GB2099887A - Slack adjustment for slip system in downhole well apparatus - Google Patents

Abstract

A well packer 10 or other downhole tool apparatus comprises a mandrel 12, a slip assembly 70 around the mandrel including wedge means 60 that are movable to force slip members 72 radially outwardly into gripping contact with the conduit and slack adjusting means 52, 54, 56 and 58 for adjustably positioning the slip assembly 70 to cause the slip members 72 to be retained in an inwardly retracted position substantially to prevent the slip members from engaging the conduit during insertion of the tool. <IMAGE>

Description

SPECIFICATION Slack adjustment for slip system in downhole well apparatus The present invention pertains to downhole tools typically used in the oil and related industries for providing an annular seal and/or anchoring system between one conduit disposed in another and, in particular, the present invention is directed to an arrangement for adjusting the slack in the anchoring mechanism for such tools.

There are a number of different downhole tools used in the well drilling industry which provide for a seal to be established in the annulus between one conduit and another in the well such as between the well bore and tubing, or between the well casing and tubing disposed within the casing.

A typical example of the class of tools described herein is known in the trade as a packer and is characterised by an elongated cylindrical inner housing or mandrel around which are disposed one or more resilient collars which may be axially compressed to expand radially outward into sealing engagement with the inner wall of a conduit to form an annular seal. Typically, downhole tools such as packers also include anchoring mechanisms known as slips comprising radially extendable toothed gripper elements which are engageable with the conduit inner wall for anchoring the tool in the desired position so that the seal elements are not required to withstand substantial axial loading. The seal elements and slip mechanism are usually arranged axially in an assembly which includes a setting mechanism disposed on and around the aforementioned mandrel.

Some downhole tools such as retrievable packers are fairly complex mechanical devices and require a number of components making up the setting mechanism, the slip assembly and the packing element assembly. The manufacturing tolerances required for maintaining reasonable production costs, as well as the inherent design characteristics of, for example, the slip assembly results in considerable slack or axial looseness of the components when the tool is assembled in the relaxed or "running" condition. The particular, the accepted and preferred design for the slip assembly results in considerable axial looseness of the coacting parts when the slip assembly is in the relaxed or retracted position.A preferred arrangement of the slip assembly comprises radially movable slip elements having gripper teeth on the exterior surface thereof, which elements are cooperable with so called cone or wedge members. The slip cones or wedge members are adapted to be moved axially on the exterior of the mandrel to force the slip elements radially outwardly into gripping engagement with the conduit inner wall surface. The slip elements and the wedge members are normally provided with cooperating tenon and groove portions of a T-slot or dovetail configuration to retain the members in assembly with each other and to provide for the relative movement necessary during the setting and retracting operations.

The relatively loose fit between coacting parts inherent in the design of elements as described above and necessary for proper mechanical operation results in the possibility of the slip elements being so loose during the running operation of the tool that they may accidentally come into contact with the interior wall of the well conduit, which contact may result in damage to the slip elements as well as other tool components. Hence, it is desirable that in the relaxed condition of the sealing elements and the slip mechanism that there be no slack in the assembly which will permit outward radial movement of the slip elements which could result in damage of these elements or unwanted snagging of the tool during the running and retrieving operations.The present invention solves the problem of providing a slack adjustment mechanism for downhole well tools employing radially movable anchoring slips or the like, which mechanism is simple, reliable and is disposed on the tool in a highly preferred location.

Moreover, the types of tools in which the present invention is embodied tend to be mechanically complex, expensive to manufacture and available in many different models for different specific purposes thereby requiring manufacturers and users to maintain a large number of different parts for the substantial number of different tool models. However, the present invention provides a mechanically simple slack adjusting feature which is located in a highly preferred position on the tool and in which position the associated tool parts are usually not required to be of a different configuration, for different tool models.

The invention provides novel apparatus that can be attached to a member within a well conduit to permit the member to be secured to the conduit. The apparatus comprises an elongated mandrel, a slip assembly around the mandrel and including wedge means positioned around the mandrel and a plurality of movable slip members having surfaces that can cooperate with the wedge means, the wedge means being movable in a first direction to force the slip members radially outwardly into gripping contact with the conduit, and slack adjusting means for adjustably positioning the slip assembly to cause slip members to be retained in a radially inwardly retracted position substantially to prevent the slip members from engaging the conduit during insertion of the apparatus.

The apparatus is generally designed so as to provide a seal that bridges the annulus between the inner member and the outer conduit and may thus also include resilient seal means disposed around the mandrel and first and second seal urging means disposed around the mandrel and facing each other with the seal means between them and with the second seal urging means being axially movable with respect to the first seal urging towards each other to force the seal means radially outwardly into forcible engagement with the conduit.

The slack adjusting means are preferably disposed between the second seal urging means and the slip assembly.

The wedge means may comprise at least one annular wedge member axially movable with respect to the slip members and the slack adjusting means may include means that are engageable with the wedge member and operable to move the wedge member axially to retract the slip members radially inwardly with respect to the mandrel. The means engageable with the wedge member may comprise an annular sleeve around the mandrel between the annular sealing means and the wedge member and engageable with the wedge member by way of cooperating threads on the sleeve and wedge member.

The sleeve may include means operable to limit axial movement of the sleeve towards the wedge member, whereby in response to rotation of the sleeve with respect to the wedge member the wedge member is caused to move axially so as to urge the slip members into the retracted position through the cooperating surfaces. The sleeve may include an annular shoulder engageable with means connected to the mandrel for limiting the axial movement of the sleeve towards the wedge member.

The wedge member may include an axially extending tubular portion having external threads formed on the distal end thereof and cooperable with internal threads formed on the sleeve. The tubular portion may include a cylindrical undercut portion between the external threads and the remainder of the wedge member. The apparatus may include locking means interconnecting the sleeve and the wedge member to prevent rotation of the sleeve with respect to the wedge member, this locking means preferably comprising at least one lock screw threadedly engaged with the sleeve and forcibly engageable with the undercut portion to prevent relative rotation between the sleeve and the wedge member.

The first seal urging means preferably comprises a downwardly facing annular shoulder formed on the mandrel and the second seal urging means preferably comprises an upwardly facing annular shoulder formed on a sleeve around the mandrel. This sleeve on which the second seal urging means are formed may be the means engageable with the wedge member.

There may be an intermediate wedge member positioned between the first and second wedge members and the radially movable slip members may be interengaged with the wedge members by way of cooperating groove and tenon means formed on the wedge members and on the slip members. The apparatus may include actuating means for moving the slip members and the sealing means radially outwardly into gripping and sealing engagement respectively with the well bore. The slack adjusting means preferably comprise cooperable threaded members disposed on the mandrel between the slip means and the sealing means.

One of the members of the slack adjusting means may include surface means engageable with means connected to the mandrel for limiting the axial movement of the one member in one direction on the mandrel and may include an elongated sleeve slidably disposed on the mandrel, the sleeve including an annular inner shoulder engageable with a cooperating shoulder on the mandrel, and the sleeve including also an outer annular shoulder engageable with the surface means on the said one member.

The slack adjusting means preferably comprises also means for engaging the mandrel and one of the annular wedge members for holding that member fixed relative to the mandrel, and means for moving the other of the annular wedge members relative to the mandrel to cause the slip members to be inwardly retracted. The holding means preferably comprise releasable means, generally ball means positioned within groove means.

Thus the invention can provide a well packer that can be rugged and capable of withstanding the substantial axial loading associated wtih setting the packer. The well packer may have single or double sets of radially extendable and retractable anchoring slips wherein a threaded annular sleeve is provided which is threadedly engaged with one of the axially slidable slip wedge members disposed on the exterior of the packer inner housing or mandrel. Accordingly, by simple rotation of the sleeve, one end of the slip assembly is moved axially to remove any slack or looseness between the interfitting parts of the slip assembly and to thereby prevent the slips from unwatned engagement with the inner wall of the conduit through which the packer is being run to and from the working position.

The invention is now described by reference to the accompanying drawings in which: Figure 1A through 10 together comprise a vertical elevation view, in section, of a downhole well apparatus including the slack adjusting mechanism of the present invention; Figure 2 is transverse section taken along the line 2-2 of Figure 1 A.

Figure 3 is a detail section view taken along the line 3-3 of Figure 1 B; and Figure 4 is detail section view taken along the line 21 4 of Figure 1 A.

In the drawings, the figures with combined number and letter designations are intended to be viewed together arranged vertically end to end with the first letter designation, in alphabetical order, arranged as the top section of the view and the last letter designation arranged as the bottom section. In the following description the terms upper and lower are used for convenience in regards to the normal arrangement of the apparatus when it is being inserted in a generally vertically disposed well or the like. However, for some applications the apparatus may be inverted, if desired, or used in a generally horizontal or angular direction.

Referring to Figures 1 A through 1C of the drawings the apparatus embodying the present invention is illustrated and generally designated by the numeral 10. The apparatus 10 comprises a downhole tool, commonly known as a well packer, forforming an annular seal between concentric conduits in a well, which seal may be provided for various purposes in developing the well. Although the slack adjusting mechanism of the present invention is particularly advantageously used with the packer 10 it will be understood by those skilled in the art that the slack adjusting mechanism may also be used with other packers as well as similar types of downhole equipment which would benefit therefrom.

The packer 10 includes an elongated cylindrical tubular inner member 12, commonly referred to as the mandrel. The mandrel 12 is made up of an elongated generally tubular section 14 which is threadedly connected at its upper end to a sub 1 6 and is connected at its lower end, referring to figure 1 B, to a second section 18. The lower end of the section 18 of the mandrel 12 is threadedly connected to a lower sub 20. The sub 1 6 is provided with an internally threaded portion 22 whereby the packer 10 may be connected to the lower end of a tubing string or other well tool for lowering the packer to the working position in a well bore or casing, not shown.The packer 10 is provided with an interior passage 24 formed bv the bores of the members 14 ana 18, through which passage various tools may be passed while performing operations in the well and through which fluids may be introduced or extracted depending on the operation being performed.

The packer 10 also includes a relatively large number of components which are held in assembled relationship around the outer cylindrical surfaces of the mandrel sections 14 and 1 8. These components perform various functions including anchoring the packer 10 in a set position in a well bore and forming a fluid tight seal in the annular passageway between the inner wall of the well bore or casing and the exterior of the packer. Referring to Figure 1 A, the sub 1 6 comprises in effect a part of the mandrel 12 and includes an axially extending tubular portion 26 which forms an annular downward facing shoulder 28. The tubular portion 26 has an enlarged interior bore 30 providing a chamber 32 into which well fluids may be introduced through a radial passage 34.The packer 10 is provided with an elongated so-called booster sleeve 36 which is slidably disposed around the exterior of the mandrel section 1-4 and is engageable with the section 14 along respective cooperating annular faces 37 and 38, as illustrated in Figure 1A.

The packer 10 is provided with suitable fluid sealing means comprising, in the exemplary arrangement shown, a radially deformable ring like member 40 made of a suitable elastomeric resilient material. The member 40 is positioned between substantially rigid force transmitting back up rings 42 of conventional design. The sealing means represented by the member 40 and the back up rings 42 is disposed between the downwardly facing shoulder 28 and an upwardly facing annular shoulder 44 formed on a tubular sleevelike member 46. The member 46 forms one component of a slack adjusting mechanism to be explained in further detail herein.

As illustrated in Figure 1 A, the member 46 is provided with an inner annular shoulder 48 engageable with a cooperating shoulder 50 formed on the booster sleeve 36. When the packer 10 is in the working condition the booster sleeve 36 is responsive to any fluid pressure differentials on opposite sides of the annular seal formed by the member 40 to urge the seal member further in the sealing position. The shoulder 48 could also be adapted to engage a cooperating shoulder on the section 14 if the booster sleeve 36 was not provided as shown. As will be appreciated viewing Figure 1A the sealing element assembly is disposed in surrounding relationship to the outer diameter of the sleeve 36 and is relatively loosely supported thereon when the packer 10 is in the relaxed or so-called running condition.

Referring to Figure 1A, the member 46 includes an axially extending portion 52 provided with internal threads 54 which are cooperable with external threads 56 formed on an upward axially extending portion 58 of a wedge member 60. The member 60, also known as a slip cone, is part of an anchoring mechanism for the packer 10 which will be explained in futher detail herein.

Referring also to Figure 2, the lower end of the axial portion 52 includes opposed radially inwardly projecting lock screws 62 which are threadedly engaged with the member 46 and are adapted to extend into engagement with a thread relieved or undercut cylindrical surface portion 63. The screws 62 are preferably of the socket head type and are provided for locking the member 46 with respect to the member 60 to prevent relative rotation therebetween. The inner bore of the member 60 is provided with an axially extending keyway 64, in which is fitted a substantially square cross-section key 66 also extending into a keyway 68 formed in the outer surface of the mandrel section 14. Accordingly, the member 60 is adapted to be axially movable with respect to the section 14 but is prevented from rotating with respect to said section by the key 66.

The aforementioned anchoring assembly for the packer 10 is generally designated by the numeral 70 and comprises, in the embodiment shown, a conventional double slip assembly of a known type. Referring to Figures 1A, 1B and Figure 4, the slip assembly 70 includes a plurality of opposed radially movable slip members 72 which are provided with spaced apart transversely extending teeth 74 along an exterior portion thereof. As shown in Figure 1 A and Figure 4, the wedge member 60 is provided with axially extending and radially inwardly sloping grooves 76 which have a somewhat T-shaped or so called dovetail cross-sectional configuration. The grooves 76 are cooperable with interfitting dovetail tenon portions 78 formed on the members 72.Referring to Figure 3, the opposite ends of the members 72 are also provided with dovetail tenon portions 80 which are interfitted in cooperating grooves 82 formed in a generally cylindrical intermediate slip cone or wedge member 84. As shown in Figures 3 and 4, the interfitted dovetail tenons and slots are dimensioned to provide a loose fit between the cooperating members of the slip assembly to provide for ease of relative movement as is needed between these parts. As shown in Figure 1 B, a plurality of oppositely projecting members 72 are similarly interfitted in oppositely projecting grooves 86 on the member 84 and having a configuration similar to the grooves 82. Th slip assembly 70 is further provided with a lower annular wedge member 88 having sloping dovetail grooves 90 similar to the grooves 76.The wedge member 88 is threadedly engaged with an elongated housing sleeve 92 which extends downwardly in sleeved relationship around the mandrel 12, as shown.

Mechanism for unlocking the anchoring assembly 70 and for setting the packer 10 will now be described briefly. Referring to Figure 1 B in particular, the member 92 is supported in spaced relationship with respect to the mandrel section 14 to form an elongated annular space which is divided by an annular piston 96 into chambers 95 and 97. The chamber 97 is in communication with the bore passageway 24 by way of radial passageways 98.

The lower distal end of the member 88 includes a reduced diameter portion 100 having opposed radially projecting holes 102, in which are disposed ball keys 104 which project radially inwardly into an annular groove 106 in the section 14 and are held in the position shown in Figure 1 B by a surface 108 on an annular sleeve member 110. The member 110 includes a radially outwardly relieved recess portion 112 which may be moved into a position overlying the ball keys 104 to permit the keys to move out of the groove 106 whereby the member 88 is free to slide axially with respect to the mandrel 12.The member 110 is retained in the position shown in Figure 1 B by suitable shear screws, not shown, interconnecting the member 110 with the housing 92 to prevent unwanted displacement of the member 110 into the alternate position described above As shown in Figure 1 B, a coil spring 113 is disposed in the chamber 95 between the member 110 and the piston 96. Alternatively, in place of the spring 113, the piston 96 could be formed to include an axially extended sleeve portion connected to or directly engageable with the member 110.

Referring now particularly to Figure 1 C, the packer 10 is provided with a locking and release mechanism including a body lock ring 122, locking segments 124, and a release sleeve 126.

Those skilled in the art will appreciate that the body lock ring 122 is of the type which has outer circumferential fine threads 123 which are cooperable with threads 93 on the inner surface of the member 92 to prevent axial movement of the mandrel 12 upward, viewing the drawing figures, with respect to the member 92. A detailed ,discussion of the locking and release mechanism including the lock ring 122, the segments 124, and the release sleeve 126 may be obtained by referring to U.S. Patent Application Serial No.

190,308 assigned to the assignee of the present invention.

As will be appreciated from the foregoing description the considerable number of parts making up the anchoring assembly, the sealing or packing assembly and the associated structure would require the maintenance of very critical dimensional tolerances of all parts in order to properly position the parts in the relaxed condition without having either an interference condition on the one hand or too much slack or looseness of the related parts on the other hand. Moreover, the tenon and groove connections between the members 72 and the members 60, 84 and 88 are dimensioned such that, in order to provide for adequate relative movement between these parts to allow the slip members to easily and reliably move radially inwardly and outwardly, a considerable amount of axial play or looseness is inherently present in the relaxed or retracted position of the members 72.

However, it is important that, when the packer 10 is being run into and out of the well bore or casing, the members 72 be held at least snugly in their retracted positions with all of the slack taken out of the dovetail connections so that the teeth 74 do not engage the interior wall of the well casing or other conduit through which the packer is being run. In order to provide reasonable manufacturing tolerances on all of the interrelated parts described above and yet permit this snug fit it has been deemed desirable to provide a slack adjusting mechanism which may be easily adjusted once the tool has been assembled.Such a mechanism eliminates the need for maintaining critical dimensional relationship of the parts of the outer housing and the anchoring and sealing assemblies during the manufacture thereof, or alternatively the requirement for either selective assembly of the parts or the addition of shims or spacers.

Moreover, in accordance with the present invention it has been determined that it is highly desirable to place the slack adjusting mechanism in the preferred position between the anchoring assembly and the sealing mechanism as exemplified by the arrangement in the packer 10.

The provision of two members which are adapted to be axially movable with respect to each other and include one of the slip cones or wedge members simplifies the overall construction of the packer since the contruction of the setting and releasing mechanisms does not have to be compromised to include a slack adjusting mechanism.

In the manufacture of a packer incorporating the slack adjusting mechanism located in the preferred position according to the arrangement of the present invention conventional dimensional tolerances in the metal working art may be maintained in manufacturing virtually all of the components disposed between the sub 1 6 and the sub 20 and mounted around the mandrel 12. In particular, the dimensions of the tenons 78 and 80 and the grooves 76, 82, 86 and 90 may be controlled so that a relatively loose fit is formed between the members 72 and cooperating members 60, 84 and 88.By maintaining relatively loose fits between the slip members 72 and the cooperating wedge members, reliability of performance of the wedging action in the radial outward movement of the members 72 is enhanced, in particular, considering the problems associated with the working environment of a downhole tool such as a well packer. By maintaining relatively loose fits between the tenon and groove portions the setting and release actuating movement of the slip members is effected without a tendency to jam the sliding connections between the slip members and the respective wedge members.

In the operation of preparing the packer 10 for insertion into a well or the like the components disposed around the mandrel 12 are assembled thereover in accordance with conventional practice and after complete assembly any slack or looseness in the slip members 72 is adjusted to virtually zero axial play by rotating the member 46 until the member 60 is moved upwardly to remove all slack in the slip assembly. The member 88 is prevented from axial movement by the ball keys 104 when the member 110 is in the position shown in Figure 1 B. When the member 46 has been rotated sufficiently to remove slack in the slip assembly 70 the lock screws 62 are inserted in the member 46 and tightened against the outer annular surface 63 to prevent further relative rotation between the members 46 and 60.Those skilled in the art will appreciate that the lock screws 62 could be replaced by interference fit type threads for the threads 54 and 56 or the threads could be provided with other locking insert type devices. However the lock screws 62, being retractable out of engagement with the surface 63, permit easy rotation of the member 46 which is of some importance on a tool which may be anywhere from 4.5 to 14 inches in diameter and 4 to 6 feet in length.

The operation of the packer 10 to be set and released in its working position forms no part of the present invention and is believed to be readily understandable to those skilled in the art from the foregoing description in conjunction with the drawings. Briefly, however, the packer 10 is set after running the packer into a well at the end of a tubing string or the like connected to the sub 1 6.

When the packer 10 has reached the position to be set, and with a fluid tight plug, not shown, installed within the passageway 24 below the passages 98, pressure fluid is introduced into the chamber 97 to move the piston 96 upwardly under the urging of the pressure fluid to compress the spring 11 3. Under the urging of the spring 113, and upon shearing of the aforementioned shear screws, the member 110 will move to a position whereby the radial clearance provided by the surface 112 will allow the ball keys 104 to be moved radially outwardly to release the member 88 for axial movement with respect to the member 14. Continued movement of the piston 96, spring 113 and wedge member 88 will result in radial outward movement of the slip member 72 into gripping relationship with the inner wall of the well conduit, such as the bore wall or casing, not shown.Once the slip members 72 have moved into gripping engagement with the well conduit the continued urging of pressure fluid in the chamber 97, acting on the axial projected face area of the section 1 8 in the chamber, will result in further axial movement of the mandrel 12 downward relative to the combined structure of the member 46, the slip assembly 70 and the housing member 92 to elastically deform the packing element 40 radially outwardly into sealing engagement with the conduit. As the lock ring 123 moves downwardly with respect to the member 92, Figure 1 C, the cooperating wicker threads 122 and 93 will operate to lock the mandrel in the maximum downwardly urged position with respect to the member 92.

When it is desired to release the packer from the set position the fluid pressure in the chamber 97 is reduced and a suitable tool is inserted through the passageway 24 to engage the sleeve member 126. Upon sufficient axial movement of the sleeve member 126, in one direction or the other, the segments 124 wil Ibe ejected into the bore of the mandrel section 1 8 to release the locking connection between the mandrel and the components disposed therearound whereby the gripping engagement of the slip assembly 70 with the well conduit will be released and the packing element 40 will retract radially inward. The components disposed along the outer circumference of the mandrel 12 will then resume the respective positions illustrated in Figures 1A through 1 C of the drawing. The relationship of the members 46 and 60, being unchanged as a result of setting or releasing the packer 10, will maintain the slips 72 in a condition wherein there is virtually no slack or axial looseness between the coacting parts of the slip assembly 70 once the packer has assumed the released position.

Accordingly, the packer 10 may be retrieved from the well conduit without damaging the slips 72 and also with minimal chance of engaging or jamming the packer in the well conduit.

Claims (17)

1. Apparatus that can be attached to a member within a well conduit to permit the member to be secured to the conduit, the apparatus comprising an elongated mandrel, a slip assembly around the mandrel and including wedge means positioned around the mandrel and a plurality of movable slip members having surfaces that can cooperate with the wedge means, the wedge means being movable in a first direction to force the slip members radially outwardly into gripping contact with the conduit, and slack adjusting means for adjustably positioning the slip assembly to cause the slip member to be retained in a radially inwardly retracted position substantially to prevent the slip member from engaging the conduit during insertion of the apparatus.

2. Apparatus according to claim 1 including also resilient seal means disposed around the mandrel and first and second seal urging means disposed around the mandrel and facing each other with the seal means between the seal urging members and with the second seal urging member being axially movable with respect to the first seal urging member in a first direction to force the seal means radially outwardly into forcible engagement with the conduit.

3. Apparatus according to claim 2 in which the slack adjusting means are positioned between the second seal urging means and the slip assembly.

4. Apparatus according to claim 3 in which the wedge means comprise at least one annular wedge member axially movable with respect to the slip members.

5. Apparatus according to claim 4 in which the slack adjusting means include means engageable with the wedge member and operable to move the wedge member axially to retract the slip members radially inwardly with respect to the mandrel.

6. Apparatus according to claim 5 in which the means engageable with the wedge member comprise an annular sleeve around the mandrel between the annular sealing means and the wedge member and engageable with the wedge member by way of cooperating threads on the sleeve and wedge member.

7. Apparatus according to claim 6 in which the sleeve includes means operable to limit axial movement of the sleeve towards the wedge member whereby, in response to rotation of the sleeve with respect to the wedge member, the wedge member is caused to move axially to urge the slip members into the retracted position through the cooperating surfaces.

8. Apparatus according to claim 7 in which the sleeve includes an annular shoulder engageable with means connected to the mandrel for limiting the axial movement of the sleeve towards the wedge member.

9. Apparatus according to claim 6 in which the wedge member includes an axially extending tubular portion having external threads formed on the distal end thereof and cooperable with internal threads on the sleeve.

10. Apparatus according to claim 6 including locking means interconnecting the sleeve and wedge member to prevent rotation of the sleeve with, respect to the wedge member.

11. Apparatus according to claim 9 in which the tubular portion of the wedge member includes a cylindrical undercut portion between the external threads and the remainder of the wedge member and the apparatus includes locking means comprising at least one lock screw thradedly engaged with the sleeve and forcibly engageable with the undercut portion tQ prevent relative rotation between the sleeve and the wedge member.

12. Apparatus according to claim 5 in which the second seal urging means comprises an annular axially facing shoulder formed on the means engageable with the wedge member.

13. Apparatus according to claim 12 in which the first seal urging means comprises an annular shoulder formed on the mandrel and facing the shoulder formed on the means engageable with the wedge member.

14. Apparatus according to claim 2 in which the first seal urging means is downwardly facing annular shoulder on the mandrel, the second seal urging means is an upwardly facing annular shoulderformed on a sleeve around the mandrel, the slip means includes an intermediate wedge member disposed between the first and second wedge members and the radially movable slip members are interengaged with the wedge members by way of cooperating groove and tenon means formed on the wedge members and on the slip members, and the slack adjusting means comprise cooperable threaded members disposed on the mandrel between the slip means and the sealing means.

1 5. Apparatus according to any of claims 2 to 14 including actuating means for moving the slip members and the sealing means radially outwardly into gripping and sealing engagement with the bore.

1 6. Apparatus according to any preceding claim in which the wedge means comprise upper and lower annular wedge members and the slack adjusting means comprises means for engaging the mandrel and one of the wedge members for holding that member fixed relative to the mandrel and means for moving the other of the wedge members relative to the mandrel to cause the slip members to be inwardly retracted.

17. Apparatus according to claim 1 6 in which the holding means are releasable holding means.

1 8. Apparatus according to claim 1 7 in which the holding means comprise ball means positioned within a groove.