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Title:
IMPROVEMENTS IN OR RELATING TO DOWNHOLE PULLING TOOLS
Document Type and Number:
WIPO Patent Application WO/2020/104770
Kind Code:
A1
Abstract:
A signalling mechanism (10) in a downhole pulling tool (12), with an arrangement of stacked pistons (22), which indicates the operational status of the downhole pulling tool. When the downhole pulling tool (12) is stroked, sleeve members (52) in the signalling mechanism travel between an inner mandrel (18) and outer housing (14) of the downhole pulling tool (12) to align a first release (40) port in the inner mandrel with a second release port (42) in the outer housing and thereby create a fluid passageway. The pressure dump to the annulus outside the tool is a signal detected at surface to indicate that the downhole pulling tool is fully stroked.

Inventors:
HILLIARD PAUL (GB)
Application Number:
PCT/GB2019/053209
Publication Date:
May 28, 2020
Filing Date:
November 13, 2019
Export Citation:
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Assignee:
ARDYNE HOLDINGS LTD (GB)
International Classes:
E21B23/01; E21B23/04; E21B31/00; E21B31/113; E21B31/18; E21B31/20
Foreign References:
US3752230A1973-08-14
US2915126A1959-12-01
US2984302A1961-05-16
US20170198558A12017-07-13
US20110030955A12011-02-10
US20160076327A12016-03-17
US8365826B22013-02-05
US20160076327A12016-03-17
Attorney, Agent or Firm:
IPENTUS LIMITED (GB)
Download PDF:
Claims:
CLAIMS

1. In a downhole pulling tool including a plurality of pistons arranged in an annular bore between an outer housing and an inner mandrel, each piston configured to move a distance equal to a stroke length of the downhole pulling tool upon application of fluid from a central bore in the inner mandrel passing through ports into the annular bore and acting on a face of each piston, providing a signalling mechanism, the signalling mechanism comprising a first release port through a wall of the inner mandrel, a second release port through a wall of the outer housing, the first release port and the second release port being arranged to align and provide a fluid path from the central bore to an outer surface of the outer housing, to create a pressure dump, when the downhole pulling tool has stroked and the pistons have travelled the stroke length.

2. A signalling mechanism according to claim 1 wherein the signalling mechanism includes a seal, the seal arranged adjacent the second release port, to prevent the passage of fluid from the second release port to between the inner mandrel and the outer housing.

3. A signalling mechanism according to claim 2 wherein the seal is an o-ring arranged circumferentially around an inner surface of the outer housing.

4. A signalling mechanism according to claim 2 or claim 3 wherein the signalling mechanism comprises a plurality of sleeve members, the sleeve members arranged axially between the inner mandrel and the outer housing in a further annular bore and wherein the seal abuts one of the plurality of sleeve members as the downhole pulling tool is stroked and the first release port and the second release port align. 5. A signalling mechanism according to claim 4 wherein a first and a second sleeve member are spaced apart and attached to the inner mandrel to create an annular chamber between the first and second sleeve members, the inner mandrel and the outer housing .

6. A signalling mechanism according to claim 5 wherein a third sleeve member is arranged in the annular chamber, the third sleeve member axially moveable in the annular chamber and biased towards the first sleeve member.

7. A signalling mechanism according to claim 6 wherein the third sleeve member is biased by action of a spring located in the annular chamber between the second sleeve member and the third sleeve member.

8. A signalling mechanism according to claim 7 wherein in a first configuration, the first sleeve member covers the second release port and the third sleeve member is biased against the first sleeve member and covers the first release port.

9. A signalling mechanism according to any one of claims 5 to 8 wherein the first sleeve member has a length greater than the stroke length.

10. A signalling mechanism according to claim 7 wherein in a second configuration, the first sleeve is on one side of the second release port and the third sleeve member is on an opposing side of the second release port there being a space between the first sleeve member and the third sleeve member, the third sleeve member is biased aga inst a stop and the first release port is alig ned with the second release port.

11. A signalling mechanism according to claim 10 wherein the first sleeve member has a length greater than the stroke length.

12. A signalling mechanism according to claim 10 wherein in the second configuration the third sleeve member covers and abuts the seal.

13. A method of signalling an operational status of a downhole pulling tool, including the steps:

(a) providing a downhole pulling tool with a signalling mechanism according to any one of claims 1 to 12;

(b) arranging the downhole pulling tool in an extended position with the signalling mechanism in the initial configuration;

(c) passing fluid through the central bore so as to enter chambers and act on the plurality of pistons to stroke the downhole pulling tool and move an object connected to a lower end of the downhole pulling tool upwards by a stroke length;

(d) aligning the first release port and the second release port at an end of the stroke and passing fluid from a central bore to an outer surface of the downhole pulling tool to create a pressure signal detectable at surface.

14. A method of signalling an operational status of a downhole pulling tool according to claim 13 wherein the method includes the step of moving the inner mandrel and the outer housing relative to each other to actuate the signalling mechanism.

15. A method of signalling an operational status of a downhole pulling tool according to claim 13 or claim 14 wherein the method includes the step of moving a plurality of sleeve members in the signalling mechanism during the stroke.

16. A method of signalling an operational status of a downhole pulling tool according to claim 15 wherein the method includes biasing a third sleeve member arranged axially between a first sleeve member and a second sleeve member against the first sleeve member.

17. A method of signalling an operational status of a downhole pulling tool according to claim 16 wherein the method includes arranging the signalling mechanism in a first configuration, wherein the first sleeve member covers the second release port and the third sleeve member is biased against the first sleeve member and covers the first release port, and running the downhole pulling tool into the well with the downhole pulling tool fully extended. 18. A method of signalling an operational status of a downhole pulling tool according to claim 16 or claim 17 wherein at step (c), as the downhole pulling tool is stroked and the inner mandrel and outer housing move relative to each other, the first sleeve member travels under the second release port while maintaining cover of the second release port, and the third sleeve member covers the first release port.

19. A method of signalling an operational status of a downhole pulling tool according to any one of claims 16 to 18 wherein, to reach step (d) at the end of a stroke:

the first sleeve member has:

travelled under the second release port, and

cleared the second release port;

the third sleeve member has:

been stopped before reaching the second release port acted against the bias and thereby moved relative to the inner mandrel to separate from the first sleeve member and created a space therebetween, and

cleared the first release port,

wherein the first release port and the second release port are aligned with the space to allow the passage of fluid from the central bore to the outer surface of the outer housing .

20. A method of signalling an operational status of a downhole pulling tool according to claim 19 wherein the method includes the step of stopping the third sleeve member when it covers and abuts the seal.

Description:
IMPROVEMENTS IN OR RELATING TO

DOWNHOLE PULLING TOOLS

The present invention relates to downhole pulling tools which are adapted to be anchored in tubing and through an arrangement of stacked pistons generate a substantial axial force to pull upward on a fishing tool connected to the lower end of the pulling tool when the fishing tool is connected to a stuck object in the well. More particularly, this invention relates to an apparatus and method to indicate an operational stage of a downhole pulling tool when in a well.

There has been a constant need in the oil and gas industry to develop tools to move objects in a wellbore such as retrieving a stuck tool or, more recently, recovering a section of cut casing in a well abandonment program.

US2011030955 describes a hydraulically powered fishing tool for retrieving another tool or tubular stuck in a well. A tool housing is supported in a well on a work string, and the housing encloses a plurality of pistons each movable in response to pressurized fluid transmitted through the work string. An anchor axially fixes the position of the tool in the well, and a tool mandrel is axially movable relative to the tool housing when the anchor is set. A fishing device engages another tool or tubular, so that axial movement of the mandrel in response to the plurality of pistons dislodges the stuck tool or tubular. This arrangement has been used as a downhole power tool, DHPT, in the TITANĀ® single trip casing cutting and pulling system provided by Ardyne Technologies Limited, UK.

US2016076327 describes a pulling tool deployed on a workstring to retrieve a well component, such as casing or a liner, stuck downhole. The tool has an anchor, a puller, and an implement. The implement is supported on the end of the puller and engages the component. Hydraulic pressure supplied downhole moves at least one puller piston coupled to the implement along a piston mandrel to pull the implement and component. An anchor mandrel coupled to the workstring and the piston mandrel anchors the pulling tool downhole. The anchor has slips disposed on the anchor mandrel that engage in surrounding casing when an anchor piston disposed on the anchor mandrel is hydraulically actuated with the communicated pressure.

Both these tools, like many pulling tools, use an arrangement of stacked pistons to generate a substantial axial force to pull upward on a fishing tool connected to the lower end of the pulling tool. The stacked pistons are arranged in an annular bore between a mandrel and an outer housing. The pistons are mounted on either the mandrel or the outer housing. The mandrel/outer housing is attached to the fishing tool and by the entry of fluid from a central bore to chambers in the annular bore, fluid acts on the pistons and the mandrel/outer housing moves upwards relative to the anchored pulling tool to pull the fishing tool upwards towards the pulling tool. The axial movement of each piston through a chamber determines the stroke length of the pulling tool.

As the fishing tool is attached to a stuck object and there is no physical displacement on the tool string as it is anchored at or above the pulling tool, it can be difficult to determine when and if the pulling tool has completed its stroke and the object has been moved.

It is therefore an object of the present invention to provide an apparatus and method to indicate an operational stage of a downhole pulling tool when in a well. According to a first aspect of the present invention, in a downhole pulling tool including a plurality of pistons arranged in an annular bore between an outer housing and an inner mandrel, each piston configured to move a distance equal to a stroke length of the downhole pulling tool upon application of fluid from a central bore in the inner mandrel passing through ports into the annular bore and acting on a face of each piston, providing a signalling mechanism, the signalling mechanism comprising a first release port through a wall of the inner mandrel, a second release port through a wall of the outer housing, the first release port and the second release port being arranged to align and provide a fluid path from the central bore to an outer surface of the outer housing, to create a pressure dump, when the downhole pulling tool has stroked and the pistons have travelled the stroke length.

In this way, at the end of a stroke, the pressure dump is detected at surface as fluid exits the tool to indicate that the downhole pulling tool has operated successfully and any object connected to the pulling tool will have been moved a distance equal to the stroke length.

Preferably, the signalling mechanism includes a seal, the seal arranged adjacent the second release port, to prevent the passage of fluid from the second release port to between the inner mandrel and the outer housing. More preferably, the seal is an o-ring arranged circumferentially around an inner surface of the outer housing. More preferably, the signalling mechanism comprises a plurality of sleeve members, the sleeve members arranged axially between the inner mandrel and the outer housing in a further annular bore and wherein the seal abuts one of the plurality of sleeve members as the downhole pulling tool is stroked and the first release port and the second release port align. In this way, the seal is held in position at all times. The mechanism therefore does not have a port passing over a seal and so prevents release or damage to the seal. Preferably, a first and a second sleeve member are spaced apart and attached to the inner mandrel to create an annular chamber between the first and second sleeve members, the inner mandrel and the outer housing. More preferably, a third sleeve member is arranged in the annular chamber, the third sleeve member axially moveable in the annular chamber and biased towards the first sleeve member. In this way, the third sleeve member can be moved with respect to the first sleeve member.

Preferably the third sleeve member is biased by action of a spring located in the annular chamber between the second sleeve member and the third sleeve member.

Preferably, the signalling mechanism is initially in a first configuration, the first sleeve member covers the second release port and the third sleeve member is biased against the first sleeve member and covers the first release port. In this way, the signalling mechanism is not operational when the downhole pulling tool is run into the well, the downhole pulling tool is fully extended and has not been stroked.

Preferably, the first sleeve member has a length greater than the stroke length. In this way, as the downhole pulling tool is stroked and the inner mandrel and outer housing move relative to each other, the first sleeve member travels under the second release port while maintaining cover of the second release port.

The signalling mechanism may be placed in a second configuration, the first sleeve is on one side of the second release port and the third sleeve member is on an opposing side of the second release port there being a space between the first sleeve member and the third sleeve member, the third sleeve member is biased against a stop and the first release port is aligned with the second release port. In this way, fluid passes through the space to enter and exit the first release port and the second release port when the pressure dump occurs for signalling. Preferably, in the second configuration the third sleeve member is covers and abuts the seal. In this way, the seal is maintained in contact with a sleeve member at all times.

According to a second aspect of the present invention there is provided a method of signalling an operational status of a downhole pulling tool, including the steps:

(a) providing a downhole pulling tool with a signalling mechanism according to the first aspect,

(b) arranging the downhole pulling tool in an extended position with the signalling mechanism in the first configuration;

(c) passing fluid through the central bore so as to enter chambers and act on the plurality of pistons to stroke the downhole pulling tool and move an object connected to a lower end of the downhole pulling tool upwards by a stroke length;

(d) aligning the first release port and the second release port at an end of the stroke and passing fluid from a central bore to an outer surface of the downhole pulling tool to create a pressure signal detectable at surface.

In this way, the signalling mechanism provides a pressure dump through a change in pressure as a signal to surface indicating that the downhole pulling tool has successfully operated and completed a stroke. At step (d) the signalling mechanism is in the second configuration.

Preferably the method includes the step of moving the inner mandrel and the outer housing relative to each other to actuate the signalling mechanism. In this way, the signalling mechanism is mechanically operated and is not dependent on fluid pressure within the downhole pulling tool. Preferably the method includes the step of moving a plurality of sleeve members in the signalling mechanism during the stroke. In this way, the first and second release ports can be selectively covered. Preferably the method includes biasing a third sleeve member arranged axially between a first sleeve member and a second sleeve member against the first sleeve member.

Preferably the method includes arranging the signalling mechanism in an initial configuration, wherein the first sleeve member covers the second release port and the third sleeve member is biased against the first sleeve member and covers the first release port, and running the downhole pulling tool into the well with the downhole pulling tool fully extended. In this way, the downhole pulling tool has not been stroked.

Preferably, at step (c), as the downhole pulling tool is stroked and the inner mandrel and outer housing move relative to each other, the first sleeve member travels under the second release port while maintaining cover of the second release port, and the third sleeve member covers the first release port.

Preferably, to reach step (d) at the end of a stroke:

the first sleeve member has:

travelled under the second release port, and

cleared the second release port;

the third sleeve member has:

been stopped before reaching the second release port

acted against the bias and thereby moved relative to the inner mandrel to separate from the first sleeve member and created a space therebetween, and

cleared the first release port, wherein the first release port and the second release port are aligned with the space to allow the passage of fluid from the central bore to the outer surface of the outer housing. In this way, at the end of the stroke the ports are brought into alignment to allow fluid under pressure to exit the signalling mechanism.

Preferably, the method includes the step of stopping the third sleeve member when it covers and abuts the seal. In this way, the seal is maintained in contact with a sleeve member at all times.

In the description that follows, the drawings are not necessarily to scale. Certain features of the invention may be shown exaggerated in scale or in somewhat schematic form, and some details of conventional elements may not be shown in the interest of clarity and conciseness. It is to be fully recognized that the different teachings of the embodiments discussed below may be employed separately or in any suitable combination to produce the desired results. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes.

All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein including (without limitations) components of the apparatus are understood to include plural forms thereof. Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings of which :

Figure 1 is a cross-sectional view through a signalling mechanism in a downhole pulling tool arranged in a first configuration according to an embodiment of the present invention;

Figure 2 is an exploded view of a portion of the signalling mechanism of Figure 1 ; Figure 3 is a cross-sectional view through the signalling mechanism in the downhole pulling tool of Figure 1 arranged in a second configuration;

Figure 4 is an exploded view of a portion of the signalling mechanism of Figure 3; and

Figures 5(a)-(c) are schematic illustrations of steps in a method of running a downhole pulling tool and operating a signalling mechanism in the downhole pulling tool, according to an embodiment of the present invention.

Reference is initially made to Figures 1 and 2 of the drawings which illustrates a signalling mechanism, generally indicated by reference numeral 10, in a downhole pulling tool 12 according to an embodiment of the present invention. In Figure 1 a downhole pulling tool 12 is illustrated and in Figure 2 an exploded view of the signalling mechanism 10 of the pulling tool 12 is shown. Downhole pulling tools are known in the art and may be referred to as a jack. A suitable design of a pulling tool 12 is shown in Figure 1. This design of pulling tool 12 is adapted to provide an outer diameter of less than 4.5 inches (114.3 mm) to be deployed through production tubing. The pulling tool 12 is based on the power section of the hydraulically powered fishing tool as described in US 8365826 and incorporated herein by reference.

Pulling tool 12 comprises an outer housing 14 with an upper connection 16 being a standard box section for connection in a string. A mandrel 18 is located in the bore 20 of the housing 14 with a series of pistons 22 mounted on the mandrel 18 extending over an annular bore 24 between the mandrel 18 and the housing 14. While only three pistons 22a-c are shown there may by any number to cause sufficient force increase based on the combined surface area of the faces 26 of each piston. The outer housing 14 includes stops 28 arranged in the annular bore 24 between the pistons 22. The mandrel 18 extends from the lower end 30 of the housing 14 and includes a coupling piece 32 to attach the mandrel 18 to a fishing tool. Ports 34 through the mandrel 18 allow fluid under pressure to be entered between the piston faces 26 and stops 28 to thereby move the pistons 22 and with them the mandrel 18 upwards in the bore 20. This pulls the fishing tool, together with any object attached thereto, connected to the coupling piece 32 upwards towards the outer housing 14. In Figure 1 the pulling tool 12 is shown in an initial extended position as would occur when being run in the well. The mandrel 18 is connected to the outer housing 14 by shear screws/pins 38 which are set to shear and allow the mandrel 18 to move relative to the outer housing 14 when pressure through the bore 20 exceeds the rating of the shear pins 38. When the mandrel 18 is released it can move upwards in the bore 20 as described above, and this strokes the pulling tool 12. As the pulling tool

12 strokes the mandrel 18 moves a length equal to the distance each piston 22 travels relative to the stops 28. This is the stroke length 60 of the pulling tool 12. Once stroked the pulling tool 12 is now as shown in Figure 3.

The pulling tool 12 also includes a locking mechanism 36 to prevent movement of the mandrel 18 relative to the housing 14 until the tool requires to be used, the locking mechanism being resettable in the well. Further, the pulling tool 12 includes a signalling mechanism 10 to provide an indication when the tool 12 has stroked and pulled the coupling piece 32 as close to the housing 14 as possible and the tool 12 is fully contracted.

It will be appreciated that to operate the pulling tool 12, the outer housing 14 must be anchored to tubing in the well. As the outer housing 14 is connected to the work string an anchor can be located on the string at any suitable position above the pulling tool 12 and work independently of the pulling tool 12. Alternatively, as for the pulling tools described in US2011030955 and US20160763327, the anchor can be formed integrally on the outer housing 14 or mandrel 18, respectively. Now referring to the signalling mechanism 10. The signalling mechanism 10 provides a first release port 40 in the mandrel 18 and a second release port 42 in the outer housing 14 which, when aligned as shown in Figures 3 and 4, provide a passageway 44 for fluid to travel from the central bore 20 to outer surface 48 of the outer housing 14 outside of the pulling tool 12. Towards an upper end of outer housing 14 above the pistons 22 the second release port 42 is located through the wall of the outer housing 14. While one aperture is shown, there may be more arranged circumferentially around the housing 14, though a larger pressure signal will be detected through a single port. On the lower side of the port 42 is located a seal 48. The seal 48 is held in a carriage 50 which provides two of four bounding walls around the seal 48. The third bounding wall is provided by the housing 14 as the carriage 50 is recessed therein. The fourth wall is initially provided by a circumferential first sleeve member 52 which abuts inner surface 54 of the outer housing 14. The seal 48 is a o- ring arranged circumferentially around the inner surface 54 of the outer housing 14 to thereby seal between the outer housing 14 and the first sleeve member 52.

The first sleeve member 52 is located over the mandrel 18 and connected and sealed thereto. The first sleeve member 52 has a length greater than the stroke length so that the seal 48 can be covered for the majority of the stroke length. At the end of the first sleeve member 52 the first release port 40 is arranged through the mandrel 18. Spaced apart from the first sleeve member 52 along the mandrel 18 is a second sleeve member 56 being fixed to the mandrel 18. This creates a chamber 58 bounded by the mandrel 18, outer housing 14, first sleeve member 52 and second sleeve member 56. Within this annular chamber 58 is located a third sleeve member 62. Third sleeve member 62 is floating so can travel along the mandrel 18 in the chamber 58. The third sleeve member 62 is biased towards the first sleeve member 52 by the incorporation of a spring 64 located in the chamber 58 between the second sleeve member 56 and third sleeve member 62. An end 66 of the first sleeve member 52 therefore abuts an end 68 of the third sleeve member 62 in the initial or first configuration shown in Figure 1. This is the configuration in which the pulling tool 12 is run in the well, with a fishing tool attached to the coupling piece 32. The first release port 40 is covered by the third sleeve member 62 and the second release port 42 is covered by the first sleeve member 52. The shear pins 38 prevent relative movement between the mandrel 18 and the outer housing 14 and the tool 12 remains in an extended configuration with the coupling piece 32 spaced apart from the lower end 30 of the outer housing 14.

When the fishing tool is attached to the object to be moved and movement is required, an anchor will be set above the pulling tool 12 to hold the outer housing 14 in a static position. Fluid pumped through the central bore 20 from surface will activate the pulling tool 12 as described herein before. The pins 38 will shear and fluid entering the ports 34 to the annular bore 24 will act on the piston faces 26. The pistons 22 will move upwards relative to the outer housing 14, pulling the coupling piece 32, the fishing tool and the object attached thereto. In the prior art pulling tool 12, the operator does not know if the object has been moved or if so, by how much. Typically pumping of fluid is merely continued for a set period of time and it is assumed that the object has been moved and the tool 12 has stroked. Only once the anchor is unset and the pulling tool 12 raised on the string can it be determined whether the object has moved and therefore the pulling tool 12 has likely stroked.

In the present invention, as the pulling tool 12 is stroked, the mandrel 18 moves up the central bore 20 taking the first sleeve member 52 and second sleeve member 56 with it. The second release port 42 remains covered by the first sleeve member 52 which also keeps the seal 48 between the mandrel 18 and the outer housing 14. The first release port 40 also remains covered by the third sleeve member 62. When the third sleeve member 62 reaches the carriage 50, a shoulder 70 on the third sleeve member 62 abuts a protruding edge 72 on the carriage 50 and its longitudinal movement along the bore 20 is stopped. As the mandrel 18 is still moving, the spring 64 is now compressed as the end 66 of the first sleeve member 52 moves away from the end 68 of the third sleeve member 62. This separation occurs at the second release port 42 and the first release port 40 becomes exposed at this position as it moves ahead of the now static third sleeve member 62. The space 74 created between the ends 66,68 lies between the now aligned first release port 40 and second release port 42. This is as shown in Figures 3 and 4 and may be considered as the second configuration. The mandrel 18 is stopped in this position as the pistons 22 have reached the stops 28 and the pulling tool 12 is fully stroked. The mandrel 18 carrying the pistons 22 have travelled the stroke length 60 and pulled the coupling piece 32, fishing tool and object up towards the end 30 of the housing by this distance. At this configuration a fluid passageway 44 is therefore created from the central bore 20, through the first release port 40, the space 74, the second release port 42 to the outer surface 46 and fluid under pressure is suddenly released through this opened passageway 44. The pressure increase in fluid within the annulus between the string and the tubing which the pulling tool 12 is run-in provides a detectable signal at surface. The operator then knows that the pulling tool 12 has fully stroked, the object has been moved and the anchor can be released. It is noted that when the third sleeve member 62 is stopped at the carriage 50, a portion of the third sleeve member has passed under the seal 48. In this way, the seal 48 is always supported and is prevented from extruding out of its housing which can occur if a port is passed over the seal 48.

The signalling mechanism 10 can be reset to the initial configuration by movement of the outer housing 14 upwards relative to the mandrel 18. This will occur when the anchor is unset and the pulling tool 12 is raised on the string. The weight of the fishing tool and object will cause the mandrel 18 to remain in place until the pistons 22 contact the stops 28 below them. The pulling tool 12 is then back at its fully extended and unstroked positioned. The pulling tool 12 with the fishing tool can then be pulled from the well or if additional pulling is required, the anchor can be set and the pulling tool 12 stroked again.

Reference is now made to Figures 5(a) to (c) which illustrate the steps in operating the signalling mechanism 10 in the downhole pulling tool 12 according to an embodiment of the present invention. In Figure 5(a), the signalling mechanism 10 is arranged in the initial configuration on the pulling tool 12 and the pulling tool 12 is in the extended unstroked configuration. The pulling tool 12 is mounted on a string 76 with an anchor 78 above and a fishing tool 80 below. There may be other tools on the string 76. The string 76 is run in tubing 82 in a well 84 and the object 86 to be moved is tagged. The fishing tool 80 is connected to the object 86 and the anchor 78 set to grip the tubing 82. This is as shown in Figure 5(b). With the outer housing 14 now static, fluid is pumped through the pulling tool 12 and the fishing tool 80 and object 86 are pulled upwards on the mandrel 18 into the outer housing 14 as the tool 12 is stroked. After the mandrel 12 has travelled the stroke length 60, the signalling mechanism 10 is actuated as described hereinbefore. Passageway 44 is opened and a pressure dump occurs from the tool 12 into the annulus 88. This creates a pressure signal 90 which is carried up the annulus 88 to be detected at surface. An operator then knows that the tool 12 has fully stroked and the anchor 78 can be released. This is as illustrated in Figure 5(c). The principle advantage of the present invention is that it provides a signalling mechanism to indicate the operational status of a downhole pulling tool in a well.

A further advantage of the present invention is that it provides a signalling mechanism on a downhole pulling tool which automatically provides a signal at the end of a stroke.

A yet further advantage of the present invention is that it provides a signalling mechanism on a downhole pulling tool which requires no electrical power or signals. The foregoing description of the invention has been presented for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. The described embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilise the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Therefore, further modifications or improvements may be incorporated without departing from the scope of the invention herein intended with the invention being defined within the scope of the claims.