U.S. patent application number 11/040141 was filed with the patent office on 2005-08-18 for cutting structure for single roller cone drill bit.
Invention is credited to Witman, George B. IV, Yong, Zhou.
Application Number | 20050178587 11/040141 |
Document ID | / |
Family ID | 34273103 |
Filed Date | 2005-08-18 |
United States Patent
Application |
20050178587 |
Kind Code |
A1 |
Witman, George B. IV ; et
al. |
August 18, 2005 |
Cutting structure for single roller cone drill bit
Abstract
A roller cone drill bit is disclosed which includes a bit body
adapted to be coupled to a drill string. A bearing journal depends
from the bit body. A single roller cone is rotatably attached to
the bearing journal. The roller cone is formed from steel and
includes a plurality of cutting elements disposed at selected
positions about the cone. At least one of the cutting elements has
an extending body which has a first end coupled to the roller cone
and a distal end extending away from the cone. The extending body
is formed from steel. A super hard element is coupled to the distal
end of the extending body to form a super hard cutting face for the
cutting element.
Inventors: |
Witman, George B. IV;
(Midland, TX) ; Yong, Zhou; (Spring, TX) |
Correspondence
Address: |
SMITH INTERNATIONAL INC.
16740 HARDY
HOUSTON
TX
77032
US
|
Family ID: |
34273103 |
Appl. No.: |
11/040141 |
Filed: |
January 21, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60538745 |
Jan 23, 2004 |
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Current U.S.
Class: |
175/365 |
Current CPC
Class: |
E21B 10/16 20130101 |
Class at
Publication: |
175/365 |
International
Class: |
E21B 010/08 |
Claims
What is claimed is:
1. A drill bit, comprising: a single rotatable cone; and at least
one cutting element disposed on the cone, the at least one cutting
element comprising: an extending body formed of steel and having a
first end connected to the cone and a distal end extending away
from the cone, a super hard element coupled to the distal end of
the extending body and forming at least part of a cutting surface
of the cutting element.
2. The bit of claim 1, wherein the extending body comprises a
milled steel tooth formed on the cone.
3. The bit of claim 1, wherein the extending body comprises an
insert body disposed in a socket formed in the cone.
4. The bit of claim 1, wherein the at least one cutting element is
disposed in a bottom contacting zone on the cone.
5. The bit of claim 1, wherein the extending body has an extension
length of at least about 12 mm.
6. The bit of claim 1, wherein the super hard element extends from
the distal end of the extending body by at least about 2 mm.
7. The bit of claim 1, wherein the super hard element comprises at
least one selected from the group of diamond, cubic boron nitride,
and carbide.
8. The bit of claim 1, wherein the super hard element comprises a
body of super hard material bonded to a substrate.
9. The bit of claim 1, wherein the super hard element is press fit
in a socket formed in the extending body.
10. The bit of claim 1, wherein the super hard element is coupled
to the extending body by brazing.
11. The bit of claim 1, wherein the super hard element comprises a
generally convex shaped surface.
12. The bit of claim 1, wherein the extended body is tapered at the
distal end.
13. The bit of claim 1, further comprising a layer of hardfacing
disposed on at least a portion of the extending body.
14. The bit of claim 1, further comprising: a bit body adapted to
be coupled to a drill string; and a bearing journal depending from
the bit body, wherein the single roller cone is formed of steel and
rotatably mounted on the bearing journal, the at least one cutting
element is disposed on the roller cone in a bottom contacting zone,
and the extending body of the at least one cutting element
comprises a milled steel tooth formed on the cone.
15. The bit of claim 13, wherein the super hard element is disposed
in a socket formed at the distal end of the extending body, the
extending body extends from the cone surface by at least about 10
mm, and the super hard element extends from the distal end of the
extending body by at least about 2 mm.
16. The bit of claim 1, further comprising: a bit body adapted to
be coupled to a drill string; a bearing journal depending from the
bit body, wherein the single roller cone is formed of steel and
rotatably mounted on the bearing journal, and the at least one
cutting element is disposed in a bottom contacting zone on the
cone, the at least one cutting element comprising an insert
disposed in a socket formed on the cone.
17. The bit of claim 16, wherein the super hard element is disposed
in a socket formed at the distal end of the extending body, the
extending body extends from the cone surface by at least about 10
mm and the super hard element extends from the distal end of the
extending body by at least about 2 mm.
18. A method for making a drill bit, comprising: rotationally
coupling a single roller cone to a journal depending from a drill
bit body, providing at a selected position on the cone at least one
cutting element having an extending body formed from steel and a
super hard element coupled to a distal end of the extending body
forming at least a part of an outer surface of the cutting
element.
19. The method of claim 18, further comprising covering at least a
portion of the outer surface of the extended body with hardfacing
material.
20. A drill bit, comprising: a single rotatable cone; and a
plurality of cutting elements disposed on the cone, the plurality
of cutting elements comprising a first set of cutting elements
disposed in a first region of the cone and a second set of cutting
elements disposed in a second region of the cone, wherein at least
one of the cutting elements in the first region comprises: an
extending body formed of steel and having a first end connected to
the cone and a distal end extending away from the cone, a super
hard element coupled to the distal end of the extending body and
forming at least part of a cutting surface of the cutting element.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(e) of U.S. Provisional Patent Application No. 60/538,745
filed on Jan. 23, 2004, titled "Cutting Structure for Single Roller
Cone Drill Bit," which is now incorporated by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The invention relates generally to the field of roller cone
("rock") bits used to drill wellbores through earth formations.
More specifically, the invention is related to the structure of
cutting elements used in roller cone bits having a single roller
cone.
[0005] 2. Background Art
[0006] Roller cone drill bits are commonly used in the oil and gas
industry to drill well bores through earth formations. One example
of a conventional drilling system used to drill a well bore is
shown in FIG. 1. The drilling system includes a drilling rig 10
used to turn a drill string 12 which extends downward into a
wellbore 14. Connected to the end of the drill string 12 is a
roller cone drill bit 20.
[0007] The most common type of roller cone bit is a three cone bit
(illustrated at 20 in FIG. 1). A three cone bit 20 includes a bit
body adapted to be coupled to a drilling tool assembly or "drill
string" which rotates the bit as it is pressed axially into the
formations being drilled. The bit body includes three legs, each
having a bearing journal thereon. A generally conical roller cone
is rotatably mounted to each bearing journal. During drilling, the
roller cones are pressed against a formation and rotate about the
respective journals while the bit is rotated under an axial load on
the formation. A plurality of cutting elements is disposed on each
of the roller cones, typically in rows. The cutting elements extend
from the surface of the cones to engage and break up formation as
the bit is rotated.
[0008] One particular type of roller cone drill bit is a single
cone bit, which includes only one leg, one bearing journal and one
roller cone rotatably mounted on the bearing journal. The drill
diameter of the single roller cone bit is substantially concentric
with an axis of rotation of the drill bit. This type of drill bit
has been shown to be particularly useful in drilling small diameter
wellbores (e.g., less than about 4 to 6 inches [10 to 15 cm])
because the bearing structure can be larger relative to the
diameter of the drilled hole when the bit has only one concentric
roller. This is in contrast to the typical three cone bit, in which
each journal must be smaller relative to the drilled hole diameter.
Having a significantly larger radial bearing for the same bit
diameter than a comparable three roller cone bit allows for higher
loads to be placed on the single cone bit to increase the rate of
penetration of the drill bit.
[0009] One of the limitations of single cone roller bits is that
the cutting elements tend to experience greater wear over time due
to shearing action, compared to cutting elements on a two or three
cone bits. The cutting elements on the single cone bit undergo as
much as an order of magnitude more shear than do the cutting
elements on a conventional two or three cone bit. Large amounts of
shear on cutting elements of single cone bits become apparent when
looking at the bottomhole patterns of each type of bit. Single
roller cone bits typically drill out a "bowl" shaped bottomhole
geometry. The cutting elements on the single cone bit generally
shear the formation creating multiple grooves laid out in
hemispherically projected hypotrochoids. In contrast, a two or
three cone bit generates a series of individual craters or
indentations during drilling. Shearing rock typically causes more
wear on a cutting element than impacting the rock to compressively
fail it. The cutting elements on single cone bits also go through
large changes in their direction of motion during drilling,
typically anywhere from 100 to 360 degrees. Such changes require
special consideration in design.
[0010] The single roller cone drill bit efficiently drills the
portion of the wellbore proximate the center of the bottom hole
because a large portion of the cutting structure near the center of
the hole remains in moving contact with the formation during
drilling. However, as a result, the wear of the cutting elements on
a single cone bit is typically not uniform. In general, cutting
elements in the zone that cuts the bottom of a borehole being
drilled typically maintain substantially constant contact with the
formation during drilling, and cutting elements in the zone that
primarily contacts the side wall of the bore hole have more
intermittent contact with the formation. Therefore, the cutting
elements near the bottom are worn more quickly. As cutting elements
are worn and became dull, the cutting efficiency of the bit
significantly declines and the effective life of the bit is unduly
limited. This is further discussed in U.S. Pat. No. 6,119,797
entitled "Single Cone Earth Boring Bit", which is incorporated
herein by reference.
[0011] Cutting element wear in the zone that primarily contacts the
side wall is also an important consideration in bit design because
an essential performance aspect of any drill bit is its ability to
drill a wellbore having the full nominal diameter of the drill bit
from the time the bit is first used to the time it becomes worn and
must be replaced. In the case of a single roller cone bit, several
of the cutting elements on the single roller cone eventually engage
the wellbore wall at the gage diameter. As the cutting structure
wears, the drilled diameter of the wellbore may be substantially
reduced. The reduction in wellbore diameter can be an intolerable
condition and may require reaming with subsequent bits or the use
of reamers or other devices designed to enlarge the wellbore
diameter. Moreover, the reduced wellbore diameter will decrease the
flow area available for the proper circulation of drilling fluids
and bit cuttings. The use of bits, reamers, or other devices to
ream the wellbore can incur substantial cost if the bottom hole
assembly must be tripped in and out of the hole several times to
complete the procedure.
[0012] Drill bit life and efficiency are of great importance
because the rate of penetration (ROP) of the bit through earth
formations is related to the wear condition of the bit.
Accordingly, various methods have been used to provide abrasion
protection for drill bits in general, and specifically for roller
cones and cutting elements. For example, roller cones, cutting
elements, and other bit surfaces have been coated with hardfacing
material to provide more abrasion resistant surfaces. Further,
specialized cutting element insert materials have been developed to
optimize longevity of the cutting elements. While these methods of
protection have met with some success, wear is still a problem for
single cone bits.
[0013] To address the problems of wear associated with single cone
bits, diamond enhanced inserts consisting of a polycrystalline
diamond layer bonded to a tungsten carbide/cobalt substrate in a
HTHP process have been proposed and used as cutting elements for
single cone bits. Examples of diamond enhanced inserts and other
super hard inserts are further described in U.S. Pat. Nos.
4,525,178, 4,606,106, 4,797,241, 4,650,776, 5,271,749, 5,326,380
and incorporated herein by reference. Such inserts have been used
on the nose portion of a cone as a "bearing surface" or on the
entire cone as cutting elements. Due to the prohibitive cost of
large diamond enhanced inserts, inserts used on single cone bits
have been generally small with very limited extensions from the
cone surface. The short extension of diamond enhanced inserts
limits penetration of the formation and cuttings removal during
drilling. Thus, while bit life has been improved, the rate of
penetration of these bits has been unduly limited. To over come
this limitation, larger diamond enhanced inserts with longer
extensions are desired, but the high cost and fragility associated
with these larger diamond enhanced inserts have shown them to be
unsuitable and unfeasible for commercial products.
[0014] A cutting element structure for a single cone roller bit
that provides wear resistance without sacrificing toughness and/or
cutter extension is desired.
SUMMARY OF INVENTION
[0015] In one aspect, the present invention relates to single
roller cone drill bit. The drill bit includes a single rotatable
cone formed from steel and having at least one cutting element
disposed at a selected position thereon. The at least one cutting
element includes an extending body formed from steel which has a
first end coupled to the cone and a distal end extending away from
the cone. A super hard element is coupled to the distal end of the
extending body to form at least a portion of a cutting surface for
the cutting element.
[0016] In another aspect, the invention relates to a method for
making a drill bit. The method includes rotationally coupling a
roller cone to a journal of a single roller cone drill bit body,
and providing at a selected position on the cone a cutting element
comprising an extending body formed from steel and a super hard
element coupled to a distal end of the extending body to form at
least a part of an outer surface of the insert.
[0017] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0018] FIG. 1 shows one example of a conventional drilling
system.
[0019] FIG. 2 shows a generalized cut away view of a single roller
cone drill bit.
[0020] FIG. 3 shows a cone of a single cone drill bit having a
cutting structure in accordance with one embodiment of the present
invention.
[0021] FIG. 4 shows a single cone drill bit having a cutting
structure in accordance with another embodiment of the present
invention.
[0022] FIG. 5 shows an enlarged cross-section view of a cutting
element in accordance with one embodiment of the present invention
shown in FIG. 4.
[0023] FIG. 5A shows another example of a super hard element in
accordance with an embodiment of the present invention.
[0024] FIG. 6 shows another example of a single cone bit in
accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
[0025] A general structure for a single cone roller cone drill bit
which can be made according to various embodiments of the invention
is shown in a cut away view in FIG. 2. The bit 22 includes a body
23 made of steel or other high strength material. The body 23
includes a coupling 24 at one end adapted to join the bit body 23
to a drill string (not shown) for rotating the bit 22 during
drilling. The bit body 23 may also include gage protection pads 25
at circumferentially spaced apart positions about the bit body 23.
The gage protection pads 25 may include gage protection inserts 26
in some embodiments. The gage protection pads 25 if used, extend to
a drill diameter 27 of the bit 22.
[0026] Another end of the bit body 23 includes a bearing journal
23A to which a single roller cone 28 is rotatably mounted. In some
embodiments, the cone 28 may be locked onto the journal 23A by
locking balls 23B disposed in the corresponding grooves on the
outer surface of the journal 23A and the interior surface of the
cone 28. The means by which the cone 28 is rotatably locked onto
the journal 23A is not meant to limit the scope of the invention.
The cone 28 is formed from steel or other high strength material
and may be covered about its exterior surface with hardfacing or
similar material intended to reduce abrasive wear of the cone 28.
In some embodiments, the cone 28 will include a seal 29 disposed to
exclude fluid and debris from entering the space between the inside
of the cone 28 and the journal 23A. Such seals are well known in
the art.
[0027] The cone 28 includes a plurality of cutting elements 31, 32
thereon at selected positions. The journal 23A depends from the bit
body 23 such that it defines an angle .alpha. between the
rotational axis 33 of the journal 23A and the rotational axis 34 of
the bit 22. The size of this angle .alpha. will depend on features
such as the nature of the earth formation being drilled by the bit.
Nonetheless, because the bit body 23 and the cone 28 rotate about
different axes, the motion of the cutting elements 31, 32 during
drilling can be roughly defined as falling within a wall contacting
zone 35, in which cutting elements 32 located therein at least
intermittently contact the outer diameter (wall) of the wellbore,
and a bottom contacting zone 36, in which cutting elements 31
located therein are in substantially continuous contact with the
earth formations, and generally do not contact the outer diameter
(wall) of the wellbore during drilling.
[0028] The cutting elements 32 in the wall contacting zone 35
define the drill diameter of the bit. Having cutting elements for
the wall contacting zone 35 which provide good toughness, minimize
axial wear, and maintain suitable cutting action against formation
being drilled, can extend the life of the bit, while helping to
provide relatively high rates of penetration. The cutting elements
31 in the bottom contacting zone 36 significantly effect on the
rate of penetration through formations. Having cutting elements in
the bottom contacting zone 36 which minimize axial wear and provide
adequate strength and toughness that allows for increase cutting
element extension to aggressively cut through formations, can also
extend the life of the bit and provide for increased rates of
penetration. Issues related to single roller cone drill bits are
further described in U.S. application Ser. No. 10/407,922, titled
"Single Cone Rock Bit Having Inserts Adapted to Maintain Hole Gage
During Drilling" and U.S. patent application Ser. No. 10/498,822,
titled "Cutting Element Structure for Single Roller Cone Bit,"
which are both assigned to the assignee of the present invention
and incorporated herein by reference.
[0029] In accordance with one aspect of the present invention, FIG.
3 shows an example cutting structure for a single cone bit. The
roller cone 42 of the bit is formed from steel and includes a
plurality of cutting elements 43 formed on the outer surface of the
cone at selected positions. The cutting elements 43 are generally
arranged in rows. At least one of the cutting elements 43 (cutting
element 44) comprises a milled steel tooth having a steel extending
body 45 formed on the outer surface of the cone 42. The extending
body 45 extends outward from the surface of the cone 42 with an
axial length (primary extension length), b. The cutting element 44
further includes a super hard element 46 press fit into a socket
(not shown separately) formed at a distal end of the extending body
45. The super hard element 46 is positioned to extend from a
surface of the extending body 45 by a distance (secondary extension
length), t, such that it engages with and cuts through earth
formations during drilling. The super hard element 46 is exposed at
the distal end of the extending body 45 to provide a super hard and
wear resistant cutting face for the cutting element 44.
[0030] Also, as shown in FIG. 3, in one or more embodiments of the
invention the extending body 45 may be configured to extend
substantially from the cone surface to form an aggressive cutting
structure for the bit. The distal end of the extending body 45 may
truncate to a substantially planar surface. The exposed surface of
the super hard element 46 which forms the cutting face of the
cutting element 44 may have a convex shape with a truncated,
substantially planar tip. The other cutting elements 43 on the cone
42 may have a configuration similar to that of cutting element
44.
[0031] The cutting structure shown in FIG. 3 is just one example of
a cutting structure for a single cone bit in accordance with the
present invention. In other embodiments, the cutting elements may
comprise inserts instead of teeth and may have different
configurations depending on their position on the cone. The super
hard material may be disposed at different selected positions
proximal the distal end of the cutting element. Also, in other
embodiments, different types of cutting elements may be included at
selected locations on the cone. The cutting elements may have
different abrasion resistances, such as higher near the nose of the
cone than near the gage, to provide for more even wear of the
cutting elements during drilling. Having cutting elements
comprising an extending body formed from steel with a super hard
cutting face, advantageously, provides greater impact toughness
than a fully diamond enhanced insert without sacrificing abrasive
resistance at the cutting face, and allows for the use of cutting
elements having greater extensions.
[0032] For example, another embodiment in accordance with aspects
of the present invention is shown in FIG. 4. The bit 50 includes a
bit body 52 and a roller cone 54 rotatably coupled to the bit body
52. Cutting elements 56, 57, 58 are disposed at selected locations
on the cone 54 and generally arranged in circumferential rows. At
least one of the cutting elements 56 comprises an insert disposed
in a socket formed in the surface of the cone 54. In the example
shown, the cutting element 56 and a plurality of other similarly
configured cutting elements are disposed in the bottom contacting
zone (36 in FIG. 2) of the bit 50. The insert (cutting element 56)
includes an extending body 56A formed of steel and having a first
end coupled to the cone 54 and a distal end extending in a
direction away from the cone 54. A super hard element 56B is
embedded, including base and sides, in the distal end of the
extending body 56A with an exposed surface to provide a wear
resistant cutting tip. An enlarged partial cross-section view of
cutting element 56 on the cone 54 is shown in FIG. 5.
[0033] Referring to FIG. 5, the extending body 56A of the insert is
disposed in the socket formed in the surface of the cone 54. The
extending body 56A may be press fit, brazed, or attached to the
cone 54 using a method known in the art. The other end of the
extending body 56A (hereafter referred to as the distal end)
extends away from the surface of the cone 54 an axial length
(primary extension length), b. The insert further includes a super
hard element 56B that is press fit or otherwise attached to a
socket formed at the distal end of the extending body 56A. The
super hard element 56B may be formed of any super hard material,
such as polycrystalline diamond or polycrystalline cubic boron
nitride. The super hard element 56B is configured such that when
placed in the socket of the extending body 56A it extends from the
surface of the extending body 56A a distance (secondary extension
length), t, to form at least a portion of a cutting face for the
cutting element. In the example shown, the super hard element 56B
forms the tip or crest of the cutting element 56 and is adapted to
engage and cut through earth formations during drilling.
[0034] As illustrated in FIG. 5A, in accordance with another
embodiment of the present invention, the super hard element may
comprise a compact of super hard material 59. The super hard
compact 59 may comprise a body of super hard material 59A bonded to
a substrate 59B. In such case, the substrate 59B is disposed in the
socket formed in the extending body (56A in FIGS. 4 and 5) of the
cutting element (56 in FIGS. 4 and 5) and the super hard material
59A is exposed proximal the distal end of the extending body (56A
in FIG. 4) to form at least part of the cutting face. The super
hard element 59 in accordance with one example of an embodiment in
accordance with the present invention may comprise a
polycrystalline diamond body or layer bonded to a substrate formed
of tungsten carbide infiltrated with a binder material.
[0035] Super hard elements 59 having substrates 59B may be brazed,
press fit, or otherwise attached to the extending body of a cutting
element in accordance with embodiments of the present invention.
Also, in various embodiments of the invention, the super hard
element may comprise any super hard material, such as
polycrystalline diamond, cubic boron nitride, natural diamond,
carbide or other super hard material. The super hard element may
further include a substrate formed from tungsten carbide, other
metal carbide and/or other hard materials known in the art for
making super hard compacts.
[0036] Referring back to the embodiment shown in FIG. 4, in
addition to cutting elements 56, the bit 50 also includes cutting
elements 57 disposed on the cone 54 which terminate into a
substantially planar upper surface. In this example, cutting
elements 57 are disposed in the wall contacting zone (35 in FIG. 2)
and define the gage diameter of the bit 50. The cutting elements 57
comprise tungsten carbide inserts disposed in sockets formed on the
cone 54. In other embodiments, these inserts may be formed from
tungsten carbide, other metal carbide, other hard materials, super
hard materials, or combinations of hard and super hard materials
known in the art, and may be formed as described in U.S.
application Ser. No. 10/152,498 ("the '498 application"), titled
"Single Cone Rock Bit Having Inserts Adapted to Maintain Hole Gage
During Drilling," which is incorporated by reference. In other
embodiments, cutting elements 57 may be teeth formed on the cone
and may include hardfacing.
[0037] The bit 50 also includes a plurality of cutting elements 58
disposed on the cone 54 which terminate in a generally convex or
rounded upper surface. In this example, cutting elements 58 are
tungsten carbide inserts press fit into sockets formed on the cone
54. Cutting elements 58 are disposed on an inner row on the cone 54
between bottom contacting cutting elements and wall contacting
cutting elements on the cone 54. Similar to cutting elements 57
above, in other embodiments cutting elements 58 may be inserts or
teeth formed on the cone and may include hardfacing.
[0038] Another embodiment in accordance with the present invention
is shown in FIG. 6. In this embodiment, the single roller cone bit
60 includes a single cone 62 rotatably mounted to the bit body 61
and having a plurality of cutting elements 63 mounted thereon. The
cone 62 is a milled cone formed of steel. At least one of the
cutting elements 63 (cutting element 64) comprises a milled steel
tooth 66 formed on the cone 62 and having a super hard element 68
partially embedded in the distal end of the tooth 66. The super
hard element 68 has an exposed surface that extends from the end of
tooth 66 to form a cutting face or tip for the tooth 66. In this
embodiment, the tooth 66 has a box-like form which tapers toward
the distal end and has a substantial height (or extension) from the
surface of the cone 62 to provide an aggressive cutting structure
for the bit 60.
[0039] In some embodiments of the invention, the extension lengths
of the cutting elements are selected to provide an aggressive
cutting structure for the bit and/or to allow for improve cutting
structure or hole cleaning. Benefits that may be obtained by
providing cutting elements having substantial extensions from the
cone surface are also disclosed in the '489 application. Referring
to the example shown in FIG. 3, the primary and secondary extension
lengths, b and t, of the components of cutting element 44 typically
will be selected based on the bit size, the cutting element
position on the cone, and the formation to be drilled. The total
extension length L (L=b+t) of a cutting element in one or more
embodiments may be from 0 to 1 inches (about 0 to 25 mm) or more.
In one or more embodiments, the primary extension length b is at
least about 0.08 inches (about 2 mm), and a secondary extension
length t is at least about 0.04 inches (about 1 mm) for drill bit
diameters (27 in FIG. 2) of between about 5 and 9 inches. For
larger single roller cone drill bits, the primary and secondary
extensions may be larger. For example, the primary extension length
b may be at least 0.30 inches (about 8 mm), and the secondary
extension length t may be at least about 0.06 inches (about 1.5 mm)
when the drill bit has a drill bit diameter (27 in FIG. 2) between
about 9 to 18 inches.
[0040] For an example in accordance with FIG. 3, the extending body
has a primary extension length, b, of about 0.47 inches (about 12
mm) from the surface of the cone, and the super hard element 46 has
a secondary extension, t, of about 0.09 inches (about 2 mm) from
the surface of the extending body. This cutting structure was for a
single cone bit having a bit diameter of about 7.875 inches. In
other embodiments, the cutting elements may have a more substantial
primary extension, such as 0.60 inches (about 15 mm) or more
depending on the type of formation being drilled.
[0041] In general, one or more cutting elements in accordance with
one or more embodiments of the invention may be disposed in a
bottom contacting zone (36 in FIG. 2) of the cone. The cutting
element may have a substantial primary extension, such as at least
0.47 inches (about 12 mm) or more, to provide an aggressive
bottomhole cutting structure for the bit. Such cutting elements may
also or alternatively be disposed in the wall contacting zone
(cutting elements 7, in FIG. 2) of the bit to maintain gage. The
ratio of secondary extension to primary extension (t/b) for a
cutting element in accordance with the present invention may be
selected to have a value between 0 (flush mounted) and 1. In
various embodiments in accordance with aspects of the invention,
the primary extension b of the extending body 45 will typically be
between 0.08 to 1 inches (about 2 to 25 mm), and the secondary
extension t of the super hard element 46 will typically be between
0 inches (flush mounted) and 0.4 inches (about 10 mm).
[0042] The super hard material inserted in the steel extending body
of the cutting element in accordance with one or more embodiments
of the invention may comprises any super hard material, including
diamond, cubic boron nitride, or tungsten carbide. The super hard
material selected will typically depend on the particular formation
expected to be drilled by the bit. In one embodiment, the super
hard element may comprise a small polycrystalline diamond compact
press fit into the extending body of the cutting element to form at
least a portion of the cutting face for the cutting element. The
polycrystalline diamond compact may comprise a mass of
polycrystalline diamond bonded to substrate formed of metal carbide
or other material. In such case, the substrate may be press fit
into the extending body of the cutting element and/or alternatively
brazed to the cutting element. Additionally, for embodiments having
polycrystalline diamond, the diamond body may also be partially or
fully depleted of catalyzing material for increased wear
resistance. Also, in other embodiments, other materials may be
disposed between the extending body and super hard insert to reduce
interface stresses, improve impact resistance, or provide better
bonding between the super hard insert to the extending body.
[0043] Those skilled in the art will appreciate that cutting
elements comprising a hybrid insert including a steel body having
super hard element embedded therein, the cone may be formed from
any material known in the art, including steel or a matrix
material, such as tungsten carbide infiltrated with a cobalt
binder. For embodiments wherein the cone is formed of matrix
material, the matrix material may be infiltrated with natural
diamond, thermally stable polycrystalline diamond (TSP), or other
super hard material.
[0044] In one or more embodiments, a wear enhanced cutting element
as described above may be used in conjunction with other types of
cutting elements on a cone. For example, one or more cutting
elements as described above may be placed selectively placed in the
high wear zones of the cone or intermittently placed in select
regions of the cone. Also, in one or more embodiments the cutting
elements may be arranged differently than that shown. For example,
in one embodiment, the cutting elements may be randomly arranged
about the outer surface of the cone or arranged in a configuration
other than rows. In one or more embodiments, the cutting elements
and/or the bit body may be coated with hardfacing material (not
shown) to reduce wear on the cutting elements and/or the surface of
the cone during drilling.
[0045] In one or more embodiments of the invention, because super
hard material is embedded in a softer more fracture resistant
material and can be limited to the region near the cutting end of
the cutting element 34, a cutting element with a larger extension
can be used to allow greater penetration in to the formation.
Additionally hardfacing can be applied over the extension material
for increased wear resistance. Having cutting elements with larger
extensions compared to conventional diamond enhanced inserts
available for single cone drill bits, also may allow for better
cuttings removal during drilling. Additionally, embodiments of the
invention allow for the use of larger inserts with longer
extensions without the high cost and fragility associated with
conventional diamond enhanced inserts.
[0046] A cutting element having a body formed from steel provides
greater toughness than a conventional diamond-enhanced insert. Bits
formed in accordance with one or more embodiments of the present
invention may comprise cutting structures which exhibit enhanced
wear resistance without significantly sacrificing toughness.
[0047] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
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