Nos. 3,153,458; 4,554,986; 5,199,511 and 5,595,252.
[0008] In another context, that of so-called "anti-whirl" drilling
structures, it has been asserted in U.S. Pat. No. 5,402,856 that a
bearing surface aligned with a resultant radial force generated by
an anti-whirl underreamer should be sized so that force per area
applied to the borehole sidewall will not exceed the compressive
strength of the formation being underreamed. See also U.S. Pat.
Nos. 4,982,802; 5,010,789; 5,042,596; 5,111,892 and 5,131,478.
[0009] While some of the foregoing patents recognize the
desirability to limit cutter penetration, or DOC, or otherwise
limit forces applied to a borehole surface, the disclosed
approaches are somewhat generalized in nature and fail to
accommodate or implement an engineered approach to achieving a
target ROP in combination with more stable, predictable bit
performance. Furthermore, the disclosed approaches do not provide a
bit or method of drilling which is generally tolerant to being
axially loaded with an amount of weight-on-bit over and in excess
what would be optimum for the current rate-of-penetration for the
particular formation being drilled and which would not generate
high amounts of potentially bit-stopping (e.g., stick-slip) or
bit-damaging torque-on-bit should the bit nonetheless be subjected
to such excessive amounts of weight-on-bit.
[0010] Various successful solutions to the problem of excessive
cutter penetration are presented in U.S. Pat. Nos. 6,298,930;
6,460,631; 6,779,613 and 6,935,441, the disclosure of each of which
is incorporated by reference in its entirety herein. Specifically,
U.S. Pat. No. 6,298,930 describes a rotary drag bit including
exterior features to control the depth of cut by cutters mounted
thereon, so as to control the volume of formation material cut per
bit rotation as well as the torque experienced by the bit and an
associated bottom-hole assembly. These features, also termed depth
of cut control (DOCC) features, provide the bearing surface or
sufficient surface area to withstand the axial or longitudinal WOB
without exceeding the compressive strength of the formation being
drilled and such that the depth of penetration of PDC cutters
cutting into the formation is controlled. Because the DOCC features
are subject to the applied WOB as well as to contact with the
abrasive formation and abrasives-laden drilling fluids, the DOCC
features may be layered onto the surface of a steel body bit as an
applique or hard face weld having the material characteristics
required for a high load and high abrasion/erosion environment, or
include individual, discrete wear resistant elements or inserts set
in bearing surfaces cast in the face of a matrix-type bit, as
depicted in FIG. 1 of U.S. Pat. No. 6,298,930. The wear resistant
inserts or elements may comprise tungsten carbide bricks or discs,
diamond grit, diamond film, natural or synthetic diamond (PDC or
TSP), or cubic boron nitride.
[0011] FIGS. 10A and 10B of U.S. Pat. No. 6,298,930, respectively,
depict different DOCC feature and PDC cutter combinations. In each
instance, a single PDC cutter is secured to a combined cutter
carrier and DOC limiter, the carrier then being received within a
cavity in the face (or on a blade) of a bit and secured therein.
The DOC limiter includes a protrusion exhibiting a bearing
surface.
[0012] The aforementioned and incorporated by reference, U.S.
patent application Ser. No. 11/818,820 discloses another solution
to the problem of excessive cutter penetration. As described
therein, interchangeable bearing blocks may be disposed in
receptacles in a bit body of a drill bit proximate to a plurality
of PDC cutters. The interchangeable bearing blocks may act to limit
the DOC of the PDC cutters proximate to the bearing blocks.
BRIEF SUMMARY
[0013] In some embodiments, the present invention includes a method
of drilling a subterranean formation comprising coupling at least
one bearing block having at least one rubbing surface and an
initial thickness to a drill bit, engaging a formation with at
least one cutter of the drill bit within an initial depth of cut
range, drilling the formation with the drill bit, and reducing the
initial thickness of the bearing block by contacting the formation
with the at least one rubbing surface to cause the initial depth of
cut range to be at least partially increased.
[0014] In additional embodiments, the present invention includes a
method of drilling a subterranean formation. The method includes
coupling at least one bearing block having at least one rubbing
surface and an initial thickness to a drill bit, engaging a
formation with at least one cutter of the drill bit within an
initial depth of cut range, drilling the formation with the drill
bit, and increasing the initial depth of cut range by contacting
the formation with the at least one rubbing surface to cause the
initial thickness of the bearing block to be at least partially
reduced. The method may, optionally, also include selecting one or
more materials for the bearing block to wear at a predictable rate
when engaged with a particular formation material or materials.
[0015] In additional embodiments, the present invention includes a
method of forming a drill bit for drilling a subterranean
formation. The method includes forming at least one bearing block
having at least one rubbing surface from at least one material
exhibiting at least one of a wear rate and a reduced coefficient of
friction as compared to another rubbing surface of the drill bit
when the at least one rubbing surface is rotated by the drill bit
in contact with the subterranean formation and coupling the at
least one bearing block having the at least one rubbing surface to
the drill bit.
[0016] In further embodiments, the present invention includes a
method of drilling comprising drilling a first formation with a
first average depth of cut and subsequently drilling a second
formation with a second, substantially greater depth of cut.
[0017] In yet additional embodiments, the present invention
includes a drill bit assembly for subterranean drilling comprising
a drill bit including a plurality of blades, a plurality of cutting
elements disposed on the plurality of blades, and at least one
receptacle located in at least one blade of the plurality of
blades. The drill bit assembly further comprises at least one
bearing block disposed in the at least one receptacle. The at least
one bearing block comprises a distal portion configured to provide
at least one cutting element of the plurality of cutting elements
with an initial depth of cut range and a base portion configured to
provide the at least one cutting element of the plurality of
cutting elements with an increased depth of cut range greater than
the initial depth of cut range.
[0018] In yet additional embodiments, the present invention
includes a bearing block for a rotary drill bit for subterranean
drilling. The bearing block includes a body portion configured to
secure to a complementary structure on a blade of a drill bit and a
non-planar rubbing surface configured to contacting a formation
during drilling with the drill bit under applied WOB. The bearing
block material may be selected for specific wear or frictional
characteristics, or both.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 shows a drill bit having an attached bearing block in
accordance with a one embodiment of the current invention.
[0020] FIG. 2 shows a partial view of the drill bit having the
attached bearing block of FIG. 1.
[0021] FIG. 3 shows a partial perspective cross-sectional view of
the drill bit having a receptacle for receiving the bearing block
shown in FIG. 1.
[0022] FIG. 4A shows a perspective view of a "peanut-shaped"
bearing block in accordance with another embodiment of the current
invention.
[0023] FIG. 4B shows a front leading view of a keyed bearing block
in accordance with yet another embodiment of the current
invention.
[0024] FIG. 4C shows a side view of a low stress "tooth" bearing
block in accordance with yet another embodiment of the current
invention.
[0025] FIG. 4D shows a side view of a tapered bearing block in
accordance with yet another embodiment of the current
invention.
[0026] FIG. 5A shows a partial cross-sectional view of a receptacle
having the peanut-shaped bearing block disposed therein in
accordance with yet another embodiment of the current
invention.
[0027] FIG. 5B shows a partial cross-sectional view of a receptacle
having the keyed bearing block disposed therein in accordance with
yet another embodiment of the current invention.
[0028] FIG. 5C shows a partial cross-sectional view of a "root"
receptacle having the tooth bearing block disposed therein in
accordance with the fourth embodiment.
[0029] FIG. 5D shows a cross-sectional view of a receptacle having
the tapered bearing block disposed therein in accordance with yet
another embodiment of the current invention.
[0030] FIG. 5E shows a cross-sectional view of a receptacle having
a concave bearing block disposed therein in accordance with yet
another embodiment of the current invention.
[0031] FIG. 5F shows a cross-sectional view of a receptacle having
a round bearing block disposed therein in accordance with yet
another embodiment of the current invention.
[0032] FIG. 5G shows a cross-sectional view of a receptacle having
a bearing block including an enlarged distal portion disposed
therein in accordance with yet another embodiment of the current
invention.
[0033] FIG. 5H shows a cross-sectional view of a receptacle having
a bearing block with a rounded, enlarged distal portion disposed
therein in accordance with yet another embodiment of the current
invention.
[0034] FIG. 6 shows a partial schematic side sectional view
illustrating a superimposed cutter profile of the drill bit and
bearing block shown in FIG. 1.
DETAILED DESCRIPTION
[0035] The illustrations presented herein are not actual views of
any particular drilling system, assembly, or device, but are merely
idealized representations which are employed to describe
embodiments of the present invention.
[0036] An embodiment of the current invention is shown in FIGS. 1,
2, 3, and 6. FIG. 1 shows an earth-boring rotary drill bit 10,
depicted as a fixed cutter or drag bit employing PDC cutting
elements, although of course the invention is not so limited. The
bit 10 includes an attached bearing block 40 as viewed by looking
upwardly at its face or leading end 12 as if the viewer was
positioned at the bottom of a borehole. Bit 10 includes a plurality
of PDC cutters 14 bonded by their substrates (diamond tables and
substrates not shown separately for clarity), as by brazing, into
pockets 16 in blades 18 extending above the face 12 of the bit 10.
While the bit 10 depicted in FIG. 1 is a steel body bit, the bit 10
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 and employed
with bearing blocks thereof.
[0037] Fluid courses 20 lie between blades 18 and are provided with
drilling fluid by nozzles 22 secured in nozzle orifices 24, nozzle
orifices 24 being at the end of passages leading from a plenum
extending into the bit body from a tubular shank at the upper, or
trailing, end of the bit 10. Fluid courses 20 extend to junk slots
26 extending upwardly along the side of bit 10 between blades 18.
Gage pads (not shown) comprise longitudinally upward extensions of
blades 18 and may have wear-resistant inserts or coatings on
radially outer surfaces 21 thereof as known in the art. Formation
cuttings are swept away from PDC cutters 14 by drilling fluid
emanating from nozzle orifices 24 which moves generally radially
outwardly through fluid courses 20 and then upwardly through junk
slots 26 to an annulus between the drill string from which the bit
10 is suspended and on to the surface.
[0038] Simultaneous reference may be made to FIGS. 2 and 3
depicting further details of the bit 10 of FIG. 1. FIG. 2 shows a
partial view of the bit 10 exposing the attached bearing block 40.
FIG. 3 shows a partial perspective cross-sectional view of the bit
10 having a receptacle 28 for receiving the bearing block 40. The
receptacle 28 substantially conforms to a portion of the bearing
block 40 for receiving and attaching it therein. Moreover, the
receptacle 28 has a defined depth in relation to the cutter pockets
16, and ultimately outer, or cutting, edges of the cutters 14. The
defined depth of the receptacle 28 is a function of a desired
target depth of cut (TDOC) as discussed below, the thickness of
bearing block 40 and the desired positioning of the cutters 14 and
size of the cutters 14 in the blade 18 of the bit 10 in order to
achieve TDOC as understood by a person of ordinary skill in the art
and discussed in the references incorporated herein.
[0039] The bearing block 40, as shown in FIGS. 1 and 2 may be
billet shaped having a bearing or rubbing surface 32 and an
interface surface 34, which in this embodiment includes a
rotationally (as the bit is rotated during drilling) leading side
35, a rotationally trailing side 36, a bottom 37, and two ends 38,
39. The interface surface 34 of the bearing block 40 is
substantially received within and may be bonded by, for example,
brazing, mechanical, or adhesive affixation to the receptacle 28 of
the blade 18. The bearing block 40 may also be attached by
interference fit or other attachment methods known to one of
ordinary skill in the art. When the bearing block 40 is secured to
the blade 18 by bonding (including brazing), the bonding material
may also act as a filler to fill any interstitial gaps or voids
between the perimeter of receptacle 28 and the bearing block 40 to
reduce the potential for damage to the bit face 12 along the
blade/block interface by abrasives-laden drilling fluids. The
receptacle 28 is located, in this embodiment, generally in the cone
region 19 of the blade 18, enabling the bearing block 40 to
rotationally trail a plurality of cutters 14. The bearing block 40
may be replaced or exchanged with a block having different
characteristics, as discussed below. While this embodiment of the
invention provides a single bearing block 40 providing a TDOC for
associated four cutters 14 on one blade 18, it is recognized that
more than one block may be used to advantage on several of the
blades for facilitating TDOC for multiple cutters in a given region
or regions (cone, nose, etc.) of the bit face 12. Also, it is
recognized that the blade 18 may carry multiple blocks thereon.
[0040] It is noted that the word "block" as used to describe the
bearing block 40 as given in the first embodiment of the invention,
or any other embodiment, is not intended to create or import
unintended structural limitations. Specifically, the word "block"
is intended to mean piece, portion, part, insert, object, or body,
without limitation, all of which have mass and shape, without
further limitation to material and/or other physical attributes
except as expressly presented herein.
[0041] The bearing block 40, trailing a plurality of cutters 14,
provides a designed bearing or rubbing area 42 affording a surface
area specifically tailored to provide support for bit 10 under
axial or longitudinal WOB on a selected formation being drilled
without exceeding the compressive strength thereof. Further, the
bearing block 40 is manufactured, in association with receptacle
28, to provide a precision TDOC relating to the distance
(thickness) 44 between the bottom 37 and the rubbing surface 32 of
the bearing block 40. Resultantly, the bearing block 40, as
inserted into the receptacle 28, defines the TDOC for the plurality
of associated cutters 14, the TDOC being indicated in FIG. 2 by the
dimension 48 as measured vertically (with respect to the bit face
at a given cutter location) between the outermost cutting edges of
cutters 14 and rubbing surface 32 of bearing block 40. Accordingly,
a bearing block 40 having a selected thickness and, in some
embodiments, a selected bearing or rubbing area 42, enables the
bearing block 40 to be custom tailored to provide desired drilling
characteristics for a bit without alteration or modification to the
bit body 10.
[0042] Tailoring the configuration of the bearing block
advantageously provides specifiable TDOC, limiting manufacturing
uncertainty as well as reducing complexity of bit production by
bringing to the manufacturing process a high precision and easily
alterable component, i.e., the bearing block, without altering the
base product, i.e., the bit body or frame. Also, the bearing block
may be configured to provide for a selectable rubbing surface area
not necessitating alteration to the bit body or frame. Moreover,
the bearing block enables a variety of TDOCs and rubbing surface
areas to be selectably chosen for a given bit body or frame,
reducing inventory loads for bit frames by enhancing design
rationalization and further facilitating refurbishment of a given
bit in order to acquire a different TDOC and bearing or rubbing
surface area by exchanging out and replacing the bearing block.
Further, the use of a discrete, separately manufactured bearing
block eliminates imprecision associated with hardfacing a steel bit
body to provide a DOC limiting feature or complex machining of a
bit mold to provide a DOC feature on a matrix bit body face,
increasing precision of cutter exposure and desired bearing or
rubbing area. Furthermore, the bearing block may be made from or
optionally include a facing of an abrasion resistant materials to
further enhance the life of the bit
[0043] Optionally, as can be seen in FIG. 1, wear-resistant
elements or inserts 30, in the form of tungsten carbide bricks or
discs (e.g., a circular-shaped bearing block), diamond grit,
diamond film, natural or synthetic diamond (polycrystalline diamond
compact (PDC) or thermally stable polycrystalline (TSP)), or cubic
boron nitride, may be added to the exterior bearing surfaces of the
blades 18 or within the rubbing area 42 of the bearing block 40 to
reduce the abrasive wear typically encountered by contact with the
formation being drilled which is further influenced by WOB as the
bit 10 rotates under applied torque. In lieu of inserts, the
bearing surfaces or rubbing area may be comprised of, or completely
covered with, a wear-resistant material such as a mosaic of
tungsten carbide bricks or discs, a layer of diamond grit or a
diamond film applied, for example, by chemical vapor
deposition.
[0044] FIG. 6 shows a partial schematic side sectional view
illustrating a superimposed cutter profile 46 in accordance with
the first embodiment of the invention. The cutter profile 46 shows
the thickness 44 of bearing block 40 which, when disposed in the
receptacle 28 of the bit 10, provides a target depth of cut (TDOC)
48 for specific cutters 14. Design criteria for TDOC for a given
bit size, profile, cutter number, cutter size and cutter exposure
is understood by a person having skill in the art, and, thus,
reference may be made to the incorporated references for additional
information. Also shown in the cutter profile 46, are optional
wear-resistant elements or inserts 30 carried on other blades 18
within the bit cone region 19 (FIG. 1).
[0045] Additional embodiments of the invention are shown in FIGS.
4A through 4D and FIGS. 5A through 5H. Turning to FIGS. 4A and 5A,
a peanut-shaped bearing block 50 is provided that includes a first
rubbing area 52, a second rubbing area 54, a first thickness 56 for
first rubbing area 52 and a second thickness 58 for second rubbing
area 54. The peanut-shaped bearing block 50 is configured to be
received into a complementary socket 60 in a bit blade 62 and
brazed 64 thereto. In this embodiment, it is emphasized that the
first and second rubbing areas 52, 54, respectively, may each have
different shapes and different rubbing areas for contact with a
formation during drilling. Also, the first and second thicknesses
56 and 58, respectively, may be different, as illustrated, enabling
the bearing block 50 to be designed specifically for a particular
application in order to achieve optimal TDOC for different cutters
14 associated with the block 50. In this aspect, the TDOC may be
modified for different applications for a given bit frame or bit
body by providing a block having the desired thickness or
thicknesses without necessitating modification to the bit frame or
bit body. It is also recognized that while the bearing block 50 of
this embodiment is "peanut-shaped," as is the complementary socket
60 of a blade 62 (FIG. 5A), that the shape of the bearing block 50
and socket 60 may take on any shape consistent with the
capabilities of manufacturing of such structures. Moreover, the
peanut-shaped bearing block 50, having different rubbing areas 52,
54 and different thicknesses 56, 58 (and, thus, different TDOCs)
may, optionally, provide for a particular or specifiable insertion
orientation, as it is to be inserted into the receptacle 60 of the
blade 62, beneficially providing an attachment orientation feature
for assurance of proper assembly of bearing block 50 with the blade
62. Also, it is recognized that bearing blocks of other shapes may
be similarly utilized to advantage.
[0046] Turning to FIGS. 4B and 5B, a keyed bearing block 70
includes three different thicknesses 76, 77, and 78 and three
different rubbing surfaces 72, 73, and 74, respectively. Generally,
the bearing block 70 is "keyed" in the sense of providing two or
more thicknesses, each thickness may be associated with one or more
adjacent cutters when bearing block 70 is attached to a bit body or
frame. Also, the bearing block 70 is "keyed" in that each rubbing
surface may exhibit an inclination (tilt) or a complex contour and
be specifically tied to the TDOC to be provided a given cutter or
cutters, in order to provide a combination of TDOCs within a single
bearing block. In the case of an inclined rubbing surface, the
angle of inclination may be selected to approximate a helix angle
traveled by a cutter as it rotates and travels with the bit at a
specific radial location on the bit face when the bit operates at a
selected rate of penetration (ROP) or range of ROPs. Accordingly,
the bearing block 70 comprises thicknesses 76, 77, 78 having
rubbing surface 72 tilted toward its leading side, the rubbing
surface 73 that is substantially flat, and the rubbing surface 74
being substantially round or convex, respectively. By providing
complex rubbing surface orientations and thicknesses, the cutters
(not shown) of a blade 82 will provide highly precise TDOCs, which
may also advantageously enable the bearing block 70 to have one or
more advantageous contact levels and orientations with the
formation being drilled. The bearing block 70 may be secured to the
receptacle 80 of the blade 82 by a brazing process 86.
[0047] In FIGS. 4C and 5C, a low stress "tooth" bearing block 90
coupled to a "root" receptacle 106 in a blade 100 is shown. In this
embodiment, the tooth bearing block 90 may be press-fit into the
root receptacle 106. The low stress design includes a smooth,
transition free, interface surface between the tooth bearing block
90 and the root receptacle 106, i.e., there are no high stress
inflection points. The tooth bearing block 90 includes a thickness
96 and a rubbing surface 92. The tooth bearing block 90 of this
embodiment may be structured as a composite comprising a base
material 102 made of tungsten matrix having superior loading
strength, and a rubbing surface material 104 (i.e., a distal
portion) comprising an array or mosaic of thermally stable
polycrystalline diamonds, or TSPs, (individual diamond not shown)
for superior abrasion resistance.
[0048] In FIGS. 4D and 5D, a tapered bearing block 110 is shown.
The tapered bearing block 110 may be bonded to a receptacle 112 in
a blade 120. The tapered bearing block 110 having a thickness 118
includes a base portion 114 and a rubbing surface 116 (i.e., a
distal portion). The base portion 114 may be received within the
receptacle 112 while the rubbing surface 116 protrudes from the
receptacle 112. The rubbing surface 116 may comprise a
substantially frustoconical shape wherein the rubbing surface 116
of the tapered bearing block 110 extends outward to form an
enlarged rubbing surface 116 at the distal end of the tapered
bearing block 110. The bearing block 110 may be secured to the
receptacle 112 of the blade 120 by a braze alloy 118. The enlarged
rubbing surface 116 may provide a greater surface area of the
rubbing surface 116 or rubbing surfaces of multiple bearing blocks
enabling for improved flexibility in the WOB applied to the drill
string. As discussed above, designed bearing or rubbing surface
areas may be specifically tailored to provide support for a drill
bit 10 under axial or longitudinal WOB on a selected formation
being drilled without exceeding the compressive strength thereof.
For example, a drill bit 10 having a greater rubbing surface area
may distribute the load applied by the WOB to a formation being
drilled. In some embodiments, as discussed below, the bearing block
110 may be formed from a combination of harder and softer
materials. While the bearing blocks 40, 50, 70, 90, 110, 130, 150,
170, and 190 of FIGS. 1, 2, and 4A through 5H are shown as having a
variety of shapes (e.g., billet shapes, peanut shapes, elliptical
shapes, etc.) the present invention is not so limited as the
bearing block may comprise any shape suitable to provide the
desired TDOC for a drilling application such as, for example,
circular shapes, oval shapes, square shapes, rectangular shapes,
etc.
[0049] Referring to FIG. 5E, a concave bearing block 130 is shown.
The concave bearing block 130 may be bonded by a braze alloy 138 to
a receptacle 132 in a blade 140. The concave bearing block 130 may
include a base portion 134 partially received within the receptacle
132 and a distal portion 135 including a rubbing surface 136. As
discussed in detail below, the bearing block 130 may include a
first material forming the distal portion 135 (e.g., the rubbing
surface 136) and a second material forming the base portion 134. In
some embodiments, the distal portion 135 may be formed from a
relatively softer material selected for wear and the base portion
134 may be foamed from a relatively harder material selected for
resistance to wear. During operation, a drill bit having the
bearing block 130 disposed in the blade 140 of the drill bit may be
designed to initially contact a subterranean formation during a
drilling process with the distal portion 135 formed from the
relatively softer material. The relatively softer material will
wear during the operation causing the DOC to increase and exposing
the relatively harder material of the base portion 134 disposed
proximate to the receptacle 132 in the blade 140 of the drill bit.
As the relatively harder material of the base portion 134 is
exposed, the amount of wear (i.e., wear rate) of the bearing block
140 will be reduced and the DOC will become substantially constant
through the remainder of the drilling process. In other
embodiments, the distal portion 135 may be formed from a relatively
harder material selected for resistance to wear and the base
portion 134 may be formed from a relatively softer material
selected for wear.
[0050] Referring to FIG. 5F, a bearing block 150 including a
rounded (i.e., a convex shape) distal portion 155 including rubbing
surface 156 is shown. The bearing block 150 may be bonded by a
braze alloy 158 to a receptacle 152 in a blade 160. The bearing
block 150 may include a base portion 154 partially received within
the receptacle 152. Similar to the bearing block 130 shown and
described with reference to FIG. 5E, the bearing block 150 may be
formed from a combination of harder and softer materials.
[0051] Referring to FIG. 5G, a bearing block 170 including an
enlarged distal portion 175 having a rubbing surface 176 is shown.
In other words, the distal portion 175 is enlarged relative to a
base portion 174 of the bearing block 170. For example, the distal
portion 175 may extend laterally outward from a receptacle 172 in a
blade 180 in which the bearing block 170 is disposed (i.e., the
distal portion 175 extends along an outer surface of the blade
180). Similar to the tapered bearing block 100 shown and described
with reference to FIGS. 4D and 5D, the bearing block 170 may
provide an enlarged rubbing surface 176 at the distal end of the
bearing block 170. The enlarged rubbing surface 176 may provide a
greater surface area of the rubbing surface 176 or rubbing surfaces
of multiple bearing blocks enabling for improved flexibility in the
WOB applied to the drill string. The bearing block 170 may be
bonded by a braze alloy 178 to the receptacle 172 in the blade 180.
For example, the base portion 174 of the bearing block 170 may be
partially received within the receptacle 172. Similar to the
bearing block 130 shown and described with reference to FIG. 5E,
the bearing block 170 may be formed from a combination of harder
and softer materials.
[0052] Referring to FIG. 5H, a bearing block 190 including a
rounded (i.e., a convex shape), enlarged distal portion 195 having
a rubbing surface 196 is shown. In other words, the distal portion
175 is enlarged relative to a base portion 194 of the bearing block
190. Similar to the tapered bearing block 100 shown and described
with reference to FIGS. 4D and 5D, the bearing block 190 may
provide an enlarged rubbing surface 196 at the distal end of the
bearing block 190. The enlarged rubbing surface 196 may provide a
greater surface area of the rubbing surface 196 or rubbing surfaces
of multiple bearing blocks enabling for improved flexibility in the
WOB applied to the drill string. The bearing block 190 may be
bonded by a braze alloy 198 to a receptacle 192 in a blade 200. For
example, the base portion 194 of the bearing block 190 may be
partially received within the receptacle 192. Similar to the
bearing block 130 shown and described with reference to FIG. 5E,
the bearing block 190 may be formed from a combination of harder
and softer materials.
[0053] In some embodiments, the bearing block may comprise a
"harder" material exhibiting high hardness and wear-resistant
properties such as abrasion- and erosion-resistant characteristics.
So-called "harder" materials may comprise materials such as
tungsten carbide, natural or synthetic diamond (polycrystalline
diamond compact (PDC) or thermally stable polycrystalline (TSP)),
ceramic materials, or impregnated materials composed of diamond
material, such as natural or synthetic diamond grit, dispersed
within a matrix of wear resistant material. Use of harder materials
in the bearing block may allow for a relatively consistent DOC
during a drilling operation through one or more formations. That
is, the harder, wear-resistant bearing block will substantially
maintain its thickness throughout the drilling operation. Thus, an
initially TDOC specified will be substantially maintained during a
drilling operation. Other materials may also be utilized, alone or
in combination, for the bearing block including homogenous or
heterogeneous block materials. For example, materials exhibiting
high hardness and abrasion- and erosion-resistant characteristics
may be carried on supporting substrates exhibiting superior
toughness and ductility such as thermally stable polycrystalline
(TSP) diamond material disposed on a supporting substrate and other
carbide materials.
[0054] In some embodiments, low friction materials (i.e., materials
exhibiting a lower frictional force when the bearing block is
rotated in contact with the formation) such as, for example,
diamond, ceramic, hardened steel, or other alloy materials, or
materials having a polished or other low-friction surface or
coating may be selected. Low friction materials may exhibit a
relatively lower coefficient of friction between the rubbing
surface of the bearing block and the formation as the rubbing
surface travels across the formation, resulting in a decrease in
the amount of frictional force. For example, referring to FIG. 2, a
portion of the bearing block 40 (e.g., the rubbing surface 32) may
be formed from a material having a dynamic coefficient of friction
of 0.2 or lower. Such a bearing block may exhibit a reduced
coefficient of friction between the rubbing surface of the bearing
block and the formation as the rubbing surface travels across the
formation as compared to another rubbing surface of the drill bit
(i.e., another surface of the drill bit that contacts the formation
during a drilling process). For example, a rubbing surface of a
portion of the bit body of the drill bit (e.g., the blades 18 of
the drill bit 10) may exhibit a dynamic coefficient of friction of
0.25 or greater between a rubbing surface of the bit body (e.g., an
outer portion of the blades 18) and the formation as the rubbing
surface of the bit body travels across the formation (e.g., a
limestone formation). A bearing block exhibiting a reduced
coefficient of friction as compared to another rubbing surface of
the drill bit (e.g., less than 0.25) may allow for reduced torque
in the drill string as the rubbing surface of the bearing block
travels across the formation. As discussed above, increasing the
WOB increases the forces between the bearing block and the cutting
elements increase and also increases the amount of torque required
to turn the drill string. Therefore, providing a bearing block with
a rubbing surface exhibiting a lower coefficient between the
rubbing surface and the formation will allow for reduced torque in
a drill operation under a given amount of WOB. Further, reduced
friction reduces the amount of torque required to rotate the drill
bit, which may be significant in directional drilling using
downhole motors wherein the torque output is limited.
[0055] Further, in some embodiments it may be desirable to form a
bearing block from a "softer" material, for example, a material
selected for wear and exhibiting diminished properties such as
wear-resistance, hardness, and abrasion- and erosion-resistant
characteristics as compared to those detailed above. So-called
"softer" materials may comprise materials such as a relatively soft
carbide material, steel, other alloy, or particle-matrix composite
materials. For example, a relatively soft carbide material may
comprise hard particles (e.g., tungsten carbide) in a metal matrix
material such as, for example, a cobalt or cobalt-based alloy. Such
a relatively soft carbide may include a higher percentage by weight
of the metal matrix material causing the resultant carbide to
exhibit a relatively lower amount of wear-resistance than a carbide
having a lower percentage by weight of the metal matrix material.
For example, a relatively soft carbide may include a cobalt or
cobalt-based alloy content of 4% to 30% by weight. In some
embodiments, the relatively soft carbide may include a cobalt or
cobalt-based alloy content of 16% by weight.
[0056] As above, the softer material may be used to form the entire
bearing block or to form the rubbing surface while another material
is used to form the base portion. The softer material may enable
the thickness of the bearing block to be varied during a drilling
process without having to modify the drill bit. For example, a
drilling process may begin with a bearing block of an initial
thickness providing for a lower TDOC. As the drilling process
progresses the softer material of the bearing block will be subject
to abrasion and erosion exhibited in the drilling process. The
abrasion and erosion may tend to reduce the thickness of the
bearing block with diminished wear-resistance. As the thickness of
the bearing block is reduced, the DOC will increase. Thus, the
bearing block formed from a softer material may enable drilling
operations to select a variable TDOC based on wellbore variables
such as the type and depth of the formations being drilled with the
bit, and the material properties of the softer material.
[0057] For example, the bearing block may be fabricated to provide
a variable DOCC and TDOC during a directional drilling operation.
In a directional drilling operation, the bottomhole assembly of a
drill string including a downhole motor such as a Positive
Displacement Motor (PDM) or hydraulic Moineau-type may be directed
to follow a desired path. Systems utilizing ribs or a bent sub to
steer a drill string are disclosed, for example, in U.S. Pat. No.
7,413,032, issued Aug. 19, 2008, entitled "Self-controlled
Directional Drilling Systems and Methods" and U.S. Pat. No.
5,738,178, issued Apr. 14, 1998, entitled "Method and Apparatus for
Navigational Drilling with a Downhole Motor Employing Independent
Drill String and Bottomhole Assembly Rotary Orientation and
Rotation" both of which are assigned to the assignee of the present
invention and the entire disclosure of each of which patents is
incorporated herein by this reference. In a directional drilling
process, the initial bearing block thickness may be selected to
exhibit an initial, relatively low TDOC allowing for better tool
face control as a curve to drill directionally is initiated. As the
curve is "kicked off" and the drill string is directed at an angle
to the original substantially vertical drilling direction, the
bearing block comprising a softer material will exhibit a reduced
thickness and provide an increased DOC for drilling the curve and
the subsequent lateral (tangent) section of the wellbore in a more
aggressive manner. As the drill string is directed in a
substantially horizontal direction, the thickness of the bearing
block may be even further reduced allowing for an ever greater
DOC.
[0058] In another scenario, it is contemplated that a first
formation requiring a lesser TDOC for an optimum rate of
penetration (ROP) may be drilled through initially, followed by
drilling through a second formation requiring a greater TDOC for an
optimum rate of penetration. Based upon the material
characteristics of a portion of the bearing block to be worn during
drilling, the formation abrasivity, erosiveness of the drilling
fluid employed, and the thickness of the first formation to be
drilled through before reaching the second formation, the bearing
block wear material and thickness of such material may be selected
to substantially optimize drilling performance in both formations.
Thus, an embodiment of a method of drilling according to the
present invention comprises drilling a first formation with a first
average depth of cut and subsequently drilling a second formation
with a second, substantially greater depth of cut.
[0059] Referring again to FIGS. 5A through 5H, it is also
contemplated by the current invention that the bearing blocks 50,
70, 90, 110, 130, 150, 170, and 190 may comprise a combination of
harder and softer materials. For example, with reference to FIGS.
4B and 5B, the bearing block 70 may comprise a first rubbing
surface 72 formed from a softer material, as discussed above. The
bearing block may also comprise a rubbing surface 74 comprising a
harder material, as also discussed above. In operation, the
thickness 76 of the bearing block 70 may provide an initial DOC.
However, as the thickness 76 of the softer rubbing surface is
reduced, the DOC will increase until the thickness 78 of the harder
rubbing surface 72 is equal to or greater than that of the
thickness 76 of the softer rubbing surface 74. Similarly, as shown
in FIG. 5E, for example, the rubbing surface 136 of the bearing
block 130 may comprise a softer material, as described above. The
base portion 134 may comprise a harder material, as also discussed
above. In operation, the rubbing surface 136 of the bearing block
130 may provide an initial DOC. However, as the rubbing surface 136
is reduced, the DOC will increase until the base portion 134 is
exposed. Thus, exposing a distal surface of the base portion 134
formed from a harder material may be utilized to provide a harder
rubbing surface 137. It is also noted that, as above, the harder
material may be disposed in the initial rubbing surface and the
softer material may be disposed below the harder layer. For
example, the bearing block 130 shown in FIG. 5E, may comprise a
rubbing surface 136 comprising a harder material such as a harder
carbide and a base portion 134 comprising a softer material such as
a relatively soft carbide.
[0060] In summary, a bearing block according to embodiments of the
invention may be configured for use with one or more blades of a
bit body or frame. The inventive bearing block is designed so that
it may be replaced or repaired, typically, without necessitating
alteration to a standardized bit frame. The interchangeable,
customizable bearing block may include one or more of a
specifically selected thickness, a rubbing surface orientation and
an area suitable for improving drilling performance of a bit.
Bearing blocks with varying thicknesses and rubbing surface
orientations, topographies and areas may be implemented. Use of
different surface orientations and, particular, shapes may be used
to create more or less rubbing at certain speeds (DOC) or at
different wear states. This variability may be enhanced by
utilizing a bearing block that exhibits a rubbing surface area
contacting the formation that changes with wear.
[0061] The bearing block may be located substantially in the cone
region on a blade of the bit frame, in the cone/nose region, in the
nose region, etc. The interchangeable, modifiable bearing block
according to embodiments of the invention brings manufacturing
selectability by providing a customizable product suitable for use
with a common bit frame, thus, not requiring a complex assortment
of stocked bit frames. Each bearing block is selectably insertable
into a bit frame, enabling a bit to be customized or adapted for
different drilling applications, including difficult formations, or
for different drilling systems. Also, by providing a block that is
selectively connectable to a bit frame, different cutting
characteristics may be advantageously obtained without affecting or
requiring alteration of the bit frame. Moreover, the bearing block
may be designed for specific associated cutters or sets of cutters
to obtain customized cutter profiles and TDOCs, due to the ability
of the bearing block with a customized profile and wear properties
to be connected to a common bit frame without alteration
thereto.
[0062] Additionally, bearing blocks fabricated from a variety of
materials may provide greater flexibility in drilling operations
utilizing bearing blocks for varied drilling applications.
Materials such as harder materials may be selected to provide a
substantially consistent DOC through a drilling process.
Alternatively, softer materials may be selected to provide a varied
depth of cut during a drilling process. Bearing blocks comprising
different combinations of materials may enable for even greater
flexibility in varying the DOC and DOCC throughout a drilling
process. Further, lower friction materials may also be selected to
increase efficiency during the drilling process.
[0063] While particular embodiments of the invention have been
shown and described, numerous variations and alternate embodiments
will occur to those skilled in the art. Accordingly, it is intended
that the invention only be limited in terms of the appended claims
and their legal equivalents.
* * * * *