U.S. patent application number 12/274709 was filed with the patent office on 2010-05-20 for hybrid drill bit.
This patent application is currently assigned to BAKER HUGHES INCORPORATED. Invention is credited to Eric E. McClain.
Application Number | 20100122848 12/274709 |
Document ID | / |
Family ID | 42171099 |
Filed Date | 2010-05-20 |
United States Patent
Application |
20100122848 |
Kind Code |
A1 |
McClain; Eric E. |
May 20, 2010 |
HYBRID DRILL BIT
Abstract
A method for optimizing drill bit design and several embodiments
of an optimized drill bit for drilling a well in an earth
formation. In one embodiment, the optimized drill bit comprises a
diamond impregnated bit body with one or more cutting elements, the
cutting element comprising a cutting table and a substrate. The
substrate preferably comprises a material that will support the
cutting table during normal drilling operations and wear when
exposed to the earth formation, thereby limiting the effects of
wear flat areas on drilling efficiency. Alternatively, or
additionally, the cutting elements may be placed, or spaced, so as
to limiting the effects of wear flat areas on drilling
efficiency.
Inventors: |
McClain; Eric E.; (Spring,
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: |
42171099 |
Appl. No.: |
12/274709 |
Filed: |
November 20, 2008 |
Current U.S.
Class: |
175/57 ;
175/428 |
Current CPC
Class: |
E21B 10/43 20130101 |
Class at
Publication: |
175/57 ;
175/428 |
International
Class: |
E21B 10/00 20060101
E21B010/00 |
Claims
1. A method of designing a drill bit, such as for drilling into an
earth formation, the method comprising the steps of: configuring
the drill bit with a diamond impregnated bit body and at least one
cutting element, the cutting element comprising a cutting table and
a substrate; and selecting a material for the substrate so that the
substrate will support the cutting table during normal drilling
operations and wear when exposed to the earth formation, thereby
limiting the effects of wear flat areas on drilling efficiency.
2. The method as set forth in claim 1, wherein the cutting table is
operable to cut the earth formation.
3. The method as set forth in claim 1, wherein the bit body is
operable to cut the earth formation.
4. The method as set forth in claim 1, wherein the cutting table
has an abrasion resistance greater than the earth formation.
5. The method as set forth in claim 1, wherein the bit body has an
abrasion resistance greater than the earth formation.
6. The method as set forth in claim 1, wherein the substrate has an
abrasion resistance less than the earth formation.
7. The method as set forth in claim 1, wherein the substrate has an
abrasion resistance less than the cutting table.
8. The method as set forth in claim 1, wherein the substrate has an
abrasion resistance less than the bit body.
9. The method as set forth in claim 1, further including the step
of arranging a plurality of diamond impregnated cutting structures
on the bit body.
10. The method as set forth in claim 1, further including the step
of arranging a plurality of diamond impregnated cutting structures
among the cutting elements.
11. A method of designing a drill bit, such as for drilling into an
earth formation, the method comprising the steps of: configuring
the drill bit with a diamond impregnated bit body and a plurality
of cutting elements, the cutting element comprising a cutting table
and a substrate; and placing the cutting elements on the bit body
to limit the effects of wear flat areas on drilling efficiency.
12. The method as set forth in claim 11, wherein the cutting
elements are spaced tighter in a shoulder section of the bit
body.
13. The method as set forth in claim 11, wherein the cutting
elements are spaced tighter in a nose section of the bit body.
14. The method as set forth in claim 11, wherein the cutting
elements have greater spacing in a cone section of the bit
body.
15. The method as set forth in claim 11, wherein the cutting
elements have greater spacing in a gage section of the bit
body.
16. The method as set forth in claim 11, further including the step
of arranging a plurality of diamond impregnated cutting structures
on the bit body.
17. The method as set forth in claim 11, further including the step
of arranging a plurality of diamond impregnated cutting structures
among the cutting elements.
18. A method of designing a drill bit, such as for drilling into an
earth formation, the method comprising the steps of: configuring
the drill bit with a diamond impregnated bit body a plurality of
diamond impregnated cutting structures and a plurality of cutting
elements, each cutting elements comprising a cutting table and a
substrate; selecting a material for the substrate so that the
substrate will support the cutting table during normal drilling
operations and wear when exposed to the earth formation, thereby
limiting the effects of wear flat areas on drilling efficiency; and
placing the cutting elements on the bit body to limit the effects
of wear flat areas on drilling efficiency.
19. The method as set forth in claim 18, wherein both the cutting
table and the bit body are operable to cut the earth formation,
while the substrate has an abrasion resistance less than the
cutting table, the bit body and the earth formation.
20. The method as set forth in claim 18, wherein the cutting
elements are spaced tighter in a shoulder section and a nose
section than in a cone section or a gage section of the bit body.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This subject matter of this application is similar to the
subject matter disclosed in U.S. patent application Ser. Nos.
12/250,443, 12/250,445, 12/250,447, and 12/250,448, all filed Oct.
13, 2008, which are incorporated herein by specific 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 inventions disclosed and taught herein relate generally
to drill bits for drilling wells; and more specifically relate to
diamond impregnated drill bits with super-abrasive cutting elements
for drilling wells in earth formations.
[0006] 2. Description of the Related Art
[0007] U.S. Pat. No. 6,095,265 discloses "a diamond impregnated bit
with an adaptive matrix in the ribs. The ribs have at least two
different areas of metal-matrix composite impregnated with diamonds
with different wear resistance such that during boring of
formation, the areas will wear at different rates and provide fluid
flow spaces across the surface of the ribs."
[0008] U.S. Pat. No. 6,296,069 discloses a "drill bit as used in
particular in the oil well drilling field comprising a central body
(2), cutting blades (3) protruding with respect to the body (2),
both at the front of this body according to a drill direction and
at the sides of this same body (2), and cutting elements (9)
divided over an outer front surface (10) and over an outer lateral
well sizing surface (11) comprised by each blade (3), wherein there
are provided as cutting elements: in a central area (13) of the
front surface (10), on at least one blade (3): at least one
synthetic polycrystalline diamond compact cutting disc (12), and in
a remaining area (14) of the front surface (10) of this blade,
situated beyond said central area (13) with respect to the rotation
axis, and on the other blades: thermally stable synthetic diamonds
and/or impregnated diamond particles."
[0009] U.S. Pat. No. 6,510,906 discloses a "drill bit employing a
plurality of discrete, post-like diamond grit impregnated cutting
structures extending upwardly from abrasive particulate-impregnated
blades defining a plurality of fluid passages therebetween on the
bit face. PDC cutters with faces oriented in the general direction
of bit rotation are placed in the cone of the bit, which is
relatively shallow, to promote enhanced drilling efficiency through
softer, non-abrasive formations. A plurality of ports, configured
to receive nozzles therein are employed for improved drilling fluid
flow and distribution. The blades may extend radially in a linear
fashion, or be curved and spiral outwardly to the gage to provide
increased blade length and enhanced cutting structure
redundancy."
[0010] U.S. Pat. No. 6,843,333 discloses a "drill bit employing a
plurality of discrete, post-like, abrasive, particulate-impregnated
cutting structures extending upwardly from abrasive,
particulate-impregnated blades defining a plurality of fluid
passages therebetween on the bit face. Additional cutting elements
may be placed in the cone of the bit surrounding the centerline
thereof. The blades may extend radially in a linear fashion, or be
curved and spiral outwardly to the gage to provide increased blade
length and enhanced cutting structure redundancy. Additionally,
discrete protrusions may extend outwardly from at least some of the
plurality of cutting structures. The discrete protrusions may be
formed of a thermally stable diamond product and may exhibit a
generally triangular cross-sectional geometry relative to the
direction of intended bit rotation."
[0011] The inventions disclosed and taught herein are directed to
an improved diamond impregnated drill bit with super-abrasive
cutting elements for drilling wells in earth formations.
BRIEF SUMMARY OF THE INVENTION
[0012] The invention relates to a method for optimizing drill bit
design and several embodiments of an optimized drill bit for
drilling a well in an earth formation. In one embodiment, the
optimized drill bit comprises a diamond impregnated bit body with
one or more cutting elements, the cutting element comprising a
cutting table and a substrate. The substrate preferably comprises a
material that will support the cutting table during normal drilling
operations and wear when exposed to the earth formation, thereby
limiting the effects of wear flat areas on drilling efficiency.
Alternatively, or additionally, the cutting elements may be placed,
or spaced, so as to limiting the effects of wear flat areas on
drilling efficiency.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0013] FIG. 1 comprises an inverted perspective view of a first
embodiment of a bit of the present invention;
[0014] FIG. 2 is a top elevation of the bit of FIG. 1 after
testing, showing wear of the discrete cutting structures and PDC
cutters; and
[0015] FIG. 3 is an enlarged perspective view of an exemplary
cutting element embodying certain aspects of the present
inventions.
DETAILED DESCRIPTION
[0016] 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.
[0017] Particular embodiments of the invention may be described
below with reference to block diagrams and/or operational
illustrations of methods. In some alternate implementations, the
functions/actions/structures noted in the figures may occur out of
the order noted in the block diagrams and/or operational
illustrations. For example, two operations shown as occurring in
succession, in fact, may be executed substantially concurrently or
the operations may be executed in the reverse order, depending upon
the functionality/acts/structure involved.
[0018] Applicants have created both a method for optimizing drill
bit design and several embodiments of an optimized drill bit for
drilling a well in an earth formation. In one embodiment, the
optimized drill bit comprises a diamond impregnated bit body with
one or more cutting elements, the cutting element comprising a
cutting table and a substrate. The substrate preferably comprises a
material that will support the cutting table during normal drilling
operations and wear when exposed to the earth formation, thereby
limiting the effects of wear flat areas on drilling efficiency.
Alternatively, or additionally, the cutting elements may be placed,
or spaced, so as to limit the effects of wear flat areas on
drilling efficiency.
[0019] The present invention includes both a method for optimizing
drill bit design and several embodiments of an optimized drill bit
10 for drilling a well in an earth formation. The bit 10 may be
similar to those disclosed in U.S. Pat. No. 6,843,333, the
disclosure of which is incorporated herein by specific reference in
its entirety. Referring now to FIGS. 1 and 2, a first embodiment of
the bit 10 of the present invention is depicted. In FIG. 1, the bit
10 is shown inverted from its normal face-down operating
orientation for clarity. The bit 10 is, in one embodiment, 81/2''
in diameter and includes a matrix-type bit body 12 having a shank
14 for connection to a drill string (not shown) extending therefrom
opposite a bit face 16. A plurality of blades 18 extends generally
radially outwardly in linear fashion to gage pads 20 defining junk
slots 22 therebetween.
[0020] The bit 10 may include conventional impregnated bit cutting
structures and/or discrete, impregnated cutting structures 24
comprising posts extending upwardly from the blades 18 on the bit
face 16. The cutting structures 24 may be formed as an integral
part of the matrix-type blades 18 projecting from the matrix-type
bit body 12 by hand-packing diamond grit-impregnated matrix
material in mold cavities on the interior of a bit mold defining
locations of the cutting structures 24 and blades 18. Thus, each
blade 18 and associated cutting structure 24 may define a unitary
structure. It is noted that the cutting structures 24 may be placed
directly on the bit face 16, dispensing with the blades. It is also
noted that, while discussed in terms of being integrally formed
with the bit 10, the cutting structures 24 may be formed as
discrete individual segments, such as by hot isostatic pressing,
and subsequently brazed or furnaced onto the bit 10.
[0021] The discrete cutting structures 24 may be mutually separate
from each other to promote drilling fluid flow therearound for
enhanced cooling and clearing of formation material removed by the
diamond grit. The discrete cutting structures 24 may be generally
of a round or circular transverse cross-section at their
substantially flat, outermost ends, but become more oval with
decreasing distance from the face of the blades 18 and thus provide
wider or more elongated (in the direction of bit rotation) bases
for greater strength and durability. As the discrete cutting
structures 24 wear, the exposed cross-section of the posts
increases, providing progressively increasing contact area for the
diamond grit with the formation material. As the cutting structures
wear down, the bit 10 takes on the configuration of a heavier-set
bit more adept at penetrating harder, more abrasive formations.
Even if discrete cutting structures 24 wear completely away, the
diamond-impregnated blades 18 will provide some cutting action,
reducing any possibility of ring-out and having to pull the bit
10.
[0022] While the cutting structures 24 are illustrated as
exhibiting posts of circular outer ends and oval shaped bases,
other geometries are also contemplated. For example, the outermost
ends of the cutting structures may be configured as ovals having a
major diameter and a minor diameter. The base portion adjacent the
blade 18 might also be oval, having a major and a minor diameter,
wherein the base has a larger minor diameter than the outermost end
of the cutting structure 24. As the cutting structure 24 wears
towards the blade 18, the minor diameter increases, resulting in a
larger surface area. Furthermore, the ends of the cutting
structures 24 need not be flat, but may employ sloped geometries.
In other words, the cutting structures 24 may change cross-sections
at multiple intervals, and tip geometry may be separate from the
general cross-section of the cutting structure. Other shapes or
geometries may be configured similarly. It is also noted that the
spacing between individual cutting structures 24, as well as the
magnitude of the taper from the outermost ends to the blades 18,
may be varied to change the overall aggressiveness of the bit 10 or
to change the rate at which the bit is transformed from a light-set
bit to a heavy-set bit during operation. It is further contemplated
that one or more of such cutting structures 24 may be formed to
have substantially constant cross-sections if so desired depending
on the anticipated application of the bit 10.
[0023] Discrete cutting structures 24 may comprise a synthetic
diamond grit, such as, for example, DSN-47 Synthetic diamond grit,
commercially available from DeBeers of Shannon, Ireland, which has
demonstrated toughness superior to natural diamond grit. The
tungsten carbide matrix material with which the diamond grit is
mixed to form discrete cutting structures 24 and supporting blades
18 may desirably include a fine grain carbide, such as, for
example, DM2001 powder commercially available from Kennametal Inc.,
of Latrobe, Pa. Such a carbide powder, when infiltrated, provides
increased exposure of the diamond grit particles in comparison to
conventional matrix materials due to its relatively soft, abradable
nature. The base 30 of each blade 18 may desirably be formed of,
for example, a more durable 121 matrix material, obtained from
Firth MPD of Houston, Tex. Use of the more durable material in this
region helps to prevent ring-out even if all of the discrete
cutting structures 24 are abraded away and the majority of each
blade 18 is worn.
[0024] It is noted, however, that alternative particulate abrasive
materials may be suitably substituted for those discussed above.
For example, the discrete cutting structures 24 may include natural
diamond grit, or a combination of synthetic and natural diamond
grit. Alternatively, the cutting structures may include synthetic
diamond pins. Additionally, the particulate abrasive material may
be coated with a single layer or multiple layers of a refractory
material, as known in the art and disclosed in U.S. Pat. Nos.
4,943,488 and 5,049,164, the disclosures of each of which are
hereby incorporated herein by reference in their entirety. Such
refractory materials may include, for example, a refractory metal,
a refractory metal carbide or a refractory metal oxide. In one
embodiment, the coating may exhibit a thickness of approximately 1
to 10 microns. In another embodiment, the coating may exhibit a
thickness of approximately 2 to 6 microns. In yet another
embodiment, the coating may exhibit a thickness of less than 1
micron.
[0025] In one embodiment, one or more of the blades 18 carry
cutting elements, shown as polycrystalline diamond compact (PDC)
cutters 26, in conventional orientations, with cutting faces
oriented generally facing the direction of bit rotation. In one
embodiment, the PDC cutters 26 are located within the cone portion
34 of the bit face 16. The cone portion 34, best viewed with
reference to FIG. 1, is the portion of the bit face 16 wherein the
profile is defined as a generally cone-shaped section about the
centerline of intended rotation of the drill bit 10. Alternatively,
or additionally, the PDC cutters 26 may be located across the
blades 18 and elsewhere on the bit 10.
[0026] The PDC cutters 26 may comprise cutters having a PDC jacket
or sheath extending contiguously with, and to the rear of, the PDC
cutting face and over a supporting substrate 32. For example, a
cutter of this type is offered by Hughes Christensen Company, a
wholly owned subsidiary of the assignee of the present invention,
as NIAGARA.TM. cutters. Such cutters are further described in U.S.
Pat. No. 6,401,844, the disclosure of which is incorporated herein
by specific reference in its entirety. This cutter design provides
enhanced abrasion resistance to the hard and/or abrasive formations
typically drilled by impregnated bits, in combination with enhanced
performance, or rate of penetration (ROP), in softer, nonabrasive
formation layers interbedded with such hard formations. It is
noted, however, that alternative PDC cutter designs may be
implemented. For example, the PDC cutters 26 may be configured of
various shapes, sizes, or materials as known by those of skill in
the art. Also, other types of cutting elements may be formed within
the cone portion 34 of, and elsewhere across, the bit 10 depending
on the anticipated application of the bit 10. For example, the
cutting elements 26 may include cutters formed of thermally stable
diamond product (TSP), natural diamond material, or impregnated
diamond.
[0027] An exemplary cutting element 26 of the present invention, as
shown in FIG. 3, includes a super-abrasive cutting table 28 of
circular, rectangular or other polygon, oval, truncated circular,
triangular, or other suitable cross-section. The super-abrasive
table 28, exhibiting a circular cross-section and an overall
cylindrical configuration, or shape, is suitable for a wide variety
of drill bits and drilling applications. The super-abrasive table
28 of the cutting element 26 is preferably formed with a
conglomerated super-abrasive material, with an exposed cutting face
30. The cutting face 30 will typically have a top 30A and a side
30B with the peripheral junction thereof serving as the cutting
region of the cutting face 30 and more precisely a cutting edge 30C
of the cutting face 30, which is usually the first portion of the
cutting face 30 to contact and thus initially "cut" the formation
as the drill bit 10 retaining the cutting element 26 progressively
drills a bore hole. The cutting edge 30C may be a relatively sharp
approximately ninety-degree edge, or may be beveled or rounded. The
super-abrasive table 28 will also typically have a primary
underside, or attachment, interface joined during the sintering of
the diamond, or super-abrasive, layer forming the super-abrasive
table 28 to a supporting substrate 32 typically formed of a hard
and relatively tough material such as a cemented tungsten carbide
or other carbide. The substrate 32 may be preformed in a desired
shape such that a volume of particulate diamond material may be
formed into a polycrystalline cutting, or super-abrasive, table 28
thereon and simultaneously strongly bonded to the substrate 32
during high pressure high temperature (HPHT) sintering techniques
practiced within the art. Alternatively, the substrate 32 may be
formed of steel, or other strong material with an abrasion
resistance less than that of tungsten carbide and/or the earth
formation being drilled. In still other embodiments, the substrate
32 may comprise a relatively thin tungsten carbide layer backed by
a steel body.
[0028] In any case, the substrate 32 may be cylindrical, conical,
tapered, and/or rectangular in over-all shape, as well as,
circular, rectangular or other polygon, oval, truncated circular,
and/or triangular, in cross-section. A unitary cutting element 26
will thus be provided that may then be secured to the drill bit 10
by brazing or other techniques known within the art, such as
gluing, press fitting, and/or using a stud mounting technique.
[0029] In accordance with the present invention, the super-abrasive
table 28 preferably comprises a heterogeneous conglomerate type of
PDC layer or diamond matrix in which at least two different nominal
sizes and wear characteristics of super-abrasive particles, such as
diamonds of differing grains, or sizes, are included to ultimately
develop a rough, or rough cut, cutting face 30, particularly with
respect to the cutting face side 30B and most particularly with
respect to the cutting edge 30C. In one embodiment, larger diamonds
may range upwards of approximately 600 .mu.m, with a preferred
range of approximately 100 .mu.m to approximately 600 .mu.m, and
smaller diamonds, or super-abrasive particles, may preferably range
from about 15 .mu.m to about 100 .mu.m. In another embodiment,
larger diamonds may range upwards of approximately 500 .mu.m, with
a preferred range of approximately 100 .mu.m to approximately 250
.mu.m, and smaller diamonds, or super-abrasive particles, may
preferably range from about 15 .mu.m to about 40 .mu.m.
[0030] The specific grit size of larger diamonds, the specific grit
size of smaller diamonds, the thickness of the cutting face 30 of
the super-abrasive table 28, the amount and type of sintering
agent, as well as the respective large and small diamond volume
fractions, may be adjusted to optimize the cutter 26 for cutting
particular formations exhibiting particular hardness and particular
abrasiveness characteristics. The relative, desirable particle size
relationship of larger diamonds and smaller diamonds may be
characterized as a tradeoff between strength and cutter
aggressiveness. On the one hand, the desirability of the
super-abrasive table 28 holding on to the larger particles during
drilling would dictate a relatively smaller difference in average
particle size between the smaller and larger diamonds. On the other
hand, the desirability of providing a rough cutting surface would
dictate a relatively larger difference in average particle size
between the smaller and larger diamonds. Furthermore, the
immediately preceding factors may be adjusted to optimize the
cutter 26 for the average rotational speed at which the cutting
element 26 will engage the formation as well as for the magnitude
of normal force and torque to which each cutter 26 will be
subjected while in service as a result of the rotational speeds and
the amount of weight, or longitudinal force, likely to be placed on
the drill bit 10 during drilling.
[0031] While PDC cutters, such as those discussed above, are used
in a preferred embodiment, other cutters may be used alternatively
and/or additionally. For example, cutters made of thermally stable
polycrystalline (TSP) diamond, in triangular, pin, and/or circular
configuration, cubic boron nitride (CBN), and/or other
superabrasive materials may be used. In some embodiments, even
simple carbide cutters may be used.
[0032] According to certain aspects of the present invention,
rather than constructing every component of the drill bit 10 from
the strongest, most durable and abrasion resistant materials
available, it may beneficial to make portions of the drill bit 10
sacrificial. For example, with drilling rig day rates often
significantly exceeding the cost of drill bits, designing a drill
bit that minimizes the cost of drilling operations is paramount.
Historically, drill bits have been designed to be as durable and
wear resistant as possible. Unfortunately, due to the extreme
environment in which they are expected to perform, all known drill
bits experience wear. More specifically, as the drill bit 10 wears,
wear flat areas develop on the bit body 12, blades 18, and the
cutters 26 themselves. These wear flat areas abrade against the
earth formation, such as rock, and cause unproductive heat, drag,
as well as other harmful byproducts of the drilling operation. The
heat and drag further degrade the drill bit 10 and increase the
wear flat problem, requiring more and more energy as well as
decreasing rate of penetration. More specifically, increased wear
flat area increases the specific energy, or the energy required to
remove a unit volume of rock. At some point, the wear flat area
becomes so great that the specific energy required is too great,
drilling efficiency is therefore lost, and the drill bit 10 must be
replaced.
[0033] Clearly, the cutting tables 28 must be made from a material
with an abrasion resistance greater than the abrasiveness of the
earth formation, in order to cut therethrough. Because the
substrate 32 is intended to provide support to the cutting table
28, rather than significantly contribute to the rate of
penetration, the substrate 32 may be made of a material with an
abrasion resistance less than the abrasiveness of the earth
formation. Therefore, in some embodiments, the substrates 32 of the
cutting elements 26 and/or other portions of the bit body 12 are
preferably made of a material with less abrasion resistance than
that of the cutting table 28 and/or the earth formation into which
the drill bit 10 is drilling. In one embodiment, cutters 26 with
sacrificial substrates 32 could be mounted on every blade 18,
spaced SO as to minimize the wear flat area's influence on the
required specific energy. The wear flat area's influence may also
be minimized by mounting cutters 26 with sacrificial substrates 32
on every other blade 18.
[0034] The above differences in abrasiveness can be accomplished in
terms of independently specified material properties. For example,
the optimized drill bit 10 according to the present invention may
be designed such that the cutting table 28 is made of a cutting
material with a minimum abrasion resistance, significantly higher
than the abrasiveness of the earth formation. The optimized drill
bit 10 according to the present invention may be designed such that
the substrate 32 is made of a substrate material with a minimum
and/or maximum abrasion resistance, which is preferably lower than
the abrasiveness of the earth formation.
[0035] Alternatively, the above differences in abrasiveness can be
accomplished in terms of specified ratios. For example, an
optimized drill bit 10 according to the present invention may be
designed to maintain a minimum ratio of abrasion resistance
between: the cutting table 28 and the earth formation; the cutting
table 28 and the substrate 32; and/or earth formation and the
substrate 32. In any case, as discussed above, the abrasiveness of
the earth formation is preferably such that at least the substrate
material erodes rather quickly when and where it comes into
frictional contact with the earth formation.
[0036] It can be appreciated that a pre-designed and
pre-manufactured drill bit may be selected based on the earth
formation predicted and/or encountered. Alternatively, a drill bit
may be specifically designed for the earth formation predicted
and/or encountered.
[0037] It has been discovered that the blades 18 rarely wear
evenly. Therefore, it may be desirable to optimize the design of
the blades 18 and the distribution and/or spacing of cutting
material along the blades 18, to increase drill bit useful life and
minimize the required specific energy while maintaining an
acceptable rate of penetration and drilling efficiency. The blades
18 of modern drill bits often have three or more sections that
serve related and overlapping functions. Specifically, each blade
18 preferably has a cone section, a nose section, a shoulder
section, and a gage section.
[0038] As discussed above, the cone section of each blade is
preferably a substantially linear section extending from near a
center-line of the drill bit 10 outward. Because the cone section
is nearest the center-line of the drill bit 10, the cone section
does not experience as much, or as fast, movement relative to the
earth formation. Therefore, it has been discovered that the cone
section commonly experiences less wear than the other sections.
Thus, the cone section can maintain effective and efficient rate of
penetration with less cutting material. This can be accomplished in
a number of ways. For example, the cone section may have fewer
cutting structures 24 and/or PDC cutters 26, smaller cutting
structures 24 and/or PDC cutters 26, and/or more spacing between
cutting structures 24 and/or PDC cutters 26. The cone angle for a
PDC bit is typically 15-25.degree., although, in some embodiments,
the cone section is essentially flat, with a substantially
0.degree. cone angle.
[0039] The nose represents the lowest point on a drill bit.
Therefore, the nose cutter is typically the leading most cutter.
The nose section is roughly defined by a nose radius. A larger nose
radius provides more area to place cutters in the nose section. The
nose section begins where the cone section ends, where the
curvature of the blade begins, and extends to the shoulder section.
More specifically, the nose section extends where the blade profile
substantially matches a circle formed by the nose radius. The nose
section experiences much more, and more rapid, relative movement
than does the cone section. Additionally, the nose section
typically takes more weight than the other sections. As such, the
nose section commonly experiences much more wear than does the cone
section. Therefore, the nose section preferably has a higher
distribution, concentration, or density of cutting structures 24
and/or PDC cutters 26.
[0040] The shoulder section begins where the blade profile departs
from the nose radius and continues outwardly on each blade 18 to a
point where a slope of the blade is essentially completely
vertical, at the gage section. The shoulder section experiences
much more, and more rapid, relative movement than does the cone
section. Additionally, the shoulder section typically takes the
brunt of abuse from dynamic dysfunction, such as bit whirl. As
such, the shoulder section experiences much more wear than does the
cone section. The shoulder section is also a more significant
contributor to rate of penetration and drilling efficiency than the
cone section. Therefore, the shoulder section preferably has a
higher distribution, concentration, or density of cutting
structures 24 and/or PDC cutters 26. Depending on application, the
nose section or the shoulder section may experience the most wear,
and therefore either the nose section or the shoulder section may
have the highest distribution, concentration, or density of cutting
structures 24 and/or PDC cutters 26.
[0041] The gage section begins where the shoulder section ends.
More specifically, the gage section begins where the slope of the
blade is predominantly vertical. The gage section continues
outwardly to an outer perimeter or gauge of the drill bit 10. The
gage section experiences the most, and most rapid, relative
movement with respect to the earth formation. However, at least
partially because of the high, substantially vertical, slope of the
blade 18 in the gage section, the gage section does not typically
experience as much wear as does the shoulder section and/or the
nose section. The gage section does, however, typically experience
more wear than the cone section. Therefore, the gage section
preferably has a higher distribution of cutting structures 24
and/or PDC cutters 26 than the cone section, but may have a lower
distribution of cutting structures 24 and/or PDC cutters 26 than
the shoulder section and/or nose section.
[0042] In one embodiment, a highest concentration of the cutting
structures 24 and/or PDC cutters 26 occurs near the border between
the shoulder section and the gage section. Alternative embodiments
may include a highest concentration of the cutting structures 24
and/or PDC cutters 26, in the shoulder section and/or the gage
section.
[0043] Upon reading this disclosure, it can be appreciated that the
design of a drill bit includes consideration of many factors, such
as the size, shape, spacing, orientation, and number of blades; the
size, shape, spacing, orientation, and number of cutters, or
cutting elements; as well as the materials of the bit body, blades,
cutting tables, and substrates. All of these factors may be
considered in light of the materials of the earth formation(s) for
which the drill bit is designed and/or matched.
[0044] The bit 10 may employ a plurality of ports 36 over the bit
face 16 to enhance fluid velocity of drilling fluid flow and better
apportion the flow over the bit face 16 and among fluid passages 38
between blades 18 and extending to junk slots 22. This enhanced
fluid velocity and apportionment helps prevent bit balling in shale
formations, for example, which phenomenon is known to significantly
retard rate of penetration (ROP). Further, in combination with the
enhanced diamond exposure of bit 10, the improved hydraulics
substantially enhances drilling through permeable sandstones.
[0045] Other and further embodiments utilizing one or more aspects
of the inventions described above can be devised without departing
from the spirit of Applicant's invention. For example, the various
methods and embodiments of the drill bit 10 can be included in
combination with each other to produce variations of the disclosed
methods and embodiments. Reading this disclosure, it can be
appreciated that there are a number of ways to impact
concentrations or distributions of cutter volume, such as by using
differently sized, shaped, and/or spaced cutters. Discussion of
singular elements can include plural elements and vice-versa.
[0046] The order of steps 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.
[0047] The inventions have been described in the context of
preferred and other embodiments and not every embodiment of the
invention has been described. Obvious 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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