U.S. patent application number 15/571048 was filed with the patent office on 2018-06-14 for mmc downhole tool region comprising an allotropic material.
This patent application is currently assigned to Halliburton Energy Services, Inc.. The applicant listed for this patent is Halliburton Energy Services, Inc.. Invention is credited to Grant O. Cook, III, Venkkateesh Parthasarathi Padmarekha, Daniel Brendan Voglewede.
Application Number | 20180163481 15/571048 |
Document ID | / |
Family ID | 57441220 |
Filed Date | 2018-06-14 |
United States Patent
Application |
20180163481 |
Kind Code |
A1 |
Padmarekha; Venkkateesh
Parthasarathi ; et al. |
June 14, 2018 |
MMC DOWNHOLE TOOL REGION COMPRISING AN ALLOTROPIC MATERIAL
Abstract
The disclosure provides rotary drill bits with bit head regions
or other downhole tools with regions in which an allotropic
material in a precursor region has been transformed from a first
allotrope to a second allotrope in response to a trigger. The
disclosure further provides methods of forming such downhole tools
and methods of triggering an allotropic phase transformation during
their use.
Inventors: |
Padmarekha; Venkkateesh
Parthasarathi; (Anna Nagar West, IN) ; Cook, III;
Grant O.; (Spring, TX) ; Voglewede; Daniel
Brendan; (Spring, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Halliburton Energy Services, Inc. |
Houston |
TX |
US |
|
|
Assignee: |
Halliburton Energy Services,
Inc.
Houston
TX
|
Family ID: |
57441220 |
Appl. No.: |
15/571048 |
Filed: |
December 18, 2015 |
PCT Filed: |
December 18, 2015 |
PCT NO: |
PCT/US2015/066704 |
371 Date: |
November 1, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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62171393 |
Jun 5, 2015 |
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62171398 |
Jun 5, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C21D 1/06 20130101; C22C
29/005 20130101; E21B 17/1092 20130101; C21D 2211/005 20130101;
E21B 10/54 20130101; C21D 2211/001 20130101; C21D 9/22 20130101;
E21B 10/42 20130101; C21D 1/18 20130101; E21B 10/46 20130101 |
International
Class: |
E21B 10/46 20060101
E21B010/46; C21D 9/22 20060101 C21D009/22; C22C 29/00 20060101
C22C029/00 |
Claims
1. A method of increasing crack resistance of a downhole tool, the
method comprising forming a precursor region in the downhole tool,
wherein the precursor region contains a first allotrope of an
allotropic material that is able to undergo an allotropic phase
transformation to a second allotrope in response to a strain caused
by a crack in the first allotrope to create an allotropic
phase-transformed region.
2. The method of claim 1, further comprising transforming the first
allotrope to the second allotrope when in response to the
strain.
3. The method of claim 2, wherein the first allotrope transforms to
the second allotrope only in a portion of the precursor region
proximate the crack.
4. The method of claim 2, further comprising halting the allotropic
phase transformation at a phase-stabilization region below the
precursor region.
5. The method of claim 1, wherein the allotropic material is
zirconium dioxide.
6. The method of claim 4, wherein the phase-stabilization region
comprises a phase-stabilization material located under a surface of
the allotropic phase-transformed region or an allotropic material
located under an exterior of the downhole tool.
7. The method of claim 6, wherein the phase-stabilization material
comprises at least one of yttrium oxide, cerium oxide, magnesium
oxide, calcium oxide.
8. A downhole tool comprising a precursor region containing a first
allotrope of an allotropic material that is able to undergo an
allotropic phase transformation to a second allotrope in response
to a strain caused by a crack in the first allotrope to create an
allotropic phase-transformed region.
9. The downhole tool of claim 8, further comprising an allotropic
phase-transformed region in which the first allotrope has
transformed to the second allotrope in response to the strain.
10. The downhole tool of claim 9, wherein the allotropic
phase-transformed region is proximate the crack.
11. The downhole tool of claim 8, a phase-stabilization region
below the precursor region.
12. The downhole tool of claim 8, wherein the allotropic material
is zirconium dioxide.
13. The downhole tool of claim 11, wherein the phase-stabilization
region comprises a phase-stabilization material located under a
surface of the allotropic phase-transformed region or an allotropic
material located under an exterior of the downhole tool.
14. The downhole tool of claim 13, wherein the phase-stabilization
material comprises at least one of yttrium oxide, cerium oxide,
magnesium oxide, calcium oxide.
15. A method of hardening a bit head region of a downhole drill
bit, the method comprising heating a precursor region on the bit
head to transform a first allotrope of an allotropic material in
the precursor region to a second allotrope in the same physical
space, thereby causing a compressive residual stress in the
precursor region and hardening it to form a corresponding
compressive residual stress-hardened region.
16. The method of claim 15, wherein the second allotrope has a
decreased atomic packing density as compared to the first
allotrope, causing the compressive residual stress.
17. The method of claim 15, wherein heating comprises induction,
flame, laser, electron beam, thermal radiation, convection,
friction, or combinations thereof.
18. The method of claim 15, wherein heating comprises carburizing,
nitridizing, boronizing, or combinations thereof.
19. The method of claim 15, wherein the first allotrope comprises
the austenite allotrope of iron (Fe) and has a face centered cubic
(FCC) crystal structure, and the second allotrope comprises the
ferrite allotrope of Fe and has a body centered cubic (BCC) crystal
structure.
20. The method of claim 15, wherein the first allotrope comprises
the austenite allotrope of iron (Fe) and has a face centered cubic
(FCC) crystal structure, and the second allotrope comprises the
ferrite allotrope of Fe with entrapped carbon (C) and has a body
centered tetragonal (BCT) crystal structure.
21. The method of claim 15, wherein the allotropic material
comprises Americium (Am), Beryllium (Be), Calcium (Ca), Cerium
(Ce), Curium (Cm), Cobalt (Co), Dysprosium (Dy), Iron (Fe),
Gadolinium (Gd), Hafnium (Hf), Holmium (Ho), Lanthanum (La),
Manganese (Mn), Neodymium (Nd), Neptunium (Np), Promethium (Pm),
Praseodymium (Pr), Plutonium (Pu), Sulfer (S), Scandium (Sc),
Samarium (Sm), Tin (Sn), Strontium (Sr), Terbium (Tb), Thorium
(Th), Titanium (Ti), Uranium (U), Yttrium (Y), Ytterbium (Yb),
Zirconium (Zr), or an alloy thereof.
Description
TECHNICAL FIELD
[0001] The present disclosure relates generally to rotary drill
bits and other downhole tools with an allotropic phase-transformed
bit head region or a precursor region able to undergo an allotropic
phase transformation in response to a trigger condition.
BACKGROUND
[0002] Various types of downhole tools are used to form wellbores
in downhole formations. These downhole tools including rotary drill
bits, reamers, core bits, under reamers, hole openers, and
stabilizers. Rotary drill bits include fixed-cutter drill bits,
roller cone drill bits, and hybrid drill bits. Rotary drill bits
may be manufactured of materials such as polycrystalline diamond
compact and metal-matrix composite (MMC). A rotary drill bit may
include more than one type of material. For instance PDC drill bits
are often also MMC drill bits.
BRIEF DESCRIPTION OF THE DRAWINGS
[0003] For a more complete understanding of the present invention
and its features and advantages, reference is now made to the
following description, taken in conjunction with the accompanying
drawings, in which:
[0004] FIG. 1 is an elevation view of a drilling system in which a
downhole tool containing a compressive residual strength-hardened
region may be used;
[0005] FIG. 2 is an isometric view of a fixed-cutter drill bit
including a bit head oriented upwardly;
[0006] FIG. 3 is an isometric view of a blade of the fixed-cutter
drill bit of FIG. 2, with cutter pockets, but with no cutters
shown;
[0007] FIG. 4 is a cross-sectional view of a cutter pocket of FIG.
3;
[0008] FIGS. 5A and 5B are cross-sectional views of a curved
portion of the fixed-cutter drill bit of FIG. 2;
[0009] FIG. 6 is a flow chart of a method for creating an
allotropic phase-transformed region by inducing an allotropic phase
transformation in a precursor region; and
[0010] FIG. 7 is a flow chart of a method for creating an
allotropic phase-transformed region during use of a rotary drill
bit by inducing an allotropic phase transformation in a precursor
region.
DETAILED DESCRIPTION
[0011] During a drilling operation, various downhole tools,
including drill bits, coring bits, reamers, hole enlargers, or
combinations thereof may be lowered into a partially formed
wellbore and used to further form the wellbore, for instance by
drilling the wellbore deeper into a formation or by increasing the
diameter of the wellbore. These downhole tools are subject to a
variety of stresses, particularly during contact with the
formation. For instance, the shaft of the drill bit may experience
different stresses than the head of the bit. Different parts of the
bit head may also experience different stresses from one another.
The present disclosure provides a rotary drill bit head or other
downhole tool portion formed from a metal-matrix composite (MMC) in
which an allotropic material in a region of the downhole tool has
been transformed from a first allotrope to a second allotrope,
thereby altering a physical property of the region. The present
disclosure also provides a rotary drill bit head or other downhole
tool portion formed from an MMC with a precursor region containing
a first allotrope of an allotropic material. During use of the bit
head or other downhole tool, if a trigger condition is encountered,
the allotropic material transforms to the second allotrope, thereby
altering a physical property of the region.
[0012] Allotropic materials can have two or more different physical
structures while in the same physical state (i.e., solid, liquid,
or gas). These different physical structures are referred to as
allotropes. The present disclosure relates to allotropic materials
with at least two allotropes in the solid state. Often different
allotropes in the solid state have different crystal structures,
although other differences in physical structure may be found in
some allotropic materials. The different physical structures of
different allotropes confer different physical properties. Graphite
(pencil lead) and diamond are a readily understood examples of how
different the physical properties of different allotropes may be.
Although both materials are composed of nearly pure carbon,
graphite may be flaked with a fingernail, while diamond is the
hardest substance known. The difference is due entirely do the
different crystal structures of the two different allotropes.
[0013] An allotropic phase transformation, as used herein, occurs
when an allotropic material changes from one allotrope to another
while remaining a solid and without reaction with another chemical.
Typically, changing from one allotrope to another causes an
increase or a decrease in the atomic packing density, a crystal
lattice parameter (if at least one of the allotropes is a crystal),
or both. An allotropic phase transformation may be caused by any
number of conditions, which commonly include a threshold level of
or amount of change in pressure, temperature, or both. For example,
the graphite allotrope undergoes an allotropic phase transformation
to the diamond allotrope, but only under very high temperature and
pressure. Most allotropic phase transformations of interest in
forming a downhole tool as disclosed herein do not require such
extreme conditions.
[0014] Allotropic elements include Americium (Am), Beryllium (Be),
Calcium (Ca), Cerium (Ce), Curium (Cm), Cobalt (Co), Dysprosium
(Dy), Iron (Fe), Gadolinium (Gd), Hafnium (Hf), Holmium (Ho),
Lanthanum (La), Manganese (Mn), Neodymium (Nd), Neptunium (Np),
Promethium (Pm), Praseodymium (Pr), Plutonium (Pu), Sulfer (S),
Scandium (Sc), Samarium (Sm), Tin (Sn), Strontium (Sr), Terbium
(Tb), Thorium (Th), Titanium (Ti), Uranium (U), Yttrium (Y),
Ytterbium (Yb), and Zirconium (Zr). Allotropic materials include
alloys of any of these allotropic elements, such as steel (Fe--C),
in which the allotropic element may still be present as at least
two different allotropes.
[0015] Allotropes may be detected and distinguished from one
another using any of a variety of known non-destructive or
destructive measurement methods. For instance allotropes may be
distinguished using X-ray diffraction.
[0016] According to the present disclosure, a precursor region is
formed on a bit head or other downhole tool portion. The precursor
region may be formed when the portion is formed, prior to formation
of a downhole tool with the portion, during formation of a downhole
tool with the portion, or after formation of the downhole tool on
the portion, but before use of the downhole tool. The precursor
region includes an allotropic material that can undergo an
allotropic phase transformation in response to a trigger condition
to cause a change in a physical property of the region.
[0017] Typically at least one physical property of the region that
is changed relates to the stress in the region, which tends to
become more or less compressive or tensile depending on whether the
region was under a compressive or tensile stress prior to the
allotropic phase transformation and whether the second allotrope
has a lower or higher packing density or shorter or longer length
of at least one lattice parameter. These changes in the stress of
the region may change other properties of the region, such as its
hardness or its crack-resistance.
[0018] In one example, the region may be a precursor region
containing a first allotrope of a metal. When the precursor region
encounters heat above a certain temperature, either during
manufacture or use of the downhole tool, the metal transforms to a
second allotrope. The first allotrope has a lower packing density,
at least one shorter lattice parameter (if a crystal), or both than
the second allotrope. The allotropic material is a solid and is
constrained in at least one dimension such that the second
allotrope occupies the same physical space as the first allotrope,
so a compressive residual stress is created in the region. The
region thus becomes compressive residual-stress hardened.
[0019] For example, the precursor region may include the austenite
allotrope of Fe, which has a face centered cubic (FCC) crystal
structure. When the precursor region is cooled, the Fe undergoes an
allotropic phase transformation to the ferrite allotrope, which has
a body centered cubic (BCC) crystal structure. The ferrite
allotrope of Fe has a lower packing density than the austenite
allotrope, so a residual compressive stress in the region is
created by the allotropic phase transformation. In other examples,
after the Fe undergoes an allotropic phase transformation to a
ferrite allotrope, the Fe may have entrapped carbon and have a body
centered tetragonal (BCT) crystal structure.
[0020] Various methods for measuring compressive residual stress
are known. Methods, such as X-ray diffraction and hardness profile
testing, are compatible with measuring compressive residual stress
in the present disclosure. X-ray diffraction may also be used to
determine the allotrope present in any portion of the downhole
tool. Although some testing may be non-destructive, such as X-ray
diffraction measured on the surface of a region, other testing,
such as testing of the interior of a region or hardness testing,
may be destructive. If destructive testing is used to determine
compressive residual stress of an allotrope, then representative
samples may be used and the test results may be assumed to apply to
other downhole tools of the same construction formed in the same
way.
[0021] A compressive residual stress increases crack-resistance of
a region as compared to a similar region that did not undergo an
allotropic phase transformation or another region that does not
contain the allotropic material. Compressive residual stress helps
arrest any cracks that may form or propagate by essentially
squeezing the crack, especially at its ends. Crack-resistance may
be measured using any of a number of known measurements techniques,
which are usually not dependent on how the material was formed.
Crack-resistance may focus on the ability to resist propagation of
cracks that have formed, rather than the ability to resist
formation of cracks in the first place. Cracks in a downhole tool
may be detected using any of a number of known detection techniques
including fluorescent-penetrant dye inspection, ultrasonic testing,
and X-ray testing.
[0022] A compressive residual stress in a region may also improve
its erosion resistance, stiffness, strength, toughness, or any
combination thereof. These improved properties may be achieved
instead of or in addition to improved crack-resistance as compared
to a similar region that did not undergo an allotropic phase
transformation or another region of the bit head that does not
contain the allotropic material. These properties may also be
measured using known measurement techniques, which are also not
usually dependent on how the material was formed.
[0023] Typically the compressive residual stress-hardened region
includes part of a surface of the downhole tool and also extends
into the tool. Typically, the compressive residual stress-hardened
region extends into the downhole tool at least 0.1 mm, at least 1
mm, at least 10 mm, or at least 250 mm, as well as between any
combinations of these endpoints.
[0024] In another example, the precursor region may include a first
allotrope of an allotropic material that transforms to the second
allotrope in response to a strain, such as a strain caused by a
crack. The first allotrope has a higher packing density, at least
one shorter lattice parameter (if a crystal), or both than the
second allotrope and both the first and second allotropes occupy
the same physical space, so the transformation creates a
compressive force in the area of the strain that helps relieve the
strain, arrest the crack, or both. Although the allotropic phase
transformation may be triggered at any time, it is often triggered
by strains generated during use of the downhole tool. After the
allotropic phase transformation has occurred, the region may
exhibit increased erosion- and crack-resistance, stiffness,
strength, and ductility along its surface as compared to regions
that lack the allotropic material or in which the phase
transformation has not occurred.
[0025] Suitable allotropic materials for use in this example
include zirconium dioxide (ZrO.sub.2). An allotropic phase
transformation may be triggered in these materials by a temperature
decrease as well as by strain. As a result, they may undergo the
transformation at an undesirable time, such as prior to use of the
downhole tool. In addition, when these materials undergo an
allotropic phase transformation as a result of cooling, the
allotropic material may expand to the point where it cracks. To
avoid a cooling-triggered allotropic phase transformation, a
phase-stabilization material may be added to the allotropic
material to suppress the allotropic phase transformation. Suitable
phase-stabilization materials for use with zirconia include yttrium
oxide (Y.sub.2O.sub.3), cerium oxide (CeO.sub.2), magnesium oxide
(MgO), calcium oxide (CaO), and any combinations thereof.
Phase-stabilization materials may be used with other allotropic
materials as well. They may be coated onto the precursor region or
they may be part of the precursor region when it is formed.
[0026] Phase-stabilization materials may also be used to control
the depth to which an allotropic phase transformation may occur. As
further illustrated in FIG. 5 the phase-stabilization material may
be located below the precursor region in a downhole tool, allowing
the allotropic phase to transform only in the overlying precursor
region.
[0027] Although the downhole tools and methods discussed herein
refer to a single precursor region and single compressive residual
stress-hardened region for simplicity, a bit head, including a
single part of the bit head, may include a plurality of such
regions. Furthermore, different precursor regions or corresponding
compressive residual stress-hardened regions or even the same
precursor region or compressive residual stress-hardened region may
contain different allotropic materials. In addition, different
precursor regions and different compressive residual
stress-hardened regions may be formed at different times and
different types of heating or multiple heating steps may be used to
cause an allotropic phase transformation in different precursor
regions or different allotropic materials. Furthermore, although
the allotropic material is referred to herein as occupying the same
physical space after the allotropic phase transformation, some
variation in physical dimensions, particularly in directions where
the material is not constrained, may occur. Typically this
variation in any direction will be less than 1% of the length of
that direction, or the volume occupied by the first allotrope will
not change by more than 10%.
[0028] Aspects of the present disclosure and its advantages may be
better understood by referring to FIGS. 1 through 7, where like
numbers are used to indicate like and corresponding parts.
[0029] FIG. 1 is an elevation view of a drilling system in which a
downhole tool containing a hardened region may be used. Drilling
system 100 includes a well surface or well site 106. Various types
of drilling equipment such as a rotary table, drilling fluid pumps
and drilling fluid tanks (not expressly shown) may be located at
well surface or well site 106. For example, well site 106 may
include drilling rig 102 that may have various characteristics and
features associated with a land drilling rig. However, downhole
tools incorporating teachings of the present disclosure may be
satisfactorily used with drilling equipment located on offshore
platforms, drill ships, semi-submersibles, and/or drilling barges
(not expressly shown).
[0030] When configured for use with a drill bit, drilling system
100 includes drill string 103 associated with drill bit 101,
typically through a bottom hole assembly (BHA). The drilling system
is used to form a wide variety of wellbores or bore holes such as
generally vertical wellbore 114a or directional wellbore, such as
generally horizontal wellbore 114b, or any combination thereof.
Drilling system 100 may be configured in alternative ways for other
downhole tools having a shaft.
[0031] In the present disclosure, drill bit 101 or another downhole
tool in drilling system 100 includes a compressive residual
stress-hardened region on its head. The compressive residual
stress-hardened region may optimize drill bit 101 or other downhole
tool for the conditions experienced during the drilling operation
to increase the life span of drill bit 101 or other downhole tool.
Although drill bit 101 is depicted as a fixed-cutter drill bit, any
drill bit having a head with a compressive residual stress-hardened
region may be used in drilling system 100.
[0032] FIG. 2 is an isometric view of fixed-cutter drill bits
oriented upwardly. Drill bit 101 formed in accordance with
teachings of the present disclosure may have many different
designs, configurations, and dimensions according to the particular
application of drill bit 101.
[0033] Drill bit 101 includes shaft 151 and head 150. Shaft 151
includes shank 152 with threaded connector 155. Shank 152 is
securely attached to head 150 such that it will not separate from
head 150 during normal operation of drill bit 101. Threaded
connector 155 [also referred to as an American Petroleum Institute
(API) connector] may be used to releasable engage drill bit 101
with drill string 103 or FIG. 1, typically through the BHA. When
engaged with drill string 103, drill bit 101 may be rotated
relative to bit rotational axis 104.
[0034] Drill bit 101 includes head 150 including one or more blades
126a-126g, collectively referred to as blades 126, that are
disposed outwardly from exterior portions of rotary bit body 124.
Rotary bit body 124 may have a generally cylindrical body and
blades 126 may be any suitable type of projections extending
outwardly from rotary bit body 124. For example, a part of blade
126 may be directly or indirectly coupled to an exterior portion of
bit body 124, while another part of blade 126 may be projected away
from the exterior portion of bit body 124. Blades 126 formed in
accordance with the teachings of the present disclosure may have a
wide variety of configurations including substantially arched,
helical, spiraling, tapered, converging, diverging, symmetrical,
asymmetrical, or any combinations thereof.
[0035] Each of blades 126 may include a first end disposed
proximate or toward bit rotational axis 104 and a second end
disposed proximate or toward exterior portions of drill bit 101
(i.e., disposed generally away from bit rotational axis 104 and
toward uphole portions of drill bit 101). Blades 126 may have apex
142 that may correspond to the portion of blade 126 furthest from
bit body 124 and blades 126 may join bit body 124 at landing 145.
Exterior portions of blades 126, cutters 128 and other suitable
elements may be described as forming portions of the bit face.
[0036] Plurality of blades 126a-126g may have respective junk slots
or fluid-flow paths 140 disposed therebetween. Drilling fluids are
communicated through one or more nozzles 156.
[0037] Although bit body 124 and blades 126 may be formed from any
material, typically they are formed from a reinforcement material
infiltrated with a binder. Any part of bit head 150, including
multiple parts thereof, may contain a precursor region or
allotropic phase-transformed region.
[0038] FIG. 3 is an isometric view of a blade of the fixed-cutter
drill bit of FIG. 2, with cutter pockets, but with no cutters
shown. Cutter pockets 160 are one example of a portion of blade 126
that is a precursor region or an allotropic phase-transformed
region. Cutter pockets 160 may have a higher crack resistance, a
higher erosion resistance, a greater stiffness, a greater strength,
a greater ductility, a greater toughness or any combination thereof
as compared to another portion of blade 126 that is not a precursor
region or an allotropic phase-transformed region. Cutter pockets
160, particularly when combined with a softer underlying material,
may result in an increased lifespan for blade 126 as cutter pockets
are prone to failure due to cracks, fatigue, or both.
[0039] FIG. 4 is a cross-sectional view of a cutter pocket of FIG.
3. Typically the precursor region or allotropic phase-transformed
region of cutter pocket 160 includes part of a surface of cutter
pocket 160 and also extends into the tool by a thickness 170.
Thickness 170 of the precursor region or allotropic
phase-transformed region of cutter pocket 160 may be a function of
the diameter of cutter pocket 160. For example, as the diameter
increases, thickness 170 may also increase. Typically, thickness
170 may be at least 0.1 mm, at least 1 mm, at least 10 mm, or at
least 250 mm, as well as between any combinations of these
endpoints.
[0040] While FIG. 4 illustrates the precursor region or allotropic
phase-transformed region with respect to cutter pocket 160, other
portions of the bit head, such as the nozzle channels, may include
one or more precursor regions or one or more allotropic
phase-transformed regions.
[0041] FIG. 5A is a cross-sectional view of a curved portion of the
fixed-cutter drill bit of FIG. 2. Phase-stabilization material 180a
may be added to a portion of the drill bit to control thickness
170a of the allotropic-phase transformed region or a portion of the
precursor region that has undergone an allotropic phase
transformation in response to a drilling condition, such as a crack
by preventing the allotropic phase transformation from extending
past phase-stabilization material 180a. Phase-stabilization
material 180a may be any suitable phase-stabilization material
including yttrium oxide (Y.sub.2O.sub.3), cerium oxide (CeO.sub.2),
magnesium oxide (MgO), calcium oxide (CaO), and any combinations
thereof. Phase-stabilization material 180a may be coated onto the
region or may be part of the region when it is formed.
[0042] FIG. 5B is another cross-sectional view of a curved portion
of the fixed-cutter drill bit of FIG. 2. Allotropic material may be
added to only a portion of the drill bit, such as inner region
180b, to control thickness, position, or location of the outer
region 170b. In this manner, outer region 170b may be free of
allotropic material. Such a configuration may maintain certain
properties of outer region 170b, such as ductility, while
preventing cracks that may form from propagating past inner region
180b.
[0043] To form an MMC downhole tool, a mold is formed by milling a
block of material, such as graphite, to define a mold cavity having
features that correspond generally with the exterior features of
drill bit 101. Various features of drill bit 101 including blades
126, cutter pockets 160, fluid-flow passageways, or combinations
thereof are provided by shaping the mold cavity, by positioning
temporary displacement materials within interior portions of the
mold cavity, or both. Precursor regions near these features,
particularly cutter pockets and fluid-flow passageways, may be
formed by placing an allotropic material adjacent to or in the
vicinity of the displacement materials. Alternatively, if
allotropic material should not be exposed to infiltration
conditions or the binder, displacements materials may be placed in
the allotropic phase-transformed regions, then removed so that the
regions may be filled with allotropic material. As another
alternative, the precursor region may be formed by coating a region
of a formed bit head. The coating may be applied using any suitable
application technique, including spraying the coating on the
precursor region, dipping the precursor region into a liquid
coating, or any combination thereof. Such a coating may also be
diffused into the downhole tool.
[0044] As noted above, a phase-stabilization material may also be
included in or near the precursor region. The phase-stabilization
material may simply be mixed with the material that forms the
precursor region prior to its formation, it may be placed below the
precursor region in the mold, or it may be coated onto the
precursor region after its formation. If coated, the coating may be
performed using any method described above. Alternatively, the
tungsten carbide powder may be coated with an allotropic material
that may interact with either the powder or binder material to
produce an allotropic phase transformation.
[0045] If the allotropic material in the precursor region is
transformed prior to use of the downhole tool, then, regardless of
when or how it is formed, at some point prior to the completion of
manufacturing and eventual use of the downhole tool, the precursor
region is subjected to a trigger condition, such as heat, to cause
an allotropic phase transformation of the allotropic material.
[0046] FIG. 6 is a flow chart of one such method 600. The steps of
method 600 may be performed by a person or manufacturing device
that is configured to identify precursor regions and create
conditions that transform the allotropic phase of the allotropic
material in that region. Either the person or the manufacturing
device may be referred to as a manufacturer.
[0047] In step 602 the manufacturer identifies a precursor region
on bit head 150, particularly on a metallic portion of bit head
150. The precursor region includes a first allotrope of an
allotropic material identified herein. In step 604, the precursor
region is subjected to a trigger condition to cause an allotropic
phase transformation, which forms an allotropic phase-transformed
region with a second allotrope of the allotropic material.
[0048] One trigger condition particularly useful with allotropic
materials containing metals is heating. Heating may include
induction, flame, laser, electron beam, thermal radiation,
convection, friction, or combinations thereof. Induction heating is
the process of heating an object through electromagnetic induction.
Flame heating is the process of heating an object by exposing the
object to a torch or flame. Laser heating is the process of heating
an object with a laser beam. Electron beam heating is the process
of heating an object by exposing an object to an electron beam.
Thermal radiation heating is the process of an object by exposing
the object to heat radiating off of another object. Convection
heating is the process of heating an object by exposing the object
to air currents that have been circulated over a heating element.
Friction heating is the process of heating an object by exposing
the object to heat generated by friction between the object and
another object. Another trigger condition is the combination of
heating and quenching where the allotropic material is heated
followed by quenching to rapidly cool the allotropic material to
finish the allotropic phase transformation.
[0049] Heating may also or alternatively include carburizing,
nitriding, boronizing, or combinations thereof. Carburizing,
nitriding, and boronizing further increase the compressive residual
stress by introducing carbon (C), nitrogen (N), or boron (B) as an
interstitial element in the compressive residual strength-hardened
region. In any of the three processes, the allotropic material is
heated in the presence of another material with a high carbon,
nitrogen, or boron content for carburizing, nitriding, or
boronizing, respectively. The amount of carbon, nitrogen, or boron
content absorbed by the allotropic material varies based on the
temperature to which the material is heated and the elapsed time of
the heating. Additionally, higher temperatures and longer elapsed
time may increase the depth of interstitial element absorption in
the allotropic material. After heating, the precursor region is
rapidly cooled to cause an allotropic phase transformation in the
allotropic material.
[0050] The compressive residual stress in a compressive residual
strength-hardened region may also be further increased by shot
peening the region or the part of the bit head containing the
region. During shot peening, the surface of the precursor region is
impacted by hard particles with a force sufficient to cause the
surface to be plastically deformed. The plastic deformation creates
a compressive residual stress on the surface and also creates
tensile stress in the interior. Other trigger conditions may
include cooling, applied stress (compressive or tensile), crack
propagation, or an applied strain.
[0051] The allotropic material in the precursor region may be
transformed during use of the downhole tool in response to a
trigger condition. FIG. 7 is a flow chart of a method for creating
an allotropic phase-transformed region during use of a rotary drill
bit by inducing an allotropic phase transformation in a precursor
region. The steps of method 700 may be performed by a person or
equipment that is configured to perform a drilling operation.
Either the person or the equipment may be referred to as an
operator.
[0052] In step 702, the operator may contact a subterranean
formation with a rotary drill bit. The rotary drill bit contains a
precursor region. The precursor region is not subjected to a
trigger condition to cause an allotropic phase transformation prior
to use. At step 704, if a trigger condition is encountered by the
rotary drill bit, the trigger condition induces an allotropic phase
transformation in the precursor region at step 708. Trigger
conditions often include strain or tensile stresses created by
cracks or temperature changes due to the environment in the
wellbore. The allotropic phase transformation may occur in only a
part of the region that experiences the trigger condition during
use of the downhole tool. If a trigger condition is not encountered
by the rotary drill bit, the precursor region of the drill bit
remains unchanged, at step 706, and the drill bit continues the
drilling operation until a trigger is encountered.
[0053] Embodiments disclosed herein include:
[0054] A. A downhole tool including an allotropic phase-transformed
region in which the allotropic phase-transformed region results at
least in part from a second allotrope of an allotropic material
occupying the same location as was occupied by a first allotrope of
the allotropic material prior to an allotropic phase
transformation.
[0055] B. A downhole tool including a precursor region, wherein the
precursor region contains a first allotrope of an allotropic
material that is able to undergo an allotropic phase transformation
to a second allotrope when a trigger condition is encountered.
[0056] C. A method of increasing crack resistance of a downhole
tool by forming a precursor region in the downhole tool, wherein
the precursor region contains a first allotrope of an allotropic
material that is able to undergo an allotropic phase transformation
to a second allotrope in response to a strain caused by a crack in
the first allotrope to create an allotropic phase-transformed
region. D. A downhole tool including a precursor region containing
a first allotrope of an allotropic material that is able to undergo
an allotropic phase transformation to a second allotrope in
response to a strain caused by a crack in the first allotrope to
create an allotropic phase-transformed region.
[0057] E. A method of hardening a bit head region of a downhole
drill bit by heating a precursor region on the bit head to
transform a first allotrope of an allotropic material in the
precursor region to a second allotrope in the same physical space,
thereby causing a compressive residual stress in the precursor
region and hardening it to form a corresponding compressive
residual stress-hardened region.
[0058] Each of embodiments A, B, C, D, and E may have one or more
of the following additional elements in any combination, so long as
such combination is not clearly impossible: i) the second allotrope
may have a decreased atomic packing density as compared to the
first allotrope; ii) the allotropic material may include Americium
(Am), Beryllium (Be), Calcium (Ca), Cerium (Ce), Curium (Cm),
Cobalt (Co), Dysprosium (Dy), Iron (Fe), Gadolinium (Gd), Hafnium
(Hf), Holmium (Ho), Lanthanum (La), Manganese (Mn), Neodymium (Nd),
Neptunium (Np), Promethium (Pm), Praseodymium (Pr), Plutonium (Pu),
Sulfer (S), Scandium (Sc), Samarium (Sm), Tin (Sn), Strontium (Sr),
Terbium (Tb), Thorium (Th), Titanium (Ti), Uranium (U), Yttrium
(Y), Ytterbium (Yb), Zirconium (Zr), Am alloy, Be alloy, Ca alloy,
Ce alloy, Cm alloy, Co alloy, Dy alloy, Fe alloy, Gd alloy, Hf
alloy, Ho alloy, La alloy, Mn alloy, Nd alloy, Np alloy, Pm alloy,
Pr alloy, Pu alloy, S alloy, Sc alloy, Sm alloy, Sn alloy, Sr
alloy, Tb alloy, Th alloy, Ti alloy, U alloy, Y alloy, Yb alloy, or
Zr alloy; iii) the first allotrope may include the austenite
allotrope of iron (Fe) and has a face centered cubic (FCC) crystal
structure; iv) the second allotrope may include the ferrite
allotrope of Fe and has a body centered cubic (BCC) crystal
structure; v) the second allotrope may include the ferrite
allotrope of Fe with entrapped carbon (C) and has a body centered
tetragonal (BCT) crystal structure; vi) the allotropic
phase-transformed region may have a decreased atomic packing
density causing a compressive residual stress; vii) the second
allotrope may have a decreased atomic packing density as compared
to the first allotrope; viii) the allotropic material may be
zirconium dioxide; ix) a phase-stabilization material may be
located under the surface of the allotropic phase-transformed
region or the precursor region; x) the phase-stabilization material
may be at least one of yttrium oxide, cerium oxide, magnesium
oxide, calcium oxide; xi) crack resistance may further include
transforming the first allotrope to the second allotrope when a
trigger condition is encountered; xii) the first allotrope may
transform to the second allotrope only in a portion of the
precursor region, such as a portion proximate a crack; xiii) the
allotropic phase transformation may be halted at a
phase-stabilization region below the precursor region; xiv) an
allotropic material located under the exterior surface of the
tool.
[0059] Although the present disclosure and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing
from the spirit and scope of the disclosure as defined by the
following claims. It is intended that the present disclosure
encompasses such changes and modifications as fall within the scope
of the appended claims. For instance, one of ordinary skill in the
art may apply the teachings herein to other downhole tool portions
such as portions of the bit shaft or portions of a downhole tool
other than a rotary drill bit. Such other downhole tool portions
may have allotropic phase-transformed regions similar to those
described herein for the bit head and formed using the methods
described herein.
* * * * *