U.S. patent application number 11/215309 was filed with the patent office on 2006-02-16 for novel bits and cutting structures.
This patent application is currently assigned to Smith International, Inc.. Invention is credited to Shelton W. Alsup, Michael George Azar, Gary Chunn, Tommy Gene Ray, Jonathan Craig Thiele.
Application Number | 20060032677 11/215309 |
Document ID | / |
Family ID | 35798918 |
Filed Date | 2006-02-16 |
United States Patent
Application |
20060032677 |
Kind Code |
A1 |
Azar; Michael George ; et
al. |
February 16, 2006 |
Novel bits and cutting structures
Abstract
This invention provides an improved cutting element for downhole
cutting tools including a support element and a beveled shearing
element disposed on the support element and a drill bit including
the cutting element; a cutting element including a support element
and a shearing element disposed on the support element, wherein the
shearing element includes TSP, a sharpened cutting edge, and at
least one blended edge that forms part of an interface with the
support element and a drill bit including the cutting element.
Cutting inserts including an insert body and the shearing elements
disclosed above are provided. Also provided are methods for forming
the cutting elements and drill bit inserts and a method for
drilling mixed earth formations using the improved downhole cutting
tools of the present invention.
Inventors: |
Azar; Michael George; (The
Woodlands, TX) ; Thiele; Jonathan Craig; (Katy,
TX) ; Ray; Tommy Gene; (Houston, TX) ; Chunn;
Gary; (Conroe, TX) ; Alsup; Shelton W.;
(Houston, TX) |
Correspondence
Address: |
OSHA LIANG L.L.P.
1221 MCKINNEY STREET
SUITE 2800
HOUSTON
TX
77010
US
|
Assignee: |
Smith International, Inc.
Houston
TX
|
Family ID: |
35798918 |
Appl. No.: |
11/215309 |
Filed: |
August 30, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11154284 |
Jun 16, 2005 |
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11215309 |
Aug 30, 2005 |
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10696535 |
Oct 29, 2003 |
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11154284 |
Jun 16, 2005 |
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10967584 |
Oct 18, 2004 |
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11154284 |
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10738629 |
Dec 17, 2003 |
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10967584 |
Oct 18, 2004 |
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60446967 |
Feb 12, 2003 |
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Current U.S.
Class: |
175/430 ;
175/432 |
Current CPC
Class: |
E21B 10/5673 20130101;
E21B 10/55 20130101 |
Class at
Publication: |
175/430 ;
175/432 |
International
Class: |
E21B 10/36 20060101
E21B010/36 |
Claims
1. A cutting element disposed on a downhole cutting tool,
comprising: a support element; and a beveled shearing element
disposed on the support element, wherein the beveled shearing
element comprises thermally stable polycrystalline diamond.
2. A cutting element disposed on a downhole cutting tool,
comprising: a support element; a shaped shearing element disposed
on the support element, wherein the shaped shearing element is
disposed proximal to a leading edge of the downhole cutting tool;
and a retaining element overlaying at least a portion of the shaped
shearing element.
3. The cutting element of claim 2, wherein the shaped shearing
element comprises at least one beveled edge.
4. The cutting element of claim 2, wherein the shaped shearing
element comprises at least one rounded edge.
5. The cutting element of claim 2, wherein the shaped shearing
element comprises at least one tapered surface.
6. The cutting element of claim 2, wherein the shaped shearing
element comprises at least one rounded cutting edge.
7. The cutting element of claim 2, wherein the shaped shearing
element comprises at least one beveled cutting edge.
8. The cutting element of claim 2, wherein the shaped shearing
element comprises at least one non-planar cutting face geometry
selected from the group consisting of concave, convex, saddle
shaped, chiseled, and beveled.
9. The cutting element of claim 2, wherein the shaped shearing
element comprises at least one selected from the group consisting
of polycrystalline diamond, thermally stable polycrystalline
diamond, a silicon carbide polycrystalline diamond composite, and a
silicon carbide thermally stable polycrystalline diamond
composite.
10. The cutting element of claim 2, wherein the retaining element
is formed integrally with the support element.
11. The cutting element of claim 2, wherein the retaining element
is at least one selected from the group consisting of a cubic boron
nitride composite, a tungsten carbide composite and a
diamond-impregnated material.
12. A cutting element disposed on a downhole cutting tool,
comprising: a support element; a shearing element disposed on the
support element, wherein the shearing element comprises; thermally
stable polycrystalline diamond; a sharpened cutting edge proximal
to a leading edge of the downhole cutting tool; and at least one
blended edge, wherein the at least one blended edge forms part of
an interface with the support element.
13. The cutting element of claim 12, wherein the shearing element
comprises a composite of silicon carbide and thermally stable
polycrystalline diamond.
14. The cutting element of claim 12, wherein the cutting element
further comprises a retaining element overlaying at least a portion
of the shearing element.
15. The cutting element of claim 12, wherein the shearing element
further comprises at least one tapered surface.
16. The cutting element of claim 12, wherein the shearing element
further comprises at least one perturbation on at least one surface
of the shearing element.
17. The cutting element of claim 12, wherein the shearing element
comprises a non-planar cutting face geometry selected from the
group consisting of concave, convex, saddle shaped, chiseled, and
beveled.
18. A drill bit for drilling earth formations comprising: a bit
body having at least one support element disposed thereon; and a
shearing element disposed on the at least one support element,
wherein the shearing element comprises; thermal stable
polycrystalline diamond; a sharpened cutting edge proximal to a
leading edge of the downhole cutting tool; and at least one blended
edge, wherein the at least one blended edge forms part of an
interface with the at least one support element.
19. The drill bit of claim 18, wherein the shearing element further
comprises at least one tapered surface.
20. The drill bit of claim 18, wherein the shearing element further
comprises at least one perturbation on at least one surface of the
shearing element.
21. A drill bit for drilling earth formations comprising: a bit
body; a plurality of inserts disposed on the bit body, wherein at
least one of the plurality of inserts comprises an insert body and
a shaped shearing element disposed on the insert body; and a
retaining element overlaying at least a portion of the shaped
shearing element.
22. The bit of claim 21, wherein the shaped shearing element
comprises at least one beveled cutting edge.
23. The drill bit of claim 21, wherein the shaped shearing element
comprises at least one rounded cutting edge.
24. The drill bit of claim 21, wherein the shaped shearing element
comprises at least one selected from the group consisting of cubic
boron nitride, polycrystalline diamond, and thermally stable
polycrystalline diamond.
25. The drill bit of claim 21, wherein the bit body comprises a
diamond-impregnated material.
26. A drill bit comprising: a bit body; a plurality of inserts
disposed on the bit body, wherein at least one of the plurality of
inserts comprises an insert body and a shearing element disposed on
the insert body, wherein the shearing element comprises; thermally
stable polycrystalline diamond; a sharpened cutting edge located
proximal a leading edge of the drill bit; and at least one blended
edge, wherein the at least one blended edge forms part of an
interface with the insert body.
27. The drill bit of claim 26, wherein the shearing element further
comprises at least one tapered surface.
28. The drill bit of claim 26, wherein the shearing element is
tapered toward the insert body.
29. The drill bit of claim 26, wherein the shearing element further
comprises at least one perturbation on at least one surface of the
shearing element.
30. The drill bit of claim 26, wherein the bit body comprises a
diamond-impregnated material.
31. The drill bit of claim 26, wherein the insert body comprises a
tungsten carbide composite.
32. The drill bit of claim 26, wherein the insert body comprises a
diamond-impregnated material.
33. The drill bit of claim 32, wherein the diamond-impregnated
insert body comprises thermally stable polycrystalline diamond.
34. The drill bit of claim 32, wherein the shearing element is
disposed on the diamond-impregnated insert body
post-infiltration.
35. A method of forming a diamond-impregnated insert having a
shearing portion, the method comprising: forming a
diamond-impregnated insert body; forming a beveled shearing
portion; and bonding the beveled shearing portion to the
diamond-impregnated insert body.
36. The method of claim 35, wherein the diamond-impregnated insert
body is formed by a hot press process.
37. The method of claim 36, wherein the hot press process is
performed with a powder material in a mold, the powder material
being selected to form the diamond-impregnated insert body.
38. A method of forming an insert having a shearing portion, the
method comprising: forming an insert body; forming a shearing
portion, wherein the shearing portion comprises, a sharpened
cutting face located proximal a leading edge of the
diamond-impregnated insert; and at least one blended edge, wherein
the at least one blended edge forms part of an interface with the
insert body; and bonding the shearing portion to the
diamond-impregnated insert body to form the diamond-impregnated
insert.
39. A composite cutting element for a drill bit comprising: an
abrasive body having a mixture of ultra-hard material and a less
abrasive resistant matrix material cemented together; and a
shearing element disposed on the abrasive body.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 11/154,284 filed on Jun. 16, 2005, which is a
continuation-in-part of U.S. patent application Ser. No.
10/696,535, filed on Oct. 29, 2003, which claims priority of U.S.
Provisional Application Ser. No. 60/446,967, filed on Feb. 12,
2003, and U.S. patent application Ser. No. 10/967,584, filed on
Oct. 18, 2004, which is a continuation of U.S. patent application
Ser. No. 10/738,629. All these parent applications are hereby
incorporated by reference in their entirety.
BACKGROUND OF INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to downhole cutting
tools used in the oil and gas industry. More specifically, the
present invention relates to improved cutting structures.
[0004] 2. Background Art
[0005] Rotary drill bits with no independently moving elements on
them are typically referred to as "drag" bits in the art. Drag bits
are often used to drill very hard or abrasive formations. Drag bits
include those having cutting elements attached to the bit body,
such as polycrystalline diamond compact insert bits, and those
including abrasive material, such as diamond, impregnated into the
surface of the material which forms the bit body. The latter bits
are commonly referred to as "impreg" bits.
[0006] An example of a prior art diamond impregnated drill bit is
shown in FIG. 1. The drill bit 10 includes a bit body 12 and a
plurality of blades 14 that are formed in the bit body 12. The
blades 14 are separated by channels 16 that enable drilling fluid
to flow between and both clean and cool the blades 14. The blades
14 are typically arranged in groups 20 where a gap 18 between
groups 20 is typically formed by removing or omitting at least a
portion of a blade 14. The gaps 18, which may be referred to as
"fluid courses," are positioned to provide additional flow channels
for drilling fluid and to provide a passage for formation cuttings
to travel past the drill bit 10 toward the surface of a wellbore
(not shown).
[0007] During abrasive drilling with a diamond impregnated bits,
the diamond particles scour or abrade away the rock. As the matrix
material around the impregnated diamond crystals is worn away, the
diamonds at the surface eventually fall out and other diamond
particles are exposed. Diamond impregnated drill bits are
particularly well suited for drilling very hard and abrasive
formations. The presence of abrasive particles both at and below
the surface of the matrix body material ensures that the bit will
substantially maintain its ability to drill a hole even after the
surface particles are worn down.
[0008] Diamond impregnated bits are typically made from a solid
body of matrix material formed by any one of a number of powder
metallurgy processes known in the art. During the powder metallurgy
process, abrasive particles and a matrix powder are infiltrated
with a molten binder material. Upon cooling, the bit body includes
the binder material, matrix material, and the abrasive particles
suspended both near and on the surface of the drill bit. The
abrasive particles typically include small particles of natural or
synthetic diamond. Synthetic diamond used in diamond impregnated
drill bits is typically in the form of single crystals. However,
thermally stable polycrystalline diamond (TSP) tables (layers of
individual diamond crystals bonded together) may also be used.
[0009] In a typical impreg bit forming process, the shank of the
bit is supported in its proper position in the mold cavity along
with any other necessary formers, e.g., those used to form holes to
receive fluid nozzles. The remainder of the cavity is filled with a
charge of tungsten carbide powder and abrasive particles such as
natural or synthetic diamond. Finally, a binder, and more
specifically an infiltrant, typically a nickel brass copper based
alloy, is placed on top of the charge of powder. The mold is then
heated sufficiently to melt the infiltrant and held at an elevated
temperature for a sufficient period to allow it to flow into and
bind the powder matrix or matrix and segments. For example, the bit
body may be held at an elevated temperature (>1800.degree. F.)
for a period on the order of 0.75 to 2.5 hours, depending on the
size of the bit body, during the infiltration process.
[0010] By this process, a monolithic bit body that incorporates the
desired components is formed. It has been found, however, that the
life of both natural and synthetic diamond is shortened by the
lifetime thermal exposure experienced in the furnace during the
infiltration process. Accordingly, prior art patents disclose a
technique for manufacturing bits that include imbedded diamonds
that have not suffered the thermal exposure normally associated
with the manufacture of such bits. Such a bit structure is
disclosed in U.S. Pat. No. 6,394,202 (the '202 patent), which is
assigned to the assignee of the present invention and is hereby
incorporated by reference.
[0011] Referring now to FIG. 2, a drill bit 20 in accordance with
the '202 patent comprises a shank 24 and a crown 26. Shank 24 is
typically formed of steel or a matrix material and includes a
threaded pin 28 for attachment to a drill string. Crown 26 has a
cutting face 22 and outer side surface 30. According to one
embodiment, crown 26 is formed by infiltrating a mass of
tungsten-carbide powder impregnated with synthetic or natural
diamond, as described above.
[0012] Crown 26 may include various surface features, such as
raised ridges 27. Preferably, formers are included during the
manufacturing process, so that the infiltrated, diamond-impregnated
crown includes a plurality of holes or sockets 29 that are sized
and shaped to receive a corresponding plurality of
diamond-impregnated inserts 10. Once crown 26 is formed, inserts 10
are mounted in the sockets 29 and affixed by any suitable method,
such as brazing, adhesive, mechanical means such as interference
fit, or the like. As shown in FIG. 3, the sockets can each be
substantially perpendicular to the surface of the crown.
Alternatively, and as shown in FIG. 3, holes 29 can be inclined
with respect to the surface of the crown 26. In this embodiment,
the sockets are inclined such that inserts 10 are oriented
substantially in the direction of rotation of the bit, so as to
enhance cutting.
[0013] As a result of the manufacturing technique of the '202
patent, each diamond-impregnated insert is subjected to a total
thermal exposure that is significantly reduced as compared to
previously known techniques for manufacturing infiltrated
diamond-impregnated bits. For example, diamonds imbedded according
to the '202 patent have a total thermal exposure of less than 40
minutes, and more typically less than 20 minutes (and more
generally about 5 minutes), above 1500.degree. F. This limited
thermal exposure is due to the hot pressing period and the brazing
process. This compares very favorably with the total thermal
exposure of at least about 45 minutes, and more typically about
60-120 minutes, at temperatures above 1500.degree. F., that occur
in conventional manufacturing of furnace-infiltrated,
diamond-impregnated bits. When diamond-impregnated inserts are
affixed to the bit body by adhesive or by mechanical means such as
interference fit, the total thermal exposure of the diamonds is
even less.
[0014] Another type of bit is disclosed in U.S. Pat. Nos.
4,823,892; 4,889,017; 4,991,670; and 4,718,505, in which
diamond-impregnated abrasion elements are positioned behind the
cutting elements in a conventional tungsten carbide (WC) matrix bit
body. The abrasion elements are not the primary cutting structures
during normal bit use.
[0015] A second type of fixed cutter drill bit known in the art are
polycrystalline diamond compact (PDC) bits. Typical PDC bits
include a bit body which is made from powdered tungsten carbide
infiltrated with a binder alloy within a suitable mold form. The
particular materials used to form PDC bit bodies are selected to
provide adequate toughness, while providing good resistance to
abrasive and erosive wear. The cutting elements used on these bits
are typically formed from a cylindrical tungsten carbide "blank" or
substrate. A diamond "table" made from various forms of natural
and/or synthetic diamond is affixed to the substrate. The substrate
is then generally brazed or otherwise bonded to the bit body in a
selected position on the surface of the body.
[0016] The materials used to form PDC bit bodies, in order to be
resistant to wear, are very hard and difficult to machine.
Therefore, the selected positions at which the PDC cutting elements
are to be affixed to the bit body are typically formed
substantially to their final shape during the bit body molding
process. A common practice in molding PDC bit bodies is to include
in the mold at each of the to-be-formed cutter mounting positions,
a shaping element called a "displacement." A displacement is
generally a small cylinder made from graphite or other heat
resistant material which is affixed to the inside of the mold at
each of the places where a PDC cutter is to be located on the
finished drill bit. The displacement forms the shape of the cutter
mounting positions during the bit body molding process. See, for
example, U.S. Pat. No. 5,662,183 issued to Fang for a description
of the infiltration molding process using displacements.
[0017] FIG. 4 shows a prior art PDC drill bit. In FIG. 4, the bit
body 100 has thereon a plurality of blades 110. Each of the blades
110 has mounted thereon mounting pads (shaped according to FIG. 3)
a PDC cutting element 112. Each PDC cutting element 112 includes a
diamond table 113 affixed to a tungsten carbide substrate 114. The
bit body 100 includes suitably positioned nozzles or "jets" 120 to
discharge drilling fluid in selected directions and at selected
rates of flow.
[0018] PDC cutting elements typically include a polycrystalline
diamond table bonded to a substrate. The substrate is typically
cylindrical in shape and is formed from a sufficiently hard and
wear-resistant material such as a tungsten-carbide composite.
Formation of the diamond table and its bonding to the substrate are
catalyzed by a metallic binder (typically cobalt) during a high
pressure, high temperature (HPHT) process. PDC cutting elements are
particularly advantageous because the polycrystalline diamond table
can be easily shaped to form a variety of cutter geometries suited
to drill various types of earth formations. For example, the
diamond table can be shaped to have a dome-shaped or curved,
semi-conical geometry suited for drilling hard, highly abrasive
formations, or may be shaped to have a chiseled geometry suited for
drilling formations of soft or medium hardness that require more
shearing action from the cutting elements.
[0019] Although PDC cutting elements offer the benefit of being
able to tailor a particular cutting element to a particular
formation, they are also subject to thermal degradation at the high
temperatures often encountered within the wellbore during the
drilling process. Thermal degradation of PDC cutting elements
occurs as a result of the significant difference in the rates of
thermal expansion of the metallic binder and the diamond table. At
temperatures at or above 350.degree. C. (662.degree. F.), the
metallic binder expands much more rapidly than the diamond,
resulting in fracturing of the diamond table and degradation of the
PDC cutting element.
[0020] Thermally stable polycrystalline diamond (TSP) cutting
elements may be used in lieu of PDC cutting elements. TSP cutting
elements are not subject to the same thermal instability of PDC as
they are thermally stable up to a temperature of 1200.degree. C.
(2192.degree. F.). TSP is typically formed by "leaching" residual
cobalt from a polycrystalline diamond table, and this process is
described in further detail herein.
[0021] Similar to PDC cutting elements, the diamond table in TSP
cutting elements can also be shaped to form various cutter
geometries. Two common TSP cutting element shapes are the
"tombstone" TSP and the "wedge" TSP. These TSP cutting elements are
shown in FIGS. 4B and 4C, respectively. The tombstone and wedge
TSPs include sharp edges 401, 402, 403, 404. The sharp edges that
form part of cutting faces 401, 403 of the TSP cutting elements
improve the ability of the cutting elements to shear formations.
The TSP cutting elements also include sharp edges 402, 404 on the
portion of the cutting elements that will be bonded to a support
(not shown). These sharp edges 402, 404 that contact the support
have been shown to create stress risers within the support, leading
to cracking of the support and delamination of the TSP cutting
element. Thus, TSP cutting elements that are shaped for improved
cutting and retention are still needed.
[0022] Different types of bits are selected based on the primary
nature of the formation to be drilled. However, many formations
have mixed characteristics (i.e., the formation may include both
hard and soft zones), which may reduce the rate of penetration of a
bit (or, alternatively, reduces the life of a selected bit) because
the selected bit is not preferred for certain zones. One type of
"mixed formation" includes abrasive sands in a shale matrix. In
this type of formation, if a conventional diamond-impregnated bit
is used, because the diamond table exposure of this type of this
bit is small, the shale can fill the gap between the exposed
diamonds and the surrounding matrix, reducing the cutting
effectiveness of the bit (i.e., decreasing the rate of penetration
(ROP)). In contrast, if a PDC cutter is used, the PDC cutter will
shear the shale, but the abrasive sand will cause rapid cutter
failure (i.e., the ROP will be sufficient, but wear characteristics
will be poor).
[0023] When drilling a typical well, a bit is run on the end of a
bottom hole assembly (BHA) and the bit drills a wellbore with a
selected diameter. However, during drilling operations, it may be
desirable to increase a diameter of a drilled hole to a selected
larger diameter. Moreover, increasing the diameter of the wellbore
may be necessary if, for example, the formation being drilled is
unstable such that the wellbore diameter decreases after being
drilled by the drill bit. Accordingly, tools such as "hole openers"
and "underreamers" have been designed to enlarge diameters of
drilled wellbores. These types of tools also may be thought of as
using fixed cutters.
[0024] In some drilling environments, it may be advantageous, from
an ease of drilling standpoint, to drill a smaller diameter hole
(e.g., and 81/2 inch diameter hole) before opening the hole to a
larger diameter (e.g., to a 171/2 inch diameter hole) with a hole
opener. Moreover, it is difficult to directionally drill a wellbore
with a large diameter bit because, for example, larger diameter
bits have an increased tendency to "torque-up" (or stick) in the
wellbore. When the larger diameter bit torques-up, the bit tends to
stick and drill a tortuous trajectory as it periodically sticks and
then unloads torque. Therefore it is often advantageous to
directionally drill a smaller diameter hole before running a hole
opener in the wellbore to increase the wellbore to a desired larger
diameter.
[0025] A typical prior art hole opener is disclosed in U.S. Pat.
No. 4,630,694 issued to Walton et al. The hole opener includes a
bull nose, a pilot section, and an elongated body adapted to be
connected to a drillstring used to drill a wellbore. The hole
opener also includes a triangularly arranged, hardfaced blade
structure adapted to increase the diameter of a wellbore.
[0026] Another prior art hole opener is disclosed in U.S. Pat. No.
5,035,293 issued to Rives. The hole opener may be used either as a
sub in a drillstring or may be run on the end of a drillstring in a
manner similar to a drill bit. The hole opener includes radially
spaced blades with cutting elements and shock absorbers disposed
thereon. A described in detail below, embodiments of the present
invention relate to hole opening technology in addition to bits,
typically found at the end of a BHA.
[0027] In light of the difficulties in dealing with mixed
formations by prior art tools, what is still needed, therefore, are
improved cutting structures that are suited to drill various types
of formations.
SUMMARY OF INVENTION
[0028] In one embodiment, the present invention relates to a
cutting element for a downhole cutting tool comprising, a support
element and a beveled shearing element disposed on the support
element, wherein the beveled shearing element comprises thermally
stable polycrystalline diamond.
[0029] In another embodiment, the present invention relates to a
cutting element for a downhole cutting tool, comprising a support
element, a shaped shearing element disposed on the support element,
wherein the shaped shearing element is disposed proximal to a
leading edge of the downhole cutting tool, and a retaining element
overlaying at least a portion of the shaped shearing element.
[0030] In another embodiment, the present invention relates to a
cutting element for a downhole cutting tool comprising, a support
element and a shearing element disposed on the support element,
wherein the shearing element comprises thermally stable
polycrystalline diamond, a sharpened cutting edge proximal to a
leading edge of the downhole cutting tool, and at least one blended
edge, wherein the at least one blended edge forms part of an
interface with the support element.
[0031] In another embodiment, the present invention relates to a
cutting element for a downhole cutting tool comprising, a support
element and a shearing element disposed on the support element,
wherein the shearing element comprises thermally stable
polycrystalline diamond, a sharpened cutting edge proximal a
leading edge of the downhole cutting tool, at least one blended
edge, wherein the at least one blended edge forms part of an
interface with the support element, at least one tapered surface,
and at least one perturbation on at least one surface of the
shearing element.
[0032] In another embodiment, the present invention relates to a
drill bit comprising, a bit body having at least one support
element disposed thereon and a shearing element disposed on the at
least one support element, wherein the shearing element comprises
thermally stable polycrystalline diamond, a sharpened cutting edge
proximal a leading edge of the downhole cutting tool, and at least
one blended edge, wherein the at least one blended edge forms part
of an interface with the at least one support element.
[0033] In another embodiment, the present invention relates to a
drill bit comprising, a bit body and a plurality of inserts
disposed on the bit body, wherein at least one of the plurality of
inserts comprises an insert body and a beveled shearing element
disposed on the insert body.
[0034] In another embodiment, the present invention relates to a
drill bit comprising a bit body and a plurality of inserts disposed
on the bit body, wherein at one of the plurality of inserts
comprises an insert body and a shearing element disposed on the
insert body, wherein the shearing element comprises thermally
stable polycrystalline diamond, a sharpened cutting edge proximal a
leading edge of the downhole cutting tool, and at least one blended
edge, wherein the at least one blended edge forms part of an
interface with the insert body. Additionally, the shearing element
may be tapered toward the insert body and at least one perturbation
on at least one surface of the shearing element may be present.
[0035] In another embodiment, the present invention relates to a
method for forming an insert comprising, forming an insert body,
forming a shearing element, wherein the shearing element comprises
a sharpened cutting edge proximal a leading edge of the downhole
tool and at least one blended edge, and bonding the shearing
portion to the diamond-impregnated insert body, wherein the bond
forms an interface including the at least one blended edge.
[0036] In another embodiment, the present invention relates to a
method for forming a diamond-impregnated insert comprising, forming
a diamond-impregnated insert body, forming a beveled shearing
element, and bonding the beveled shearing element to the
diamond-impregnated insert body.
[0037] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0038] FIG. 1 shows a prior art diamond impregnated bit;
[0039] FIG. 2 is a perspective view of a second type of diamond
impregnated bit;
[0040] FIG. 3 shows rotated inserts;
[0041] FIG. 4 shows a prior art PDC drill bit;
[0042] FIGS. 4B-4C show various TSP cutting shapes.
[0043] FIGS. 5A-5B show a cutting structure formed in accordance
with an embodiment of the present invention;
[0044] FIGS. 5C-5D show shearing elements made in accordance with
embodiments of the present invention;
[0045] FIG. 6 shows a drill bit formed using cutting structures in
accordance with embodiments of the present invention;
[0046] FIG. 7A shows a drill bit formed using cutting structures
formed in accordance with embodiments of the present invention that
further includes PDC cutting elements;
[0047] FIG. 7B shows a drill bit formed using cutting structures
formed in accordance with embodiments of the present invention that
further includes PDC cutting elements;
[0048] FIG. 7C shows a drill bit formed using cutting structures
formed in accordance with embodiments of the present invention that
further includes PDC cutting elements;
[0049] FIG. 8 shows a downhole cutting tool in accordance with one
embodiment of the present invention;
[0050] FIG. 9 shows a flow chart illustrating one method of forming
a cutting structure in accordance with an embodiment of the present
invention
[0051] FIG. 10 shows a removable overlay that is attached to a TSP
in accordance with an embodiment of the present invention;
[0052] FIG. 11 shows a coated TSP shearing element in accordance
with an embodiment of the present invention;
[0053] FIG. 12 shows an insert made in accordance with an
embodiment of the present invention;
[0054] FIG. 13 shows a drill bit made in accordance with
embodiments of the present invention;
[0055] FIG. 14 shows an insert made in accordance with embodiments
of the present invention;
[0056] FIGS. 15A-15B show inserts having shearing elements made in
accordance with the present invention;
[0057] FIG. 16 shows an insert made in accordance with an
embodiment of the present invention;
[0058] FIGS. 17A-17B show inserts made in accordance with
embodiments of the present invention;
[0059] FIGS. 18A-18D illustrate methods for enhancing a bond
between a shearing portion and a substrate in accordance with an
embodiment of the present invention;
[0060] FIG. 19 shows an impreg bit formed in accordance with one
embodiment of the present invention;
[0061] FIG. 20 shows a PDC bit, which includes inserts formed in
accordance with one embodiment of the present invention;
[0062] FIG. 21 shows a flow chart illustrating one method of
forming an insert in accordance with the present invention;
[0063] FIG. 22A-22B show exemplary shearing portions for use in
inserts in accordance with the present invention; and
[0064] FIG. 23 shows an insert in accordance with one embodiment of
the present invention.
DETAILED DESCRIPTION
[0065] One aspect of the present invention relates to a cutting
structure that uses a shearing element, disposed on a support. In
particular, the present invention relates to a cutting structure
for use in lieu of, or in combination with, PDC cutter elements to
provide a shearing action. Embodiments of the present invention are
particularly useful in high speed applications, such as
applications that use a mud motor and/or turbines.
[0066] In another embodiment of the present invention, at least a
portion of the shearing element is overlaid by a retaining element
to provide an additional retention mechanism to prevent the
shearing element from dislodging from the support. The retaining
element may be integrally formed with the support, or may be
discretely applied to the shearing element and formed from either
the same composition as the support or a different composition.
[0067] In another embodiment of the present invention, diamond
impregnated blades, which are used in lieu of the matrix or steel
blades commonly used in PDC bits, provide the support for a TSP
diamond shearing element.
[0068] The manufacturing of TSP is known in the art, but a brief
description of a process for manufacturing TSP is provided herein
for convenience. A diamond table is a layer of randomly oriented
individual diamond "crystals" that are bonded together at bonding
lines known as diamond-diamond boundaries in the art. The bonding
of individual diamond crystals in the diamond table forms a lattice
structure. A metallic binder, typically cobalt, serves as a
catalyst in the formation of bonds between individual diamond
crystals, and is often found within the interstitial spaces in the
diamond table's lattice structure. Cobalt has a significantly
different coefficient of thermal expansion as compared to diamond,
so upon heating of the diamond table, the cobalt will expand more
rapidly than the diamond table, causing cracks to form in the
lattice structure, and eventually resulting in deterioration of the
diamond table.
[0069] In order to impede crack initiation and propagation in the
diamond table resulting from differential thermal expansion, strong
acids are used to "leach" the cobalt from the diamond lattice
structure. The removal of cobalt from the diamond table results in
thermal stability of the diamond table at higher temperatures but
also increases its brittleness. Accordingly, in certain cases, only
a select portion (measured in any dimension) of a diamond table is
leached, in order to gain thermal stability without losing impact
resistance. As used herein, the term TSP includes both of the above
(i.e., partially and completely leached) compounds.
[0070] As a result of these structures, embodiments of the present
invention provide a "shear bit" with shearing cutting elements
positioned at a leading edge of the blade that are supported by a
selected material. In some embodiments, the shearing element (which
may be TSP), is coated with a titanium carbide or silicon carbide
coating, to enhance its retention through chemical means. Further,
the shearing element may be shaped, as discussed with reference the
FIGS. below, to mimic the shapes of traditional PDC cutters or,
depending on the application, to have other selected
geometries.
[0071] A cutting structure in accordance with an embodiment of the
present invention is now described, with reference to FIGS. 5A and
5B. In FIG. 5A, a support 502 is shown. In certain embodiments, the
support 502 comprises a diamond impregnated support. In the
embodiment shown in FIG. 5A, the support 502 comprises a blade, as
is known for PDC bits. Shaped shearing elements 500, are disposed
at selected locations on the support 502. The shaped shearing
elements 500 may comprise polycrystalline diamond compact (PDC) or
thermally stable polycrystalline diamond (TSP). The shearing
elements 500 are placed proximal to a leading edge 508. Moreover,
in this embodiment, a retaining portion 504 is provided to cover at
least a portion of the shaped shearing element 500 (as shown in
FIG. 5B).
[0072] In this embodiment, the retaining portion 504 is formed from
the support 502, and is created during the manufacturing process.
However, in other embodiments, the retaining portion may comprise a
discretely applied support, which may be formed from the same
materials as the support 502 or different materials. The retaining
portion 504 may be a diamond-impregnated material, a tungsten
carbide composite, a cubic boron nitride composite, or any other
suitable materials known in the art. By covering at least a portion
of the shearing elements 500, the retaining portion 504 provides a
"mechanical" retention mechanism, and decreases the likelihood of
the shearing element 500 coming free from the support 502.
[0073] Moreover, in FIGS. 5A and 5B, the shearing elements 500 are
shown having a "teardrop" shape, so that an exposed portion 510
(i.e., the portion of the shearing element 500 not covered by the
retaining portion 504) mimics the shape of a typical PDC cutter.
Because the shearing elements 500 can be so shaped, and because the
support can be molded into the shape of a blade, embodiments of the
present invention can be used in applications where PDC bits are
typically used. Thus, embodiments of the present invention provide
the advantages of PDC bits, such as shearing action and hydraulics
cleaning. In some embodiments, these advantages may be realized
without the limitation of high wear in abrasive formations that PDC
bits typically experience, because TSP may be used as a shearing
element.
[0074] The shearing elements 500 in FIG. 5B are backed by a
material 506 on the drill bit (not shown). The backing material 506
provides support for the shearing element 500 during the drilling
process. The backing material may comprise a diamond impregnated
material. In other embodiments, the backing material may be
tungsten carbide.
[0075] A shearing element having sharp edges may cause cracking or
chipping of the support element at an interface between the
shearing element and the support material. Thus, in an embodiment
of the present invention, the shearing element may have rounded or
beveled edges at the portion of the shearing element that contacts
the support element.
[0076] Referring to FIG. 5c, a shearing element 516 in accordance
with the present invention, comprises at least one rounded edge 520
on a portion of the shearing element 516 that is bonded to a
support element (not shown). The shearing element may comprise PDC
or TSD. A retaining element 524 may overlay at least a portion of
the shearing element 516. The retaining element 524 may be formed
integrally with the support element or discretely applied to the
shearing element and may comprise a cubic boron nitride composite,
a tungsten carbide composite, or a diamond-impregnated material
such as a diamond-impregnated tungsten carbide composite. The
retaining element 524 provides increased retention of the shearing
element 516 and supplements the retention provided by the bonding
of the shearing element 516 to the support element. When the
shearing element 516 is disposed on the support element (not
shown), which may comprise a blade or a bit body, the at least one
rounded edge 520 minimizes stress risers within the support element
that may cause cracks to form within the support element and
separation of the shearing element 516 from the support element.
Further, the shearing element 516 may comprise at least one tapered
surface 528. The tapered surface 528 provides a "gripping" action
of the shearing element 516 to the attached support element and
increased retention of the shearing element 516. Additionally, the
shearing element 516 may comprise a rounded edge 530 on a cutting
face of the shearing element 516. The rounded edge 530 on the
cutting face may improve impact resistance of the shearing element
516 during drilling. Also, the shearing element 516 may have a
non-planar contoured cutting face that may comprise various cutting
geometries such as convex, concave, "saddle" shaped, chiseled,
etc.
[0077] Referring to FIG. 5d, a shearing element 540 in accordance
with the present invention, comprises at least one beveled edge 542
on a portion of the shearing element that is bonded to a support
element (not shown). The shearing element 540 may comprise PDC or
TSD. Additionally, a retaining element 544 may overlay at least a
portion of the shearing element 540 and may comprise any of the
materials discussed above in reference to FIG. 5c. When the
shearing element 540 is disposed on the support element (not
shown), which may be a blade or a bit body, the at least one
beveled edge 542 minimizes stress risers within the support element
that may cause cracking in the support element and separation of
the shearing element 540 from the support element. Consequently,
the at least one beveled edge 542 improves retention of the
shearing element to the support element. Further, the shearing
element 540 may comprise at least one tapered surface 546 which
also provides for increased retention of the shearing element 540
to the attached support element through a "gripping" action,
whereby stresses acting on the shearing element 540 are distributed
throughout the support element. Additionally, the shearing element
540 may comprise at least one beveled edge 550 on a cutting face of
the shearing element. The at least one beveled edge 550 on the
cutting face may improve impact resistance of the shearing element
during drilling and help prevent abrasive wear of the shearing
element and extend its drilling life. The shearing element 540 may
have a non-planar contoured cutting face that may comprise various
cutting geometries such as convex, concave, "saddle" shaped,
chiseled, etc.
[0078] FIG. 6a illustrates a drill bit having cutting elements
formed in accordance with an embodiment of the present invention.
In FIG. 6a, a bit body 600 has a plurality of blades 610 extending
from the bit body 600. In this embodiment, the blades 610 are
formed from a diamond impregnated material, which may be
manufactured using any technique known in the art. The bit body 600
itself may also be formed from a diamond impregnated material, or
may be formed from a high strength matrix material (known to those
having ordinary skill in the art), or may be steel (which may be
overlaid with hardfacing).
[0079] The blades 610 have cutting elements 612 mounted at select
locations. The cutting elements 612 include at least one shaped
shearing element, comprising PDC or TSP supported by diamond
impregnated material, that forms the blades 610. Moreover, a
retaining portion 614 is disposed over at least a portion of the
shearing element 612, to help prevent improve retention. The
cutting elements 612 are arranged proximal to a leading edge 630 of
the blades 610, such that the shearing portion (not separately
numbered) contacts the formation to be drilled. The shearing
element 612 is so disposed to provide substantially continuous
shearing engagement with an earth formation during drilling.
Furthermore, the bit body 600 includes suitably positioned nozzles
or "jets" 620 to discharge drilling fluid in selected directions
and at selected rates of flow.
[0080] Moreover, in certain embodiments, the shearing element may
be coated with a material to either create or enhance a bond
between the support (e.g., the blades 610 in the embodiment
described above) and the shearing element (e.g., cutting element
612 in the embodiment described above). In various embodiments, the
coating may comprise a titanium based coatings, tungsten based
coatings, nickel coatings, silicon coatings, various carbides,
nitrides, and other materials known to those skilled in the art. In
particular embodiments, a TSP shearing element is provided with a
titanium or silicon carbide coating. FIG. 11 illustrates a titanium
carbide coating 1110 deposited on shearing element 1100, which is
disposed on a support element 1120. In another embodiment, the
coating comprises silicon carbide.
[0081] FIG. 7A illustrates another embodiment of the present
invention. In this embodiment, shearing elements formed in
accordance with an embodiment of the present invention are used in
combination with standard PDC inserts. In particular, as shown in
FIG. 7A, two groups of cutting elements 710, 720 are shown
extending from bit body 700. The first group of cutting elements
710, which extend slightly further and, therefore, will engage the
formation first, comprise PDC inserts. The PDC inserts comprise a
cylindrical tungsten carbide substrate to which a diamond table
made from various forms of natural and/or synthetic diamond is
bonded. The substrate is brazed or otherwise bonded to the bit body
700 in a selected position.
[0082] The second group of cutting elements 720 comprise a shaped
shearing element having a retaining portion 724 overlaying at least
a portion of the cutting elements 720 to help prevent cutting
element 720 loss. The shaped shearing element 720 may comprise at
least one rounded edge and at least one beveled edge.
[0083] When drilling, the first group of cutting elements 710
(which include the "standard" PDC cutters) interact with the
formation first. After drilling for a period of time, the PDC
cutting elements 710 will begin to wear. At some point during the
drilling process, the PDC cutters will wear to the point where the
cutting elements 720 begin to interact with and shear the
formation.
[0084] In some embodiments, the shearing elements (which may
comprise PDC or TSP) may be disposed to follow or track PDC cutters
(on the same radius) to minimize PDC wear progress. In other
embodiments, the shearing elements may be arranged at a different
exposure than the PDC cutter where the diamond volume (assuming
that the shearing element comprises diamond) increases once PDC
cutters are worn beyond a certain degree (i.e., both sets of
cutting elements begin to interact with the formation). Also, in
some embodiments, the different cutting elements may alternate
where elements having similar characteristics track. The higher
wear on the PDC cutters will leave more pronounced scallops on the
hole bottom to stabilize the bit and reduce vibration.
[0085] This structure for a drill bit, which uses two different
types of cutters, is particularly advantageous for formations that
go from "soft" to "hard." PDC cutters wear relatively quickly in
hard formations, causing a significant drop in the rate of
penetration (ROP). However, by using a structure as described
above, the shearing elements begin to interact with the formation
as the PDC cutters wear, maintaining or even increasing ROP.
[0086] Again, it is noted that while reference has been made to
particular compositions and structures in the above embodiments,
the present invention is not so limited. In particular, embodiments
of the present invention relate to a shearing element disposed on a
support, the shearing element being disposed to provide shearing
engagement with an earth formation during drilling. In certain
embodiments, the shearing element may be formed from TSP, CBN,
and/or polycrystalline diamond.
[0087] Further, as shown in FIG. 7B, in certain embodiments, the
support 730 comprises a diamond impregnated material, but may be
formed from matrix materials (any suitable material known in the
art), or steel, for example. In some other embodiments, the support
730 is layered with tungsten carbide. Those having ordinary skill
in the art will recognize that other materials may be used.
[0088] Still referring to FIG. 7B, in certain embodiments, the
shaped shearing element 750 is formed such that the leading edge
consists of essentially a single type of material. Moreover, in
certain embodiments, a retaining element 754 is provided. The
retaining element 754 may be formed integrally from the support
element 730, or may comprise a discrete element that may or may not
be formed from the same material as the support 730.
[0089] In FIG. 7B, the supports 730 include PDC cutters 740 as well
as shaped shear cutters 750. The shear cutters 750 may be formed of
TSP, CBN and/or polycrystalline diamond and may comprise at least
one rounded edge or at least one beveled edge. In some embodiments,
a retaining portion 754 covers at least a portion of the shear
cutters 750 to help prevent shear cutter loss. In some embodiments,
such as the one shown in FIG. 7B, the PDC cutters 740 and the shear
cutters 750 are alternately positioned on the support 730. The
retention portion 754 is positioned to cover at least a portion of
the shear cutters 750, but not any of the PDC cutters 740. Other
arrangements of a retention member, such as one that also covers a
portion of the PDC cutters, may be used, without departing from the
scope of the invention.
[0090] The cutters 740, 750 may be arranged on the support 730 to
have various positions and exposures that are advantageous for the
particular formation to be drilled. In one example, a shear cutter
750a is positioned to at least partially track a PDC cutter 740. In
another example, a PDC cutter element 740b may be positioned to at
least partially track a shear cutter 750b.
[0091] Additionally, the exposures of the cutters 740, 750 may be
varied to suit a particular application. In some embodiments, the
PDC cutters 740 may have substantially the same exposure as the
shear cutters 750. In other embodiments, the PDC cutters 740 and
the shear cutters 750 may have different exposures. For example,
the PDC cutters 740 may have a higher exposure than shear cutters
750. Alternatively, the shear cutters 750 may have a higher
exposure than the PDC cutters.
[0092] In addition, some embodiments may be arranged so that a
cutting element that partially tracks another cutting element has a
different exposure than the cutting element that it tracks. For
example, a PDC cutter 740a may have a higher exposure than a shear
cutter 750a that tracks the PDC cutter 740a. Alternatively, the
shear cutter 750a may have a higher exposure than the PDC cutter
740a that it tracks. The same is true for a shear cutter 750b that
is tracked by a PDC cutter 740b. The shear cutter 750b may have a
higher exposure than the PDC cutter 740b, or the PDC cutter 740b
may have a higher exposure than the shear cutter 750b.
[0093] FIG. 7C shows another embodiment of a drill bit 760 with
cutters 770, 780 positioned on a support 764. The inner profile
766, which extends from the axis of the drill bit 760 to a selected
radial distance from the axis, is comprised of PDC cutters 770 that
are disposed on the support 764. The outer profile 767 of the drill
bit 760, which extends from the inner profile 766 to the outside
radius of the drill bit 760, is comprised of shear cutters 780 that
are disposed on the support 764. The shaped shear cutters 780 may
be formed of TSP, CBN and/or polycrystalline diamond and may
comprise at least one rounded edge, at least one beveled edge,
and/or at least one tapered surface. A retaining element 774 covers
at least a portion of the shear cutters 780 to help prevent shear
cutter loss. In at least one other embodiment, the inner profile
766 is comprised of shear cutters 780 and the outer profile is
comprised of PDC cutters 770.
[0094] In other embodiments of the present invention, cutting
structures formed in accordance with the present invention may be
used in a downhole drilling tool, which in one embodiment may be a
hole opener. FIG. 8 shows a general configuration of a hole opener
830 that includes one or more aspects of the present invention. The
hole opener 830 comprises a tool body 832 and a plurality of blades
838 disposed at selected azimuthal locations about a circumference
thereof. The hole opener 830 generally comprises connections 834,
836 (e.g., threaded connections) so that the hole opener 830 may be
coupled to adjacent drilling tools that comprise, for example, a
drillstring and/or bottom hole assembly (BHA) (not shown). The tool
body 832 generally includes a bore therethrough so that drilling
fluid may flow through the hole opener 830 as it is pumped from the
surface (e.g., from surface mud pumps (not shown)) to a bottom of
the wellbore (not shown). The tool body 832 may be formed from
steel or from other materials known in the art. For example, the
tool body 832 may also be formed from a matrix material infiltrated
with a binder alloy.
[0095] The blades 838 shown in FIG. 8 are spiral blades and are
generally positioned at substantially equal angular intervals about
the perimeter of the tool body, i.e. the hole opener 830. This
arrangement is not a limitation on the scope of the invention, but
rather is used merely for illustrative purposes. Those having
ordinary skill in the art will recognize that any prior art
downhole cutting tool may be used. In this embodiment, the blades
838 are formed from matrix material infiltrated with a binder
alloy, and cutting elements 840 such as those described above with
reference to FIG. 5 are disposed on the blades 838. Other blade
arrangements may be used with the invention, and the embodiment
shown in FIG. 8 is not intended to be limiting.
[0096] Moreover, in addition to downhole tool applications such as
a hole opener, reamer, stabilizer, etc., a drill bit using cutting
elements according to various embodiments of the invention such as
disclosed herein may have improved drilling performance at high
rotational speeds as compared with prior art drill bits. Such high
rotational speeds are typical when a drill bit is turned by a
turbine, hydraulic motor, or used in high rotary speed
applications.
[0097] As known in the art, various types of hydraulically,
pneumatically, or rotary operated motors can be coupled to the bit.
These so-called "mud motors" are operated by pumping drilling fluid
through them. Generally, there are two basic types of mud motors.
One type of motor is called "positive displacement." Positive
displacement motors include a chambered stator in the interior of
the motor housing which is usually lined with an elastomeric
material, and a rotor which is rotationally coupled to the motor
output shaft (and thence to the drill bit).
[0098] Movement of drilling fluid through chambers defined between
the stator and rotor causes the rotor to turn correspondingly to
the volume of fluid pumped through the motor. The other type of mud
motor is called "turbine," because the output of the motor is
coupled to a turbine disposed inside the motor housing. As those
having ordinary skill in the art will appreciate, the additional
motors cause a higher rotational speed in the bit. By coupling
cutting structures in accordance with embodiments of the present
invention with motors, turbines, and the like, higher penetration
rates can be achieved. The cutting structures in accordance with
the present invention provide the necessary flow required, as well
as providing the necessary durability, to survive under these
conditions.
[0099] In one embodiment of the invention, the support (which may
comprise the blades and/or the body of the bit) is made from a
solid body of matrix material formed by any one of a number of
powder metallurgy processes known in the art. During the powder
metallurgy process, abrasive particles and a matrix powder are
infiltrated with a molten binder material. Upon cooling, the
support includes the binder material, matrix material, and the
abrasive particles suspended both near and on the surface of the
drill bit. The abrasive particles typically include small particles
of natural or synthetic diamond. As noted above, synthetic diamond
used in diamond impregnated drill bits is typically in the form of
single crystals. However, TSP diamond particles may also be
used.
[0100] One suitable method of forming a cutting structure in
accordance with an embodiment of the present invention is now
described, with reference to FIG. 9. In the present invention, as
illustrated in FIG. 9, a shaped shearing element is placed into a
mold (step 900). Depending on the embodiments, the shearing element
may comprise TSP diamond. Further, in certain embodiments, the
shearing element may be coated with a chemical coating, such as
titanium carbide or silicon carbide. In order to form the retaining
portion that overlays the shearing element in embodiments of the
present invention, a removable overlay is attached to the shearing
element, prior to being placed in the mold. This structure is shown
in FIG. 10.
[0101] In FIG. 10, removable overlay 1020 is shown attached to TSP
diamond shearing element 1010. The removable overlay 1020 is also
shown in contact with mold bottom 1030. The removable overlay 1020
is formed from a material such that during the diamond infiltration
process (resulting in the diamond impregnated support) it is
destroyed. In one embodiment, the removable overlay 1020 may be
formed from sand.
[0102] Returning to FIG. 9, after the shearing elements (and the
removable overlay) are placed into the mold, one of two steps may
occur. A discrete retaining portion may be added or, a "charge" of
matrix powder (which may be tungsten carbide) is added to "fill"
the mold (step 910).
[0103] A binder, and more specifically an infiltrant, (which may be
a nickel brass copper based alloy), along with the diamonds (in the
case where the support comprises a diamond impregnated support), is
placed on top of the charge of powder. The mold is then heated
sufficiently to melt the infiltrant and held at an elevated
temperature for a sufficient period to allow it to flow into and
bind the powder matrix or matrix and segments. For example, the bit
body may be held at an elevated temperature (>1800.degree. F.)
for a period on the order of 0.75 to 2.5 hours, depending on the
size of the bit body, during the infiltration process (step
920).
[0104] The diamond particles which are used to form the diamond
impregnated support may be either natural or synthetic diamond, or
a combination of both. The matrix in which the diamonds are
embedded to form the diamond impregnated material should satisfy
several requirements. The matrix preferably has sufficient hardness
so that the diamonds exposed at the cutting face are not pushed
into the matrix material under the very high pressures encountered
in drilling. In addition, the matrix preferably has sufficient
abrasion resistance so that the diamond particles are not
prematurely released.
[0105] To satisfy these requirements, as an exemplary list, the
following materials may be used for the matrix in which the
diamonds are embedded: tungsten carbide (WC), tungsten alloys such
as tungsten/cobalt alloys (W--Co), and tungsten carbide or
tungsten/cobalt alloys in combination with elemental tungsten (W)
(all with an appropriate binder phase to facilitate bonding of
particles and diamonds) and the like. Those of ordinary skill in
the art will recognize that other materials may be used for the
matrix, including titanium-based compounds, nitrides (in particular
cubic boron nitride), etc.
[0106] It will be understood that the materials commonly used for
construction of bit bodies can be used in the present invention.
Hence, in one embodiment, the bit body may itself be
diamond-impregnated. In an alternative embodiment, the bit body
comprises infiltrated tungsten carbide matrix that does not include
diamond. If this is the case, the blades which form the support for
the shearing element may or may not be separately formed from
diamond impregnated material. In an alternative embodiment, the bit
body can be made of steel, according to techniques that are known
in the art. The bit can optionally be provided with a layer of
hardfacing. Again, if this is the case, the blades may be formed
from diamond impregnated material.
[0107] Advantageously, cutting structures formed in accordance with
embodiments of the present invention provide drill bits and
downhole cutting tools that provide good shearing action, even in
hard formations. Moreover, embodiments of the present invention
provide drill bits and downhole cutting tools that may be run at
high speeds (i.e., higher bit RPM's).
[0108] In another embodiment, the present invention relates to a
cutting element disposed on a downhole cutting tool comprising a
support element and a shearing element, wherein the shearing
element comprises thermally stable polycrystalline diamond (TSP), a
sharpened cutting edge proximal to a leading edge of the downhole
tool, and at least one blended edge, wherein the blended edge forms
part of an interface with the support element.
[0109] FIG. 12 shows a TSP shearing element in accordance with an
embodiment of the invention. The shearing element 1200 is disposed
on a support element 1206. The support element 1206, in this
embodiment, comprises a blade, but may also comprise a bit body or
an insert body. The shearing element 1200 and the support element
1206 together form a cutting element 1210 that may be disposed on a
downhole cutting tool (not shown). The shearing element 1200
comprises at least one sharpened cutting edge 1201 which is
disposed proximal a leading edge of the downhole tool. Further, the
shearing element 1200 may comprise a non-planar cutting face having
various cutting geometries such as convex, concave, "saddle"
shaped, chiseled, etc. Additionally, the shearing element 1200
comprises at least one blended edge 1202 on a portion 1205 of the
shearing element 1200. The blended edge 1202 may take on any
geometry whereby the intersection of the two surfaces that form the
edge 1202 is not a single line. The blended edge 1202 forms part of
an interface 1207 between the shearing element 1200 and the support
element 1206 to which it is bonded. The blended edge 1202 minimizes
stress risers in the support element 1206 that cause cracks to form
and propagate within the support element 1206 and eventually lead
to loss of the shearing element 1200.
[0110] Traditional TSP cutting elements include a TSP shearing
element having sharp edges on the portion of the shearing element
that is bonded to a support element. Examples of such shearing
elements are the "tombstone" and "wedge" TSP shearing elements
discussed earlier. The sharp edges create large stresses within the
support element, and more particularly, at the interface between
the shearing element and the support element during drilling. The
stresses lead to crack formation within the support element and
eventual delamination of the shearing element from the support
element. The shearing element 1200 in accordance with the
invention, minimizes these stresses within the support element 1206
and at the interface between the support element 1206 and the
shearing element 1200.
[0111] Additionally, the shearing element 1200 may comprise at
least one tapered surface 1203. The tapered surface 1203 provides
for increased retention of the shearing element 1200 to the support
element 1206 through a "gripping" action that distributes stresses
acting on the shearing element 1200 throughout the support element
1206 rather than having them localize at the interface 1207.
[0112] The shearing element 1200 may also comprise at least one
perturbation 1204 on at least one surface of the shearing element
1200. In one embodiment, the perturbation 1204 is an indentation
extending along a surface of the shearing element 1200. The
perturbation 1204 may be convex or concave. The perturbation 1204
may improve retention by anchoring the shearing element 1200 to the
support element 1206. The increased bond area at the interface 1207
provided by the perturbation 1204 may contribute to increased
retention. The at least one perturbation 1204 shall not be limited
by the embodiment depicted in FIG. 12. Alternatively, the at least
one perturbation 1204 may comprise at least one raised ridge on a
surface of the shearing element 1200. Moreover, the perturbation
1204 may comprise any alteration of any surface of the shearing
element 1200.
[0113] Referring to FIG. 13, in another embodiment, the invention
relates to a drill bit 1300 including a bit body 1312 having
support elements 1310 disposed thereon. The bit body 1312 may
comprise tungsten carbide with a metallic binder, such as cobalt, a
diamond-impregnated material, or may comprise steel that may be
layer with hardfacing. In this embodiment, the support elements
1310 comprise blades arranged circumferentially around the bit body
1312 in a spiral configuration. In other embodiments, the blades
1310 may be arranged in equal angular intervals around the bit body
1312. The particular arrangement of the blades 1312 shall not limit
the scope of the invention, as any arrangement known in the art may
be used. The blades 1312 may comprise a matrix material such as a
tungsten carbide composite or may comprise a diamond-impregnated
material. The diamond-impregnated material may comprise PDC or TSD.
Cutting elements 1315 are disposed on the support elements 1310. At
least one of the cutting elements 1315 is a shearing element formed
in accordance with the invention. The shearing element 1315
comprises TSP, a sharpened cutting edge 1318 proximal to a leading
edge 1330 of the drill bit 1300, and at least one blended edge on a
portion of the shearing element that is bonded to the support
element 1310. As mentioned above, the blended edge minimizes stress
risers that develop within the support element 1310 and at an
interface between the shearing element and the support element.
These stress risers lead to cracking of the support element 1310
and eventual loss of the shearing element 1315. Additionally, the
shearing element 1315 may comprise a contoured, non-planar cutting
face having various cutting geometries such as concave, convex,
"saddle" shaped, chiseled, etc.
[0114] Still referring to FIG. 13, the shearing element 1315 may
further comprise at least one tapered surface (not shown). The
tapered surface provides for better retention of the shearing
element 1315 to the support element 1310. Additionally, the
shearing element 1315 may comprise at least one perturbation (not
shown) on at least one surface of the shearing element 1315. The
perturbation may be convex or concave and provides increased
retention of the shearing element 1315 to the support element 1310.
The perturbation may comprise an indentation, a raised surface, or
any alteration of a surface of the shearing element 1315.
[0115] Further, a retaining element 1340 may overlay at least a
portion of the shearing element 1315. The retaining element 1340
provides an additional "mechanical" locking mechanism for retention
of the shearing element 1315 to the support element 1310. The
retaining element 1340 may be formed integrally from the support
element 1310, or may be discretely applied to the shearing element
1315. The retaining element 1340 may comprise a tungsten carbide
matrix material, a cubic boron nitride composite, or a
diamond-impregnated material. Jets or nozzles 1320 that expel
drilling fluid in selected directions may also be present. The
drilling fluid removes cuttings from the cutting elements 1315 and
transports cuttings from the bottom of the wellbore to the
surface.
[0116] In one aspect, the present invention relates to
diamond-impregnated inserts that have specialized compositions. In
particular, the present invention relates to inserts that provide a
combination of shearing and grinding action from a single element.
Accordingly, in a preferred embodiment, the present invention
includes the combination of a diamond-impregnated insert with a
second, shearing, "miniature" element.
[0117] According to one embodiment, diamond-impregnated inserts
that will comprise the cutting structure of a bit are formed
separately from the bit. Because the inserts are smaller than a bit
body, they can be hot pressed or sintered for a much shorter time
than is required to infiltrate a bit body. The inserts may be
"brazed" into sockets in order to prevent diamond degradation.
[0118] Referring to FIG. 14, a TSP insert in accordance with an
embodiment of the invention comprises an insert body 1400 to which
a shearing element 1401 is bonded. The insert body 1400 is
typically cylindrical in shape and may comprise a
diamond-impregnated material or a tungsten carbide composite. If
the insert body comprises a diamond-impregnated material (which may
comprise polycrystalline diamond or thermally stable
polycrystalline diamond), it may further comprise a thin layer of
matrix material 1406 to promote efficient brazing of the TSP insert
to a bit body (not shown). Alternatively, the insert body 1400 may
be sintered to the bit body or mechanically attached through
interference fit.
[0119] Still referring to FIG. 14, the shearing element 1401
comprises a sharpened cutting edge 1402 and a blended edge 1403
that forms part of an interface between the shearing element 1401
and the insert body 1400. Any number of sharpened cutting edges and
blended interface edges may be present. Additionally, the shearing
element 1401 may comprise at least one tapered surface 1405 and at
least one perturbation 1404 on at least one surface of the shearing
element 1401. The at least one perturbation 1404 may take on any of
the geometries previously discussed. The tapered surface 1405
provides improved retention of the shearing element 1401 to the
insert body 1400.
[0120] In another embodiment, the present invention relates to a
drill bit having a bit body and a plurality of inserts disposed on
the bit body, wherein at least one of the inserts is the embodiment
described in FIG. 14.
[0121] In a preferred embodiment of the invention, the inserts 1500
are manufactured as individual components, as shown for example in
FIG. 14A. According to one preferred embodiment, diamond particles
and powdered matrix material are placed in a mold. The contents are
then hot-pressed or sintered at an appropriate temperature,
preferably between about 1000 and 2200.degree. F., more preferably
not higher than 1800.degree. F., to form a composite insert.
Heating of the material can be by furnace or by electric induction
heating, such that the heating and cooling rates are rapid and
controlled in order to prevent damage to the diamonds.
[0122] If desired, a very long cylinder having the outside diameter
of the ultimate insert shape can be formed by this process and then
cut into lengths to produce diamond-impregnated inserts 1500 having
the desired length. The dimensions and shape of the
diamond-impregnated inserts 1500 and of their positioning on the
bit can be varied, depending on the nature of the formation to be
drilled.
[0123] The diamond particles can be either natural or synthetic
diamond, or a combination of both. The matrix in which the diamonds
are embedded to form the diamond impregnated inserts 1500 must
satisfy several requirements. The matrix must have sufficient
hardness so that the diamonds exposed at the cutting face are not
pushed into the matrix material under the very high pressures
encountered in drilling. In addition, the matrix must have
sufficient abrasion resistance so that the diamond particles are
not prematurely released. Lastly, the heating and cooling time
during sintering or hot-pressing, as well as the maximum
temperature of the thermal cycle, must be sufficiently low that the
diamonds imbedded therein are not thermally damaged during
sintering or hot-pressing.
[0124] To satisfy these requirements, as an exemplary list, the
following materials may be used for the matrix in which the
diamonds are embedded: tungsten carbide (WC), tungsten alloys such
as tungsten/cobalt alloys (W--Co), and tungsten carbide or
tungsten/cobalt alloys in combination with elemental tungsten (all
with an appropriate binder phase to facilitate bonding of particles
and diamonds) and the like. Those of ordinary skill in the art will
recognize that other materials may be used for the matrix,
including titanium-based compounds, nitrides (in particular cubic
boron nitride), etc.
[0125] In the present invention, at least about 15%, more
preferably about 30%, and still more preferably about 40% of the
diamond volume in the entire cutting structure is present in the
inserts, with the balance of the diamond being present in the bit
body. However, because the diamonds in the inserts have 2-3 times
the rock cutting life of the diamonds in the bit body, in a
preferred embodiment the inserts provide about 57% to about 67% of
the available wear life of the cutting structure. It will further
be understood that the concentration of diamond in the inserts can
vary from the concentration of diamond in the bit body. According
to a preferred embodiment, the concentrations of diamond in the
inserts and in the bit body are in the range of 50 to 100 (100=4.4
carat/cc.sup.3).
[0126] It will be understood that the materials commonly used for
construction of bit bodies can be used in the present invention.
Hence, in the preferred embodiment, the bit body may itself be
diamond-impregnated. In an alternative embodiment, the bit body
comprises infiltrated tungsten carbide matrix that does not include
diamond.
[0127] In an alternative embodiment, the bit body can be made of
steel, according to techniques that are known in the art. Again,
the final bit body includes a plurality of holes having a desired
orientation, which are sized to receive and support inserts 1500.
Inserts 1500 may be affixed to the steel body by brazing,
mechanical means, adhesive or the like. The bit can optionally be
provided with a layer of hardfacing. In another embodiment, the
diamond-impregnated inserts may comprise large, coated (discussed
below) natural diamonds. For example, in certain embodiments,
diamonds as large as one carat per stone may be used.
[0128] In another embodiment, one or more of the
diamond-impregnated inserts include imbedded TSP diamond, so as to
enhance shearing of the formation. The TSP can take any desired
form, and is preferably formed into the insert during the insert
manufacturing process.
[0129] In various embodiments of the invention, TSP may be embedded
in a diamond impregnated support, embedded in a body (substrate) of
an insert, or may form a shearing element of a cutting element. In
accordance with the invention, TSP may be formed by leaching
residual cobalt from a polycrystalline diamond table that is formed
by sintering diamond, a metal carbide (typically tungsten carbide),
and a metallic binder (typically cobalt) at high temperature and
high pressure. Alternatively, a TSP or PDC composite may be used to
form cutting elements in accordance with the present invention. The
TSP or PDC composite may comprise TSP or PDC combined with silicon
carbide (or other materials) and may be formed by a hot press
process, a hot isostatic press process, or any other powder
metallurgy process known in the art.
[0130] Referring to FIGS. 15A-15B, a novel cutting element in
accordance with an embodiment of the present invention is shown. In
this embodiment, the insert 1500 includes a leading edge 1502
having a given thickness. In a particular embodiment, the leading
edge 1502 comprises a diamond table having a selected thickness,
which is formed in a manner similar to conventional PDC diamond
tables with a tungsten carbide substrate. In the embodiment shown,
the leading edge 1502 has a thickness of about 0.080 inches to
about 0.120 inches. The thickness and nature of this leading edge
may be varied, depending on a user's requirements.
[0131] In particular, the leading edge 1502 may be formed from a
number of compounds, such as cubic boron nitride (CBN), PDC, or
TSP.
[0132] Returning to FIGS. 15A and 15B, the remainder of the insert
1500 comprises a body 1504, which may be formed in the manner
described above. In a preferred embodiment, the body 1504 is an
impregnated substrate comprising tungsten carbide impregnated with
diamond. In an alternative embodiment, the body 1504 may comprise
tungsten carbide impregnated with TSP or PDC.
[0133] Furthermore, in certain embodiments, the insert 1500 is
provided with an outer layer 1506, which provides a brazing
surface. In a preferred embodiment, the outer layer 1506 comprises
a thin "virgin" (i.e., not impregnated) tungsten carbide layer, in
order to promote effective brazing (i.e., maintain the braze
strength) of the insert 1500 into a socket (not shown) on a drill
bit (not shown).
[0134] By brazing the insert 1500 into a socket, which occurs at
significantly lower temperature than diamond impregnation, thermal
degradation of the leading edge 1502 may be avoided.
Advantageously, therefore, the integrity of the leading edge 1502
is maintained. During drilling, the leading edge 1502 provides
shearing cutting action similar to that of a PDC cutter. As wear
progresses, the body 1504 of the insert 1500 introduces impregnated
diamonds to the formation, increasing drilling efficiency and
limiting the progression of wear. Thus, an insert formed in this
manner includes both a shearing portion (1502) and an abrasive
portion (1504).
[0135] While FIGS. 15A and 15B illustrate an insert 1500 having a
"post" shape, no limitation on the present invention is intended by
the shown geometry. For example, FIG. 16 shows an insert 1600
having a "saddle" shaped top portion. Additionally, an insert in
accordance with the present invention may have any non-planar top
cutting portion geometry such as a convex or concave geometry.
[0136] FIGS. 17A and 17B show alternative embodiments of the
present invention. In FIG. 17A, an insert 1700 having a shearing
portion 1710 and an abrasive portion 1712 is shown. In this
embodiment, the shearing portion 1710 has a "V" shape. Again, other
geometries for the shearing portion are possible and are expressly
within the scope of the present invention. In particular, the
shearing portion 1710 may comprise at least one beveled edge or at
least one blended edge at an interface with the abrasive portion
1712. In FIG. 17A, the shearing portion 1710 may comprise TSP or
PDC deposited on a diamond-impregnated substrate (the abrasive
portion 1212).
[0137] In FIG. 17B, a bonding portion 1720 is disposed between the
shearing portion 1710 and the abrasive portion 1712. In one
embodiment, the shearing portion 1710 comprises TSP, the abrasive
portion 1712 comprises diamond-impregnated tungsten carbide, and
the bonding portion 1720 comprises "virgin" (i.e., non-impregnated)
tungsten carbide. The bonding portion is provided to increase the
bond strength between the shearing and abrasive portion. For
certain combinations of the compounds described herein, such as
PDC, TSP, CBN, or ceramic materials, the bond between the shearing
portion and abrasive portion may be too weak to survive sustained
drilling. In this case, a bonding portion may be provided.
[0138] Accordingly, in certain embodiments, such as those where
there is no tungsten carbide bonding portion, and the shearing
portion comprises TSP, the shearing portion may be coated with a
material to either create or enhance a bond between the
diamond-impregnated body and the shearing portion. Typically, in
preferred embodiments, this occurs in one of two ways, which are
described with reference to FIGS. 18A-18D below.
[0139] In FIGS. 18A and 18B, a coating 1850 is applied to the
shearing portion 1852 to strengthen a bond between the shearing
portion 1852 and the diamond-impregnated body 1854. In a preferred
embodiment, the coating 1850 comprises a layer of virgin tungsten
carbide, applied to a TSP shearing portion, to enhance the
metallurgical bond between the body 1854 and the shearing portion
1852. FIG. 18B shows the same technique, but shows an insert having
a different geometry than that depicted in FIG. 18B. In various
embodiments, the coating may comprise a titanium based coatings,
tungsten based coatings, nickel coatings, various carbides,
nitrides, and other materials known to those skilled in the
art.
[0140] FIGS. 18C and 18D, in contrast, illustrate a case in which a
shearing portion having a substrate is used. In FIG. 18C, a
shearing portion 1860 includes a cap 1861 and a substrate 1862. In
one embodiment, the shearing portion 1860 is a TSP shearing
element. In one embodiment, the substrate 1862 includes a binder
metal, such as cobalt, which can migrate into the
diamond-impregnated body 1864. Accordingly, cobalt from the
substrate 1862 may migrate into diamond-impregnated body 1864, and
vice versa, enhancing the bond between the diamond-impregnated body
1864 and the substrate 1862.
[0141] Further, in certain embodiments, such as those in which the
abrasive portion comprises diamond impregnated tungsten carbide,
the bonding portion is virgin tungsten carbide, and the shearing
portion comprises PDC or TSP, the bonding layer wears faster than
the abrasive or shearing portions. This has the effect of
"sharpening" the shearing portion (which is the leading edge of the
insert). As the bonding portion wears, new surfaces of the shearing
portion are constantly being exposed, which assists in maintaining
good shearing action.
[0142] The present invention allows bits to be easily constructed
having inserts in which the size, shape, and/or concentration of
diamond in the cutting structure is controlled in a desired manner.
Likewise, the inserts can be created to have different lengths, or
mounted in the bit body at different heights or angles, so as to
produce a bit having a multiple height cutting structure. This may
provide advantages in drilling efficiency. For example, a bit
having extended diamond-impregnated inserts as a cutting structure
will be able to cut through downhole float equipment that could not
be cut by a standard diamond-impregnated bit, thereby eliminating
the need to trip out of the hole to change bits.
[0143] Additionally, a bit having such extended diamond-impregnated
inserts will be able to drill sections of softer formations that
cannot be efficiently drilled with conventional diamond-impregnated
bits. In contrast, embodiments of the present invention makes
efficient drilling of softer formations possible due to shearing
action of inserts that extend beyond the surface of the bit
body.
[0144] Referring now to FIG. 19, a drill bit head 1900 according to
one embodiment of the present invention is shown. According to one
preferred embodiment, the drill bit head 1900 is formed by
infiltrating a mass of tungsten-carbide powder impregnated with
synthetic or natural diamond, as described above. Preferably,
formers are included during the manufacturing process, so that the
infiltrated, diamond-impregnated drill bit head 1900 includes a
plurality of holes or sockets 1922 that are sized and shaped to
receive a corresponding plurality of diamond-impregnated inserts
1900. Once the sockets 1922 are formed, inserts 1900 are mounted in
the sockets and affixed by any suitable method, such as brazing,
adhesive, mechanical means such as interference fit, or the
like.
[0145] While reference has been made to impreg bits, inserts formed
in accordance with the present invention may also be adapted to be
used in "conventional" PDC cutting structures. In particular,
inserts in accordance with the present invention may replace some
or all of the polycrystalline diamond inserts used in PDC bits.
FIG. 20 illustrates one such embodiment.
[0146] In FIG. 20, a drill bit 2090 having at least one insert 2000
in place of a PDC cutter is depicted. As shown in FIG. 8, the drill
bit 2090 is formed with at least one blade 2091, which extends
generally outwardly away from a central longitudinal axis 2095 of
the drill bit 2090. The at least insert 2000 is disposed on the at
least one blade 2091. The number of blades 2091 and/or inserts 2000
is related to the type of rock to be drilled, and can thus be
varied to meet particular rock drilling requirements.
[0147] The at least one insert 2000 in the present example
comprises an impregnated diamond base and a shearing element
comprising a sharpened cutting edge and at least one blended edge
that forms part of an interface between the base and the shearing
element mounted thereon. The at least one blade 2091 has at least
one socket or mounting pad (not numbered separately), which is
adapted to receive the at least one insert 2000. In the present
embodiment, the at least one insert 2000 is brazed onto the at
least one socket. Accordingly, in a preferred embodiment, the at
least one insert 2000 may be provided with an outer layer of virgin
tungsten carbide to improve braze strength.
[0148] It should be noted that references to the use of specific
substrate compositions are for illustrative purposes only, and no
limitation on the type of substrate used is intended. As an
example, it is well known that various metal carbide compositions,
in addition to tungsten carbide, may be used.
[0149] Further, embodiments of the present invention may include
non-planar geometry to form a non-planar interface between the
abrasive portion and shearing portion to reduce the inherent
stresses present at the interface. The use of non-planar interfaces
is known in the art. For example, U.S. Pat. No. 5,494,477 discloses
one such non-planar interface and is hereby incorporated by
reference.
[0150] A second system using a non-planar interface is disclosed in
U.S. Pat. No. 5,662,720. In this system, the surface topography of
the substrate system is altered to create an "egg-carton"
appearance. The use of an "egg-carton" shape allows the stress
associated with the cutting to be distributed over a larger surface
area, thereby reducing the probability of delamination of the
shearing portion from the substrate.
[0151] One suitable method of forming an insert in accordance with
the present invention is now described, with reference to FIG. 21.
First, a mold, which defines dimensions of an insert, is formed
(2100). The mold may be made of any suitable material known in the
art, such as graphite. In one embodiment, the mold comprises a
block having one or more holes and at least an upper and a lower
plunger for each hole (not shown). Alternatively, a series of upper
and lower plungers may be used. The upper and lower plunger are
used to define the height of the insert. Alternatively, the hole
may have a fixed bottom and only an upper plunger is required for
defining the height of the insert. After forming the mold, powder
of a suitable material, as noted above, that forms the
diamond-impregnated body of the insert upon heating and pressure is
loaded into the holes, with the lower plungers in place (2104).
Then, the upper plunger is placed into the hole, "capping" the hole
shut (2108). In a preferred embodiment, the mold assembly is then
pre-pressed in a hand operated press (2110). Finally, the mold
assembly is placed in the hot press furnace (2112) for the
production of a diamond-impregnated insert body. In one embodiment,
a second cutting structure (e.g., the shearing portion) is added
after the formation of the diamond-impregnated insert body.
[0152] In a preferred embodiment, however, the second cutting
structure is placed into the hole (2106) on top of the powder
material that is to form the diamond-impregnated insert body,
before or at the time the upper plunger is placed into the hole to
cap this hole (2108). No specific geometry of cutting structure is
required by this invention. With this embodiment, the bonding
between the diamond-impregnated insert body and the second cutting
structure (the shearing portion) is formed during hot press.
[0153] In a preferred embodiment, the second cutting structure is
physically attached to a surface of the upper plunger, prior to
placing the upper plunger in the hole. Because the upper plunger is
designed and manufactured based on the shape of the
diamond-impregnated body and second cutting structure, the second
cutting structure "mates" with the upper plunger. Accordingly, the
orientation and position of the second cutting element may be set
at this stage. Additionally, the surface of the upper plunger to
which the second cutting structure is attached may be "scribed" or
marked to aid in proper positioning of the second cutting element.
The upper plunger/second cutting element may then be placed into
the hole, "capping" the hole shut (2108). In a preferred
embodiment, the mold assembly is then pre-pressed in a hand
operated press (2110). Finally, the mold assembly is then placed in
the hot press furnace (2112) for the production of an insert having
a diamond-impregnated body with a shearing portion disposed
thereon.
[0154] Accordingly, based on this method, diamond-impregnated
inserts having a specified geometry may be formed. Further, based
on this method, a shearing portion having a specified geometry may
be used in conjunction with the diamond-impregnated insert. The
resulting insert, therefore, can have a specific geometry, which is
adapted to more effectively drill a formation.
[0155] Alternate methods of forming an insert may be used. For
example, a high pressure, high temperature (HPHT) process for
sintering diamond or cubic boron nitride may be used. Such a
process has been described in U.S. Pat. Nos. 5,676,496 and
5,598,621, and their teachings are incorporated by reference
herein. Another suitable method for hot-compacting pre-pressed
diamond/metal powder mixtures is hot isostatic pressing, which is
known in the art. See Peter E. Price and Steven P. Kohler, "Hot
Isostatic Pressing of Metal Powders", Metals Handbook, Vol. 7, pp.
419-443 (9th ed. 1984). As noted above, the HPHT process can be
done with both the powder and the shearing portion present, or the
diamond-impregnated body can be formed prior to attachment of a
shearing portion.
[0156] FIGS. 22A and 22B show particular shearing portions for use
in embodiments of the present invention. FIG. 22A shows a circular
TSP cutter that may be used as a shearing portion in accordance
with embodiments of the present invention. The TSP shearing element
includes a sharpened cutting edge 2200 and at least one blended
edge 2201 that forms part of an interface with a support element.
In FIG. 22A, the TSP cutter having a diameter .phi. (which, in
certain embodiments, ranges from 6-9 mm) and a thickness .omega.
(which, in certain embodiments, ranges from 2-4 mm). In FIG. 22B, a
triangular CBN shearing portion is shown. In FIG. 22B, the CBN
shearing portion is shown having a length B (which, in certain
embodiments, is 6-9 mm) and a thickness .omega. (which, in certain
embodiments, ranges from 2-4 mm).
[0157] FIG. 23 illustrates another aspect of the present invention.
In FIG. 23, an insert 2300 is shown having a varying composition
from a center portion 2302 to an exterior portion 2304. By varying
the composition (such as the diamond content) of the insert 2300,
the relative hardness of the insert can be tailored to a given
formation. Also, wear characteristics may be better controlled by
such control. The composition may vary in either a uniform or
non-uniform manner. In particular, while FIG. 20 illustrates the
insert 2300 having similar compositions on either side of the
center portion 2302 (i.e., exterior portion 2304 has the same
composition) this is not necessarily required. Depending on the
requirements of the user, the composition may be altered around the
location where the shearing portion is to be placed.
[0158] Further, while embodiments of the present invention have
disclosed various matrix materials, it should be noted that other
suitable materials will be apparent to those of ordinary skill in
the art. In particular, the matrix material may be a CBN composite,
rather than a tungsten carbide composite. CBN composites have the
advantage of being more thermally stable than tungsten carbides. In
addition, materials may be selected in order to improve certain
manufacturing processes. For example, by judiciously selecting
compositions, frictional heat generation during abrasion of the
composite may be reduced. This can be achieved by selecting matrix
material with abrasion resistance lower than diamond and with lower
friction coefficient. For example, CBN instead of WC may be used in
the matrix with ceramic binder.
[0159] Further, mixtures of any of the materials disclosed herein,
or those known to one of ordinary skill in the art may be used. For
example, it is expressly within the scope of the present invention
that an insert body may be formed that comprises diamond, CBN, TiC
(or TiN), or cobalt aluminide pressed using the HPHT or other
processes described above.
[0160] While reference to particular diameters, lengths, and
thicknesses are discussed, no limitation on the scope of the
present invention is intended thereby. In particular, the size of
the insert, and the shearing portion will vary depending on the
nature of the formation to be drilled and/or other criteria
selected by the user.
[0161] Further, other structures known in the art may be used in
conjunction with the shearing portion disposed on a
diamond-impregnated body disclosed above. For example, in certain
embodiments, a "wear" portion may be present on the insert.
Specifically, a wear portion may comprise a bearing surface used in
gauge pads.
[0162] Advantageously, embodiments of the present invention provide
cutting elements that can "grind" a formation as well as "shear" a
formation, to increase the overall rate of penetration and/or wear
resistance of a bit. Furthermore, advantageously, embodiments of
the present invention provide better drilling results when drilling
mixed formations (i.e., formations having both hard and soft
characteristics such as sand/shale formations). Furthermore,
embodiments of the invention advantageously minimize stresses
acting on support elements to which shearing elements are bonded
that can lead to cracking of the support elements, thereby
improving retention of the shearing elements.
[0163] 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.
* * * * *