CA1226274A - Shock absorbing tool for a well drilling string - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A shock absorbing tool for a well drilling string having a mandrel which connects to the well string, a telescoping barrel which connects to a rotary drilling bit and a fluid-filled annular chamber between the mandrel and the barrel enclosed at one end by a free-floating annular piston to maintain the chamber fluid pres-sure at ambient pressure, the chamber also containing a resilient shock absorbing element which is always placed under compression to dampen longitudinal movement of the mandrel and the barrel with respect to one another regardless of the direction of the longitu-dinal movement.

Description

~X26274.

This invention relates to drilling tools and is specific gaily concerned with a shock absorbing tool for cushioning the drill string against longitudinal movement caused by the drill bit.
In drilling a well the drill bit is constantly moving up and down. These movements if not eliminated result in shock loads being delivered to the drill string causing an excessive amount of wear on the equipment.
The industry, therefore, has developed shock tools or vi-rations dampers which are usually connected at the base of the lo drill string between the drill collar and the drill bit. The shock tool there absorbs a large portion of the vertical impacts caused by the drill bit which would otherwise be passed up the drill string.
Such a shock tool is disclosed in the Canadian patent to Mason and Anderson, 1,014,140, in which a mandrel is telescopically mount-Ed in a barrel with an annular chamber there between containing a resilient element, a series of elastomeric rings which absorb long-tudinal movements as they are compressed. To keep the resilient element from being reloaded by the high pressures at -the base of a well the annular chamber is filled with a fluid and has at one end a floating steel ring which compresses the fluid in response to the external well pressure while leaving the resilient element us-compressed. The structure is such that the resilient element is compressed only when the tool contracts on itself so as to tote-scope close. There is no means for preventing sudden extension of the tool except for the weight of the drill string bearing down on the mandrel. Also, no advantage is taken of the presence of the ambient pressure absorbing fluid to aid in dampening longitudinal movement.
A purpose of this invention therefore is to provide a drilling well shock absorbing tool which operates to dampen and absorb long-~2~7~

tudinal movements in two directions.
A purpose of this invention is to provide a drilling well shock absorbing tool which operates to place a resilient shock absorbing element under-increasing compression regardless of whether the tool is being extended or contracted.
A further purpose of this invention is to provide a drilling well shock absorbing tool which reduces bit bounce, extends bit life by reducing impact loads, and reduces shock loads on the drill string.
Another purpose of the invention is to provide in a drilling well shock absorbing tool having a fluid filled chamber and a pros-sure equalizing piston fluid flow regulator to assist in dampening longitudinal movement of the tool parts with a dash pot effect.
Another purpose of this invention is to combine in one struck lure, a resilient shock absorbing element which dampens longitude-net movement by being placed under compression and a dash pot mow lion dampening system.
Another purpose of this invention is to provide a means for keeping the barrel from slipping off the mandrel in the event of the breakdown of the tool.
The purposes of this invention are achieved by a well drilling shock absorbing tool comprising a barrel, a mandrel longitudinally movable within the barrel in a telescoping manner, an annular champ bier between the barrel and the mandrel, a resilient shock absorb-in element in the annular chamber, and means associated with the mandrel and the barrel for engaging and compressing the shock Abe sorbing element in response to longitudinal movement in either dip reaction of the mandrel and the barrel with respect to one another.
The engaging and compressing means may comprise two long-tudinally spaced members situated on the wall of the barrel within 22627~

the chamber and extending radially inward so as to radially over-lap the shock absorbing element and two longitudinally spaced mom-biers situated on the wall of the mandrel within the chamber and extending radially outward so as to radially overlap the shock absorbing element so that with longitudinal movement of the mandrel with respect to the barrel in either direction one of the barrel wall members and one of the mandrel wall members will move toward one another to compress the shock absorbing element there between.
The engaging and compressing means may comprise two long-tudinally spaced first and second members situated in the chamber which move with the mandrel relative to the barrel and extend ray dually outward to radially overlap the shock absorbing means. The shock absorbing means situated between the first and second members is divided into two portions separated by a member situated on the barrel wall and extending radially inward so as to radially over-lap the shock absorbing means whereby longitudinal movement of the barrel and the mandrel relative to one another in either direction will result in movement of the barrel wall member toward one of the first and second members resulting in compression of one of the shock absorbing means portions, dampening of the longitudinal movement and returning of the barrel and the mandrel to an equip librium position.
The shock absorbing tool may also include a fluid filling the annular chamber, a divider separating the annular chamber into two portions, a volume changing means for varying the volume of one of the chamber portions in relation to changes in relative long-tudinal position of the barrel and the mandrel and a mechanism providing unrestricted fluid flow in one direction through the champ bier divider as the barrel and the mandrel change relative long-tudinal position in one direction and for providing restricted fluid flow in the opposite direction through the chamber dividers the barrel and the mandrel change relative longitudinal posy lion in the other direction so as to provide a dash pot effect in that direction.
The invention will now be described by way of example only, reference being had to the accompanying drawings in which:
Figure l is a side elevation Al view partially in section showing a shock absorbing tool according to this invention;
Figure 2 is a sectional view taken along the line 2-2 of lo Figure l and viewed in the direction of the arrows;
Figure 3 is an enlarged fragmentary sectional view showing the chamber divider and valve structure which serves as a fluid flow regulator;
Figure 4 is an enlarged side elevation Al view partially in section showing a shock absorbing tool according to this invention.
with a modified shock absorbing mechanism;
Figure 5 is an enlarged side elevation Al view partially in section showing the use of splints in the structure of the invention;
Figure 6 is a sectional view taken along the line 6-6 of Figure 5 and viewed in the direction of the arrows;
Figures 7 through 12 are schematic drawings showing the shock absorbing tool of this invention in various stages of opera-lion;
Figure 13 is a front elevation Al view of a backup ring used to prevent shearing of the shock absorbing disc elements;
Figure 14 is a side elevation Al view of the backup ring of Figure 13;
Figure 15 is a sectional view taken along the line 15-15 of Figure 1 and viewed in the direction of the arrows; and ~LZ2~i~7~

Figure 16 is a sectional view taken along the line 16-16 of Figure 4 and viewed in the direction of the arrows.
Referring to Figure 1, a shock absorbing tool has a cylinder-eel barrel 12 in which a cylindrical mandrel 14 is mounted. The mandrel 14 and barrel 12 are longitudinally movable with respect to one another so that they co-operate in a telescoping manner.
The tool 10 will extend or open if the mandrel 14 moves out of the barrel 12 or if the barrel 12 moves off the mandrel 14. The tool 10 will contract or close if the mandrel 14 moves into the barrel 12 or if the barrel 12 moves onto the mandrel 14. Situated be-tweet the barrel 12 and the mandrel 14 is an annular chamber 16 which contains a hydraulic fluid such as an oil. The hydraulic fluid is added to the annular chamber 16 by means of fill ports 18, 20 and bleed port 22 which are closed off by lock screws when not in use.
The mandrel 14 has at one end thereof a box connection 24 for attachment to corresponding threads on a drill collar. The barrel 12 terminates in a bottom sub 26 which has threads 28 for attachment to the connection box on a bit.
Including the bottom sub 26, the barrel 12 is made up of four longitudinal sections having threaded interconnections.
At the opposite end of the barrel 12 from the bottom sub 26 is a seal sub 30 having at an adjacent one end, a series of annular recesses containing an annular wiper 32, an annular mud seal 34, and an annular oil seal 36, all of which serve to seal the annum far chamber 16 from drill- no mud about the tool 10 during long-tudinal movement of the mandrel 14 and barrel 12.
Also located in an annular recess of the seal sub 24 is a guide ring 38 having a special bearing surface. I t is important that the mandrel 14 be maintained in as near perfect vertical alignment with respect to the barrel 12 as possible to prevent lateral loads which could jam the barrel 12 and mandrel 14 so as to prevent free longitudinal movement or could cause lateral wobble in the tool 10 resulting in a badly aligned drill hole. The guide ring 38 along with the pressure equalizing annular piston 40 (to be discussed hereinafter) serve this purpose.
While the barrel 12 and mandrel 14 may move longitudinally relative to one another, it is necessary that they not be capable of relative rotation so that rotary motion may be imparted to the drill bit through the drill string. This function may be served by a drive key arrangement shown in Figures 1 and 2 or by the splint structure of Figure 5 and 6.
Referring to Figures 1 and 2, the mandrel 14 is formed from two longitudinal sections which have a threaded interconnection.
The upper mandrel 42 which terminates in the box connection 24 has two pairs of longitudinally extending shoulders 44, 46 and 48, 50 which define Casey in which are located drive keys 52. The drive keys 52 are situated in notches 54 in the drive key housing 56 which forms one of the longitudinal sections of the barrel 12.
These notches 54 are partially bounded by the end of the seal sub 30 and by means of these notches 54, the drive keys 52 are fixed in position relative to the barrel 12. Thus the barrel 12 and mandrel 14 are prevented from relative rotary movement while free to travel to and fro longitudinally with the drive keys 52 travel-lying in the Casey defined by the shoulders 44, 46, and 48,50.
The drive keys 52 are covered with a compressible, low friction, temperature resistant material on the sliding drive surfaces.
Also, while this discussion has been limited to two drive keys 52, the tool 10 can be designed with a different number of drive keys 52.

~;~2Çi27~

The Casey end at shoulder 58 and at stops 60. While not then of these end points are reached in normal operation, in the event of a breakdown of the tool 10 the stops 60 act to prevent the bar-net 12 from coming off the mandrel 14 as the drill string is lifted from the well. Before this can happen the drive keys 52 will engage the stop 60.
Referring to Figures 5 and 6 an alternative way to prevent relative rotary movement of the barrel 12 and mandrel 1~1 is shown in which an inter engaging splint arrangement is used. The upper 10 mandrel 42' has situated thereon a plurality of longitudinally extending male splints 62 which inter engage longitudinally extend-in female splints 64 projecting from a barrel splint housing 56'.
To permit free flow of the fluid contained in the chamber 16 through-out the chamber 16, the splints 62 are provided with fluid grooves 66.
Extending further into the barrel 12 from the upper mandrel 42 is a wash pipe 68 which completes the mandrel assembly. The mandrel 14 has a central conduit 70 for the flow of drilling mud there through. Situated about the wash pipe 68 is an annular mom-20 bier or chamber divider 72 which forms a part of the barrel Wylie and extends therefrom to divide the annular chamber 16 into two portions leaving only a small restricted annular flow path 74 for the chamber fluid between the two portions of the chamber 16.
The chamber divider 72 has situated therein, passing through the chamber divider 72, a plurality of conduits 76, connecting the two portions of the chamber 16. While twenty such conduits are shown, the tool 10 can work with any number of conduits 76 although at least one must be present. Each conduit 76 contains a one-way valve 78 so that unrestricted longitudinal flow of fluid through 30 the conduits 76 will be permitted in one direction but not in the ~2~2q4 other. Each one-way valve 78 is a spring-biased ball valve which, when no fluid is flowing, rests closed on seat 80 and is held in position by threaded plug 81.
Referring to Figure 1, positioned in annular chamber 16 is a resilient shock absorbing element 82 capable of absorbing shocks by undergoing compression and deformation and returning to its original form when the force is removed. Element 82 is a plurality of resilient annular discs which generally define a cry-finder in the annular chamber 16. Situated at each longitudinal end of the plurality of discs 82 is an annular backup ring 84 which acts to prevent longitudinal movements from shearing the annular discs 82 as will be explained hereinafter. In order not to hinder fluid flow about the plurality of discs 82, each backup ring 84 has a plurality of channels 86 there through as can be best seen in Figures 13 and 14. Other type shock absorbing elements 82 may be used. For instance, the element 82 may be a coil spring with end discs thereon equivalent to the backup rings 84 of the present embodiment.
The shock absorbing element 82 is positioned in annular no-cusses 88, 90 located in the walls of the barrel 12 and the man-drew 14 within the chamber 16. The recesses 88, 90 have the same longitudinal length and are generally opposed to one another. The longitudinal ends of the recesses 88, 90 define annular shoulders 92, 94, 96, 98. The mandrel annular shoulder 98 is formed by the addition of a stop nut 100 mounted about the wash pipe 68. The shock absorbing element 82 has radial dimensions such that it extends into the barrel and mandrel recesses 88, 90 and can be en-gaged by any of the four shoulders 92, 94, 96, 98.
The barrel shoulders 92, 94 constitute longitudinally spaced members situated on the wall of the barrel 12 which extend radially ;~26Z74 inward so as to radially overlap the shock absorbing element 82 while the mandrel shoulders 96, 98 constitute corresponding long-tudinally spaced members which extend outward to engage the shock absorbing element 82. These shoulders 92, 94, 96, 98 will act to engage and compress the shock absorbing element 82 in response to longitudinal movement in either direction of the barrel 12 and the mandrel 14 with respect to one another as will be more fully disk cussed hereinafter.
Situated at one end of the annular chamber 16 is a pressure 10 equalizing annular piston 40 which engages the opposing walls of the barrel 12 and the mandrel 14. As mentioned previously, the piston 40 functions as a guide to prevent lateral movement of the barrel 12 and the mandrel 14 with respect to one another. The pistons 40 also functions as a fluid tight chamber seal to prevent drilling mud from entering the annular chamber 16 and fluid from leaking out. For this purpose the piston 40 has annular recesses containing annular mud seals 102 and annular chamber fluid seals 104.
The piston 40 is, however, freely longitudinally movable with respect to the barrel 12 and the mandrel 14 and because of 20 this acts to maintain the fluid pressure within the annular champ bier 16 at the ambient pressure of the drilling mud. As the tool 10 is lowered into a well and the drill string is placed in opera-lion, the great pressures of the tool's environment will force the piston 40 inward on the chamber fluid thus maintaining an equivalent t pressure in the chamber 16. Without such a piston 40, the increased external pressures will act to partially or completely close or con-tract the tool 10 thus leaving a reduced amount or no longitudinal travel available for absorbing shocks. With the piston 40 the tool 10 is not therefore reloaded. The entire load range of the tool 30 10 is available to take out shock loads.

Located on the upper mandrel 42 it annular shoulder 58.
With long urinal movement of the barrel 12 and the mandrel 14 with respect to one another the barrel 12 will of then travel up Over or come off this shoulder 58 while the shoulder 58 blocks a corresponding movement by the fluid in the chamber 16. Thus, the effect of the shoulder 58 is to cause the chamber fluid to remain relatively stationary with respect to the barrel 12. The pressure equalizing piston 40 being caught between the balanced pressures of the chamber fluid and the drilling mud is thus con-strained to remain stationary with respect to the mandrel 14 or, to view it from the point of view of the barrel 12, to move to and fro with the mandrel 14 relative to the barrel 12.
While the fluid moves with the mandrel 14, the chamber dip voider 72 moves with the barrel 12. The effect of this is to cause fluid flow across the chamber divider 72 in relation to changes in relative longitudinal position of the barrel 12 and the mandrel 14. The shoulder 58 acts to change the volume of the portion of the chamber 16 on its side of the divider 72. However, the one-way valves 78 in the conduit 76 across the divider 72 will only open to permit unrestricted flow in one direction. Fluid flow in the opposite direction will cause them to close and limp t fluid flow to the restricted annular flow path 74 between the divider 72 and the wall of the mandrel 14. Thus, longitudinal movement of the barrel 12 and the mandrel 14 relative to one another close in or contracting the tool 10 will result in unrestricted fluid flow through the conduits 76 while longitudinal movement of the barrel 12 and the mandrel 14 relative to one another opening or extending the tool lo, will result in restricted fluid flow through the flow path 74 causing a dash pot effect dampening that longitu-dial movement. The divider 72 along with the other elements of 12Z~ 74 the structure make use of the fluid contained in the annular champ bier 16 to assist in dampening longitudinal movement. With the dip voider 72 system, longitudinal free play in the tool 10 is cut to a minimum.
Referring to Figures 7 through 10, it can be seen how the structure of the tool lo will work in both directions. The shock absorbing element 82 will be placed under compression to absorb longitudinal shocks regardless of which direction the tool 10 is displaced from equilibrium. Figure 9 represents the configure-lion of the tool lo after being placed in position at the base ova well. With the barrel 12 connected to the bit resting on the bottom and the mandrel 14 under the weight of the drill string the tool lo has contracted slightly with the shock absorbing element 82 being compressed by a mandrel shoulder 96 and a barrel shoulder 94. The shoulders 92 and 98 are spaced from the element 82. The valves 78 are closed as no fluid motion is occurring at the moment.
In Figure lo the tool lo is responding to a shock contracting it.
The shock absorbing element 82 is placed under greater compression by the one barrel shoulder 94 and the one mandrel shoulder 96.
Figure 7 depicts the return of the tool 10 to an equilibrium post-lion after being contracted. Although the element 82 is not at this point absorbing the motion, a dampening effect is provided on the longitudinal motion by the close of the valves 78. Figure 8 rep-resents the tool lo being subjected to an extension. In addition to the dash pot effect of the closed valves 78, the shock absorbing element 82 is still being engaged and placed under compression by one mandrel shoulder and one barrel shoulder moving toward one another to dampen the longitudinal movement and return tool lo to an equilibrium position. However! in this instance the mandrel shoulder 98 and the barrel shoulder 92 are acting rather than their ~Z262~

counterparts.
The backup rings 84 located at the ends of the shock absorb-in element 82 give the element 82 Cypriot prevent its being sheared since each end of the element 82 is compressed by only one shoulder of the mandrel 14 of barrel 12 never by both when the element 82 is under load.
Figure 4 shows a modified tool 104 in which a shock absorb-in element divided into two portions 106,108 is situated. This tool 104 also functions to engage and compress a shock absorbing element 106, 108 in response to longitudinal movement regardless of the direction of travel of the barrel 110 with respect to the mandrel 112. The tool 104 thus provides shock absorption in both directions.
The tool 104 is similar in structure to the tool 10 having a split retaining ring 114 in place of the chamber divider 72.
The split retaining ring 114 is an annular member mounted on the mandrel 112 and extends across the annular chamber 116 where it makes contact with the wall of the barrel 110 and acts as a bear-in surface to assist in preventing relative lateral movement of the mandrel 112 with respect to the barrel 110. The ring 114 is split having passages 118 to permit fluid flow past it. The ring 114 also has bronze bearing surfaces.
Longitudinally spaced from the ring 114 is a pressure equalizing piston 120 which as previously discussed moves with the mandrel 112 relative to the barrel 110 and thus is used as one member for engaging and compressing the shock absorbing eye-mint 106,108.
Situated on the wall of the barrel 110 between the ring 114 and the piston ]20 is an annular member 122 which extends radially inward to radially overlap the two portions 106, 108 i;226~74 of the shock absorbing element each of which is generally Solon-Dracula in form. The barrel annular member 122 also radially over-laps the ring 114 and the piston 120. The two shock absorbing eye-mint portions 106, 108 are each therefore longitudinally bounded by the barrel wall member 122 and a member 114, 120 which moves with the mandrel 112 relative to the barrel 110 and extends radial-lye otltward to overlap the shock absorbing element portion.
Thus, referring to Figures 11 and 12, with relative longitu-dial movement of the barrel 110 and the mandrel 112 closing or contracting the tool 104 the barrel wall member 122 and the ring 114 will move toward one another resulting in compression of the shock absorbing element portion 106, dampening of the longitudinal movement and returning of the barrel 110 and the mandrel 112 to their equilibrium position. Likewise with movement opening or ox-tending the tool 104 the barrel wall member 122 and the piston 120 will move toward one another thus compressing the shock absorbing element portion 108 there between to dampen that longitudinal mow lion.
While this invention has been described as having a preferred 20 design, it will be understood that it is capable of further modify-cation. This application is, therefore, intended to cover any variations, uses, or adaptations of the invention following the general principles thereof and including such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains, and as may be applied to the essential features herein before set forth and fall within 27 the scope of this invention or the limits of the claims.

Claims (24)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A shock absorbing tool for a well drilling string, comprising:
a barrel adapted to be connected to the well drilling string adjacent one end of said shock absorbing tool;
a mandrel longitudinally movable within said barrel in a telescoping manner and adapted to be connected to the well drilling string at the end of said shock absorbing tool opposite said end at which said barrel is connected to the well drilling string;
a sealed annular chamber between said barrel and said mandrel, said chamber containing a fluid;
a resilient shock absorbing means positioned in said chamber;
means associated with said mandrel and said barrel within said annular chamber for compressing at least a portion of said shock absorbing means in response to relative longi-tudinal movement of said barrel and said mandrel extending said tool and for compressing at least a portion of said shock ab-sorbing means in response to relative longitudinal movement of said barrel and said mandrel contracting said tools, said com-pressing means comprising two longitudinally spaced members situated on the wall of said barrel within said chamber, said barrel wall members extending radially inward so as to radially overlap said shock absorbing means, and, two longitudinally spaced members situated on the wall of said mandrel within said chamber, said mandrel wall members extending radially outward so as to radially overlap said shock absorbing means so that with longitudinal movement of said barrel and said mandrel with re-spect to one another in either direction one of said barrel wall members and one of said mandrel wall members will move toward one another and said shock absorbing means will be compressed there-between, wherein the wall of said barrel and the wall of said mandrel within said chamber each have an annular recess therein and said barrel wall members and said mandrel wall members are the annular shoulders at the longitudinal ends of said mandrel recess and said barrel recess, and, said resilient shock absorb-ing means is generally cylindrical in form and has radial dimensions such that it extends radially into said barrel and mandrel recesses whereby said shock absorbing means may be en-gaged by the annular shoulders of said mandrel recess and said barrel recess.

2. The shock absorbing tool of Claim 1, further including means for maintaining the pressure of said chamber fluid at the pressure of the well fluid.

3. The shock absorbing tool of Claim 2 wherein the chamber is divided into two portions, and further including means for changing the respective volumes of said chamber portions in relation to changes in relative longitudinal position of said barrel and said mandrel and for thereby causing fluid flow with respect to said chamber dividing means, said chamber dividing means acting to control the rate of fluid flow between said chamber portions.

4. The shock absorbing tool of Claim 3 wherein said chamber dividing means includes means for providing unrestricted fluid flow in one direction through said chamber dividing means as said barrel and said mandrel change relative longitudinal position in one direction and for providing restricted fluid flow in the opposite direction through said chamber dividing means as said barrel and said mandrel change relative longi-tudinal position in the other direction so as to provide a dashpot effect in that direction.

5. The shock absorbing tool of Claim 4 wherein:
said chamber portion volume changing means moves said fluid longitudinally with said mandrel whereby said fluid remains generally stationary with respect to said mandrel but moves with respect to said barrel; and, said chamber dividing means comprises an annular member on the wall of said barrel which extends radially across said annular chamber and engages the wall of said mandrel in such a manner as to permit restricted fluid flow between said annular member and the wall of said mandrel, said annular mem-ber including at least one conduit therein connecting said two portions of said annular chamber and a one way valve in each of said at least one conduit permitting longitudinal fluid flow in one direction between said two portions of said annular chamber but not in the other so that with the longitudinal movement of said barrel and said mandrel relative to one another in one direction said at least one valve will open thus permitting unrestricted fluid flow and with relative movement direction said at least one valve will close restrict-ing fluid flow to the space between said annular member and the wall of said mandrel thus achieving a dashpot effect.

6. The shock absorbing tool of Claim 5 wherein:
said pressure maintaining means is an annular member engaging the opposing walls of said barrel and said mandrel in a fluid tight manner but freely longitudinally movable with respect to said mandrel and said barrel; and, one of said first and second members of said com-pressing means is connected to said mandrel and the other of said first and second members is said pressure maintaining means.

7. A shock absorbing tool for a well drilling string, comprising:
a barrel adapted to be connected to the well drilling string adjacent one end of said shock absorbing tool;
a mandrel longitudinally movable within said barrel in a telescoping manner and adapted to be connected to the well drilling string at the end of said shock absorbing tool opposite said end at which said barrel is connected to the well drilling string;
a sealed annular chamber between said barrel and said chamber;
a resilient shock absorbing means positioned in said chamber;
the wall of said barrel and the wall of said mandrel within said chamber each having an annular recess therein limited by annular shoulders at the longitudinal ends of said mandrel recess and said barrel recess;
said resilient shock absorbing means being generally cylindrical in form and having radial dimensions such that it extends radially into said barrel and mandrel recesses whereby said shock absorbing means may be engaged by the annular shoulders of said mandrel recess and said barrel recess, whereby said shock absorbing means is adapted to be compressed by one axially opposed pair of shoulders on the mandrel and the barrel in response to relative longitudinal movement of said barrel and said mandrel extending said tool and to be compressed by the other axially opposed pair of shoulders in response to relative longitudinal movement of said barrel and said mandrel contracting said tool.

8. A shock absorbing tool as defined in Claim 7 wherein the resilient shock absorbing means is generally cylindrical in form and is unattached to either the barrel or the mandrel.

9. A shock absorbing tool as defined in Claim 8 wherein the shock absorbing means comprises a stack of discrete annular spring elements.

10. A shock absorber as defined in Claim 9, further including means to limit telescopic extension and contraction of said structure.

11. A shock absorber for bore hole drilling strings, comprising a telescopic structure including an outer tubular member, an inner tubular member within said outer member, said members having means for connecting said structure in a drilling string, whereby drilling fluid can be conducted through the drilling string and said inner and outer tubular members, rotary drive means for trans-mitting torque between said members while said members are moving axially with respect to each other, a single spring means between said outer and inner members, said outer member having longitudinally spaced upper and lower shoulders at opposite ends of said spring means, said inner member having longitudinally spaced upper and lower shoulders at opposite ends of said spring means, the upper shoulder of one member and the lower shoulder of the other member simultaneously engaging and stressing said spring means upon longitudinal contraction of said members with respect to each other, the upper shoulder of the other member and the lower shoulder of said one member simultaneously engaging and stressing said spring means upon extension of said members with respect to each other, said inner and outer members having transverse surfaces responsive to the pressure of the fluid flowing through said members which tends to extend said members relative to each other.

12. A shock absorber as defined in Claim 11, said single spring means being placed under compression in response to longitudinal contraction and extension of said members with respect to each other.

13. A shock absorber as defined in Claim 12, said spring means comprising an assembly of coengageable frustoconical parts.

14. A shock absorber as defined in Claim 11, said inner member extending longitudinally in one direction beyond one end of said outer member and terminating within said outer member, means beyond one end of said spring means providing a first seal between an outer periphery of said inner member and the inner wall of said outer member, means beyond the other end of said spring means providing a second seal between the outer periphery of said inner member and the inner wall of said outer member, and means for conducting a lubricating fluid into an annular space between said inner and outer members and extending from said first seal to said second seal.

15. A shock absorber as defined in Claim 14, said rotary drive means being located in said annular space.

16. A shock absorber as defined in Claim 14, said second seal comprising a compensating piston slidably sealingly engaged with the outer periphery of said inner member and the inner wall of said outer member.

17. A shock absorber as defined in Claim 16, said inner and outer members having transverse surfaces responsive to the pressure of the drilling fluid flowing through said members which tends to extend said members relative to each other.

18. A shock absorber as defined in Claim 11, said inner member extending upwardly beyond the upper end of said outer member and having its lower terminus within said out-er member, means above said spring means and upper shoulders providing a seal between an outer periphery of said inner member and the inner wall of said outer member, compensating piston means below said spring means and lower shoulders slidably sealingly engaged with an outer periphery of said inner member and the inner wall of said outer member, and means for conducting a lubricating fluid into the annular space between said inner and outer members and extending from said first seal means to said piston means.

19. A shock absorber as defined in Claim 18, said seal means being located above said rotary drive means.

20. A shock absorber as defined in Claim 11, said spring means comprising an assembly of coengageable frustoconical parts, said inner member extending longitudinally in one direction beyond one end of said outer member and terminating within said outer member, means beyond one end of said spring means providing a first seal between the outer periphery of said inner member and the inner wall of said outer member, means beyond the other end of said spring means providing a second seal between the outer periphery of said inner member and the inner wall of said outer member, and means for conducting a lubricating fluid into an annular space between said inner and outer members and extending from said first seal to said second seal.

21. A shock absorber as defined in Claim 20, said rotary drive means being located in said annular space.

22. A shock absorber as defined in Claim 18, said spring means comprising an assembly of coengageable frustoconical parts.

23. A shock absorber as defined in Claim 22, said rotary drive means being located in said annular space.

24. A shock absorber as defined in Claim 23, said inner and outer members having transverse surfaces responsive to the pressure of the drilling fluid flowing through said members which tends to extend said members relative to each other.