U.S. patent application number 11/509404 was filed with the patent office on 2006-12-21 for stepped polycrystalline diamond compact insert.
Invention is credited to Johnny Castle, Roy Estes.
Application Number | 20060283640 11/509404 |
Document ID | / |
Family ID | 34633050 |
Filed Date | 2006-12-21 |
United States Patent
Application |
20060283640 |
Kind Code |
A1 |
Estes; Roy ; et al. |
December 21, 2006 |
Stepped polycrystalline diamond compact insert
Abstract
The present invention addresses this need in the art by
providing a cutter insert comprising a plug section and a cutter
pedestal. The cutter insert in preferably formed of tungsten
carbide, except for two exterior surfaces covered with PDC. The
plug section may be circular or oval in cross section perpendicular
to the axis of the insert. The plug section and the pedestal each
defines a shoulder which is coated with a PDC layer. In this way,
two cutting surfaces are applied to the formation, enhancing the
cutting ability of the insert.
Inventors: |
Estes; Roy; (Weatherford,
TX) ; Castle; Johnny; (Weatherford, TX) |
Correspondence
Address: |
STORM LLP
BANK OF AMERICA PLAZA
901 MAIN STREET, SUITE 7100
DALLAS
TX
75202
US
|
Family ID: |
34633050 |
Appl. No.: |
11/509404 |
Filed: |
August 24, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11151766 |
Jun 14, 2005 |
|
|
|
11509404 |
Aug 24, 2006 |
|
|
|
10600662 |
Jun 20, 2003 |
6904984 |
|
|
11151766 |
Jun 14, 2005 |
|
|
|
Current U.S.
Class: |
175/434 |
Current CPC
Class: |
E21B 10/5735 20130101;
E21B 10/5673 20130101 |
Class at
Publication: |
175/434 |
International
Class: |
E21B 10/36 20060101
E21B010/36 |
Claims
1. A PDC cutter comprising: a plug; a pedestal atop the plug; the
pedestal having a side wall and a substantially flat top; a step
between the plug and the pedestal; and the step and the pedestal
top being substantially parallel.
2. The PDC cutter of claim 1, further comprising: a pedestal
shoulder connecting the top and the side wall.
3. The PDC cutter of claim 1, further comprising: a plug shoulder
connecting the plug and the step.
4. The PDC cutter of claim 1, further comprising: a fillet between
the step and the pedestal.
5. The PDC cutter of claim 1, further comprising: wherein the side
wall is slanted.
6. The PDC cutter of claim 1, further comprising: a pedestal
shoulder connecting the top and the side wall; and, a plug shoulder
connecting the plug and the step.
7. The PDC cutter of claim 6, further comprising: wherein the
cutter defines an axis and the cutter defines a back rake angle;
and, wherein the plug shoulder and pedestal shoulders define angles
to the axis approximately equal to the back rake angle.
Description
CROSS REFERENCE TO A RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/151,766 entitled "STEPPED POLYCRYSTALLINE
DIAMOND COMPACT INSERT," filed on Jun. 20, 2003, which is a
continuation of U.S. patent application Ser. No. 10/600,662
entitled "STEPPED POLYCRYSTALLINE DIAMOND COMPACT INSERT," filed on
Jun. 20, 2003, now U.S. Pat. No. 6,904,984, wherein each related
application is incorporated by reference herein for all
purposes.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to earth boring
drill bits, and in particular to a polycrystalline diamond compact
(PDC) insert exhibiting a stepped profile structure for use in a
fixed cutter earth boring bit or reamer.
[0004] 2. Description of Related Art
[0005] PDC inserts are commonly used to increase the wear
resistance of surfaces in certain types of downhole tools. For
example, inserts on a reamer, in association with a drill bit, are
used on outer blade surfaces to resist wear from the bore hole
wall. The reamer enlarges the bore hole to a diameter larger than
that created by the drill bit.
[0006] The function of the reamer is to maintain the diameter of
the hole as the drill bit proceeds downwardly through the rock
formation. As the bore hole is being drilled, the rock drill bit
gradually wears to undersize and thus the hole which is cut
gradually becomes of undersize diameter. The function of the
reamer, which typically has PDC inserts along the outer blade edge,
is to grind the circumference of the hole, shortly after it has
been cut by the rock drill bit, and thus keep the hole diameter to
size.
[0007] Inserts are also commonly used in fixed cutter drill bits
along a cutting blade which is stationary in respect of the drill
string, in contrast to roller cone bits. Such a fixed cutter drill
bit typically has a leading face from which a plurality of blades
extend, each blade carrying a plurality of cutting elements
comprising PDC inserts. Inserts may also be placed along a gauge
pad at the extreme outer diameter of each blade.
[0008] PDC inserts have a polycrystalline diamond surface formed on
wear surfaces, which may be formed in a variety of ways,
principally in a conventional process under heat and pressure, or
by sintering. The inserts are formed of a tungsten carbide
material, and the wear surface is then applied. In the past, such
inserts commonly have had a flat or slightly ovoid outer contact
region, where the insert contacts the rock formation being cut.
Regardless of the configurations of the inserts, they have all had
a characteristic in common, and that is the inserts define one
point, line, or area contact with the rock formation. As the rock
formation increases in hardness, the resistance or "work load"
necessary to disintegrate the formation at that area also
increases. The increased resistance causes two common problems. The
increased resistance on individual inserts can cause premature
chipping or breakage failure of the inserts. Also, the combined
increase of resistance on all the PDC inserts increases the amount
of torque required to drive the bit and causes the bit to stop
momentarily while drilling, a condition known as "stick slip"
drilling. There is a present need in this art for PDC inserts that
can drill harder formations with less risk of failure and with less
risk of "stick slip". The present invention is directed to this
need in the art.
SUMMARY OF THE INVENTION
[0009] The present invention addresses both of these noted problems
in the art by providing a PDC insert comprising a plug section and
a pedestal section. The cutter insert is preferably formed of
tungsten carbide, except for two exterior surfaces covered with
PDC. The plug section may be circular or oval in cross section
perpendicular to the axis of the insert. The plug section and the
pedestal each defines a shoulder which is coated with a PDC layer.
In one preferred embodiment of the invention, the pedestal section
provides a second smaller cutting area or edge which precedes the
cutting area of the plug. This leading cutting edge cuts a narrow
groove in the formation just ahead of the larger plug cutting area.
This narrow groove reduces the rock strength of the formation cut
by the plug surface and obviously reduces the amount of rock cut by
the plug surface. Dividing the work load over two edges reduces the
load per edge resulting in less risk of PDC failure.
[0010] In another preferred embodiment, the pedestal section is
designed to limit the depth that the plug edge can embed into the
rock formation. As additional weight is applied to a PDC bit during
normal operation, the PDC inserts are forced to embed deeper into
the formation. As the inserts embed deeper, work load is increased
and this results in more torque being required to turn the bit. As
previously described, at some point, the torque reaches a level
causing a "stick slip" drilling condition. "Stick slip" drilling is
very detrimental to PDC bits often resulting in premature failure
of the bits.
[0011] The deeper embedding of the insert into the formation also
causes many other problems with the drill string and rig. The
pedestal of the present invention is designed to slide across the
formation rather than embed and cut the formation. This action
limits the depth which the plug edge can embed into the formation.
In the additional embodiment of the invention, the amount of
embedding of the plug edge remains about the same even as the WOB
(weight on bit) is increased substantially. Limiting the amount of
embedding of the inserts limits the amount of torque required to
rotate the bit and reduces the risk of "stick slip" drilling and
all the problems associated with it.
[0012] Thus, the present invention is directed to improving PDC
drilling in harder formations. These and other features and
advantages of this invention will be readily apparent to those
skilled in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] So that the manner in which the above recited features,
advantages and objects of the present invention are attained and
can be understood in detail, a more particular description of the
invention, briefly summarized above, may be had by reference to
embodiments thereof which are illustrated in the appended
drawings.
[0014] FIG. 1 is a perspective view of a fixed cutter bit wherein
the PDC insert of the present invention finds application.
[0015] FIG. 2 is an elevation view of a reamer on a rotary cone
drill bit wherein the PDC insert of the present invention finds
application.
[0016] FIG. 3 is a perspective view of a presently preferred
embodiment of a PDC insert of the invention.
[0017] FIG. 4 is a perspective view of another presently preferred
embodiment of a PDC insert of the invention.
[0018] FIG. 5 is a side section view of a PDC insert of the
invention as it cuts into a formation.
[0019] FIG. 6a is a side view of a PDC insert of this invention
which limits the depth of the cut of the plug.
[0020] FIG. 6b is a side view of another PDC insert which further
limits the depth of the cut of the plug.
[0021] FIG. 6c is a side view in partial section, illustrating the
depth limiting aspect of this embodiment of the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0022] FIG. 1 shows a fixed cutter drill bit 10 including cutter
inserts 12 of the present invention. The drill bit 10 has a central
axis of rotation 13 and a bit body 14 having a leading face 16, an
end face 18, a gauge region 20, and a shank 22 for connection to a
drill string (not shown). A plurality of blades 26 extend from the
leading face 16 of the bit body away from the central axis of
rotation 13 of the bit 10. Each blade 26 terminates in a gauge pad
28 having a gauge surface 29 which faces a wall 30 of a borehole
(not shown).
[0023] A number of cutter inserts 12 are mounted on the blades 26
at the end face 18 of the bit 10 in both a cone region 36 and a
shoulder region 38 of the end face 18. Each cutter 12 partially
protrudes from its respective blade 26 and the cutter inserts are
spaced apart along the blade 26, typically in a given manner to
produce a particular type of cutting pattern. The structure of the
cutter insert of the invention is shown in greater detail in FIGS.
3, 4, and 5, below.
[0024] The cutter insert of the invention also may find application
in a reamer 44 as shown in the reaming assembly 40 shown in FIG. 2.
The reamer 44 follows a roller cone bit 42 of conventional design
and a reamer section 44. The roller cone bit 42 may be joined to
the reamer section 44 with a threaded connection 46 and another
threaded connection 48 is provided to join the reamer section to a
drill string (not shown). The reamer section includes a plurality
of blades 50 and each blade includes a plurality of cutter inserts
52, constructed in accordance with the teachings of this invention,
as will now be described.
[0025] FIGS. 3, 4, and 5 illustrate the cutter insert of the
invention. FIG. 3 shows a cutter insert 60 comprising a plug
section 62 and a cutter pedestal 64. The cutter insert 60 is
preferably formed of tungsten carbide, except for two exterior
surfaces covered with PDC. The plug section, which in FIG. 3 is
circular in cross section perpendicular to the axis of the insert,
defines a shoulder 66 which is coated with a PDC layer extending
part way onto a step or shelf 68. Also, the cutter pedestal section
64 is covered with a PDC layer, which extends part way down onto a
slanted wall 70. Thus, the pedestal section also defines a pedestal
shoulder 72, covered with PDC. The wall 70 may be slanted to
provide a tapered profile for the pedestal section, thereby
providing a stronger base for a top surface 74. The plug shoulder
66 and the pedestal shoulder 72 define two distinct cutting
surfaces for the cutter insert 60.
[0026] FIG. 4 shows another preferred embodiment of a cutter insert
80, which is similar in most respects to the insert illustrated in
FIG. 3, except that a pedestal 82 has an oval cross section when
taken perpendicular to the axis of the cutter segment. The insert
80 is modestly more expensive to manufacture, but provides the
advantage of allowing a pedestal shoulder 84 to cut a narrow, deep
leading groove through rock. The geometry of the insert 80 places
less work load on the top which initiates the groove, and places
more on the lower cutting surface which scrapes away less supported
formation on the sides of the initial groove.
[0027] FIG. 5 shows how the cutter insert works. A cutter insert
60, constructed as just described, is inserted into a hole 92 in a
body 94, preferably a blade in a fixed cutter of FIG. 1 or a reamer
of FIG. 2. The shoulders 66 and 72 of the cutter 60 engage the
formation at two points. Thus, as the cutter moves across the face
of the formation in a direction 96, more material may be worn or
chipped away, increasing the speed of the cutter through the
formation.
[0028] FIGS. 6a, 6b, and 6c show another preferred embodiment of
the invention, in which the degree of embedding into a formation
100 is limited in order to alleviate the problem of stick slip, and
to maintain a more constant torque on the bit while drilling in
hard formations. In the embodiment of FIG. 6a, an insert 101
comprises a plug 102 integrally formed with a pedestal 104, in a
manner previously described. A fillet 106 joins the pedestal to the
plug to reduce stress cracking at the joint. Then, in ascending
order, the pedestal defines a vertical surface 108, a first convex
curved surface 110, a straight, frustoconical bevel surface 112, a
second convex curved surface 114, and a flat top 116. The bevel
surface 112 preferably forms an angle .beta. with an axis 118 of
the insert 101, as shown in FIG. 6c. The bevel angle .beta. is also
approximately equal to an insert back rake angle a, so that the
pedestal tends to ride along the surface of the formation 100,
rather than digging into it.
[0029] Another embodiment which limits the depth of cut is shown in
FIG. 6b. An insert 120 includes a plug 122 and a pedestal 124. The
pedestal 124 defines a circular flat top 125 and a substantially
vertical or cylindrical wall 126 in which is formed a large, flat
bevel 128. Viewed another way, the bevel 128 defines a surface
which cuts across the flat top, thereby forming a chord across the
top. The bevel rides against the formation, rather than cutting
into it. Thus, as the weight on bit increases, the bevel keeps the
insert from digging down into the formation, maintaining a fairly
constant torque and reducing the likelihood of stick slip.
[0030] The principles, preferred embodiment, and mode of operation
of the present invention have been described in the foregoing
specification. This invention is not to be construed as limited to
the particular forms disclosed, since these are regarded as
illustrative rather than restrictive. Moreover, variations and
changes may be made by those skilled in the art without departing
from the spirit of the invention.
* * * * *