CA1037464A - Drilling string shock-absorbing tool - Google Patents

Abstract

"DRILLING STRING SHOCK-ABSORBING TOOL"

ABSTRACT OF THE DISCLOSURE
A shock absorbing tool is provided having a low spring rate deformable element disposed in an oil bath in a sealed, annular chamber formed between the barrel and mandrel. The deformable element comprises an annular stack of alternating rigid washers and deformable rings. The washers are operative to prevent the deformable rings from bridging the walls of the mandrel and barrel, which bridging would transmit shock load between them. Thus the stack of rings function as a long unit to absorb the axial movement of the mandrel originating from the action of the bit on bottom.
One of the chamber seals is a floating seal, exposed to the drilling fluid outside the tool so that the pressure within the chamber is equalized with the hydrostatic bottom hole pressure. As a result, the tool is not pre-loaded, when lowered to the bottom of the well bore, leaving the most effective shock-absorbing capability of the element available to absorb the axial thrusts of the drilling bit.

Description

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FIELD ~F THE INVENTION
Thi~ patent application is a division of co-pending patent application Serial t~o. 204,532 filed July 10, 1974.
- 5 This invention relates to a tool for use in a drilling string. More particularly, it relates to a tool having utility for absorbing shock loading arising from axial displacement of the bit during drill~ng operations.

BACKGROUND OF THE INVENTION
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When a drilling bit is rotating on the bottom of a well bore, it is constantly bouncing up and down.
col~nonly accepted explanation for this action :is that the three-cone bit Ponns three lobes on the bottom of the well bore - as the bit moves over -these lobes, it is axially dis-placed three times during each rotation.
Acceleration of the bit off bottom causes high loading of the drilling string. More particularly, the bit has a load on it arising from the weight of the drilling string.
For exemple, the string might weigh 120,000 pounds, of which ' .~
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60,000 pounds mlght be held suspended by the rig; the remaining 60,000 pounds would bear on the bit~ When the loaded bit is accelerated off bottom through a travel of perhaps 1/2 inch to 1 inch, the esst:ntially rigid drilling string above the bit i5 subjected to a very hi~h shock load, which is immediately relieved as the bit begins to return to bottom. By way of example, this cyclic loading on the drilling string may vary between 0 and 100,000 pounds or more from one moment to the nextO
There are several deleterious effects which arise from ~he severe cyclic loading to which the drilling string is subjected. ~or example, it is a pr;rne ~actor in the weax and ailure o the clrill;ng striny It also punishes the rig; in particularly rough drilling, the whole rig structure i 15 is shaken violently and the only course of action available to relieve the vibration is to reduce the rotational speed of and/or weight on the bit. This causes a reduction in the drilling rate~
It has long been common in the industry to insert a tool, known as a vibration damper or shock absorber, in the drilling string above the bit with the aim of isolating the :~ string from the bit.
In general, a typical vibration damper would compxise an inner, tubular mandrel, attached at its upper end to the drilling string r and an outer, tubular barrel attached at its lower end to the bit, or the collars which are directly above the bit. The mandrel slides or telescopes within the barrel. The two parts are connected by means, such as a spline assembly, so that they are locked for rotation together but can move longitudinally r~lative to each other~ Means are also provided to limit the extent o~ longitudinal movement of the parts so that they c~nnot separate one from the other.

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In one basic type of tool, a portion of the mandrel is reduced in outside diameter so that an annular chamber i5 formed between the mandrel and barrel. O~ring seals are provided betwcen the mandrel and barrel at each end of the chamber to prevent drilling mud from entering therein. The mandrel and barrel carry opposed upper and lower compression shoulders respectively; these shoulders extend transversely into the annular chamber adjacent its upper and lower ends. A deform-able element is provided within the chamber between the io compression shoulders.
In opera~lon, when the bit is accelerated upwardly the barrel compre~ssion sl~oulder acts ayainst ~hc base oE the deformable elernent. 'l'he element is prevented from moving axially by the mandrel cornpression shoulder located at its other end. As the shoulders sgueeze together, the element is deformed. In theory, the deformable element should absorb the axial thrust of the bit and prevent the shock load from being transmitted to the drilling string~ In practise, this is usually not the case, fsr reasons which will now be dis-cussed.
The prior art tool5 can be divided into three types.
In the first type, the O-ring seals are fixed in the wall of the barrel at each end of the def~rmable elemenk chamber. As a result, the well bore hydrostatic pressure acting on the tool forces the barrel upwardly against the deormable element with a force e~ual to said pressure times the difference in cross-sectional area of the two seals. To try to cope with this "pre-loading" action which takes place when the tool is in the well bore but before drilling commences, ~t is conventional to use a "hard" deformable element in the ~hamber. By a hard element is meant an element having a spring a ~

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rate o~ at least 100lOOO ~ounds/inch, usually in the ord~r of 150,000 - 250~000 pounds/inch, where the spring rate is described as the load re~uire~ to deflect the tool an inch. In these prior art tools, the tool may telescope 3/4 inches with a load of 100,000 pounds, hut will telescope less than 1/4 inch with the next 100,000 pounds. In eff2ct, the tool becomes extremely hard or rigid as the load increases. According to our calcula-tions, in deep wells the deformable element in this type of tool will have lost any shock absor~ing capability it had by the time that the tool lS at total depth, even before drilling commences. For example, if one were to consider a 12,000 foot deep well bore containing a tool having a differential in seal area of 30 inches, the upward thrust on the barrel created by the hydrosta~ic pressurc could be in the ord~r of 300,000 pounds.
In this circumstance, the de~ormable element would essentially be rigid and ineffective since the tool would have collapsed through most of its stroke. It is evident that in these tools, an element that is relatively soft at the surface would be extremely hard at operating depth due to the very high "pre-load" that it would carry~
- The second type of tool is disclosed in Canadian patent 837,970, issued to Faulkner. In this tool, a floating seal is provided at the base o~ the deformable elemen~ chamber to equalize the pressure internal of the chamber with the bottom hole hydrostatic pressure. However, Faulkner teaches combining this feature with compressible, metal wire elements which are hard elements to begin with and which rapidly pack in use and form virtually non-deformable elements having little shock-absorbing capability. The element taught by Faulkner also has the disadvantage that it is in contact with both of the walls of the chamber, thus tending to prevent axial movement of the telescoping tool parts, as the element packs in the chambex, and to transmit axial load between the tubular parts along the length Of the portion of the element which is bridging.

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The thixd type o~ ~ool attempts to provide a re~atively "soft" element in the chamber, i~e. one having ~ low spring rate, and couples it with means for equalizin~ the pressure within the chamber with the well bore pressure This tool is described in Canadian patent 826529, issued to Galle.
It involves providing a sealed zone, filled at surface with co~npressible gas at a pre-determined pressure, in the chamber.
The chamber is fillea with operating oil and a membrane is provided to segregate the gas fxom the operating oil. A bag, or membrane, open to the welq bore, extends into the oil-filled section of the chamber~ ~he chamber is sealed at each end with fixed O-ring seals Expansion of the bag with the well kore fluid pressurizes the oil and, in turn, the shock-absorbing, compressible yas. However, the pressure and thus the spring rate of the gas body must be varied significantly as the tool i5 used at different depths. Pu~lished reports show that at a depth of 16,000 f~et and a bit weight of 80,000 pounds, the spring rate of this device is about 140,000 pounds per inch, while at a depth of 3,000 feet at the same bit weight, the spring rate is about 60,000 pounds per inch. Therefore at the deeper depth~ this tool has a l'hard" element with a high spring rate, while at the shallow depth~ the element can be classed as being moderate3y soft with a moderate spring rate.
A characteristic of most shock absorhing elements whîch rely on deformation of a material to absorb shock is that the spring rate of the element increases as the load on the - element is increased~ In other words, with l~w loading on an element, the element is much softer than with high loading.
The graph illustrated in Figure 15shows the deflection-load chaxacteristics in curve form or three elements A, B, and C.
As is evident from the graph, the spring rate of the elements (i.e. the slope of ~he curve) varies continuously as the load S

on the element changes. Cons~quently, we must xefer to the spring rate as being an average ~igure for a certain amoun~ of deflection. We describe the spring rate as the load required to deflect the tool one inch.
Element A of the graph can be classified as being hard, having a spring rate for its first inch o~ travel of about 300,000 pounds per inch. If, at operating depth, the element was pre-loaded, (operatiny point X on the graph), with 3000,000 pounds as described earlier, it is evident that t~e element would be extremely hard.
Element B o~ the graph can be classi~ied as being moderate, having a spring rate of 55,000 pounds per inch for its first inch of travel. If at operating depth, the element was pre-loaded (operating point X on the yraph~ to 300,000 pounds, it is evident that the element would be cxtx~m~ly hard, i.e.
it would take an enormous load to ~urther de~orm the element.
If at operating dept~, the element was only pre-loaded to 30,000 pounds (operating point Y on the graph), then the element would be moderately so~t, having a spring rate of about 60,000 pounds per -inch. It could be further deformed, with a relati~ely s~ll load~
Element C of the graph can be classi~ied as being so~t, having a spring rate of 75,000 pounds per inch ~or its ~irst inch o travel. At operating point X on the graph, the spring rate would be very high and the element would be extremely hard. However, at operating point Y, the element would have a spring rate of about 20,000 pounds per inch.

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SUMMARY OF TH~ INVENTION
In order to provide a shock absorbing drilling tool whose deformable element remains capable of significant t deformation at various well bore depths and bit weights and pump pressureS, it is necessary to provide a soft defoxmable element, i.e. one with a low spring rate, in combination with a tool assembly adapted, when subjected to well bore hydrostatic pressure, to ensure low "pre-loading7' of the deformable element.
The latter may be attained in the following manner: the mandrel and barrel are formed to pro~ide a chamber therebetween, said chamber containing the deformable element and a body of operating liquid. The chamber is sealed at each of its ends. Means are provided to e~ualize the pressure within the chamber with the bottom hole pressure internal o~ the tool, and thereby reduce or elirninate pre-loading. One such means comprises providing a "floatingl' seal assembly, exposed .o the well bore fluid, at one end of the chamber to pressurize the chamber contents.
The deformable element means is adapted to permit of a relatively large amount of telescoping action by the tool.
More particularly, the element means chosen must have a relatively low spring rate,-that is its spring rate should be less than 100,000 pounds per inch. In a preferred embodiment, the element means is adapted, when operational in the tool, to permit at least two inches of telescoping movement by the tool when the latter is loaded with 80,000 pounds. It is assumed that the tool assembly will be designed to permit at least two inches of tool travel to occur - however the tool could be designed to have a lesser travel before its telescoping parts contact to limit further movement. For example, the tool travel could be limited to 1 1~2 inches; however, the type of . .

element means used should meet the criteria that it is capable of permitting at least two inches ~f tool tra~el with 80,000 pounds load. What we are trying to say here is that the desired qualities ~f the deformable element means in the con-text of this invention are conveniently determined when the element means is operating within the environment of the tool chamber. These characteristics of the element means are de-fined in the claims in terms of the capability of the element means when operative in the tool, i.e. in terms of its capabil-ity for permitting a minimum tool travel ttwo inches) at a particular tool loading (80,000 pounds). However, we do not ¦~
intend that the claims be interpreted to require that the tool must have the capability of closing at least two inches, al~
though this is desirable - as stated, a tool loaded with the desired t~pe of elemen~ means but having a stroke less th~n two inches would be operable and have many of the advantages of the invention. The element means should also be (1) of substantial length, (2) solid, resilient and deformable, and (3) out of contact with the adjacent moving barrel or mandrel side wall.

2~ A typical length might be in the order of 40 inches. The element means prefera~ly consists of a stack of annular segments comprising, in alternating sequence, non-deformable steel rings and deormable elastomer rings; Each steel ring pre~erably has ribs, upstanding from its inner and outer ed~es, which form a recess in which the elastomer ring which it supports seats. The annular segments preferably each have an inner diameter greater than the outside diameter of the adjacent portion of the mandrel and an outside diameter less than the insi~e diameter of the adjacent portion of the barrel.
The steel rings distribute the load to the elastomer rings and the xibs function to limit outward ~ .

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deformation of ~he elastomeric material. This arrangement ic operativë to prevent the elastomeric material from cGntacting 'I
the chamber walls as deformation and resulti~g bulging of the elastomeric segments occurs. It has been found that if the elastomer segments are allowed to contact the moving chamber wall during operation of the tool, rapid des-tructiOn of the elastomer occurs in the area of contact.
Also, the characteristics ~f the tool are changed due to the friction generated by the elastomer contact with the moving surface of the chamber walls. Finally, by having the element segments so that they do not bridge the chamber walls, one obtains a deformable element means whlch experiences substantially~
the total axial shock load throughout its length.
Other conigurations o elemenk segments can, of course, be used. Alternative embodiments are described below.
A problem which sometimes arises with drilling string shock absorbin~ tools is that, when they are used in a drilling string above the bit, they cause the well bore being drilled to deviate from the vertical. This problem may be caused by a lack of lateral rigidity of the tool as a result of the telescoping elements not performing as an integral unit. We refer to t~is as lack of sta~ility; it results in the portion of the tool attached to the bit moving one way while the portion of the tool attached to the drill collars moves another way.
In a preferred feature of the invention, we have provided in our tool a high degree of stability by providing ef~ective contact between the mandrel and barrel at three bear-ing locations spaced along the length o~ the tool. At eachof these locations, the internal bearing surface of the barrel 9 "'".

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co-acts with a mating bearing surface on the mandrel to pr~vide a close fit therewith. The first barrel bearing surface is positioned above the spline means; the second is positioned between the element chamber and the spline means; and the third is positioned immediately below the element chamberD Optimum stability is obtained by providing an interference fit between the mandrel and barrel at the bearing locations. Preferably, the combination of a clearance of about .002 inches between the steel surfaces and the provision o~ a hard e~astomeric ring in one of the surfaces is used to create the necessary liquid-tight fit. This arrangement is effecti~e to minimize dif~er-ential lateral movement between the telescoping members at the ~earing locations. In the tool, passage means are provided in or between the telescoping parts when required to allow the operating fluid to bypass the liqu~d~tight it of the elastomeric ring. These grooves may be sized to be restrictive, so that the operating fluid flowing back and forth tends to dampen the telescoping movement. It will be noted that the stabilizing ring can be formed of othex materials, such as phosphor bronze or berillium copper, to substantially prevent differential lateral movement. The passage means may be grooves, flutes or bores~
A further problem which is inherent in drill string shock absorbing tools relates to the rotary locking mechanism, which is normally a male and female interlocking spline system. The spline systems in prior art tools are fo~d to wear rapidl~ as a result of the continuouS relative motion between the driving surfaces. These surfaces are subjected to relative sliding motions in the order of 10,000 to 20,000 times per hbur~ It is found that the conventional steel splines of prior art devices rapidly wear out, even when operating in an oil environment and when e~periencing relatively small differential movement.

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In the present to~l, due to the relati~ely large telescoping mov~ment allowe~ for, and in order to reduce the rapid wearin~ o~ the splines as experienced in prior art t devices, we haYe found it desirable to provide a novel spline 5 system. This pre~erred system is comprised, in one embodiment, of rotary, interlocking, telescopically related male and female splines, in which the female ~pline is provided with a re-latively hard, abrasion-resistant, elastomeric material on its driving and backlash surfaces and in its spline roots 10 and crests. In the elastomeric driving surfaces of the female spline, oil pockets and grooves are provided to ensure lub-rication of the mating male and female spline suraces as they ~ove relative to each other. Other arrangements of the novel spline system could provide the same function, such as pro-15 ~iding the elastomeric dxiving and backlash suraces on the male portion of the spline unit~ Also, 1utes are provided in the roots of the male spline to allow free movement of the operating li~uid.
A tool is therefore provided which incorporates 20 the following combination of features: (1) a relatively long defoxmable element means is provided which has a low spring rate and is substantially out of contact with the moving side wall of the chambex when the tool is in use; and (2) this element means is housed in a sealed chamber containing a bath 25 of operating oil and means are proviaed in -the tool to equalize the pressure in the chamber with the bottom hole pxessure internal of the tool, i.e. in its axial boxe. When these features are included, a tool characterized by a relatively long stroke can be constructed to provide a desirable degree 30 of shock load absorption at various drilling depths. In pxeferred embodime~ts, the elastomer rings are formed of material which permits at least two inches of telscoping tool movement with an axial load of 80,000 pounds and no~ more than two inches of tool movement with a load of 10,000 po~nds.
In addition, metal rings or segments are provided in the stack which are adapted to restrain the deformable segments from contactiny the walls of the tool chamber when the tool is in use.
Because the pressure in the chamber is equalized with the hydrostatic bottom hole pressure, no significant pre-loading of the deformable element se~ments takes place. The full range o~ de~ormability of the stack is there~ore available to cope with and absoxb the bit-in~uced axial movement of the barrel. Since the greakest amount O~ deormation inherent in the de~o~nable segments is available in khe 0 - 40l000 pound load range, the tool i8 able to absorb most if not all the axial moveme~t o~ the barrel before the stack sti~fens to a sub-stantially rigid condition, with t~e result that the drill string is protected from large shock loads.
Broadly stated, the invention is a tool for use in ~ drill string util~zin~ drilling ~luid to drill a well bore, s~id tool having utility for absorbing shock loading arising ~rom axial movement o~ the drilling bit, which tool comprises.
telescopically ~rr~nged tubular parts comprisin~ an outer barxel and an inner mandrel received in the b~xrel, said parts forlning an annular space between them which i~cludes a de~ormable element chamber, said parts being movable lon~itudin-ally relative to each other; means at the outer ends o~ the parts for threadably connecting them into the drill string; means carried by the parts ~or limitin~ their relative longitudinal movement; said parts comprising means connecting them so that they rotate together but may move lon~itudinally relative to each other; solid resilient deformable element means disposed ~3~
in the chamber and extending substantially thxou~hout its length, said el~ment means having a spring rate o~ less than 100,000 pounds per inch and being substantially out of contact with the adjacent barrel or mandrel side wall which is movable by the axial mo~ement of the drilling bit, whereby said element means, in use, experiences throu~hout its length substantially the total axial load; a pair of opposed compression means, one such means being carried by the mandrel and extending into the chamber adjacent one end thereo~, the other such means being carried by the barrel and extending into the chamber adjacent the other end thereof, said compression means being operative to act against the ends of the element means; a body of operat-ing liquid disposed in the space together with the element means;
seal means disposed in the space above and below the chan~er for seaiin~ that portion of the space between s~id seal means against the entry of well bore drilling fluid thereinto; and means for pre'ssurizin~ the operating liquid to substantially equalize it with the bottom hole pressure 1nternal of the tool~
DES~CRIPTION ~F THE DRAWING
Figures la, lb and lc are views of three parts in ele~ation o~ one embodiment of the drilling string vibration d~mper according to t~e present in~ention in its unloadPd or extended condition;
Figures 2a, 2b and 2c are views in elevation simi-lar to ~igure 1 of the damper in a compressed or loaded condition;
Figure 3a is a view in elevation o~ the lower portion of another embodiment o~ the drill string vibration damper in the unloaded condikion.
Fi~ure 4a is a view in elevation of the lower por-tion o~ still another embodiment o~ the drill string vibration - 12 a -~3~
damper in the unloaded condition;
Figure 4b is a view in elevation of.the 1:
embodiment of Fi~ure 4a in the loaded condition;
Figure 5 is a view in cross section along line 5--5 of Figure 2a;
Figure 6 is a view in cross section along line G--6 of Figure 2b;
Figure 7 is a view in cross section along line 7--7 of Figure 2b;
Figure 8 is a view in cross section along line 8--8 of Figure 2c;
Figure 9 is a pl~n view of one type of deformable element used in the damper of the present invention;
Figure 10 is a view in section along line 10 -- 10 of Figure 9;
Figure 11 is a plan view of another type of deEormable element;
Figure 12 is a view in section along line 12--12 of Figure 11; ' Figure 13 is a plan view of still another type of deformable element;
Fiyure 14 is a ~iew in section along line 14--14 of Figure 13; and ..
Figure 15 is a graph showing the spring rate characteristics of "soft", "moderate" and ''hard" deformable elements.
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DES~RIPTI~N-OF ~HE PREFERRED EMBODI~NT
According to the present invention, the improved drilling string vibration damper comprises a telescoping mandrel and barrel having a de~ormable element means acting therebetween.
~he deformable element means is adapted to provide low spring ' 1~

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rate shock absorption- The mandrel and barrel combine to form between th~n a plurality of interconnected chambers or an annular space having portions of different thicknesses, ~illed with a body of rela~ively non-compressible operating liquid. The chambers are interconnected by annular zones of small tolerance form~d by close fitting bearing suraces. These bearing surfaces provide axial stability between the mandrel and barrel. The bearing surfaces are preferably provided with passageways for movement of fluid from one chamber to another.
'line mandrel and barrel are sealed together at each end of the cha~ber system by liquid tight seal means therebetween, with one end being provided with a movable seal el~nent to prevent well bore fluid entering the chamber system and to pressuri~e the operating liquid therein to equalize it with the bottom hole pressure lnternal of the tool.

Referring to the Figures, in ~igure 1 is shown an e~nbodiment of the present invention having a tubular barrel generally :identified by reference numeral 10 and a tubular man-drel identified as 12. The mandrel 12 is received within and is movable with respect to the barrel 10. The upper end of the mandrel 12 is in the form of a male spline memher 13 which isprovided with a ~ox connection l4 o~ suitable tool-joint design to connect to the drilling string (not shown). Below the box connection 14 i5 a section 16 of reduced diameter and below this is a length of male splines 18 cut into the surface of the mandrel. The splines 18 are chrome plated and finished to close tolerance. Below the splines 18 is a smaller diameter portion 20 having a close tolerance, chrome-plated sur~ace having a plurality of flutes or grooves 22 cut into the sur~ace thereof, said flutes extending along the roots of the male spline. As shown, the grooves 2~ are l~near and parallel to one another, although other configurations may be used. At the lower end .. ~ . .

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of the spline m~ber 13 is a pin connection 24. Down the s center of the spline member 13 is a rentral b~re 25 for carrying drilling mud thr~ugh t~e tool to the drilling bit~ not shown. ' -The next lower portion of the mandrel 12 is the wash pipe 26, the upper end of which is provided with a box connection 28 adapted to mate with the pin connection 24 of the male spline member 13. The wash pipe 26 has a reduced diameter portion 32 below the box connection 28, and together they form a compression sh~ulder 27. The box connection , ' 28, is provided with an O-ring 30 to seal with the pin con-nection 24 of the male spline member 13. The box connection 28 is spaced from the barrel 10 to provide an annular passaye 31.
The shoulder 27 is provided wi ~ radially extending grooves 110, all for a purpose to be explained.
' The reduced diameter portion 32 of the wash pipe 26 has threads 34 at its lower end threadably receiving nut 36, The reduced diameter portion 32 is of a size to be received in and support a plurality of alternating non-deform-dble and deformable rings 38 making up the deformable element means 40. The surface of the reduced diameter portion 32 is also provided with linear flutes or grooves 37 for a purpose to be explained. The reduced diameter portion 32 is also pro-vided with a central bore 33, in communication with b~re 25, for carrying drilling mud to the tool bit.
The barrel 10 comprises at the upper end thexeo~
a seal cap 42 having an axial bore extending therethrough. Part o the inner surface of the seal cap 42 provides a ~irst bearing surface 42a which closely fits a matiny bearing sur-face 16a on the male spline member 13. ~Je provide a tolerance of about .002 inches. The first bearing surface ~2a'forms four circum~erential grooves 45 in which are seated liquid-3L~

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sealing rings 45a, a hard stabilizing ring 45b, and a sweeper ring 45c. The male spline member portion 16 has an interference fit in the stabilizing rings 45b- The seal cap 42 pro~ides a liquid-tight seal with the chrome portion 16 o the male spline member and stabilizeS the barrel 10 on the ~andrel 12. The lower end of the seal cap 42 is provided with a pin connection 46 which mates with a box connection 48 on the upper end of the emale spline barrel section 50. P.n O-ring 52 seals the threaded connection.
The female spline barrel section 50 has an internal bore 54 having female splines 56 cut into the sur~ace thereof. The splines 56 are sized to mesh with the male splines 18 o the male spline member 13.
As show~n in Figure 5, the female splines 56 are pre~erably provided with a steel core 56a onto which i5 moulded a synthetic coating layer 58 possessing superior wear and abrasion resistance~ and which ofers a cushioning ef~ect to the torsional meshing of the splines. A suitable coating Iayer 58 is formed of a molybdenum disulphide-filled urethane composition having a shore "D" har~ness of 50. The material is applied to provide a ~uarter inch thick layer 60 on the leading (i.e. driving) edges of the splines and an eighth inch thick layer 62 on the trailing (backlash) edyes - see Figure 5.

The spline assembly provides means connecting the barrel and mandrel so that they rotate together but may move longitudinally relative to each other.

The lower end o the emale spline barrel section 50 is provided with a pin connection 6~ carrying an O-ring 65 to provide a seal. The lower portion 66 of the bore 54 is o reduced diame~er orming a shoulder 68 delineating a second seal and bearing surace 68a. The second beariny ~;

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~3'746~ -surface 68a has a close fit with the mating bearing surface 66a of the lower end portion 66 of the male spline member 130 Several stabilizer rings 67 are provided in portion 66 to provide stabilization.
The pin connection 64 of the barrel section 50 is seen to mate with a box connection 70 on the upper end of the deformable element barrel section 72. An inner bore 74 is provided in the barrel section 72. The bore 74 extends nearly to the lower end of the barrel section 73, where a bore 76 of reduced diameter is provided to form a compression shoulder 77 .
The bore 76 is of a size to receive the lower end of the wash pipe 32 in a journalled and stab~lizing relation within th~ i bearing surface 76a. Otherwise stated, the barrel section 72 has a third bearing sur~Eace 72a which cooperates with a matin~
bearing suxface on the wash p;pe 32 to pro~ide a close fit.
Stabil~zer rings 78 are mounted in grooves, cut into the wall of the barrel section 72, to provide a liquid-tight interference' fit about the mandrel 12.

The lower end of the barrel section 72 terminates in a pin connection 80, which mates with a box connection 82 formed in the upper en~ of the pressure ring sub 84. An O~ring 86 is provided in the pin connection 80 to seal the threaded ConneCtiQn.
The pressure ring sub 84 is provided with a ~5 chromed, axial bore 88 of a diameter larger than the lower end of the wash pipe 26. Floating sleeve 90 is slidably mounted on the lower end of wash pipe 32 and carries internal and external O-rin~ seals 92, 94 for providing a liquid-tight seal with the surface of bore 88 of the pressure ring sub 84 and the exterior sur~ace of the reduced diameter portion 32 o:E
the wash pipe 26. The annular sleeve 90 is retained on the ~7 ~ ~, ~D3~
wash pipe 26 by means of nut 36. The lower end of the pressure ring sub 84 is provided with a pin connection 96 for connection back intO the lower end of the drilling string, not shown. The b~re 88 has a reduced diameter portion 98 in the lower part of the pressure ring sub 84, for a purpose to be explained.
A port 97 is provided in the wall of the de-formable element barrel section 72. The port 97 is closed by plug 99, which may be removed to permit the insertion of hydraulic fluid or the like into the interior of the tool, as will be explained. A similar port 101 and plug 103 are pxo-vided in the upper end of the female spline barrel section 50.
Referring now to Fi~ure 5, a groove 22 is pro-vided longitudinally in the land of every second spline, as also seen in Figure 6. Also shown in Figure 6 are oil passage grooves 108 across the pin 64 of the female spline. Referr.ing to ~igure 7, the grooves 110 are shown across the shoulder 27 of the box connection 28 of wash pipe 26. It will be seen that the rings 45 between the spline member section 16 and the seal cap 42 form one stabil:izer pair. The rings 67 20 between spline barrel section 50 and male spline section 13 form another stabilizer pair. The rings 78 between the lower end of the barrel section 7~ and the wash pipe 26 form a third stabilizing zone, while the seal sleeve 90 provides still another stabilizer between the pressure ring sub 84 and the 25 lower end of the wash pipe 26. All of these stabilizing structures tend to tie the barrel 10 and mandrel together laterally and stiffen the tool~
An annular space 107a is defined between the outer surface of the mandrel 12 and the inner surface of the 30 barrel 10. The ends of this space 107a are closed by the liquid tight seals 45, 92, 99; The stabilizer rings 67 , 78 :l8 ~}; .

7~4 sub-divide the annular space 107a into an internal spline chamber 107, deformable element chamber 109, and floating seal chamber 111, respectively. The space 107a is filled with the stack of element units 38 ~which comprise def~rmable element S segments 114 and non-deformable element seyments 100) and operating fluid. The fluid can move freely between chambers 107 and 109 via grooves 22, 108 and 31 and between chambers 109 and 111 via annular passage 31 and grooves 110 and 37.

Figures 9 and 10 illustrate one foxm that the element units 38 may take, in plane and section. The element unit 38 of Figure 9 comprises a metal washer 100, having a pair of upstanding ribs 102 and 104 de~ining an annular recess 112 therebetween. A solid, resilient, deormable annular elastomer ring 114, having a thickness greater than the upstanding 15 dimension of ribs 102 and 10~, is positioned within the recess 112. The elastomer ring 114 de~orms under pressure, but being resilient!resumes its original shape when the pressure is relieved. The metal washer 100 i9 the non-deformable segment of the element or stack; the elastomer ring 114 is the de-f~rmable segment. ~en assemblea in alternating fashion they ----form a sDlid resilient deormable stack. Ho~ever, the inclusion of the metal washers is only a preferred feature. The essential reature is having a stack of deformable sesments, saia stack being characterized by the necessary spring rate, each segment being arranged so that it is out of contact with ~he chamber walls and thus experiences substantially the total axial load delivered by the ~it when the tool is working.
The element units 3 of Figures 11 and 1~ are each seen to comprise a flat metal washer 116 to which is attach-ed by suitable means an annular ring 118 of elastomer having a cross section of a trapezoid with the major base contacting the metal washer 116.
l9 ~ :.

~3~6~
The deformable segments of Fiyures 13 and 14 are seen to comprise the metal washers 120 and 121, each washer having an outer rib 122 and an inner rib 126, respecti~e-ly, de~ining annular recesses 130 and 132. An annular ring 1~4 of an elastomer is positioned in each recess and sandwiched between adjacent washers. The side sur~aces 136 of the elastomer rings 134 are of concave shape, to facllitate seating and retention within the recesses of the washers.
The design of each of these deformable segments is such that at low loads, de~lection of the tool is higher than it is at high loads. The performance characteristics of the deformable element preferably falls within the shaded band shown in Figure 15.
Xt is contemplated that elastomers other than urethane, such as rubber, silicone rubber and neoprene, may be used in the de~ormable element ~eans. It is also contemplated that a hard non-metallic washer may be used instead of metal washers. It will be seen in Figure lb that the shoulder of the box connection Z8 on the mandrel 1~ contacts the shoulder of the barxel pin 64 to limit the upward movement of the mandrel and prevent them coming apart; Similarly, the shoulder of the mandrel box 13 cont~cts the top of the seal cap 42 t~ limit the do-~nward movement of the mandrel into the barrel.
In operating the tool, the pin connection 96 on the pressure ring sub 84 is screwed into the drill bit while the box connection 14 o~ the male spline 16 is screwed into th0 collars or stabilizers on the bottom of the drilling string.
The tool is designed to operate under conditions encountered in the drilling industry in shallo-.. or deep wells and in rough or smooth drilling. For example, when the damper is used directly above the bit in a deep hole in a rough drilling application, under the ~ollowing conditions, ~3~
hydrostatic head = 10,000 psi pressure drop across bit = 1,000 p5i bit weight = 55,000 total string weight =105,000 pounds vertical bit motion = - 1/2 inch rotary speed = 60 rpm i i it will operate as follows.
The fully extended tool is lowered into the well bore on the drilling string, until the bit is on bottom. The internal pressure within the annular space 107a equalizes with the 10,000 psi pressure at the bottom o the well bore, arising from the head of fluid standing therein, as said bottom hole pressure biases the 10a~ing sleeve 90 upwardly~ ~eight is then set on the bit, therehy loadiny the toul. The element segments 38 are de~ormed by the compression shoulders 27, 77 as the mandrel 12 and barrel 10 telescope together. The rig's mud pump is then kicked in, increasing the pressure internal of the drilling string at the tool by ltO00 psi. When this occurs, the load on the element segments 38 is reduced due to the pressure, attributable to the pump, ~cting against th~
cross sectional area of the wash pipe 26 and the male spline member 13. This pressure will tend to pump the tool open - in the typical case where the area is 30 square inches, the pump-apart force will amount to 30,000 pounds for the example conditions which we have choosen hereinabove. Thus the load on the element segments will be xecluced from 55,000 pounds to 25,000 pounds, althouc;h the bit is still loaded with 55,000 pounds.
The drill string is then caused to rotate. As rotation occurs and the bit moves ~ertically perhaps plus or 2:1 ~ ~

minuS 1/2 inch about a meAian point ~t a frequency of 3 cps, the deformable elemen~ means 40 is compressed and expanded 1/2 inch (~or a total movement of one inch) at hat ~requency.
~lore particularly~ the urethane rings 114 are deformed, ~orcing operating liauid through the flu~es 37l in the wash pipe re-duced diameter section 32, into the floating seal chamber 111, thereby downwardly biasing the ~loating sleeve 90. Since ~he spring rate of the element means 40 at this loading is pre~er-ably about 20,000 pounds/inch, the load on the element means 40 during these deflections will vary between 15,000 and 35,000 pounds. The net effect is that the bit load will vary from about 45,000 to 65,000. As the tool compresses and expands, the operating oil is pumped back and forth be-tween the chambers, thus absorbing energy. ^
rrhe desiyn of the vibration damper of this invention is such as to: (1) provide equalization o~ the pressure within the de~ormable element chamber with the bottom hole pressure internal of the tool, to reduce the problem of pre-loading; (2~ pre~erab~ly provide a differential seal area, 2D so that the rig's pump pressure, as reflected at the tool, operates to pump the mandrel and barrel apart, thereby pre-serving the most flexi~le portions o~ the tool stroke for the absorption of the axial thrusts of the bit; (3) provide a "soft" deformable elementr pre~erably having spring rate characteristic such that the tool will telescope at least two inches when loaded with 80,000 pounds, and not more than two inches when loaded with la,000 pounds, to ensure that the greatest part o~ the cyclic loading arising from the drill bit movement is ta~en up b~- the tool; (4) preferably provide stabilization o~ the tool in an efort to minimize hole deviation; (5) provide deormable segments which are spaced 2~

6~
from khe moving walls of the element chamber a sufficient distance to permit deformation of the urethane rings to occur without contact with the walls; (6) preferably provide damping of the telescopic movements by arranging for the operating oil to have to pass back and forth across the liquid-tight bearing zones through restricted flutes ha~ing a pre-selected cross-sectional area; and (7) preferably provide an improved spline assembly adapted to cope with the relatively longer stxoke and high requency telescoping of the tool.
Referring now to ~igures 3a and 3b, there is shown another embodiment wherein the configuration of the lower end of the wash pipe 26 and the pressure ring sub 84 is modified. It will be noted that the bore 88 of the pressure ring sub 84 connects to,a bore 140 of intermediate diameter of a size to receive the xeduced diameter portion 32 of wash pipe 26 in close fit relation~ A pair of seals 142 are provided at the upper end of bore 140.l One or more openings 144 are provided through the side walls of pressure ring sub 84 to communicate the outside thereof with the lower portion of bore 88. The threads 34 and nut on the lower end o~ the wash pipe 26 are eliminated an~ the reduced diameter portion 32 is provided with an extension 146 to be received within the bore 140 and to be lapped by seals 142 in the unloaded condition.
Figure 3b shows the damper under loaded condition In this Z5 configuration, the pressure sleeve 90 is subjected to well bore pressure rather than internal string pressure. The result of this configuration is that fluid in the inner chambers of the damper is maintained at well bore pressure, consequently the differential pressure across the bit acts only on the cross sectional area of wash pipe extension 146. Thus the force pumping the damper open is significantly reduced over that ~L~93~
necessary with the embodl~ent of Figures 1 and 2 while main-taining the pressure e~ualization feature. This configuration is particularly use~ul in large diameter tools used in shallow holes where bit weight may not be substantially greater than the force generated by differential pressure on the pressure ring area.
Figures ~a and 4b show a damper configuration absent the pressure sleeve 90 and grooves 37 and does not allow for equalization of internal and external pressures. In this configuration the damper is underfilled with fluid and is particularly use~ul in large diametex shallow holes. Additional stabilization is obtained by the use of stabilizer rings 7~ ¦
both above and below seals 79.
In the emboaimen~ of Fiyures 1 and 2 it has been shown how the floatîng 51eeve 90 e~ualizes the 1uid pressure in the internal chambers with th~ mud pressure.
Further it has been shown that the differential pressure across the drill bit acts on the floating sleeve 90 and mandrel to pump the damper open with a force equal to the differential pressure times the area enclosed by the outside diameter of the pressure seal ring.
As may occur in some cases, the area enclosed by the outside diameter of the pressure sleeve tLmes the differential pressure may be in excess of the loAd to be carried on the bit~ In this case the damper would remain pumped open and would not function as intended. In such case, tlhe pressure sleeve is not permittec~ to float. This is accomplished by placing an elastomer spacer 146, shown dotted, between the pressure sleeve and the pin 80 of the deformable element barrel section 7~. In addition, the damper is only partially filled with fluid~ I'hus, the hydrostatic pressure holds the pressure sleeve against the spacer 196, while the 2~ ' wash pipe moveS axially thro,u ~ ~e seals on 9~ the inside diameter of the pressure sleeve 90. The result is that no pres-sure equalization is present in the annular chamber of the dampc~r which results in the hydrostatic head pumping the damper closed.
The differential pressure'across the bit, however, acts on the area of the mandrel 32 attempting to pump the tool open. Thus the damper according to this invention can be'modified for use in shallow holes simply by adding the spacer 146 and under-filling the internal cha'mber.

Obvious variations in the specific constructional details described may be made without departing from the spirit of the invention and such embodiments of the invention as come within the scope and purview of the appended claims are to be considered as part of t~is inventionl 2~

Claims (16)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A tool for use in a drill string utilizing drilling fluid to drill a well bore, said tool having utility for absorbing shock loading arising from axial movement of the drilling bit, said tool comprising:
telescopically arranged tubular parts comprising an outer barrel and an inner mandrel received in the barrel, said parts forming an annular space between them which includes a deformable element chamber, said parts being movable longi-tudinally relative to each other;
means at the outer ends of the parts for thread-ably connecting them into the drill string;
means carried by the parts for limiting their relative longitudinal movement;
said parts comprising means connecting them so that they rotate together but may move longitudinally relative to each other;
solid resilient deformable element means dis-posed in the chamber and extending substantially throughout its length, said element means having a spring rate of less than 100,000 pounds per inch and being substantially out of contact with the adjacent barrel or mandrel side wall which is movable by the axial movement of the drilling bit, whereby said element means, in use, experiences throughout its length substantially the total axial load;
a pair of opposed compression means, one such means being carried by the mandrel and extending into the chamber adjacent one end thereof, the other such means being carried by the barrel and extending into the chamber adjacent the other end thereof, said compression means being operative to act against the ends of the element means;
a body of operating liquid disposed in the space together with the element means;
seal means disposed in the space above and below the chamber for sealing that portion of the space between said seal means against the entry of well bore drilling fluid thereinto; and means for pressurizing the operating liquid to substantially equalize it with the bottom hole pressure internal of the tool.

2. The tool as set forth in claim 1 wherein:
the element means is adapted to permit at least two inches of telscoping tool movement when the tool is axially loaded with 80,000 pounds and not more than two inches of telescoping tool movement when axially loaded with 10,000 pounds.

3. The tool as set forth in claim 1 wherein:
the deformable elements are substantially non-metallic.

4. The tool as set forth in claim 2 wherein:
the element means comprises a stack of alternating deformable elastomer segments and non-deformable metal segments.

5. The tool as set forth in claim 4 wherein:
each non-deformable segment has ribs, upstanding from its inner and outer edges, for restraining the deformable segment which it supports out of contact with the adjacent barrel and mandrel side walls.

6. The tool as set forth in claim 5 wherein:
each non-deformable segment is annular and has an inner diameter greater than the outside diameter of the adjacent portion of the mandrel and an outer diameter less than the inside diameter of the adjacent portion of the barrel.

7. A tool for use in a drill string utilizing drilling fluid to drill a well bore, said tool having utility for absorbing shock loading arising from axial movement of the drilling bit, said tool comprising:
telescopically arranged tubular parts comprising an outer barrel and an inner mandrel received in the barrel, said parts forming an annular space between them which includes a deformable element chamber, said parts being movable longitu-dinally relative to each other;
means at the outer ends of the parts for thread-ably connecting them into the drill string;
means carried by the parts for limiting their relative longitudinal movement;
said parts comprising means connecting them so that they rotate together but may move longitudinally relative to each other;
solid resilient deformable element means dis-posed in the chamber and extending substantially throughout its length, said element means having a spring rate of less than 100,000 pounds per inch and being substantially out of contact with the adjacent barrel or mandrel side wall which is movable by the axial movement of the drilling bit, whereby said element means, in use, experiences throughout its length substantially the total axial load;
a pair of opposed compression means, one such means being carried by the mandrel and extending into the chamber adjacent one end thereof, the other such means being carried by the barrel and extending into the chamber adjacent the other end thereof, said compression means being operative to act against the ends of the element means;

a body of operating liquid disposed in the space together with the element means;
one or more fixed seal means carried by at least one of the parts and spaced above the chamber, for sealing that portion of the space below said seal means against the entry of well bore drilling fluid thereinto;
and a floating sleeve carrying one or more seal means, positioned on the mandrel and spaced below the chamber, for sealing that portion of the space above said sleeve against the entry of well bore drilling fluid thereinto and for pres-surizing the operating liquid to substantially equalize it with the bottom hole pressure internal of the tool.

8. The tool as set forth in claim 7 wherein:
the element means is adapted to permit at least two inches of telescoping tool movement when the tool is axially loaded with 80,000 pounds and not more than two inches of telescoping tool movement when axially loaded with 10,000 pounds.

9. The tool as set forth in claim 8 wherein:
the element means comprises a stack of alternating deformable elastomer segments and non-deformable metal segments.

10. The tool as set forth in claim 9 wherein:
each non-deformable segment has ribs, upstanding from its inner and outer edges, for restraining the deformable segment which is supports out of contact with the adjacent barrel and mandrel side walls.

11. The tool as set forth in claim 10 wherein:
each non-deformable segment is annular and has an inner diameter greater than the outside diameter of the adjacent portion of the mandrel and an outer diameter less than the inside diameter of the adjacent portion of the barrel.

12. A tool for use in a drill string utilizing drilling fluid to drill a well bore, said tool having utility for absorbing shock loading arising from axial movement of the drilling bit, said tool comprising:
telescopically arranged tubular parts comprising an outer barrel and an inner mandrel received in the barrel, said parts forming an annular space between them which includes a deformable element chamber, said parts being movable longi-tudinally relative to each other;
the barrel having first, second and third bear-ing surfaces spaced longitudinally therealong, each bearing surface co-acting with a mating bearing surface on the mandrel to provide a close fit therewith;
means at the outer ends of the parts for thread-ably connecting them into the drill string;
means carried by the parts for limiting their relative longitudinal movement;
said parts comprising spline means connecting them so that they rotate together but may move longitudinally relative to each other;
solid resilient deformable element means dis -posed in the chamber and extending substantially throughout its length, said element means having a spring rate of less than 100,000 pounds per inch and being substantially out of contact with the adjacent barrel or mandrel side wall which is movable by the axial movement of the drilling bit, whereby said element means, in use, experiences throughout its length substantially the total axial load;
a pair of opposed compression means, one such means being carried by the mandrel and extending into the chamber adjacent one end thereof, the other such means being carried by the barrel and extending into the chamber adjacent the other end thereof, the other such means being carried by the barrel and extending into the chamber adjacent the other end thereof, said compression means being operative to act against the ends of the element means;
a body of operating liquid disposed in the space together with the element means;
said spline means being positioned above the chamber in spaced relationship therewith;
said first bearing surface being positioned above the spline means and the second bearing surface being postioned between the spline means and the chamber;
one or more fixed seal means, carried by at least one of the parts at the first bearing surface, for sealing that portion of the space below the seal means against the entry of well bore drilling fluid thereinto;
the third bearing surface being positioned below the chamber; and a floating sleeve carrying one or more seal means, positioned on the mandrel below the third bearing surface, for sealing that portion of the space above the sleeve against the entry of well bore drilling fluid thereinto and for pressurizing the operating liquid to substantially equalize it with the bottom hole pressure internal of the tool.

13. The tool as set forth in claim 12 wherein:
the element means is adapted to permit at least two inches of telescoping tool movement when the tool is axially loaded with 80,000 pounds and not more than two inches of telescoping tool movement when axially loaded with 10,000 pounds.

14. The tool as set forth in claim 13 wherein:

the element means comprises a stack of alternating deformable elastomer segments and non-deformable metal segments, each deformable segment being supported by a non-deformable segment.

15. The tool as set forth in claim 14 wherein:
each non-deformable segment has ribs, upstanding from its inner and outer edges, for restraining the deformable segment which it supports out of contact with the adjacent barrel and mandrel side walls.

16. The tool as set forth in claim 15 wherein:
each non-deformable segment is annular and has an inner diameter greater than the outside diameter of the adjacent portion of the mandrel and an outer diameter less than the inside diameter of the adjacent portion of the barrel.