A wellbore plug assembly

Abstract

A wellbore plug assembly (1) comprising a sealing part (3) configured to move radially between an outer sealing mode and an inner non-sealing mode, and a barrier ring (5) comprising a plurality of ring segments (5a) radially movable between an expanded mode and a retracted mode The wellbore plug assembly (1) further comprises a segment tensioning arrangement (7) tensioning the ring segments towards the retracted mode, wherein the segment tensioning arrangement (7) comprises torsion bars (21).

Description

A WELLBORE PLUG ASSEMBLYTechnical Field

[0001] The present invention relates to an elastomer-based wellbore plug assembly for sealing a wellbore.Background Art

[0002] Wellbore plug assemblies for sealing off a portion of a subsea well are well known and exist in a vast variety of designs. The sealing part comprises one or more elastomer bodies or rings that are radially expanded to seal against a bore.

[0003] A problem with such plug assemblies arises at elevated pressure and temperatures, since the elastomer tends to extrude. This not only damages the plug but represent a risk of leakage through the plug assembly.

[0004] To solve this problem, several designs comprise an extrusion barrier ring that supports the elastomer material at opposite axial sides. The barrier ring must expand radially along with the elastomer material when setting the plug and must retract when releasing it.

[0005] Publication WO2019014482 discloses such a plug assembly, wherein an extrusion barrier ring abuts the sealing material and prevents it from extrusion.

[0006] An object of the present invention may be to provide a wellbore plug assembly with a barrier ring wherein the barrier ring retracts when the plug assembly shall be released from its sealing state.Summary of invention

[0007] There is provided a wellbore plug assembly comprising a sealing part configured to move radially between an outer sealing mode and an inner non-sealing mode, and a barrier ring for prevention of material extrusion of the sealing part in the outer sealing mode. The barrier ring has a plurality of ring segments radially movable between an expanded mode and a retracted mode. The wellbore plug assembly further comprises a segment tensioning arrangement that tensions the ring segments towards the retracted mode. The segment tensioning arrangement comprises torsion bars.

[0008] In this manner, when the wellbore plug assembly shall be removed and the sealing part is retracted, the barrier ring will retract due to the force exerted onto the ring segments from the torsion bars.

[0009] Different types of material can be used for the torsion bars. For instance, the torsion bars can be made of metal or a composite material having carbon fibers.

[0010] In some embodiments, the segment tensioning arrangement further comprises an engagement element fixed to the respective torsion bars, and a forcetransmitting connection, such as a hinge connection, between the respective engagement elements and ring segments. In this manner, a retraction force can be transmitted from the torsion bars to the ring segment, such that the barrier ring retracts.

[0011] The segment tensioning arrangement may further comprise tensioning elements fixed to the respective torsion bars and a tension application arrangement in engagement with the tensioning elements for rotational tensioning of the respective torsion bars.

[0012] The tension application arrangement can typically comprise one or more tension application screws acting on the respective tensioning elements.

[0013] The respective ring segments may comprise a ring-forming portion that together form a complete ring, and an engagement arm extending axially out from the ring-forming portion. The force-transmitting connection (e.g. an hinge connection) can then at least partially be arranged in the engagement arm.

[0014] In some embodiments, the segment tensioning arrangement comprises a housing with axially extending housing bores, wherein the torsion bars extend through the housing bores. This solution provides an effective support for the torsion bars, while allowing them to be twisted I tensioned.

[0015] In some embodiments, the segment tensioning arrangement comprises an overlapping portion that axially overlaps with the extension of the tension bars, wherein the overlapping portion is metal-free outside an outer diameter that is smaller than the outer diameter of the barrier ring when in the retracted mode.Advantageously, the overlapping portion can be recessed compared to the segment tensioning arrangement at both axial ends of the overlapping portion.

[0016] If the wellbore plug assembly for some reason should be stuck inside the wellbore and needs to be milled out, the milling tool will not need to mill out any metal along the overlapping portion. Thus, such embodiments may comprise a non-metallic element arranged outside the said overlapping portion. Such a non-metallic element should advantageously be made of a material that can be easily or rapidly milled.

[0017] Also provided is a wellbore plug assembly comprising a sealing part configured to move radially between an outer sealing mode and an inner non-sealing mode, and a barrier ring for prevention of material extrusion of the sealing part when in the outer sealing mode. The barrier ring comprises a plurality of ring segments radially movable between an expanded mode and a retracted mode. The ring segments comprise an overlapping portion at their ends when in the expanded mode and when in the retracted mode.

[0018] With the term overlapping portion is meant that the two ends of the curved segment shape of the ring segments extend a distance that overlaps the adjacent ends of neighbouring ring segments. As a result, the total accumulated distance of the curved shapes of the ring segments is longer than the circumference of the barrier ring.

[0019] In some embodiments, the ring segments can comprise end fingers at their respective ends, extending in a tangential direction. Furthermore, the ring segments can comprise slots between the end fingers, wherein end fingers of adjacent ring segments are arranged in the slots.

[0020] The engagement of the end fingers and slots of the adjacent ring segments contribute to the shape stability of the barrier ring during movement between the expanded mode and the retracted mode.

[0021] As will be discussed with the discussion of an example embodiment further below, the end fingers and slots can constitute the said overlapping portion.

[0022] Advantageously, the ring segments can each comprise, at each of their two ends, at least two end fingers and at least two slots.

[0023] The end fingers can in some embodiments comprise a slanted face facing partially radially outwards and tangentially. The slanted faces will contribute to remove debris from the slots when the barrier ring moves towards its retracted mode.

[0024] The ring segments may comprise a tangentially extending edge finger at one end and an axially facing edge surface at an opposite end, wherein the edge surface of one ring segment supports the edge finger of an adjacent ring segment.

[0025] The edge finger can have an inclined face at its end, wherein the inclined face faces in a partial axial and tangential direction.

[0026] The inclined faces will contribute to remove debris from the edge surfaces when the barrier ring moves towards its retracted mode.

[0027] The axial extension of the edge finger can advantageously be less than a third of the axial extension of the barrier ring. As will be discussed further below, this reduces the deformation of the sealing part at excessive pressure or temperature.Detailed description of the invention

[0028] While various features of the invention have been discussed in general terms above, a detailed and non-limiting example of embodiment is presented in the following with reference to the drawings, in whichFig. 1 is a side view of a wellbore plug assembly;Fig. 2 is an enlarged perspective view of the wellbore plug assembly shown in Fig. 1;Fig. 3 is a principle view illustrating a barrier ring having ring segments in an expanded and a retracted mode;Fig. 4 is an enlarged perspective view illustrating a barrier ring in a retracted mode;Fig. 5 is an enlarged perspective view illustrating the barrier ring in an expanded mode;Fig. 6 is a side view illustrating a segment tensioning arrangement having torsion bars that apply tension onto the barrier ring segments towards the inner position (retracted mode);Fig. 7 is an enlarged perspective view of the segment tensioning arrangement;Fig. 8 is another enlarged perspective view of the segment tensioning arrangement;Fig. 9 is a perspective view of one barrier ring segment;Fig. 10 is a perspective view of an engagement element attached to the end of a torsion bar;Fig. 11 is a perspective view of an actuation ring; andFig. 12 is a cross-section view of a portion of the segment tensioning arrangement.

[0029] Fig. 1 and Fig. 2 depict a wellbore plug assembly 1. It has a sealing part 3, which in the shown embodiment comprises three sealing sections 3a. The sealing part 3 could also have one sealing section 3a, or two, or even more than three. The sealing part 3 comprises an elastomeric material and is configured to expand radially from an inner non-sealing mode to an outer sealing mode, such that it seals against the inner bore of a well pipe (for instance a casing). The actuation of the sealing part 3 is typically by axial compression.

[0030] At opposite sides of the sealing part 3 there is arranged a barrier ring 5. The barrier rings 5 are configured to expand radially from a retracted mode to an expanded mode when the sealing part 3 expands to the outer sealing mode.

[0031] The material of the barrier ring 5 is harder than the material of the sealing part 3. The barrier ring 5 is typically made of metal. Hence, to enable such radial expansion, the barrier ring 5 comprises a plurality of ring segments 5a. When the sealing part 3 is in the outer sealing mode, the barrier ring 5 prevents extrusion of the sealing part 3. Such extrusion could otherwise occur at excessive temperatures and / or pressures.

[0032] Fig. 3 is a schematic illustration showing the functional principle of the barrier ring 5, seen along the axial direction. In this example, the barrier ring 5 has four ring segments 5a. The barrier ring 5 in Fig. 3 is shown in its expanded mode (outer ring) and retracted mode (inner ring). The ends of each ring segment 5a has been marked with a short line to indicate the location of the ends. In the expanded mode, the four ring segments 5a together form a circle wherein the radii of each ring segment coincide. The radii of two of the ring segments 5a are indicated with dashed lines in Fig. 3, extending radially outwards from a common center. The outer face of the respective ring segments 5a are thus substantially aligned with the inner bore of the well pipe (not shown).

[0033] When in the retracted mode, the radii of the respective ring segments 5a do not coincide.

[0034] Notably, both when in the retracted mode and when in the expanded mode, the ring segments 5a have an overlapping portion A.

[0035] Consequently, when in the expanded mode, the angular extension of the respective ring segments 5a extends beyond 360° divided by the total number of ring segments 5a. In the shown example wherein the barrier ring 5 has four ring segments 5a, the angular extension of each ring segment 5a is thus more than 90°. This is indicated with the angle a shown in Fig. 3.

[0036] The overlapping portion A, overlapping between two adjacent ring segments 5a, is shown in Fig. 4. In this image, the barrier ring 5 is shown in the retracted mode. The ring segments 5 comprise end fingers 9 at the respective ends of each ring segment 5a. The end fingers 9 extend along the curve of the ring segment 5a (i.e. having the same radius as the ring segment 5a). Between the end fingers 9 there are slots 11 that receive end fingers 9 of the adjacent ring segment 5a. This engagement between the end fingers 9 and slots 11 of the adjacent ring segments 5a provides axial stability during movement between the expanded and retracted modes of the barrier ring 5.

[0037] Fig. 5 shows a similar image of the interface between two ring segments 5a, however when in the expanded mode. When in the expanded mode, the end fingers 9 are still positioned in the slots 11 of the adjacent ring segment 5a and there is still an overlapping portion A. However, the end fingers 9 have been moved a distance outwards in the tangential direction, corresponding to the outer schematic circle shown in Fig. 3.

[0038] Still referring to Fig. 4 and Fig. 5, at an axial edge of the barrier ring 5, the ring segments 5a comprise an edge finger 13. The edge finger 13 slides against an axially facing edge surface 15 of the adjacent ring segment 5a. Furthermore, at the free end of the edge finger 13, the edge finger 13 comprises an inclined face 17 that faces in a partial axial and tangential direction. The inclined face 17 contributes to remove possible debris and impurities from the edge surface 15 when the barrier ring 5 moves towards the retracted mode.

[0039] The edge finger 13 is arranged at the axially facing edge of the ring segment 5a that is configured to abut against the sealing part 3 (cf. Fig. 1 and Fig. 2).Referring to Fig. 5, if the material of the sealing part 3 is prone to extrude, such as due to excessive pressure and temperature, some of the material will move into the groove 16 adjacent the inclined face 17 (wherein the edge surface 15 constitutes the bottom of the groove 16). To obtain a shallow groove 16, the edge finger 13 has a small axial extension. In this manner, by limiting the depth of the groove 16, one avoids excessive extrusion of the material of the sealing part 3. Preferably, the axial extension of the edge finger 13 is less than a third of the axial extension E of the barrier ring 5. In some embodiments, the axial extension of the edge finger 13 can be less than a fourth or a fifth of the axial extension E of the barrier ring 5.

[0040] The axial extension E of the barrier ring 5 is indicated in Fig. 4, Fig. 6, and Fig. 9. Notably, as appears from e.g. Fig. 9, the total axial extension of a ring segment 5a is longer than the axial extension E of the barrier ring 5. The axial extension E relates to the part of the ring segment 5a that contributes to forming the ring configuration.

[0041] At the free ends of the end fingers 9, the end fingers 9 comprise slanted faces 19 that face partially tangentially and radially outwards. The slanted faces 19 contribute to remove debris and impurities from the slots 11.

[0042] The overlapping portion A of the ring segments 5a is also indicated in Fig. 4 and Fig. 5.

[0043] The radial movement of the barrier ring 5 between the expanded mode and the retracted mode will now be discussed.

[0044] To move the barrier ring 5 towards its retracted mode, there is arranged a segment tensioning arrangement 7. In Fig. 1 , two segment tensioning arrangements 7 are shown, as the wellbore plug assembly 1 comprises two barrier rings 5.

[0045] Fig. 6 shows a side-view of one segment tensioning arrangement 7 with a housing 7a (cf. Fig. 1 and Fig. 12) removed for illustrational purpose. Also shown in Fig. 6 is a barrier ring 5, on which the segment tensioning arrangement 7 functions.

[0046] The segment tensioning arrangement 7 comprises a plurality of torsion bars 21. The torsion bars 21 are configured to apply a radially inwardly directed force onto the respective ring segments 5a.

[0047] At one end, the torsion bars 21 are suspended to a respective tensioning element 23. The tensioning element 23 is fixed to the torsion bar 21 , such that a pivoting movement of the tensioning element 23 results in a corresponding pivoting movement of the end of the torsion bar 21.

[0048] At the opposite end of the torsion bar 21 , the torsion bar 21 is fixed to an engagement element 25. The engagement element 21 is configured to apply a radially inwardly directed force to the ring segment 5a. This will be discussed further below.

[0049] To rotationally tension the torsion bar 21, the segment tensioning arrangement 7 comprises a tension application arrangement, which in the present embodiment is in form of tension application screws 27. In the shown example, two tension application screws 27 are associated with each tensioning element 23. However, in other embodiments, one tension application screw 27 could suffice. The tension application screws 27 are supported in the housing 7a of the segment tensioning arrangement 7 (cf. Fig. 1 and Fig. 12). When rotated in a tensioning direction, they pivot the tensioning element 23 radially inwards. When pivoting the tensioning element 23 radially inwards, the torsion bar 21 will be rotationally tensioned.

[0050] Radially within the torsion bars 21 , the segment tensioning arrangement 7 comprises a main body 29.

[0051] The interface between the engagement element 25 and the ring segment 5a will now be discussed with reference to Fig. 8, Fig. 9, and Fig. 10. Fig. 8 shows the end portion of a torsion bar 21 and the attached engagement element 25 that exerts a radially inwardly directed force on the ring segment 5a. Fig. 9 is a perspective view of one single ring segment 5a. Moreover, Fig. 10 depicts the end of a torsion bar 21 and the engagement element 25.

[0052] The engagement element 25 engages the ring segment 5a in a pivoting manner with a hinge connection. In the shown embodiment, the engagement element25 comprises a pivot pin 31 (Fig. 10) that extends into a receiving pivot bore 33 of the ring segment 5a (Fig. 8 and Fig. 9). As the skilled person will appreciate, the pivoting engagement, or hinge connection, between the engagement element 25 and the ring segment 5a could also be provided in other ways. For instance, the ring segment 5a could comprise a pin that extends into a bore in the engagement element 25. The curved arrow in Fig. 10 illustrates the radially inwardly directed force exerted on the ring segment 5a via the hinge connection made up by the pivot pin 31 and the pivot bore 33.

[0053] As illustrated with the curved arrow in Fig. 8, the torsion bar 21 now tensions the ring segment 5a radially inwards.

[0054] With the perspective view of Fig. 9 there is further shown a guide bore 35, through which a guide pin 37 extends (Fig. 8 depicts the head of the guide pin 37). The engagement between the guide pin 37 and the guide bore 35 of the ring segment 5a, maintains the ring segment 5a in its correct axial position, while allows for its radial movement between the expanded and retracted modes.

[0055] As shown in Fig. 8 and Fig. 9, the ring segment 5a comprises an engagement arm 39 that further comprises the pivot bore 33 and the guide bore 35. Moreover, the engagement arm 39 extends out from a ring-forming portion 41. When installed, the engagement arm 39 is arranged radially within the housing 7a of the segment tensioning arrangement 7 (Fig. 1 and Fig. 2).

[0056] Merely indicated and not well shown in Fig. 9, the ring segment 5a further comprises a segment actuation face 43. The segment actuation face 43 is configured to slide against an inclined face 45 of an actuation ring 47. The actuation ring 47 is shown in Fig. 11 , and comprises a plurality of inclined faces 45, one for each ring segment 5a.

[0057] Although not readily visible, the actuation ring 47 is axially interposed between the barrier ring 5 and the sealing part 3. Hence, when the wellbore plug assembly 1 is actuated by axial compression, the ring segments 5a will be moved radially outwards as their actuation faces 43 slide on the respective inclined faces 45 of the actuation ring 47.

[0058] Fig. 12 depicts a cross section view of a portion of the segment tensioning arrangement 7. The torsion bar 21 extends through a receiving bore 49 of the housing 7a. In the image of Fig. 12, the torsion bar 21 is shown without the engagement element 25 attached.

[0059] Still referring to Fig. 12, there is shown in overlapping portion 51 wherein the segment tensioning arrangement 7 has an outer diameter which is less than the outer diameter at the position of the ends of the torsion bars 21. This is advantageous in situations where the wellbore plug assembly 1 has become stuck and needs to be milled. The milling tool (not shown) will then not need to mill metal along the overlapping portion 51. The overlapping portion 51 is also indicated in Fig. 1.

[0060] The skilled person will appreciate that the segment tensioning arrangement 7 could have a non-metallic part, such as a plastic sleeve (not shown) arranged outside the said outer diameter of the overlapping portion 51. In such embodiments, the segment tensioning arrangement 7 would have a larger diameter at the overlapping portion 51 , but it would be metal-free outside the said outer diameter. Such a plastic sleeve would be easy and rapidly milled away if the said situation should arise.

Claims

Claims1 . A wellbore plug assembly (1 ) comprising- a sealing part (3) configured to move radially between an outer sealing mode and an inner non-sealing mode, and- a barrier ring (5) comprising a plurality of ring segments (5a) radially movable between an expanded mode and a retracted mode, characterized in that the wellbore plug assembly (1 ) further comprises a segment tensioning arrangement (7) tensioning the ring segments towards the retracted mode, wherein the segment tensioning arrangement (7) comprises torsion bars (21 ).

2. A wellbore plug assembly (1 ) according to claim 1 , characterized in that the segment tensioning arrangement (7) further comprises- an engagement element (25) fixed to an end of the respective torsion bars (21 );- a hinge connection (31 , 33) between the respective engagement elements (25) and ring segments (5a).

3. A wellbore plug assembly (1 ) according to one of the preceding claims, characterized in that the segment tensioning arrangement (7) further comprises- tensioning elements (23) fixed to the respective torsion bars (21 );- a tension application arrangement (27) in engagement with the tensioning elements (23) for rotational tensioning of the respective torsion bars (21 ).

4. A wellbore plug assembly according to one of the preceding claims, characterized in that the respective ring segments (5a) comprises a ringforming portion (41 ) that together form a complete ring, and an engagement arm (39) extending axially out from the ring-forming portion (41 ), wherein the hinge connection (31 , 33) at least partially is arranged in the engagement arm (39).

5. A wellbore plug assembly (1 ) according to one of the preceding claims,characterized in that it the segment tensioning arrangement (7) comprises a housing (7a) with axially extending housing bores (49), wherein the torsion bars (21 ) extend through the housing bores (49).

6. A wellbore plug assembly according to one of the preceding claims, characterized in that the segment tensioning arrangement (7) comprises an overlapping portion (51 ) that axially overlaps with the extension of the tension bars (21 ), wherein the overlapping portion (51 ) is metal-free outside an outer diameter that is smaller than the outer diameter of the barrier ring (5) when in the retracted mode.

7. A wellbore plug assembly (1 ) comprising- a sealing part (3) configured to move radially between an outer sealing mode and an inner non-sealing mode, and- a barrier ring (5) comprising a plurality of ring segments (5a) radially movable between an expanded mode and a retracted mode, characterized in that the ring segments (5a) comprise an overlapping portion (A) at their ends when in the expanded mode and when in the retracted mode.

8. A wellbore plug assembly (1 ) according to claim 7, characterized in that the ring segments (5a) comprise- end fingers (9) at their respective ends, extending in a tangential direction;- slots (1 1 ) between the end fingers (9), wherein end fingers (9) of adjacent ring segments (5a) are arranged in the slots (1 1 ).

9. A wellbore plug assembly (1 ) according to claim 8, characterized in that the end fingers (9) comprise a slanted face (19) facing partially radially outwards and tangentially.

10. A wellbore plug assembly (1 ) according to claim 8 or claim 9, characterized in that the ring segments (5a) comprise an edge finger (13) at one end and an axially facing edge surface (15) at an opposite end, wherein the edge surface (15) of one ring segment (5a) supports the edge finger (13) of an adjacent ring segment (5a).11 . A wellbore plug assembly (1 ) according to claim 10, characterized in that the edge finger (13) comprises an inclined face (17) at its end, wherein the inclined face (17) faces in a partially axial and tangential direction.

12. A wellbore plug assembly according to claim 10 or claim 11 , characterized in that the axial extension of the edge finger (13) is less than a third of the axial extension (E) of the barrier ring (5).

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