U.S. patent application number 14/722193 was filed with the patent office on 2016-12-01 for hybrid drill bit.
The applicant listed for this patent is Smith International, Inc.. Invention is credited to Xiaoge Gan, Yuelin Shen, Jian Wu, Jiaqing Yu, Youhe Zhang, Yong Zhou.
Application Number | 20160348440 14/722193 |
Document ID | / |
Family ID | 57399593 |
Filed Date | 2016-12-01 |
United States Patent
Application |
20160348440 |
Kind Code |
A1 |
Gan; Xiaoge ; et
al. |
December 1, 2016 |
HYBRID DRILL BIT
Abstract
A drill bit includes a bit body having a longitudinal bit axis
extending there through, a plurality of journals extending from the
bit body, each journal having a journal axis extending from a base
of the journal through the length of the journal, a roller cone
rotatably mounted to each of the journals, and at least one blade
protruding from the bit body center and extending radially outward
to less than an outer diameter of the drill bit.
Inventors: |
Gan; Xiaoge; (Houston,
TX) ; Yu; Jiaqing; (Conroe, TX) ; Shen;
Yuelin; (Spring, TX) ; Zhang; Youhe; (Spring,
TX) ; Zhou; Yong; (Spring, TX) ; Wu; Jian;
(Houston, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Smith International, Inc. |
Houston |
TX |
US |
|
|
Family ID: |
57399593 |
Appl. No.: |
14/722193 |
Filed: |
May 27, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E21B 10/08 20130101;
E21B 10/14 20130101; E21B 10/50 20130101 |
International
Class: |
E21B 10/08 20060101
E21B010/08; E21B 10/50 20060101 E21B010/50; E21B 10/14 20060101
E21B010/14 |
Claims
1. A drill bit, comprising: a bit body having a longitudinal bit
axis extending there through; a plurality of journals extending
from the bit body, each journal having a journal axis extending
from a base of the journal through the length of the journal; a
roller cone rotatably mounted to each of the journals; and at least
one blade protruding from the bit body center and extending
radially outward to less than an outer diameter of the drill
bit.
2. The drill bit of claim 1, wherein the at least one blade
comprises a plurality of cutting elements having planar cutting
faces.
3. The drill bit of claim 2, wherein the blades extend to a nose
region of the drill bit.
4. The drill bit of claim 2, wherein the blades extend to a
shoulder region of the drill bit.
5. The drill bit of claim 1, wherein the plurality of journals
extend downward and radially outward such that an acute angle
ranging from about 15 degrees to about 25 degrees is formed between
the journal axis and the longitudinal bit axis.
6. The drill bit of claim 5, wherein the plurality of roller cone
cutting elements having an installation back rake angle ranging
from about 10 degrees to about 90 degrees.
7. The drill bit of claim 5, wherein the plurality of roller cone
cutting elements having an installation side rake angle ranging
from about 0 degrees to about 60 degrees.
8. The drill bit of claims 6 and 7, wherein the plurality of roller
cone cutting elements having an equivalent back rake ranging from
about 10 degrees to about 30 degrees.
9. The drill bit of claims 6 and 7, wherein the plurality of roller
cone cutting elements having an equivalent side rake ranging from
about 0 degrees to about 30 degrees.
10. A drill bit, comprising: a bit body having a longitudinal bit
axis extending there through; a plurality of journals, extending
from the bit body; and a roller cone having an outer diameter
rotatably mounted to each of the journals, wherein at least two of
the outer diameters are different, and wherein an offset angle
ranging from about 0 degrees to about 90 degrees is formed between
a line perpendicular to the bit axis and extending through the bit
axis and a center of a backface of the roller cone.
11. The drill bit of claim 10, wherein the roller cone comprises a
plurality of roller cone cutting elements having planar cutting
faces, wherein the roller cone cutting elements comprise a roller
cone cutting profile.
12. The drill bit of claim 11, wherein the smallest roller cone
cutting profile extends an axial height greater than the largest
roller cone cutting profile.
13. The drill bit of claim 12, wherein the smallest roller cone
cutting profile radially overlaps with the largest roller cone
cutting profile.
14. A drill bit, comprising: a bit body having a longitudinal bit
axis extending there through; a plurality of journals, extending
from the bit body, each journal having a journal axis extending
from a base of the journal through the length of the journal;
wherein the plurality of journals extend from the bit body such
that an acute angle ranging from about 15 degrees to about 25
degrees is formed between the journal axis and the bit axis; and a
roller cone rotatably mounted to each of the journals, wherein at
least one roller cone comprises a plurality of roller cone cutting
elements having planar cutting faces and at least one roller cone
comprises a plurality of roller cone cutting elements having
non-planar cutting faces, wherein the roller cone cutting elements
comprise a roller cone cutting profile.
15. The drill bit of claim 14, wherein the roller cones each have
an outer diameter, and wherein at least two of the outer diameters
are different.
16. The drill bit of claim 15, wherein each of the roller cone
cutting profiles radially overlaps with one another.
17. The drill bit of claim 16, wherein the plurality of roller cone
cutting elements having an installation back rake angle ranging
from about 10 degrees to about 90 degrees.
18. The drill bit of claim 16, wherein the plurality of roller cone
cutting elements having an installation side rake angle ranging
from about 0 degrees to about 60 degrees.
19. The drill bit of claims 17, wherein the plurality of roller
cone cutting elements having an equivalent back rake ranging from
about 10 degrees to about 30 degrees.
20. The drill bit of claims 17, wherein the plurality of roller
cone cutting elements having an equivalent side rake ranging from
about 0 degrees to about 30 degrees.
Description
BACKGROUND
[0001] Historically, there have been two main types of drill bits
used for drilling earth formations, drag bits and roller cone bits.
The term "drag bits" refers to those rotary drill bits with no
moving elements. Drag bits include those having cutting elements
attached to the bit body, which predominantly cut the formation by
a shearing action. Roller cone bits include one or more roller
cones rotatably mounted to the bit body. These roller cones have a
plurality of cutting elements attached thereto that crush, gouge,
and scrape rock at the bottom of a hole being drilled.
[0002] Bit type may be selected based on the primary nature of the
formation to be drilled. However, many formations have mixed
characteristics (i.e., the formation may include both hard and soft
zones), which may reduce the rate of penetration of a bit (or,
reduce the life of a selected bit) because the selected bit is not
as desirable for certain zones. For example, both milled tooth
roller cone bits and PDC bits can efficiently drill soft
formations, but PDC bits will often have a rate of penetration
several times higher than roller cone bits.
[0003] PDC Drill Bits
[0004] Drag bits, often referred to as "fixed cutter drill bits,"
include bits that have cutting elements attached to the bit body,
which may be a steel bit body or a matrix bit body formed from a
matrix material such as tungsten carbide surrounded by a binder
material. Drag bits may generally be defined as bits that have no
moving parts. However, there are different types and methods of
forming drag bits that are known in the art. For example, drag bits
having abrasive material, such as diamond, impregnated into the
surface of the material which forms the bit body are commonly
referred to as "impreg" bits. Drag bits having cutting elements
made of an ultra hard cutting surface layer or "table" (often made
of polycrystalline diamond material or polycrystalline boron
nitride material) deposited onto or otherwise bonded to a substrate
are known in the art as polycrystalline diamond compact ("PDC")
bits.
[0005] PDC bits drill soft formations easily, but they may
frequently be used to drill moderately hard or abrasive formations.
They cut rock formations with a shearing action using small cutters
that do not penetrate deeply into the formation. Because the
penetration depth is shallow, high rates of penetration are
achieved through relatively high bit rotational velocities.
[0006] Roller Cone Drill Bits
[0007] Roller cone drill bits may be used to drill formations that
fail more efficiently by crushing and gouging as opposed to
shearing. Roller cone drill bits are also used for heterogeneous
formations that initiate vibration in drag bits. Roller cone drill
bits include milled tooth bits and insert bits. Milled tooth roller
cone bits may be used to dill relatively soft formations, while
insert roller cone bits are suitable for medium or hard formations.
Roller cone drill bits include a bit body with a threaded pin
formed on the upper end of the bit body for connecting to a drill
string, and one or more legs extending from the lower end of the
bit body. The threaded pin end is adapted for assembly onto a drill
string for drilling oil wells or the like. Roller cone bits, on the
other hand, may have better steerability when building curve
section of a wellbore.
[0008] Hybrid Drill Bits
[0009] Both roller cone and PDC bits have their own advantages. Due
to the difference in cutting mechanisms and cutting element
materials, they are best suited for different drilling conditions.
Roller cone bits predominantly use a crushing mechanism in
drilling, which gives roller cone bits overall durability and
strong cutting ability (particularly when compared to previous bit
designs, including disc bits). PDC bits use a shearing mechanism
for cutting, which allows higher performance in soft formation
drilling than roller cone bits are able to achieve.
[0010] Thus, in drilling operations facing mixed formations, using
one type of drill bit over the other may not be adequate for the
entire operation. Hybrid drill bits that use a combination of one
or more crushing mechanisms and one or more shearing mechanisms
have been proposed previously. However, problems arise during the
design of these hybrid bits in trying to combine rolling cutters
and fixed blades within a limited amount of space.
SUMMARY OF DISCLOSURE
[0011] This summary is provided to introduce a selection of
concepts that are further described below in the detailed
description. This summary is not intended to identify key or
essential features of the claimed subject matter, nor is it
intended to be used as an aid in limiting the scope of the claimed
subject matter.
[0012] In one aspect, embodiments disclosed herein relate to a
drill bit including a bit body having a longitudinal bit axis
extending there through, a plurality of journals extending from the
bit body, each journal having a journal axis extending from a base
of the journal through the length of the journal, a roller cone
rotatably mounted to each of the journals, and at least one blade
protruding from the bit body center and extending radially outward
to less than an outer diameter of the drill bit.
[0013] In another aspect, embodiments disclosed herein relate to a
drill bit including a bit body having a longitudinal bit axis
extending there through, a plurality of journals, extending from
the bit body, and a roller cone rotatably mounted to each of the
journals, wherein at least one roller cone having a different outer
diameter than the others, wherein an offset angle ranging from
about 0 degrees to about 90 degrees is formed between a line
perpendicular to the bit axis and extending through the bit axis
and a center of a backface of the roller cone.
[0014] In yet another aspect, embodiments disclosed herein relate
to a drill bit including a bit body having a longitudinal bit axis
extending there through, a plurality of journals, extending from
the bit body, each journal having a journal axis extending from a
base of the journal through the length of the journal, wherein the
plurality of journals extend from the bit body such that an acute
angle ranging from about 15 degrees to about 25 degrees is formed
between the journal axis and the bit axis. The drill bit further
includes a roller cone rotatably mounted to each of the journals,
wherein at least one roller cone comprises a plurality of roller
cone cutting elements having planar cutting faces and at least one
roller cone comprises a plurality of roller cone cutting elements
having non-planar cutting faces, wherein the roller cone cutting
elements comprise a roller cone cutting profile.
[0015] Other aspects and advantages of the claimed subject matter
will be apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0016] FIG. 1 is a perspective view of a bit according to
embodiments of the present disclosure.
[0017] FIG. 2 shows a side view of the Cartesian coordinate system
and roller cone orientation according to one embodiment of the
present disclosure.
[0018] FIG. 3 shows a top view of the Cartesian coordinate system
and roller cone orientation according to one embodiment of the
present disclosure.
[0019] FIG. 4 is a schematic of a roller cone retained on a journal
according to one embodiment of the present disclosure.
[0020] FIG. 5 is a schematic side view of a roller cone cutting
element having back rake according to embodiments of the present
disclosure.
[0021] FIG. 6 is a schematic top view of a roller cone cutting
element having side rake according to embodiments of the present
disclosure.
[0022] FIG. 7 is a perspective view of a bit according to
embodiments of the present disclosure.
[0023] FIG. 8 is a top view of roller cones according to
embodiments of the present disclosure.
[0024] FIG. 9 is a perspective view of a bit according to
embodiments of the present disclosure.
DETAILED DESCRIPTION
[0025] Embodiments disclosed herein relate generally to drill bits.
In particular, embodiments disclosed herein relate to roller cone
drill bits having radially offset journals such that the roller
cones engage and cut different regions of a borehole.
[0026] Referring to FIG. 1, a perspective view of a roller cone
drill bit according to one embodiment of the present disclosure is
shown. As shown in FIG. 1, a roller cone drill bit 130 includes a
bit body 139 having a longitudinal axis 110 extending axially there
through. At one end of the bit 130 is a threaded pin end (not
shown) for coupling bit 130 to a drill string (not shown). At the
other end of the bit (generally oriented as the lower end when the
bit is installed on a drill string within a well) is the cutting
end of bit 130, the side of the bit substantially facing the
direction of drilling and that may engage the bottom hole of the
wellbore being drilled. In particular, bit body 139 terminates at
its cutting end with at least one blade 126 protruding from the bit
body center and a plurality of journals 135. Each journal 135 may
be integral with the rest of bit body 139, or in other embodiments,
may have separately formed and attached to the bit body 139. Each
journal 135 has a journal axis extending from the base of the
journal through the length of the journal. On each journal 135, a
roller cone 136 having a frustoconical shape is rotatably mounted.
Each roller cone 136 has disposed thereon a plurality of rows of
roller cone cutting elements 137: at least two rows of cutting
elements 137 in some embodiments or at least four or five rows of
cutting elements in other embodiments. The at least one blade
protruding from the bit body center has disposed thereon a
plurality of blade cutting elements 127.
[0027] In this embodiment, the rolling cone cutting elements 137
and the blade cutting elements 127 have planar cutting faces.
However, different types of cutting elements may be used on the
blades 126 and roller cones 136. For example, as shown in FIG. 11
(which is discussed below), some of the rolling cone cutting
elements may have non-planar cutting faces. Rolling cones having
cutting elements with planar cutting faces are also known as
shearing rolling cones since the cutting elements shear the
formation. Alternatively, rolling cones having cutting elements
with non-planar cutting faces are also known as crushing rolling
cones since the cutting elements crush/fracture the formation.
Cutting elements used with hybrid drill bits of the present
disclosure may include polycrystalline diamond compacts (PDCs),
diamond grit impregnated inserts ("grit hot-pressed inserts"
(GHIs), natural diamond, milled steel teeth, tungsten carbide
inserts (TCIs), diamond enhanced inserts (DEIs), or conical shaped
(or other substantially pointed) cutting elements.
[0028] As discussed above, a roller cone may be rotatably mounted
to journals extending from a bit body. Roller cones may include
bodies having rounded, conical, or disc shape and a plurality of
cutting elements disposed thereon. For example, referring again to
FIG. 1, a roller cone 136 has a frustoconical shaped body with a
plurality of cutting elements 137 disposed thereon. Roller cone
sizes may differ with respect to one or more of a roller cone's
outer radius, nose projection, radius of curvature, etc. As shown,
the roller cone 136 has three circumferential rows of cutting
elements 137. However, other embodiments may have more or less than
three rows of cutting elements. Further, roller cones may have
cutting elements disposed thereon in arrangements other than in
rows.
[0029] Further, according to some embodiments, the plurality of
roller cones 136 may be arranged in such a manner that they engage
with and cut the nose and shoulder regions of a bottom hole, but do
not engage with the center of a bottom hole whereas the at least
one blade 126 may engage and cut the center of a bottom hole. The
blade cutting elements 127 form a blade cutting profile, and the
roller cone cutting elements 137 form a roller cone cutting
profile. As used herein, a cutting profile (e.g., a blade cutting
profile and a roller cone cutting profile) refers to the profile or
outline of cutting elements as they would appear in rotated view,
i.e., when the bit rotated about its longitudinal axis and the
roller cones are rotated about their rotational axes. The extent of
overlap between roller cone 136 cutting profile and blade 126
cutting profile depends on the radial extension of the at least one
blade 126, each blade 126 extending to less than an outer diameter
of the drill bit 130.
[0030] Further, journals may extend from the bit body at different
angles with respect to the longitudinal axis of the bit, as
compared to a conventional roller cone bit. Specifically, as shown
in FIG. 1, in addition to being pointed axially downward (away from
the pin end of the bit), the cones 136 may also be pivoted such
that the tip or nose of the cone is pointing radially outward of
the bit center. For example, greater details of the orientation are
shown in FIGS. 2 and 3, which show a side view of the Cartesian
coordinate system and cone orientation and a top view,
respectively, where the z-axis is the bit axis, the y-axis extends
from the bit axis through the center of the backface of the cone
(represented with a circled "x"), and the x-axis extends from the
bit axis perpendicular to the y axis and z-axis. Referring to FIG.
2, a cone 136 is mounted on a journal (not shown). The journal
extends downward and at an angle .beta., which may be referred to
as the journal angle, with respect to the bit or z-axis. In one or
more embodiments, angle .beta. may range from about -90 degrees to
about 90 degrees. In more specific embodiments, angle .beta. may
have a lower limit of any of at least -90, -60, -30, 0, or 30
degrees, and an upper limit of any of -30, 0, 30, 60, or 90
degrees, where any lower limit can be used in combination with any
upper limit. As also shown in FIGS. 1 and 2, the cones (and
journals) may extend from a leg (139 in FIG. 1) that extends from
the bit body 139. The extension of the legs is represented in FIG.
2 as length S (the length between point B and point C), which may
extend, for example, a distance ranging from about 1/4 of the
radius of drill bit 130 to about 3/4 of the radius of drill bit
130. Further, cone radius (the length between point C and point D)
may range from about 1/4 of the radius of drill bit 130 to about a
full radius of drill bit 130.
[0031] FIG. 3 shows a top view of the coordinate system in FIG. 2,
where points A, B, C, and D shown in FIG. 2 are also shown in FIG.
3 based on their location in the Cartesian coordinate system. As
shown in FIG. 3, the leg 140 (extending from B to C) also has a
horizontal offset Rb from the bit or z-axis to the cone axis 140
(illustrated as the length between point O on the z-axis and point
A on the cone axis 140), according to an embodiment. In one or more
embodiments, such horizontal offset may range from about 1/4 of the
radius of drill bit 130 to about 1/2 of the radius of drill bit
130. In addition, as mentioned above, the cones 136 are pivoted
relative to the bit axis Z to form a cone offset angle. The cone
offset angle may be defined as the angle a that is between the
backface of the cone 136 and the y axis, which, as mentioned above,
is defined as the axis (perpendicular to the bit axis) that extends
through the bit axis and the center of the backface of the cone
136. In one or more embodiments, the cone offset angle, as defined
herein, may range from about 0 to about 180 degrees. In more
specific embodiments, cone offset angle may have a lower limit of
any of at least 0, 15, 30, 45, or 60 degrees, and an upper limit of
any of 60, 90, 120, 150, or 180 degrees, where any lower limit can
be used in combination with any upper limit.
[0032] Additionally in accordance with various embodiments of the
present disclosure, as shown in FIGS. 4-5 together, roller cone 136
may be retained on journal 135 through a ball bearing retainer
system. In an embodiment, a plurality of bearing balls 440 are
fitted into complementary ball races 437, 439 in the journal 135
and cone 136, respectively, to retain cone 136 on journal 135. A
cone 136 is first fitted on the journal 135, and then the bearing
balls 440 are inserted through ball passage (not shown) to fit in
the space between ball races 437 and 439. Balls 440 are retained in
ball races 437 and 439 by a ball retainer, which is inserted into
passage (not shown) after balls 440, and then secured in place
(such as by a plug welded in place). The balls 440 carry any thrust
loads tending to remove the cone 136 from the journal 135 and
thereby retain the cone 136 on the journal 135. Lubricant or grease
is retained in the bearing structure by a resilient seal 452 within
a seal gland formed between the cone 136 and journal 135.
[0033] Due to the orientation of the cone 136, disclosed above, the
cutting elements used on roller cones may have a unique orientation
for roller cone cutting elements so as to enable the cutting
elements to shear the formation. Specifically, cutting elements may
be oriented or installed on the cones with a particular back rake
and/or side rake. For example, referring now to FIG. 5, a schematic
side view of a roller cone cutting element 501 having back rake is
shown within the Cartesian coordinate system defined above in FIGS.
2 and 3. The roller cone cutting element 501 has a cutter axis 502
extending therethrough where the installation back rake 511 angle
is defined as the angle with respect to the roller cone surface, or
the angle subtended between the cutter axis 502 and a line parallel
to the axis of the roller cone 503. In one or more embodiments, the
installation back rake angle, as defined herein, may range from
about 0 degrees to about 180 degrees. In more specific embodiments,
the installation back rake angle may have a lower limit of any of
at least 0, 15, 30, 45, or 60 degrees, and an upper limit of any of
60, 90, 120, 150, or 180 degrees, where any lower limit can be used
in combination with any upper limit.
[0034] Equivalent back rake 520 is defined as the resultant of
installation back rake angle with the combination of journal angle,
and measured by the journal angle .beta. less the installation back
rake 511 angle. As previously discussed, the journal angle forms an
angle .beta., between a longitudinal axis 510 of the bit and the
center of roller cone back surface 509. According to some
embodiments, the equivalent back rake angle, as defined herein, may
range from about 10 degrees to about 30 degrees. In more specific
embodiments, the equivalent back rake angle may range from about 15
to about 25 degrees.
[0035] Referring now to FIG. 6, a schematic top view of a roller
cone cutting element 501 having side rake is shown in the Cartesian
coordinate system set forth in FIG. 3 above, according to an
embodiment. The roller cone cutting element 501 has a cutter axis
502 extending therethrough where installation side rake angle 605
is defined with respect to the roller cone axis, or the angle
subtended between the cutter axis 502 and the roller cone axis 603
(extending through the center of roller cone back surface 509). The
engage point velocity 607 is defined as the velocity of the lowest,
engaged point of the roller cone to the formation. In one or more
embodiments, the installation side rake angle, as defined herein,
may range from about 0 degrees to about 60 degrees. In more
specific embodiments, the installation side rake angle may range
from about 15 degrees to about 45 degrees.
[0036] Equivalent side rake 609 is defined as the resultant of
installation side rake angle with the combination of journal
offset, and measured by the angle formed between the engage point
velocity 607 and the roller cone axis 603 less the installation
side rake 605 angle. As previously discussed and shown in FIG. 4,
journal offset forms an angle .alpha., between the backface of the
cone 136 and the y axis. According to some embodiments, the
equivalent side rake angle, as defined herein, may range from about
0 degrees to about 45 degrees. In more specific embodiments, the
equivalent side rake angle may range from about 15 degrees to about
25 degrees. When viewed along the longitudinal axis of the bit, a
negative side rake results from counterclockwise rotation of a
cutting element, and a positive side rake, from clockwise
rotation.
[0037] Referring to FIG. 7, a perspective view of a roller cone
drill bit according to another embodiment of the present disclosure
is shown. As shown in FIG. 7, a roller cone drill bit 730 includes
a bit body 732 having a longitudinal axis 710 extending axially
there through. In particular, bit body 732 terminates at its upper
end into a plurality of journals 735, each having a journal axis
extending from the base of the journal through the length of the
journal. In an embodiment, each journal is integral with the rest
of bit body 732. On each journal 735, a roller cone 736A/B having a
frustoconical shape is rotatably mounted. Each roller cone 736A/B
has disposed thereon a plurality of rows of roller cone cutting
elements 737: at least two rows of cutting elements 737 in some
embodiments or at least four or five rows of cutting elements in
other embodiments.
[0038] In such embodiments, the rolling cone cutting elements 737
have planar cutting faces, such as those conventionally referred to
as polycrystalline diamond compact (PDC) cutters. As discussed
above, rolling cones having cutting elements with planar cutting
faces are also known as shearing rolling cones since the cutting
elements shear the formation. Alternatively, rolling cones having
cutting elements with non-planar cutting faces are also known as
crushing rolling cones since the cutting elements crush/fracture
the formation. For example, in some embodiments, rolling cones
having cutting elements with non-planar cutting faces may have a
pointed, or conical shaped, dome shaped, chisel shaped, and/or
saddle shaped cutting face geometry. In some embodiments, rolling
cones may have a combination of cutting elements with planar and
non-planar cutting faces. Cutting elements used with hybrid drill
bits of the present disclosure may include polycrystalline diamond
compacts (PDCs), diamond grit impregnated inserts ("grit
hot-pressed inserts" (GHIs), natural diamond, milled steel teeth,
tungsten carbide inserts (TCIs), diamond enhanced inserts (DEIs),
or conical shaped (or other substantially pointed) cutting
elements.
[0039] According to various embodiments of the present disclosure,
roller cone drill bit 730 may include a plurality of gauge cutters
740 disposed on the bit body 732 and along a gauge region of the
bit which extends parallel to bit axis 710 at the outer radial
periphery of the overall bit cutting profile. In such embodiments,
gauge cutters 740 are arranged to engage a side wall of the
formation. The plurality of gauge cutters 740 may include rotatable
and non-rotatable cutting elements having planar and non-planar
cutting faces. In some embodiments, gauge cutters 740 may be
substantially similar in material, shape, and size as roller cone
cutting elements 737. Further, gauge cutters may be oriented or
installed on the bit body 732 with a particular back rake and/or
side rake angle.
[0040] Additionally in accordance with various embodiments of the
present disclosure, at least one roller cone has a different outer
diameter than the others. As shown in FIGS. 7-9, roller cones 736A
have a larger outer diameter than roller cones 736B, according to
an embodiment. In some embodiments, the cutting profile of the
smallest roller cone may radially overlap with the cutting profile
of the largest roller cone cutting. In such embodiments, the
cutting profile of the smallest roller cone may extend an axial
distance greater than the cutting profile of the largest roller
cone. For example, the cutting profile of the smallest roller cone
may extend an axial distance ranging from about 1/4 of the radius
of drill bit 730 to about 3/4 of the radius of drill bit 730
further from the bit body than the cutting profile of the largest
roller cone.
[0041] One of ordinary skill in the art will appreciate that a
roller cone may be characterized by its diameter to height ratio.
Referring to FIGS. 7 and 9, embodiments of the present disclosure
may include roller cones 736A/B having a diameter to height ratio
ranging from about 4:1 to about 2:1.
[0042] Referring to FIG. 8, a top view of two roller cones with
different outer diameters is shown. As shown in FIG. 8, smaller
roller cone 836B has outer diameter A and cone height B whereas
larger roller cone 836A has outer diameter C and cone height D.
However, in particular embodiments, the diameter to height ratio of
C:D may be about 1 to about 2 times that of the diameter to height
ratio of A:B (not shown). Further, the plurality of roller cones
836A and 836B may be arranged in such a manner that roller cone
836B engages with and cuts the nose and shoulder regions of a
bottom hole whereas roller cone 836A engages with and cuts the
center of a bottom hole.
[0043] Referring to FIG. 9, a perspective view of a roller cone
drill bit according to yet another embodiment of the present
disclosure is shown. This embodiment is similar to the embodiment
disclosed previously and illustrated in FIG. 7; however, at least
one roller cone has cutting elements with planar cutting faces
while the other roller cones have non-planar cutting faces disposed
thereon.
[0044] As shown in FIG. 9, a roller cone drill bit 930 includes a
bit body 932 having a longitudinal axis 910 extending axially there
through. In particular, bit body 932 terminates at its upper end
into a plurality of journals 935, each having a journal axis
extending from the base of the journal through the length of the
journal. In an embodiment, each journal is integral with the rest
of bit body 932 On each journal 935, a roller cone 936A/B having a
frustoconical shape is rotatably mounted. At least one roller cone
936A/B has a different outer diameter than the others. Each roller
cone 936AB has disposed thereon a plurality of rows of roller cone
cutting elements 937A/B: at least two rows of cutting elements
937A/B in some embodiments or at least four or five rows of cutting
elements in other embodiments. In this embodiment, at least one
roller cone 936A has cutting elements 937A with planar cutting
faces. In an embodiment, at least one roller cone 936B has cutting
elements 937B with non-planar cutting faces. The planar cutting
elements 937A on larger roller cones 936A shear the formation,
while the non-planar cutting elements 937B on smaller roller cones
936B crush the formation, according to an embodiment. The combined
shearing and crushing action may improve bit performance under
certain conditions.
[0045] Though two sizes of roller cone are illustrated in each of
FIGS. 7 and 9, the drill bit may have more than two sizes of roller
cones. The differently-sized roller cones may have a variety of
configurations. In an embodiment, there are an even number of each
different size of roller cone, so that pairs of each size of roller
cone may be configured in a symmetric manner with respect to the
bit axis in order to balance the bit and minimize bit vibrations
while drilling. In addition, each roller cone may have a variety of
orientations in order to target different portions of the
formation. For example, a roller cone may be oriented so that its
cutting elements contact at least one of: the nose region, the
shoulder region, or the center region of the bottom hole.
[0046] While FIG. 9 shows planar cutting elements 937A on larger
roller cones 936A and non-planar cutting elements 937B on smaller
roller cones 936B, in other embodiments a variety of cutting
element arrangements may be used. For example, one or more larger
roller cones may have non-planar cutting elements, while one or
more smaller roller cones may have planar cutting elements. In
another embodiment, one or more roller cones may each have a
combination of non-planar and planar cutting elements. As described
above with respect to FIGS. 5 and 6, the cutting elements--whether
planar or non-planar--may have a variety of back rake and side rake
orientations. In an embodiment, bit 932 includes gauge cutting
elements (not shown), similar to that shown and described with
respect to gauge cutters 740 in FIG. 7.
[0047] Although only a few example embodiments have been described
in detail above, those skilled in the art will readily appreciate
that many modifications are possible in the example embodiments
without materially departing from this invention. Accordingly, all
such modifications are intended to be included within the scope of
this disclosure as defined in the following claims.
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