Mechanical Jar

Abstract

A well jar including a mandrel telescopically disposed within a housing, the mandrel and housing being adapted to be disposed in a pipe string and having spaced apart impact surfaces that can be brought together to deliver a jarring blow, an expansible latch sleeve having gripping engagement with the mandrel, cam means for expanding the latch sleeve to release said gripping engagement, a locking sleeve fixed to the housing and having longitudinally spaced internal locking surfaces slidably engaging companion external surfaces on the latch sleeve to prevent expansion of the latch sleeve, the locking surfaces being disengaged from each other by longitudinal relative movement to enable the cam means to expand the latch sleeve, and means for yieldably resisting such longitudinal relative movement to enable a stretch to be taken in the pipe string before the gripping engagement is released.

Description

This invention relates generally to jars used in boreholes, and more specifically to a new and improved tripping structure for mechanical jars used in extricating stuck objects from well bores.

When drilling boreholes through earth formations where sticking is a problem, most drillers will run a jar in the drill string. A jar is a device having impact surfaces which can be brought together by manipulation of the drill string at the surface in order to deliver jarring blows to the stuck tools with the hope of freeing them. Because of the environment in which a jar must function, such devices must be extremely rugged in order to remain operational.

The heart of most mechanical jars is the tripping device which prevents the jar from hitting until a predetermined release force is applied to the pipe string. This force strains the drill pipe, causing it to stretch and store energy. When the tripping device releases, the energy stored in the pipe string 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 freed, and in fact, continuous jarring for quite a number of hours is not uncommon. Moreover, the jar may be in the borehole for days or even weeks before it is needed, and of course must still be fully operational.

The tripping devices used in prior art mechanical jars have not been highly successful primarily due to their inability to withstand wear due to friction and the like. Thus, these jars may hit a few times, but not very long, so that either the jar soon quits operating or else must be substantially repaired when it is removed from the well. Moreover, wearing action on the tripping device may change, by either reducing or increasing the hitting force which the jar can deliver, yet it is desirable for a jar to deliver a constant and predictable hitting force for optimum operation.

Many prior art mechanical jars also require torquing the drill pipe in order to condition it to jar, and some require the continued application of torque during jarring. The use of torque in operating the jar is undesirable for several reasons. Most importantly, in deviated wells the torque applied at the surface may not get to the jar because of pipe friction against the borehole wall. In any event, it is usually impossible to ascertain how much torque is being applied to the jar. An additional reason is that torquing the drill pipe is an inconvenience to the rig operator and can be dangerous to drilling crews.

It is accordingly and object of the present invention to provide a new and improved jar apparatus which is extremely rugged and which will remain operational over considerable lengths of time in the borehole.

Another object of the present invention is to provide a new and improved mechanical jar apparatus having a tripping device which is relatively wear free so that it will remain operational after many days or even weeks in the well, and after long continued hitting efforts in attempting to free stuck tools.

Yet another object of the present invention is to provide a new and improved mechanical jar having a tripping device which is operable solely in response to longitudinal motion of the drill pipe, so that the jar can be positively and safely operated.

These and other objects are attained in accordance with the concepts of the present invention by an apparatus comprising a mandrel and a housing having cooperable impact surfaces which can be brought together by telescoping movement in order to deliver a jarring blow to an object which is stuck in a borehole. A tripping structure is mounted between the mandrel and housing and includes a laterally shiftable latch sleeve contracted around, and in gripping engagement with, the mandrel. Cam means on the mandrel and latch sleeve are arranged to shift the latch sleeve outwardly, however a locking means within the housing has locking surfaces which engage the latch sleeve and function temporarily to prevent outward shifting thereof. The locking surfaces are spaced longitudinally apart, extend parallel to the axis of the latch sleeve, and slidably engage companion external surfaces on the latch sleeve. The locking surfaces are disengaged by longitudinal relative movement, such movement being resisted by a strong spring positioned between opposed transverse surfaces on the latch sleeve and the housing, respectively. Thus, longitudinal force on the housing is transmitted via the spring to the latch sleeve and tends to cause expansion of the latch sleeve by the cam means. However, the latch sleeve can not expand until the spring has foreshortened enough to allow the longitudinal movement necessary to disengage the locking surfaces, whereupon the cam means expands the latch sleeve out of gripping engagement with the mandrel, suddenly releasing the housing and mandrel for telescoping movement and engagement of the impact surfaces. When such deflection has occurred, a releasing means enables outward shifting of the latch sleeve to suddenly free the housing and mandrel for unrestricted movement relative to each other and engagement of the impact surfaces.

The present invention has other objects and advantages which will become more clearly apparent in connection with the following detailed description of a preferred embodiment when taken in conjunction with the appended drawings, in which:

FIG. 1 is a schematic view of a drill string and jar in a borehole;

FIG. 2 is an enlarged sectional view of the tripping device of the present invention in cocked position;

FIG. 3 is an isometric view of the laterally movable sleeve member;

FIG. 4 is a sectional view to illustrate the tripping device just prior to release; and

FIG. 5 is a view similar to FIG. 4 of the tripping device in released position.

Referring initially to FIG. 1, a borehole 10 is being drilled through earth formations by using conventional rotary drilling techniques. A drill bit 11 is attached to the lower end of a drill string which includes a number of heavy drill collars 12 which weight the drill bit and force it to make hole as it is rotated. A jar 13, in accordance with the present invention, is coupled in the string of drill collars as shown, or can be positioned immediately above the drill bit 11, or between the upper one of the drill collars 12 and the drill pipe 14, whichever location is suitable to the driller. In any event, when positioned as shown, the jar 13 is usually located at or above the "neutral" point in the drill collar string, that is to say, the point in the drill collar string which is neither in compression nor tension. Under certain borehole conditions, such as soft or highly permeable formations, particularly when encountered in deviated wells, there is the risk that the bit and/or the drill collars may become stuck. When sticking occurs for any reason, the jar 13 can be operated to free the stuck tools.

The jar 13 includes an outer tubular housing 20 having a threaded box portion 21 at its upper end, and an inner tubular mandrel 22 having a similar portion 23 at its lower end to enable coupling the jar in the drill string. The mandrel 22 has a central bore 24 which continues the drilling fluid circulation path through the drill string. The housing 20 and the mandrel 22 are telescopically related, the housing being movable upwardly relative to the mandrel in order to cause a "hammer" provided by an inwardly extending annular shoulder 25 on the housing to strike an "anvil" provided by an outwardly extending annular shoulder 26 on the mandrel, the impact force being transmitted through the mandrel and applied to the stuck tools therebelow. The housing 20 and the mandrel 21 have coengaging splines 27 for transmitting rotation through the jar during drilling. A seal packing 28 prevents drilling fluids from entering in between the housing 20 and the mandrel 22 at their lower ends, whereas a floating seal assembly 29 can be used to prevent fluids from entering at their upper end. The spaces between the housing 20 and mandrel 22 can be filled with a suitable lubricating oil.

To enable energy to be stored in the drill string 14 before the jar 13 hits so that a blow of considerable magnitude can be struck, a tripping device 30 is positioned between the mandrel 22 and the housing 20 and functions to restrain longitudinal movement until a predetermined strain has been applied at the surface to the drill pipe 14, the strain causing the pipe to stretch and store energy. However, when the predetermined release force has been applied, the tripping device 30 will release and allow unrestricted upward movement of the housing 20. Due to the substantial mass of drill collars above the housing 20 and to the energy stored in the drill pipe by stretching it, it will be appreciated that a considerable impact force will be delivered by the hammer 25 to the anvil 26 and to the stuck tools. After the jar 13 hits, the drill pipe 14 can be lowered and the housing 20 will move downwardly relative to the mandrel 22, causing the tripping device 30 to recock so that another blow can be struck. This operating sequence can be repeated until the stuck tools are driven loose.

As shown in detail in FIG. 2, the tripping device 30 includes a laterally movable latch means in the form of an expansible and contractible sleeve member 31. The sleeve member 31 has threads 32 formed on its inner periphery which normally mesh with companion threads 33 formed on the outer periphery of the mandrel 22. The sleeve member 31, shown also in FIG. 3, can have slots 34 extending in alternating longitudinal directions for less than the full length of the sleeve member and terminating in stress relief points 35 to enable expansion and contraction. Other equivalent constructions can, of course, be used to enable lateral movement of the member 31. The threads 32 and 33 are stub threads having inclining wall surface and flat top or crest surfaces and are formed on a reduced diameter portion 36 of the mandrel 22. Annular thickened portions 37 and 38 of the mandrel are provided above and below the threads 33, the projections having larger lateral dimensions than the height of the threads 33, but are considerably long with respect to the lead of the threads. The sleeve member 31 has similar inwardly extending projections 40 and 41 which engage above and below the respective projections 37 and 38 on the mandrel 22. Further, the crests of the threads 33 are formed on a smaller diameter than the outer diameter of the mandrel 22, whereas the bore size through the sleeve threads 32 is larger than the projections 40 and 41. Thus, if the sleeve member 31 is permitted to expand and move upwardly relative to the mandrel 22, the upper projection 40 on the sleeve member will ride along the outer surface 42 of the mandrel 22, while the lower sleeve projection 41 will ride first over the outer surface of the lower mandrel projection 38, and then along the crests of the threads 33. The crests of the sleeve member threads 32 will slide along the upper mandrel projection 37, with the result being that the respective sleeve member and mandrel threads 32 and 33 are held out of engagement once the sleeve member 31 is permitted to expand and move upwardly as described.

In order to prevent expansion of the sleeve member 31 and thus hold the threads 33 and 32 in engagement with one another, the sleeve member is provided with threads 45 formed on its outer periphery, the threads 45 being conventional stub threads having flat crest surfaces 46 and inclined wall surfaces 47. The surfaces 46 abut against the top surfaces 49 of companion threads 50 formed on the inner periphery of a locking and releasing sleeve 51. The sleeve 51 is fixed against longitudinal movement within the housing 20 by any suitable means, such as annular lock rings 52 and 53 which are received within recesses above and below the sleeve. The upper lock ring 52 can also engage an annular stop ring 54 which limits upward movement of the sleeve member 31 relative to the housing 20. The sleeve 51 can be preferably rotationally fixed within the housing 20 by a set screw or the like (not shown). The spaces 55 between the threads 50 have inclined wall surfaces 48 and provide release grooves which can receive the threads 45 on the sleeve member 31 and permit the sleeve member to expand outwardly. However, as long as the surfaces 49 and 46 are engaging one another, the sleeve member 31 cannot be expanded.

It will be appreciated that in order for the threads 45 to move into the release grooves 55, the sleeve member 31 must move downwardly relative to the housing 20. Such downward movement can occur, but is restricted by a strong spring means 58 surrounding the mandrel 22 and arranged to press upwardly on the lower end of the sleeve member 31 through the medium of a stop ring 59, and downwardly on an inwardly extending shoulder 60 (FIG. 1) on the housing 20. The spring means 58 can be formed for example, by a plurality of Bellville washers 61 providing a composite resilient structure having a high spring rate so that it functions to provide a large reaction force opposing deflection thereof. As upward force is applied to the housing 20 however, the spring means 58 is compressed to permit upward movement of the release sleeve 51 relative to the latch sleeve 31. When a sufficient magnitude of force has been applied, a proportional amount of relative movement will have occurred to disengage the surfaces 46 and 49, and the threads 45 and 50 can mesh to enable radial expansion of the sleeve member 31, such expansion being caused by the camming action of the inclined walls of the threads 33 and 32 on the sleeve member 31 and the mandrel 22. Such expansion will, of course, cause release of the threads 32 and 33, and suddenly free the housing 20 for upward movement relative to the mandrel 22, so that the hammer 25 can strike the anvil 26. During movement of the housing 20, the various projections 40, 37 and 41 prevent contraction of the sleeve member 31 and thus hold the threads 32 and 33 out of engagement.

It is desirable to maintain the longitudinal relative positions of the latch sleeve 31 with respect to the mandrel 22 and the locking and releasing sleeve 31 each time the jar is recocked to ensure proper meshing of the threads 32 and 33 as well as the locking surfaces 46 and 49. To this end, the sleeve 51 can be fixed by a set screw or the like as previously described, and a key 65 can engage as within a transverse slot 67 in the latch sleeve 31 as shown in FIG. 2. The slot 66 is long enough to enable upward movement of the release sleeve 51 relative to the latch sleeve 31 to a releasing position, and the slot 67 is deep enough to enable lateral expansion of the latch sleeve 31 during release. However, it will be appreciated that the various members are rotatively fixed relative to each other by virtue of the foregoing structure, in combination with the splines 27 which prevent relative rotation between the mandrel 22 and the housing 20.

In operation, the jar 13 can be connected in the drill string 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 27. In case the tools below the jar 13 become stuck, the jar is operated as follows. An upward strain applied to the drill pipe 14 at the top of the borehole will tend to pull the housing 20 upwardly relative to the mandrel 22. However, such relative movement is resisted by the spring means 58 which couples between the housing 20 and the sleeve member 31 having threaded or gripping engagement with the mandrel 22. The threads 32 and 33, due to their inclined wall surfaces, will attempt to disengage; however, the crest surfaces 46 and 49 on the respective threads 45 and 50 lock the sleeve member 31 in gripping engagement with the mandrel 22. As upward force is built up, the drill pipe 14 will stretch and store energy, and the spring 58 will compress to enable upward movement of the sleeve 51 relative to the sleeve 31. The relationship of parts at the instant just before the jar hits is shown in FIG. 4 with the housing 20 having moved upwardly relative to the sleeve member 31 and to the mandrel 22, but with the top surfaces of the threads 45 and 50 still engaged to hold the sleeve member 31 in gripping engagement with the mandrel.

When a predetermined magnitude of release force has been applied, the spring means 58 will compress sufficiently to enable the relative movement required for entry of the outer threads 45 on the sleeve member 31 into the release grooves 54 as shown in FIG. 5. When this occurs, the gripping engagement of the sleeve member 31 with the mandrel 22 is suddenly lost as the sleeve member expands radially outwardly. The housing 20 will be accelerated upwardly relative to the mandrel 22, causing the hammer 25 to strike the anvil 26 with a sharp impact blow. The impact force is transmitted via the mandrel 22 to the stuck tools therebelow. As the sleeve member 31 shifts upwardly along the mandrel 22, the projections 40, 37 and 41 engage as previously described to prevent any chattering or ratcheting of the threads 32 and 33.

To recock the jar 13, the drill pipe 14 is lowered to effect corresponding downward movement of the housing 20 and sleeve member 31 relative to the mandrel 22. When the sleeve member 31 arrives opposite the threads 33 on the mandrel 22 the sleeve member will contract into gripping engagement with the mandrel, such contraction being assisted by the radial inward components of force on the sleeve 31 due to the inclined wall surfaces of the threads 45 and 54 and the upward force on the sleeve provided by the spring 58. The projections 40, 37 and 41 function in such a manner that there is only one longitudinal position where the sleeve member 31 can contract, thus eliminating any wear due to contact of the threads 32 and 33 before contraction. Accordingly, once the housing 20 has been reciprocated downwardly, the jar is recocked for delivery of another blow.

Although the present invention has been described in connection with an upwardly hitting jar, it will be equally appreciated that by placing another spring and stop ring assembly that is a mirror image of the elements 58 and 59 above the sleeve member 31, and by providing a second hammer and anvil combination, the jar can be constructed to hit in both directions, upwardly and downwardly. Also, although threads have been shown as the means to provide the locking and releasing surfaces it will be appreciated that annular ribs or the like will serve equally as well. Even though the present invention has been described in connection with a drilling operation, it will also be apparent that it can be used in other operations such as fishing, washing over, whipstocking and coring.

A new and improved jar apparatus has been disclosed which is extremely rugged and subject to minimal wearing action in a well bore. Since certain changes and modifications may be made by those skilled in the art without departing from the inventive concepts involved, it is the aim of the appended claims to cover all such changes and modifications falling within the true spirit and scope of the present invention.

Claims

I claim:

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; laterally shiftable latch means on said inner member and having gripping engagement therewith; cam means for shifting said latch means outwardly and out of gripping engagement with said inner member; locking means on said outer member having longitudinally spaced locking surfaces slidably engaging companion locking surfaces on said latch means for preventing outward shifting of said latch means, said locking surfaces being disengaged by longitudinal relative movement; and yieldable means acting between said outer member and said latch means for opposing said longitudinal movement with a reaction force that is a function of the amount of said longitudinal movement, disengagement of said locking surfaces enabling outward shifting of said latch means and permitting said reaction force to cause said cam means to shift said latch means outwardly to release said gripping engagement, whereby said members can telescope freely to bring said impact surfaces together in a violent manner.

2. The apparatus of claim 1 wherein said locking surfaces extend parallel to the longitudinal axis of said members.

3. The apparatus of claim 2 further including release grooves between said locking surfaces on said outer member, said release grooves being sized and arranged to receive said companion locking surfaces on said latch means upon outward shifting thereof.

4. The apparatus of claim 3 wherein said release grooves have inclined wall surfaces to provide a camming action for forcing said latch means laterally inwardly.

5. The apparatus of claim 4 further including means for preventing inward shifting of latch means during said telescoping movement of said members.

6. 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; laterally shiftable latch means on said inner member having threaded engagement therewith, said threaded engagement being provided by thread formations having inclined wall surfaces to provide a camming action for shifting said latch means outwardly to release said threaded engagement; locking means including a locking sleeve secured within said outer member and having axially spaced locking surfaces slidably engaging companion locking surfaces on the exterior of said latch means for preventing outward shifting of said latch means, said locking surfaces being disengaged by longitudinal movement of said outer member and said locking sleeve along said inner member and said latch means to enable outward shifting of said latch means and release of said threaded engagement; and yieldable means acting between said outer means and said latch means for providing a reaction force resisting said longitudinal movement so that predetermined longitudinal force must be applied to said member before said locking surfaces are disengaged.

7. The apparatus of claim 6 wherein said locking surfaces extend parallel to the longitudinal axis of said members so that said reaction force is independent of the sliding engagement of said locking surfaces.

8. The apparatus of claim 7 further including release grooves formed in said locking sleeve between said locking surfaces thereon, said release grooves being sized and arranged to receive said companion locking surfaces on said latch means upon outward shifting thereof.

9. The apparatus of claim 8 wherein said release grooves and said locking surfaces on said locking sleeve and said latch means are provided by stub thread formations having flat top surfaces and inclined wall surfaces.

10. The apparatus of claim 9 further including means for preventing angular displacement of said locking sleeve and latch means during said longitudinal movement.