An Apparatus For Sealing A Bore, A System Comprising The Apparatus And A Method For Using Apparatus

Abstract

This invention relates to a sealing apparatus, system and method for use in a well pipe. The apparatus has a mandrel arranged around a centre axis through the apparatus, a radially movable gripping device arranged around the mandrel, a radially movable packer element arranged around the mandrel, and an axially movable activation device designed to set up axial forces for activating the apparatus. The apparatus also includes a radially movable centralizer arranged around the mandrel for centring the apparatus. The activation device being operatively connected to the gripping device, the packer element and the centralizer for the respective activation and radial movement of each, via power transmission of axial forces, between retracted, passive positions and expanded, active positions relative to the centre axis of the apparatus.

Claims

1. A sealing apparatus (1) for use in a well pipe (2), the sealing apparatus (1) comprises: a mandrel (44) arranged around a centre axis (22) through the apparatus (1), a radially movable gripping device (4) arranged around the mandrel (44); a radially movable packer element (6) arranged around the mandrel (44); and an axially movable activation device (10) designed to set up axial forces for activating the apparatus (1), characterized in that the apparatus (1) further comprises a radially movable centralizer (8) arranged around the mandrel (44) for centring the apparatus (1); and that the activation device (10) is operatively connected to the gripping device (4), the packer element (6) and the centralizer (8) for the respective activation and radial movement of these, via power transmission of said axial forces, between retracted, passive positions and expanded, active positions relative to the centre axis (22) of the apparatus (1).

2. The apparatus according to claim 1, wherein the packer element (6) is arranged between the gripping device (4) and the centralizer (8).

3. The apparatus according to claim 1 or 2, wherein the centralizer (8) is arranged to be activatable before the gripping device (4) and the packer element (6) are activated.

4. The apparatus according to claim 1, 2 or 3, wherein the gripping device (4) and the packer element (6) are blocked from activation before the centralizer (8) is at least partially activated.

5. The device according to any one of claims 1 to 4, wherein the activation device (10) comprises an activator (24) which is rotatable around the centre axis (22) and is in threaded engagement with a central mandrel (44) through the apparatus (1).

6. The apparatus according to any one of claims 1 to 5, wherein the apparatus (1) comprises a releasing device (12) which is operatively connected to the mandrel (44), the gripping device (4), the packer element (6) and the centralizer (8); and the releasing device (12) is arranged for selectively releasing, in a given state between the inactive retracted position and the active set position, by any axial activating forces that may arise between the mandrel (44) on one side, and the gripping device (4), the packer element (6) and the centralizer (8) on the other side.

7. The apparatus according to any one of claims 1 to 6, wherein the apparatus (1) comprises a valve (14) which is in flow communication with an axial bore (98) extending through the mandrel (44); and wherein the valve (14) is arranged for selectively opening and closing to the flow of a fluid through the valve (14), and thereby through the bore (98) of the mandrel (44).

8. A system comprising an apparatus (1) and a well pipe (2), the apparatus (1) being arranged in the well pipe (2) and comprises: a mandrel (44) arranged around a centre axis (22) through the apparatus (1); a radially movable gripping device (4) arranged around the mandrel (44) for fixing the apparatus (1) to an inside of the well pipe (2); a radially movable packer element (6) arranged around the mandrel (44) for sealing against the inside of the well pipe (2) and the mandrel (44); and an axially movable activation device (10) designed to set up axial forces for activating the apparatus (1) in the well pipe (2), characterized in that the apparatus (1) of the system comprises a radially movable centralizer (8) arranged around the mandrel (44) for centring the apparatus (1) in the well pipe (2); and that the activation device (10) is operatively connected to the gripping device (4), the packer element (6) and the centralizer (8) for the respective activation and radial movement of these, via power transmission of said axial forces, between retracted, passive positions and expanded, active positions relative to the centre axis (22) of the plug (1).

9. A method for using the apparatus (1) according to claim 1 in a well pipe (2), characterized in that the method comprises the following steps: arranging the apparatus (1) with at least one radially movable gripping device (4) and a packer element (6) in a retracted, passive position; placing the apparatus (1) in a desired location in the well pipe (2); and activating the apparatus (1) by means of an activation device (10) to bring the apparatus (1) into its active position in which both a centralizer (8), the gripping device (4) and the packer element (6) are brought into expanded, active positions, the centralizer (8) in its active position being in contact with the inside of the well pipe (2), thereby centring the apparatus (1) in the well pipe (2).

10. The method according to claim 9, wherein the centralizer (8) is activated towards its active position before the gripping device (4) and the packer element (6) are activated towards their active positions.

11. The method according to claim 9, wherein the centralizer (8) is activated at least partially into its active position before the apparatus (1) is run into the well (2).

12. The method according to claim 9, wherein the method further includes bringing the apparatus (1) from its active position into its passive position before the apparatus (1) is moved axially in the well (2) again.

13. The method according to claim 12, wherein the packer element (6) is brought into its passive position before the gripping device (4) and the centralizer (8) are brought into their passive positions.

14. The method according to claim 13, wherein the gripping device (4) is brought into its passive position before the centralizer (8) is brought into its passive position.

Description

[0159] In what follows, an exemplary embodiment of a sealing apparatus, a system and a method according to the invention is described, which is visualized in the accompanying drawings, in which:

[0160] FIG. 1 shows a sealing apparatus according to the invention which is being displaced in a well pipe;

[0161] FIG. 2 shows the apparatus after it has been activated and set in the well pipe;

[0162] FIG. 3 shows a longitudinal section of the gripping device of the apparatus in a retracted or passive position;

[0163] FIG. 4 shows the same as FIG. 3, but the gripping device is in an activated, expanded position;

[0164] FIG. 5 shows details of the gripping device;

[0165] FIG. 6 shows a perspective section viewed along the section line III-III shown in FIG. 3;

[0166] FIG. 7 shows a longitudinal section through the packer element of the apparatus;

[0167] FIG. 8 shows a longitudinal section through the centralizer of the apparatus in a passive position;

[0168] FIG. 9 shows the same as FIG. 8, but the centralizer is being activated;

[0169] FIG. 10 shows the same as FIG. 8, but the centralizer has been activated and brought into an active position;

[0170] FIG. 11 shows a longitudinal section through the activation device of the apparatus and a releasing device in their initial position;

[0171] FIG. 12 shows the same as FIG. 11, but after the releasing device has been activated and the activation device has been tightened;

[0172] FIG. 13 shows a perspective section viewed along the section line XI-XI shown in FIG. 11;

[0173] FIG. 14 shows a perspective section viewed along the section line XV-XV shown in FIG. 15;

[0174] FIG. 15 shows a longitudinal section through the valve of the apparatus in a closed position;

[0175] FIG. 16 shows the same as FIG. 15, but the valve is being opened;

[0176] FIG. 17 shows the same as FIG. 15, but the valve is open; and

[0177] FIG. 18 shows the valve of FIG. 15, but the valve has been opened in an alternative manner.

[0178] In the drawings, the reference numeral 1 denotes a sealing apparatus according to the invention, positioned in a well pipe 2.

[0179] The apparatus 1 according to the invention includes a radially movable gripping device 4, a radially movable packer element 6, a radially movable centralizer 8, an axially movable activation device 10, a releasing device 12 and a valve 14. The activation device 10, releasing device 12 and valve 14 are in the housing 16 of the apparatus 1 and are thereby not shown in FIG. 1 or 2. The designs and operations of these will be explained in what follows. Each of the gripping device 4, packer element 6 and centralizer 8 are radially movable between a passive, retracted position and an active, expanded position relative to a centre axis 22 of the apparatus 1.

[0180] The housing 16 is composed of several components which are described in detail in what follows. The housing 16 is provided with a holding-up element 18, that is to say a force-resistant anchoring device, which is arranged to absorb both torsional forces and axial forces. The holding-up element 18 is formed with a fishing neck 20 of a design known per se. An activator 24 which is rotatable around the centre axis 22 of the apparatus 1 projects axially and centrally from the holding-up element 18, whereas a valve activator which is rotatable around the centre axis 22 projects axially and centrically from the activator 24.

[0181] In FIG. 1, a setting device 28 is connected to the holding-up element 18. The setting device 28 includes an actuator 30 which is arranged to rotate the activator 24 in an optional direction of rotation around the centre axis 22, whereby the activator 24 can be moved in an axial direction along the centre axis 22.

[0182] During the axial displacement of the apparatus 1 into the well pipe 2 by means of the setting device 28, the apparatus 1 may be in a non-centred position in the well pipe 2, as indicated in FIG. 1.

[0183] When the apparatus 1 is to be set, the gripping device 4 and the centralizer 8 are activated towards their active, expanded positions before the packer element 6 is brought out into its active, expanded position. This is achieved by rotating the activator 24 in a corresponding direction of rotation. In their active, expanded positions, the gripping device 4, packer element 6 and centralizer 8 are in contact with an inside of the well pipe 2. Thereby the apparatus 1 is centred in the well pipe 2, whereby it is ensured that the packer element 6 will come into the correct position in the well pipe 2 when the activator 24 is rotated further in the same plug-setting direction, see FIG. 2.

[0184] It is advantageous if the centralizer 8 is activated at least partially before the gripping device 4 is activated. The reason for this is that the gripping device 4, when this has been activated and fixed to the inside of the well pipe 2, could prevent the centralizer 8 from moving the plug 1 into a centred position in the well pipe 2.

[0185] In one embodiment (not shown), the centralizer 8 is activated at least partially before or while the apparatus 1 is run into the well pipe 2.

[0186] The gripping device 4, see FIGS. 3 to 6, includes a number of radially movable and wedge-shaped gripping bodies 36, five gripping bodies 36 shown in FIG. 6, distributed around the centre axis 22. In the embodiment shown, a portion of the external surface of the gripping bodies 36 is formed with teeth 38 which are arranged to engage with the well pipe 2 when the gripping bodies are pressed against the inside of the well pipe 2. The well pipe 2 is shown only in FIGS. 1 and 2. On their radial inside, the gripping bodies 36 rest against a rest 40, 42 shown, here, as wedge cones 40, 42. In what follows, the wedge cone 40 will be referred to as the first wedge cone 40 and the wedge cone 42 as the second wedge cone 42.

[0187] By means of a guide nut 46, the first wedge cone 40 is attached to a leading end portion of a centrally placed (in the apparatus 1) mandrel 44. The gripping bodies 36 are biased towards their passive position by means of springs 48, here in the form of helical springs, see FIGS. 3 and 6. The mandrel 44 and the guide nut 46 transmit the axial displacement of the activation device 10 to the gripping device 4, among other things. In this exemplary embodiment, the mandrel 44 and the guide nut 46 may therefore be considered as being part of the activation device 10.

[0188] The second wedge cone 42, which is displaceably arranged along the mandrel 44, is restrictedly displaceable axially relative to a first housing portion 50, which forms part of the housing 16. A segmented intermediate ring 52 is attached to the first housing portion 50 and is provided with internal annular grooves 54 in which a flange-shaped ridge 56 of the second wedge cone 42 is displaceably arranged.

[0189] The intermediate ring 52 has several sloping faces 58, each resting against a ball 60. Each ball 60 pushes, by means of a spring 62, against a radially displaceable grip block 64 which thereby abuts against the mandrel 44. The grip block 64 is provided with saw-tooth-shaped locking teeth 66 complementarily fitting saw-tooth-shaped locking teeth 68 on the mandrel 44. The grip block 64 engages with the mandrel 44 when the mandrel 44 has been displaced to a position in which the locking teeth 66 of the grip block 64 are aligned with the locking teeth 68 of the mandrel 44.

[0190] On two opposite sides, the grip block 64 is proved with slanted grooves 70 fitting with guides 72 on the intermediate ring 52, see FIG. 5.

[0191] Each gripping body 36 has been assigned four return arms 74 which are pivotably attached to the first wedge cone 40 and the second wedge cone 42 and which extend in gripping grooves 76 in the gripping body 36. The return arms 74 are arranged to pull the gripping body 36 out of engagement with the well pipe 2.

[0192] Between each gripping body 36, there is arranged an elongated segment 78 which is attached to the first wedge cone 40 by means of the guide nut 46 and displaceably arranged relative to the first housing portion 50. The elongated segment 78 may be a leaf spring, for example. At the first housing portion 50, the elongated segment 78 is held in position by means of a segment sleeve 80 which also holds the segmented intermediate ring 52 in position. The segment sleeve 80 is arranged to hold the segmented intermediate ring 52 in position on the first housing portion 50.

[0193] When the mandrel 44 is displaced in the direction of the first housing portion 50, the intermediate ring 52 is first moved closer to the second wedge cone 42. The ball 60 is displaced radially inwards by the sloping surface 58, whereby the biasing of the grip block 64 increases.

[0194] When the mandrel 44 is displaced further in the direction of the first housing portion 50, the first wedge cone 40 and the second wedge cone 42 are displaced in directions towards each other, whereby the gripping bodies 36 are displaced radially outwards into engagement with the well pipe 2. At the same time, the locking teeth 66 of the grip block 64 engage with the locking teeth 68 of the mandrel 44.

[0195] The gripping device 4 is thereby prevented from loosening from the well pipe 2, even if the axial force on the mandrel 44 should be reduced or disappear. The reason is that the saw-tooth-shaped locking teeth 64, 66 will have to be pulled away from each other to release.

[0196] It is still possible to release the gripping device 4 from the well pipe 2 by pulling on the housing 16. Typically, a pulling or fishing tool not shown is attached to the fishing neck 20, after which a tensile force is applied to the housing 16 and thereby also to the first housing portion 50.

[0197] Thereby there will be a limited displacement of the intermediate ring 52 in the direction away from the second wedge cone 42. The guides 72 of the intermediate ring 52, which are resting against the grooves 70 of the grip block 64, thereby pull the grip block 64 out of its engagement with the mandrel 44. Further displacement of the housing 16 in the direction away from the gripping device 4 has the effect of making the return arms 74 and springs 48 pull the gripping bodies 36 out of their engagements with the well pipe 2 and further in into their passive positions.

[0198] In FIG. 7, a longitudinal section of the packer element 6 is shown. An elastic sealing element 86 is arranged on a packer boss 88 appurtenant the first housing portion 50. The packer boss 88 extends in a displaceable manner into a bore 90 of a second housing portion 92 and is prevented from slipping out of the second housing portion 92 by a nut 94 which comes into abutment against a shoulder 96 in the bore 90.

[0199] The packer element 86 is activated in a manner known per se by displacing the first housing portion 50 and the second housing portion 92 towards each other, here by means of the mandrel 44 which is provided with an axial bore 98 extending through it.

[0200] The centralizer 8 includes a number of double, hingedly joined link arms 100, here five link arms 100, each of which is arranged to be moved from its passive position, as is shown in FIG. 8, into its active, extended position, as is shown in FIG. 10.

[0201] Each of the link arms 100 includes a first link arm 102, which is attached by means of a link joint to a link-locking sleeve 104, and a second link arm 106, which is attached by means of a link joint to a sliding sleeve 108.

[0202] The link-locking sleeve 104 is fixedly connected to the second housing portion 92 by means of attachment means not shown, which, in one embodiment, may be screws. The sliding sleeve 108 is restrictedly displaceable in a bore 110 in a third housing portion 112.

[0203] Springs 114, here in the form of disc springs, bias the sliding sleeve 108 in the direction of the link-locking sleeve 104, but it is prevented from slipping out of the bore 110 by a nut 116.

[0204] The link-locking sleeve 104 is formed with external lugs 118. The sliding sleeve 108, which is restrictedly displaceable relative to the link-locking sleeve 104, is provided with internal lugs 120. The external lugs 118 and the internal lugs 120 are arranged to come into abutment against each other. Both the link-locking sleeve 104 and the sliding sleeve 108 are arranged in a displaceable manner on the mandrel 44.

[0205] A link-locking body 122, which is radially displaceable in a guide opening 124 in the link-locking sleeve 104, is in engagement with an annular groove 126 in the mandrel 44 in its initial position, as is shown in FIG. 8. Together with other link-locking bodies, not shown, arranged around a centre axis 22, the link-locking body 122 is prevented from disengaging from the mandrel 44 before the link-locking body 122 is aligned with an annular, internal release groove 128 of the third housing portion 112.

[0206] In FIG. 9, the mandrel 44 has been pulled into axial abutment against the link-locking body 122. The second housing portion 92, and thereby the link-locking sleeve 104, has been displaced somewhat in the direction of the sliding sleeve 108, but not sufficiently for the link-locking body 122 to be displaceable into the release groove 128. This displacement between the second housing portion 92 and the third housing portion 112 has the effect of the link arms 100 having been displaced somewhat towards their active positions.

[0207] The mandrel 44 is prevented from getting further displaced relative to the link-locking sleeve 104, and thereby relative to the second housing portion 92. In this exemplary embodiment, the effect of this is that the centralizer 8 must be activated towards its active position before the gripping device 4 (see FIGS. 3 and 4) and the packer element 6 (see FIG. 7) can be activated towards their respective, active positions.

[0208] When the mandrel 44 has been moved sufficiently far relative to the third housing portion 112, as is shown in FIG. 10, the link-locking body 122 is displaced radially out into the release groove 128. With this, the mandrel 44 is released from the link-locking body 122 and can thereby be displaced further in the direction of the third housing portion 112.

[0209] In this position, the link-locking body 122 is prevented from being displaced out of the release groove 128. The centralizer 8 is thereby held in its active, expanded position. The centralizer 8 cannot be released until the annular groove 125 of the mandrel 44 has been moved back to the link-locking bodies 122, that is to say when the annular groove 126 is axially aligned with the link-locking body 122.

[0210] If the link arms 100 are prevented from being fully displaceable into their activated and extended positions, the springs 114 are being tensioned while the sliding sleeve 108 is displaced somewhat in the bore 110.

[0211] From the description above, it will therefore be understood that the centralizer 8 is provided with a link-locking body 122 which is directly or indirectly in conditional, blocking engagement with the activation device 10; when the link-locking body 122 is in conditional engagement with the mandrel 44, that is dependent on it not being in engagement with the housing with which it may be engaged in another state.

[0212] The activation device 10 and releasing device 12 of the apparatus 1 are shown in FIGS. 11-13.

[0213] A splined nut 136 is displaceably arranged in the third housing portion 112 and is provided with external splines 138 complementarily fitting internal splines 140 of the third housing portion 112. The splined nut 136 is fixedly connected to the mandrel 44.

[0214] The activator 24, which projects into the third housing portion 112, is provided with an external thread 142 fitting an internal thread 144 of the splined nut 136. A cylindrical portion 146 of the activator 24 projects displaceably and sealingly into the through bore 98 of the mandrel 44. The activator 24 is also formed with a centric bore 148 extending through it.

[0215] The activator 24 is supported in a bearing bush 152 by means of a number of bearing flanges 150 projecting outwards. The bearing bush 152, which forms a suspension part 153, is internally provided with annular bearing surfaces 154 resting against the bearing flanges 150.

[0216] The bearing bush 152 is held in the axial position in the third housing portion 112 by means of a number of release blocks 156, here eight release blocks 156. Each release block 156 has a toothed surface 158 facing the bearing bush 152 and fitting against the teeth 160 of the bearing bush 152.

[0217] A fourth housing portion 162, which is attached to the holding-up element 18, encircles the releasing device 12. The housing 16 and the activator 24 constitute equipment components 163.

[0218] The eight release blocks 156 are arranged around the centre axis 22, as shown in FIG. 13 in which the fourth housing portion 162 is not shown.

[0219] When the apparatus 1 is to be activated, the activator 24 is rotated around the centre axis 22. The activator 24 is supported in the bearing bush 152 and thereby pulls the splined nut 136, which is prevented from rotating in the third housing portion 112, and the mandrel 44 in the axial direction towards the activator 24. If the activator 24 is rotated in the opposite direction, the splined nut 136 and the mandrel 44 are moved in the axial direction away from the activator.

[0220] During a displacement of the activator 24 relative to the mandrel 44, the cylindrical portion 146 is displaced axially in the bore 98.

[0221] The third housing portion 112 and the fourth housing portion 162 are held fixed to each other by means of shear bolts, called release bolts 164 below. Release bolts 164 are shown in FIG. 13, whereas their axial positions in the third housing portion 112 are indicated by bolt-centre lines 166 in FIGS. 11 and 12.

[0222] The third housing portion 112 and the fourth housing portion 162 are prevented from becoming fully separated by a ring nut 168 which is threadedly connected to the fourth housing portion 162, and which is arranged to come into abutment against a shoulder 170 encircling the third housing portion 112, see FIGS. 11 and 12.

[0223] If the third housing portion 112 and the fourth housing 162 are displaced in the axial direction away from each other, the release blocks 156 that normally rest against the inside of the fourth housing portion 162 may be displaced radially outwards into release grooves 172 in the fourth housing portion 162. The release blocks 156 then lose their engagement with the bearing bush 152, whereby the bearing bush 152 with the activator 24 and the splined nut 136 may be displaced axially in the third housing portion 112 without the activator 24 having to be rotated.

[0224] If it becomes necessary to disengage the apparatus 1 in some other way than by rotating the activator 24, a pulling tool not shown may be connected to the fishing neck 20, which is attached to the fourth housing portion 162, and then pull the fourth housing portion 162 until the release bolts 164 break. Said axial displacement between the third housing portion 112 and the fourth housing portion 162 may then take place.

[0225] Moreover, the housing 16 consists of the first, second, third and fourth housing portions 50, 92, 112, 162.

[0226] The valve 14, see FIGS. 14-18, is arranged inside the activator 24, which then forms a valve housing 173.

[0227] A valve slide 180 is externally provided with two outer seals 182 which are arranged to provide a seal between the valve slide 180 and the activator 24. An intermediate seal 184 is designed to control a flow rate through the valve 14.

[0228] Valve openings 186 in the valve slide 180 are closed relative to valve openings 188 in the activator 24 and in the fourth housing portion 162 when the valve 14 is in its closed position, as shown in FIG. 15.

[0229] The valve slide 180 is formed with a screw spindle 190 extending axially and extending centrically in the direction away from a valve bore 178. Moreover, the screw spindle 190 is provided with longitudinal grooves 192 fitting internally in an externally splined holding-up plate 194. The holding-up plate 194, which is arranged to prevent the screw spindle 190 from being rotatable relative to the activator 24, fits in an axially displaceable manner in internal complementary splines 196 of the activator 24.

[0230] A blocking nut 198 is screwed onto the screw spindle 190. The screw spindle 190 and the blocking nut 198 form a screw-and-nut connection 199. Externally, the blocking nut 198 is provided with a number of encircling blocking grooves 200. A blocking ring 202 is arranged to be in engagement with the blocking grooves 200 in order thereby to prevent or counteract an axial displacement of the blocking nut 198 in the direction away from the holding-up plate 194.

[0231] The valve activator 26 is supported in a bearing bush 204 in the activator 24. The valve activator 26 is kept in position axially via the bearing bush 204, which is connected to the activator 24 by means of a number of shear pins 206 in the form of shear screws 206, see FIG. 14.

[0232] In its radially external end portion, also called inward-projecting portion 208 in what follows, the valve activator 26 is in an axially displaceable rotary engagement with the blocking nut 198. A number of valve-stopping blocks 210 are arranged in corresponding radial openings 212 in the blocking nut 198. By means of the inward-projecting portion 208 of the valve activator 26, the valve-stopping blocks 210 are held in position in a block groove 214 in the activator 24.

[0233] By rotating the valve activator 26 relative to the activator 24, the valve can be opened and closed repeatedly. The valve-stopping blocks 210 stay in and are rotated in the block groove 124 as the valve slide 180 is simultaneously moved axially back and forth in the activator 24 depending on the direction of rotation of the valve activator 26 relative to the activator 24.

[0234] In FIG. 16, the valve 14 is shown in an intermediate position in which the relative position of the intermediate seal 184 in the valve housing 180 determines the flowrate through the valve 14.

[0235] In FIG. 17, the valve 14 is shown in the open position in which the opening 186 of the valve slide 180 is aligned with the opening 188 of the valve housing 173 so that fluid communication is provided between the valve bore 178 and the surroundings of the apparatus 1.

[0236] Should it be necessary to bring the valve 14 from the closed to the open position without rotating the valve activator 26, a compressive force may be applied to the valve activator 26 in the axial direction towards the valve 14, so that the shear pins or shear screws 206 break. The valve activator 26, with the associated inward-projecting portion 208, may thereby be moved somewhat into the blocking nut 198. The inward-projecting portion 208 thereby does not block the valve-stopping blocks 210 any longer. The valve-stopping blocks 210 are displaced axially out of the block groove 214 into a recess 209 in the external surface of the valve activator 26, after which the valve slide 180 can be displaced axially into its open position, see FIG. 18.

[0237] The engagement of the blocking ring 202 with the blocking nut 198 prevents the valve slide 180 from being axially displaceable towards its closed position, even if there is an overpressure inside the valve slide 180.

[0238] If the pressure is largest above the valve 14 relative to the orientation of the well, the pressure helps to push the valve slide 180 towards its open position. By above is meant, here, up towards the surface and towards the top of the apparatus or plug 1. If the pressure is largest below the valve 14, the pressure seeks to move the valve slide towards its closed position. The blocking ring 202 prevents the valve slide 180, even if it is in an intermediate position, from being displaceable towards its closed position. The blocking ring 202 also prevents adjacent components, such as the valve-stopping blocks 210, from falling out.

[0239] It should be noted that all the above-mentioned embodiments illustrate the invention, but do not limit it, and persons skilled in the art may construct many alternative embodiments without departing from the scope of the dependent claims. In the claims, reference numbers in brackets are not to be regarded as restrictive. The use of the verb “to comprise” and its different forms does not exclude the presence of elements or steps that are not mentioned in the claims. The indefinite article “a” or “an” before an element does not exclude the presence of several such elements.