US3685599A

US3685599A - Mechanical jar

Info

Publication number: US3685599A
Application number: US82284A
Authority: US
Inventors: James W Kisling
Original assignee: Schlumberger Technology Corp
Current assignee: Schlumberger Technology Corp
Priority date: 1970-10-20
Filing date: 1970-10-20
Publication date: 1972-08-22
Anticipated expiration: 1989-08-22
Also published as: CA961845A; JPS543801B1; BR7107027D0; FR2111713A1; FR2111713B1

Abstract

An illustrative embodiment in accordance with the present invention in jars includes a mandrel and housing which are telescopically disposed and adapted for connection in a pipe string, said mandrel and housing having spaced impact surfaces which can be brought together to deliver a jarring blow, an expansible sleeve member having threads meshed with threads on said mandrel, cam surfaces on said threads for expanding said sleeve member and releasing said threads from mesh with one another, means released by longitudinal relative movement between said housing and said sleeve member for locking said sleeve member in threaded engagement with said mandrel; and a resilient column structure coacting between said housing and said sleeve member for yieldably resisting longitudinal relative movement so that a force of a predetermined magnitude can be applied to said housing before said threads are permitted to release.

Description

United States Patent- Kisling, III

54 MECHANICAL JAR [72] Inventor: JamesW, Kisling IlI, Houston,

Tex. 73 Assignee: Schlumberger Technology Corporation, New York, NY.

22 Filed: Oct. 20, 1970 21 Appl.No.: 82,284

[52 us. c1 ..175/304,175/302 [58] FieldofSearch ..175/293,298, 300, 302, 303, 175/304, 299-, 166/178 [56] References Cited UNITED STATES PATENTS 2,008,765 7/1935 McCullough ..175/304x 2,016,607 10/1935 McCullough ..175/302 2,059,540 11/1936 Stephan ..175/304x 2,618,466 11/1952 Bagnelletal ..175/298 2,618,467 11/1952 Bagnelletal ..175/298 2,621,025 12/1952 Denning ..175/304 2,978,048 4/1961 Walker ..175/299x 3,050,131 8/1962 Siracusa ..175/303x 45 Aug. 22, 1972 Primary Examiner-David H. Brown Attorney-Emest R. Archambeau, Jr., Stewart F. Moore, David L. Moseley, Edward M. Roney and William R. Sherman [57] ABSTRACT An illustrative embodiment in accordance with the .present invention in jars includes a mandrel and housing which are telescopically disposed and adapted for connection in a pipe string, said mandrel and housing having spaced impact surfaces which can be brought together to deliver a jarring blow, an expansible sleeve member having threads meshed with threads on said mandrel, cam surfaces on said threads for expanding said sleeve member and releasing said threads from mesh with one another, means released by longitudinal relative movement between said housing and said sleeve member for locking said sleeve member in threaded engagement with said mandrel; and a resilient column structure coacting between said housing and said sleeve member for yieldably resisting longitudinal relative movement so that a force of a predetermined magnitude can be applied to said housing before said threads are permitted to release.

13 Claim, 7 Drawing Figures Patented Aug. 22, 1972 3,685,599

3 Sheets-Sheet 1 F G. 7. I

33 2 i i I x P i E 32 i I3- 1 E w s I A l James W Kisling,1F INVENTOR A HORNE Y Patented Aug. 22, 1972 Ja mes W KislingJZT :5 Sheets-Sheet z FIG.2B

Fl INVENTOR BY Xflud/flA 7 ATTORNEY Patented Aug.. 22, 1972 3,685,599

5 Sheets-Sheet 5 James w. KislingJH INVENTOR ATTORNEY 1 MECHANICALJAR This invention relates generally to well jars used to extricate stuck objects from well bores, and more specifically to a new and improved mechanical jar hav- 1 ing a tripping or release mechanism that is constructed Y and arranged to be wear resistant during long" con- I tinued usage. A

When drilling boreholes through earth 7 formations where sticking'is a problem, mostdrillers will tuna jar in the drill string. A jar is a device having telescoping members with spaced apart impact surfaces which can be brought together in a violent manner in order to deliver a jarring blow to 'a stuck tool with the hope of freeing it. The jar includes a tripping mechanism that functions to prevent telescoping motion" until a predetermined release force has been applied to the drill string, the force causing the drill string to' stretch and store energy. When. the tripping mechanism releases, the drill string contracts and causes the jar to hit and deliver a considerable impact force to the stuck tools. Usually, the jar must be operated many times before the stuck tools are driven free, and in fact circumstances requiring many hours of continuous jarring are not uncommon. a

A number of the problems associated with prior art.

itself 'due to excessive stress and loading applied to the" parts thereof. In any event, because of the environmental in which a jar mustfunction, such devices must be extremely rugged in order to remain operational.

One object of the present. invention is to provide a new and improved well jar apparatus having-a tripping or release mechanism which is. adapted to be extremely rugged and wear resistant. v

Another object of the present invention is to provide a new and. improved jar apparatus havinga' substantially constant and predictable release force for an extended period of time of use. These and other objects are attained with the concepts of the present invention by a jar apparatus comprising telescopically disposed mandrel I and housing members adapted for connection in a drill however expansion is prevented by locking surfaces on the sleeve member and the housing, the locking surfaces being releasable by longitudinalmovement of the housing along the sleeve member. The use of threads as above mentioned provides a new and improved structure which distributes applied. loads over a considerable drilled throughearthformationsbyusing conventional. rotary drilling techniques. A drill bit l liis attached to the lower end of'a drill string which normally-includes a in accordance nermost element and the outermost element placesalconnection with the following detaileddes'criptionjof 3 an'embodiment taken'in conjunction withthe aplength of area to maintain compression stresses withinacceptable limits, thereby keeping wear on thetripping mechanism to a minimum and providing a jar having a substantially constant release force over an extended period oftimeofuse. I

In order to enable'energy tobe stored in the drill stringby stretching" it before the tripping mechanism releases, a resilient structure isdisposed in opposition to the longitudinal movement required to disengage the lockingsurfaces on the housing and'the sleeve member..

In accordance with fa preferred embodiment 'of the present invention, the resilient structure, includes a plurality of concentrically disposed tubular elements having altemate opposite ends coupled to one another in such a manner that oppositely disposed force on the internate elements in compression and tension."llius the composite structure is in the. nature of a short "column having aver y high modulus of elasticity, the one or more "elements that" arein tension also providinga degree of lateral'support to prevent buckling of those elements having compression loading.

The present invention has other objects, features and advantages which will become more clearly apparent in pended drawings in which:

I FIG. -l'is a somewhat schematic viewjof a drill string and jar in a borehole;

nos. 2A-2C are longitudinal sectional at of the tripp' g mechanism and"associated structure in ac-' cordance with the present invention; r V

FIG. 3 is an isometric view of the tripping sleeve; FIG. 4 is a cross-section on line 4-4 of FIG. 2B; and

. no. 5 is a longitudinal half-section view'to illustrate keying system used inthetripping further detail of the mechanism..,

Referring initially to FIG. 1, aboreholelfl is being selectively, coupled at various locations in the drill I string, but is preferably located at a point'between the uppermost drill collar andthe drill pipe Under certain borehole conditions,such as soft orv highly permeable formations, particularly when encountered in v deviated wells, there is therisk that the bit and/or the drill collars may become stuck. When such sticking 'occurs for any reason, the jar 13 can be operated to free I the stuck tools. I The jar l3 includesv a tubular housing 29 that is telescopically disposed over a tubular mandrel 21, the

ward movement causing one hammer provided-by an anvil" provided by an outwardly, extending shoulder housing having a threaded box portion 22 and the mandrel 21 having a similar portion 23 for coupling the jar in the drill string; The mandrel 21 has'a central bore 24' which continues the drilling fluid circulation path throughthefdrill string. The housing 20 is movable to I some extent in both longitudinal directions along the mandrel 21 from 'a central or cocked" position, up-

inwardly extending shoulder surface 25 to strike an until the stuckv tools are driven loose.

.26 on the mandrel, downward movement causing another hammer surface 27 to strike a second anvil surface 28. vThus the jar" 13 is adapted to hit in. both directions, upward and downward. The impact force in either direction is transmitted bythe mandrel 21 to the longitudinal movement required beforedisengagement can occur. The release grooves 48 have inclined wall v

surfaces

49 and 50 in order to provide an. inward camming action in the presence of longitudinal force stuck tools therebelow. The housing and the mandrel 21 have coengaging splines 29 for transmitting rotation .through the jar during drilling operations. A seal packing 30 prevents drilling fluids from entering in between'the housing 20 and mandrel 21 at their lower ends, whereas a floating or compensating seal packing unit 31 is used to prevent fluids from entering at their upper ends. The vacant spaces between the housing 20 and the mandrel 21 can be filled a typical lubricatingoilorthelike. v

A tripping mechanism indicated generally at 32 is disposed in between upper and lower resilient structures 33 and 34' and functions to restrainlongitudinal' movement of the housing 20 in either direction from the cocked or intermediate position to enable energy to be stored in the drill string before the jar hits so that a blow of considerable magnitude can be struck. Once the tripping mechanism 32 releases however, movement of the housing 20 along the mandrel 21 is unrestricted as the, hammers approa'chthe respective anvils. After a blow is struck,the housing 20 i's mov'ed by.

the drill pipe 14 in the opposite direction, and the tripping'mechanism 32 is automatically recocked in the intermediate position. The jarn'ng action is repeated As shown in greater detailin FIG. 2B,

' locking sleeve .45 is alsoslotted-at circumferentiallyspaced locations to receive outwardly extending

projections

54 and 55 formed on depending

portions

56 and 57 of upper and lower drive rings 58 and 59 which on the sleeve member 35 when the threads'47 are meshed with the release grooves j Theupper end ofthe locking sleeve 45 abuts against an inwardly extending shoulder 51- onv the housing 20, whereas the lower end is engaged by a'bushing 52 that is disposed above an inwardly extending shoulder 53 (FIG. 2C) on'the housing to fix the lockin g'sleev e longitudinally with respect to the housing. Each end of the are keyed to the mandrel 21 in a manner and for purposes tobe more fully describedbelow. 1 Y

Annular thickened portions60-and 61 :or the mandrel 21 are provided aboveandibelow the threads 37,

the portions having larger lateral dimensions than the height of the threads, but:are-considerably long with respect to the lead of thethreads. The sleeve member 35 has similar inwardly-thickened

portions

62 and, 63 which'engage above and below the

respective portions

60,and 61 on the mandrel 21. Further, the crests of the threads 37 are formed on a' smaller diameter than the the tripping mechanism 32 includes an expansible and contractable sleeve r'nember that is normally contractedaround thev mandrel 21, the sleeve member having internal threads 36that mesh with companion external threads 37 formed on a reduced diameter section of the mandrel. The

threads

36 and 37 have a stub form providing inclined wall surfaces 39 and 40. When the 'sleeve member 35 and the mandrel 21 are'forced inopposite however, the sleeve member 35 is locked in contracted condition around the mandrel 21 by locking surfaces '43 (FIG. 28) provided by threads 44 on a locking sleeve 45, the surfaces slidably engaging like surfaces 46 provided by threads 47 formed on the exterior of the sleeve member 35. As disclosed in full detail in application, Ser. No. 82287, Berryman, filed concurrently herewith and assigned to the assignee of this invention, the release grooves'48 formed between the locking surfaces 43iare adapted to receive the threads 47 on the sleeve member 35 upon relative longitudinal movement of the locking sleeve 45 and the member 35, thus permitting expansionof the'sleeve member to a condition where the

threads

36 and 37 are disengaged. The

. locking surfaces 43 and 46 extend parallel to theaxis of the sleeve'member 35 and thus positively prevent any outward expansionof the sleeve member during the outer diameter of the mandrel21, whereas the bore size through the sleeve threads 36"is larger than the transverse dimension of the

portions

60 and 61. Thus, when the sleeve member 35 is'permitted to expand and move upwardly, for example, alongthe mandrel 21,- the.

- portion 62 will ride along the outer surface 64 or'the -mandrel 21', while .the lower portion 63 will ride first over the outer surface'of the lower-mandrel portion 61 and then along the crests of the threads 37. The crests of the sleeve member threads 36 will slide along the upper mandrel portion 60, with the result beingfthat the respective sleeve member and

mandrel threads

36 and 37 are positively held out of engagement as the sleeve member 35 moves relatively along the mandrel 21 in either direction.

It will be apparent thatin .order for the sleeve member 35 to be released from the mandrel 21 to enable unrestricted telescoping movementrthe housing 20 and the locking sleeve 45 must move either upwardly 1 or downwardly relative to the sleeve member 35. Such relative movement is restrained however by the

resilient structures

33 and 34. Since each structure is madeof identical, oppositely dispowd parts, the upper I structure will be discussed in detail with the appropriate numbers -referred to in the drawings, the lower resilient structure 34 having parts numbered in the same manner but with the prime notation. The upper resilient structure 33 is shown in FIG. 2A as including an outer tube 68, an intermediate tube 69 and an inner tube 70 all concentrically disposed and made of metallic materials. The intermediate tube .69 has I thickened

sections

71 and 72 at its ends, the lower section providing an upwardly facing shoulder'73 and the upper section providinga downwardly facing shoulder 74. The lower end of the outer tube .68 abuts against the shoulder 73, whereas the upper end of the inner tube abuts the shoulder ,74'. Thus it will be ap-' preciated that oppositely directed longitudinal'forces applied to the outer tube 68 and the inner tube 70 will place these tubes in compression and the intermediate tube 69 in tension. The total deflection of the composite structure of course will be the sum of the respective elongation and foreshortenings of the individual tubes, so that the tubes provide a resilient structure in the nature of a spring having a high modulus of elasticity. The upper end of the outer tube 68 and the lower end of the inner tube 70 extend beyond the adjacent ends of the intermediate tube 69.

The drive rings 58 and 59 are located between the sleeve member 35 and the respective

resilient structures

33 and 34, each drive ring having an internal annular recess 76 (FIG. 2B) that receives a washer 77. The washer 77 has a concave annular groove 78 that receives a rounded end of a thrust sleeve 79. The other end of each thrust sleeve 79 is also rounded andis received within an annular groove 80 in the end of the sleeve member 32. Each of the thrust sleeves 79 is also made to be radially expansible and contractable by slots 81 (FIG. 5) extending in alternating longitudinal directions for less than the full length thereof in the same manner as the slots in the sleeve member 35 shown in FIG. 4. The provision of the slotted thrust sleeves 79 having the same capability for expansion as the sleeve member 35, together with the rounded end surface construction thereof, substantially prevents any inward component of force that resists expansion of the ends of the sleeve member 35 such as might occur for example, between two sliding surfaces were the thrust rings 58 and 59 to engage the ends of the sleeve member 35 directly. 7

Each of the

resilient structures

33 and 34 can be adjustably positioned within the housing in order to selectively adjust the required tripping force. As disclosed in full detail in application, Ser. No. 82,285, Nutter, filed concurrently herewith and assigned to the assignee of the present invention, this is accomplished by providing upper and

lower jack mandrels

85 and 86, each having an end portion adapted to engage the outermost tube 68 of the respective

resilient structures

33, 34. Each jack mandrel is threaded to the housing at 87 so that relative rotation will cause feeding thereof along the housing 20. Suitable windows 88 are provided in the wall of the housing 20 adjacent to the distal end section of each jack mandrel, the windows being normally closed by plugs 89. Removal of the plugs 89 provides access openings through which a suitable tool (not shown) can be inserted and engaged in circumferentially spaced recesses 90 and used to rotate the jack mandrel with respect to the housing 20. Such rotation causes the threads 87 to feed the jack mandrel along the housing in one direction or the other, depending upon the direction of rotation, to correspondingly change the amount the

resilient structures

33 and 34 must be foreshortened in order to position the release grooves 48 opposite the outer sleeve member threads 47. Since the required tripping force is a direct function of the amount of longitudinal deflection of the

resilient structures

33 and 34, the tripping force can be adjusted as desired. A stop plug 91 having a tang 92 that projects into one of a plurality of circumferentially spaced external grooves 93 on the jack mandrel is of course removed during rotation and is then engaged to lock the jack mandrel in the selected longitudinal position by preventing rotation thereof.

To prevent relative rotation of the various parts'of the tripping mechanism 32 and thereby maintain the proper alignment of the threads and the locking surfaces during operation as well as the slots in the sleeve member35 and thrust sleeves 79 for proper expansion during operation, a system of keys is used as shown more clearly in FIGS. 4 and 5. The sleeve member 35 can have, for example, sixteen slots (eight opening in each direction as shown in FIG. 3) with the mandrel 21 and the release sleeve 45 each having eight radially aligned keyways provided by longitudinally extending

grooves

95 and 96. In this example, each of the thrust sleeves 79 also has eight slots 81 extending in each direction. Thus the upper thrust sleeve can have its downwardly opening slots longitudinallyaligned with the upwardly opening slots in the sleeve member 35, and a series of elongated keys are provided, each extending into the aligned slots. The inner edge of each key 100 rides in a respective mandrel keyway 95, whereas the outer edge is received by the radially aligned keyway 96 in the locking sleeve 45. A separate set of shorter keys 101 ride in the same mandrel keyways 95 and extend into slots of the lower thrust sleeve so that the upwardly opening slots in the lower thrust sleeve are longitudinally aligned with the downwardly opening slots 42 in sleeve member 35. Also upper and lower sets of

short keys

102 and 103 are received in radially extending

slots

104 and 105 cut in the drive rings 58 and 59 and ride in the mandrel keyways 96 to rotatively position the drive rings and thus the locking sleeve 44 with respect to the mandrel 21 and the sleeve member 35. Accordingly, the

release threads

36 and 37 and the locking surfaces 43 and 46 are fixed rotationally for the proper meshing relationship, and the slots that enable expansionof the sleeve member 35 and the thrust sleeves 79 are properly aligned for opening and closing movement during such expansion.

In operation, the jar 13 in its fully open or extended condition is connected in the drill string above the drill collars 12 and lowered into the borehole for drilling operations. During drilling, rotary motion is transmitted through the jar 13 by virtue of the interengagement of the splines 29, and during normal operations the jar is always in tension. In case the tools below the jar 13 become stuck, the jar is operated as follows. The drill pipe is lowered until a restraint is seen on the rig weight indicator which means that the tripping mechanism 32 is in the cocked position as shown in FIG. 2B. To hit upwardly, an upward strain is applied to the drill pipe 14 at the top of the borehole, causing the string to stretch and store energy. The upward force will tend to pull the housing 20 upwardly relative to the mandrel 21, however such upward movement is resisted by the resilient structure 34 disposed between the lower jack mandrel 86 and the lower drive ring 59, which is held against'upward movement by the sleeve member 33 and the thrust sleeve 79. The upward force on the sleeve member 35 and the

threads

36 and 37, due to their inclined wall surfaces of the latter, will tend to cause expansion of the sleeve member; however the top or crest surfaces 43 and 46 lock the sleeve member in gripping engagement with the mandrel 21. As the where the release grooves 48 are positioned laterally opposite the threads 47. At this point, which corresponds to a predetermined tripping or release force, the inclined walls of the

threads

36 and 37 will cause the sleeve member 35 to expand outwardly and suddenly release the gripping engagement with the mandrel 21. The housing will be accelerated upwardly,

. causing the hammer surface to strikethe anvil surface 26 in a violent manner. The impact force is transmitted via the mandrel 21 to the stuck tools ther'ebelow. As the sleeve member shifts upwardly drel 21. When the sleeve member 35 arrives opposite the threads 37 it will contract into gripping engagement the reaction force of the deflected structure 34 which is translated to radial inward force components by the inclined wall surfaces 49 of the release grooves 48. The mandrel portions 60' and 61 coact with the internal configuration of thesleeve member 35 and function in such a manner that there is only one longitudinal position where the sleeve member can contract, thus minimizing thread wear.

Jarring blows can be applied repeatedly in an upward direction, or downward jarring can be effected by slacking off the weight of the drill pipe onto the jar housing 20. The same coaction of parts will occur as I described above except involving the upper resilient V 37 as the gripping means between the sleeve member 35 and the mandrel 21 minimizes wear on the parts.

This is because the maximum stress on the threads'36 "and 37 is directly proportional to the contact pressure and inversely proportional to the total length of contact surface. In order to keep the maximum stress within values which will minimize wear, it is important to profor example, by eliminating the upper resilient struc- I ture, jack mandrel and associated structure and'cor respondingly shortening the housing and the mandrel.

Since certain changes or modifications may be made in the disclosed embodiment without departing from the inventive concepts involved, it is the aim of the appended claims to cover all such changes and modifica tions falling within the true. spiritand scope of the with the mandrel 21, such contraction being assisted by member vide the longest possible contact surface, which the

threads

36 and 37 do provide as opposed to other structure such as parallel ribs or the like. Moreover, threads can be conveniently formed for the proper full length contact with conventional tooling. The thrust sleeves 79 having rounded end surfaces engaging the annular grooves in the ends of the sleeve member 35 practically invention is illustrated in connection with a two-way hitting jar (both upward and downward), it will be appreciated that the jar could be readily modified to an embodiment that hits only in one direction, upwardly present invention.

I claim:

1. A well jar apparatus comprising: inner and outer members telescopically related and having impactsub' faces that can be engaged ;by telescoping motion to deliver a jarring blow to an object that is stuck in a well bore; a tripping mechanism'for preventing substantial telescoping motion of saidmembers until a predetermined longitudinal tripping force is applied to said members including an expansible and contractible sleeve member surrounding said innermember; axial cam means formed in an external surface of said inner member and adapted to mesh with companion :cam means formed in an internal surface of said sleeve for providing gripping engagement therebetween and for causing expansion of said sleeve Y member, said cam means being arranged to provide continuous bearing contact=surfaces which are considerably longer than the outside circumference of saidinner member in order to distribute the .stress on said. cam means in such a manner as to minimizewear thereon due to'repeated engagement under high load conditions; and means for preventing relative rotation between said sleeve member and said inner member.

deliver a jarring blow toan object that is stuck in a well bore; an expansible sleeve member contracted'around said inner member andhaving internal threads that mesh with external threads formed in an outer surface of said inner member to prevent relative longitudinal movement, said threads having inclined wall surfaces adapted to expand said sleeve member outwardly; locking means released by a predetermined amount of longitudinal movement of said outer member relative to said sleeve member for preventing expansion of said sleeve member; resilient means for resisting longitudinal movement of said housing member with a reaction force that is a function of the-amount of such longitudinal movement, release of said locking means enabling expansion of said sleeve member and disengagement of said threads, whereby said members can telescope freely to'bring said impact surfaces together in a violent manner; and radially disposed means for preventing relative rotation between said sleeve member and said inner member.

4. The well jar apparatus of claim 3 wherein said sleeve member has slots extending in alternating longitudinal direction for less thanthe full length thereof I to divide said sleeve member into a plurality of segments with the ends of each segment being joined to an end of an adjacent segment.

5. The well jar apparatus of claim 4 wherein said radially disposed means includes at least one key extending through a slot in said sleeve member and having its inner edge slidably disposed in a groove extending longitudinally in the periphery of said inner member.

6. A well jar apparatus comprising: inner and outer telescopically related members adapted for connection in a pipe string and having impact surfaces that can be brought together by telescoping movement to deliver a jarring blow to an object that is stuck in a well bore; an expansible sleeve member contracted around said inner member and having internal threads that mesh with external threads formed in an external surface portion of said inner member to prevent relative longitudinal movement, said threads having inclined wall surfaces adapted to expand said sleeve member outwardly; locking means released by a predetermined amount of longitudinal movement of said outer member relative to said sleeve member; and resilient means disposed in opposition to said longitudinal movement and yieldably resisting such longitudinal movement with a reaction force that is a function of the amount of such longitudinal movement, said resilient means comprising a tubular column structure having a plurality of concentrically disposed tubes and being capable of longitudinal deflection, release of said locking means enabling expansion of said sleeve member and disengagement of said threads, whereby said members can telescope freely to bring said impact surfaces together in a violent manner.

7. The well jar apparatus of claim 6 wherein said plurality of concentrically disposed tubes have ends coupled in such a manner that longitudinal force applied to one of said tubes places alternate tubes in tension and compression.

8. The well jar apparatus of claim 6 wherein said plurality of concentrically disposed tubes comprises an outer tube coupled to said outer member, an inner tube coupled to said sleeve member and an intermediate tube disposed between said inner and outer tubes, said intermediate tube having a first outwardly extending shoulder that is engaged by one end of said outer tube and a second inwardly extending shoulder that is engaged by one end of said inner tube, whereby longitudinal force applied to said outer tube places said outer tube and said inner tube in compression and said intermediate tube in tension.

9. The well jar apparatus of claim 8 wherein the other respective ends of said inner and outer tubes extend beyond the adjacent ends of said intermediate tube.

10. In a well jar apparatus having inner and outer members telescopically disposed and a releasable tripping mechanism for resisting telescoping movement, said tripping mechanism being released by longitudinal movement of one of said members, resilient means disposed in opposition to said longitudinal movement and including concentrically disposedtubes having ends coupled in such a manner that longitudinal force tending to cause telescoping movement in opposite directions of said inner and outer members places alternate tubes in compression and tension.

1 1. A well jar apparatus comprising: inner and outer members telescopically related and having impact surfaces at can engaged by telescoping motion to deliver a jarring blow to an object that is stuck in a well bore; an expansible sleeve member contracted around said inner member and having gripping engagement therewith; cam means responsive tolongitudinal force on said sleeve member for expanding said sleeve member radially outwardly; releasable locking means for preventing expansion of said sleeve member until a predetermined tripping force is applied to said members; resilient means coupled between one of said members and said sleeve member for resisting longitudinal relative movement; and means including an annular member disposed between said resilient means and said sleeve member and having an end surface in bearing contact with said sleeve member for substantially isolating said sleeve member from radially inward force components during expansion of said sleeve member.

12. The well jar apparatus of claim 11 wherein said end surface is rounded and rolls during expansion within an annular concave groove formed in the end of said sleeve member.

13. The well jar apparatus of claim 12 wherein said annular member is constituted by a plurality of adjacent segments having the capability for expansio with said sleeve member.

Claims

1. A well jar apparatus comprising: inner and outer members telescopically related and having impact surfaces that can be engaged by telescoping motion to deliver a jarring blow to an object that is stuck in a well bore; a tripping mechanism for preventing substantial telescoping motion of said members until a predetermined longitudinal tripping force is applied to said members including an expansible and contractible sleeve member surrounding said inner member; axial cam means formed in an external surface of said inner member and adapted to mesh with companion cam means formed in an internal surface of said sleeve member for providing gripping engagement therebetween and for causing expansion of said sleeve member, said cam means being arranged to provide continuous bearing contact surfaces which are considerably longer than the outside circumference of said inner member in order to distribute the stress on said cam means in such a manner as to minimize wear thereon due to repeated engagement under high load conditions; and means for preventing relative rotation between said sleeve member and said inner member.

2. The well jar apparatus of claim 1 wherein said axial cam means are provided by stub threads having flat top surfaces and inclined side wall surfaces.

3. A well jar apparatus comprising: inner and outer members telescopically related and having impact surfaces that can be engaged by telescoping motion to deliver a jarring blow to an object that is stuck in a well bore; an expansible sleeve member contracted around said inner member and having internal threads that mesh with external threads formed in an outer surface of said inner member to prevent relative longitudinal movement, said threads having inclined wall surfaces adapted to expand said sleeve member outwardly; locking means released by a predetermined amount of longitudinal movement of said outer member relative to said sleeve member for preventing expansion of said sleeve member; resilient means for resiSting longitudinal movement of said housing member with a reaction force that is a function of the amount of such longitudinal movement, release of said locking means enabling expansion of said sleeve member and disengagement of said threads, whereby said members can telescope freely to bring said impact surfaces together in a violent manner; and radially disposed means for preventing relative rotation between said sleeve member and said inner member.

4. The well jar apparatus of claim 3 wherein said sleeve member has slots extending in alternating longitudinal direction for less than the full length thereof to divide said sleeve member into a plurality of segments with the ends of each segment being joined to an end of an adjacent segment.

10. In a well jar apparatus having inner and outer members telescopically disposed and a releasable tripping mechanism for resisting telescoping movement, said tripping mechanism being released by longitudinal movement of one of said members, resilient means disposed in opposition to said longitudinal movement and including concentrically disposed tubes having ends coupled in such a manner that longitudinal force tending to cause telescoping movement in opposite directions of said inner and outer members places alternate tubes in compression and tension.

11. A well jar apparatus comprising: inner and outer members telescopically related and having impact surfaces that can be engaged by teLescoping motion to deliver a jarring blow to an object that is stuck in a well bore; an expansible sleeve member contracted around said inner member and having gripping engagement therewith; cam means responsive to longitudinal force on said sleeve member for expanding said sleeve member radially outwardly; releasable locking means for preventing expansion of said sleeve member until a predetermined tripping force is applied to said members; resilient means coupled between one of said members and said sleeve member for resisting longitudinal relative movement; and means including an annular member disposed between said resilient means and said sleeve member and having an end surface in bearing contact with said sleeve member for substantially isolating said sleeve member from radially inward force components during expansion of said sleeve member.

13. The well jar apparatus of claim 12 wherein said annular member is constituted by a plurality of adjacent segments having the capability for expansion with said sleeve member.