U.S. patent application number 12/171070 was filed with the patent office on 2008-10-30 for auto adaptable cutting structure.
This patent application is currently assigned to Varel International, Ind., L.P.. Invention is credited to Bruno Cuillier, Alfazazi Dourfaye.
Application Number | 20080264696 12/171070 |
Document ID | / |
Family ID | 39885654 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080264696 |
Kind Code |
A1 |
Dourfaye; Alfazazi ; et
al. |
October 30, 2008 |
AUTO ADAPTABLE CUTTING STRUCTURE
Abstract
A cutter is configured with a diamond table made from a thin
hard facing material layer of polycrystalline diamond bonded to a
backing layer made from cemented tungsten carbide. The face of the
diamond table includes a concavity formed with a curved shape
wherein at least a portion of the face in a center of the cutter is
recessed with respect to at least some portion of the face about
the perimeter of the cutter. This concave curved shape is formed in
the diamond table itself such that the diamond table has a varying
thickness depending on the implemented concavity. Alternatively,
the concave curved shape is formed in the backing layer and a
substantially constant thickness diamond table layer is attached
thereto.
Inventors: |
Dourfaye; Alfazazi; (Paris,
FR) ; Cuillier; Bruno; (Pau, FR) |
Correspondence
Address: |
GARDERE WYNNE SEWELL LLP;INTELLECTUAL PROPERTY SECTION
3000 THANKSGIVING TOWER, 1601 ELM ST
DALLAS
TX
75201-4761
US
|
Assignee: |
Varel International, Ind.,
L.P.
Carrollton
TX
|
Family ID: |
39885654 |
Appl. No.: |
12/171070 |
Filed: |
July 10, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11643718 |
Dec 20, 2006 |
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12171070 |
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60949419 |
Jul 12, 2007 |
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60751835 |
Dec 20, 2005 |
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Current U.S.
Class: |
175/428 |
Current CPC
Class: |
E21B 10/5671 20200501;
E21B 10/573 20130101 |
Class at
Publication: |
175/428 |
International
Class: |
E21B 10/00 20060101
E21B010/00 |
Claims
1. A cutter, comprising: a backing layer; and a thin hard facing
material layer bonded to the backing layer, wherein a thickness of
the thin hard facing material layer varies along at least a part of
a length of the cutter to define a face of the cutter having a
curved surface.
2. The cutter of claim 1 wherein the cutter has one of a round,
half-round, elliptical and half-elliptical shape.
3. The cutter of claim 1 wherein the length of the cutter extends
along an orientation axis of the cutter, and the thickness of the
thin hard facing material layer in the part of the length varies
along that orientation axis.
4. The cutter of claim 3 wherein the cutter has a round shape and
the orientation axis is a first orientation axis for the round
shape, the thickness of the thin hard facing material layer
increasing along at least a portion of a length of the first
orientation axis.
5. The cutter of claim 4 wherein the cutter having the round shape
further includes a second orientation axis orthogonal to the first
orientation axis, the thickness of the thin hard facing material
layer further increasing along at least a portion of a length of
the second orientation axis.
6. The cutter of claim 3 wherein thickness of the thin hard facing
material layer increases in a continuous curved manner along the
orientation axis.
7. The cutter of claim 3 wherein the cutter has an elliptical shape
and the orientation axis is one of a major and minor axis for the
elliptical shape, the thickness of the thin hard facing material
layer increasing along at least a portion of a length of one of the
major and minor axes.
8. The cutter of claim 7 wherein the thickness of the thin hard
facing material layer increases along at least a portion of a
length of both the major and minor axes.
9. The cutter of claim 3 wherein the cutter has a half-round shape
and the orientation axis is a first orientation axis for the
half-round shape, the thickness of the thin hard facing material
layer increasing along at least a portion of a length of the first
orientation axis.
10. The cutter of claim 9 wherein the cutter having the half-round
shape further includes a second orientation axis orthogonal to the
first orientation axis, the thickness of the thin hard facing
material layer further increasing along at least a portion of a
length of the second orientation axis.
11. The cutter of claim 3 wherein the cutter has a half-elliptical
shape and the orientation axis is one of a major and minor axis for
the half-elliptical shape, the thickness of the thin hard facing
material layer increasing along at least a portion of a length of
one of the major and minor axes.
12. The cutter of claim 11 wherein the thickness of the thin hard
facing material layer increases along at least a portion of a
length of both the major and minor axes.
13. A cutter, comprising: a backing layer; and a thin hard facing
material layer bonded to the backing layer, wherein a thickness of
the thin hard facing material layer varies to define a paraboloid
front surface concavity for the cutter.
14. The cutter of claim 13 wherein the paraboloid front surface
concavity is defined by a continuously curved surface.
15. The cutter of claim 13 wherein the cutter has a round shape and
the paraboloid front surface concavity follows a first axis of the
cutter round shape.
16. The cutter of claim 15 wherein the paraboloid front surface
concavity also follows a second axis of the cutter round shape
which is perpendicular to the first axis.
17. The cutter of claim 15 wherein round cutter shape is a
half-round shape.
18. The cutter of claim 13 wherein the cutter has an elliptical
shape and the paraboloid front surface concavity follows one of a
major or minor axis of the elliptical round shape.
19. The cutter of claim 18 wherein the elliptical shape is a
half-elliptical shape.
20. The cutter of claim 13 wherein the cutter has an elliptical
shape and the paraboloid front surface concavity follows both of a
major and minor axis of the elliptical round shape.
21. The cutter of claim 20 wherein the elliptical shape is a
half-elliptical shape.
22. The cutter of claim 13 wherein the paraboloid front surface
concavity comprises a first portion of a face of the cutter, and
wherein a thickness of the thin hard facing material layer in a
second portion of the face of the cutter is substantially
constant.
23. A cutter, comprising: a cylindrical backing layer having a
front surface; and a thin hard facing material layer bonded to the
front surface of the backing layer, the thin hard facing material
layer having a front surface including a paraboloid concavity.
24. The cutter of claim 23 wherein the paraboloid concavity is
defined by a continuously curved surface.
25. The cutter of claim 23 wherein the paraboloid concavity is a
spherical cavity.
26. The cutter of claim 23 wherein the paraboloid concavity is an
elliptical paraboloid cavity.
27. The cutter of claim 23 wherein the paraboloid concavity is a
hyperbolic paraboloid cavity.
28. The cutter of claim 23 wherein a thickness of the thin hard
facing material layer varies across the front surface of the
backing layer to define the paraboloid concavity.
29. The cutter of claim 23 wherein a thickness of the cylindrical
backing layer varies across the front surface of the backing layer,
and the thin hard facing material layer has a substantially
constant thickness, so as to define the paraboloid concavity.
30. A drill bit, comprising: a bit matrix including a cutter pocket
formed therein; a cutter, comprising: a backing layer which is
attached by brazing to the cutter pocket; and a thin hard facing
material layer bonded to the backing layer, wherein a thickness of
the thin hard facing material layer is not constant so as to define
curved cutter surface presenting a counter angle.
31. The drill bit of claim 30 wherein the curved surface of the
cutter defines a variable back rake angle as a function of depth of
cut.
32. The drill bit of claim 30 wherein the cutter has one of a
round, half-round, elliptical and half-elliptical shape.
33. The drill bit of claim 30 wherein the curved surface of the
cutter defines a variable back rake angle as a function of depth of
cut extending from a positive angle to a negative angle.
34. The drill bit of claim 30 wherein the curved surface defines a
concave front surface of the cutter.
35. The drill bit of claim 30 wherein the curved surface defines a
parabolic front surface of the cutter.
36. A drill bit, comprising: a bit matrix including a cutter pocket
formed therein; a cutter, comprising: a cylindrical backing layer
which is attached by brazing to the cutter pocket and which defines
a relief angle; and a thin hard facing material layer bonded to the
front surface of the backing layer, the thin hard facing material
layer having a front surface including a paraboloid concavity which
defines both a counter angle and back rake angle; wherein the back
rake angle and relief angle are not equal to each other.
37. The drill bit of claim 36 wherein the back rake angle is a
positive back rake angle.
38. The drill bit of claim 36 wherein the counter angle of the
paraboloid concavity is such that the back rake angle is a positive
back rake angle over a range of depth of cut.
39. The drill bit of claim 38 wherein the back rake angle varies
over that range of depth of cut.
40. The drill bit of claim 36 wherein the paraboloid concavity is
defined by a continuously curved surface.
41. The drill bit of claim 36 wherein the paraboloid concavity is a
spherical cavity.
42. The drill bit of claim 36 wherein the paraboloid concavity is
an elliptical paraboloid cavity.
43. The drill bit of claim 36 wherein the paraboloid concavity is a
hyperbolic paraboloid cavity.
44. The drill bit of claim 36 wherein a thickness of the thin hard
facing material layer varies across the front surface of the
backing layer to define the paraboloid concavity.
45. The drill bit of claim 36 wherein a thickness of the
cylindrical backing layer varies across the front surface of the
backing layer, and the thin hard facing material layer has a
substantially constant thickness, so as to define the paraboloid
concavity.
Description
PRIORITY CLAIMS
[0001] The present application claims the benefit of U.S.
Provisional Application for Patent 60/949,419 filed Jul. 12, 2007
entitled "Auto Adaptable Cutting Structure", and is a
continuation-in-part of U.S. application for patent Ser. No.
11/643,718 filed Dec. 20, 2006, which claims the benefit of U.S.
Provisional Application for Patent 60/751,835 filed Dec. 20, 2005,
the disclosures of which are hereby incorporated by reference to
the maximum extent allowable by law.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field of the Invention
[0003] The present invention relates to earth boring bits, and more
particularly to those having polycrystalline diamond compact (PDC)
cutters.
[0004] 2. Description of Related Art
[0005] Efficiently drilling rock of various hardness or in
overbalanced formations has always been related to the amount of
power (RPM.times.WOB) injected in the drilling system
(RPM=revolutions per minute; WOB=weight on bit). A linear
relationship between ROP (rate of penetration) and WOB has always
been taken into consideration for PDC bit performance, and cutting
structure efficiency ranking can be evaluated through an
examination of MSE (mechanical specific energy). Generally, this
brought about the usage of high forces in order to be efficient.
Usage of high cutting forces, however, can cause problems like BHA
(bottom hole assembly) buckling, deviation issues, and dynamic
problems resulting at the end in an inefficient usage of the power
input to the drilling system. In addition, the usage of these high
forces can induce on the cutting element itself premature failures
due to potential impacts of various magnitude or frequency and
higher frictional heat resulting in a faster cutting element wear
rate.
[0006] PDC cutters are typically formed from a mix of material
subjected to high temperature and high pressure. A common trait of
a PDC cutter is the use of a catalyst material during their
formation. These cutters are known to have several different shapes
and geometries.
[0007] A PDC cutter with improved durability uses an elliptical
shape. These cutters have been marketed as "oval" cutters. These
cutters have an elliptical form (with a major axis and a minor
axis). An elliptical cutter has a better indentation action than a
round cutter. Thus, these elliptical cutters generate a more
concentrated crushed zone in the formation and deeper tensile
cracks in the surrounding non-crushed zone.
[0008] A conventional PDC cutter is placed with the diamond table
facing the direction of bit rotation. The edge of the cutter is
pushed into the formation by the WOB. When an elliptical cutter is
used, the small end of the cutter (in the direction of the major
axis) is typically presented to the formation. This has the effect
of presenting a "sharper" edge, which generates a higher point
loading at a lower WOB versus a round cutter. By replacing a 13 mm
round PDC cutter by a 19*13 mm elliptical PDC cutter, the diamond
volume (density or radial diamond content) of the cutter remains
the same, but the cutter exposure and axial diamond volume can be
increased significantly.
[0009] There is a need in the art for a PDC cutter having a
configuration of its cutting structure which increases drilling
efficiency (presenting a lower MSE level). For example, there is a
need for a specific cutter shape and configuration that requires
less WOB than conventional cutters for a given ROP, thus lessening
the wear rate (thermal and dynamic) and further resulting in a
higher cutting efficiency which brings about a higher ROP and
durability. This cutting structure could thus be considered to be
"sharper" than that of the prior art. Additionally, there would be
an advantage if this improved cutting structure presented better
diamond table cooling and an easier evacuation of cutting chips
during operation.
[0010] The following references are incorporated herein by
reference: U.S. Pat. Nos. 4,538,690, 4,558,753, 4,593,777,
4,679,639, 4,784,023, 5,078,219, and 5,332,051; and U.S. Patent
Application Publication Nos. 2005/0247492, 2005/0269139 and
2007/0235230.
SUMMARY OF THE INVENTION
[0011] In an embodiment, a cutter comprises: a backing layer; and a
thin hard facing material layer bonded to the backing layer,
wherein a thickness of the thin hard facing material layer varies
along at least a part of a length of the cutter to define a face of
the cutter having a curved surface. The curved surface of the
cutter face may present a spherical, paraboloid or ovaloid
surface.
[0012] In an embodiment, a cutter comprises: a backing layer; and a
thin hard facing material layer bonded to the backing layer,
wherein a thickness of the thin hard facing material layer varies
to define a concave front surface of the cutter. The concave
surface may present a spherical, paraboloid or ovaloid surface.
[0013] In an embodiment, a cutter comprises: a backing layer; and a
thin hard facing material layer bonded to the backing layer,
wherein a thickness of the thin hard facing material layer varies
to define a paraboloid front surface concavity for the cutter.
[0014] In an embodiment, a cutter comprises: a cylindrical backing
layer having a front surface; and a thin hard facing material layer
bonded to the front surface of the backing layer, the thin hard
facing material layer having a front surface including a paraboloid
concavity.
[0015] In an embodiment, a drill bit comprises: a bit matrix
including a cutter pocket formed therein; a cutter, comprising: a
backing layer which is attached by brazing to the cutter pocket;
and a thin hard facing material layer bonded to the backing layer,
wherein a thickness of the thin hard facing material layer is not
constant so as to define curved cutter surface presenting a counter
angle. The curved surface may present a spherical, paraboloid or
ovaloid surface.
[0016] In an embodiment, a drill bit comprises: a bit matrix
including a cutter pocket formed therein; a cutter, comprising: a
cylindrical backing layer which is attached by brazing to the
cutter pocket and which defines a relief angle; and a thin hard
facing material layer bonded to the front surface of the backing
layer, the thin hard facing material layer having a front surface
including a paraboloid concavity which defines both a counter angle
and back rake angle; wherein the back rake angle and relief angle
are not equal to each other.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] Other features and advantages of the invention will become
clear in the description which follows of several non-limiting
examples, with references to the attached drawings wherein:
[0018] FIG. 1 illustrates a side view of a conventional cylindrical
PDC cutter configuration engaging a formation;
[0019] FIG. 2 illustrates a side view of a conventional conical PDC
cutter configuration engaging a formation;
[0020] FIG. 3 illustrates a side view of a PDC cutter with a
concave surface configuration engaging a formation;
[0021] FIG. 4 illustrates a portion of a drill bit (such as a
blade) to which an elliptical cutter having a concave shape cutter
face has been mounted;
[0022] FIGS. 5A and 5B show a perspective view and side view,
respectively, for the elliptical cutter having a concave shape
cutter face used in FIG. 4;
[0023] FIGS. 6A and 6B show a perspective view and side view,
respectively, for an elliptical cutter having a concave shape
cutter face;
[0024] FIGS. 7A, 7B and 7C show a perspective view and two
cross-sectional views, respectively, for an elliptical cutter
having a concave shape cutter face;
[0025] FIGS. 8A and 8B show a perspective view and side view,
respectively, for a round cutter having a concave shape cutter
face;
[0026] FIGS. 9A, 9B and 9C show a perspective view and two
cross-sectional views, respectively, for a round cutter having a
concave shape cutter face;
[0027] FIGS. 10A and 10B show a perspective view and side view,
respectively, for a round cutter having a concave shape cutter
face;
[0028] FIGS. 11A, 11B and 11C show a perspective view, a
cross-sectional view and an end view, respectively, for a
half-elliptical cutter having a concave shape cutter face;
[0029] FIGS. 12A and 12B show a perspective view and a side view,
respectively, for a half-elliptical cutter having a concave shape
cutter face;
[0030] FIGS. 13A and 13B show a perspective view and a side view,
respectively, for a half-elliptical cutter having a concave shape
cutter face;
[0031] FIGS. 14A and 14B show a perspective view and a side view,
respectively, for a half-round cutter having a concave shape cutter
face;
[0032] FIGS. 15A, 15B and 15C show a perspective view, a
cross-sectional view and an end view, respectively, for a
half-round cutter having a concave shape cutter face;
[0033] FIGS. 16A and 16B show a perspective view and side view,
respectively, for an elliptical cutter having a concave shape
cutter face;
[0034] FIGS. 17A and 17B show a perspective view and side view,
respectively, for an elliptical cutter having a concave shape
cutter face;
[0035] FIGS. 18A, 18B and 18C show a top view and two alternate
side views, respectively, for an elliptical cutter having a concave
shape cutter face;
[0036] FIGS. 19A and 19B show a perspective view and side view,
respectively, for an elliptical cutter having a concave shape
cutter face; and
[0037] FIGS. 20A and 20B show a perspective view and side view,
respectively, for an elliptical cutter having a concave shape
cutter face.
DETAILED DESCRIPTION OF THE DRAWINGS
[0038] Reference is now made to FIG. 1 which illustrates a side
view of a conventional cylindrical PDC cutter 10 configuration
engaging a formation 12. The cutter 10 is mounted to a bit matrix
14, for example by being brazed into a cutter pocket formed on a
blade of the bit, and configured with a negative back rake at an
angle a. It will further be noted that the relief angle b for the
cutter in this configuration is equal to the back rake angle a. A
PDC cutter set with a negative back rake, as shown in prior art
FIG. 1, will fracture the rock of the formation 12 by compressing
the rock until tensile stress failure occurs. The cutter tends to
compress the cutting chips and collapse tensile cracks in the
formation which may reinforce the strength of the rock under the
front face of the cutter. Thus, the cutting forces increase,
particularly in a direction normal to the surface of the cutter.
This compression effect increases with increases in negative back
rake angle. It will further be noted that a cylindrical cutter 10
of the shape shown in FIG. 1 cannot be used in low back rack angle
a configurations because of the corresponding low relief angle b
and the risk of rubbing on the cutting groove in the formation
12.
[0039] The cutter 10 of FIG. 1 is configured with a diamond table
18 comprising a thin hard facing material of substantially constant
thickness bonded to a backing layer 16 having a cylindrical
configuration. The surface of the diamond table 18 is essentially
planar. Conventionally, the backing layer 16 is made from cemented
tungsten carbide, and the constant thickness diamond table 18 layer
is a layer of polycrystalline diamond (which may, in certain
situations, be leached in manner known to those skilled in the
art).
[0040] Reference is now made to FIG. 2 which illustrates a side
view of a conventional conical PDC cutter 20 configuration engaging
a formation 12. The cutter 20 is configured with a small back rake
at an angle a. It will further be noted that the relief angle b for
the conical cutter in this configuration is not equal to the back
rake angle a due to the conical geometry of the cutter 20. Cutters
having low back rake angles are more aggressive and less loading.
However, the conical cutters still have a cylindrical diamond table
and a small tungsten carbide substrate which limits the use of low
back rake angles.
[0041] The cutter 20 of FIG. 2 is configured with a diamond table
18 comprising a thin hard facing material of substantially constant
thickness bonded to a backing layer 16 having a conical
configuration. Again, the front surface of the diamond table 18 is
essentially planar. Conventionally, the backing layer 16 is made
from cemented tungsten carbide, and the constant thickness diamond
table 18 layer is a layer of polycrystalline diamond (which may, in
certain situations, be leached in manner known to those skilled in
the art).
[0042] When the effective back rake angle for a cutter is, however,
positive, tensile cracks are expanded. Cutting force normal to the
face of the cutter is reduced. Additionally, the compression effect
due to normal stress is lower (or nil). Advantageously, cutting
chips are removed under the action of the propagation of tensile
cracks. Cutting force is constant as a function of rock tensile
strength. It is accordingly preferable with respect to some
formations to use a cutter with a positive back rake angle.
[0043] Reference is now made to FIG. 3 which illustrates a side
view of a PDC cutter 30 with a concave (or paraboloid) face
configuration engaging a formation 12. The cutter 30 is mounted to
bit matrix 14, for example by being brazed into a cutter pocket
formed on a blade of the bit. In this implementation, which can
represent generally either a round or an elliptical cutter, the
face of the cutter 30 includes a concavity, for example having a
spherical, paraboloid or ovaloid shape. In other words, a portion
of the face of the diamond table, in this instance at the center,
is recessed with respect to at least some portion of the perimeter
of the diamond table face. The effect of the concavity in the face
(and specifically for the diamond table itself) is to allow for the
use of a cylindrical substrate cutter configuration (like that
shown in FIG. 1) while supporting low back rake angles a. Still
further, this configuration potentially and beneficially enables
the use of positive back rake angles a (depending on cutter pocket
orientation) while still using a cylindrical substrate cutter
configuration brazed into a pocket on the bit matrix with a high
relief angle b.
[0044] It will be noted that when a concavity is present in the
cutter face, the back rake angle a changes as a function of depth
of cut (and rate of penetration). The illustrated back rake angle a
represents the angle when the cutter is substantially new and/or
when the depth of cut is shallow. As the end 36 of the diamond
table wears, or penetration increases, the back rake angle changes
due to the shape of the concavity on the face. Thus, the
relationship between the back rake angle and the relief angle that
is present and fixed in the FIG. 1 implementation with a
cylindrical substrate (back rake angle=relief angle), and further
which is present and fixed in connection with a conical substrate
(relief angle=back rake angle+1/2 cone angle), is no longer valid
with respect to the cutter having the configuration generally shown
in FIG. 3.
[0045] The configuration of FIG. 3 with a concavity in the cutter
face disconnects relief angle from back rake angle and provides a
back rake angle that varies with diamond table wear and/or bit
penetration (depth of cut). By selectively choosing the geometric
properties of the concavity, a curved shape may be presented which
can maintain an effective back rake (for example, even positive)
over a wide range of depth of cut. It will be noted, however, that
as depth of cut increases, the effective back rake angle changes
and moves from positive to negative. At this point, issues with
respect to increased normal stress and increases cutting forces due
to compressive effect become more of an issue. Thus, the evolution
of cutting forces with respect to a cutter generally of the
configuration shown in FIG. 3 can be divided into three phases: a)
an indentation phase where cutting forces increase; b) a tensile
phase where cutting forces remain constant; c) and an increased
back rake angle phase where forces increase due to increased depth
of cut (the forces increasing towards a value corresponding to an
effective back rake angle equal to a pocket back rake angle).
[0046] The cutter 30 of FIG. 3 is configured with a diamond table
32 comprising a thin hard facing material bonded to a backing layer
34 having a cylindrical configuration (the concave curved face
obviating the need to consider use of a conical configuration as in
FIG. 2). Conventionally, the backing layer 34 is made from cemented
tungsten carbide, and the diamond table 32 layer is a layer of
polycrystalline diamond (which may, in certain situations, be
leached in manner known to those skilled in the art). The
cylindrical surface 31 of the backing layer 34 is brazed within a
pocket formed in the bit matrix 14. Through effective selection of
the geometric configuration of the pocket, a desired back rake
orientation can be provided for the installed cutter 30.
[0047] In one implementation, the diamond table 32 layer of FIG. 3
has a varying thickness which depends on (or is a function of) the
geometry of the implemented concavity. This is unlike the diamond
table 18 layer used in FIGS. 1 and 2 which has a substantially
constant thickness. Thus, in the exemplary implementation of FIG.
3, the diamond table 32 layer is thicker towards a perimeter of the
cutter 30 at opposed ends 36 and 38 and thinner towards a center 40
of the cutter 30. The end 36 is shown positioned in a direction for
engaging the formation to be drilled. The face of the diamond table
32 layer may be said to be generally defined by a curve (for
example, of a parabolic shape). The interface 35 between the rear
of the diamond table 32 layer and the front of the backing layer 34
in this implementation is typically, but not exclusively, planar
and parallel to a rear surface 39 of the backing layer 34. The
thickness of the diamond table, however, is taken without regard to
any thickness variations due to a non-planar (or non-smooth
surface) interface between the diamond layer and carbide substrate.
The top surface of the carbide substrate at the diamond table
interface may include grooves, bumps, wedges, raised/lowered lands,
etc., as taught by U.S. Pat. No. 4,784,023 and U.S. Patent
Application Publication No. 2007/0235230. With such features being
present, the interface surface against which thicknesses are
measured may be defined as a hypothetical smooth surface, for
example defined as a mean between a rough bottom surface of the
diamond and a corresponding rough top surface of the carbide
substrate.
[0048] In another implementation, the diamond table 32 layer of
FIG. 3 has a substantially constant thickness like the diamond
table 18 layer used in FIGS. 1 and 2. The concave curve face of the
cutter is provided by varying the thickness of the backing layer 34
depending on (or as a function of) the desired geometry of the
implemented concavity. The interface 37 (see, dotted line) between
the rear of the diamond table 32 layer and the front of the backing
layer 34 in this implementation is non-planar and presents a
certain desired concavity to be mimicked by the face of the cutter.
Thus, in this alternative implementation of FIG. 3, the backing
layer 34 is thicker towards a perimeter of the cutter 30 at opposed
ends 36 and 38 and thinner towards a center 40 of the cutter 30.
With a substantially constant thickness, the face of the diamond
table 32 layer may still be said to be generally defined by a
curved concavity corresponding to that presented by the backing
layer 34 at the interface 37.
[0049] Still further, in yet another implementation, the interface
37 may be used in connection with a diamond table 32 layer having a
varying thickness. With this configuration, the concave curve shape
of the face of the diamond table 32 layer depends on (or is a
function of) the combination of the varying thickness of the
diamond table layer and the geometry of the implemented concavity
on the front surface of the backing layer 34.
[0050] The exemplary implementation of FIG. 3 shows a cutter 30
with a concave curved cutter face defined generally by three
portions or segments (comprising two curvilinear segments generally
associated with the ends 36 and 38 and a middle curvilinear segment
associated with the center 40). The concave curved shape cutter
face in this implementation, with different radii of curvature for
two or more of the surfaces in the concavity, thus does not present
a continuously curved shape (or concave geometry possessing a
smooth curved surface defined by a circle or sphere, or a parabola
or paraboloid, for example). It will be understood, however, and
will be further illustrated and described herein, that either a
segmented curve or continuous curve shape for the concavity formed
in the cutter face is within embodiments of the present
invention.
[0051] With respect to drilling in plastic formations, cutters
having a positive back rake angle fracture the rock of the
formation by shearing. Since rock tensile strength is lower than
compressive strength, cutters set with a positive back rake angle
generate lower drag and normal forces than cutters set with a
negative back rake angle. The concavity in the cutter face of FIG.
3 defines a curve which supports use of a positive back rake (for
example, as illustrated) thus enabling a shearing rock destruction
mode. Additionally, the concave curved shape of the cutter face
generates smaller cutting chips 42 in a plastic formation. This is
because the cutting chips break off from the formation before
reaching a critical size thanks to the concave curvature of the
face of the diamond table 32. The generation of smaller chips 42
serves to accelerate the evacuation of cuttings and avoids balling
(especially in connection with drilling in a plastic formation). As
a consequence, the cutter configuration generally shown in FIG. 3,
and further described with other implementations herein, provides
for better bit cleaning.
[0052] With respect to drilling in hard formations, it is typical
to experience a high level of vibration due to the cyclic load of
the cutter and the failure mode of these rocks under compression
solicitation. The loading fluctuation creates a variety of
disadvantages such as premature bit wear and a reduction of ROP due
to frictional energy dissipation. Thus, drillers will increase the
WOB to maintain the ROP, but this consequently will generate drill
string bending and maintaining directional control will be an
issue. That aspect is more critical in vertical drilling. The use
of a concave curved cutter face as shown in FIG. 3, and further
described with other implementations herein, will suppress or
reduce drastically that phenomenon.
[0053] With respect to motor drilling applications, the most common
problem faced while drilling with a down hole motor is stalling of
the motor due to high torque loads being created at the cutting
face of the bit. The use of a concave curved cutter face as shown
in FIG. 3, and further described with other implementations herein,
generates lower torque (a function of the drag force or cutting
force) compared to conventional planar cutter configurations like
those shown in FIGS. 1 and 2.
[0054] Mechanical specific energy (MSE) presents a commonly used
criteria for assessing drill bit efficiency. This measurement is
composed with the torque (function of the drag force) and WOB
(function of the normal force) at the bit and both of these
parameters are drastically lower while using a concave curved
cutter face as shown in FIG. 3, and further described with other
implementations herein. Use of such a cutter boosts bit efficiency
and helps to tackle some challenging applications where energy
transmission is an issue. A drill bit set with paraboloid concavity
cutters are more steerable due to a higher aggressiveness of the
cutters and high dog leg severity (DLS) or rate of directional
change can be reached with a less powerful motor.
[0055] The concave curved face PDC cutter implemented in FIG. 3,
and further described with other implementations herein, can have
either an elliptic or round face shape, as well as have other face
shapes as desired. The concavity of the face means that the face of
the diamond table of the cutter facing the formation is non-planar,
and more specifically a spherical, paraboloid or ovoidal shape.
Advantageously, this presents a sharper tip at a given depth of cut
presented to the formation with a variation of the bit efficiency
versus depth of cut. Cutting angles will vary at the cutter/rock
interface. The geometry of the cutter further supports improved
chip flow (cleaning) and improved diamond table cooling.
[0056] As an example, with a relief angle b equal to 20 degrees,
and a counter angle c (for the face concavity) of 15 degrees, a
cylindrical PDC cutter with a concave curved face can present a
variable back rake angle a from 5 degrees to 20 degrees depending
on depth of cut. The counter angle c is measured between a tangent
line of the concave curve surface at the perimeter edge of the
cutter and the flat back surface of the cylindrical substrate 34
(or parallel rear attaching surface of the diamond table 32).
[0057] As another example, with a relief angle b equal to 10
degrees, and a counter angle c (for the face concavity) of 15
degrees, a cylindrical PDC cutter with a concave curved face can
present a variable back rake angle a from -5 degrees to 10 degrees
depending on depth of cut.
[0058] Reference is now made to FIG. 4 which illustrates a portion
50 of a drill bit (for example, that portion being on one of the
blades of the drill bit) to which a cutter 30 having a concave
curved cutter face has been mounted (for example, to the bit matrix
14 through brazing into a formed cutter pocket). The cutter 30 in
FIG. 4 is, for example, an elliptical cutter having a major axis
and a minor axis. The concavity present in the face of the cutter
30 is defined by a curved or parabolic shape oriented along the
major axis extending from end 36 to end 38 to form a parabolic (or
hyperbolic paraboloid) concavity. In a preferred but not exclusive
implementation, the thickness of the diamond table 32 layer varies
as a function of the concave shape cutter face. The diamond table
32 layer is thicker towards a perimeter of the cutter 30 at the
opposed ends 36 and 38 (along the major axis) and thinner towards a
center 40 of the cutter 30 (and along the minor axis). Still
further, it will be noted, as distinct from the illustration in
FIG. 3, that the concave cutter face in the implementation of FIG.
4 presents a continuous curve from end to end along and in the
direction of the major axis. The cutter is installed with the major
axis and end 36 oriented toward the formation to be drilled.
Reference is also made to FIGS. 5A and 5B which show a perspective
view and side view (along the major axis), respectively, for the
elliptical cutter 30 used in FIG. 4. The cutter 30 further includes
an optional chamfer 52 provided about the front perimeter edge of
the diamond table 32 as well an optional chamfer 52 at the rear
perimeter edge of the substrate 34. The concavity on the face as
defined by the curve presents a counter angle c in the direction of
the major axis.
[0059] It will be understood that the cutter 30 shown mounted in
FIG. 4 can have any one of a number of configurations. Examples of
configurations for the cutter 30, in addition to that shown in
FIGS. 4 and 5A-5B, are presented in FIGS. 6-20 which are discussed
in more detail below. Any of these cutters 30 can be brazed into
the bit structure of FIG. 4. Additionally, although varying
thickness diamond tables are illustrated, it will be understood
that configurations in accordance with the alternative
implementations described in connection with FIG. 3 are equally
applicable to each of the configurations of FIGS. 4-20.
[0060] FIGS. 6A and 6B also illustrate an elliptical cutter having
a major axis and a minor axis. The concavity present in the face of
the cutter 30 is defined by a curved or parabolic shape oriented
along the minor axis extending from end 54 to end 56 to form a
parabolic (or hyperbolic paraboloid) concavity. The concave cutter
face presents a continuous curve from end to end along the minor
axis. In a preferred but not exclusive implementation, the
thickness of the diamond table 32 layer varies as a function of the
concave shape cutter face. In this elliptical cutter, as
differentiated from that shown in FIGS. 5A-5B, the diamond table 32
layer is thicker towards a perimeter of the cutter 30 at the
opposed ends 54 and 56 (along the minor axis) and thinner towards a
center 40 of the cutter 20 (and along the major axis). The cutter
30 would likely be installed in the structure shown in FIG. 4 with
its minor axis and end 54 oriented toward the formation to be
drilled. The concavity on the face defined by the curve presents a
counter angle c for the face concavity in the direction of the
minor axis.
[0061] FIGS. 7A, 7B and 7C also illustrate an elliptical cutter
having a major axis and a minor axis. FIGS. 7B and 7C are
cross-sectional views taken along the major and minor axes,
respectively, of the elliptical cutter. The concavity present on
the face of the cutter 30 is defined by a curved or parabolic shape
oriented along each of the major axis and minor axis which results
in the formation of spherical, elliptical paraboloid or ovoidal
concavity. The concave cutter face accordingly presents a
continuous curve along any selected orientation from end to end
across the face. In a preferred but not exclusive implementation,
the thickness of the diamond table 32 layer varies as a function of
the concave shape cutter face. In this elliptical cutter, the
diamond table 32 layer is thicker towards a perimeter of the cutter
20 at all locations along and about that perimeter elliptical edge.
Thus, the diamond table 32 is thicker towards a perimeter of the
cutter 30 at the opposed ends 36 and 38 (along the major axis) as
well as being thicker at the opposed ends 54 and 56 (along the
minor axis), while being thinner towards a center 40 of the cutter
30. The cutter could be installed in the structure shown in FIG. 4
with either its minor axis (and ends 54/56) or its major axis (and
ends 36/38) oriented toward the formation to be drilled. The
concavity on the face presents a first counter angle c.sub.1 in the
direction of the major axis, and a second counter angle c.sub.2 in
the direction of the minor axis. These counter angles need not be
equal to each other.
[0062] FIGS. 8A and 8B illustrate a round cutter having a first
orientation axis. The concavity present on the face of the cutter
30 is defined by a curved or parabolic shape oriented along the
first axis extending from end 58 to end 60 to form a parabolic (or
hyperbolic paraboloid) concavity. The concave cutter face presents
a continuous curve from end to end along the first axis. In a
preferred but not exclusive implementation, the thickness of the
diamond table 32 layer varies as a function of the concave shape
cutter face. In this round cutter, the diamond table 32 layer is
thicker towards a perimeter of the cutter 30 at the opposed ends 58
and 60 (along the first orientation axis) and thinner towards a
center 40 of the cutter 30 (and along a second axis orthogonal to
the first axis). The cutter is installed in the structure shown in
FIG. 4 with its first orientation axis and end 58 oriented toward
the formation to be drilled. The concavity on the face presents a
counter angle c in the direction of the first axis.
[0063] FIGS. 9A, 9B and 9C also illustrate a round cutter. FIGS. 9B
and 9C are cross-sectional views taken along two orthogonal axes,
respectively, of the round cutter. The concavity present on the
face of the cutter 30 is defined by a curved or parabolic shape
oriented along each of the two orthogonal axes which results in the
formation of spherical, elliptical paraboloid or ovoidal concavity.
The concave cutter face accordingly presents a continuous curve
along any selected orientation from end to end across the face. In
a preferred but not exclusive implementation, the thickness of the
diamond table 32 layer varies as a function of the concave shape
cutter face. In this round cutter, the diamond table 32 layer is
thicker towards a perimeter of the cutter 30 at all locations along
and about that perimeter edge. Thus, it is thicker towards a
perimeter of the cutter 20 at the opposed ends 58 and 60 (along a
first axis) as well as being thicker at the opposed ends 62 and 64
(along a second, orthogonal, axis), while being thinner towards a
center 34 of the cutter 30. The cutter could be installed in the
structure shown in FIG. 4 with any selected axis (or end or edge
portion) oriented toward the formation to be drilled. The concavity
on the face presents a first counter angle c.sub.1 in the direction
of the first axis, and a second counter angle c.sub.2 in the
direction of the second axis. These counter angles need not be
equal to each other.
[0064] FIGS. 10A and 10B also illustrate a round cutter having a
first orientation axis. The concavity present on the face of the
cutter 30 is defined by a curved or parabolic shape oriented along
the first axis extending from center 40 towards end 60 to form a
parabolic (or hyperbolic paraboloid) concavity at that end and a
planar surface at opposite end 58. The concave cutter face presents
a continuous curve extending along the first axis from the flat
surface associated with the second end 58 and center 40 and
terminating at the first end 60. In a preferred but not exclusive
implementation, the thickness of the diamond table 32 layer varies
as a function of the concave shape cutter face. In this round
cutter, the diamond table 32 layer is thicker towards a perimeter
of the cutter 30 at only a first end 60 (along the first
orientation axis) and thinner towards a center 40 and towards the
second end 58 along the first orientation axis. More specifically,
the diamond table 32 layer has a substantially constant thickness
from the second end toward the center along the first axis. The
thickness of the diamond table 32 layer then increases from the
center 40 towards the first end 60 along the first orientation
axis. The cutter is installed in the structure shown in FIG. 4 with
its first orientation axis, and first end 60, oriented toward the
formation to be drilled. The concavity on the face presents a
counter angle c in the direction of the first axis.
[0065] FIGS. 11A, 11B and 11C illustrate a half-elliptical cutter
having a major axis and a minor axis. FIG. 11B is a cross-sectional
view taken along the major axis of the half-elliptical cutter. FIG.
11C is a end view looking in the direction of the major axis of the
half-elliptical cutter. This cutter is referred to as a
half-elliptical cutter because only half of the elliptical shape
along the major axis is included (in essence, half of the cutter
shown in FIGS. 7A-7C). The concavity present on the face of the
cutter 30 is defined by a curved or parabolic shape oriented along
each of the major axis and minor axis which results in the
formation of spherical, elliptical paraboloid or ovoidal concavity
associated with the included half. The concave cutter face
accordingly presents a continuous curve along any selected
orientation from end to end across the face. In a preferred but not
exclusive implementation, the thickness of the diamond table 32
layer varies as a function of the concave shape cutter face. In
this elliptical cutter, the diamond table 32 layer is thicker
towards a curved perimeter of the cutter 20 at all locations along
and about that curved perimeter edge. Thus, the diamond table 32 is
thicker towards a perimeter of the cutter 30 at the end 38 (along
the major axis) as well as being thicker at the opposed ends 54 and
56 (along the minor axis), while being thinner towards a center 40'
at the cut-off flat edge of the cutter 30 along the minor axis. The
cutter is installed in the structure shown in FIG. 4 with its major
axis and end 38 oriented toward the formation to be drilled. The
concavity presents a first counter angle c.sub.1 in the direction
of the major axis, and a second counter angle c.sub.2 in the
direction of the minor axis. These counter angles need not be equal
to each other.
[0066] FIGS. 12A and 12B illustrate a half-elliptical cutter having
a major axis and a minor axis. FIG. 12B is a side view of the
half-elliptical cutter taken along the major axis. This cutter is
referred to as a half-elliptical cutter because only half of the
elliptical shape along the major axis is included (in essence, half
of the cutter shown in FIGS. 5A-5B). The concavity present on the
face of the cutter 30 is defined by a curved or parabolic shape
oriented along the major axis extending from center 40' to end 38
to form a parabolic (or hyperbolic paraboloid) concavity. The
concave cutter face presents a continuous curve from center 40' to
end 38 along the major axis. In a preferred but not exclusive
implementation, the thickness of the diamond table 32 layer varies
as a function of the concave shape cutter face. In this elliptical
cutter, the diamond table 32 layer is thicker towards a perimeter
of the cutter 30 at the end 38 (along the major axis), while being
thinner towards a center 40' of the cutter 30 at the flat edge of
the cutter where the half section is defined. The cutter is
installed in the structure shown in FIG. 4 with its major axis and
end 38 oriented toward the formation to be drilled. The concavity
on the face presents a counter angle c in the direction of the
major axis.
[0067] FIGS. 13A and 13B illustrate a half-elliptical cutter having
a major axis and a minor axis. FIG. 13B is a side view of the
half-elliptical cutter taken along the minor axis. This cutter is
referred to as a half-elliptical cutter because only half of the
elliptical shape along the minor axis is included (in essence, half
of the cutter shown in FIGS. 6A-6B). The concavity present on the
face of the cutter 30 is defined by a curved or parabolic shape
oriented along the minor axis extending from center 40' to end 56
to form a parabolic (or hyperbolic paraboloid) concavity. The
concave cutter face presents a continuous curve from center 40' to
end 56 along the major axis. In a preferred but not exclusive
implementation, the thickness of the diamond table 32 layer varies
as a function of the concave shape cutter face. In this elliptical
cutter, the diamond table 32 layer is thicker towards a perimeter
of the cutter 30 at the end 56 (along the minor axis), while being
thinner towards a center 40' of the cutter 30 at the flat edge of
the cutter where the half section is defined. The cutter is
installed in the structure shown in FIG. 4 with its minor axis and
end 56 oriented toward the formation to be drilled. The concavity
on the face presents a counter angle c in the direction of the
minor axis.
[0068] FIGS. 14A and 14B illustrate a half-round cutter having a
first axis and a second, orthogonal, axis. FIG. 14B is a side view
of the half-round cutter taken along the first axis. This cutter is
referred to as a half-round cutter because only half of the round
shape along the first axis is included (in essence, half of the
cutter shown in FIGS. 8A-8B). The concavity present on the face of
the cutter 30 is defined by a curved or parabolic shape oriented
along the first axis extending from center 40' to end 60 to form a
parabolic (or hyperbolic paraboloid) concavity. The concave cutter
face presents a continuous curve from center 40' to end 60 along
the first axis. In a preferred but not exclusive implementation,
the thickness of the diamond table 32 layer varies as a function of
the concave shape cutter face. In this elliptical cutter, the
diamond table 32 layer is thicker towards a perimeter of the cutter
30 at the end 60 (along the first axis), while being thinner
towards a center 40' of the cutter 30 at the flat edge of the
cutter where the half section is defined. The cutter is installed
in the structure shown in FIG. 4 with its first axis and end 60
oriented toward the formation to be drilled. The concavity on the
face presents a counter angle c in the direction of the first
axis.
[0069] FIGS. 15A, 15B and 15C illustrate a half-round cutter having
a first axis and a second, orthogonal, axis. FIG. 15B is a
cross-sectional view taken along the first axis of the half-round
cutter. FIG. 15C is a end view looking in the direction of the
first axis of the half-round cutter. This cutter is referred to as
a half-round cutter because only half of the round shape along the
first axis is included (in essence, half of the cutter shown in
FIGS. 9A-9C). The concavity present on the face of the cutter 30 is
defined by a curved or parabolic shape oriented along each of the
first and second axes which results in the formation of spherical,
elliptical paraboloid or ovoidal concavity associated with the
included half. The concave cutter face accordingly presents a
continuous curve along any selected orientation from end to end
across the face. In a preferred but not exclusive implementation,
the thickness of the diamond table 32 layer varies as a function of
the concave shape cutter face. In this half-round cutter, the
diamond table 32 layer is thicker towards a curved perimeter of the
cutter 30 at all locations along and about that curved perimeter
edge. Thus, it is thicker towards a perimeter of the cutter 30 at
the end 60 (along the first axis) as well as being thicker at the
opposed ends 62 and 64 (along the second, orthogonal, axis), while
being thinner towards a center 40' of the cutter 30 along the
second axis. The cutter is installed in the structure shown in FIG.
4 with its first axis and end 60 oriented toward the formation to
be drilled. The concavity presents a first counter angle c.sub.1 in
the direction of the first axis, and a second counter angle c.sub.2
in the direction of the second axis. These counter angles need not
be equal to each other.
[0070] FIGS. 16A and 16B also illustrate an elliptical cutter
having a major axis and a minor axis. FIG. 16B is a side view of
the elliptical cutter taken along the major axis. The concavity
present on the face of the cutter 30 is defined by a curved or
parabolic shape oriented along the major axis extending from center
40 towards end 38 to form a parabolic (or hyperbolic paraboloid)
concavity at that end and a planar surface at opposite end 36. The
concave cutter face presents a continuous curve extending along the
major axis from the flat surface associated with the end 36 and
center 40 and terminating at the end 38. In a preferred but not
exclusive implementation, the thickness of the diamond table 32
layer varies as a function of the concave shape cutter face. In
this elliptical cutter, the diamond table 32 layer is thicker
towards a perimeter of the cutter 20 at a first end 38 (along the
major axis) and thinner towards a center 40 of the cutter 30 and at
the second end 36 (along the major axis). More specifically, the
diamond table 32 layer has a substantially constant thickness from
the end 36 toward the center 40 along the major axis. The thickness
of the diamond table 32 layer then increases from the center 40
towards the end 38 along the major axis. The cutter is installed in
the structure shown in FIG. 4 with its major axis and end 38
oriented toward the formation to be drilled. The concavity on the
face presents a counter angle c in the direction of the major
axis.
[0071] FIGS. 17A and 17B also illustrate an elliptical cutter
having a major axis and a minor axis. FIG. 17B is a side view of
the elliptical cutter taken along the minor axis. The concavity
present on the face of the cutter 30 is defined by a curved or
parabolic shape oriented along the minor axis extending from center
40 towards end 56 to form a parabolic (or hyperbolic paraboloid)
concavity at that end and a planar surface at opposite end 54. The
concave cutter face presents a continuous curve extending along the
minor axis from the flat surface associated with the end 54 and
center 40 and terminating at the end 56. In a preferred but not
exclusive implementation, the thickness of the diamond table 32
layer varies as a function of the concave shape cutter face. In
this elliptical cutter, the diamond table 32 layer is thicker
towards a perimeter of the cutter 30 at the first end 56 (along the
minor axis) and thinner towards a center 40 of the cutter 30 and
the second end 54 (along the minor axis). More specifically, the
diamond table 32 layer has a substantially constant thickness from
the end 54 toward the center 40 along the minor axis. The thickness
of the diamond table 32 layer then increases from the center 40
towards the end 56 along the minor axis. The cutter is installed in
the structure shown in FIG. 4 with its minor axis and end 56
oriented toward the formation to be drilled. The concavity on the
face presents a counter angle c in the direction of the minor
axis.
[0072] Reference is now made to FIGS. 18A, 18B and 18C which
illustrate an elliptical cutter having a major axis and a minor
axis. FIG. 18A is a top view which shows the major and minor axes.
It will be noted that the sizes of the major and minor axis are
illustrated to be almost identical, and when they are identical the
cutter has a round configuration with the axes becoming first and
second, orthogonal, axes, respectively. FIGS. 18B and 18C each show
a side view of the cutter along the major axis. One difference
between FIGS. 18B and 18C is that FIG. 18B shows the use of a
chamfer 52 around the perimeter of the diamond table 32, while FIG.
18C does not include a chamfer. Thus, it will be recognized that
the chamfer 52 at the perimeter edge of the diamond table 32 is an
optional feature with respect to any of the cutters described
herein.
[0073] FIGS. 19A and 19B also illustrate an elliptical cutter
having a major axis and a minor axis. FIG. 19B is a side view of
the elliptical cutter taken along the major axis. In this
implementation, there is again a concave cutter face configuration,
but it is configured differently from those previously described.
Along the major axis of the elliptical cutter, the face is divided
into two halves. A first half 70 extends from the center 40 towards
the end 36. A second half 72 extends from the center 40 towards the
end 38. The concavity present on the face of the cutter 30 is
defined in only the second half 72 by a curved or parabolic shape
oriented along the major axis extending from center 40 towards end
38 to form a parabolic (or hyperbolic paraboloid) concavity in the
second half 72, while the first half 70 presents a planar surface.
The concave cutter face presents a continuous curve extending along
the major axis from the center 40 and terminating at the end 38. In
a preferred but not exclusive implementation, the thickness of the
diamond table 32 layer in the first half 70 is substantially
constant. However, the thickness of the diamond table 32 layer in
the second half 72 varies as a function of the concave shape cutter
face. With respect to the second half 72, the diamond table 32
layer is thicker towards the center 40 and a perimeter of the
cutter 30 at the end 38 (along the major axis) while being thinner
a points between the center 40 of the cutter 30 and the end 38
(along the minor axis). The thickness of the diamond table 32 in
the first half 70 is generally equal to the maximum thickness of
the diamond table in the second half 72. The cutter is installed in
the structure shown in FIG. 4 with its major axis and end 38
oriented toward the formation to be drilled.
[0074] FIGS. 20A and 20B also illustrate an elliptical cutter
having a major axis and a minor axis. FIG. 20B is a side view of
the elliptical cutter taken along the major axis. In this
implementation, there is again a concave cutter face configuration,
but it is configured differently from those previously described.
Along the major axis of the elliptical cutter, the face is divided
into two halves. A first half 70 extends from the center 40 towards
the end 36. A second half 72 extends from the center 40 towards the
end 38. The concavity present on the face of the cutter 30 is
defined such that each of the first half 70 and second half 72
presents a separate or distinct concave cutter shape defined by a
curved or parabolic shape oriented along the major axis extending
from center 40 towards either end 36 or 38 to form a distinct
parabolic (or hyperbolic paraboloid) concavity in each of the first
half 70 and second half 72. Each concave cutter face presents a
continuous curve extending along the major axis from the center 40
and terminating at either end 36 or 38. In a preferred but not
exclusive implementation, the thickness of the diamond table 32
layer in each of the first half 70 and second half 72 varies as a
function of the concave shape cutter face. With respect to the
first half 70, the diamond table 32 layer is thicker towards the
center 40 and a perimeter of the cutter 30 at the end 36 (along the
major axis) and thinner at points between the center 40 of the
cutter 30 and the end 36 (along the minor axis). With respect to
the second half 72, the diamond table 32 layer is thicker towards
the center 40 and a perimeter of the cutter 30 at the end 38 (along
the major axis) and thinner at points between the center 40 of the
cutter 30 and the end 38 (along the minor axis). The cutter could
be installed in the structure shown in FIG. 4 with its major axis
and either end 36 or 38 oriented toward the formation to be
drilled.
[0075] Although preferred embodiments of the method and apparatus
have been illustrated in the accompanying Drawings and described in
the foregoing Detailed Description, it will be understood that the
invention is not limited to the embodiments disclosed, but is
capable of numerous rearrangements, modifications and substitutions
without departing from the spirit of the invention as set forth and
defined by the following claims.
* * * * *