U.S. patent application number 11/937969 was filed with the patent office on 2009-05-14 for impregnated drill bits and methods for making the same.
This patent application is currently assigned to SMITH INTERNATIONAL, INC.. Invention is credited to Jonan Fulenchek, Gregory T. Lockwood.
Application Number | 20090120008 11/937969 |
Document ID | / |
Family ID | 40139622 |
Filed Date | 2009-05-14 |
United States Patent
Application |
20090120008 |
Kind Code |
A1 |
Lockwood; Gregory T. ; et
al. |
May 14, 2009 |
IMPREGNATED DRILL BITS AND METHODS FOR MAKING THE SAME
Abstract
An impregnated cutting structure that includes a plurality of
first encapsulated particles, each first encapsulated particle
comprising a first abrasive particle encapsulated by a first matrix
material shell; and a plurality of second encapsulated particles,
the second encapsulated particles comprising a second abrasive
particle encapsulated by a second matrix material shell, wherein
the first encapsulated particles and the second encapsulated
particles have at least one property difference is disclosed.
Inventors: |
Lockwood; Gregory T.;
(Pearland, TX) ; Fulenchek; Jonan; (Tomball,
TX) |
Correspondence
Address: |
OSHA, LIANG LLP / SMITH
TWO HOUSTON CENTER, 909 FANNIN STREET, SUITE 3500
HOUSTON
TX
77010
US
|
Assignee: |
SMITH INTERNATIONAL, INC.
Houston
TX
|
Family ID: |
40139622 |
Appl. No.: |
11/937969 |
Filed: |
November 9, 2007 |
Current U.S.
Class: |
51/295 ;
175/435 |
Current CPC
Class: |
B22F 2005/005 20130101;
E21B 10/46 20130101; C22C 26/00 20130101; B22F 1/025 20130101; B22F
2005/001 20130101; C22C 1/1036 20130101; C09K 3/1445 20130101 |
Class at
Publication: |
51/295 ;
175/435 |
International
Class: |
E21B 10/55 20060101
E21B010/55 |
Claims
1. An impregnated cutting structure comprising: a plurality of
first encapsulated particles, each first encapsulated particle
comprising a first abrasive particle encapsulated by a first matrix
material shell; and a plurality of second encapsulated particles,
the second encapsulated particles comprising a second abrasive
particle encapsulated by a second matrix material shell, wherein
the first encapsulated particles and the second encapsulated
particles have at least one property difference.
2. The cutting structure of claim 1, wherein the first matrix
material and second matrix material comprise different wear
rates.
3. The cutting structure of claim 2, wherein the first matrix
material is softer than the second matrix material.
4. The cutting structure of claim 1, wherein the first encapsulated
particle is coarser than the second encapsulated particle.
5. The cutting structure of claim 1, wherein the first abrasive
particle is coarser than the second abrasive particle.
6. The cutting structure of claim 1, wherein the first abrasive
particle has less compressive strength than the second abrasive
particle.
7. The cutting structure of claim 1, wherein the encapsulating
first matrix material shell is thicker than the encapsulating
second matrix material shell.
8. The cutting structure of claim 1, wherein at least one of the
first abrasive particle and second abrasive particle have a
retention coating deposited thereon.
9. The cutting structure of claim 8, wherein the first abrasive
particle has a weaker retention coating deposited thereon as
compared to the second abrasive particle.
10. The cutting structure of claim 1, where the first and the
second matrix materials individually comprise at least one of
sintered tungsten carbide, cast tungsten carbide, and carbides of
tungsten, vanadium, chromium, titanium, tantalum, and niobium.
11. The cutting structure of claim 1, where the first and the
second matrix materials individually comprise at least one of
copper, cobalt, nickel, iron, and alloys thereof.
12. The cutting structure of claim 1, wherein the first and second
abrasive particles individually comprise at least one of synthetic
diamond, natural diamond, TSP, and CBN.
13. The cutting structure of claim 1, further comprising: a
plurality of third encapsulated particles, each third encapsulated
particle comprises a third abrasive particle encapsulated by a
third matrix material shell.
14. A drill bit, comprising: a bit body; and a plurality of ribs
formed in the bit body, wherein at least one rib comprises: a
plurality of first encapsulated particles, each first encapsulated
particle comprising a first abrasive particle encapsulated by a
first matrix material shell; a plurality of second encapsulated
particles, each second encapsulated particle comprising a second
abrasive particle encapsulated by a second matrix material shell,
wherein the first encapsulated particles and the second
encapsulated particles comprise at least one property difference
therebetween.
15. The drill bit of claim 14, wherein the first matrix material
and second matrix material comprise different wear properties.
16. The drill bit of claim 15, further comprising: a third matrix
material infiltrated between the first and second encapsulated
materials.
17. The drill bit of claim 14, wherein a consolidated insert
comprising the first and second encapsulated particles are brazed
or cast into the rib.
18. A drill bit, comprising: a bit body; and a plurality of ribs
formed in the bit body, wherein a portion of at least one rib has a
height to width ratio of greater than about 1.75 with a minimum
diamond concentration of 100 and comprises: a plurality of first
encapsulated particles, each first encapsulated particle comprising
a first abrasive particle encapsulated by a first matrix material
shell.
19. The drill bit of claim 18, wherein the at least one rib further
comprises: a plurality of second encapsulated particles, each
second encapsulated particle comprising a second abrasive particle
encapsulated by a second matrix material shell, wherein the first
encapsulated particles and the second encapsulated particles
comprise at least one property difference therebetween.
20. The drill bit of claim 19, wherein the first matrix material
and second matrix material comprise different wear properties.
21. The drill bit of claim 19, wherein the at least one rib further
comprises: a third matrix material infiltrated between the first
and second encapsulated materials.
22. A method of forming an impregnated cutting structure
comprising: loading a plurality of first encapsulated particles and
a plurality of second encapsulated particles into a mold cavity,
each first encapsulated particle comprising a first abrasive
particle encapsulated by a first matrix material shell and each
second encapsulated particle comprising a second abrasive particle
encapsulated by a second matrix material shell, wherein the first
encapsulated particles and the second encapsulated particles
comprise at least one property difference therebetween; and heating
the mold contents to form an impregnated cutting structure.
23. The method of claim 22, further comprising: applying pressure
to the first and second encapsulated particles within the mold.
24. The method of claim 22, further comprising: loading a third
matrix material into the mold with the first and second
encapsulated particles; and infiltrating the mold contents with a
infiltrating binder.
25. The method of claim 22, wherein the at least one property
difference comprises at least one of different wear rates between
the matrix materials, different toughness between the matrix
materials, different size of the encapsulated particles, different
size of the abrasive particles, different compressive strengths
between the abrasive particles, different shell thicknesses, and
presence or type of retention coatings.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of the Invention
[0002] Embodiments disclosed herein relate generally to drill bits,
and more particularly to drill bits having impregnated cutting
surfaces and the methods for the manufacture of such drill
bits.
[0003] 2. Background Art
[0004] An earth-boring drill bit is typically mounted on the lower
end of a drill string and is rotated by rotating the drill string
at the surface or by actuation of downhole motors or turbines, or
by both methods. When weight is applied to the drill string, the
rotating drill bit engages the earth formation and proceeds to form
a borehole along a predetermined path toward a target zone.
[0005] Different types of bits work more efficiently against
different formation hardnesses. For example, bits containing
inserts that are designed to shear the formation frequently drill
formations that range from soft to medium hard. These inserts often
have polycrystalline diamond compacts (PDC's) as their cutting
faces.
[0006] Roller cone bits are efficient and effective for drilling
through formation materials that are of medium to hard hardness.
The mechanism for drilling with a roller cone bit is primarily a
crushing and gouging action, in which the inserts of the rotating
cones are impacted against the formation material. This action
compresses the material beyond its compressive strength and allows
the bit to cut through the formation.
[0007] For still harder materials, the mechanism for drilling
changes from shearing to abrasion. For abrasive drilling, bits
having fixed, abrasive elements are preferred. While bits having
abrasive polycrystalline diamond cutting elements are known to be
effective in some formations, they have been found to be less
effective for hard, very abrasive formations such as sandstone. For
these hard formations, cutting structures that comprise particulate
diamond, or diamond grit, impregnated in a supporting matrix are
effective. In the discussion that follows, components of this type
are referred to as "diamond impregnated."
[0008] Diamond impregnated drill bits are commonly used for boring
holes in very hard or abrasive rock formations. The cutting face of
such bits contains natural or synthetic diamonds distributed within
a supporting material to form an abrasive layer. During operation
of the drill bit, diamonds within the abrasive layer are gradually
exposed as the supporting material is worn away. The continuous
exposure of new diamonds by wear of the supporting material on the
cutting face is the fundamental functional principle for
impregnated drill bits.
[0009] The construction of the abrasive layer is of critical
importance to the performance of diamond impregnated drill bits.
The abrasive layer typically contains diamonds and/or other
super-hard materials distributed within a suitable supporting
material. The supporting material must have specifically controlled
physical and mechanical properties in order to expose diamonds at
the proper rate.
[0010] Metal-matrix composites are commonly used for the supporting
material because the specific properties can be controlled by
modifying the processing or components. The metal-matrix usually
combines a hard particulate phase with a ductile metallic phase.
The hard phase often consists of tungsten carbide and other
refractory or ceramic compounds. Copper or other nonferrous alloys
are typically used for the metallic binder phase. Common powder
metallurgical methods, such as hot-pressing, sintering, and
infiltration are used to form the components of the supporting
material into a metal-matrix composite. Specific changes in the
quantities of the components and the subsequent processing allow
control of the hardness, toughness, erosion and abrasion
resistance, and other properties of the matrix.
[0011] Proper movement of fluid used to remove the rock cuttings
and cool the exposed diamonds is important for the proper function
and performance of diamond impregnated bits. The cutting face of a
diamond impregnated bit typically includes an arrangement of
recessed fluid paths intended to promote uniform flow from a
central plenum to the periphery of the bit. The fluid paths usually
divide the abrasive layer into distinct raised ribs with diamonds
exposed on the tops of the ribs. The fluid provides cooling for the
exposed diamonds and forms a slurry with the rock cuttings. The
slurry must travel across the top of the rib before reentering the
fluid paths, which contributes to wear of the supporting
material.
[0012] An example of a prior art diamond impregnated drill bit is
shown in FIG. 1. The impregnated bit 10 includes a bit body 12 and
a plurality of ribs 14 that are formed in the bit body 12. The ribs
14 are separated by channels 16 that enable drilling fluid to flow
between and both clean and cool the ribs 14. The ribs 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
rib 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).
[0013] 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) particles may also
be used.
[0014] In one impregnated 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. 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.
[0015] By this process, a monolithic bit body that incorporates the
desired components is formed. One method for forming 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.
[0016] Referring now to FIG. 2, a drill bit 22 in accordance with
the '202 patent comprises a shank 24 and a crown 26. Shank 24 is
typically formed of steel and includes a threaded pin 28 for
attachment to a drill string. Crown 26 has a cutting face 29 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.
[0017] Crown 26 may include various surface features, such as
raised ridges 32. Preferably, formers are included during the
manufacturing process so that the infiltrated, diamond-impregnated
crown includes a plurality of holes or sockets 34 that are sized
and shaped to receive a corresponding plurality of
diamond-impregnated inserts 36. Once crown 26 is formed, inserts 36
are mounted in the sockets 34 and affixed by any suitable method,
such as brazing, adhesive, mechanical means such as interference
fit, or the like. As shown in FIG. 2, the sockets can each be
substantially perpendicular to the surface of the crown.
Alternatively, and as shown in FIG. 2, holes 34 can be inclined
with respect to the surface of the crown 26. In this embodiment,
the sockets are inclined such that inserts 36 are oriented
substantially in the direction of rotation of the bit, so as to
enhance cutting.
[0018] 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 methods disclosed in 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 shortened hot pressing
period and the use of the brazing process.
[0019] The total thermal exposure of methods disclosed in the '202
patent 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 occurs in conventional
manufacturing of furnace-infiltrated, diamond-impregnated bits. If
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.
[0020] With respect to the diamond material to be incorporated
(either as an insert, or on the bit, or both), diamond granules are
formed by mixing diamonds with matrix power and binder into a
paste. The paste is then extruded into short "sausages" that are
rolled and dried into irregular granules. The process for making
diamond-impregnated matrix for bit bodies involves hand mixing of
matrix powder with diamonds and a binder to make a paste. The paste
is then packed into the desired areas of a mold. The resultant
irregular diamond distribution has clusters with too many diamonds,
while other areas are void of diamonds. The diamond clusters lack
sufficient matrix material around them for good diamond retention.
The areas void or low in diamond concentration have poor wear
properties. Accordingly, the bit or insert may fail prematurely,
due to uneven wear. As the motors or turbines powering the bit
improve (higher sustained RPM), and as the drilling conditions
become more demanding, the durability of diamond-impregnated bits
needs to improve. However, generally, as durability of a bit
increases (with a harder matrix), diamond exposure (and thus ROP)
generally decreases, and vice versa. Accordingly, there exists a
continuing need for improvements in diamond impregnated cutting
structures to improve wear properties, rate of penetration, and
diamond distribution.
SUMMARY OF INVENTION
[0021] In one aspect, embodiments disclosed herein relate to an
impregnated cutting structure that includes a plurality of first
encapsulated particles, each first encapsulated particle comprising
a first abrasive particle encapsulated by a first matrix material
shell; and a plurality of second encapsulated particles, the second
encapsulated particles comprising a second abrasive particle
encapsulated by a second matrix material shell, wherein the first
encapsulated particles and the second encapsulated particles have
at least one property difference.
[0022] In another aspect, embodiments disclosed herein relate to a
drill bit that includes a bit body; and a plurality of ribs formed
in the bit body, wherein at least one rib comprises: a plurality of
first encapsulated particles, each first encapsulated particle
comprising a first abrasive particle encapsulated by a first matrix
material shell; a plurality of second encapsulated particles, each
second encapsulated particle comprising a second abrasive particle
encapsulated by a second matrix material shell, wherein the first
encapsulated particles and the second encapsulated particles
comprise at least one property difference therebetween.
[0023] In another aspect, embodiments disclosed herein relate to
drill bit that includes a bit body; and a plurality of ribs formed
in the bit body, wherein a portion of at least one rib has a height
to width ratio of greater than about 1.75 with a minimum diamond
concentration of 100 and comprises: a plurality of first
encapsulated particles, each first encapsulated particle comprising
a first abrasive particle encapsulated by a first matrix material
shell.
[0024] In yet another aspect, embodiments disclosed herein relate
to a method of forming an impregnated cutting structure that
includes loading a plurality of first encapsulated particles and a
plurality of second encapsulated particles into a mold cavity, each
first encapsulated particle comprising a first abrasive particle
encapsulated by a first matrix material shell and each second
encapsulated particle comprising a second abrasive particle
encapsulated by a second matrix material shell, wherein the first
encapsulated particles and the second encapsulated particles
comprise at least one property difference therebetween; and heating
the mold contents to form an impregnated cutting structure.
[0025] Other aspects and advantages of the invention will be
apparent from the following description and the appended
claims.
BRIEF DESCRIPTION OF DRAWINGS
[0026] FIG. 1 is an impregnated bit.
[0027] FIG. 2 is an impregnated cutting structure according to one
embodiment of the present disclosure.
[0028] FIG. 3 is an impregnated cutting structure according to one
embodiment of the present disclosure.
[0029] FIG. 4 is an impregnated bit according to one embodiment of
the present disclosure.
[0030] FIG. 5 is a rib according to one embodiment of the present
disclosure.
[0031] FIG. 6A-B is an impregnated bit according to one embodiment
of the present disclosure.
DETAILED DESCRIPTION
[0032] In one aspect, embodiments disclosed herein relate to
encapsulated particles. In other aspects, embodiments disclosed
herein relate to impregnated cutting structures or impregnated
drill bits containing encapsulated particles. The use of
encapsulated particles in cutting structures is described for
example in U.S. Patent Publication No. 2006/0081402 and U.S.
application Ser. Nos. 11/779,083 and 11/779,104, all of which are
assigned to the present assignee, and herein incorporated by
reference in their entireties.
[0033] Referring to FIG. 2, a cross-section of an embodiment of a
cutting structure is illustrated. As shown in FIG. 3, cutting
structure 200 includes encapsulated particles 210 and encapsulated
particles 220. Each encapsulated particle 210, 220 is formed of an
abrasive particle 212, 222 coated or surrounded by encapsulating
shell 214, 224 of matrix powder material. Referring to FIG. 3, a
cross-section of an embodiment of an alternative cutting structure
is illustrated. As shown in FIG. 4, similar to FIG. 2, cutting
structure 300 includes encapsulated particles 310 and encapsulated
particles 320, where each encapsulated particle 310, 320 is formed
of an abrasive particle 312, 322 coated or surrounded by
encapsulating shell 314, 324 of matrix powder material.
Additionally, a third matrix powder material 304 is infiltrated
through the cutting structure 300.
[0034] As shown in FIGS. 2 and 3, encapsulated particles 210, 310
differ from encapsulated particles 220, 320 in several ways;
however, in a particular embodiment, only one difference between
two (or otherwise multiple) encapsulated particles in a cutting
structure need exist. Of the types of differences that may exist,
variation in total encapsulated particle size; matrix material
composition, shell thickness, or wear properties; or abrasive
particle type, size, strength, or retention coating may exist among
encapsulated particles. As illustrated, encapsulated particles 210,
310 differ from encapsulated particles 220, 320, for example, in
their total size, in the size of abrasive particles 212, 312 as
compared to abrasive particles 222, 322, and the type of
encapsulating shell 214, 314 as compared to encapsulating shell
224, 324. However, one of ordinary skill would appreciate that
other combinations of the component parts may be used, depending on
the particular application. Each of these component parts will be
further discussed, including a description of embodiments of
various impregnated cutting structures.
[0035] Abrasive Particles
[0036] In some embodiments, abrasive particles may be selected from
synthetic diamond, natural diamond, reclaimed natural or synthetic
diamond grit, silicon carbide, aluminum oxide, tool steel, boron
carbide, cubic boron nitride (CBN), thermally stable
polycrystalline diamond (TSP), or combinations thereof.
[0037] The shape of the abrasive particles may also be varied as
abrasive particles may be in the shape of spheres, cubes, irregular
shapes, or other shapes. In some embodiments, abrasive particles
may range in size from 0.2 to 2.0 mm in length or diameter; from
0.3 to 1.5 mm in other embodiments; from 0.4 to 1.2 mm in other
embodiments; and from 0.5 to 1.0 mm in yet other embodiments.
[0038] However, particle sizes are often measured in a range of
mesh sizes, for example -40+80 mesh. The term "mesh" actually
refers to the size of the wire mesh used to screen the particles.
For example, "40 mesh" indicates a wire mesh screen with forty
holes per linear inch, where the holes are defined by the
crisscrossing strands of wire in the mesh. The hole size is
determined by the number of meshes per inch and the wire size. The
mesh sizes referred to herein are standard U.S. mesh sizes. For
example, a standard 40 mesh screen has holes such that only
particles having a dimension less than 420 .mu.m can pass.
Particles having a size larger than 420 .mu.m are retained on a 40
mesh screen and particles smaller than 420 .mu.m pass through the
screen. Therefore, the range of sizes of the particles is defined
by the largest and smallest grade of mesh used to screen the
particles. Particles in the range of -16+40 mesh (i.e., particles
are smaller than the 16 mesh screen but larger than the 40 mesh
screen) will only contain particles larger than 420 .mu.m and
smaller than 1190 .mu.m, whereas particles in the range of -40+80
mesh will only contain particles larger than 180 .mu.m and smaller
than 420 .mu.m. Thus, in some embodiments, abrasive particles may
include particles not larger than would be filtered by a screen of
10 mesh. In other embodiments, abrasive particles may range in size
from -15+35 mesh. In a particular embodiment, a first encapsulated
particle, i.e., encapsulated particles 210, 310 as shown in FIGS. 2
and 3, may include abrasive particles, i.e., particles 212, 312,
ranging in size from -20+25 mesh, while a second capsulated
particle, i.e., encapsulated particles 220, 320 as shown in FIGS. 2
and 3, may include abrasive particles, i.e., particles 222, 322,
ranging in size from -25+35 mesh. However, one of ordinary skill
would recognize that the particle sizes and distribution of the
particle sizes of the abrasive particles may be selected to allow
for a broad, uniform, or bimodal distribution, for example,
depending on a particular application, and that size ranges outside
the distribution discussed above may also be selected. Further,
although particle sizes or particle diameters are referred to, it
is understood by those skilled in the art that the particles may
not necessarily be spherical in shape.
[0039] Further, as discussed above, various abrasive particles that
may be selected for use in the encapsulated may vary in type (i.e.,
chemical composition) such that the multiple types of encapsulated
particles may use different types of abrasive particles; however,
one of ordinary skill in the art would appreciate that among these
particles, there may also be a difference in compressive strength
of the particles. For example, some synthetic diamond grit may have
a greater compressive strength than natural diamond grit and/or
reclaimed grit. Furthermore, even within the general synthetic grit
type, there may exist different grades of grit having differing
compressive strengths, such as those grades of grit commercially
available from Element Six Ltd. (Berkshire, England).
[0040] In addition to varying the strength of the abrasive
particles, the presence and identity of an interior, retention
coating on the surface of the abrasive particle may also optionally
be varied. Thus, in some embodiments, one type of encapsulated
particle formed from abrasive particles having an interior,
retention coating thereon may be used in combination with another
type of encapsulated particle formed from abrasive particles which
do not have an interior, retention coating. In other embodiments,
different coatings may be used between the encapsulated particle
type, such as for example, a weaker PVD coating on abrasive
particles in a first type of encapsulated particles, and a stronger
CVD coating on abrasive particles in a second type of encapsulated
particles. Such interior coatings may be applied by conventional
techniques such as CVD or PVD, and are in contrast to the
encapsulating outer shell of matrix powder material used in
embodiments of the present disclosure. One of ordinary skill in the
art would appreciate that the interior, thin coatings (having a
thickness of only a few micrometers as compared to the thicker
encapsulating shell) may be more helpful for high temperature
protection (e.g., SiC coatings) while others are helpful for grit
retention (e.g., TiC). In certain embodiments, the "interior"
coating (TiC in the above example) may help bond the diamond to the
"outer" matrix coating. Additionally, in certain applications the
interior coating may reduce thermal damage to the particles.
[0041] Encapsulating Shell
[0042] The encapsulating shell of matrix powder material may
include a mixture of a carbide compounds and/or a metal alloy using
any technique known to those skilled in the art. For example,
encapsulating matrix material may include at least one of
macrocrystalline tungsten carbide particles, carburized tungsten
carbide particles, cast tungsten carbide particles, and sintered
tungsten carbide particles. In other embodiments non-tungsten
carbides of vanadium, chromium, titanium, tantalum, niobium, and
other carbides of the transition metal group may be used. In yet
other embodiments, carbides, oxides, and nitrides of Group IVA, VA,
or VIA metals may be used. A binder powder may also optionally
include a binder powder that may, for example, include cobalt,
nickel, iron, chromium, copper, molybdenum and other transition
elements and their alloys, and combinations thereof. Further, a
non-metallic binder phase, such as polyethylene glycol (PEG) or
organic wax.
[0043] Tungsten carbide is a chemical compound containing both the
transition metal tungsten and carbon. This material is known in the
art to have extremely high hardness, high compressive strength and
high wear resistance which makes it ideal for use in high stress
applications. Its extreme hardness makes it useful in the
manufacture of cutting tools, abrasives and bearings, as a cheaper
and more heat-resistant alternative to diamond.
[0044] Sintered tungsten carbide, also known as cemented tungsten
carbide, refers to a material formed by mixing particles of
tungsten carbide, typically monotungsten carbide, and particles of
cobalt or other iron group metal, and sintering the mixture. In a
typical process for making sintered tungsten carbide, small
tungsten carbide particles, e.g., 1-15 micrometers, and cobalt
particles are vigorously mixed with a small amount of organic wax
which serves as a temporary binder. An organic solvent may be used
to promote uniform mixing. The mixture may be prepared for
sintering by either of two techniques: it may be pressed into solid
bodies often referred to as green compacts; alternatively, it may
be formed into granules or pellets such as by pressing through a
screen, or tumbling and then screened to obtain more or less
uniform pellet size.
[0045] Such green compacts or pellets are then heated in a vacuum
furnace to first evaporate the wax and then to a temperature near
the melting point of cobalt (or the like) to cause the tungsten
carbide particles to be bonded together by the metallic phase.
After sintering, the compacts are crushed and screened for the
desired particle size. Similarly, the sintered pellets, which tend
to bond together during sintering, are crushed to break them apart.
These are also screened to obtain a desired particle size. The
crushed sintered carbide is generally more angular than the
pellets, which tend to be rounded.
[0046] Cast tungsten carbide is another form of tungsten carbide
and has approximately the eutectic composition between bitungsten
carbide, W.sub.2C, and monotungsten carbide, WC. Cast carbide is
typically made by resistance heating tungsten in contact with
carbon, and is available in two forms: crushed cast tungsten
carbide and spherical cast tungsten carbide. Processes for
producing spherical cast carbide particles are described in U.S.
Pat. Nos. 4,723,996 and 5,089,182, which are herein incorporated by
reference. Briefly, tungsten may be heated in a graphite crucible
having a hole through which a resultant eutectic mixture of
W.sub.2C and WC may drip. This liquid may be quenched in a bath of
oil and may be subsequently comminuted or crushed to a desired
particle size to form what is referred to as crushed cast tungsten
carbide. Alternatively, a mixture of tungsten and carbon is heated
above its melting point into a constantly flowing stream which is
poured onto a rotating cooling surface, typically a water-cooled
casting cone, pipe, or concave turntable. The molten stream is
rapidly cooled on the rotating surface and forms spherical
particles of eutectic tungsten carbide, which are referred to as
spherical cast tungsten carbide.
[0047] The standard eutectic mixture of WC and W.sub.2C is
typically about 4.5 weight percent carbon. Cast tungsten carbide
commercially used as a matrix powder typically has a hypoeutectic
carbon content of about 4 weight percent. In one embodiment of the
present invention, the cast tungsten carbide used in the mixture of
tungsten carbides is comprised of from about 3.7 to about 4.2
weight percent carbon.
[0048] Another type of tungsten carbide is macro-crystalline
tungsten carbide. This material is essentially stoichiometric WC.
Most of the macro-crystalline tungsten carbide is in the form of
single crystals, but some bicrystals of WC may also form in larger
particles. Single crystal monotungsten carbide is commercially
available from Kennametal, Inc., Fallon, Nev.
[0049] Carburized carbide is yet another type of tungsten carbide.
Carburized tungsten carbide is a product of the solid-state
diffusion of carbon into tungsten metal at high temperatures in a
protective atmosphere. Sometimes it is referred to as fully
carburized tungsten carbide. Such carburized tungsten carbide
grains usually are multi-crystalline, i.e., they are composed of WC
agglomerates. The agglomerates form grains that are larger than the
individual WC crystals. These large grains make it possible for a
metal infiltrant or an infiltration binder to infiltrate a powder
of such large grains. On the other hand, fine grain powders, e.g.,
grains less than 5 .mu.m, do not infiltrate satisfactorily. Typical
carburized tungsten carbide contains a minimum of 99.8% by weight
of WC, with total carbon content in the range of about 6.08% to
about 6.18% by weight.
[0050] According to one embodiment of the present disclosure, the
encapsulating shell of a first encapsulated particle is chosen to
be different from the encapsulating shell of a second encapsulated
particle. This difference(s) between the matrix powder materials of
the encapsulated particles may include variations in chemical
make-up or particle size ranges/distribution, which may translate,
for example, into a difference in wear or erosion resistance
properties of the encapsulating shell. Thus, for example, different
types of carbide (or other hard) particles may be used among the
different types of encapsulated particles. One of ordinary skill in
the art would appreciate that a particular variety of tungsten
carbide, for example, may be selected based on hardness/wear
resistance. Further, chemical make-up may also be varied by
altering the percentage s/ratios of the amount of hard particles as
compared to binder powder. Thus, by decreasing the amount of
tungsten carbide particle and increasing the amount of binder
powder in an encapsulating shell, a softer encapsulating shell may
be obtained, and vice versa.
[0051] Further, with respect to particle sizes, each type of matrix
material (for respective types of encapsulated particles) may be
individually be selected from particle sizes that may range in
various embodiments, for example, from about 1 to 200 micrometers,
from about 1 to 150 micrometers, from about 10 to 100 micrometers,
and from about 5 to 75 micrometers in various other embodiments or
may be less than 50, 10, or 3 microns in yet other embodiments. In
a particular embodiment, each type of matrix material (for
respective types of encapsulated particles) may have a particle
size distribution individually selected from a mono, bi- or
otherwise multi-modal distribution.
[0052] Thus, referring to FIG. 2, one of ordinary skill in the art
would recognize that the wear properties of an encapsulating shell
214 relative to an encapsulating shell 224 may be tailored by
changing their respective chemical makeup. Depending on the
anticipated final use of the cutting structure, encapsulating shell
214 may be softer and less wear resistant than encapsulating shell
224. In another embodiment, encapsulating shell 214 may be
substantially softer and less wear resistant than encapsulating
shell 224. In such an embodiment, the relative ease of erosion of
encapsulating shell 214 would allow the abrasive particles 212 to
be exposed to the formation quickly, while providing the bit matrix
with increased durability and life through encapsulating shell 224,
which does not wear or erode near as quickly. Thus, variable wear
among the encapsulated particle may allow for dual optimization of
rate of penetration (ROP) and durability, which are otherwise
inapposite performance characteristics. That is, for increased ROP,
increased rates of diamond exposure are necessary (and thus less
wear resistance of the matrix material in which the diamonds are
impregnated); however, for durability, greater wear resistance of
the matrix material is desirable so that the bit does not wear away
as quickly. Further, the variable wear of the encapsulating shell
may also allow for fluid pathways to be created in the cutting
structure that may allow for efficient cuttings removal. However,
as the variable wear is on a micro-level (the material around
neighboring abrasive particle in the formed cutting structure may
possess differential wear properties, as compared to a larger or
macro-region), the fluids channels that form are similarly on such
a micro-level.
[0053] A desirable shell thickness may vary depending on the final
intended use of the cutting structure. Also, the thickness may vary
depending on the sizes of abrasive grit used in forming
encapsulated particle. In some embodiments, an encapsulating shell
may have an average thickness ranging from 0.1 to 1.5 mm. In other
embodiments, a shell may have an average thickness ranging from 0.1
to 1.3 mm; from 0.15 to 1.1 mm in other embodiments; and from 0.2
to 1.0 mm in yet other embodiments. In most embodiments, a shell
may have an average thickness ranging from 750 micrometers to 1000
micrometers.
[0054] Further, while the encapsulated particles are shown in FIGS.
2 and 3 as having shells of approximately the same thickness, the
present invention is not so limited. The thickness and chemical
composition of the encapsulating shells may be tailored to achieve
a desirable wear rate. Thus, abrasive grits may be of different
sizes or of different kinds, and the encapsulating shells may be of
various thicknesses and comprise matrices, which may wear at
different rates thereby exposing the grits at different rates. The
composition and thickness of this second matrix may also affect the
rate at which the encapsulated grit is exposed. For example, it may
take a longer time to expose the abrasive grit in an encapsulated
particle with a larger shell thickness than a grit with a smaller
shell thickness of same chemical composition.
[0055] Encapsulated Particles
[0056] Encapsulated particles may be formed by encapsulating or
coating abrasive particles with matrix powder material using
encapsulation techniques known to one skilled in the art. In a
particular embodiment, at least two types of encapsulated particles
are used to form a variable impregnated cutting structure. In
embodiments where two types of encapsulated particles are used, the
ratio of those particles may range from 20:80 to 80:20 in one
embodiment, and 30:70-70:30 in another embodiment. However, one of
ordinary skill in the art would appreciate that other number of
types of encapsulated particles may find use in the cutting
structures of the present disclosure. For example, where three
encapsulated particle types are desired, a first particle type may
represent 5 to 30 percent, a second particle type representing
10-40 percent, and a third particle type representing 30-85 percent
of the total amount of encapsulating particles. However, one of
ordinary skill in the art would appreciate the particular
combination of encapsulated particle types and amounts may be
varied depending on the particular application.
[0057] In some embodiments, each type of encapsulated particle may
have an individually selected average diameter (or equivalent
diameter) ranging from 0.3 to 3.5 mm. In other embodiments,
encapsulated particles may have an average diameter ranging from
0.4 to 3.0 mm; from 0.5 to 2.5 mm in other embodiments; and from
0.7 to 2.0 mm in yet other embodiments. In other embodiments,
encapsulated particles 38 may include particles not larger than
would be filtered by a screen of 5 mesh. In other embodiments,
encapsulated particles may range in size from -10+25 mesh. While
the encapsulated particles are primarily shown as spheres, one of
ordinary skill in the art would appreciate that the present
disclosure is not so limited.
[0058] In various embodiments, encapsulated particles may be
obtained from commercial sources, or synthesized using
encapsulation techniques known to those of ordinary skill in the
art.
[0059] Infiltrating Matrix Material
[0060] For embodiments where an infiltrating matrix material is
used, the infiltrating matrix material may include hard particles
and a binder phase. Such exemplary hard particles include tungsten
(W) or a derivative such as tungsten carbide (WC), sintered
tungsten carbide/cobalt (WC--Co) (spherical or crushed), cast
tungsten carbide (particulate or crushed), macro-crystalline
tungsten carbide, carburized tungsten carbide, other carbides, or
combinations of these materials with an optional binder. In other
embodiments, the infiltrating matrix material may be formed from
hard particle materials such as carbides or nitrides of tungsten,
vanadium, boron, titanium, or combinations thereof. Typically, a
binder phase may be formed from a powder component and/or an
infiltrating component. In some embodiments of the present
invention, hard particles may be used in combination with a powder
binder such as cobalt, nickel, iron, chromium, copper, molybdenum
and their alloys, and combinations thereof. In various other
embodiments, the first matrix material 44 may include a Cu--Mn--Ni
alloy, Ni--Cr--Si--B--Al--C alloy, Ni--Al alloy, and/or Cu--P
alloy. In other embodiments, the infiltrating matrix material may
include carbides in amounts ranging from 50 to 70% by weight in
addition to at least one binder in amount ranging from 30 to 50% by
weight thereof to facilitate bonding of matrix material and
impregnated materials. In one embodiment, the resulting
infiltrating matrix material may be chosen to be very tough, yet
maintain good cutting properties. Additionally, tungsten carbide,
in particular a fine-grained tungsten carbide, may present an
optimum matrix for controlled wear and cuttings removal.
[0061] In various embodiments, the infiltrating matrix may include
hard particles ranging in size from about 1 to 200 micrometers, or
about 5 to 150 micrometers, or about 10 to 100 micrometers. One of
ordinary skill in the art would recognize that the particular
combination of hard particle material and particle size used in the
matrix material may depend, for example, on whether the particles
disclosed herein are being used in a insert or a rib of a bit body
so that desired properties such as wear resistance and ability to
be infiltrated may be optimized.
[0062] One of ordinary skill in the art would recognize that the
particular combination of carbides and binders used in the
infiltrating matrix material may be tailored depending on the
anticipated final use of the cutting structure. For example, the
combination used may be customized for desired properties such as
wear resistance and ability to be infiltrated. The infiltrating
matrix material may be chosen to have sufficient hardness so that
the impregnated materials, namely the encapsulated particles,
exposed at the cutting face are not pushed into the matrix material
under the very high pressures commonly encountered in drilling. In
addition, the infiltrating matrix material may be selected to
withstand continuous mechanical action such as rubbing, scraping,
or erosion that typically occurs during drilling so that the
impregnated materials are not prematurely released.
[0063] Manufacture of Cutting Structures Using Encapsulated
Particles
[0064] In one embodiment, uniformly coated encapsulated particles
are manufactured prior to the formation of the impregnated bit. An
exemplary method for achieving "uniform coatings" is to mix the
abrasive particles, and a matrix material in a commercial mixing
machine such as a Turbula Mixer or similar machine used for
blending diamonds with matrix. The resultant mix may then be
processed through a "granulator" in which the mix is extruded into
short "sausage" shapes which are then rolled into balls and dried.
The granules that are so formed must be separated using a series of
mesh screens in order to obtain the desired yield of uniformly
coated particles. At the end of this process, a number of particles
of approximately the same size and shape can be collected, and
optionally pre-sintered. Another exemplary method for achieving a
uniform matrix coating on the abrasive grits is to use a machine
called a Fuji Paudal pelletizing machine. The uniformly coated
particles may then be transferred into a mold cavity and formed
into an insert or other cutting structure, i.e., rib of a drill
bit. One such process is described in U.S. Patent Application
Publication No. 2006/0081402, which is herein incorporated by
reference in its entirety.
[0065] One of ordinary skill in the art would appreciate that the
encapsulated particles disclosed herein may be used to form
inserts, cutting structures or bit bodies using any suitable method
known in the art. 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. The inserts may be heated by resistance heating in a
graphite mold, while bit bodies may be formed by infiltration of a
mold. The dimensions and shapes of the inserts and of their
positioning on the bit can be varied, depending on the nature of
the formation to be drilled.
[0066] Infiltration processes that may be used to form an
infiltrated bit body of the present disclosure may begin with the
fabrication of a mold, having the desired body shape and component
configuration. Pellets of uniformly coated encapsulated particles
may be loaded into the mold in the desired location, i.e., ribs,
and, a matrix material, and optionally a metal binder powder, may
be loaded on top of the encapsulated particles. The mass of
particles may be infiltrated with a molten infiltration binder and
cooled to form a bit body. In a particular embodiment, during
infiltration at least a portion of the loaded matrix material may
be carried down with the molten infiltrant to fill the gaps between
the encapsulated particles. Depending on the size of the
encapsulated particles, as well as additional properties, a size
distribution of the additional matrix material may be likewise
selected such that the additional matrix material possess a
sufficient amount of "fine" particles that may be carried down
between the encapsulated particles to fill the gaps
therebetween.
[0067] It will further be understood that the concentration of
diamond or abrasive particles in a consolidated insert, for
example, can differ from the concentration of diamond or abrasive
particles in the bit body. Diamond concentration may be obtained,
for example by varying shell thickness and the matrix loading of
the first matrix material. According to one embodiment, the
concentrations of diamond in the inserts and in the bit body are in
the range of 50 to 120 (100=4.4 carat/cm.sup.3). Other embodiments
may have a diamond concentration greater than 110, while yet other
embodiments may have a diamond concentration less than 85. A
diamond concentration of 120 is equivalent to 30 percent by volume
of diamond. Those having ordinary skill in the art will recognize
that other concentrations of diamonds may also be used depending on
particular applications. Further, in some embodiments, the various
types of encapsulated particles may have a varied concentration,
such as a concentration of at least 110 for one type of particle,
and a concentration of at most 100 for another type of particles.
However, one of ordinary skill in the art would appreciate that
other combinations may be used.
[0068] Further, while reference has been made to a hot-pressing
process above, embodiments disclosed herein may use a
high-temperature, high-pressure press (HTHP) process.
Alternatively, a two-stage manufacturing technique, using both the
hot-pressing and the HTHP, may be used to promote the development
of high concentration (>120 conc.) while achieving maximum bond
or matrix density. The HTHP press can improve the performance of
the final structure by enabling the use of higher diamond volume
percent (including bi-modal or multi-modal diamond mixtures)
because ultrahigh pressures can consolidate the bond material to
near full density (with or without the need for low-melting alloys
to aid sintering).
[0069] The HTHP process has been described in U.S. Pat. No.
5,676,496 and U.S. Pat. No. 5,598,621. 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).
[0070] Further, the processing times during sintering or
hot-pressing, such as heating and cooling times, may be selected to
be sufficiently short, as well as the maximum temperature of the
thermal cycle may be selected to be sufficiently low, so that the
impregnated materials are not thermally damaged during these
processes.
[0071] In some embodiments, the multiple types of encapsulated
particles on rib may include particles of varying size, varying
composition, or combinations thereof. In other embodiments, the
multiple encapsulated particles may include shells of varying
thickness, varying composition, or combinations thereof. In yet
other embodiments, the multiple encapsulated particles may include
abrasive particles of varying size, varying composition, varying
size distribution, and combinations thereof. In yet other
embodiments, the drill bit or a rib on a drill bit may additionally
include (be impregnated with) standard grit.
[0072] In various embodiments, the encapsulated particles disclosed
herein may have localized placement in a drill bit. For example,
encapsulated particles may be placed at the top of the bit being
the first section of the bit to drill or solely imbedded deeper
within the bit for drilling of the latter sections encountered
during a bit run. Additionally, one of skill in the art would
recognize that it may be advantageous to place the encapsulated
particles at other strategic positions, such as, for example, in
the gage area, and leading, or trailing sides of a rib/blade.
[0073] Further, as discussed above, the encapsulated particles may
be used in a consolidated or hot pressed insert, such as the type
described in U.S. Pat. No. 6,394,202, which is assigned to the
present assignee and herein incorporated by reference in its
entirety. As shown in FIG. 4, such inserts may be inserted into a
drill bit. Bit 422 includes a shank 424 and a crown 426. Crown 426
has a cutting face 429 and outer side surface 430. According to one
embodiment, crown 426 is formed by infiltrating a mass of
tungsten-carbide powder impregnated with synthetic or natural
diamond, or alternatively by infiltrating encapsulated particles as
described herein.
[0074] Crown 426 may include various surface features, such as ribs
427, which may optionally be formed with spacers in the mold during
the manufacturing process so that the infiltrated,
diamond-impregnated crown includes a plurality of holes or sockets
434 that are sized and shaped to receive a corresponding plurality
of diamond-impregnated inserts 436. Once crown 426 is formed,
inserts 436 formed from the encapsulated particles of the present
disclosure may be mounted in the sockets 434 and affixed by any
suitable method, such as brazing, adhesive, mechanical means such
as interference fit, or the like. As shown in FIG. 4, the sockets
434 may each be substantially perpendicular to the surface of the
crown 426 so that once inserted into sockets 434, inserts are
substantially perpendicular to the surface of crown 426 (and may be
flush with or extend beyond surface of crown 426). Alternatively,
holes 434 can be inclined with respect to the surface of the crown
426. In this embodiment, the sockets are inclined such that inserts
436 are oriented substantially in the direction of rotation of the
bit, so as to enhance cutting.
[0075] Alternatively, inserts may be stacked within a rib, as shown
in FIG. 5. Specifically, a rib 527 may include a plurality of
inserts 536 (formed from encapsulated particles as disclosed
herein) stacked within the rib, along its length, in a side by side
fashion. Thus, the particular orientation of the diamond
impregnated inserts of the present disclosure within a bit does not
have any limitation on the scope of the present disclosure.
[0076] Further, it is also within the scope of the present
disclosure that a bit is formed without impregnated inserts, but
with the encapsulated particle loaded into bit mold cavity and
infiltrated, as described above. FIGS. 6A-B illustrate partial
views of an alternative embodiment of an impregnated bit, generally
indicated by arrow 610. In FIGS. 6A-B, approximately one half of
the circular face 611 is shown, with the other half being
approximately the mirror image of the part that is shown. The bit
body 613 is cylindrical in form, with the upper end thereof (not
shown) forming a threaded pin which is adapted to be connected to
the lower end of a drill string. The lower end of the bit body 613
forms the end face 611. The end face 611 has a plurality of
elevated ribs 165 formed thereon, with channels 617 formed between
the ribs 615.
[0077] The bit body 613 is preferably made of a steel core 612
having an outer shell 614 comprised of matrix material. The ribs
615 include diamonds (not illustrated) embedded within a matrix
material, where the rib was formed from the encapsulated particles
of the present disclosure. The diamond particles then function to
wear away the bore hole formation as the bit rotates. The channels
617 function to allow drilling fluid to pass through a central
plenum (not shown) from the interior of the bit body 613 and run
along the channels 617 to cool the ribs 615 and to carry the
formation cuttings up the annulus formed between the bit and the
bore hole. Thus, in forming the bit, encapsulated particles and a
matrix material are loaded into a mold cavity and heated, such as
by infiltration or sintering, to form the resulting impregnated
bit. Further, as the use of encapsulated particles may allow for a
unique tailoring of the bit composition, taller ribs (for a given
rib width) may be obtained, without high risk of failure by rib
breakage. The inclusion of tall ribs may be determined by the ratio
of the rib height (indicated as 640 on FIGS. 6A-B) to rib width
(indicated as 650 on FIGS. 6A-B). Conventional bit designs
generally require a ratio of rib height to width of no more than
1.5. However, by using at least one type of encapsulated particles
(or at least two in other embodiments) of the present disclosure,
bit having a ratio of rib height to rib width (along any portion of
the rib) of greater than 1.75 may be obtained using a minimum
diamond concentration of 100. In other embodiments, a ratio of rib
height to width of greater than 2.0 may be obtained using a minimum
diamond concentration of 75. In yet other embodiments, a ratio of
rib height to width of greater than 2.25 may be obtained using a
minimum diamond concentration of 50. Such ratios translate, for
example, to a rib height of greater than 30 mm on an 83/8 inch bit.
In various embodiments, the specified ratio of bit height to width
refers to a portion of the rib along the bit center (nose) or bit
top (nose). Most of the catastrophic rib breakage typically occurs
near these areas, the bit center (cone) and bit top (nose), because
ribs typically have less width at these locations as compared to
the gage area due to space restrictions and load concentrations
when used in drilling.
[0078] Use of the encapsulated particles disclosed herein may
provide increased TRS bending strength of at least 15 percent in
some embodiment, at least 20 or 25 percent in other embodiments,
and at least 30 percent in yet other embodiments. Further, one
skilled in the art would appreciate that the recited ratios may be
obtained by either reducing the rib width (to fit more ribs and
thus more surface area for wear resistance) and/or by increasing
blade height (to increase bit life before tripping), both of which
may use the encapsulated particles disclosed herein.
[0079] Referring again to FIGS. 5-6B, impregnated bits may include
a plurality of gage protection elements disposed on the ribs and/or
the bit body. In some embodiments, the gage protection elements may
be modified to include evenly distributed diamonds. By positioning
evenly distributed diamond particles at and/or beneath the surface
of the ribs, the impregnated bits are believed to exhibit increased
durability and are less likely to exhibit premature wear than
typical prior art impregnated bits.
[0080] Embodiments disclosed herein, therefore, may find use in any
application in which impregnated cutting structures may be used.
Specifically, embodiments may be used to create diamond impregnated
inserts, diamond impregnated bit bodies, diamond impregnated wear
pads, or any other diamond impregnated material known to those of
ordinary skill in the art. Embodiments may also find use as inserts
or wear pads for 3-cone, 2-cone, and 1-cone (1-cone with a bearing
& seal) drill bits. Further, while reference has been made to
spherical particles, it will be understood by those having ordinary
skill in the art that other particles and/or techniques may be used
in order to achieve the desired result, namely more even
distribution of diamond particles. For example, it is expressly
within the scope of the present invention that elliptically coated
particles may be used.
EXEMPLARY EMBODIMENTS
[0081] An impregnated cutting structure formed in accordance with
the present disclosure may include two types of encapsulated
particles. The first type of particle may constitute 35% of the
total volume of particles. It may include synthetic grit having a
mesh size of -25+35, such as SDB1100, which is a strong grit
commercially available from Element Six Ltd, coated with a TiC
coating applied by chemical vapor deposition (CVD). A hard matrix
comprising 70% WC (<10 micrometer standard WC type) and a binder
mixture of Co and Cu may be used to encapsulate the particles
sufficient to form a 110 diamond concentration. The second type of
particle may constitute 65% of the total volume of particles. It
may include synthetic grit having a mesh size of -20+25, such as
MBS950, which is a medium strength grit commercially available from
Diamond Innovations, Inc., coated with a TiC or SiC coating applied
by CVD. A soft matrix comprising 30% WC (<10 micrometer standard
WC type) and a binder mixture of Co and Cu may be used to
encapsulate the particles sufficient to form a diamond
concentration of 80. Such embodiment may be used to form hot
pressed inserts, as described above, or may be used in conjunction
with an infiltrating matrix material to form an impregnated bit
body.
[0082] A second impregnated cutting structure formed in accordance
with the present disclosure may also include two types of
encapsulated particles. The first type of particle may constitute
35% of the total volume of particles. It may include synthetic grit
having a mesh size of -25+35, such as MBS960, which is a high
strength grit commercially available from Diamond Innovations,
Inc., coated with a strong SiC coating applied by CVD. A soft
matrix comprising 30% WC (<10 micrometer standard WC type) and a
binder mixture of Co and Cu may be used to encapsulate the
particles sufficient to form a 110 diamond concentration. The
second type of particle may constitute 65% of the total volume of
particles. It may include synthetic grit having a mesh size of
-20+25, such as MBS960, which is commercially available from
Diamond Innovations, Inc., coated with a SiC coating applied by
CVD. A soft matrix comprising 30% WC (<10 micrometer standard WC
type) and a binder mixture of Co and Cu may be used to encapsulate
the particles sufficient to form a diamond concentration of 100.
Such embodiment may be used in particular when high ROP is desired
(due to the soft/high toughness nature of the encapsulating
material).
[0083] A third impregnated cutting structure formed in accordance
with the present disclosure may include three types of encapsulated
particles. The first type of particle may constitute 55% of the
total volume of particles. It may include synthetic grit having a
mesh size of -18+20, such as NDG120, which is a strong grit
commercially available from Element Six Ltd, coated with a TiC
coating applied by CVD. A soft matrix comprising 30% WC (<10
micrometer standard WC type) and a binder mixture of Co and Cu may
be used to encapsulate the particles sufficient to form a 120
diamond concentration. The second type of particle may constitute
30% of the total volume of particles. It may include synthetic grit
having a mesh size of -25+35, such as SBD1100, which is a strong
grit commercially available from Element Six Ltd, coated with a TiC
coating applied by CVD. A medium hardness matrix comprising 50% WC
(<10 micrometer standard WC type) and a binder mixture of Co and
Cu may be used to encapsulate the particles sufficient to form a
diamond concentration of 120. A third type of particle may
constitute 15% of the total volume of particles. It may include
synthetic grit having a mesh size of -35+40, such as MBS950, which
is a medium strength grit commercially available from Diamond
Innovations, Inc., coated with a SiC coating applied by CVD. A hard
matrix comprising 70% WC (<100 micrometer mixture of standard WC
and cast WC/W.sub.2C types) and a binder mixture of Co and Cu may
be used to encapsulate the particles sufficient to form a diamond
concentration of 120. Such embodiment may be used to form hot
pressed inserts, as described above, or may be used in conjunction
with an infiltrating matrix material to form an impregnated bit
body.
[0084] Advantageously, embodiments of the present disclosure may
provide for at least one of the following. As discussed above,
embodiments disclosed herein may provide more controllable wear
properties, improved diamond retention, and increased diamond
concentration (without diamond cluttering) for a given volume.
Embodiments disclosed herein may also provide for the controlled
exposure of fresh grit for increased ROP, as removal of the grit to
expose fresh grit may be controlled by the hardness of the shell
and the relative wear properties of the various matrix materials
used, and may be tailored for the hardness of the earth
formation.
[0085] Additionally, in the embodiments disclosed herein, the
various combinations of encapsulated particle components that may
be used may provide improved cutting structures to drill through
formations of specific hardnesses and/or may make a bit
particularly suitable for drilling through a variety of formations,
including mixed formations, due to the adaptive nature of the bit.
Further, a first encapsulating matrix material may be selected for
its toughness, which may reduce blade breakage and allow the blade
height to increase, which would increase the drilling life of the
blade. Improvements in properties, such as bending strength, may be
obtained by using encapsulated particles, which may allow for an
increase in rib height to width ratios. Such ratio may be realized
by either reducing rib width (to increase the number of ribs and
thus surface area for wear resistance) and/or increasing the rib
height (to increase bit life before tripping). Further, by blending
at least two distinct pellets to form ribs having increased height
to width ratios, it may be possible to effectively drill through
mixed formation types. For example, a first pellet type may be
selected to provide optimum drilling through abrasive sandstones,
while a second pellet type may be selected to provide optimum
drilling through shale, limestone, or chert (hard nodules).
Typically, during formation changes, an operator is typically
forced to pull an impregnated bit (despite having remaining bit
life) due to reduced ROP to drill with another bit type, such as a
roller cone bit, which have less life to bearing and seal failure.
Thus, the combination of increased bit height and the unique
encapsulated particles, may provide for increase bit life despite
formation changes.
[0086] However, certain quantities of abrasive particles may be
more readily exposed by the softer encapsulating material, which
also increases ROP. Further, a second matrix material may be
selected to be more wear resistant than the first matrix material
in order to expose the concentrated grit at a slower rate. This may
result in a robust cutting instrument wherein the grit is exposed
in a controlled fashion.
[0087] Further, the disparity in wear properties between multiple
matrices may allow for tailoring of the some of the properties of
the cutting structure such as grit concentration, wear rate,
controlled exposure of encapsulated grit to the formation, cuttings
removal and robustness. If a high grit concentration is required
for drilling a particularly hard formation, the shell thickness may
be small. This may advantageously allow more encapsulated grit to
be packed into the same cutting structure.
[0088] If more efficient cuttings removal is required, the cutting
instrument may have a first matrix that is selected to be more wear
resistant than the second matrix material. The second matrix may
preferentially partially wear away creating fluid pathways within
the cutting instrument, while exposing abrasive particles. This may
result in a cutting instrument with superior cuttings removal
properties.
[0089] Further, conventional bits rely on grit hot pressed inserts
for a large portion of the wear; however, such segments are
typically restricted to approximately thirty to forty percent of
the rib volume due to design limitations. Because the cutting
structures of the present disclosure may provide for improved rate
of penetration by virtue of improved wear patterns, a bit that
typically relies on grit hot pressed inserts for wear may instead
be provided with ribs infiltrated with the encapsulated particles
as disclosed herein. Such bits may possess improved wear across a
larger volume of rib, as compared to conventional bits having grit
hot pressed inserts.
[0090] Thus, embodiments disclosed herein may allow for an
effective diameter of the encapsulated materials without such
drastic increases in cost. Furthermore, some embodiments may
include a hard particle, such as tungsten or silicon carbide, which
has even lower costs as compared to diamond or other super
abrasives. Therefore, cost savings may be achieved while
maintaining or even improving rate of penetration (ROP), thus
lowering the drilling cost per foot.
[0091] While the invention has been described with respect to a
limited number of embodiments, those skilled in the art, having
benefit of this disclosure, will appreciate that other embodiments
can be devised which do not depart from the scope of the invention
as disclosed herein. Accordingly, the scope of the invention should
be limited only by the attached claims.
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