U.S. patent application number 12/481410 was filed with the patent office on 2010-06-24 for hybrid drill bit with high pilot-to-journal diameter ratio.
This patent application is currently assigned to BAKER HUGHES INCORPORATED. Invention is credited to Don Q. Nguyen, Rudolf C. Pessier, Anton F. Zahradnik.
Application Number | 20100155146 12/481410 |
Document ID | / |
Family ID | 42264427 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100155146 |
Kind Code |
A1 |
Nguyen; Don Q. ; et
al. |
June 24, 2010 |
HYBRID DRILL BIT WITH HIGH PILOT-TO-JOURNAL DIAMETER RATIO
Abstract
The invention disclosed and taught herein is directed to an
improved hybrid drill bit and associated elements having at least
two rolling cutters, each rotatable around separate spindles on the
bit, and at least one fixed blade. The improved drill bit expands
the pilot pin to journal diameter ratio within the body of the
rolling cutter, but within the confines of the allowable space of
the rolling cutter.
Inventors: |
Nguyen; Don Q.; (Houston,
TX) ; Zahradnik; Anton F.; (Sugar Land, TX) ;
Pessier; Rudolf C.; (Galveston, TX) |
Correspondence
Address: |
LOCKE LORD BISSELL & LIDDELL LLP;ATTN: IP DOCKETING
600 TRAVIS, SUITE 3400
HOUSTON
TX
77002-3095
US
|
Assignee: |
BAKER HUGHES INCORPORATED
Houston
TX
|
Family ID: |
42264427 |
Appl. No.: |
12/481410 |
Filed: |
June 9, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61139392 |
Dec 19, 2008 |
|
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|
Current U.S.
Class: |
175/336 |
Current CPC
Class: |
E21B 10/22 20130101;
E21B 10/14 20130101 |
Class at
Publication: |
175/336 |
International
Class: |
E21B 10/14 20060101
E21B010/14; E21B 10/00 20060101 E21B010/00 |
Claims
1. A hybrid drill bit for use in drilling through subterranean
formations, the hybrid drill bit comprising: a shank disposed about
a longitudinal centerline and adapted to be coupled to a drilling
string; at least one fixed blade extending from the shank, the
fixed blade comprising at least one cutting element extending from
a surface of the fixed blade; at least two rolling cutter legs
extending from the shank, comprising a spindle having an axis of
rotation, the spindle comprising: a journal disposed about the axis
of rotation, the journal having a journal diameter; and a pilot pin
coupled to the journal and extending along the axis of rotation
toward the longitudinal centerline, the pilot pin having a pilot
pin diameter, the pilot pin diameter to journal diameter having a
ratio of equal to or greater than 0.60; and at least two rolling
cutters coupled to the rolling cutter legs distally from the shank
and adapted to rotate about the axis of rotation on the journal and
pilot pin, the rolling cutters comprising cutting elements
extending from a surface of the rolling cutters.
2. The hybrid drill bit of claim 1, wherein the pilot pin diameter
to journal diameter ratio is equal to or greater than 0.60 and less
than or equal to 1.0.
3. The hybrid drill bit of claim 1, wherein the pilot pin diameter
to journal diameter ratio is equal to or greater than 0.70 and less
than or equal to 1.0.
4. The hybrid drill bit of claim 1, wherein the pilot pin diameter
to journal diameter ratio is equal to or greater than 0.80 and less
than or equal to 1.0.
5. The hybrid drill bit of claim 1, wherein the pilot pin diameter
to journal diameter ratio is equal to or greater than 0.90 and less
than or equal to 1.0.
6. The hybrid drill bit of claim 1, further comprising a bearing
disposed around the journal, the pilot pin, or a combination
thereof, the bearing having a contact length along the axis of
rotation with the journal, the pilot pin, or a combination
thereof.
7. The hybrid drill bit of claim 6, wherein the pilot pin diameter
to journal diameter ratio is calculated including the bearing on
the journal, pilot pin, or a combination thereof.
8. The hybrid drill bit of claim 1, wherein the rolling cutters
comprise an end having a truncated surface.
9. The hybrid drill bit of claim 1, wherein the pilot pin comprises
a thrust face approximately perpendicular to the axis of
rotation.
10. A hybrid drill bit for use in drilling through subterranean
formations, the hybrid drill bit comprising: a shank disposed about
a longitudinal centerline and adapted to be coupled to a drilling
string; at least one fixed blade extending from the shank, the
fixed blade comprising at least one cutting element extending from
a surface of the fixed blade; at least two rolling cutter legs
extending from the shank, comprising a spindle having an axis of
rotation, the spindle comprising: a journal disposed about the axis
of rotation, the journal having a journal diameter; and a pilot pin
coupled to the journal and extending along the axis of rotation
toward the longitudinal centerline, the pilot pin having a pilot
pin diameter, the pilot pin diameter to journal diameter having a
ratio of equal to or greater than 0.60.
11. The hybrid drill bit of claim 10, wherein the pilot pin
diameter to journal diameter ratio is equal to or greater than 0.60
and less than or equal to 1.0.
12. The hybrid drill bit of claim 10, wherein the pilot pin
diameter to journal diameter ratio is equal to or greater than 0.70
and less than or equal to 1.0.
13. The hybrid drill bit of claim 10, wherein the pilot pin
diameter to journal diameter ratio is equal to or greater than 0.80
and less than or equal to 1.0.
14. The hybrid drill bit of claim 10, wherein the pilot pin
diameter to journal diameter ratio is equal to or greater than 0.90
and less than or equal to 1.0.
15. The hybrid drill bit of claim 10, further comprising a bearing
disposed around the journal, the pilot pin, or a combination
thereof, the bearing having a contact length along the axis of
rotation with the journal, the pilot pin, or a combination
thereof.
16. The hybrid drill bit of claim 15, wherein the pilot pin
diameter to journal diameter ratio is calculated including the
bearing on the journal, pilot pin, or a combination thereof.
17. The hybrid drill bit of claim 10, wherein the pilot pin
comprises a thrust face approximately perpendicular to the axis of
rotation.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This applications claims the benefit of U.S. Provisional
Appl. No. 61/139,392 filed on Dec. 19, 2008 and is incorporated
herein by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
REFERENCE TO APPENDIX
[0003] Not applicable.
BACKGROUND OF THE INVENTION
[0004] 1. Field of the Invention
[0005] The disclosure described herein generally relates to drill
bits for use in drilling operations in subterranean formations.
More particularly, the disclosure relates to hybrid drill bits, and
apparatus and methods for increasing the strength of the support
surfaces in such drill bits.
[0006] 2. Description of the Related Art
[0007] Drill bits are frequently used in the oil and gas
exploration and the recovery industry to drill well bores (also
referred to as "boreholes") in subterranean earth formations. There
are two common classifications of drill bits used in drilling well
bores that are known in the art as "fixed blade" drill bits and
"roller cone" drill bits. Fixed blade drill bits include
polycrystalline diamond compact (PDC) and other drag-type drill
bits. These drill bits typically include a bit body having an
externally threaded connection at one end for connection to a drill
string, and a plurality of cutting blades extending from the
opposite end of the bit body. The cutting blades form the cutting
surface of the drill bit. Often, a plurality of cutting elements,
such as PDC cutters or other materials, which are hard and strong
enough to deform and/or cut through earth formations, are attached
to or inserted into the blades of the bit, extending from the bit
and forming the cutting profile of the bit. This plurality of
cutting elements is used to cut through the subterranean formation
during drilling operations when the drill bit is rotated by a motor
or other rotational input device.
[0008] The other type of earth boring drill bit, referred to as a
roller cone bit, typically includes a bit body with an externally
threaded connection at one end, and a plurality of roller cones
(typically three) attached at an offset angle to the other end of
the drill bit. These roller cones are able to rotate about
bearings, and rotate individually with respect to the bit body.
[0009] An exemplary roller cone bit and cutting roller cone are
illustrated in FIGS. 1 and 2 and described in U.S. Pat. No.
6,601,661, incorporated herein by reference. The roller cone bit 10
includes a bit body 12 having a longitudinal centerline 8 and
having a threaded pin-type connector 14 at its upper end known as a
"shank" for coupling the bit body 12 with the lower end of a drill
string (not shown). The bit body 12 has generally three downwardly
depending legs (two shown as legs 16, 18) with a lubricant
compensator 20 provided for each. Nozzles 22 (one shown) are
positioned between each of the adjacent legs to dispense drilling
fluid during drilling. The drilling fluid is pumped down through
the drill string and into a cavity (not shown) in the bit body 12.
A roller cone is secured to the lower end of each of the three
legs. The three roller cones 24, 25, and 26 are visible in FIG. 1
secured in a rolling relation to the lower ends of the legs of bit
body 12.
[0010] The roller cone 24 is rotatably retained by bearings 27 on a
spindle 28, where the spindle has an axis of rotation 6 disposed at
an angle to the longitudinal centerline 8 of the bit body (the axis
of rotation 6 in FIG. 1 is non-planar to the sheet due to the
orientation of the bit 10). The spindle 28 includes a journal 29
and a pilot pin 30 with a shoulder 31 formed between the journal 29
and the pilot pin 30. The diametrical surfaces of the journal 29
and pilot pin 30 are useful for supporting the roller cone in
radial loading, and resisting angular misalignment between the
spindle and cone. The surface of the shoulder, and at times the end
surface of the pilot pin, is useful for supporting the roller cone
in thrust (end) loading. The diameter and length of the journal,
the diameter and length of the pilot pin, and size of the shoulder
formed therebetween is constrained by the size and shape of the
roller cone coupled thereto. For a given optimum journal diameter,
a larger pilot pin diameter results in either having to shorten the
overall length of the journal and/or pilot pin, or reducing the
cone shell thickness, either of which can lead to failure.
Similarly, too small of a surface on the shoulder may cause a
failure of the spindle and roller cone interface.
[0011] The roller cone 24 has a cutter body 32 that is typically
formed of suitably hardened steel. The cutter body 32 is
substantially cone-shaped. A plurality of primary cutting elements
34, 36, 38 extend from the cutter body 32. When the cutter body 32
is rotated upon the spindle 28, the primary cutting elements engage
earth within a borehole and crush it. The plurality of cutting
elements may be one or a combination of milled steel teeth (called
steel-tooth bits), tungsten carbide (or other hard-material)
inserts (called insert bits), or a number of other formed and/or
shaped cutting elements that are formed of materials having a
hardness and strength suitable enough to allow for the deformation
and/or cutting through of subterranean formations. In some
instances, a hard facing material is applied to the exterior of the
cutting elements and/or other portions of the roller cone drill
bit, to reduce the wear on the bit during operation and extend its
useful working life.
[0012] These type general classes of earth boring bits have
limitations, particularly with the bit life and the types of
subterranean formations through which they can drill. Fixed blade
bits using PDC cutting elements, and therefore known as "PDC bits",
usually can be used with success in soft to medium-hard nonabrasive
formations. Hard and/or abrasive formations are generally
considered unsuitable for PDC bits in that their use in such
formations results in excessive wear and shortened working life.
For example, mudstone and siltstone have been drilled well;
however, sandstones, particularly if coarse-grained and cemented,
are very difficult to drill economically and are highly destructive
to fixed blade drill bits. [See, for example, Feenstra, R., et al.,
"Status of Polycrystalline-Diamond-Compact Bits: Part
1--Development" and "Part 2--Applications", Journal of Petroleum
Technology, Vol. 40 (7), pp. 675-684 and 817-856 (1988).] Success
is fully dependent on a good match between the bit, the formation
to be drilled, and the operating conditions. Experience has shown
that for fixed blade bits such as PDC bits, the type of mud, the
bit hydraulics, and bit design affect bit performance much more
than variations in mud properties.
[0013] Repeated experience shows that a preferred practice is to
develop the best bit design for a particular field rather than to
select one from a range. Increased aggressiveness in earth-boring
bits is not always desirable, because of the increase torque
requirements that are generally associated with it. The ability to
design and/or tailor a bit to a particular subterranean operation
or application can be an invaluable tool for the bit designer.
Thus, in recent years, attempts have been made to develop
earth-boring drill bits that use a combination of one or more
rolling cutters and one or more fixed blades having PDC or
similarly abrasive cutting elements formed or bonded thereon. Some
of these combination type bits are referred to as "hybrid drill
bits".
[0014] One previously described hybrid drill bit is disclosed in
U.S. Pat. No. 4,343,371 "wherein a pair of opposing extended nozzle
drag bit legs are positioned with a pair of opposed tungsten
carbide roller cones. The extended nozzle face nearest the hole
bottom has a multiplicity of diamond inserts mounted therein. The
diamond inserts are strategically positioned to remove the ridges
between the kerf rows in the hole bottom formed by the inserts in
the roller cones." A cross section of the pilot pin and journal is
not shown in the above patent, but is typically the same as a
roller cone bit.
[0015] Significant stresses are placed on the journal and the pilot
pin as radial and thrust loads are applied to the drill bits during
the drilling operations. The journal and the pilot pin support a
radial load along their respective lengths that acts transverse to
the axis of rotation, and the face between the journal and the
pilot pin supports a thrust load that acts in parallel to the axis
of rotation. On a hybrid drill bit, a rotatable rolling cutter is
generally smaller for a given size of bit than a corresponding
roller cone bit, because the hybrid drill bit must allow for both
the rotatable cutter assemblies as well as the fixed blades. The
journal and pilot pin about which the rotatable rolling cutter
rotates is necessarily smaller, which can result in higher stresses
for the same loads with the smaller area. However, the stresses on
the rotatable rolling cutter itself dictate that a minimum of
material remain on the shell thickness of the rolling cutter that
restricts the size and length of both the journal and pilot pin.
For example, increasing the pilot pin diameter requires a shorter
pin to accommodate the larger diameter within the confines of the
rolling cutter, or requires a thinner wall on the rolling
cutter.
[0016] There remains a need for an improved load carrying capacity
for a hybrid drill bit.
BRIEF SUMMARY OF THE INVENTION
[0017] The invention disclosed and taught herein is directed to an
improved hybrid drill bit and associated elements having at least
two rolling cutters, each rotatable around separate spindles on the
bit, and at least one fixed blade. The improved drill bit expands
the pilot pin to journal diameter ratio within the body of the
rolling cutter but within the confines of the allowable space of
the rolling cutter.
[0018] The disclosure provides hybrid drill bit for use in drilling
through subterranean formations, the hybrid drill bit comprising: a
shank disposed about a longitudinal centerline and adapted to be
coupled to a drilling string; at least one fixed blade extending
from the shank, the fixed blade comprising at least one cutting
element extending from a surface of the fixed blade; and at least
two rolling cutter legs extending from the shank, comprising a
spindle having an axis of rotation. The spindle comprises: a
journal disposed about the axis of rotation, the journal having a
journal diameter; and a pilot pin coupled to the journal and
extending along the axis of rotation toward the longitudinal
centerline, the pilot pin having a pilot pin diameter, the pilot
pin diameter to journal diameter having a ratio of equal to or
greater than 0.58. The disclosure further provides at least two
rolling cutters coupled to the rolling cutter legs distally from
the shank and adapted to rotate about the axis of rotation on the
journal and pilot pin, the rolling cutters comprising cutting
elements extending from a surface of the rolling cutters.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0019] The following figures form part of the present specification
and are included to further demonstrate certain aspects of the
present invention. The invention may be better understood by
reference to one or more of these figures in combination with the
detailed description of specific embodiments presented herein.
[0020] FIG. 1 illustrates a schematic side view of a typical roller
cone bit.
[0021] FIG. 2 illustrates a schematic cross sectional side view of
a typical roller cone bit journal and pilot pin configuration.
[0022] FIG. 3 illustrates a schematic side view of an exemplary
hybrid drill bit.
[0023] FIG. 4 illustrates a schematic bottom view of an exemplary
hybrid drill bit.
[0024] FIG. 5 illustrates a schematic cross sectional side view of
an exemplary enlarged pilot pin to journal diameter configuration
according to the disclosure.
[0025] FIG. 6 illustrates a schematic cross sectional side view of
another exemplary enlarged pilot pin to journal diameter
configuration according to the disclosure.
[0026] While the invention disclosed herein is susceptible to
various modifications and alternative forms, only a few specific
embodiments have been shown by way of example in the drawings and
are described in detail below. The figures and detailed
descriptions of these specific embodiments are not intended to
limit the breadth or scope of the inventive concepts or the
appended claims in any manner. Rather, the figures and detailed
written descriptions are provided to illustrate the inventive
concepts to a person of ordinary skill in the art and to enable
such person to make and use the inventive concepts.
DETAILED DESCRIPTION
[0027] The Figures described above and the written description of
specific structures and functions below are not presented to limit
the scope of what Applicants have invented or the scope of the
appended claims. Rather, the Figures and written description are
provided to teach any person skilled in the art to make and use the
inventions for which patent protection is sought. Those skilled in
the art will appreciate that not all features of a commercial
embodiment of the inventions are described or shown for the sake of
clarity and understanding. Persons of skill in this art will also
appreciate that the development of an actual commercial embodiment
incorporating aspects of the present inventions will require
numerous implementation-specific decisions to achieve the
developer's ultimate goal for the commercial embodiment. Such
implementation-specific decisions may include, and likely are not
limited to, compliance with system-related, business-related,
government-related and other constraints, which may vary by
specific implementation, location and from time to time. While a
developer's efforts might be complex and time-consuming in an
absolute sense, such efforts would be, nevertheless, a routine
undertaking for those of skill this art having benefit of this
disclosure. It must be understood that the inventions disclosed and
taught herein are susceptible to numerous and various modifications
and alternative forms. Lastly, the use of a singular term, such as,
but not limited to, "a," is not intended as limiting of the number
of items. Also, the use of relational terms, such as, but not
limited to, "top," "bottom," "left," "right," "upper," "lower,"
"down," "up," "side," and the like are used in the written
description for clarity in specific reference to the Figures and
are not intended to limit the scope of the invention or the
appended claims. The terms "couple," "coupled," "coupling,"
"coupler," and like terms are used broadly herein and may include
any method or device for securing, binding, bonding, fastening,
attaching, joining, inserting therein, forming thereon or therein,
communicating, or otherwise associating, for example, mechanically,
magnetically, electrically, chemically, directly or indirectly with
intermediate elements, one or more pieces of members together and
may further include without limitation integrally forming one
functional member with another in a unity fashion. The coupling may
occur in any direction, including rotationally.
[0028] Applicants have created an improved hybrid drill bit and
associated elements with an expanded pilot pin to journal diameter
ratio within the body of the rolling cutter, where the hybrid drill
bit includes at least two rolling cutters, each rotatable around
separate spindles on the bit, and at least one fixed blades.
[0029] FIG. 3 illustrates an exemplary side view of a hybrid drill
bit. FIG. 4 illustrates an exemplary bottom view of a hybrid drill
bit. FIG. 5 illustrates an exemplary enlarged pilot pin to journal
diameter configuration according to the disclosure. FIG. 6
illustrates another exemplary enlarged pilot pin to journal
diameter configuration according to the disclosure. The figures
will be described in conjunction with each other.
[0030] A hybrid drill bit 50 has a longitudinal centerline 52 that
defines an axial center of the hybrid drill bit. A shank 54 is
formed on one end of the hybrid drill bit and is designed to be
coupled to a drill string of tubular material (not shown) with
threads according to standards promulgated for example by the
American Petroleum Institute (API). At least one fixed blade 58
extends downwardly from the shank 54 relative to a general
orientation of the bit inside a borehole. A plurality of fixed
blade cutting elements 60, 62 are arranged and secured to a surface
63 on each of the fixed blades 58, such as at the leading edges of
the hybrid drill bit relative to the direction of rotation.
Generally, the fixed blade cutting elements 60, 62 comprise a
polycrystalline diamond (PCD) layer or table on a rotationally
leading face of a supporting substrate, the diamond layer or table
providing a cutting face having a cutting edge at a periphery
thereof for engaging the formation. The term PCD is used broadly
and includes other materials, such as thermally stable
polycrystalline diamond (TSP) wafers or tables mounted on tungsten
carbide substrates, and other, similar superabrasive or super-hard
materials, such as cubic boron nitride and diamond-like carbon.
Fixed-blade cutting elements 60, 62 may be brazed or otherwise
secured in recesses or "pockets" on each fixed blade 58 so that
their peripheral or cutting edges on cutting faces are presented to
the formation.
[0031] The hybrid drill bit 50 further includes at least two
rolling cutter legs 64 and rolling cutters 72 coupled to such legs.
The rolling cutter legs 64 extend downwardly from the shank 54
relative to a general orientation of the bit inside a borehole.
Each of the rolling cutter legs 64 include a spindle 66 at the
legs' distal end. The spindle 66 has an axis of rotation 67 about
which the spindle is generally symmetrically formed and the rolling
cutter rotates, as described below. The axis of rotation 67 is
generally disposed at a pin angle ".alpha." of 33 degrees to 39
degrees from a horizontal plane 7 that is perpendicular to the
longitudinal centerline 52 and intersects a base of the spindle,
that is, the region of the junction between the spindle 66 and the
roller cone leg 64, generally located proximate to the intersection
of the rear face of the roller cone and the spindle axis of
rotation. In at least one embodiment, the axis of rotation 67 can
intersect the longitudinal centerline 52. In other embodiments, the
axis of rotation can be skewed to the side of the longitudinal
centerline to create a sliding effect on the cutting elements as
the rolling cutter rotates around the axis of rotation. However,
other angles and orientations can be used including a pin angle
pointing away from the longitudinal centerline.
[0032] The spindle 66 generally forms two portions--a journal 68
disposed at a base of the spindle, and a pilot pin 70 adjacent the
journal and extending axially along the axis of rotation 67. A
shoulder 71 is established as a result of the different diameters
between the journal 68 and the pilot pin 70. The journal, pilot
pin, and shoulder support a rolling cutter 72 rotatably disposed
about the journal and pilot pin.
[0033] A rolling cutter 72 is generally coupled to each spindle 66.
The rolling cutter 72 generally has an end 73 that in some
embodiments can be truncated compared to a typical roller cone bit
illustrated in FIG. 2. The rolling cutter 72 is adapted to rotate
around the spindle 66 when the hybrid drill bit 50 is being rotated
by the drill string through the shank 54. Generally, a plurality of
cutting elements 74, 75 is coupled to a surface 77 of the rolling
cutter 72. At least some of the cutting elements are generally
arranged on the rolling cutter 72 in a circumferential row
thereabout. A minimal distance between the cutting elements will
vary according to the application and bit size, and may vary from
rolling cutter to rolling cutter, and/or cutting element to cutting
element. Some cutting elements can be arranged "randomly" on the
surface of the rolling cutter. The cutting elements can include
tungsten carbide inserts, secured by interference fit into bores in
the surface of the rolling cutter, milled- or steel-tooth cutting
elements having hard faced cutting elements integrally formed with
and protruding from the surface of the rolling cutter, and other
types of cutting elements. The cutting elements may also be formed
of, or coated with, superabrasive or super-hard materials such as
polycrystalline diamond, cubic boron nitride, and the like. The
cutting elements may be chisel-shaped as shown, conical, round, or
ovoid, or other shapes and combinations of shapes depending upon
the application.
[0034] In the hybrid drill bit, the cutting elements 60, 62 of the
fixed blade 58 and the cutting elements 74, 75 of the rolling
cutter 72 combine to define a congruent cutting face in the leading
portions of the hybrid drill bit profile. The cutting elements 74,
75 of the rolling cutter 72 crush and pre- or partially fracture
subterranean materials in a formation in the highly stressed
leading portions, easing the burden on the cutting elements 60, 62
of the fixed blade 58.
[0035] A ball bearing 80 can assist in securing the rolling cutter
to the spindle. One or more sealed or unsealed radial bearings 82,
84 provide a contact length along the axis of rotation that can
assist the rolling cutter 72 in being rotated about the spindle 66
and support radial loading. The bearings can include sleeve
bearing, roller bearings, floating bushings, shrink fit sleeves,
and other bearings types and materials. In some embodiments, a
thrust bearing 86 can be placed on the shoulder or an end of the
pilot pin to provide thrust load capacity and facilitate the
rotation of the rolling cutter about the spindle as the rolling
cutter contacts the shoulder or the end of the pilot pin.
[0036] The rolling cutter 72 generally includes a seal 88 disposed
between the spindle 66 and an inside cavity of the rolling cutter.
The seal 88 can be from well-known sealing systems, such as
elastomeric seals and metal face seals.
[0037] Other features of the hybrid drill bit such as back up
cutters, wear resistant surfaces, nozzles that are used to direct
drilling fluids, junk slots that provides a clearance for cuttings
and drilling fluid, and other generally accepted features of a
drill bit are deemed within the knowledge of those with ordinary
skill in the art and do not need further description.
[0038] Having described the general aspects of the hybrid drill
bit, the focus returns to the spindle with the journal, pilot pin,
and shoulder. The journal, pilot pin, and shoulder are stressed in
radial and thrust loading when the hybrid drill bit is used to
drill the subterranean formations. It is important to enlarge the
diameters of the journal and pilot pin in relation to the shoulder,
and lengthen the journal and pilot pin without compromising the
integrity of the rolling cutter by having too thin of a shell
thickness on the rolling cutter or too small of supporting surfaces
on the spindle.
[0039] Conventional design for roller cone bits, such as shown in
FIGS. 1 and 2, has well established certain restrictions on the
size of the journal, pilot pin, and shoulder for a given size of
roller cone. The size has been limited to the shape and
configuration of the roller cone and minimum shell thickness to
support the loads on the roller cone. As one metric, the relative
size of the pilot pin diameter to the journal diameter can be
expressed as a ratio. The typical ratio is about 0.50 and is less
than 0.56. Larger ratios typically compromise the bearing length
for a given optimum journal diameter or cause an unwanted reduction
in shell thickness.
[0040] To the knowledge of the inventors, these same ratios have
heretofore been followed on hybrid drill bits. This following has
been in spite of the need to maximize the journal and pilot pin
diameters and lengths. Thus, heretofore, it has not been an obvious
variation to increase the pilot pin to journal diameter ratio
beyond the well-accepted standard of up to 0.56.
[0041] The present inventors have reevaluated from ground up the
journal and pilot pin diameters and resultant ratios relative to a
rolling cutter shell thickness and have discovered that the ratios
can be altered for the rolling cutter. This adjustment is
especially important because on a hybrid drill bit, the rolling
cutter is generally smaller for a given size of hybrid drill bit
than a corresponding roller cone bit. The hybrid drill bit must
allow for both the rolling cutters and the fixed blades, resulting
in a smaller journal and pilot pin and higher stresses for the same
loads.
[0042] The inventors have discovered that contrary to conventional
wisdom, the ratio of the pilot pin diameter to the journal diameter
(P:J ratio) can be increased to at least 0.60 up to and including
1.0, and any value in between, inclusively. For example and without
limitation the P:J ratios can be about 0.60, about 0.62, about
0.64, about 0.66, about 0.68, about 0.70, about 0.72, about 0.74,
about 0.76, about 0.78, about 0.80, about 0.82, about 0.84, about
0.86, about 0.88, about 0.90, about 0.92, about 0.94, about 0.96,
and about 0.98, as well as values within this range, for example
(and without limitation), a P:J ratio ranging from about 0.71 to
about 0.95, or from about 0.83 to about 0.99, inclusive. For a
ratio 1.0, the pilot pin 70 becomes the same diameter as the
journal 68 and the spindle portions effectively merge into a
continuous surface. As the pilot pin 70 increases in diameter, the
shoulder 71 decreases in surface area. However, the pilot pin
itself can support thrust loads on the end of the pilot pin that
interfaces with the rolling cutter. As discussed above, a thrust
bearing 86 can be included between the pilot pin 70 and the rolling
cutter 72. Further, some ratios can be greater than 1.0, where the
pilot pin is greater in diameter than the journal.
[0043] For calculation of the ratios, radial bearings can be
included if present. Thus, if radial bearing 82 was present on the
journal that had a contact surface along the axis of rotation that
would support a radial load, then the thickness of the bearing that
supports the radial load can be calculated into the effective
diameter of the journal and compared with the pilot pin diameter.
Similarly, a radial bearing 84 on the pilot pin with a contact
length along the axis of rotation can effectively create a larger
pilot pin and thus larger pilot pin diameter to be calculated in
the ratio.
[0044] Other and further embodiments utilizing one or more aspects
of the inventions described above can be devised without departing
from the spirit of the invention. For example, multiple bearings,
such as two sets of ball bearings spaced apart from each other
along the length of the journal and/or pilot pin can be used to
establish a projected line of contact between the two bearing sets
along the axis of rotation. As such, the effective diameter of the
journal and/or pilot pin would be changed and can be used in
calculating the ratios of pilot pin to journal diameters. Such
modifications are within the scope of the invention and the
definitions herein of "diameter" of the journal and/or pilot pin.
Further, the various methods and embodiments of the hybrid drill
bit can be included in combination with each other to produce
variations of the disclosed methods and embodiments. Discussion of
singular elements can include plural elements and vice-versa.
[0045] The order of any steps explicitly or implicitly disclosed
herein can occur in a variety of sequences unless otherwise
specifically limited. The various steps described herein can be
combined with other steps, interlineated with the stated steps,
and/or split into multiple steps. Similarly, elements have been
described functionally and can be embodied as separate components
or can be combined into components having multiple functions.
[0046] The invention has been described in the context of
advantageous and other embodiments and not every embodiment of the
invention has been described. Modifications and alterations to the
described embodiments are available to those of ordinary skill in
the art. The disclosed and undisclosed embodiments are not intended
to limit or restrict the scope or applicability of the invention
conceived of by the Applicants, but rather, in conformity with the
patent laws, Applicants intend to fully protect all such
modifications and improvements that come within the scope or range
of equivalent of the following claims.
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