U.S. patent application number 09/802838 was filed with the patent office on 2001-08-30 for method of applying a wear-resistant layer to a surface of a downhole component.
Invention is credited to Evans, Stephen Martin, Matthias, Terry R., Roberts, Tom Scott.
Application Number | 20010017224 09/802838 |
Document ID | / |
Family ID | 26315288 |
Filed Date | 2001-08-30 |
United States Patent
Application |
20010017224 |
Kind Code |
A1 |
Evans, Stephen Martin ; et
al. |
August 30, 2001 |
Method of applying a wear-resistant layer to a surface of a
downhole component
Abstract
A method of applying a wear-resistant material to a surface of a
downhole component for use in subsurface drilling comprises forming
a plurality of bearing elements, applying a layer of an
electrically conductive, less hard material to each bearing
element, and then bonding each bearing element to the surface of
the component by welding or brazing to the surface of the component
a part of the surface of the bearing element which comprises said
less hard material, wherein the layer is of thickness greater than
0.05mm.
Inventors: |
Evans, Stephen Martin;
(Standish, GB) ; Matthias, Terry R.; (Upton St.
Leonards, GB) ; Roberts, Tom Scott; (Abbeymead,
GB) |
Correspondence
Address: |
SCHLUMBERGER OILFIELD SERVICES
JEFFREY E. DALY
7211 N. GESSNER
HOUSTON
TX
77040
US
|
Family ID: |
26315288 |
Appl. No.: |
09/802838 |
Filed: |
March 9, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09802838 |
Mar 9, 2001 |
|
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|
09340984 |
Jun 28, 1999 |
|
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6234261 |
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Current U.S.
Class: |
175/374 |
Current CPC
Class: |
E21B 10/46 20130101;
E21B 17/1092 20130101; E21B 10/567 20130101 |
Class at
Publication: |
175/374 |
International
Class: |
E21B 010/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 18, 1999 |
GB |
9906114.5 |
Claims
What is claimed is:
1. A method of applying a wear-resistant material to a surface of a
downhole component, the method comprising forming a plurality of
bearing elements, applying a layer of an electrically conductive,
less hard material to each bearing element, and then bonding each
bearing element to the surface of the component using one of a
welding process and a brazing process to bond to the surface of the
component a part of the surface of the bearing element which
comprises said less hard material, wherein the layer is of
thickness greater than about 0.05mm.
2. The method of claim 1, wherein each bearing element comprises a
body of thermally stable polycrystalline diamond.
3. The method of claim 1, wherein the layer of less hard material
comprises a coating applied to at least part of each bearing
element.
4. The method of claim 1, wherein the layer of less hard material
is of high electrically conductivity.
5. The method of claim 4, wherein the layer of less hard material
is formed from a material selected from a group consisting of
nickel and alloys containing nickel.
6. The method of claim 1, wherein each bearing element is bonded to
the surface using an electrical resistance welding technique.
7. The method of claim 1, further comprising applying a layer of a
carbide forming metal to each bearing element prior to the
application of the layer of less hard material thereto.
8. The method of claim 1, wherein the layer of less hard material
is of thickness of between about 0.1mm and about 0.3mm.
9. The method of claim 8, wherein the layer of less hard material
is of thickness of between about 0.15mm and about 0.25mm.
10. The method of claim 9, wherein the layer of less hard material
is of thickness of between about 0.15mm and about 0.2mm.
11. The method of claim 1, further comprising a step of applying a
layer of a hardfacing material over and around the bearing
elements.
12. A downhole component having a surface to which a plurality of
bearing elements are bonded, each bearing element having previously
had a layer of a less hard, electrically conductive material
applied thereto, the layer of less hard material having a thickness
greater than about 0.05mm.
13. The downhole component of claim 12, and shaped to act as one of
a roller cone bit, a fixed cutter bit, a stabilizer unit and a bias
unit.
14. The downhole component of claim 12, wherein each bearing
element comprises a body of thermally stable polycrystalline
diamond.
15. The downhole component of claim 12, wherein the layer of less
hard material comprises a coating applied to at least part of each
bearing element.
16. The downhole component of claim 12, wherein the layer of less
hard material is of high electrically conductivity.
17. A method as claimed in claim 16, wherein the layer of less hard
material is formed from a material selected from a group consisting
of nickel and alloys containing nickel.
18. The downhole component of claim 12, wherein each bearing
element is bonded to the surface using an electrical resistance
welding technique.
19. The downhole component of claim 12, wherein the layer of less
hard material is of thickness of between about 0.1mm and about
0.3mm.
20. The downhole component of claim 19, wherein the layer of less
hard material is of thickness of between about 0.15mm and about
0.25mm.
21. The downhole component of claim 20, wherein the layer of less
hard material is of thickness of between about 0.15mm and about
0.2mm.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a Continuation-in-Part of U.S. Patent application
Ser. No. 09/340,984, filed Jun. 28, 1999, by Stephen Martin Evans,
et al., entitled "Method of Applying a Wear-Resistant Layer to
Surface of a Downhole Component" now pending.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to methods of applying a
wear-resistant material to a surface of a downhole component for
use in subsurface drilling. The method is suitable for use both
with drill bits and with other downhole components.
[0004] 2. Description of Related Art
[0005] The invention is applicable to downhole components of the
kind which include at least one surface which, in use, engages the
surface of the earthen formation surrounding the borehole. The
invention relates particularly to rotary drill bits, for example of
the drag-type kind having a leading face on which cutters are
mounted and a peripheral gauge region for engagement with the
surrounding walls of the borehole in use or of the rolling cutter
kind. The invention will therefore be described with particular
reference to polycrystalline diamond compact (PDC) drag-type and
rolling cutter type drill bits, although it will be appreciated
that it is also applicable to other downhole components having
bearing surfaces. For example, bearing surfaces may be provided on
downhole stabilizers, motor or turbine stabilizers, or modulated
bias units for use in steerable rotary drilling systems, for
example as described in British Patent No. 2289909. Such bias units
include hinged paddles having bearing surfaces which engage the
walls of the borehole in order to provide a lateral bias to the
bottom hole assembly.
[0006] In all such cases the part of the downhole component
providing the bearing surface is not normally formed from a
material which is sufficiently wear-resistant to withstand
prolonged abrasive engagement with the wall of the borehole and it
is therefore necessary to render the bearing surface more
wear-resistant. For example, the bodies of rotary drag-type and
rolling cutter type drill bits are often machined from steel and it
is therefore necessary to apply bearing elements to the gauge
portion of such drill bit to ensure that the gauge is not subject
to rapid wear through its engagement with the walls of the
borehole. This is a particular problem with steel bodied drill bits
where the gauge of the bit comprises a single surface extending
substantially continuously around the whole periphery of the bit,
for example as described in British Patent No. 2326656.
[0007] One well known method of increasing the wear-resistance of
the gauge of a drag-type or rolling cutter type drill bit is to
form the gauge region with sockets in which harder bearing inserts
are received. One common form of bearing insert comprises a
circular stud of cemented tungsten carbide, the outer surface of
which is substantially flush with the outer surface of the gauge.
Smaller bodies of natural or synthetic diamond may be embedded in
the stud, adjacent its outer surface. In this case the stud may
comprise, instead of cemented tungsten carbide, a body of solid
infiltrated tungsten carbide matrix material in which the smaller
bodies of natural or synthetic diamond are embedded. Bearing
inserts are also known using polycrystalline diamond compacts
having their outer faces substantially flush with the gauge
surface.
[0008] Another known method of increasing the wear-resistance of
the gauge surface of a PDC drill bit is to cover the surface of the
gauge, or a large proportion thereof, with arrays of rectangular
tiles of tungsten carbide. Such tiles may be packed more closely
over the surface of the gauge than is possible with bearing
inserts, of the kind mentioned above, which must be received in
sockets, and therefore allow a greater proportion of the area of
the gauge surface to be covered with wear-resistant material at
lesser cost. However, it would be desirable to use bearing elements
which have greater wear-resistance than tungsten carbide tiles.
[0009] A known method for increasing the wear-resistance of the
rolling cone cutter in rolling cutter bits is to include one or
more rows of inserts on the gauge reaming portion of the rolling
cutter. Typically, the inserts are cylindrical bodies which are
interference-fitted into sockets formed on the gauge reaming
surface of the rolling cutter, as shown in U.S. Pat. No. 5,671,817.
The inserts may be formed of a very hard and wear and abrasion
resistant grade of tungsten carbide, or may be tungsten carbide
cylinders tipped with a layer of polycrystalline diamond. In
addition, the gauge portion of each bit leg facing the borehole
wall may be provided with welded-on hard facing and/or the same
type of tungsten carbide cylinders are as fitted into the rolling
cutters.
[0010] A material which is significantly more wear-resistant than
tungsten carbide, and is also available in the form of rectangular
blocks or tiles, is thermally stable polycrystalline diamond (TSP).
As is well known, thermally stable polycrystalline diamond is a
synthetic diamond material which lacks the cobalt which is normally
present in the polycrystalline diamond layer of the two-layer
compacts which are frequently used as cutting elements for rotary
drag-type drill bits. The absence of cobalt from the
polycrystalline diamond allows the material to be subjected to
higher temperatures than the two-layer compacts without sufficient
significant thermal degradation, and hence the material is commonly
referred to as "thermally stable".
[0011] In one commercially available form of thermally stable
polycrystalline diamond the product is manufactured by leaching the
cobalt out of conventional non-thermally stable polycrystalline
diamond. Alternatively the polycrystalline diamond may be
manufactured by using silicon in place of cobalt during the high
temperature, high pressure pressing stage of the manufacture of the
product.
[0012] While TSP has the wear-resistance characteristics
appropriate for a bearing element on a downhole component, it has
hitherto been difficult to mount TSP on downhole components. Where
blocks of TSP are to be used as cutting elements on drag-type drill
bits it is necessary either to mould the bit body around the
cutting elements, using a well-known powder metallurgy process, or
to embed the blocks into bodies of less hard material which are
then secured in sockets in the bit body. Where a bearing element is
to be applied to a surface of a downhole component for the purpose
of wear-resistance, however, it is preferable for the bearing
element to be mounted on the surface of the component, particularly
if the component is formed by machining, from steel or other metal,
so that the bearing element cannot readily be embedded in the
component. The present invention therefore sets out to provide
novel methods for mounting TSP bearing elements on to a bearing
surface of a downhole component.
SUMMARY OF THE INVENTION
[0013] According to the present invention, there is provided a
method of applying a wear-resistant material to a surface of a
downhole component for use in subsurface drilling, the method
comprising forming a plurality of bearing elements, applying a
layer of an electrically conductive, less hard material to each
bearing element, and then bonding each bearing element to the
surface of the component by welding or brazing to the surface of
the component a part of the surface of the bearing element which
comprises said less hard material, wherein the layer is of
thickness greater than 0.05mm.
[0014] The layer of less hard material may comprise a thin coating
pre-applied to some or, preferably, all of the surface of the
bearing element. Each bearing element preferably comprises a body
of thermally stable polycrystalline diamond. The layer is
preferably formed from a material of high electrical conductivity,
such as nickel or nickel alloy. In this case the bearing element
may be held in position on the surface of the component by
electrical resistance welding. The body of thermally stable
polycrystalline diamond may be pre-coated with a layer of a
carbide-forming metal before application of the coating of less
hard material, since the carbide-forming metal may form a stronger
bond with the TSP than does the nickel or nickel alloy alone.
[0015] Each bearing element may be inter engaged with a locating
formation on the surface of the component to which it is welded or
brazed. For example, the locating formation may comprise a socket
or recess into which the bearing element is at least partly
received. The bearing element may be fully received in the socket
or recess so that an exposed surface of the bearing element is
substantially flush with the surface of the component surrounding
the socket or recess.
[0016] The use of a layer of less hard material of thickness
greater than 0.05mm is advantageous in that it is capable of
carrying the electrical current applied thereto during a resistance
welding operation without breaking down. The thickness of the layer
preferably falls within the range of 0.1mm to 0.3mm. More
preferably, the layer thickness falls within the range 0.15mm to
0.25mm, and conveniently within the range of 0.15 to 0.2mm.
[0017] The use of a layer of thickness falling within the range
0.15mm to 0.2mm is advantageous in that the resistance welding
operation can be performed relatively easily. After securing the
bearing elements in position, a layer of a hard facing material may
be applied over and around the bearing elements. The layer may be
of depth such that the bearing surfaces of the bearing elements are
left exposed, or the bearing surfaces may be covered, some of the
hard facing material subsequently being removed, either before or
during use.
[0018] In any of the above arrangements the downhole component may,
as previously mentioned, comprise a drill bit, a stabilizer, a
modulated bias unit for use in steerable rotary drilling, or any
other downhole component having one or more bearing surfaces which
engage the wall of the borehole in use.
[0019] Where the component is a drill bit, it may be a rotary
drag-type drill bit having a leading face on which the cutters are
mounted and a peripheral gauge region for engagement with the walls
of the borehole, in which case the methods according to the
invention may be used to apply bearing elements to the outer
surface of the gauge region.
[0020] The methods of the invention may also be applied to increase
the wear-resistance of surfaces of roller-cone bits or other types
of rock bit.
[0021] The invention also includes within its scope a downhole
component, such as a drill bit, having at least one surface to
which bearing elements have been applied by any of the methods
referred to above, and a coated bearing element for use in the
methods defined hereinbefore.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The following is a detailed description of embodiments of
the invention, reference being made to the accompanying drawings in
which:
[0023] FIG. 1 is a perspective view of a PDC drill bit to the gauge
sections of which wear-resistant materials have been applied in
accordance with the method of the present invention,
[0024] FIG. 2 is a diagrammatic enlarged cross-section of a part of
the gauge section of the drill bit, showing the structure of the
wear-resistant material,
[0025] FIG. 3 is a similar view to FIG. 2 showing an alternative
method of forming the wear-resistant material,
[0026] FIG. 4 is an enlarged view illustrating the structure of a
bearing element mounted in position,
[0027] FIG. 5 is a perspective view of a rolling cutter drill bit,
to the gauge sections of which wear-resistant materials have been
applied,
[0028] FIG. 6 is a view of a stabilizer unit to at least part of
which a wear-resistant material has been applied,
[0029] FIG. 7 is a view of a bias unit to at least part of which a
wear-resistant material has been applied,
[0030] FIG. 8 is a view of a bottom hole assembly of a drill string
having tools or components with surfaces to at least some of which
a wear-resistant material has been applied, and
[0031] FIG. 9 is a view of another bottom hole assembly having
tools or components with surfaces to at least some of which a
wear-resistant material has been applied.
DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED
EMBODIMENT
[0032] Referring to FIG. 1: the PDC drill bit comprises a bit body
10 machined from steel and having eight blades 12 formed on the
leading face of the bit and extending outwardly from the axis of
the bit body towards the peripheral gauge region 14. Channels 16a,
16b are defined between adjacent blades.
[0033] Extending side-by-side along each of the blades 12 is a
plurality of cutting structures, indicated at 18. The precise
nature of the cutting structures does not form a part of the
present invention and they may be of any appropriate type. For
example, as shown, they may comprise circular preform PDC cutting
elements brazed to cylindrical carriers which are embedded or
otherwise mounted in the blades, the cutting elements each
comprising a preform compact having a polycrystalline diamond front
cutting table bonded to a tungsten carbide substrate, the compact
being brazed to a cylindrical tungsten carbide carrier. In another
form of cutting structure the substrate of the preform compact is
of sufficient axial length to be mounted directly in the blade, the
additional carrier then being omitted.
[0034] Back-up abrasion elements or cutters 20 may be spaced
rearwardly of some of the outer cutting structures, as shown.
[0035] Nozzles 22 are mounted in the surface of the bit body
between the blades 12 to deliver drilling fluid outwardly along the
channels, in use of the bit. One or more of the nozzles may be so
located that they can deliver drilling fluid to two or more
channels. All of the nozzles communicate with a central axial
passage (not shown) in the shank 24 of the bit, to which drilling
fluid is supplied under pressure downwardly through the drill
string in known manner.
[0036] Alternate channels 16a lead to respective junk slots 26
which extend upwardly through the gauge region 14, generally
parallel to the central longitudinal axis of the drill bit, so that
drilling fluid flowing outwardly along each channel 16a flows
upwardly through the junk slot 26 between the bit body and the
surrounding formation, into the annulus between the drill string
and the wall of the borehole.
[0037] Each of the other four alternate channels 16b does not lead
to a conventional junk slot but continues right up to the gauge
region 14 of the drill bit. Formed in each such channel 16b
adjacent gauge region is a circular opening 28 into an enclosed
cylindrical passage which extends through the bit body to an outlet
(not shown) on the upper side of the gauge region 14 which
communicates with the annulus between the drill string and the
borehole.
[0038] Accordingly, the gauge region 14 of the drill bit comprises
four peripherally spaced bearing surfaces 30 each bearing surface
extending between two junk slots 26 and extending continuously
across the outer end of an intermediate channel 16b.
[0039] In accordance with the present invention, there is applied
to each peripheral bearing surface 30 in the gauge region a
wear-resistant layer comprising an array of rectangular bearing
elements 32 in mutually spaced relationship on the bearing surface
30, each bearing element being formed, at least in part from
thermally stable polycrystalline diamond.
[0040] In the example shown in FIG. 1 the bearing elements 32 are
rectangular and closely packed in parallel rows extending generally
axially of the drill bit. However, this arrangement is by way of
example only and many other shapes and arrangements of bearing
elements may be employed, but still using the methods according to
the present invention. For example the bearing elements might be
square, circular or hexagonal and may be arranged in any
appropriate pattern. Also, the bearing elements may be more widely
spaced than is shown in FIG. 1 and may cover a smaller proportion
of the surface area of the bearing surface 30. Referring now to
FIG. 5, a perspective view of a rolling cutter drill bit 100 is
shown. The rolling cutter drill bit 100 has a body portion 112 and
a plurality of legs 114 which each support rolling cutters 116. A
typical rolling cutter 116 has a plurality of cutting inserts 118
arranged in circumferential rows 120. An orifice arrangement 122
delivers a stream of drilling fluid 124 to the rolling cutter 116
to remove the drilled earth, in use. Weight is applied to the
rolling cutter drill bit 100, and the bit 100 is rotated. The earth
then engages the cutting inserts 118 and causes the rolling cutters
116 to rotate upon the legs 114, effecting a drilling action.
[0041] The gauge portion 126 of each leg 114 may define a bearing
surface which engages the borehole wall during operation. This
engagement often causes excessive wear of the gauge portion 126 of
the leg 114. In order to minimize the wear, a plurality of
rectangular bearing elements 32 are provided, the elements 32 being
spaced apart in either a vertical alignment 128 or horizontal
alignment 130 on the gauge portion 126 of the leg(s) 114. The
particular arrangement of bearing elements 32 used will depend upon
several factors, such as the curvature of the gauge portion 126,
the amount of wear resistance required, and the bit size. Although
the vertical alignment 128 and the horizontal alignment 130 are
shown on separate legs in the figure, it is anticipated that both
may be used on a single gauge portion 126 of a leg 114.
[0042] Each rolling cutter 116 has a gauge reaming surface 132
which defines a further bearing surface and also experiences
excessive wear during drilling. The rectangular bearing elements 32
may be used on the gauge reaming surface 132 to minimize this wear.
The advantage of placing the rectangular bearing elements 32 on the
gauge reaming surface 132 of the rolling cutter 116 is that they
can be placed in a particularly dense arrangement compared to the
traditional interference fitted cylindrical cutting elements. The
rectangular bearing elements 32 may be placed in a circumferential
manner on the gauge reaming surface 132 of the rolling cutter 116
as indicated by numeral 134. Alternately, the rectangular bearing
elements 32 may be in a longitudinal arrangement as indicated by
numeral 136. It is anticipated that a combination of longitudinal
and circumferential arrangements of the rectangular bearing
elements 32 would also be suitable.
[0043] The method of the present invention also allows the
rectangular bearing elements 32 to be placed on the gauge reaming
surface 132 of the rolling cutter 116 without particular regard to
the placement of the cutting inserts 118. Prior to the invention,
great care was required to arrange the cylindrical cutting elements
of the gauge reaming surface 132 in a manner that prevented the
bases of their mating sockets from overlapping.
[0044] FIGS. 2 and 3 show diagrammatic cross-sections through the
bearing surface 30 and applied wear-resistant layer, and methods of
applying the wear-resistant layer will now be described with
reference to these figures.
[0045] As will be seen from FIG. 2, the bearing elements 32 lie on
the outer bearing surface 30 of the gauge portion 14 of the drill
bit and the spaces between adjacent bearing elements 32 are filled
with a settable hardfacing material 34.
[0046] In one method according to the invention, the bearing
elements 32 comprise solid blocks or tiles of TSP and are first
attached to the bearing surface 30 in the desired configuration.
The settable hardfacing material 34 is then applied to the spaces
between the TSP blocks 32 so as to bond to the bearing surface 30
of the drill bit and to the blocks themselves. Upon solidification,
the hardfacing material 34 serves to hold the TSP elements 32
firmly in position on the surface 30.
[0047] The hardfacing material 34 may be of any of the kinds
commonly used in providing a hardfacing to surface areas of drill
bits, and particularly to steel bodied drill bits. For example, the
hardfacing material may comprise a powdered nickel, chromium
silicon, boron alloy which is flame sprayed on to the surface 30
using a well known hardfacing technique. The hardfacing may also be
provided by other known techniques such as electrical plating, PDC,
and metal spraying.
[0048] In the arrangement shown in FIG. 2 the hardfacing material
34 is in the form of a broken layer of generally the same depth as
the TSP bearing elements 32 so that the outer surfaces of the
bearing elements are substantially flush with the outer surface of
the hardfacing layer. In the alternative arrangement shown in FIG.
3 the hardfacing layer 34 is applied to a depth which is greater
than the depth of the elements 32 so as to overlie the outer faces
of the bearing elements, as indicated at 36. The overlying layer 36
can be left in position so that, during use of the bit the layer 36
will wear away exposing the surfaces of the TSP bearing elements 32
which will then bear directly on the surface of the wall of the
borehole. However, if required, the layer 36 may be ground away to
expose the outer surfaces of the bearing elements before the bit is
used.
[0049] The bearing elements 32 are attached to the bearing surface
30 by electrical resistance welding. Since it is extremely
difficult to weld or braze TSP directly to steel using conventional
techniques, such as electrical-resistance welding, the TSP blocks
are coated with a less hard material, of higher electrical
conductivity, before welding or brazing them to the surface 30. For
example, the blocks may be coated with a thin layer of nickel or a
nickel alloy, for example by using the techniques of electroless
plating, CVD, or immersion in a molten alloy. Before coating the
TSP with the nickel or nickel alloy, the TSP blocks may first be
coated with a suitable carbide-forming metal, since such metal will
bond to the TSP forming a firmly attached base surface to which the
nickel or nickel alloy coating may subsequently be applied. Once
the TSP blocks have had a suitable coating layer applied thereto,
the blocks may more readily be welded or brazed to the surface 30,
for example by using electrical-resistance spot welding.
[0050] As, during the electrical resistance welding process, high
currents are applied and must be conducted by the nickel or nickel
alloy coating, in order to ensure that the coating is able to
withstand the applied current, the coating is of thickness greater
than 0.05mm. In order to withstand the current applied in a typical
electrical resistance welding process, the coating thickness is
preferably within the range 0.1mm to 0.3mm and is preferably within
the range 0.15mm to 0.25mm. More preferably, the layer thickness
falls within the range 0.15mm to approximately 0.2mm, and the layer
thickness is conveniently approximately 0.2mm. FIG. 4 illustrates a
bearing element comprising a block 38 of thermally stable diamond
coated with a layer 40 of nickel of thickness approximately 0.2mm.
Prior to applying the nickel layer 40, a carbide forming material
42 is applied to the block 38. The coated block is then secured in
position on a bit body 44 by electrical resistance welding, and a
hard facing material 46 applied.
[0051] In any of the arrangements described the bearing surface 30
may be preformed with appropriate formations to assist in locating
or holding the TSP elements 32 on the surface 30. For example, each
element 32 may be partly received in a suitably shaped groove in
the bearing surface 30 or in an individual recess which matches the
shape of the element. In another arrangement the undersides of the
elements 32 are preformed with shaped formations which mechanically
inter-engage with corresponding shaped formations on the surface
30. In any of the described arrangements the sides of the elements
32 may be so shaped that they mechanically interlock with the
surrounding hardfacing material. For example, the elements may
increase in width towards the surface 30.
[0052] In the above-described arrangements, the hardfacing layer 34
serves to hold the TSP elements 32 on the bearing surface 30, the
welding or brazing of the elements 32 to the surface 30 merely
serving to locate the elements temporarily in the desired
configuration on the bearing surface while the hardfacing layer is
applied. However, since the above-described coating of the TSP
elements enables them to be welded or brazed to the bearing surface
30, arrangements are also possible where the TSP elements are
welded or brazed to the bearing surface with sufficient strength
that the hardfacing layer 34 may be dispensed with, each element 32
being held on the bearing surface 30 by the welded or brazed joint
alone. In this case it may be desirable for the elements 32 to be
wholly or partly received in recesses or grooves in the bearing
surface 30 in order to improve the strength of the attachment of
the elements to the surface.
[0053] Similar techniques to these described hereinbefore are
suitable for use in securing the bearing elements 32 to the bearing
surfaces of the drill bit illustrated in FIG. 5.
[0054] Although the invention has been described with particular
reference to applying a wear-resistant surface to the gauge section
of a drag-type or rolling cutter type steel-bodied drill bit, as
previously mentioned the invention is not limited to this
particular application and may be used for applying
TSP-incorporating bearing elements to a bearing surface of any
other downhole component, such as a stabilizer, or a modulated bias
unit, as described below. The description below is intended to be
illustrative of the parts of the components to which a
wear-resistant layer should preferably be applied rather than to
take the form of a detailed description of these components.
[0055] FIG. 6 illustrates a stabilizer unit for use in a bottom
hole assembly. The stabilizer unit 200 illustrated in FIG. 6
includes a plurality of radially outwardly extending blades 202,
the outer surfaces 204 of which engage, in use, the wall of the
borehole in which the bottom hole assembly is located. These
surfaces 204 must be able to withstand the severe abrasion and
loads applied thereto, in use. In order to improve the wear
resistance of the blades 202, these surfaces 204 are provided with
wear-resistant materials using the methods described hereinbefore
to secure bearing elements 206 to the surfaces 204 and, if desired,
to apply a layer of a hard facing material over or around the
bearing elements 206.
[0056] The component illustrated in FIG. 7 is a rotary steerable
unit 208 having a bias pad 210. The bias pad 210 repeatedly engages
the wall of the bore, in use to push an associated drill bit to one
side as directed by a control unit. It will be appreciated that the
bias pad 210 is subject to severe loads and so is subject to wear.
In order to improve the wear-resistance of the bias pad 210, a
plurality of bearing elements 212 are secured thereto using the
method described hereinbefore. If desired, a hard facing material
may also be applied to the bias pad using the technique described
hereinbefore.
[0057] Referring now to FIGS. 8 and 9, are shown other applications
utilizing downhole tools 214, 216 having a wear-resistant material
applied using the method described hereinbefore. In FIG. 8 a number
of different tools 214, 216 are shown in the drill string 218.
These tools 214, 216 may include, but are not limited to, downhole
motors, measuring while drilling tools, logging tools, vibration
dampers, shock absorbers, and centralizers. These tools 214, 216
benefit from wear-resistant materials applied by the process of the
present invention. In particular, the bottom hole assemblies 220,
as shown in FIG. 9, are often operated while gravity is pushing
them against the borehole wall. Once again the extreme abrasion and
loads applied to the sides of these tools make them benefit from
the application of wear-resistant materials using the process of
the present invention.
[0058] Whereas the present invention has been described in
particular relation to the drawings attached hereto, it should be
understood that other and further modifications apart from those
shown or suggested herein, may be made within the scope and spirit
of the present invention.
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