U.S. patent application number 11/555547 was filed with the patent office on 2007-11-22 for drill bit with staged durability, stability and rop characteristics.
This patent application is currently assigned to VAREL INTERNATIONAL IND., L.P.. Invention is credited to Graham Mensa-Wilmot.
Application Number | 20070267227 11/555547 |
Document ID | / |
Family ID | 38710985 |
Filed Date | 2007-11-22 |
United States Patent
Application |
20070267227 |
Kind Code |
A1 |
Mensa-Wilmot; Graham |
November 22, 2007 |
DRILL BIT WITH STAGED DURABILITY, STABILITY AND ROP
CHARACTERISTICS
Abstract
Drill bit with multiple stages of durability and ROP
characteristics is disclosed. The drill bit has multiple layers of
cutters established by deploying the cutters on blades of different
heights or maintaining the blades at the same height and deploying
the cutters to have different heights on one or more blades. Each
layer provides independent bottom hole coverage and has independent
stabilization, ROP, and durability characteristics so as to
effectively drill through different subsurface formations. Cutters
deployed on the different layers have their respective centers at
substantially different radial positions. Due to the different
radial positions, cutters in different layers cut different swaths
in the subsurface formation. Cutters in different layers may also
have different initial peripheral portions or shear lengths,
resulting in different impact resistance characteristics for the
different layers. This changes the wear and/or cutter deterioration
processes for the different layers, resulting in different and/or
improved toughness characteristics.
Inventors: |
Mensa-Wilmot; Graham;
(Spring, TX) |
Correspondence
Address: |
JENKENS & GILCHRIST, PC
1445 ROSS AVENUE
SUITE 3200
DALLAS
TX
75202
US
|
Assignee: |
VAREL INTERNATIONAL IND.,
L.P.
1434 Patton Place, Suite 106
Carrollton
TX
75007
|
Family ID: |
38710985 |
Appl. No.: |
11/555547 |
Filed: |
November 1, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60746767 |
May 8, 2006 |
|
|
|
Current U.S.
Class: |
175/426 |
Current CPC
Class: |
E21B 10/43 20130101 |
Class at
Publication: |
175/426 |
International
Class: |
E21B 10/36 20060101
E21B010/36 |
Claims
1. A drill bit, comprising: a drill bit body; blades formed on said
drill bit body, said blades having a plurality of cutting element
positions radially located thereon; and cutting elements deployed
on said blades, said cutting elements forming a primary layer of
cutting elements and a secondary layer of cutting elements, said
primary layer of cutting elements having a different height
relative to said drill bit body from said secondary layer of
cutting elements; wherein at least one primary layer cutting
element and a corresponding secondary layer cutting element occupy
substantially different cutting element positions on said blades
such that their cutting element profiles overlap, said at least one
primary layer cutting element and said corresponding secondary
layer cutting element together defining a cutting zone equal to a
diameter of one of said at least one primary layer cutting element
and said corresponding secondary layer cutting element plus a
predetermined fraction of said diameter.
2. The drill bit according to claim 1, wherein said predetermined
fraction is from approximately 1/10 to approximately 1/3.
3. The drill bit according to claim 1, wherein said predetermined
fraction is approximately 1/5.
4. The drill bit according to claim 1, wherein said diameter is a
diameter of said at least one primary layer cutting element.
5. The drill bit according to claim 1, wherein said diameter is a
diameter of said corresponding secondary layer cutting element.
6. The drill bit according to claim 1, wherein said cutting
elements in said primary layer and said cutting elements in said
secondary layer have substantially different shear lengths.
7. The drill bit according to claim 6, wherein said shear lengths
are average shear lengths derived from multiple shear lengths for
said cutting elements in said primary layer and said cutting
elements in said secondary layer.
8. The drill bit according to claim 1, wherein said cutting
elements in said primary layer and said cutting elements in said
secondary layer have substantially different sizes.
9. The drill bit according to claim 1, wherein said cutting
elements in said primary layer and said cutting elements in said
secondary layer have substantially different shape.
10. The drill bit according to claim 9, wherein said substantially
different shapes result in said cutting elements in said primary
layer and said cutting elements in said secondary layer having
substantially different axial volumes.
11. The drill bit according to claim 1, wherein said cutting
elements in said primary layer and said cutting elements in said
secondary layer have substantially different abrasion
resistances.
12. The drill bit according to claim 1, wherein said cutting
elements in said primary layer and said cutting elements in said
secondary layer have substantially different impact
resistances.
13. The drill bit according to claim 1, wherein said cutting
elements in said primary layer and said cutting elements in said
secondary layer have substantially different thermal
stabilities.
14. The drill bit according to claim 1, wherein said cutting
elements in said primary layer and said cutting elements in said
secondary layer have substantially different back rake angles.
15. The drill bit according to claim 14, wherein one or more
cutting elements in said primary layer have a larger back rake
angle than one or more cutting elements in said secondary
layer.
16. The drill bit according to claim 14, wherein one or more
cutting elements in said primary layer have a smaller back rake
angle than one or more cutting elements in said secondary
layer.
17. The drill bit according to claim 1, wherein said cutting
elements form a tertiary layer of cutting elements and said primary
layer of cutting elements have a different height relative to said
drill bit body from said tertiary layer of cutting elements, and
wherein at least one primary layer cutting element and a
corresponding tertiary layer cutting element occupy substantially
different cutting element positions on said blades such that their
cutting element profiles overlap, said at least one primary layer
cutting element and said corresponding tertiary layer cutting
element together defining a cutting zone equal to a diameter of one
of said at least one primary layer cutting element and said
corresponding tertiary layer cutting element plus a predetermined
fraction of said diameter.
18. A method of assembling a drill bit, comprising: providing a
drill bit body having blades formed thereon said blades having a
plurality of cutting element positions radially located thereon;
and deploying cutting elements on said blades, said cutting
elements forming a primary layer of cutting elements and a
secondary layer of cutting elements, said primary layer of cutting
elements having a different height relative to said drill bit body
from said secondary layer of cutting elements; wherein at least one
primary layer cutting element and a corresponding secondary layer
cutting element occupy substantially different cutting element
positions on said blades such that their cutting element profiles
overlap, said at least one primary layer cutting element and said
corresponding secondary layer cutting element together defining a
cutting zone equal to a diameter of one of said at least one
primary layer cutting element and said corresponding secondary
layer cutting element plus a predetermined fraction of said
diameter.
19. The method according to claim 18, wherein said cutting elements
of said primary layer and said cutting elements of said secondary
layer are mounted on blades having substantially different heights
relative to said drill bit body.
20. The method according to claim 18, wherein said cutting elements
of said primary layer and said cutting elements of said secondary
layer are mounted on blades having substantially identical heights
relative to said drill bit body.
21. The method according to claim 20, wherein said cutting elements
of said primary layer and said cutting elements of said secondary
layer are mounted on separate blades.
22. The method according to claim 20, wherein one or more cutting
elements of said primary layer and one or more cutting elements of
said secondary layer are mounted on a single blade.
23. The method according to claim 20, wherein said one or more
cutting elements of said primary layer and said one or more cutting
elements of said secondary layer are mounted on said single blade
in multiple rows.
24. The method according to claim 23, wherein at least one of said
rows contains a combination of cutting elements from said primary
layer and cutting elements from said secondary layer.
25. The method according to claim 23, wherein at least one of said
rows contains only cutting elements from said primary layer or only
cutting elements from said secondary layer.
26. The method according to claim 18, wherein said primary layer of
cutting elements establishes approximately 100% bottom hole
coverage.
27. A drill bit body, comprising: blades formed on said drill bit
body, and cutting element positions formed on said blades, said
cutting element positions radially located thereon such that when
cutting elements are deployed on said blades, said cutting elements
form a primary layer of cutting elements and a secondary layer of
cutting elements, said primary layer of cutting elements having a
different height relative to said drill bit body from said
secondary layer of cutting elements; wherein at least one primary
layer cutting element and a corresponding secondary layer cutting
element occupy substantially different cutting element positions on
said blades such that their cutting element profiles overlap when
said cutting elements are deployed on said blades, said at least
one primary layer cutting element and said corresponding secondary
layer cutting element together defining a cutting zone equal to a
diameter of one of said at least one primary layer cutting element
and said corresponding secondary layer cutting element plus a
predetermined fraction of said diameter.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application for patent claims priority to, and hereby
incorporates by reference, U.S. Provisional Application Ser. No.
60/746767, entitled "Drill Bit with Staged Durability and ROP
Characteristics," filed May 8, 2006 with the United States Patent
and Trademark Office.
FIELD OF THE INVENTION
[0002] The present invention relates to rotary drill bits for
rotary drilling of subterranean formations and, more specifically,
to a rotary drill bit having multiple stages of durability and ROP
(rate of penetration) characteristics.
BACKGROUND OF THE INVENTION
[0003] Subsurface formation drilling to recover hydrocarbons is
well known in the art. The equipment for such subsurface formation
drilling typically comprises a drill string having a rotary drill
bit attached thereto that is lowered into a borehole. A rotary
table or similar device rotates the drill string, resulting in a
corresponding rotation of the drill bit. The rotation advances the
drill bit downwardly, causing it to cut through the subsurface
formation (e.g., by abrasion, fracturing, and/or shearing action).
Drilling fluid is pumped down a channel in the drill string and out
the drill bit to cool the bit and flush away any debris that may
have accumulated. The drilling fluid travels back up the borehole
through an annulus formed between the drill string and the
borehole.
[0004] Many types of drill bits have been developed, including
roller cone bits, fixed cutter bits ("drag bits"), and the like.
For each type of drill bit, several patterns or layouts of cutting
elements ("cutters") are possible, including spiral patterns,
straight radial patterns, and the like. Different types of cutting
elements have also been developed, including milled cutting
elements, tungsten carbide inserts ("TCI"), polycrystalline-diamond
compacts ("PDC"), and natural diamond cutting elements. The
selection of which particular drill bit, cutting element type, and
cutting element pattern (i.e., cutting structure) to use for a
given subsurface formation can depend on a number of factors. For
example, certain combinations of drill bit, cutting element type,
and cutting element pattern drill more efficiently and effectively
in hard formations than others. Another factor is the range of
hardness encountered when drilling through the different formation
layers.
[0005] One common pattern for drill bit cutting elements in a fixed
cutter drill bit is a spiral configuration an example of which is
shown in FIGS. 1A-1B. As can be seen, a spiral pattern drill bit
100 is composed of several sections, including a bit body 102, a
shank 104, and a threaded connector 106 for connecting the drill
bit 100 to a drill string. Flats 108 on the shank 104 allow a tool,
such as wrench to grip the drill bit 100, making it possible (or at
least easier) to screw the drill bit 100 onto the drill string.
Blades 110a, 110b, 110c, 110d, 110e, and 110f are formed on the
drill bit 100 for holding a plurality of cutting elements 112. The
cutting elements 112 include superabrasive faces that usually have
identical geometries (i.e., size, shape, and orientation), but
different positions and/or cutting angles (back rake angles) on the
blades 110a-f Also visible are drill fluid outlets 114 that conduct
the drilling fluid away from the drill bit 100, thereby removing
any debris and cuttings that may have accumulated.
[0006] With existing drill bit configurations, it is known to have
blades 110a-f and/or cutting elements 112 that are offset (i.e.,
have different heights) relative to other blades and/or cutting
elements on the drill bit 100. The height of the blades 110a-f
and/or cutting elements 112 is measured herein relative to the
drill bit body 102. For blades 110a-f that are offset, the cutting
element tips are set at the same height relative to each other, but
one or more of the blades 110a-f have a height that is greater than
one or more other blades 110a-f. Where the cutting elements 112 are
offset, the blades 110a-f have the same height, but the tips of
certain cutting elements are set at different heights relative to
other cutting elements. In either case, the end result is a primary
layer of cutting elements that performs the initial drilling,
followed by a secondary layer of cutting elements, and in some
applications, a tertiary layer and so forth as needed.
[0007] Because of the difference in height, the primary layer of
cutting elements wears away or deteriorates faster than the
secondary layer of cutting elements. As the primary cutting
elements progressively wear away, however, the secondary cutting
elements compensate increasingly more for the decreased
effectiveness of the primary cutting elements in terms of bit
durability and ROP. This allows the drill bit 100 to be able to
drill at an acceptable ROP for longer durations before having to be
replaced, in essence performing the work of multiple (e.g., two in
this instance) drill bits 100.
[0008] The above arrangements are illustrated in FIGS. 2A-2B, where
a segment of a drill bit profile 200 for a drill bit having
multiple layers of cutting elements is shown. The term "profile,"
as understood by those having ordinary skill in the art, refers to
the area outlined by the cutting elements when rotated onto the
same radial plane. As can be seen, the drill bit profile segment
200 includes two layers of cutting elements, a primary layer 202
and a secondary layer 204, that are offset from each other. The
offset in the layers of cutting elements 202 and 204 is indicated
here by the letter H. Each layer 202 and 204 is composed of a
plurality of individual cutting elements 206a-n and 208a-n,
respectively. For clarity purposes, the layers of cutting elements
202 and 204 shown here and in the remaining figures are depicted as
relatively flat. Those having ordinary skill in the art will
recognize that, in practice, the layers of cutting elements 202 and
204 may have a degree of curvature.
[0009] In existing drill bits, the cutting elements are essentially
uniform in size and shape (typically a round shape). In addition,
the cutting elements 206a-n of the primary layer 202 and the
cutting elements 208a-n of the secondary layer 204 share
substantially the same radial positions on their respective blades,
or share a common reference axis. FIG. 2B illustrates an example of
such radial position sharing where, for clarity purposes, only one
cutting element from each layer 202 and 204 is shown. As can be
seen, the centers C of the primary layer cutting elements (e.g.,
cutting element 206a) and the centers C' of the secondary layer
cutting elements (e.g., cutting element 208a) substantially line up
on a common radial position (see radial displacement X) when
rotated onto the same radial plane.
[0010] Furthermore, the cutting elements 206a-n of the primary
layer 202 and the cutting elements 208a-n of the secondary layer
204 have substantially the same shear length (SL), shown in FIG. 2A
by the heavy arcuate line. "Shear length" refers to the portion of
a cutting element's periphery that is in direct contact with the
formation being drilled when all cutting elements on the drill bit
(and particularly in the vicinity of the cutting element being
measured) are rotated onto a single radial plane. A cutting
element's shear length is typically measured while the drill bit is
new (i.e., unused) and depends in large part on the size of the
cutting element and adjacent cutting elements, although it is
possible to vary the shear length for different drill bits even
when the cutting elements are all of the same size.
[0011] The shear length affects the ability of the drill bit to
penetrate various types of formation material. For example, hard
and abrasive formations requiring a high level of bit stabilization
are more effectively drilled with drill bits having longer shear
lengths. Soft formation materials, on the other hand, cause minimal
impact damage and may therefore be effectively drilled with either
longer or shorter shear lengths. Shear length also affects the
level of stabilization needed to minimize impact damage, thus
reducing the amount of cutting element deterioration For existing
drill bits with the type of dual-layer profile shown in FIG. 2A,
the cutting elements in the primary and secondary layers have
identical shear lengths.
[0012] Because of the identical shear lengths, and also because of
the shared radial positions, the cutting elements 206a-n and 208a-n
in the primary and secondary layers 202 and 204 cut identical
swaths through the subsurface formation. This is illustrated in
FIGS. 3A-3B, where different implementations of drill bits having a
dual-layer profile are shown.
[0013] Referring first to FIG. 3A, a dual-layer drill bit profile
may be achieved by providing a drill bit 300 where the blades 302a
and 302b have different heights. In the portion shown here, the
blade in the lower half of the figure, blade 302a, has a greater
height than the other blade 302b. Therefore, the cutting elements
306a-n on the first blade 302a constitute the primary layer of
cutting elements, while the cutting elements 306a-n on the second
blade 302b constitute the secondary layer of cutting elements.
[0014] Turning now to FIG. 3B, a dual-layer drill bit profile may
also be achieved by providing a drill bit 310 where the blades 312a
and 312b have the same heights, but the cutting elements 314a-n and
316a-n are set at different heights relative to each other. In the
portion shown here, the non-shaded cutting elements 314a-n are set
at a greater height than the shaded cutting elements 316a-n. These
non-shaded cutting elements 314a-n are therefore part of the
primary layer of cutting elements, whereas the shaded cutting
elements 316a-n constitute part of the secondary layer of cutting
elements. Both the shaded and non-shaded cutting elements 314a-n
and 316a-n may be intermixed across the blades 312a and 312b, as
depicted here, or cutting elements of different heights may be
mounted on different blades, respectively (similar to the
implementation of FIG. 3A).
[0015] Because of the same shear lengths and common radial
positions, primary layer and secondary layer cutting elements at a
given radial position necessarily cut the same swath (see dashed
lines) in the subsurface formation This is the case regardless of
the specific deployment of cutting elements used to achieve the
primary layer and secondary layers. The width of the swath or
"cutting zone" created by cutting elements on different blades
sharing a common radial position is indicated here by the letter Z
and is equal to the diameter D of the cutting elements. Because
they cut the same swath the primary layer and secondary layer do
not establish independent coverage of the bottom hole. In addition,
and from a geometry standpoint and also based on their shear
lengths, the wear and/or deterioration process on the cutting
element typically starts from the same peripheral locations on the
cutting elements for cutting elements in the different layers. This
arrangement has a negative effect on overall bit performance,
especially durability or longevity.
[0016] Thus, despite certain advances made in the industry, there
remains a need for a drill bit having an improved cutting element
arrangement that enhances stabilization as well as durability and
ROP characteristics, and permits the drill bit to drill at
economical ROPs for longer durations and through a wider range of
formation materials without having to replace the drill bit,
thereby reducing costly and time-consuming bit trips.
SUMMARY OF THE INVENTION
[0017] Embodiments of the invention are directed to a drill bit,
and method of assembling same, that can drill at economical ROPs
for longer durations and in a wider range of formation materials.
The drill bit has multiple layers of cutting elements established
by deploying the cutting elements on blades of different heights or
maintaining the blades at the same height and deploying the cutting
elements to have different heights on one or more blades. Each
layer provides independent bottom hole coverage and has independent
stabilization, ROP, and durability characteristics so as to
effectively drill through different subsurface formations. Cutting
elements deployed in different layers have their respective centers
at substantially different radial positions. Due to the different
radial positions, cutting elements in different layers cut
different respective swaths in the subsurface formation, and are
thus loaded and deteriorate differently and independently of the
other layers. Cutting elements in different layers may also have
different initial peripheral portions or shear lengths, resulting
in different impact resistance characteristics for the different
layers. This drastically changes the wear and/or cutting element
deterioration processes for the different layers, which results in
different and improved toughness characteristics. In some
embodiments, cutting elements deployed on different layers have
different sizes, shapes, and/or back rake angles, respectively. In
other embodiments, cutting elements deployed on different layers
have different thermal stability, impact resistance, and/or
abrasion resistance, respectively.
[0018] In general, in one aspect, the invention is directed to a
drill bit. The drill bit comprises a drill bit body, blades formed
on said drill bit body, said blades having a plurality of cutting
element positions radially located thereon. The drill bit further
comprises cutting elements deployed on said blades, said cutting
elements forming a primary layer of cutting elements and a
secondary layer of cutting elements, said primary layer of cutting
elements having a different height relative to said drill bit body
from said secondary layer of cutting elements. At least one primary
layer cutting element and a corresponding secondary layer cutting
element occupy substantially different radial cutting element
positions on said blades such that their cutting element profiles
overlap, said at least one primary layer cutting element and said
corresponding secondary layer cutting element together defining a
cutting zone equal to a diameter of one of said at least one
primary layer cutting element and said corresponding secondary
layer cutting element plus a predetermined percentage or fraction
of said diameter.
[0019] In general, in another aspect, the invention is directed to
a method of assembling a drill bit. The method comprises providing
a drill bit body having blades formed thereon, said blades having a
plurality of cutting element positions radially located thereon.
The method further comprises deploying cutting elements on said
blades, said cutting elements forming a primary layer of cutting
elements and a secondary layer of cutting elements, said primary
layer of cutting elements having a different height relative to
said drill bit body from said secondary layer of cutting elements.
At least one primary layer cutting element and a corresponding
secondary layer cutting element occupy substantially different
cutting element positions on said blades such that their cutting
element profiles overlap, said at least one primary layer cutting
element and said corresponding secondary layer cutting element
together defining a cutting zone equal to a diameter of one of said
at least one primary layer cutting element and said corresponding
secondary layer cutting element plus a predetermined percentage or
fraction of said diameter.
[0020] In general, in yet another aspect, the invention is directed
to a drill bit body. The drill bit body comprises blades formed on
said drill bit body and cutting element positions formed on said
blades. The cutting element positions are radially located such
that when cutting elements are deployed on said blades, said
cutting elements form a primary layer of cutting elements and a
secondary layer of cutting elements, said primary layer of cutting
elements having a different height relative to said drill bit body
from said secondary layer of cutting elements. At least one primary
layer cutting element and a corresponding secondary layer cutting
element occupy substantially different cutting element positions on
said blades such that their cutting element profiles overlap when
said cutting elements are deployed on said blades, said at least
one primary layer cutting element and said corresponding secondary
layer cutting element together defining a cutting zone equal to a
diameter of one of said at least one primary layer cutting element
and said corresponding secondary layer cutting element plus a
predetermined percentage or fraction of said diameter.
[0021] In general, in another aspect, the invention is directed to
a drill bit capable of drilling effectively in long intervals of
formation material or sections having grossly different mechanical
and/or geologic properties (i.e. sandstone, carbonates and chert or
pyrite).
[0022] In general, in still another aspect, the invention is
directed to a drill bit capable of effectively drilling in
formations infested with chert, pyrite or nodules, where these
specific materials are located at the top, middle or bottom
sections of the formation interval, and where conventional drilling
practices typically require the use of multiple drill bits, which
may have drastic effects on drilling and operational costs.
[0023] Additional aspects of the invention will be apparent to
those of ordinary skill in the art in view of the detailed
description of various embodiments, which is made with reference to
the drawings, a brief description of which is provided below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The foregoing and other advantages of the invention will
become apparent from the following detailed description and upon
reference to the drawings, wherein:
[0025] FIGS. 1A-1B, described previously, illustrate a side view
and a bottom view of a prior art fixed cutting element drill
bit;
[0026] FIGS. 2A-2B, described previously, illustrate a segment of a
drill bit profile for a drill bit having multiple cutting element
tip heights where cutting elements with different tip heights
occupy substantially the same radial positions and have
substantially the same size, shape, and shear length;
[0027] FIGS. 3A-3B, described previously, illustrate blades for
drill bits having the profile shown in FIGS. 2A-2B;
[0028] FIGS. 4A-4B illustrate a segment of a drill bit profile for
a drill bit having multiple layers of cutting elements where
cutting elements with different tip heights occupy substantially
different radial positions;
[0029] FIGS. 5A-5B illustrate exemplary implementations of a drill
bit having the drill bit profile shown in FIGS. 4A-4B;
[0030] FIGS. 6A-6B illustrate alternative implementations for a
drill bit having the drill bit profile shown in FIGS. 4A-4B;
[0031] FIGS. 7A-7B illustrate a segment of a drill bit profile for
a drill bit having multiple layers of cutting elements where
cutting elements with different tip heights occupy substantially
different radial positions and have substantially different shear
lengths;
[0032] FIGS. 8A-8B illustrate a segment of a drill bit profile for
a drill bit having multiple layers of cutting elements where
cutting elements with different tip heights occupy substantially
different radial positions and have substantially different
diameters;
[0033] FIGS. 9A-9B illustrate a segment of a drill bit profile for
a drill bit having multiple layers of cutting elements where
cutting elements with different tip heights occupy substantially
different radial positions and have substantially different axial
volumes;
[0034] FIGS. 10A-10C illustrate a segment of a drill bit profile
for a drill bit having multiple layers of cutting elements where
cutting elements with different tip heights occupy substantially
different radial positions and have substantially different back
rake angles; and
[0035] FIGS. 11A-11B illustrate a segment of a drill bit profile
for a drill bit having multiple layers of cutting elements where
cutting elements with different tip heights occupy substantially
the same radial positions and have substantially different shear
lengths.
DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION
[0036] Following is a detailed description of the invention with
reference to the drawings. It should be noted that the drawings are
provided for illustrative purposes only and are not intended to be
a blueprint or manufacturing drawings, nor are they drawn to any
particular scale.
[0037] As mentioned above, existing drill bits have primary layer
and secondary layer cutting elements that are uniform in size and
shape and share the same radial positions. This results in the
cutting elements of the secondary layers following an identical
swath through the subsurface formation as the cutting elements of
the primary layers. Consequently, the primary layer and secondary
layer cutting elements do not establish independent coverage of the
bottom hole. In this regard, the tips of the cutting elements in
the different layers, which are the first points of contact with
the formation being drilled, begin to fail or deteriorate along a
common line. Such failure initiation at the tips of the cutting
elements in the primary layer immediately exposes the cutting
elements in the secondary or other layers to failure also because
the mentioned tips are in a straight line. As such, the secondary
or other layer's failure is dependent on the initiation and rate of
failure of the secondary or other layer. This arrangement or
deployment in existing drill bits has a negative effect on bit
performance. In addition, the cutting elements of the primary
layers and the cutting elements of the secondary layers have
substantially the same shear lengths. This decreases the
effectiveness of existing drill bits, in terms of their durability,
stabilization and ROP, thus narrowing the range of formation
materials with which they can be used.
[0038] Embodiments of the invention provide a drill bit where at
least one cutting element of the primary layer occupies a
substantially different radial position from a corresponding
cutting element of the secondary layer. Specifically, the at least
one primary layer cutting element and the corresponding secondary
layer cutting element together define a cutting zone that spans a
predetermined distance. In some embodiments, the predetermined
distance may be the diameter of one of the cutting elements plus a
certain percentage or fraction of that diameter. The diameter may
be that of the primary layer cutting element or it may be that of
the secondary layer cutting element, and the fraction may be about
1/10 to about 1/3 of that diameter. As a result, the different
layers establish bottom hole coverages that are independent of each
other. In one embodiment, the primary layer establishes nearly 100%
coverage of the bottom hole and the secondary layer establishes at
least 80% coverage. This determination is typically based on the
intended application and may be influenced by bit size, blade
count, bit profile, as well as the lengths of the secondary and
tertiary blades used in the bit design.
[0039] The cutting elements of the different layers having
different cutting element tip heights are deployed so as to define
different layouts or cutting structures. In one embodiment, the
different layers are adapted for specific applications based on the
ROP, durability, and stabilization requirements of different
drilling environments. The cutting elements may be any suitable
type of cutting element known to those having ordinary skill in the
art, including TCI cutting elements, PDC cutting elements, natural
diamond cutting elements, and combinations thereof. Furthermore,
cutting elements deployed on the primary layer and cutting elements
deployed on the secondary layer may have substantially different
shear lengths, sizes, shapes, back rake angles, thermal stability,
abrasion resistance and/or impact resistance. Based on the blade
count and cutting element type and deployment, the drill bit of the
invention may be customized for specific subsurface formations,
including formations infested with chert, nodules, and/or pyrite.
The drill bit of the invention is capable of drilling through
formations with such infestations at acceptable ROPs regardless of
the location of the chert, nodules, and/or pyrite in a given
formation interval or hole section Such an arrangement results in a
drill bit that can drill at economical ROPs for longer durations
and with a wider formation bandwidth, thus reducing costly and
time-consuming bit trips. Note that while embodiments of the
invention are described herein mainly with respect to drill bits
having a primary layer and a secondary layer of cutting elements,
the teachings and principles discussed are fully applicable to
drill bits having one or more additional layers of cutting elements
(e.g., a tertiary layer, etc.).
[0040] Referring now to FIGS. 4A-4B, a segment of a drill bit
profile 400 for a drill bit having multiple layers of cutting
elements, achieved by deploying the cutting elements on blades of
different heights or maintaining the blades at the same height,
then deploying the cutting elements so as to have different heights
on one or more blades, is shown. As can be seen in FIG. 4A, the
drill bit profile segment 400 includes a primary layer 402 that is
offset in height relative to a secondary layer 404. Note that the
two layers 402 and 404 are shown here in isolation (i.e., the
amount of offset is exaggerated) so that the cutting elements
406a-n and 408a-n may be more easily seen. Those having ordinary
skill in the art will understand that, in practice, the offset is
much smaller than illustrated and more closely resembles the offset
shown in FIGS. 2A-2B. It should also be noted that the number of
layers of cutting elements is not necessarily limited to two. In
some instances, depending on the drilling application and the
challenges presented, there may be a primary layer, a secondary
layer, a tertiary layer, as well as other layers, with each layer
being offset in height relative to the immediately preceding layer.
The amount of offset may be any value commonly used by those having
ordinary skill in the art, but may depend on the expected ROP and
durability of the primary layer as well as the specific location
and presence of the formation material having grossly different
mechanical and/or geologic properties (e.g., chert, pyrite,
nodules, etc.) in a given interval. The amount of offset may also
depend on the anticipated overall ROP and durability of the drill
bit over the total interval to be drilled.
[0041] In accordance with embodiments of the invention the primary
layer cutting elements and the secondary (and possibly tertiary)
cutting elements occupy substantially different radial positions on
their respective blades. This is illustrated in FIG. 4B, where one
of the primary layer cutting elements 406a and a corresponding
secondary layer cutting element 408a are shown. As can be seen, the
primary layer cutting element profile 406a has a center C that
lines up on one radial displacement X, whereas the corresponding
secondary layer cutting element profile 408a has a center C' that
lines up on a substantially different radial displacement X'. As a
result, the corresponding cutting element in the secondary layer
(and tertiary layer where applicable) cuts a substantially
different swath (i.e., follows a substantially different path)
through the subsurface formation from the primary layer cutting
element.
[0042] The width of the combined swath or cutting zone for the two
corresponding cutting elements, in accordance with embodiments of
the invention, spans a predetermined distance that, in some
embodiments, is at least equal to the diameter of one of the
cutting elements (i.e., where one cutting element has a larger
diameter than the other) and at most equal to the diameter of one
of the cutting elements plus a predetermined fraction of that
diameter. This is illustrated FIGS. 5A-5B, with FIG. 5A showing
blades of different heights and FIG. 5B showing blades of the same
height, but corresponding cutting elements deployed so as to have
different heights. For either case, however, the corresponding
cutting elements in the different blades occupy different radial
positions.
[0043] In FIG. 5A, a drill bit 500 has blades 502a and 502b that
are offset at different heights, but with cutting elements 504a-n
and 506a-n that are set at the same height on their respective
blades. Specifically, the blade in the lower half of the figure,
blade 502a, has a greater height than the blade 502b in the upper
half of the figure. Therefore, the cutting elements 504a-n on the
first blade 502a form part of the primary layer of cutting
elements, while the cutting elements 506a-n on the second blade
502b constitute part of the secondary layer of cutting
elements.
[0044] The cutting zone Z', spanned by a given primary layer
cutting element and corresponding secondary layer cutting element,
is at least equal to the diameter D of one of these cutting
elements and at most equal to the diameter D of one of the cutting
elements plus a predetermined fraction of that diameter. That is,
Z'=D+0.Y*D, where 0.Y is the predetermined fraction In some
embodiments, the diameter D used to define the cutting zone Z' is
the diameter of the primary layer cutting element, while in other
embodiments, the diameter D is that of the secondary layer cutting
element. In still other embodiments, the diameter D used to define
the cutting zone Z' may be the diameter of whichever cutting
element has the larger diameter. And as for the predetermined
fraction of the diameter, in some embodiments, this value may be
about 1/10 to about 1/3, and preferably about 1/5, of the diameter
of whichever cutting element is used.
[0045] While the above arrangement has advantages, in some drilling
applications, it is desirable to have all the blades be at the same
height for stability and durability purposes. FIG. 5B shows a drill
bit 508 with blades 510a and 510b that are the same height, but
each blade has cutting elements 512a-n and 514a-n that are deployed
so as to have different heights relative to each other. The
technique used in deploying the cutting elements so as to have
different heights may be any technique known to those having
ordinary skill in the art. For example, the cutting elements may be
recessed into the blades so as to have different degrees of
exposure, or each cutting element may be exposed by the same
amount, but the surface of the blades may be contoured so that
certain cutting elements are seated higher than others.
[0046] In the drill bit portion shown here, the non-shaded cutting
elements 512a-n are deployed so as to have a greater height than
the shaded cutting elements 514a-n. These non-shaded cutting
elements 512a-n accordingly constitute the primary layer of cutting
elements, whereas the shaded cutting elements 514a-n constitute the
secondary layer of cutting elements. Both shaded and non-shaded
cutting elements 512a-n and 514a-n may be intermixed across
different blades 510a and 510b, as depicted here, or cutting
elements of different heights may be mounted on their own blades
(similar to the implementation of FIG. 5A). In either case, the
resulting cutting zone Z' created by a given primary layer cutting
element and corresponding secondary layer cutting element is at
least equal to the diameter D of one of these cutting elements and
at most equal to the diameter D of one of the cutting elements plus
a predetermined fraction of that diameter (i.e, Z'=D+0.Y*D).
[0047] In the drill bits described thus far, multiple layers of
cutting elements have been achieved using a single row of cutting
elements on each blade. However, embodiments of the invention may
also be implemented using multiple rows of cutting elements on a
single blade. Examples of such an arrangement are illustrated in
FIGS. 6A-6B. In the first implementation FIG. 6A, a drill bit 600
has blades that are of the same height, but at least one blade 602
has multiple (e.g., two) rows of cutting elements 604a and 604b
deployed thereon. The first row 604a (lower half of the figure) has
cutting elements 606a-n that are deployed so as to have a greater
height than cutting elements 608a-n in the second row 604b. These
cutting elements 606a-n, which may have different shear lengths,
therefore constitute part of the primary layer of cutting elements,
whereas the cutting elements 608a-n in the second row 604b, which
may also have different shear lengths, constitute part of the
secondary layer.
[0048] The implementation of FIG. 6B is similar to the
implementation of FIG. 6A insofar as the drill bit 610 has blades
that are of the same height, with at least one blade 612 having
multiple (e.g., two) rows of cutting elements 614a and 614b.
However, instead of the same cutting element height, each row 614a
and 614b contains a mix of cutting element heights, with non-shaded
cutting elements 616a-n deployed so as to have a greater height
than shaded cutting elements 618a-n.
[0049] In both of the above implementations, the primary layer
cutting elements 606a-n & 616a-n and the corresponding
secondary layer cutting elements 608a-n & 618a-n occupy
substantially different radial positions. As a result, they cut
substantially different swaths in the subsurface formation. The
width of the swath or cutting zone, indicated again as Z', is at
least equal to the diameter D of one of these cutting elements and
at most equal to the diameter D of one of the cutting elements
(e.g., the primary cutting element) plus a predetermined fraction
of that diameter, or Z'=D+0.Y*D.
[0050] Referring back to the drill bit profile in FIGS. 4A-4B, in
addition to occupying substantially different radial positions, the
primary layer cutting elements 406a-n have a shear length SL that
is substantially equal to the shear length SL' of the secondary
layer cutting elements 408a-n. This may be desirable in some
drilling applications, but as explained above, the shear length
affects a drill bit's stability and durability, as well as its
ability to effectively drill much longer sections of different
types of formation material. Therefore, in some embodiments, by
endowing the primary and secondary layers of cutting elements with
substantially different shear lengths SL and SL', the range of
formation material that may be effectively drilled is significantly
increased.
[0051] FIGS. 7A-7B illustrate a segment of a drill bit profile 700
for another drill bit having primary and secondary cutting element
layers 702 and 704 where the primary layer cutting elements 706a-n
and the secondary layer cutting elements 708a-n have substantially
different shear lengths SL and SL'. Referring to FIG. 7A, the drill
bit profile segment 700 is similar to the drill bit profile segment
400 (see FIGS. 4A-4B) insofar as it represents a drill bit that may
be achieved by deploying the cutting elements 706a-n and 708a-n on
blades of different heights or maintaining the blades at the same
height, then deploying the cutting elements 706a-n and 708a-n so as
to have different heights on one or more blades. In addition, the
primary layer cutting elements 706a-n and the secondary cutting
elements 708a-n (and possibly tertiary layer cutting elements) also
occupy substantially different radial positions on their respective
blades. This is illustrated in FIG. 7B, where a center C of one of
the primary cutting elements 706a lines up on a radial displacement
X, and a center C' of the corresponding secondary layer cutting
element 708a lines up on a substantially different radial
displacement X'.
[0052] Unlike the drill bit profile segment 400, however, the drill
bit profile segment 700 represents a drill bit where the primary
layer cutting elements 706a-n have a shear length SL that is
different from the shear length SL' of the secondary layer cutting
elements 708a-n. In the specific embodiment of FIG. 7A, the primary
layer shear length SL is smaller than the secondary layer shear
length SL'. In other embodiments, however, the primary layer shear
length SL may be larger than the secondary layer shear length SL',
depending on the particular subsurface formation to be drilled or
application challenges presented. In embodiments where the primary
layer cutting elements and/or secondary layer cutting elements
(and/or tertiary layer cutting elements) have more than one shear
lengths, the average shear length of the secondary (or tertiary)
layer cutting elements is substantially different (e.g., larger or
smaller) from the average shear length of the primary layer cutting
elements. As a result of the different shear lengths and radial
positions, the cutting elements in the different layers cut
independent swaths in the formation being drilled, and will
therefore have different characteristics in terms of durability,
stability and ROP.
[0053] The width of the swath, or cutting zone, cut by a given
primary layer cutting element and a corresponding secondary (or
tertiary) layer cutting element in FIGS. 7A-7B spans a
predetermined distance Z' that, in some embodiments, is at least
equal to the diameter D of one of these cutting elements and at
most equal to the diameter D of one of the cutting elements plus a
predetermined fraction of that diameter (i.e., Z'=D+0.Y*D). Note
that with different shear lengths SL, the swath or cutting zone Z'
will vary with radial displacement (i.e., it is not a fixed value).
As mentioned above, in some embodiments, the diameter may be the
primary layer cutting element's diameter or it may be the secondary
layer cutting element's diameter, and the predetermined fraction
may be about 1/10 to about 1/3 percent of that diameter. In other
embodiments, the diameter used to define the cutting zone Z' may be
the diameter of whichever cutting element has the larger
diameter.
[0054] In some embodiments, the sizes and shapes, and hence the
diameters, of the primary and secondary layer cutting elements are
substantially the same. FIGS. 8A-8B illustrate an embodiment of the
invention where the sizes of the primary and secondary layer
cutting elements are substantially different. Referring to FIG. 8A,
the embodiment shown here is similar to the embodiment shown in
FIGS. 4A-4B in that the drill bit profile segment 800 represents a
drill bit having primary and secondary cutting element layers 802
and 804. As before, the different layers 802 and 804 may be
achieved by deploying the cutting elements 806a-n and 808a-n on
blades of different heights or maintaining the blades at the same
height, then deploying the cutting elements 806a-n and 808a-n so as
to have different heights on one or more blades. Like the
embodiment shown in FIGS. 4A-4B, the primary and secondary layers
have cutting elements in substantially different radial positions
(see FIG. 8B), and thus have independent and different bottom hole
coverages and cut different swaths in the formation being drilled.
In some instances, the different cutting elements belonging to the
primary and secondary layers may also have substantially different
shear lengths SL and SL' (or average shear lengths as applicable),
similar to the embodiment of FIGS. 7A-7B.
[0055] Unlike the embodiments shown in FIGS. 4A-4B and 7A-7B, the
cutting elements 808a-n deployed on the secondary layer 804 in
FIGS. 8A-8B have a substantially different size from the cutting
elements 806a-n deployed on the primary layer 802. In the specific
embodiment shown, the secondary layer cutting elements 808a-n have
a diameter D' that is larger than the diameter D of the primary
layer cutting elements 806a-n. It is of course possible for the
secondary layer cutting elements 808a-n to have a diameter D' that
is smaller than the diameter D of the primary layer cutting
elements 806a-n, depending on the particular sequence of subsurface
formation materials to be drilled in an interval. In embodiments
where there are several sizes of cutting elements deployed on the
primary and secondary layers, the average size of the secondary
layer cutting elements 808a-n may be substantially different (e.g.,
larger or smaller) from the average size of the primary layer
cutting elements 806a-n. Note again that with different shear
lengths SL, the swath or cutting zone Z' will vary with radial
displacement (i.e., it is not a fixed value).
[0056] While the drill bits discussed thus far have primary layer
and secondary layer cutting elements that are of substantially the
same shape, namely, a round shape, other shapes may also be used.
Examples of other shapes that may be used include elliptical
shapes, egg shapes, pear shapes, and teardrop shapes (hereinafter,
collectively referred to as oval shapes), as well as other common
and customized shapes known to those having ordinary skill in the
art. In some cases, even non-circular shapes may be used where at
least a portion of the shape is flat (e.g., semicircular, diamond,
rectangular, etc). Moreover, embodiments of the invention also
provide a drill bit where the primary layer or primary cutting
element tip profile and the cutting elements, and the secondary
layer or secondary cutting element tip profile and the cutting
elements, have substantially different shapes and geometries.
[0057] FIGS. 9A-9B illustrate an embodiment of the invention where
the primary layer cutting elements and the secondary layer cutting
elements have substantially different shapes. Referring to FIG. 9A,
the embodiment shown here is similar to the previous embodiments
insofar as the drill bit profile segment 900 represents a drill bit
having primary and secondary cutting element layers 902 and 904. As
before, the different layers 902 and 904 may be achieved by
deploying the cutting elements 906a-n and 908a-n on blades of
different heights or maintaining the blades at the same height,
then deploying the cutting elements 906a-n and 908a-n so as to have
different heights on one or more blades. Like the previous
embodiments, the primary and secondary layers have cutting elements
in substantially different radial positions (see FIG. 9B), and thus
have independent and different bottom hole coverages and cut
different swaths in the formation being drilled. In some
embodiments, the different cutting elements belonging to the
primary and secondary layers may also have substantially different
shear lengths SL and SL' (or average shear lengths as applicable),
similar to the embodiment of FIGS. 7A-7B.
[0058] Unlike the embodiments shown in the previous figures, the
cutting elements 908a-n deployed on the secondary layer 904 in
FIGS. 9A-9B have a substantially different shape from the cutting
elements 906a-n deployed on the primary layer 902. The difference
in shape results in substantially different axial volumes Av for
the primary and secondary layers 902 and 904. The term "axial
volume," as understood by those having ordinary skill in the art,
refers to the distance from the center of the cutting element face
to the cutting tip. In the specific embodiment shown, the secondary
layer cutting elements 908a-n have an oval shape, whereas the
primary layer cutting elements 906a-n are round. The oval cutting
elements provide the secondary layer 904 with an axial volume Av'
that is greater than the axial volume Av of the round cutting
elements of the primary layer 902.
[0059] The substantially different axial volumes affect the
durability of the cutting elements in hard and abrasive formations.
A larger axial volume increases the ability of the cutting element
to withstand higher rotational speeds during the drilling process
than a smaller axial volume due to the substantially higher diamond
content. For this reason, oval cutting elements are known to be
highly effective in abrasive formations or lithologies, such as
sandstone and siltstone, from an axial volume perspective. In
addition, oval shaped cutting elements are more effective at
pre-fracturing of brittle formations, a characteristic that
improves ROP in carbonate bearing formations. Round cutting
elements, on the other hand, are more effective for shearing
non-brittle formations or lithologies, such as shale, sandstones
and siltstone.
[0060] By deploying oval cutting elements on the secondary layer
904 and round cutting elements on the primary layer 902,
embodiments of the invention combine the advantages of both round
and oval cutting elements. A similar benefit may be obtained by
deploying the round cutting elements on the secondary layer 904 and
the oval cutting elements on the primary layer 902. Alternatively,
oval shaped cutting elements may be deployed on both the primary
and secondary layers 902 and 904, but of substantially different
types. For example, elliptical shaped cutting elements may be
deployed on the primary layer 902 while teardrop cutting elements
may be deployed on the secondary layer 904, and so on.
[0061] In addition to substantially different shapes, in some
embodiment, the cutting elements of the primary layer and the
cutting elements of the secondary layer may have substantially
different back rake angles. The term "back rake angle," as
understood by those having ordinary skill in the art, refers to the
angle formed between a line parallel to the cutting element face
and a vertical line drawn through the center of the cutting
element. Such back rake ankles control how aggressively the cutting
element engages the subsurface formation. In general, a smaller
back rake angle increases cutting element aggressiveness (i.e.,
high ROP), but leaves the cutting element vulnerable to impact
breakage. On the other hand, a larger back rake angle decreases
cutting element aggressiveness (i.e., low ROP), but gives the
cutting element longer life.
[0062] FIGS. 10A-10C illustrate an embodiment of the invention
where the primary layer cutting elements and the secondary layer
cutting elements have substantially different back rake ankles.
Referring to FIG. 10A, the embodiment shown here is similar to the
embodiments shown in the previous figures in that the drill bit
profile segment 1000 represents a drill bit having primary and
secondary cutting element layers 1002 and 1004. As before, the
different layers 1002 and 1004 may be achieved by deploying the
cutting elements 1006a-n and 1008a-n on blades of different heights
or maintaining the blades at the same height, then deploying the
cutting elements 1006a-n and 1008a-n so as to have different
heights on one or more blades. Like the previous embodiments, the
primary and secondary layers have cutting elements in substantially
different radial positions (see FIG. 10B), and thus have
independent and different bottom hole coverages and cut different
swaths in the formation being drilled. In some embodiments, the
different cutting elements belonging to the primary and secondary
layers may also have substantially different shear lengths SL and
SL' (or average shear lengths as applicable), similar to the
embodiment of FIGS. 7A-7B.
[0063] Unlike the previous embodiments, the cutting elements
1008a-n deployed on the secondary layer 1004 here have a
substantially different back rake angle from the cutting elements
1006a-n deployed on the primary layer 1002. FIG. 10C shows a side
view of one of the cutting elements 1010 deployed on the primary
layer 1002 and one of the cutting elements 1012 deployed on the
secondary layer 1004. As can be seen, the secondary layer cutting
element 1012 has a back rake angle A' that is substantially
different from the back rake angle A of the primary layer cutting
element 1010 relative to a subsurface formation 1014. In the
specific embodiment shown, the back rake angle A' of the secondary
layer cutting elements 1012 is larger (e.g., 30.degree.) than the
back rake angle A (e.g., 20.degree.) of the primary layer cutting
elements 1010. This substantial difference in back rake angle
results in the secondary layer cutting element 1012 having
decreased cutting element aggressiveness, but higher impact
resistance. In other embodiments, it is possible to have the back
rake angle A' of the secondary layer cutting element 1012 be
smaller than the back rake angle A of the primary layer cutting
element 1010, depending on the levels of hardness and/or
abrasiveness of the formation sequences to be drilled.
[0064] Although the embodiments described thus far have focused on
the different radial positions and shear lengths (or average shear
lengths as applicable), in some embodiments, it may be desirable to
provide a drill bit where the primary layer cutting elements and
the secondary layer cutting elements having different shear
lengths. An example of such an embodiment is illustrated in FIGS.
11A-11B, where the drill bit profile segment of 1100 is shown
representing a drill bit having primary and secondary cutting
element layers 1102 and 1104. As before, the different layers 1102
and 1104 may be achieved by deploying the cutting elements 1106a-n
and 1108a-n on blades of different heights or maintaining the
blades at the same height, then deploying the cutting elements
1106a-n and 1108a-n so as to have different heights on one or more
blades.
[0065] Unlike the previous embodiments, the primary and secondary
layers 1102 and 1104 have cutting elements 1106a-n and 1108a-n
mounted in substantially identical radial positions (see FIG. 11B).
Nevertheless, in accordance with embodiments of the invention, the
cutting elements belonging to the primary and secondary layers may
still have substantially different shear lengths S L and SL' (or
average shear lengths as applicable). In some embodiments, the
different shear lengths SL and SL' (or average shear lengths as
applicable) may be achieved by deploying cutting elements having
different shapes (e.g., round, oval, etc.) in the primary layer
1102 versus the secondary layer 1104, or vice versa. In other
embodiments, although not expressly shown, the different shear
lengths SL and SL' (or average shear lengths as applicable) may be
achieved by deploying cutting elements having different sizes
(e.g., 16 mm, 19 mm, etc.) in the primary layer 1102 versus the
secondary layer 1104, or vice versa. Thus, although they share
common radial positions, the cutting elements 1106a-n and 1108a-n
of the primary and secondary layers 1102 and 1104 still provide
independent and different bottom hole coverages and cut different
swaths in the formation being drilled.
[0066] In some embodiments, based on the specifics of an
application as well as the formation types to be drilled, the
primary layer cutting elements and the secondary layer cutting
elements may have substantially different properties in terms of
abrasion and impact resistance. For example, either the primary
layer cutting elements or the secondary layer cutting elements may
be made more abrasion resistant (i.e., have a finer diamond grain),
or both the primary layer cutting elements and secondary layer
cutting elements may have improved abrasion resistance. In a
similar manner, the primary layer cutting elements may be made more
impact-resistant than the secondary layer cutting elements, or vice
versa, or both the primary layer and secondary layer cutting
elements may have improved impact resistance.
[0067] In other embodiments, either the primary layer cutting
elements or the secondary layer cutting elements may be treated to
remove catalyzing material (e.g., cobalt), a process commonly
referred to as "leaching." As is well known in the art, leaching or
removal of catalyzing material from cutting elements can improve
their thermally stability, thus allowing them to withstand much
higher drilling temperatures before failing. Improved thermal
stability drastically reduces the wear initiation process of the
cutting elements. This process may be used to further enhance the
performance properties of the primary layer cutting elements or the
secondary layer cutting elements, as described herein. Techniques
for removal of catalyzing material from cutting elements are
generally known and may be found, for example, in U.S. Pat. No.
8,544,408 entitled "High Volume Density Polycrystalline Diamond
with Working Surfaces Depleted of Catalyzing Material," which is
incorporated herein by reference.
[0068] It should be noted that regardless of the diamond material
types (e.g., fine grain or coarse grain diamond materials) that may
be used for the primary layer and/or secondary layer cutting
elements, or the leaching or catalyzing material depletion
processes employed, all advantages, principles and teachings herein
discussed for the present invention remain valid and fully
applicable to these various embodiments.
[0069] In operation, the cutting elements in the primary layer of
the drill bit initially bear most of the load during drilling of a
specific dominant formation type (e.g., sandstone, shale,
siltstone, etc.). As the cutting elements in the primary layer
wears and/or deteriorates due to formation hardness and/or
abrasiveness, the cutting elements in the secondary and subsequent
layers define a new bit, having independent bottom hole coverage
that cut different swaths in the formation, and also have different
and unique ROP, durability and stability characteristics. Based on
the specific layout of a drill bit according to embodiments of the
invention, but mainly due to the substantially different radial
positions of the cutting elements in the different layers and/or
substantially different shear lengths (SL) of the different layers,
such drill bits are adapted to effectively drill in chert, pyrite
and or nodules due to the controlled and specifically staged
durability and ROP characteristics of the drill bit of the
invention. In such instances, the cutting elements in the primary
layer fail, but in do doing so, expose the cutting elements in the
secondary layer (and possibly tertiary layer, and so forth), which
are then able to re-establish the drill bit's ROP and durability
characteristics, thus enabling the drill bit to continue drilling
for longer periods of time at an effective ROP. In other words,
because the secondary layer cutting elements have independent
bottom hole coverage and may be customized with a substantially
different shear length, size, shape, thermal stability, abrasion
resistance, and/or impact resistance according to embodiments of
the invention, the drill bit is able to continue drilling at an
economical ROP through the subsequent formation type, eventually
reentering the dominant formation type or a different formation
that is devoid of chert, pyrite or nodules.
[0070] While the present invention has been described with
reference to one or more particular embodiments, those skilled in
the art will recognize that many changes may be made thereto
without departing from the scope of the invention Accordingly, each
of the foregoing embodiments and obvious variations thereof is
contemplated as falling within the scope of the claimed invention,
as is set forth in the following claims.
* * * * *