GB2184760A - Well fishing tool - Google Patents

Abstract

A well tool for retrieving objects from wells is described which has a locking mechanism which is actuatable by rotation of the drill string once the object has been gripped by the tool. This causes compression of a spring (86) within the fishing tool which causes a much tighter locking force on grapple fingers (70) to grip the object 110. In the case of damaged objects a cutting head is mounted on the bottom of the fishing tool and the fishing tool can be coupled to drive means (132, 22) located on the upper portion of a connecting sub (38) to rotate the cutting head when a damaged object is encountered to remove the damaged portion. <IMAGE>

Description

SPECIFICATION Improved well tool The present invention relates to well tools for retrieving objects from a well. Such tools are generally referred to as "fishing tools" and the objects to be retrieved as "fish".

One particular type of fishing tool to which the invention may be applied is an overshot which consists of a plurality of radially movable grapple fingers which can be lowered around the fish, for example a piece of drill string or the like, and then contracted inwardly to grip the fish by surrounding chamber having deflecting surfaces. Another particular type of tool in which the present invention can be incoporated is a spear which has similar radially movable slips which can be lowered into a fish, for example, a length of casing and then expanded outwardly to grip the fish by an expander, also having deflecting surfaces.

For a fishing tool to be completely effective, it should satisfy a number of basic design criteria in addition to being reliable and easily operable from a remote distance. It should securely grip the object to be retrieved so that when it is pulled out of the well the object does not slip out of the tool. It should readily be modifiable to retrieve objects of differing sizes and it should also be capable of retrieving damaged, broken or irregularly shaped objects from a well. It should also be readily controllable from the surface to permit each of these operations to be effectively and quickly carried out.

In one proposed type of fishing tool grapple fingers which are forced readily inwards in the case of an overshot or grapple slips which are forced readily outwards in the case of a spear are controlled to a certain extent by tension in a spring within a fishing tool. This tension is set in part by the relative movement of surfaces of a camming mechanism in the longitudinal direction and also to a certain extent on the coil spring and in the relative size of the contours on the outside of the grapple surface. However, with such an arrangement it has been found that the tension generated by the spring and by the relative movement on the grapple fingers is insufficient to provide an adequate locking force on the fish particularly if the hole is restricted and substantial tension has to be placed on the drill string to remove the fishing tool from the hole.In addition, in situations where the object to be retrieved has a damaged top surface or is irregular so that it does not readily fit into a chamber in the case of an overshot or cannot readily receive the spear in the case of the damaged casing, it is frequently very difficult and sometimes impossible to retrieve such damaged objects.

An object of the present invention is to obviate or mitigate disadvantages associated with such aforedescribed prior art structures.

This is achieved by providing a locking mechanism in the fishing tool which is actuatable by rotation of the drill string once the fish has been retrieved and which acts to compress a spring within the fishing tool which in turn provides a much tighter locking force on the grapple fingers to grip the tool. In addition, in the case of damaged tools, a cutting head can be mounted on the bottom of the fishing tool and the fishing tool can be coupled to drive means located on the upper portion of a connecting sub to rotate the cutting means when a damaged tool is encountered to remove the damaged portion and permit the tool to be engaged for reception by the chamber or by the spear.

Accordingly, in one aspect of the present invention there is provided a locking mechanism for use with a well tool comprising an upper outer well tool casing; a camming mechanism having a first fixed portion coupled to the upper outer well tool casing and to a lower outer well tool casing, said lower housing having a contoured inner surface defining a tool receiving chamber;; an inner sub having an upper sub portion adapted to be secured to a drill pipe and a lower sub end coupled to a second movable portion of said camming mechanism via said locking mechanism and via a resilient member disposed between said locking mechanism and said second movable portion of said camming mechanism, and said second movable camming mechanism being coupled to grapple means disposed within said tool receiving chamber and said lower outer casing, the inner sub and camming mechanism being movable longitudinally in response to longitudinal movement of said drill string and said camming mechanism being rotatable in response to said longitudinal movement to permit the grapple means to be moved relative to said lower housing between a tool release position and a tool catch position, said grapple means having a contoured outer surface adapted to engage with said contoured inner surface of said lower housing when in said catch position to force said grapple means to define a smaller chamber to grip any object located in said chamber, said resilient means being biassed to force said grapple means tightly onto an object in said catch position.

said locking mechanism comprising a longitudindally movable coupling coupled between said resilient means and said inner sub, the longitudinal coupling being movable longitudinally relative to said tool in response to the rotary movement drill string when said tool is in a catch position to urge said resilient means to provide an increased biassing force on said objects retained in said chamber.

Preferably, said longitudinal coupling is an externally threaded sleeve which includes a lower portion disposed for abutment of said resilient means. Conveniently, said resilient means is a coiled spring.

Preferably, said bottom portion of said longitudinal coupling includes torque limiting means to limit the force that can be applied to said resilient means and hence to said grapple means.

Conveniently, said torque limiting means comprises a pair of interlocking castellated surfaces and the flank angle of protrusions can be varied to provide a variable torque limit.

Preferably also, said locking mechanism includes longitudinal movement limiting means to limit the longitudinal movement of said locking mechanism, said longitudinal movement limiting means consisting of a pin disposed in said bottom portions and the slot located in said upper weld tool housing, the ends of the slot defining the degree of travel of said pin and hence of said threaded sleeve.

Preferably also, the threaded sleeve and the inner threaded surface of said inner sub is left hand thread so that clockwise rotation of said drill string derives said sleeve downwards towards said camming mechanism and anti-clockwise movement of said sleeve causes upward movement of said sleeve away from said camming mechanism.

Preferably also, said lower well tool housing is removable and is replaceable by a well tool housing having a different wall thickness to define different sizes of chamber for retrieving objects of different sizes from a well.

Preferably also, the locking mechanism can be applied to a fishing tool of the spear type.

Accordingly, in another aspect of the invention there is provided a locking mechanism for use with a well tool, said locking mechanism comprising a longitudinally movable coupling coupled between an inner sub for connecting said well tool to a drill string and a resilient means for urging grapple means into contact with an object to be retrieved, the longitudinal coupling being movable longitudinally relative to said tool in response to rotary movement of the drill string to urge said resilient means to provide a greater biassing force from said grapple means and said object retained in said chamber.

Preferably, said longitudinal coupling is an externally threaded sleeve and includes a bottom portion adapted to abut said resilient means.

Conveniently said resilient means is a coiled spring.

Preferably also, said longitudinal coupling includes torque limiting means for limiting a force that can be applied through said longitudinal coupling to said grapple means. Conveniently said torque limiting means has an adjustable torque limit.

Accordingly, in another aspect of the present invention there is provided a well tool for retrieving a damaged object from a well, said well tool comprising: an object machining means disposed at a lower end of said well tool, drive coupling means located at a top portion of said weld tool for permitting rotary drive to be provided from said drill string to said object machining means, the arrangement being such that whereby, in use, said drive coupling means is engageable by downward movement of said drill string to permit rotation of said tool and said object machining means by said drill string to machine said damaged object for subsequent retrieval.

Preferably, said object machining means comprises cutter means disposed in the extremity of the lower end of the housing for machining the surface of said encountered object to be retained.

Preferably also, said drive coupling means includes first and second drive engagement means normally spaced apart by a predetermined amount, said first drive engagement means being located on said upper sub, and said second drive engagement means being located on the top of said upper weld tool housing, said first and second drive engagement means being adapted to be engaged by longitudinal downward movement of said drill string. Conveniently, said first and said second engagement means are provided by generally castellated surfaces arranged opposite each other.

Preferably also, said cutting means is provided by a removable cutter which is adjustable to vary the machining of said object.

These and other aspects of the invention will now be described by way of example with reference to the accompanying drawings when taken with the following description of the embodiment of the invention in which: Figs. 1 A and 1 B are longitudinal sectional views of an overshot fishing tool shown in the running in position and including a locking mechanism and damaged tool machining means in accordance with the present invention; Fig. 2 is a developed view of surfaces of the camming mechanism shown in Fig. 1 in the running in position; Fig. 3 is a developed view similar to Fig. 2 which shows the camming surfaces of the camming mechanism when in the catch position;; Figs. 4A and 4B illustrate a longitudinal sectional view through a fishing tool similar to that shown in Fig. 1 but with a fish retained by the overshot and the camming mechanism in a first switching position; Figs. 5A and 5B show a similar view to Figs. 1 and 4 with the fishing tool retained in the overshot and the camming mechanism in a catch position; Fig. 6 is a longitudinal sectional view of an upper part of the fishing tool illustrating actuation of the locking mechanism to compress a resilient spring to increase the force of the fish; Fig. 7 is an exploded perspective view of part of a locking mechanism as shown in Fig. 6; Fig. 8 is a cross-sectional view taken on the lines 8--8 of Fig. 6;; Fig. 9 is a longitudinal, part sectional and part broken away view of an overshot tool having a bottom cutter mechanism shown engaged with a damaged fish; and Fig. 10 is a cross-sectional view taken in the direction 1 1 0 of Fig. 9 showing the relationship between the cutters on the cutting mechanism and the outer surface of the damaged fish.

Reference is first made to Fig. 1A and Fig. 1 B of the drawings which illustrates a longitudinal sectional view of an overshot fishing tool shown in the running in position. This fishing tool is similarto that shown in US Patent Application No. 4124245 to Kuenzel issued on 7 November 1978.

For clarity and ease of understanding a brief description of the general fishing tool will be given together with its operation and then the locking mechanism of the fishing tool and machining structure for retrieving damaged tools will be described in detail.

As seen in Figs. 1A and 1 B a fishing tool generally indicated by reference numeral 10 consists of an outer structure which includes an upper housing 22 which is threadedly connected at its bottom portion 24 to a first portion 26 of a camming mechanism generally indicated by reference numeral 28 and which is threadedly connected at a lower portion 30 to a lower generally hollow housing 32 defining a fish receiving chamber 34 for receiving and catching a fish, as will be later described in detail.

The upper housing 22 effectively hangs on a shoulder 36 of an inner sub 38 which has a threaded top end 40 adapted to be coupled to a piece of drill pipe, as shown in broken outline. The sub 36 has an enlarged internally threaded base portion 42 which threadedly receives a locking mechanism generally indicated by reference numeral 44. The locking mechanism consists of an upper threaded portion 46 which has an integral lower flange 48 with a castellated under surface 50 as best seen in Fig. 7 which mates with a co-operating surface 52 on a lower annular sleeve 54.

An inner washpipe 56 has its top end 58 disposed within the interior shoulder 60 of the locking mechanism and the bottom end 62 of the wash pipe is threadedly engaged with the second portion 64 of the camming mechanism 28. The lower portion of the camming mechanism is threadedly engaged with an inner sub 66 the lower end of which is, in turn, coupled to a carrier member 68. A plurality of grapple members 70 are carried by the carrier member and the chain between a shoulder 72 of the sub 66 and a shoulder 74 of the carrier member by a coiled spring 76.

It will be seen that the outer surface of each grapple finger is configurated to mate with a complimentary inner surface 80 of the lower housing 32. The inner housing surface consists of a first generally downwardly extending portion 82 and a shorter generally inwardly extending portion 84 which are shown mated with corresponding portions on the exterior surface 78 of the grapple member 70.

The lower portion of the annular sleeve 54 is abutted by a coil spring 86 which surrounds washpipe 56 and which abuts on its lower portion with a top surface 88 of a sleeve 90.

As seen in Figs. A and 1B and Fig. 2, the tool is shown in the running in position and the camming mechanism consists of fingers 92 integral with portion 64 which are engaged in shallow V-shaped notches 94 of the first portion 26 of the camming mechanism. The V-shaped notches 94 are separated by deeper V-shaped notches generally indicated by reference numeral 96 which is best seen in the developed view shown in Fig. 2. The camming mechanism portion 26 has a plurality of lower sawtooth shaped teeth 98 which are spaced from complimentary shaped teeth 100 associated with the second portion 64. The teeth 98 have a generally vertically extending portion 102 joined by an oblique portion 104. Similarly, teeth 100 are defined by vertically extending portion 106 and joined by oblique portion 108.

In this release position the tool 20 is lowered into the well bore until the lower end of the housing 32 strikes or locates the fish to be retrieved. This abutment prevents further downward movement of the inner assembly and, upon exertion of further downward force in the tool, the inner assembly is pushed up against spring 86 resulting in the camming mechanism portion 64 being forced upon up and rotated by engagement of surfaces 108 and 104 in the direction of the arrows as shown in Fig. 2.

The tool adopts the position as shown in Figs. 4A and 4B and this is known as the first switching position. It will be seen in Figs. 4A and 4B that the spring 86 is substantially compressed and the fingers 92 have been rotated clockwise relative to notches 94 and 96 and teeth 98 and 100 interlock as shown in Fig. 4B. The fish 110 is also shown received in chamber 34, and indeed top portion 112 is also shown received in a resilient rubber seal 114 which permits circulation of fluid through the tool to wash away any obstructions that might be present.

Also, the grapple members 70 form the same position as shown in Fig. 1 B in the release position.

An upward pull is exerted on the drill string and this results in expansion of the main spring as shown in Fig. 5A which forces the portion 64 of the camming mechanism down so that fingers 92 abut cam surface portions 95 at the top of the V-shaped notches 96. This in turn causes rotation of the camming mechanism to the catch position as shown in Fig. 5A and Fig. 3 in which fingers 93 are received in notches 96. The expansion of spring 86 forces the camming mechanism portion 64 and inner sub 66 downwards together with grapple members 70 so that the outer grapple surface 78 is moved down relative to the inner housing surface 80 and are at the same time forced inwardly to tightly grip the fish 110.The fish 110 is thus firmly gripped in the chamber 34 and if the engagement of the grapple fingers is sufficiently tight further telescopic movement of the inner assembly will be prevented. Continued exertion of an upward pull on the tool will cause the entire tool and the engaged fish to be extracted from the well.

However, should the tension of the spring 86 be insufficient to fully expand the spring then the fish 110 may not be adequately held by the grapple member 70. In addition, should a restriction be encountered in the well and the drill string lowered for some reason grapple fingers may move up through the compression of spring 86 and consequently the fish 110 could be inadvertently released from the tool requiring a further fishing operation.

Accordingly, the aforedescribed locking mechanism 44 and its operation will now be described in detail with reference to Figs. 6 and 7 of the drawings.

As best seen in Fig. 7, the locking mechanism 44 consists of an upper threaded portion generally indicated by reference numeral 46 and a lower hollow sleeve 50. The upper threaded portion 46 is spaced from the flange 48 by a non-threaded portion 49 of smaller diameter than threaded portion 46 and, when assembled, there is clearance between portion 49 and the internal threads 39 of the sub 38. The lower castellated surface 50 of the flange 48 is defined by protrusions 51 which mesh with corresponding recesses 53 in castellated surface 52. It will be seen from Fig. 7 the protrusions have flank angles 55 which oblique to generally vertical line. The flank angle determines the maximum torque which can be applied through a locking mechanism as will be later explained.

When the tool is in the catch position as shown in Figs. 5A and 5B a slight upward pull is exerted on the top sub 38 which is also rotated clockwise simultaneously as best seen in Fig. 6. Accordingly, the portion 46 is screwed down so that the gap between the top of the washpipe 58 and the inner shoulder 60 of the lock nut is closed. The protrusions 51 engage in the recesses 53 and the locking mechanism 44 is screwed down compressing spring 86 as shown in Fig. 6. The movement of pin 57 in the slot 59 acts as a guide for the mechanism 44 until it abuts the end of the slot as shown in Fig. 6. In this position the top of the washpipe and abutment of pin 57 defines the maximum compression of the spring 86 which increases the force on the grapple members 70 to achieve a tight grip.

If the sub 38 continues to be rotated threaded portion 48 will be rotated with it overcoming friction between the castellated surfaces which are determined by the flank angle of the protrusions 55 and the pressure of the main spring 86. Thus pressure is maintained on the main spring 86 to prevent cycling through catch release positions and inadvertent release of the fish.

Reference is now made to Figs. 8,9 and 10 of the drawings in order to explain how a deformed fish is retrieved by the fishing tool. As best seen in Fig. 9 a milling head, generally indicated by reference numeral 116, is threadedly secured onto the bottom of housing 32. The milling head 116 carries four cutter supports 118 spaced about its periphery and each support 118 is adapted to receive a cutter 120 by means of bolts 122 which are received in threaded apertures 124. The cutters 120 have a cutting face 126 which is shown engaged with the surface of the deformed fish 110 at various positions around the periphery of the fish for machining the surface of the fish as will be later described.

The top of housing portion 22 is castellated as best seen in Fig. 8 having a plurality of protrusions 128 upstanding from the top surface of the housing 22. Sub 38 has a threaded portion 130 on which is carried locking flange 132 which has a lower castellated surface 134 having protrusions which are adapted to engage with the surface of the top of the housing 22. The locking flange 132 is secured to the sub by means of a lock screw 136.

In use, when the fishing tool is run in in the release position and a deformed fish is encountered a substantial downward load is placed on the sub 38 and the inner assembly of the fishing tool moves downward relative to the outer housings defining a gap 37 between the housing 22 and sub 38. This displacement causes the castellated surfaces of the top of the housing 22 and locking flange 132 to become engaged as shown in Fig. 9. In this position when the cutting edge has engaged the upper surface of the deformed fish 110 rotation of the drill string causes the entire outer shell of the fishing tool to rotate with the top sub causing the cutting edges 126 to effectively "mill" or machine the outer surface of the fish. Locking mechanism 44 is deactivated and rotation of the tool does not cause longitudinal movement of the locking mechanism or compression of spring 86.

The milling operation can take a relatively short time such as an hour or it can take days until the deformed fish is sufficiently machined to permit the lower housing grapple members to slip over the fish. When this occurs the main spring expands and causes the castellated surfaces of the top of the housing 22 and locking flange 132 to become disengaged so that the top sub can swivel and the fish can be retrieved in the normal manner as hereinbefore described.

It will be appreciated that various modifications may be made to the apperture hereinbefore described without departing from the scope of the invention. For example, any number of cutters may be used with a drive coupling which could be by way of other than castellated surfaces. It will also be appreciated that the threaded portion 48 could have a right hand thread for rotation in an anti-clockwise direction by a sub 38. Also, the cutters are removable and are adjustable to vary the machining of the fish as required.

Advantages of the apparatus are that locking mechanism permits a fish to be securely gripped that when the fishing tool and fish is pulled out of the well the fish does not inadvertently slip out of the tool. The apparatus is readily modifiable to retrieve objects of differing sizes and the machining head and drive through the outer housing of the fishing tool permits, damaged, broken or irregularly shaped fish or objects to be retrieved from a well.

The apparatus is also readily controllable from the surface and permits each of these operations to be effectively and quickly carried out.

Claims (20)

1. A locking mechanism for use with a well tool comprising: an upper outer well tool casing; a camming mechanism having afirstfixed portion coupled to the upper outer well tool casing and to a lower outer wall tool casing, said lower housing having a contoured inner surface defining a tool receiving chamber, an inner sub having an upper sub portion adapted to be secured to a drill pipe and a lower sub end coupled to a second movable portion of said camming mechanism via said locking mechanism and via a resilient member disposed between said locking mechanism and said second movable portion of said camming mechanism, and said second movable camming mechanism being coupled to grapple means disposed within said tool receiving chamber and said lower outer casing, the inner sub and camming mechanism being movable longitudinally in response to longitudinal movement of said drill string and said camming mechanism being rotatable in response to said longitudinal movement to permit the grapple means to be moved relative to said lower housing between a tool release position and a tool catch position, said grapple means having a contoured outer surface adapted to engage with said contoured inner surface of said lower housing when in said catch position to force said grapple means to define a smaller chamber to grip any object located in said chamber, said resilient means being biassed to force said grapple means tightly onto an object in said catch position;; said locking mechanism comprising a longitudinally movable coupling coupled between said resilient means and said inner sub, the longitudinal coupling being movable longitudinally relative to said tool in response to the rotary movement drill string when said tool is in a catch position to urge said resilient means to provide an increased biassing force on said objects retained in said chamber.

2. A locking mechanism as claimed in claim 1 wherein said longitudinal coupling is an externally threaded sleeve which includes a lower portion disposed for abutment of said resilient means.

3. A locking mechanism as claimed in claim 1 or claim 2 wherein said resilient means is a coiled spring.

4. A locking mechanism as claimed in any preceding claim wherein said bottom portion of said longitudinal coupling includes torque limiting means to limit the force that can be applied to said resilient means and hence to said grapple means.

5. A locking mechanism as claimed in 4 wherein said torque limiting means comprises a pair of interlocking castellated surfaces and the flank angle of protrusions can be varied to provide a variable torque limit.

6. A locking mechanism as claimed in any preceding claim wherein said locking mechanism includes longitudinal movement limiting means to limit the longitudinal movement of said locking mechanism, said longitudinal movement limiting means consisting of a pin disposed in said bottom portions and the slot located in said upper weld tool housing, the ends of the slot defining the degree of travel of said pin and hence of said threaded sleeve.

7. A locking mechanism as claimed in any one of claims 2 to 6 wherein the threaded sleeve and the inner threaded surface of said inner sub is a left hand thread so that clockwise rotation of said drill string derives said sleeve downwards towards said camming mechanism and anti-clockwise movement of said sleeve causes upward movement of said sleeve away from said camming mechanism.

8. A locking mechanism as claimed in any preceding claim wherein said lower well tool housing is removable and is replaceable by a well tool housing having a different wall thickness to define different sizes of chamber for retrieving objects of different sizes from a well.

9. A locking mechanism as claimed in any preceding claim wherein the locking mechanism can be applied to a fishing tool of the spear type.

10. A locking mechanism for use with a well tool, said locking mechanism comprising a longitudinally movable coupling coupled between an inner sub for connecting said well tool to a drill string and a resilient means for urging grapple means into contact with an object to be retrieved, the longitudinal coupling being movable longitudinally relative to said tool in response to rotary movement of the drill string to urge said resilient means to provide a greater biassing force from said grapple means and said object retained in said chamber.

11. A locking mechanism as claimed in claim 10 wherein said longitudinal coupling is an externally threaded sleeve and includes a bottom portion adapted to abut said resilient means.

12. A locking mechanism as claimed in claim 10 or claim 11 wherein said resilient means is a coiled spring.

13. A locking mechanism as claimed in any one of claims 10 to 12 wherein said longitudinal coupling includes torque limiting means for limiting a force that can be applied through said longitudinal coupling to said grapple means.

14. A locking mechanism as claimed in any one of claims 10 to 13 wherein said torque limiting means has an adjustable torque limit.

15. A well tool for retrieving a damaged object from a well, said well tool comprising: an object machining means disposed at a lower end of said well tool; drive coupling means located at a top portion of said well tool for permitting rotary drive to be provided from said drill string to said object machining means, the arrangement being such that whereby, in use, said drive coupling means is engageable by downward movement of said drill string to permit rotation of said tool and said object machining means by said drill string to machine said damaged object for subsequent retrieval.

16. A well tool as claimed in claim 15 wherein said object machining means comprises cutter means disposed in the extremity of the lower end of the housing for machining the surface of said encountered object to be retained.

17. Awell tool as claimed in claim 15 or 16 wherein said drive coupling means includes first and second drive engagement means, normally spaced apart by a predetermined amount, said first drive engagement means being located on said upper sub, and said second drive engagement means being located on the top of said upper weld tool housing, said first and second drive engagement means being adapted to be engaged by longitudinal downward movement of said drilling string.

18. Awell tool as claimed in any one of claims 15 to 18 wherein said first and said second engagement means are provided by generally castellated surfaces arranged opposite each other.

19. A well tool as claimed in any one of claims 16 to 18 wherein said cutting means is provided by removable cutter which is ajustable to vary the machining of said object.

20. A locking mechanism substantially as herein before described with reference to the accompanying drawings.