CA2070352A1

CA2070352A1 - Diamond thrust bearing and method for manufacturing same

Info

Publication number: CA2070352A1
Application number: CA002070352A
Authority: CA
Inventors: David Hall
Original assignee: David Hall; Schlumberger Canada Limited
Current assignee: Schlumberger Canada Ltd
Priority date: 1991-06-04
Filing date: 1992-06-03
Publication date: 1992-12-05
Also published as: MX9202585A; US5092687A; NO922072D0; NO922072L; EP0517316A1

Abstract

ABSTRACT OF THE INVENTION
A diamond thrust bearing and method for manufacturing the diamond thrust bearing wherein diamond bearing pads are interference fitted at ambient temperature into a plurality of equidistantly spaced bearing pad recesses located in a circle in a receiving surface of a bearing pad retainer. The bearing faces of the diamond bearing pads are located coplanar with a predetermined common bearing plane by pressing the bearing faces into the bearing pad retainer with a ram and inflexible pressing plate until the pressing face of the pressing plate is stopped by a press stop block. The diamond thrust bearing manufactured using the method will be free from heat induced stresses that cause bearing face misalignment.

Description

2~7~3~2 BACRGROUND

I. Field of the Invention .~
; This invention relates to improvements in the structure 6 and method of manufacturing thrust bearings. More particularly, this invention relates to diamond thrust 8 bearings for use in downhole drilling operations and a process 9 for manufacturing same.

ackaround Art 13 Exploratory bore holes are drilled in the earth to gain 14 access to materials located therein. The cost of exploratory equipment i9 high, and therefore, many companies prefer to 16 lease exploratory equipment for short-term or sporadic needs.
17 Leased drilling equipment requires large quantities of 18 drilling fluid, skilled manpower, and frequent maintenance.
19 These factors of overhead, when added to the cost of leasing drilling equipment, make even leasing exploratory eguipment 21 an expensive process. Downtime from equipment failure or 22 maintenance impinges on the time this expensive equipment is 3 in productive use.

2~7~3~

1 A. The Exploratory Environment ~! To illustrate the environment in which this exploration .~ ta~es place, Figure 1 shows a drill rig lo erected over a surface 12 of the earth at an area to be explored for oil.

A bore hole is drilled below drill rig 10 through surface 12 6 and strata 13, to a desired depth. Advancement of drilling end 14 into the earth is accomplished by a drill bit 15 which 8 progresses through strata 13 by the action of rotating teeth 9 located on the end thereof.

B. The Downhole Drilling Motor l2 Drill bit 15 is powered by a downhole drilling motor 16.
l3 Downhole drilling motor 16 is located at the end of a series l~ of pipe sections comprising drill string 18. The housing o~
downhole drilling motor 16 is located in drilling end 14 of 16 drill string 18 and remains stationary with drill string 18 17 a~ it powers drill bit 15. Downhole drilling motor 16 is 18 powered by drilling fluid, commonly referred to as drilling 19 mud, which is pumped under pressure through drill string 18 and through downhole drilling motor 16.
21 Downhole drilling motors such as downhole drilling 22 motor I6 are cylindrical so as to be capable of passing 23 through the bore hole drilled by drill bit 15. Downhole drilling motors must, therefore, conform to the size 2s restriction imposed by the outside diameter of the drill pipe 26 ¦ in drill ~tring a. The longth Or downhole rotor 16, however, , :- , 2~7~5~

l often ranges up to thirty feet. Downhole drilling motors :~ utilize the effect of drilling mud pressure and momentum :~ change of drilling mud as it passes through turbine blades to provide torque to turn drill bit 15. Drill bit 15 penetrates earth and rock by a com~ination of the downward pressure 6 exerted by the weight of drill string 18 and the rotary action _ imparted to drill bit 15 by downhole drilling motor 16. As 8 the bore hole deepens, additional sections of pipe are added 9 to drill string 18 at drill rig 10.

Il C. Downhole Thrust Bearinas l2 Figure 2 illustrates in more detail drilling end 14 of 13 drill string 18 shown in Figure 1. A casing 17 of downhole l4 drilling motor 16 is shown attached to the last segment o~
drill string 18. Located within casing 17 of downhole l6 drilling motor 16 are two thrust bearing assemblies, an upper l7 thrust bearing assembly 20 and a lower thrust bearing 18 assembly 21. Downhole drilling motor 16 powers drill bit 15 l9 located at the free end of drilling end 14.
Thrust bearing assemblies 20, 21 allow for the rotation 21 of drill bit 15 relative to casing 17 of downhole drilling 22 motor 16. To maintain the rotation of drill bit 15 when 2~ downhole drilling motor 16 is powering drill bit 15, thrust 2~ bearing assemblies 20, 21 must be capable of operating under compressive pressure from the weight of drill string 18 and ` 2~7~3~2 I tensile pressure from the force of the pressurized drilling , mud passing through downhole drilling motor 16.

.~ 1. Off-bottom Thrust .; Drilling mud is pumped through drill string 18 to 6 downhole motor 16 in a direction shown by arrow A, a direction referred to as "downhole." The high pressure drilling mud 8 exerts a force downhole on drilling motor 16 that tends to 9 push drilling motor 16 toward the bottom 22 of bore hole 23.

o This force is referred to as "off bottom thrust" since the thrust is exerted whenever drilling mud is pumped through 12 downhole drilling motor 16 and drill bit 15 i~ off the bottom 13 of bore hole 23.

IS 2. On-bottom Thrust 16 When drill bit 15 is in contact with bottom 22 of bore 17 hole 23, the weight of drill string 18 exerts a force on 18 drilling end 14 which tends to compress drilling motor 16.
I9 This force is referred to as "on-bottom thrust," as it is 20 experienced only when drill bit lS is in contact with 21 bottom 22 of borehole 23.
22 During drilling, on-bottom thrust caused by the weight 23 of drillstring 18 i5 countered by off-bottom thrust caused by 2~ the hydraulic pressure of the drilling mud. The interaction of on-bottom and off-bottom thrusts lessens the overall thrust 2~ 3~r~

that must be borne by thrust bearing assemblies 20, 21, during actual drilling.
Periodically, during the drilling process, drill bit 15 wears out requiring drill string 18 to be pulled up out o~
;, bore hole 23 to gain access to drill bit 15. After replacing 6 drill bit 15, drill string 18 is reassembled as drill bit 15 is lowered back into bore hole 23. During this period of 8 lowering drill string 18 back to the previously achieved g depth, drilling mud is pumped under pressure through drill lo string 18 to turn downhole drilling motor 16 and thereby cause Il drill bit 15 to rotate and clean bore hole 23 as drill bit 15 l2 descends.
13 The period durinq which drill bit 15 is descending into l~ bore hole 23 exposes thrust bearing assemblies 20, 21 to off-bottom thrusts caused by drilling mud pressing downhole l6 drilling motor 16 in a downhole direction. Thrust bearing 17 assemblies 20, 21, do not have the ad~antage of offsetting on-18 bottom thrust dur ng this time, and 50, must bear the entirety Is of the off-bottom thrust. Typical on-bottom thrusts may exceed 40,000 pounds and off-bottom thrusts may exceed 30,000 21 pounds.

2~ 3. Diamond Drill Bits ~ Previously, a typical drill bit would last approximately fifteen hours before needing replacement. To lengthen the 26 interval between drill bit replacement, drill bits were 2 ~ 3~

introduced which incorporated synthetic diamonds into the surface of the drill bit. These diamond drill bits have increased the useful life of drill bit 15 from fifteen hours to onQ hundred fifty hours. This increase in useful life allows much longer intervals befors drill-bit replacement is 6 necessary.

-8 D. The Evolution of the Diamond Thrust Bearinq 9 With the introduction of diamond drill bits, however, a lo new problem arose. While the new diamond drill bits had a Il useful life of one hundred fifty hours, the thrust bearings l2 had a useful life of only fifty hours. Thrust bearing 13 as~emblies 20, 21 became the limiting factor in downhole I4 operations. When a thrust bearing as~embly 20, 21 wears out, I; drill string 18 must be pulled out of bore hole 23 to access 16 downhole drilling motor 16 and the thrust bearingassemblies 20, 21 contained therein. Thrust bearing assembly l8 failure required drilling to be halted every fifty hours to l9 replace the thrust bearing assemblies 20, 21 in downhole drilling motor 16.

22 1. Roller Thrust Bearings 23 To cope with the forces operating on downhole drilling 2~ motor 16, the earliest thrust bearings utilized ball bearings travelling in races. Thrust bearing assemblies, such 26 as 20, 21 were positioned at both ends of downhole drilling 2 P~ 3 2 motor 16 to cope with both on-bottom and off-bottom thrusts.
, In a first attempt to increase thrust bearing life, ball bearingR were replaced with roller bearings to increase the bearing surface carrving ~he load from on-bottom and off-bottom thrusts.
6 Roller thrust bearings first used in downhole motors had a useful life of approximately fifty hours. Since drill bits 8 used at the introduction of suc~ bearings had a useful life 9 of only fifteen hours, roller thrust bearings were not a lo limiting factor in causing downtime. ~oller thrust bearings Il were simply replaced concurrently with drill bit 15 after l2 several intervening drill bit changes. With the introduction l3 of diamond drill bits 15, however, roller thrust bearings l4 beca~e a limiting factor in the efficient use of drilling lS equ~pment. The solution to this disparity in useful life 16 between diamond drill bit 15 and roller thrust bearings was l7 to develop thrust bearings with longer useful lifetimes. This 18 was accomplished by incorporating synthetic diamonds into the l9 bearing surfaces of thrust bearings 20, 21.

21 2. Diamond Thrust Bearings 22 Diamond thrust bearings are paired to create thrust 23 bearing assemblies 20, 21 like those shown in Figure 3. Each diamond thrust bearing is manufactured with diamond bearing pad retainer 28 having interference fitted within bearing pad 26 recesses a plurality of diamond bearing pads like bearing 2~7~

1 pad 26. Diamond bearing pad 26 is cylindrical and comprise , a bearing end 32 terminating in a substantially planar bearing face 34. Opposite bearing end 32 is an insertion end 36 which is held in bearing pad retainer 28. Insertion end 36 has a bevel 37 to facilitate insertion into the bearing pad 6 retainer 28. Diamond bearing pad 26 is often constructed of tungsten carbide in which the synthetic diamonds are bonded.
8 The synthetic diamonds of substantially planar bearing face 34 9 give diamond thrust bearings a useful life that approximates lo that of diamond drill bits like drill bit 15, su~stantially increasing the productive operational time that drilling l2 equipment is in use in a given period.
l3 As illustrated in Figure 4, diamond bearing pads 26 are l4 typically arranged in a circle inside of an annular bearing pad retainer 28. Bearing end 32 projects above a receiving 16 surface 40 and terminates in substantially planar bearing 17 facQ 34.
18 Thrust bearing assembly 21 comprises two thrust 19 bearings 29 like that illustrated in Figure 4. Two thrust bearings 29 are located such that the substantially planar 21 bearing faces 34 of diamond bearing pads 26 of one bearing pad 22 retainer are in contact with the corresponding substantially 2~ planar bearing faces 34 of the opposing bearing pad retainer.
~4 This orientation assures uniform contact between all diamond bearing faces 34 contributing to the longer useful life of 26 diamond thrust bearing assemblies.

2~7~3~,~

~ 3. The Predetermined Common Bearing Plane :~ Maximizing the load-carrying capacity of two opposing thrust bearings 29 requires that the load carried by bearing pad retainer 28 be spread over the maximum bearing surface of 6 all of diamond bearing pads 26. To açcomplish this, the substantially planar bearing faces 34 of each diamond bearing pad 26 must be parallel with the bearing faces 34 of diamond 9 bearing pads 26 of the opposing bearing pad retainer.
Io Maximizing the total bearing surface of the overall Il thrust bearing 29, requires that all bearing faces 34 in each 12 thrust bearing 29 be disposed and must remain disposed 13 coplanar with each other in a theoretical predetermined common 14 bearing plane. Any deviation of a bearing race out o~ the Is predetermined common bearing plane contributes to premature 16 thrust bearing failure, a~ some diamond bearing pads 26 are 17 required to carry a greater load than the others in the 18 bearing pad retainer 28.

19 . .
4. Bearing Pad Recess Depth 21 To produce a thrust bearing 29, bearing pad recesses 42 æ are drilled to precise depths in bearing pad retainer 28.
~3 This method requires equipment capable of drilling bearing pad 2~ recesses with precise tolerances on a continual basis. This equipment requires frequent adjustment, as the drill bit wears 26 from drilling the bearing pad recesses in the hard bearing pad 2~7~ 3~

retainer. This need for constant adjustment results in bearing pad recesses 42 that vary slightly in their dimensions.
As diamond bearing pads 26 are inserted into bearing pad recesces 42, any deviation in bearing pad recess depth results 6 in substantially planar bearing faces 34 that are no longer , coplanar with the predetermined common bearing plane.

9 5. Brazing lo To retain diamond bearing pads 26 in bearing pad recesses 42 during drilling operations, diamond bearing 12 pads 26 are brazed into bearing pad recesses 42. Flux is 13 placed in the bottom of each of the bearing pad recesses 42 14 ~ollowed by a diamond bearing pad 26. Bearing pad retainer 28 1.; i9 then heated to a t~mperature high enough to braze diamond 16 bearing pad 26 to bearing pad recesses 42. Bearing pad 17 retainer 28 is then cooled to ambient temperature.

~8 As bearing pad retainer 28 cools, however, heat 19 distortion of bearing pad retainer 28 may occur. This heat 20 distortion may cause misalignment of substantially planar 21 bearing faces 34 of diamond bearing pads 26. Heat-distorted 22 bearing pad retainers elevate some bearing faces 34 out of the 23 predetermined common bearing plane, thereby causing some 2~ bearing face~ 34 to carry more thrust loading than others.

2.; Heat distortion of even a very small degree can result 26 in premature thrust bearing failure. Small distortions caused 2 0 7 $ ~3 t.~ (d by heating bearing pad retainer 28 during the brazing process are difficult to discover and are, therefore, difficult to eliminate. Processes designed to establish substantially ~ planar bearing faces 34 coplanar with the predetermined ; bearing plane during brazing are ineffective in maintaining 6 substantially planar bearing faces 34 in a coplanar orientation during cooling.

9 OBJECTS AND BRIEF SUM~RY_OF THE INVENTION
lo Accordingly, one object of the present invention is to Il reduce the cost of drilling oil wells for exploration and 12 production, thereby reducing the cost of petroleum products 13 to the consumer.
14 Another object of the present invention is to provide an improved thrust bearing that lengthens the operating time of 16 leased equipment during the term of the lease.
17 A further object of the present invention is to reduce 18 the time needed for maintenance and repair of thrust bearings 1~ by providing an improved thrust bearing with a useful lifetime approximately equal to that of a diamond drill bit thereby 21 allowing both parts to be replaced simultaneously.
22 Another object of the present invention js to provide an 23 improved thrust bearing with bearing faces that are all 24 coincident with a predetermined co~mon bearing plane.
A further object of the present invention is to provide 26 an improved thrust bearing that is not dependent on repeated , , 2~7~2 drilling tool adjustment to achieve uniform recess depth and ~ planar alignment of the bearing faces in a predetermined :3 common bearing plane.
~ A still further object of the present invention is to ;, provide an improved thrust bearing that is capable of 6 maintaining the substantially planar bearing faces of the diamond bearing pads in the predetermined bearing plane when 8 the diamond bearing pads are sub~ected to the dynamic stresses 9 caused by on-bottom and off-bottom thrusts.
o Another object of the present invention is to provide a method of thrust bearing manufacture which overcomes bearing 12 face misalignment from heat-induced stresses imposed by the 13 manufacturing process.
14 Additional objects and advantages of the invention will 1; be set forth in the description which follows, and in part 16 will be obvious from the description, or may be learned by the 17 practice of the invention. The objects and advantages of the 18 invention may be realized and obtained by means of the 19 instruments and combinations particularly pointed out in the appended claims.
21 To achieve the foregoing objects, and in accordance with 22 the invention as embodied and broadly described herein, a 23 diamond thrust bearing is provided for use in downhole ~4 drilling operations. The diamond thrust bearing is comprised of a bearing pad retainer, a plurality of malleable shims, and 26 a plurality of diamond bearing pads. The bearing pad retainer ~ .. ,. ~

2~7 ~

1 is an annular plate having a plurality of bearing pad recesses ;7 formed in a receiving surface thereof. The bearing pad recesses are equidistantly spaced in a circle concentric with ~ the bearing pad retainer. Each of the bearing pad recesses ; comprise a receiving end in the receiving surface of the 6 bearing pad retainer, an insertion chamber, and a deformation end contiguous with the bottom of the insertion chamber. In 8 addition, an overflow chamber i5 formed in the deformation end 9 of the ineertion chamber.
One of the plurality of malleable shims is cold pressed in each of the bearing pad recesses in the deformation end of 12 the bearing pad recess. The malleable shims each have an 13 upper surface that supports the diamond bearing pad and a 1~ lower surface which is cold pressed into the deformation end 1~; of the bearing pad reces3 as the diamond bearing pad is 16 inserted at ambient temperature. A portion of the malleable 17 shim that exceeds the capacity of the deformation end of the 18 bearing pad recess is cold formed into the overflow chamber 19 as the lower surface of the malleable shim is cold pressed into the deformation end of the bearing pad recess during 21 insertion of the diamond bearing pad.
22 Each of the plurality of diamond bearing pads comprises 23 an insertion end, and a bearing end. The insertion end is 2~ interference fitted into a corresponding one of the bearing 2~ pad recesses into the insertion chamber. The bearing end 26 projects from the receiving surface of the bearing pad . .~ ., ~ ..

2 ~ 5 2 retainer and terminates in a substantially planar bearing , face. The substantially planar bearing faces of all of the plurality of diamond bearing pads are coplanar with a predetermined common bearing plane.
To manufacture the diamond thrust bearing, a press is 6 provided to position diamond bearing pads into the bearing pad _ recesse~ in th~ receiving surface of the bearing pad retainer.
8 The press positions the substantially planar bearinq face~ of 9 the diamond bearing pads in a predetermined common bearing lo plane by pressing until a locating means is encountered.
The press is made up of a press table, a ram, an l2 inflexible pressing plate, and a locating means for limiting 13 the travel of a pressing face of the inflexible pressing plate 14 to a position coplanar with the predetermined common bearing plane.

16 The press table is provided to support the bearing pad retainer during pressing by the ram. The ram is capable of 18 producing a pressure exceeding the pressure exerted on less 19 than all of the diamond bearing pads by off-bottom thrust during drilling operations. The ram presses on an inflexible 21 pres~ing plate with a pressing face which presses three of the æ diamond bearing pads into three of the bearing pad recesses.
23 The inflexible pressing plate travels until its pressing face 24 is stopped by the locating means.
2, one embodiment of the locating means comprises a press 26 stop block that is placed inside the bearing pad retainer on 2 ~ 7 `~ ~? ~? !~

the press table. The press stop block has a planar surface that is coplanar with the predetermined common bearing plane.
When the pressing face of the inflexible plate encounters the press stop block, travel of the pressing plate is stopped and the bearing faces of the diamond bearing pads are positioned coplanar with the predetermined common bearing plane.
The invention also contemplates a method for 8 manufacturing the diamond thrust bearing.

BRIEF DESCRIPTION OF TH~ DRAWINGS
In order that the manner in which the above-recited and 12 other advantages and objects of the invention are obtained, 1~ a more particular description of the invention briefly 14 described above will be rendered by reference to specific embodiments thereof which are illustrated ln the appended 16 drawings. Understanding that these drawings depict only 17 typical embodiments of the invention and are therefore not to 18 bo considered limiting of its scope, the invention will be 19 described with additional specificity and detail through the use of the accompanying drawings in which:
21 Figure l is a schematic view of the environment in which æ the inventive thrust bearing is used, showing a drilling rig, 2~ a drill string, a hydraulic downhole drilling motor, and a 74 drill bit at the drilling end of the drill string;
7~ Figure 2 is an enlarged schematic view of the drilling 26 end of the drill string of Figure l;

~ -16-` 20703~2 l Figure 3 is an enlarged perspective view of a diamond 2 bearing pad from the thrust bearing assembly shown in s Figure 2;
~ Figure 4 is a cutaway view of one of the thrust bearings ; shown in the thrust bearing assembly in Figure 2:
Figure 5 is a cross-sectional view of a thrust bearing , incorporating the teachings of the present invention:
8 Figures 6-8 are schematic views illustrating the steps 9 of a method utilized according to the teachings of the present o invention to manufacture the thrust bearing of Figure 5;

11 and 12 Figure 9 illustrates an apparatus for performing the 13 steps of the method illustrated in Figures 6-8.

~
~E~AILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

16 Figure 5 is a cross section of a thrust bearing assembly 17 functioning in the same location as thrust bearing 18 assembly 2l, shown in Figure l, but incorporating the 19 teachings of the present invention. Two bearing pad zo retainers, a first bearing pad retainer 30a and a second 21 bearing pad retainer 30b, make up thrust bearing assembly 31.

22 In the preferred embodiment illustrated in Figure 5, bearing 23 pad retainers 30a, 30b are both annular. Bearing pad retainer 24 30b has a receiving surface 40 in which a plurality of bearing pad recesses 42 are formed. By way of example and not 26 limitation, diamond bearing pads 26 are equidistantly spaced ~ -17-from each other in receiving surface 40 of bearing pad retainer 30b in a circle concentric with bearing pad retainer 3Ob.
Bearing pad recess 4~ has a cross-sectional shape that ; is circular, like that of diamond bearing pad 26 which is held 6 therein. Diamond bearing pads 26 are spaced about bearing pad _ retainer 30 so that the distance between each of diamond 8 bearing pads 26 is less than the outside diameter of diamond 9 bearing pads 26. This spacing assures that two thrust lo bearings 30a, 30b will have a planar interface without depressions in which a ~iamond bearing pad 26 could become l2 caught. The spacing also provides egress for the drilling l3 fluid being pumped through downhole drilling motor 16. The l4 passagQ of drilling ~luid through the spaces between diamond l~; bearing pads 26 cools thrust bearing 3Oa.
16 Each of bearing pad recesses 42 comprise an insertion l7 chamber formed in receiving surface 40 of bearing pad l8 retainer 30b. Each of the plurality of diamond bearing l~ pads 26 has a dia~eter which is greater than the diameter of each of the plurality of bearing pad recesses 42. The 21 difference between the outside diameter of each of the 22 plurality of diamond bearing pads 26 and the inside diameter 23 of each of the bearing pad recesses 42 is in a tolerance range 24 from about 0.003 to about 0.0002 inches. The disparity in the diameters of bearing pad recesses 42 and diamond bearing 26 pads 26 creates an interference fit that enables bearing bad .

2070~52 l retainers 30a, 30b, to hold diamond bearing pads 26 in place 2 during drilling operations.
s ~o overcome the disparity in diameters, a device capable of generating high compressive force is used to press diamond , bearing pad 26 into bearing pad recess 42. To facilitate the 6 insertion of diamond bearing pad 26 into bearing pad recess 42, insertion end 46 of diamond bearing pad 26 is 8 beveled 47. Diamond bearing pads 26 are interference fitted 9 in groups of two or three at a time. An interference fit exceeding the larger limits of the tolerance range would 11 produce a strain that would accumulate in the remaining empty 12 bearing pad recesses 42 as each diamond bearing pad 26 was 13 interference fitted. This accumulated strain would result in 14 a bearing pad retainer 30 that was broken or severely stressed by insertion of the last diamond bearing pads 26.
16 A diamond bearing pad 26 which is interference fitted 17 with a tolerance below the smaller end of the range will 18 result in a bearing pad retainer 3Oa that cannot retain 19 diamond bearing pads 26 during drilling operations.
In the thrust bearing assembly illustra ed in Figure 5, 21 bearing pad retainer 30a is located with the re.ceiving 22 surface 40 thereof juxtaposed to receiving sur~ace 40 of 23 bearing pad retainer 30b. In this orientation, substantially 2~ planar bearing faces 34 of bearing pad retainer 30b are in direct contact wi~h the substantially planar bearing faces 34 26 of bearing pad retainer 30a in a predetermined bearing plane.

1 To more fully understand the orientation of substantially planar bearing faces 34 in thrust bearing assembly 21, Figure 5 illustrates a cross-section of thrust bearing assembly 21 showing the contact between opposing substantially planar bearing faces 34. This contzct occurs in a 6 predetermined common bearing plane 50. All of the plurality of diamond bearing pads 26 must have bearing faces 34 $ coincident with the predetermined bearing plane 50 if on-9 bottom and off-bottom thrusts are to be evenly distributed o over the entire thrust bearing 29.
I AB used herein, when referring to the substantially l2 planar bearing faces 34, the term "substantially planar" is l3 intended to include bearing faces which may exhibit a planar l~ face on only a portion of the exposed bearing face. Such bearing faces may include frustoconics and other geometric l6 shapes with a planar surface incorporated into one of their l7 faces. Such planar faces may be interrupted by grooves, 18 striations, or other indentations that do not protrude outward I9 from the planar face. Due to the unique nature of synthetic . .
diam~nds, juxtaposed diamond faces wear well in contact with 21 other synthetic diamonds. Because diamonds have a low 22 coefficient of friction and are able to bear on surfaces 23 composed of like materials, it is not necessary that diamond 24 bearing pads have the large planar surfaces necessary with other materials. One advantage deriving from the use of 26 diamond bearing faces is that the useful life of thrust bearings utilizing diamond bearing faces approximates the useful life of diamond drill bits. Concomitant replacement of both the drill bit and the thrust bearing results in a reduction in the downtime needed for maintenance and repair.
During drilling operations, thrust bearing assembly 21 6 is sub~ected to on-bottom and off-bottom thrusts in addition - to shoc~s from drill bit 15 as it encounters varying strata.

8 As pipe sections are added to drill string 18, and a~ downhole 9 components wear out, thrust bearing assembly 31 must bear lo alternating full on-bottom and off-bottom thrusts. These Il varying forces create an environment that causes diamond 12 bearing pad 26 to pivot within bearing pad recess 42 as l3 alternating thrusts are applied during the raising and l4 lowering of drill string 18.
I5 According to one aspect of the present invention, a 16 support means for maintaining substantially planar bearing l~ faces in a predetermined common bearing plane is provided 18 which is cold formed in the bottom of each of the plurality 19 of bearing pad recesses.
By way of example and not limitation, the support means 21 in the preferred embodiment comprises a malleable shim 52 22 located in the bottom of bearing pad recess 42 in a shim ~3 deformation end 54 thereof. Shim deformation end 54 is located in the bottom of bearing pad recess 42 contiguous with insertion chamber 44. A portion of malleable shim 52 is cold 26 formed in an overflow chamber 56 capable of accepting some of 20703~2 l malleable shim 52. It is important that overflcw chamber 56 2 be so sized as to be capable of remaining partially unfilled by malleable shim 52. Total filling of overflow chamber 52 ~ would re~ult in resistance to insertion of diamond bearing ; pad 26 and possibly prevent bearing face 34 from being pressed 6 coplanar with the predetermined common bearing plane 50.
As used herein, the term "cold pressed" indicate~ a 8 pressure applied to a malleable shim without heat that results 9 in no deformation of the malleable shim.
The term "cold formed" indicates a pressure applied to a malleable shim without heat that resultc in shim 12 deformation. For a shim to be cold formed, it must therefore 13 be cold pressed to a point of deformation at which time it 14 will b~ cold formed. The tarm cold formed includes cold 1i pressing. In the pre~erred embodiment illu~trated in 16 Figura 5, a malleable shim 52 is cold formed into a shim 17 deformation end 54 of bearing pad recess 42. To maintain 18 bearing faca 34 of diamond bearing pad 26 in coplanar 19 orientation with the predetermined common bearing plane 50 under the dynamic conditions of drilling, malleable shim 52 21 supports insertion end 36 of diamond bearing pad 26.
22 Malleable shim 52 is comprised of a material such as ~3 copper or aluminum that will resist the movements of diamond 24 bearing pad 26 and yet will not melt when exposed to tha heat generated by normal drilling conditions. By resisting the 26 movement of diamond bearing pad 26, the malleable shim acts as a spring to return diamond bearing pad 26 to a coplanar position in predetermined common bearing plane 50.
Malleable shim 52 may also be comprised of other ~ materials which provide sufficient resistance to plastic ; strain such as aluminum, brass, or silver. A material chosen 6 for a malleable shim must exhibit three characteristics to perform adequately. The material must have a lower elastic 8 modulus than bearing pad retaiher 30, sufficient elastic 9 strength to resist hardening, and must not melt at normal operational drilling temperatures.
First, an elastic modulus lower than bearing pad 12 retainer 30 is required so that as forces are exerted on 13 substantially planar bearing face 34, malleable shim 52 will 14 be tomporarily compressed, then rega$n its previous shape.
Because of the elastic character of the material chosen for 16 malleable shim 52, it can spring back and reorient 17 substantially planar bearing face 34 to a position coplanar 18 with predetermined bearing plane 50. If the modulus of 19 elasticity were higher than bearing pad retainer 30, bearing pad retainer 30 would be deflected before malleable shim 52 21 and would allow diamond bearing pad 26 to shift out of the 22 predetermined common bearing plane and remain in that ~73 position. It is therefore desirable to choose malleable 2~ shim 52 with a lower elastic modulus than bearing pad retainer 30 so that malleable shim 52 will deflect and absorb 26 ' shoaks bofor bearing pad retalner 30 does.

~ .

Second, the material chosen must have sufficient elastic strength to be able to resist work hardening after repeated strain. Some ~laterials with an appropridte modulus of elacticity may not have sufficient elastic strength to repeatedly be deflected and return to their original shape.
6 After repeated deflection, some materials lose their , elasticity and become work hardened.
8 Third, in addition to serving as a support for diamond 9 bearing pad 26, malleable shim 52 serves as a heat sink to remove from bearing pad 26 heat that is developed in therein ll from friction at bearing face 34. Very high heat in bearing 12 pad 26 will lead to premature failure of thrust bearings 29A
13 and 29B. It i8, therefore, important to choose a malleable 14 shim that has the highest heat conductivity possible to carry l~ away accumulating heat from diamond bearing pad 26.
16 Fourth, even though malleable shim 52 has a high heat 17 conductivity, the passage of heat through malleable shim 52 18 causes elevated temperatures within malleable shim 52. In 19 order for malleable shim 52 to continue to support bearing pad 26 under thi~ elevated temperature, malleable shim 52 must 21 also have a high thermal capacity. If malleable shim 52 does 72 not possess the necessary thermal capacity, it will melt under 23 the elevated temperatures of operation and will fail to 24 provide the reguired support for bearing pad 26.
To satisfy all of the requirements discussed above, a 26 malleable shim of copper approximately one eighth of an inch 207~352 ~hickness is used in the preferred embodiment of the present invention. It will be appreciated, however, that the four requirements set forth above are only by way of example and, ~ although desirable, are not all necessary to satisfy the ; teachings of the present invention.
6 The use of malleable shim 52 results in a thrust bearing that is capable of maintaining the substantially planar 8 bearing faces of the diamond bearing pads in the predetermined 9 bearing plane when the diamond bearing pads are being subjected to the dynamic stresses caused by on-botto~ and off-bottom thrusts.

12 An additional advantage deriving from the use of a cold t3 formed malleable shim is that the resulting bearing pad 14 retainer is free from heat induced stresses. The bearing pad retainer will not experience heat during the process, and so 16 has no possibility of altering the bearing face alignment ~7 during some cooling stage of manufacturing required of brazed 18 bearing pad retainers.
19 Figures 6,7,8, and 9 illustrate the steps of a method for manufacturing the thrust bearing illustrated in Figure 5.
21 Figure 6 illustrates the step of forming in a bearing pad 22 retainer a bearing pad recess. Bearing pad recess 42 is 23 located in receiving surface 40. Bearing pad recess 42 ~4 comprises insertion chamber 44, shim deformation end 54, and 2s overflow chamber 56. The three components of bearing pad ~6 recess 42 are formed in bearing pad retainer 30 with a drill.

1 After forming a plurality of bearing pad recesses 42, malleable shim 52 is introduced into insertion chamber 44.
Malleable shim 52 is disk-shaped and is so sized as to lay flat when placed in the bottom of insertion chamber 44.
Figure 7 depicts the step of placing malleable shim 52 6 into the bottom of bearing pad recess 42. Malleable shim 52 rests on shim deformation end 54 directly above overflow 8 chamber 56.
9 Figure 8 depicts the step of press fitting at ambient temperature each of the plurality of diamond bearinq pads 26 into a corresponding one of the plurality of insertion 12 chambers 44 of bearing pad recesses 42. Diamond bearing 13 pad 26 must be pressed into bearing pad recess 42 to attain 1~ the interference fit necessary to retain diamond bearing pad 26 in bearing pad retainer 30 during drilling operations.
16 The pressure used in pressing diamond bearing pad 26 into 17 bea~ing pad recess 42 must exceed the on-bottom and off-bottom 18 pressures that will be experienced during drilling operations.
19 Figure 9 illustrates the cold forming of malleable shim 52 into shim deformation end 54 and overflow chamber 56.
21 An inflexible pressing plate 60 presses some of the plurality 22 of diamond bearing pads 26 into their corresponding bearing 23 pad recesses 42 simultaneously. In the preferred embodiment of the present invention, three diamond bearing pads 26 are pressed simultaneously. Inflexible pressing plate 60 assures 20703~2 that the planar bearing faces 34 are coplanar with each other and with predetermined common bearing plane 50.
:~ Figure lO illustrates an apparatus for use in ~ manufacturing thrust bearing 29. A press table 62 supports .; bearing pad retainer 30 during pressing. A ram 64 applies 6 pressure to inflexible pressing plate 60. Between ram 64 and pressing plate 60 is a compensating shim 66. Compensating 8 shim 66 is capable of absorbing uneven pressure caused by 9 nonparallel orientation between ram 64 and pressing plate 60.
The pres~ illustrated in Figure lO has a locating means for limiting the travel of a pressing face 67 of pressing l2 plate 60 to a position wherein pressing face 67 is coplanar 13 with the predetermined common bearing plane. By way of 1~ example and not limitation, one example o~ a locating means 1~ is a press stop block 68. Press stop block 68 halts the 16 progress of pre~qing face 67 of pressing plate 60 at a point 17 wherein bearing face 34 of diamond bearing pad 26 is coplanar 18 with the predetermined common bearing plane 50.
19 It will be appreciated that the locating means of the present invention is not limited to a press stop block, but 2l may take the form of a beam that is broken by the passing of 22 the pressing face of the inflexible pressing plate, or an 23 electronic sensor that measures and limits the travel of the 2~ ram or the inflexible pressing plate at a point wherein the bearing face of the diamond bearing pad is coplanar with the 26 predetermined bearing plane.

' .

~ 2070352 The result of pressing the bearing faces of the diamond bearing pads coincident with the predetermined bearing plane is that the thrust bearing is not dependent on repeated drilling tool adjustment to achieve uniform recess depth and . planar alignment of the bearing faces. variations in recess 6 depth and tolerances will be accommodated as the diamond ~ earing pad deforms the malleable shim into the overflow 8 chamber. The inflexible presslng plate forces the diamond 9 bearing pad into the bearing pad recess to a point where the lo bearing face is coplanar with the predetermined bearing plane.
The present invention may be embodied in other specific 12 forms without departing from its spirit or essential 13 characteristics. The described embodiments are to be 14 considered in all respects only as illustrative and not restrictive. The scope o~ the invention is, therefore, l6 indicated by the appended claims rather than by the foregoing 17 description. All changes which come within the meaning and 18 range of equivalency of the claims are to be embraced within 19 their scope.

2~.

Claims

1. A diamond thrust bearing for use in downhole drilling operations, the thrust bearing including at least one bearing pad retainer and a plurality of diamond bearing pads projecting from a receiving surface of the at least one bearing pad retainer, each of the diamond bearing pads having an insertion end interference fitted into a corresponding bearing pad recess formed in the receiving surface and a bearing end projecting from the receiving surface and terminating in a substantially planar bearing face, the bearing face of each of the bearing pads being disposed in coplanar relationship in a predetermined bearing plane, the thrust bearing being characterized by:
a. a malleable shim having an upper surface and a lower surface and being disposed in the bottom of each of the bearing pad recesses, the upper surface supporting the insertion end of a corresponding one of the diamond bearing pads and the lower surface being cold formed in the bottom of the bearing pad recess; and b. the bearing pad retainer being free of heat-induced stress.

2. A diamond thrust bearing as recited in claim 1, further characterized in that the bearing faces of the bearing pads are cold pressed coplanar with the predetermined bearing plane.

3. A diamond thrust bearing as recited in either claim 1 or claim 2, wherein an overflow chamber is formed in the bottom of each of the bearing pad recesses, the overflow chamber being configured so as to be capable of receiving a portion of the malleable shim cold formed in the bottom of the bearing pad recess.

4. A diamond thrust bearing as recited in claim 3, wherein each of the overflow chambers is configured to provide volumetric capacity in excess of that needed to accept that portion of the malleable shim cold formed therein.

5. A diamond thrust bearing as recited in any one of claims 1-4, wherein each of the diamond bearing pads has an outside diameter greater than the inside diameter of each of the bearing pad recesses, thereby to produce and interference fit therebetween.

6. A diamond thrust bearing as recited in any one of claims 1-5, wherein the malleable shims are cold formed in the bottom of each bearing pad recess in a temperature range from about 125°C to about 0°C.

7. A diamond thrust bearing as recited in any one of claims 1-6, wherein the malleable shims are compressed of aluminum or brass.

8. A diamond thrust bearing as recited in any one of claims 1-7, wherein the bearing pad retainer comprises an annular plate with a substantially planar receiving surface.

9. A diamond thrust bearing as recited in any one of claims 1-8, wherein the plurality of bearing pad recesses are equidistantly spaced in the receiving surface of the bearing pad retainer in a circle concentric with the bearing pad retainer.

10. A method for manufacturing the diamond thrust bearing as recited in any one of claims 1-9.