GB2123880A - Jar accelerator - Google Patents

Abstract

Disclosed is a jar accelerator 11. The accelerator 11 includes an elongated tubular tool body (12) and an elongated mandrel (13) axially slidingly mounted within the tool body (12) and having an outwardly facing shoulder (18). A plurality of frusto-conical disc springs (29) are disposed inside the tool body (12) about the mandrel (13) and between the shoulders (17, 18). The jar accelerator 11 is used in conjunction with a jar 20. <IMAGE>

Description

SPECIFICATION Jar accelerator The present invention relates generally to fishing apparatus utilized within a well bore to free stuck objects. More specifically, the present invention relates to an accelerator for use with a jar having a operating stroke between a set position and an impact position, and a force responsive jar latch that main tainsthejar in the set position until a preselected tension force is applied thereto.

During the drilling and completion of deep wells, such as wells for producing petroleum products, objects such as drill pipe, tubing, well tools and other apparatus sometimes becomes stuck within the well bore and cannot be removed by the application of ordinary upward forces. In such cases, it is necessary to deliver sharpjarring forces to the stuck object in orderto free it for extration from the well bore.

Apparatus have been developed for delivering such jarring forces and are known asjars.

Jars generally include a bodystructurethat is attached to the stuck object and a mandrel slidingly mounted in the body structure,that is attached to the surface through pipe or wire. The bodystructure has an anvil and the mandrel has a hammer. Means are provided for releasably connecting the mandrel and bodytogetherto holdtheanvil and hammer in spaced apart relationship, the distance of such spacing being known as the stroke of the jar. The releasable connection means are adapted to release when the tension overthe jar exceeds a certain level. When the connection means releases, the hammer is free to travel upwardly to strike the anvil.

In orderforthe mandrel to move upwardly upon the release of the connection means, there must be stored rebound energy in the string of pipe or wire connected between the surface and the mandrel. Typically, the stored rebound energy is spread th roughoutthe system and includes pipe stretch, wire stretch in the hoisting gear, and some compression of the derrick.

There are several limitations upon the efficiency of jars. For example, in deviated orcrooked holes, friction ofthepipeofwireagainstthewall ofthe hole reducesthespeed at which the stored stretch energy is delivered to the jar upon release ofthe connection means, which reduces the jarring forces. Also, at shallow depths, there is only a small length of pipe or wireoverwhich rebound energy may be stored. Thus, at shallow depths, the effectiveness of jars is limited.

In an effortto improve the efficiency of jars, there have been developed a numberof devices known variousiy as accelerators, jar boosters, or intensifiers.

The primaryfunction of such devices isto store the rebound energy in the device, which is inserted in the string immediatelyabovethejarsand drill collars or sinker bars, ratherthan in the pipeorwire. Onesuch device is made by Bowen Tools Inc., and is shown generally in the 1976-77 Composite Catalog at page 734, and in greater detail in the Bowen Tools Inc.

Techical Manual No. 4019. The Bowen accelerator stores enegy by compressing a compressible fluid.

Another such device is manfactured by Johnston and is shown generally in the 1976-77 Composite Catalog at page 3625. The Johnston device stores energy by compressing a gas.

There are a number of shortcomings in both the Johnston and Bowen devices. If any seal in either shall fail, then the device becomes inoperative. Moreover, both devices develop high pressures during operation and are subject to mechanical failure when operated at or near the surface. Additionally because of the gas or fluid charge ofthe priordevices,the spring force developed overthe jar increases with temperatures. Thus, as well bore temperature conditions change, so does the force generated by the device.

The present invention provides a tubulartool body and an elongated mandrel axially slidingly mounted within the tool body. The tool body has an internal shoulder and the mandrel has an outwardly facing shoulderwhich shoulders together define an internal spring chamber between the mandrel and the body. A pluralityoffrusto-conical disc springs are stacked aboutthe mandrel within the spring chamber. Means are provided for maintaining the pressure within the spring chamber at substantially the same level as the pressure outside the tool bodythroughoutthe operation ofthe jar accelerator.

The disc springs are selected so as to have a composite spring constant such that compression of the plurality of disc springs over a length greaterthan the stroke ofthejarwithwhich the jaraccelerator of the present invention is used, generates a force less than the force required to release the connection means of the jar. Stated in anotherway, the disc springs are selected such that during operation of the acceleratorwill elongate more than the stroke of the jar, whereby substantially all ofthe movement during the stroke ofthe jar is supplied by the accelerator.

In one aspect ofthe invention, the plurality of disc springs includes a first set having a length of compression at least as long as the stroke of jars and a total spring constants such thattheforce developed overthe length of the compression is than the force required to release the jars, and a second set of disc springs having a composite spring constant larger than that ofthefirst set.

The presentinvention will befurtherdescribed, by way of example only, with reference to the accompanying drawings, in which: Figure lisa daigrammatic view ofthe accelerator of the present invention in combination with drill collars and a jar immediately priorto release of the jar latch mechanism.

Figure 2 is a diagrammatic view similarto Fig. 1 wherein the jar is shown after release ofthe latch but before impact.

Figure 3 is a diagrammatieview similarto Figs. 1 and 2 wherein the jar is shown in the impact position.

Figure 4a is a sectional viewofthetop end of the jar acceleratorofthe present invention.

Figure 4b is a sectional view of the bottom end ofthe jar accelerator ofthe present invention.

Referring now to the drawings, and first to Figs. 1 to 3, the jar accelerator ofthe present invention is designated generally by the numeral 11. Accelerator 11 includes a tubulartool body 12 and a tubular mandrel 13 axiallyslidingly mounted in tool body 12.

Mandrel 13 has at its upper end a tool connection 14 which is adapted to connect with drill pipe or other tool support means. The lower end oftool body 12 is formed to define a tool connection 15 which is adapted to connectwith weighting means, as for example drill collars 16 or sinker bars.

Jaraccelerator 11 is adapted for use with a limited upstroke jar designated generally bythe numeral 20.

Jar 20 is preferably a mechanical jar of the type disclosed in U.S. Patent No. 4,333,542; however, jar accelerator 11 may be used with other limited upstroke jars, including oil jars.

Jar20 includesan elongated body21 and an elongated operator mandrel 22. Jar body 21 is formed to define an internal anvil 23 and operator mandrel 22 is formed to define a hammer 24. Jar 20 includes a latch 25 which establishes a releasable connection between jar body 21 and operator mandrel 22. When jar body 21 and operator mandrel 22 are latched together, anvil 23 and hammer 24 are spaced apart a distance S as shown in Fig. 1. Distance S is known as the stroke ofthejar. The connection of latch 25 is releasable when the axial tension between jar body 21 and operator mandrel 22 exceeds a certain level.

Spring means 26 are provided for setting the level of tension ofwhich latch 25 releases.

Operator mandrel 22 of jar 20 includes at its upper end a tool connection 27 which is adapted to connect with drill collars 16. Jar body 21 includes at its lower end stool connection 28 which is adapted to connect with a fishing tool, ifjar 20 is used as a fishing jar, or with drill collars ifjar 20 is used as a drilling jar.

Tool body ofjar accelerator 11 is formed to define an internal shoulder 17 and jar accelerator mandrel 13 is formed to define a facing shoulder 18. Shoulder 17 and 18cooperatetoform aspring chamber 19 which contains a stack offrusto-conical disc springs 29. Disk springs29urgeshoulders17and 18apart.

In Fig. 1,jar20 is shown immediately priorto the release of latch 25. Spring means 26 of jar 20 is compressed to develop a force slightly less than the set force ofthe latch. Disk springs 29 ofjar accelerator 11 are compressed by the movement together of shoulder 17 and 18. The compression of disc springs 29 stores energy, which upon release of latch 25 is delivered to drill collars 16 and jar 20. Disc springs 29 are selected and arranged to have a composite spring constant such thatthe elongation of jar accelerator 11 during loading is greaterthan the stroke S of jar 20.

Referring specifically to Fig. 2, jar 20 is shown at an instant afterthe release of latch 25. When latch 25 is released, jar body 21 and operator mandrel 22 are free to move axially with respect to each other thereby allowing hammer24to move toward anvil 23. The force causing the movement of hammer 24 toward anvil 23 is provided byjar accelerator 11. The energy stored in disc springs 29 is delivered to drill collars 16 and operator mandrel 22. Upon release of latch 25, operator mandrel 22, drill collars 16 and accelerator tool body 12, which are substantially rigidly intercon nected, accelerate rapidly upward as a unit and the potential energy stored in springs 29 is converted into kinetic energy.

In Fig. 3, jar 20 is shown atthe instant of impact between hammer 24 and anvil 23. The impact between hammer 24 and anvil 23 brings the movement of drill collars 16 and acceleratortool body 12 to a substantially instantaneous stop, which in turn delivers a tremendous impulse through lowerjartool connection 28 to the stuck object. As shown in Fig. 3, jar accelerator 11 is still in a slightly elongated position and disc springs 29 are still slightly compressed. Thus, at all times prior to impact, jar accelerator 11 provides acceleration to drill collars 16 and jar operator mandrel 22.

Referring nowto Figs. 4a and 4b there is shown the preferred embodiment of jar accelerator 11. Acceleratortool body 12 includes an upper body 30 which is threaded connected to an upper middle body 35.

Upper body 30, upper middle body35, lower middle body 40, and lower body 45 thus forms a unitary body and appropriate double O-ring seals, as for example seals 31 and 36 at the threaded inner connection between upper body 30 and upper middle body 35, are provided at all ofthe threaded inner connections between the portions of body 12,thereby making body 12fluidtight.

Accelerator mandrel 13 includes an upper portion 50, which includes upper tool connection 14and a lower portion 60. Upper mandrel portion 50 and lower mandrel portion 60 arethreadedly connected together by a connector 62. Appropriate seals, as for example seal 63, are provided for sealing the interconnections between upper mandrel portion 50 and lower mandrel portion 60 with connector 62,thereby making the unitary mandrel 13fluidtight.

Shoulder17 of body 12 is formed by the lower end of upper middle body 35 and a spring load ring 37 disposed between lower middle body 40 and lower mandrel portion 60. Lower shoulder 18 is formed by an adjusting nut61 which is engaged with an elongated threaded portion 64 on lower mandrel portion 60. A lock nut 65 is provided for locking in position and preventing axial movement of adjusting nut 61. Spring chamber 19 thus includes the annular space between lower mandrel portion 60 lower middle body 40 which is axially bounded by spring load ring 37 at one end and adjusting nut 61 at the other.

Disc springs 29 include a first set 29a of relatively stiff disc springs and a second 29b of relatively less stiff disc springs. The respective numbers and stiffness ofthe dise springs of sets 29a and 29b, are selected in accordance with the stroke and latch release load characteristics of the jarwith which jar accelerator 11 is used. More specifically, the disc springs of second set29b are selected so asto have a composite spring constant and length such that compression of second set 29b over a distance equal to the stroke ofthe jar produces a force less than the latch release load of the jar. Stated in anotherway, the length and composite spring constant of second set 29b allows the elongation of mandrel 13 with respect to accelerator tool body 12 during operation to be greaterthanthestroke of the jar.

Second set 29b is formed to have a greater composite spring constantthan that of second set 29b.

Disc springs 29 thus cause accelerator 11 to have a progessive spring characteristic in which a first portion of elongation accelerator 11 (compression of disc springs 29) by a length equal tothe stroke of the jar is provided by second set 29b and provides a force less than the force required to release the jar. A second portion of elongation of accelerator 11 is provided by compressing second set 29b over a relatively small distancetoproduceaforce necessarytoreleasethe jar.

The progressive spring characteristic featu re of the present invention is particularly advantageous in situations where a premium is placed upon length and the jar is setable over a wide range of release forces. In such situations, second set 29b is selected such that elongation of accelerator 11 over a length equal to the stroke of the jar produces a force less than the minimum release setting. First set 29a is selected such that relatively small additional elongation of accelerator 11 produces sufficient additional forceto release the jar at the highestsetting. Thus, the progressive spring characteristic of accelerator 11 allows the length of disc springs 29 to be minimized while at the same time insuring that the elongation of accelerator 11 will always exceed the stroke of the jar.

For a comprehensive discussion of disc springs, please seethe pamphlet entitled "Precision (Bellville) Disc Springs Engineering Handbook" published by Key Bellvilles Inc., R.D. No.2, Box 191 C, Leech burg, Pennsylvania 15656. Different configurations of disc springs 29 may be accommodated by changing the position of adjusting nut 61 upon threaded portion 64.

The space between acceleratortool body 12 and accelerator mandrel 13, including spring chamber 19, is preferablyfilled with a lubricating oil. A set of upper mandrel seals, including a seal 51, is provided for forming a sliding seal between upper body 30 and upper mandrel portion 50 to isolate the lubricating oil from the outside environment of accelerator 11. Also included on either side of seal 51 is a pair of protector rings, including protector ring 52. The other end of accelerator 11 is sealed by a free piston 66 which is slidingly mounted between lower mandrel portion 60 and lower body 45 in a reservoir67. Free piston 66 is sealingly engaged with both mandrel portion 60 and lower body 45 by a set of seals and protector rings including seal 68 and protector ring 69.Free piston 66 is freely movable thereby to accommodate volumetric changes in the lubricating oil during operation of accelerator 1 1.Also, free piston 66 balances the pressure on both sides thereof, thereby to keep the pressure ofthe lubricating oil between acceleratortool body 12 and mandrel 13 including that within spring chamber 19, at a level substantially equal to ambient pressure. Since accelerator 11 operates in a pressure balanced condition the failure of any or all ofthe seals will not affectthe operation of accelerator 11. Seal failure can only cause contamination or loss of lubricating oil but will not disable the tool. Fill plugs 54 and 55 are provided forfilling accelerator 11 with lubricating oil. In certain embodiments, the seals and lubricating oil may be omitted so that spring chamber 19may communicate directly with the well bore. In orderthattorque may be transmitted across accelerator 11, upper body 30 and upper mandrel portion 50 have cooperating splines 57 and 58 respectively. The splines enable accelerator 11 to be used with drilling jars.

From the foregoing it will be seen that this invention is one well adapted to attain all ofthe ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the apparatus.

Itwill be understood that certain features and sub-combinations are of utility and may be employed with referenceto otherfeaturesandsubcombina- tions. This is contemplated by and is within the scope

Claims (16)

of the claims. As many possibie embodiments may be made of the invention without departing from the scope thereof it is to be understood that all matters herein setforth are shown in the accompanying drawings as to be interpreted as illustrative and not in a limiting sense. CLAIMS

1. Ajar acceleratorfor use with a jar having a stroke and force responsive jar release means, which comprises an elongated tubulartool body having an inwardly facing shoulder; an elongated mandrel axially mounted within said tool body having an outwardly facing shoulder axially fixed thereto, said shoulders defining an internal spring chamber between said mandrel and said body; and a plurality of frusto-conical disc springs disposed within said spring chamber about said mandrel between said shoulders.

2. An accelerator as claimed in claim 1, wherein said plurality of disc springs includes a first set of disc springs, said first set having a length of compression at least as long as the stroke ofthejars and a composite spring constant such thattheforce developed over said length of compression is less than the force required to release said jars.

3. An accelerator as claimed in claim 2, wherein said plurality of disc springs includes a second set of disc springs, said second set having a total spring constant greaterthan the composite spring constant of said first set.

4. An accelerator as claimed in claim 3, wherein the composite spring constant of said second set is such that a force greaterthan the force required to operate the jars is developed in a length of compression of said second set that is less than the stroke of the jars.

5. An accelerator as claimed in any one ofthe preceding claims including means for maintaining substantially equal the pressure inside said spring chamber and exterior of said tool body.

6. An accelerator as claimed in claim 5, wherein siad maintaining means includes piston slidingly sealingly disposed about said mandrel and within said tool body.

7. An accelerator as claimed in any one ofthe preceding claims including a substantially incom pressiblefluidfilling said chamber; meansfor compensating for changes for volume of said cham- ber and balancing the pressure of said fluid filling said chamber and the pressure exterior of said tool body during operation of said accelerator.

8. An accelerator as claimed in claim 7, wherein said compensating and balancing means includes closure means received in movable relationship between said mandrel and said tool body.

9. An accelerator as claimed in claim 8, wherein said closure means includes a piston movably disposed between said mandrel and said tool body and including meansforforming a seal with both said mandrel and said tool body.

10. An accelerator as claimed in any one ofthe preceding claims including means for transmitting torque between said mandrel and said tool body.

11. An accelerator as claimed in any one of the preceding claims including means for changing the spacing between said shoulders to accommodate different lengths of sets of disc springs.

12. An accelerator as claimed in any one of the preceding claims including means for slidingly sealing between said tool body and mandrel at axially opposite ends of said spring chamber; and a substantially incompressible fluid filling the space between said seal means inside said tool and outside said mandrel.

13. An accelerator as claimed in claim 12, including meansfor maintaining the pressure of said incompressible fluid substantially constant during the operation of said accelerator.

14. An acceleratoras claimed in claim 12,includes ing means for balancing the pressure of said fluid with the pressure exterior of said seal means.

15. An accelerator as claimed in claim 13, wherein said pressure balancing means includes piston means having one end exposed to said fluid and the other end exposed to pressure exterior of said seals.

16. An accelerator as claimed in claim 1 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.