APPARATUS FOR FORMING TUBULAR CONNECTIONS AND METHOD OF USE

Abstract

The invention in one aspect provides an apparatus and method for forming a connection between an inner tubular and a caisson of an offshore structure. The apparatus comprises a mandrel, and a seal arrangement disposed on the mandrel and configured to create a seal between the mandrel and an inner surface of an inner tubular in which the apparatus is located. The seal arrangement comprises first and second cup seals, axially separated on the mandrel, and configured to define a substantially annular volume between the mandrel and the inner tubular in use. A pressure transmission path delivers a pressurised fluid to the annular volume, and the apparatus is configured to pressurise the annular volume and thereby expand the inner tubular in a radial direction and into contact with the caisson to form a connection between the inner tubular and the caisson.

Claims

1. An apparatus for forming a connection between an inner tubular and a caisson of an offshore structure, the apparatus comprising: a mandrel; a seal arrangement disposed on the mandrel and configured to create a seal between the mandrel and an inner surface of the inner tubular in which the apparatus is located; wherein the seal arrangement comprises first and second cup seals, axially separated on the mandrel, and configured to define a substantially annular volume between the mandrel and the inner tubular in use; a pressure transmission path for delivering a pressurised fluid to the substantially annular volume; wherein the apparatus is configured to pressurise the substantially annular volume and thereby expand the inner tubular in a radial direction and into contact with the caisson to form a connection between the inner tubular and the caisson.

2. The apparatus according to claim 1, wherein the first and second cup seals each define an open end, and are axially separated on the mandrel such that the open ends of the cup seals face towards one another.

3. The apparatus according to claim 1, wherein the first and/or second cup seals further comprise an anti-extrusion member which is substantially annular in form and which at least partially surrounds the outer surface of the first and/or the second cup seal.

4. The apparatus according to claim 3, wherein the anti-extrusion member of the first and/or the second cup seal is formed from a material which is harder than that of the first and/or second cup seal.

5. The apparatus according to claim 1, further comprising a support pin assembly comprising a plurality of support pins which are operable to extend radially outwards to bear the load of the inner tubular.

6-8. (canceled)

9. The apparatus according to claim 5, wherein the support pin assembly is hydraulically actuated, and wherein hydraulic extension lines and hydraulic retraction lines are provided between each support pin of the plurality of support pins and a hydraulic control system to provide hydraulic actuation to extend the support pins and hydraulic actuation to retract the support pins, respectively.

10. The apparatus according to claim 1, further comprising at least one centralizer assembly comprising a plurality of centraliser members and having a retracted condition and an extended condition in which the plurality of centraliser members is configured to extend radially outwards and into contact with the inner surface of the inner tubular such that the mandrel of the apparatus is separated from the inner tubular by at least a minimum stand-off distance around its circumference

11. (canceled)

12. (canceled)

13. The apparatus according to claim 10, wherein the centraliser assembly is connected to the pressure transmission path and is configured to be hydraulically actuated by the same pressurised fluid which pressurises the substantially annular volume.

14. (canceled)

15. The apparatus according to claim 13 wherein the centraliser assembly is configured to be actuated into its extended condition at a first pressure upon delivery of the pressurised fluid, prior to expansion of the inner tubular, and wherein expansion of the inner tubular is configured to begins at a second pressure, and wherein the first pressure is lower pressure than the second pressure.

16. (canceled)

17. The apparatus according to claim 13 wherein the apparatus is configured such that the centraliser assembly is caused to move into its retracted condition when pressurised fluid is removed or drained from the apparatus.

18. (canceled)

19. The apparatus according to claim 1, wherein the apparatus is configured to deform the inner and/or outer surfaces of the inner tubular such that the inner tubular is brought into contact with the caisson, and wherein a force from the expanded inner tubular on the caisson deforms the inner and/or outer surfaces of the caisson.

20. The apparatus according to claim 1, wherein the apparatus is configured to expand the inner tubular in a radial direction to form a shoulder in the inner tubular and wherein a force from the expanded inner tubular on the caisson expands and forms a shoulder in the caisson.

21. The apparatus according to claim 1, wherein the apparatus is configured to expand the inner tubular in a radial direction to form a shoulder in the inner and outer surfaces of the inner tubular and wherein a force from the expanded inner tubular on the caisson expands and forms a shoulder in the inner and outer surfaces of the caisson.

22. A method of forming a connection between an inner tubular and a caisson of an offshore structure comprising: providing an apparatus comprising a mandrel, a seal arrangement disposed on the mandrel and configured to create a seal between the mandrel and an inner surface of the inner tubular in which the apparatus is located, wherein the seal arrangement comprises first and second cup seals, axially separated on the mandrel; delivering a pressurised fluid to a substantially annular volume between the mandrel and the inner tubular in use; pressurising the substantially annular volume and thereby expanding the inner tubular in a radial direction and into contact with the caisson to form a connection between the inner tubular and the caisson.

23. The method according to claim 22, wherein the apparatus further comprises a support pin assembly comprising a plurality of support pins, and wherein the method comprises actuating the support pin assembly into an extended condition such that the plurality of support pins extend radially outwards into apertures in the inner tubular to engage with the inner tubular and bear the load of the inner tubular.

24. (canceled)

25. The method according to claim 22, wherein the apparatus further comprises a fluid delivery system configured to be coupled to a source of pressurised fluid and a pressure transmission path which enables the pressurised fluid to be delivered to the substantially annular volume, and wherein the method comprises filling the substantially annular volume with low pressure water.

26. The method according to claim 22, wherein the apparatus further comprises a centraliser assembly which is hydraulically actuated by the same fluid which is used to pressurise the substantially annular volume, and wherein the method comprises actuating the centraliser assembly by delivering low pressure water to the substantially annular volume.

27. (canceled)

28. The method according to claim 22, comprising operating a high pressure pump to pump water into the substantially annular volume such that the first and second cup seals are energised by the water to form a seal between the apparatus and the inner surface of the inner tubular, and the substantially annular volume is pressurised.

29. The method according to claim 28, wherein the inner tubular reacts to the pressure in the substantially annular volume and is deformed into an expanded position into contact with the caisson.

30. The method according to claim 29, comprising continuing the application of pressure using the high pressure pump such that the caisson is expanded and deformed into an expanded diameter.

31. The method according to claim 22, comprising forming a swaged connection between the inner tubular and the caisson.

32. The method according to claim 22, wherein after the connection has been formed between the inner tubular and the caisson, the method comprises releasing residual pressure within the apparatus and/or the substantially annular volume and causing the centraliser assembly to retract.

33. (canceled)

34. The method according to claim 22, wherein after the connection has been formed between the inner tubular and the caisson, the method comprises retracting the support pins from the inner tubular to release the apparatus from the inner tubular.

35. (canceled)

36. The method according to claim 22, comprising using the apparatus to form more than one swaged connection between the inner tubular and the caisson.

37. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0099] There will now be described, by way of example only, an embodiment of the invention with reference to the following drawings, of which:

[0100] FIG. 1A is an asymmetric view of an apparatus according to an embodiment of the invention;

[0101] FIG. 1B is a longitudinal section view through the apparatus of FIG. 1A;

[0102] FIG. 2 is a sectional view through a seal arrangement in accordance an embodiment of the invention;

[0103] FIGS. 3 to 8 show schematically sequential steps for a method of use of the apparatus of FIG. 1A in a caisson repair operation;

[0104] FIG. 9 is an enlarged view of a retention pin mechanism of the apparatus of FIG. 1A engaged with a liner; and

[0105] FIG. 10 is a plan view of a retention pin arrangement according to an embodiment of the invention.

[0106] FIGS. 11A and 11B are asymmetric and longitudinal sectional views of an apparatus according to an embodiment of the invention;

[0107] FIGS. 12A to 12C are prospective, plan and sectional views of a centraliser assembly of the apparatus of FIGS. 11A and 11B;

[0108] FIG. 13 is a longitudinal sectional view of the apparatus of FIGS. 11A and 11B within a liner; and

[0109] FIGS. 14A, 14B and 14C are part-section plan views of showing the gradual expansion of the centraliser assembly of the apparatus of FIGS. 11A and 11B.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0110] Referring firstly to FIGS. 1A, 1B and 2, there is shown an apparatus in accordance with an embodiment of the invention. The apparatus is a swaging tool for a caisson repair operation, generally depicted at 10. The tool comprises a mandrel 12, which is generally cylindrical in form having a first upper end and second lower end. A longitudinal axis of the mandrel defines the longitudinal axis of the tool.

[0111] An upper end of the tool is provided with a lift bracket 14, and a lower end of the tool is provided with a guide bracket 16 and guide cone 18. Accommodated within the guide bracket is a support pin assembly 20, which will be described in more detail below.

[0112] The tool comprises an upper seal retaining ring 22a and a lower seal retaining ring 22b, disposed respectively between an upper seal assembly 24a and the lift bracket, and a lower seal assembly 24b and the guide bracket. The seal assemblies (together 24) contact an outer surface of the mandrel, and define the outermost diameter of the tool.

[0113] An annular volume 25 is formed between the upper and lower seal assemblies, the outer surface of the mandrel, and the inner surface of a liner into which the tool is located in use. The tool also comprises a fluid delivery system configured to be coupled to a source of pressurised fluid. The fluid delivery system comprises a pressure transmission path which enables a pressurised fluid to be delivered to the annular volume 25, a water fill valve (not shown), vent valves, a fluid drain path comprising a fluid drain valve (neither shown), a flow meter for measuring the volume of fluid flowing through the system, and air bleed valves.

[0114] In this example, the seal assemblies 24 are upper and lower cup seals, described in more detail with reference to FIG. 2. The seal assembly 24 comprises a cup member 26 formed from a relatively soft, flexible elastomeric material. The cup member defines an open end of the seal assembly. An inner surface of the cup member is substantially cylindrical at the open end. An outer surface of the cup member is tapered towards its open end to define a generally conical shape between its maximum outer diameter and the open end of the seal.

[0115] The cup member 26 also comprises a neck portion 27, which is substantially cylindrical and is of reduced inner diameter and reduced outer diameter relative to the maximum outer diameter of the cup member. The neck portion 27 is disposed within a seal retaining ring 30, formed from a metal such as steel. The seal retaining ring 30 comprises a generally cylindrical body which partially surrounds the neck portion of the cup member. An end of the seal retaining ring, disposed axially away from the open end of the cup seal, is formed with a reduced inner diameter for axial engagement with a corresponding recess on the mandrel. A groove 32 is provided for accommodating an o-ring seal between the seal retaining ring and the mandrel.

[0116] The seal assembly 24 also comprises an anti-extrusion member 28, which is substantially annular in form and partially surrounds the cup member 26. The anti-extrusion member extends from the seal support ring towards the open end of the cup. An inner surface of the anti-extrusion member 28 abuts an outer surface of the cup member, and is substantially conical in form, opening towards the open end of the seal, and corresponding to a conical outer profile of the cup member between the neck portion 27 and the maximum outer diameter of the cup member.

[0117] This arrangement is beneficial as the anti-extrusion members are less susceptible to flow under pressure than the cup members. The anti-extrusion members therefore reduce or prevent the material of the cup members from flowing axially outwards between the liner and the components of the swage tool, and instead influence the material of the cup members to move radially outwards against the liner, when pressurised. The provision of the anti-extrusion members therefore improves the effectiveness of the seal between the cup members and the inner tubular.

[0118] The anti-extrusion member is formed from a relatively hard, flexible elastomeric material. In this embodiment, the cup member is formed from nitrile butadiene rubber (NBR) with hardness 80 on the Shore A hardness scale. The anti-extrusion member is formed from a nitrile butadiene rubber (NBR) with hardness 90 on the Shore A hardness scale. It will be appreciated that alternative materials and/or hardness values may be used in other aspects of the invention. Preferred embodiments use a material in the anti-extrusion member which is relatively hard compared with the material of the cup member. The anti-extrusion portion will therefore be less susceptible to flow under pressure and will improve, the effectiveness of the seal.

[0119] Embedded into the anti-extrusion member is a spring in the form of a helical garter spring 40, which extends circumferentially around the annular anti-extrusion member, and therefore around the cup member of the seal arrangement. Optionally, the spring has a core of harder anti-extrusion material, to reduce the risk of the cup material from flowing into and within the spring.

[0120] The spring may function to improve the seal which is created by the cup seals in use, as when the cup members are pressurised, the spring will be forced radially outwards against the liner to further improve the seal between the cup seals and the liner.

[0121] The seal arrangement of this embodiment comprises a cup member which is selectively bonded to at least one of the spring, the anti-extrusion member, and the seal retaining member to permit relative movement at contact areas between the components of the seal. The cup member is securely bonded by an adhesive at the base of the cup member where it abuts the seal retaining ring, and at the edge of the anti extrusion member 28 which is axially furthest from the spring. Thus the majority of the contact between the anti-extrusion member 28 and the cup member is unbonded.

[0122] In use, the open end of the cup member is inflated by an increase in pressure in the interior of the cup, and the cup member is expanded into contact with the liner, thereby preventing flow of fluid past the device cup member. As pressure within the cup member increases, the spring is pushed outwards, and the spring moves outward and downward into contact with the liner. This improves the seal created by the device, while the anti extrusion member is also forced into contact with the liner, and reduces or prevents flow of the softer cup member between the liner and the support member or the spring.

[0123] The relatively large unbonded surface area of the cup member allows the cup member to inflate and stretch without being restricted unduly by the anti-extrusion member 28 or the spring, while controlling the extent of the inflation of the seal. The double layer construction allows the cup member to be formed from a thinner and/or softer material, which enables it to respond to relatively low pressures. On release of fluid pressure the resilience of the cup member in combination with the spring return the seal to its original shape.

[0124] The sealing arrangement of this embodiment is selected to be effective in sealing the inner surface of typical liner dimensions used in caisson swaging applications.

[0125] In this embodiment, the outer diameter of the seal arrangement is approximately 23 inches (584 mm) and is configured to be operable to form a swaged connection of a liner into a 26 inch outer diameter caisson. A typical space between the outer diameter of the liner and the inner diameter of the caisson is approximately 15 mm, and the liner will typically have a uniform thickness of approximately 15 mm.

[0126] A typical expansion of the caisson is approximately two percent (2%) of the outer diameter. A consequence that the inner liner is required to expand over a greater range, and internal seals are required to maintain a seal over the entirety of the expansion range. This is in contrast to downhole applications, in which the outer tubular is not required to expand, and which may rely on conventional seal arrangements. For example, the tool of US 2004/0031615 is designed to expand a cladding into casing downhole. In typical downhole arrangements, casing is surrounded by cement and so it may be undesirable, and in fact it may cause damage to the surrounding cement, to expand the outer tubular.

[0127] Conventional seals, for example the smaller diameter seals used in downhole tools such as that described in US 2004/0031615, suffer from a number of disadvantages. In particular, they tend to be made of relatively thick rubber or other elastomer and require a small gap between the cup and a bore wall. If the gap between the cup and bore is increased, the pressure the cup will hold drops considerably and therefore not suitable for the repair of caissons. For internal swaging in caisson repair applications, it is necessary to expand both the liner and caisson to a point of permanent deformation in order to provide a method of liner retention. It has been necessary to utilise a seal that has high expansion properties. US 2005/0098313 describes a seal for downhole applications, with a similar construction to the large diameter seals used in embodiments of the present invention.

[0128] A method of use of the swaging tool 10 in a caisson repair operation will now be described with particular reference to FIGS. 3 to 8. FIG. 3 shows a caisson 101 of a platform 100. Prior to deploying the swaging tool 10, a caisson repair liner assembly 102 formed from an upper liner section 102a, a middle liner section 102b, and a lower liner section 1-2c, is installed within the caisson 101. The liner assembly 102 is supported at the top of the caisson by support brackets 104. A transit frame 130 initially containing the swage tool 10 is located at a suitable location adjacent to the top of the caisson, and within an area accessible by installation lifting rigging. The swage tool is removed from the transit frame cover by attaching a main lift line 106 to the lift bracket 14 at the upper end of the swage tool, and an auxiliary lift line (not shown) to the guide bracket at the lower end of the swage tool. The swage tool is lifted horizontally out of the transit frame, and a cross haul of the tool towards the caisson location is carried out whilst simultaneously upending the tool so that it is vertically-oriented above the caisson. With the swage tool fully upended and vertically disposed, the auxiliary lift line is removed from the guide bracket and the tool is positioned directly over the top of the caisson with the repair liner assembly already suspended. A control umbilical is connected to the swage tool and pre-operation checks of the functional components of the swage tool are performed.

[0129] With the swage tool supported on the main lift line 106, liner lift lines 108 are connected to the liner support brackets connected to the top of the liner assembly, and the liner is raised slowly up over the swage tool, as shown in FIG. 4. The liner is raised until the slots 110 in the upper liner section 102a align with the liner support pins 141 on the swage tool. The support pins are hydraulically actuated to extend radially outwards into the slots on the liner, to a position which the support pins can bear the load of the liner assembly (FIG. 9). The liner lift lines are relaxed so that the liner assembly is supported on the swage tool liner support pins.

[0130] The main lift line 106 is then used to lower the tool, complete with the liner assembly, to the floor level. With the air bleed valve open, the annular volume between the seal assemblies and the liner is filled with low pressure water. When the annular volume is full with low pressure water, the air bleed valve is closed. The liner lift lines can then be removed and the liner support brackets are removed from the liner assembly.

[0131] The swage tool 10, complete with the liner assembly 102, is then lowered on the main lift line 106 to a pre-determined depth, such that a caisson defect 120 is aligned with a mid-position of a middle section of the liner assembly, as shown in FIG. 5. With the liner assembly at the correct location, the main lift line is secured in position.

[0132] The swage tool may then be operated to form a swaged connection of an upper liner section in the caisson: an air bleed valve on the top side control panel is opened, and the water fill valve is opened to enable to the system to be filled with low pressure water. The air bleed valve is closed when the system is full.

[0133] Using a high pressure pump, water is pumped into the annular space via the pressure transmission path until swaging pressure is reached. The seal assemblies 24 are energised and form a seal between the swage tool and the inner surface of the liner, as depicted in FIG. 6. The liner section reacts to the pressure in the annular volume, and is deformed and swaged into an expanded position in contact with the caisson. With continued application of pressure, the caisson is expanded and deformed to an expanded diameter. With the liner section swaged in position, the vent valves are opened to release residual pressure.

[0134] The upper liner section 102a is now swaged in position and supported in the caisson. The liner support pins are retracted by hydraulic actuation, to release the swage tool from the liner. Hydraulic actuation of the swage pins to a retracted position is preferred over alternative techniques such as shear pins, as the forces required to shear the pins may result in a hazardous acceleration of the swage tool, and/or in some cases may have an adverse effect on an incompletely formed connection between the liner and the caisson.

[0135] FIG. 10 shows the liner support pin assembly 20 in more detail. The assembly 20 comprises a pair of support pin actuators 140a, 140b, connected to respective support pins 141a, 141b. The actuators are coupled to a hydraulic control system via a manifold 145, and are provided with extension lines 142a, 142b which provide hydraulic actuation to extend the support pins, and retraction lines 143a, 143b which provide hydraulic actuation to retract the support pins. Redundancy is provided by backup retraction lines 144a, 144b, which provide hydraulic actuation to retract the support pins and release the tool from the liner assembly in the event of failure of the primary system.

[0136] The swage tool is then lowered in the liner assembly until the swage tool is positioned within a lower liner section of the liner assembly, below the caisson defect 120, as shown in FIG. 7. The main lift line 106 is secured in this position.

[0137] The swage tool is now operated to form a swaged connection of the lower liner section. The air bleed valve on the top side control panel is opened, and the water fill valve is opened to top up the system with low pressure water. The air bleed valve is closed.

[0138] Using a high pressure pump, water is pumped into the annular space formed between the seal assembly, the mandrel and the inner surface of the liner section. The seals are energised and the water pressure in the annular space is increased to swaging pressure, as depicted in FIG. 8. At the swaging pressure, the liner section reacts by deforming and expanding to a swaged position, in which it contacts the caisson. The caisson is deformed and expanded into an expanded condition.

[0139] During swaging, shoulders are formed in the liner and the caisson above and below the annular volume. The shoulders extend circumferentially around the liner and caisson, and provide a radially extending portion of the liner and caisson between the unexpanded liner and caisson and the deformed liner and caisson. The shoulders assist with the support of the liner in the caisson in conjunction with friction between the adjoining walls of external liner and inner caisson, and therefore the resulting connection has improved mechanical grip. The creation of a shoulder in the absence of pre-formed recesses or the use of non-uniform (thick-thin walled) liners enables relatively cheap liners to be used in the methods of the present invention.

[0140] The profile of shoulder from original caisson diameter to maximum deformed diameter has a transitional gradient that is dictated by the material properties of the liner/caisson. The pressure applied, and therefore the expansion of the seals, takes the original material of both the liner and caisson past the elastic state into the plastic state so that when pressure is removed the permanent deformation of the shoulder is in place.

[0141] The creation of the shoulder profile is facilitated by the choice of seal. The start of the shoulder profile at original caisson diameter is created at the position of the seal retainer ring area which does not move outwards during pressurisation. The finalised shoulder profile of maximum deformed diameter occurs at the seal spring location as this is the point that the liner first affected by the full hydrostatic pressure/expansion of seal.

[0142] With both upper and lower liner sections now swaged in position, the drain valve (not shown) at the lower end of the swage tool is opened to allow the water trapped between the cup seals and the swage tool to drain away, while the swage tool is raised from the liner. The main lift line is used to slowly raise the swage tool clear of the top of the caisson, where the control umbilical is disconnected. With the swage tool supported on the main lift line, an auxiliary lift line is attached to commence the cross-hauling operation to return the swage tool to the transit frame 130. The tool can them be washed down with fresh water and all valves flushed to complete the operation.

[0143] FIGS. 11A and 11B show a preferred embodiment of the invention. The swage tool (and its components) is substantially similar to the swage tool which has been described throughout the foregoing description and will generally be understood from the foregoing description. However, in this preferred embodiment of the tool, it is provided with two centraliser assemblies 250a, 250b. The centraliser assemblies 250a, 250b are provided between each cup seal assembly 224a, 224b and its respective seal retaining ring 222a, 222b.

[0144] The centraliser assemblies 250a, 250b are hydraulically actuated, and retractable, such that they do not hinder axial movement of the swage tool within the liner. The centraliser assemblies 250a, 250b are provided outwardly from each cup seal assembly 224a, 224b such that they are out with the area of pressure application (i.e. the annular volume shown generally at 225 which is defined between the seal assemblies 224a, 224b, the mandrel 212 and the liner (not shown)). In addition, the centraliser assemblies 250a, 250b are actuated by the same pressurised fluid which is used to perform the swaging operation. As such, in this embodiment the fluid delivery system comprises a pressure transmission path which further comprises an auxiliary fluid transmission path 260 which enables the same pressurised fluid to be concurrently delivered to the centraliser assemblies 250a, 250b as that which is delivered to the annular volume 225.

[0145] A centraliser assembly 250 is shown in more detail, in isolation, in FIGS. 12A to 12C. The centraliser assembly is made up of a cylindrical body portion and comprises three hydraulically actuated centraliser members 252, with rectangular pads 254 on their ends, The outer surfaces of the rectangular pads 254 are rounded, and the cylindrical body portion 251 comprises recesses which correspond in location and shape to the pads 254 such that a flush outer surface is defined by the pads 254 and the outer surface of the cylindrical body 251 when the centraliser members 252 are in their retracted condition.

[0146] FIG. 13 shows a sectional view of the swage tool within a liner section 202, with the centraliser assemblies in their retracted condition. With reference to the plan sectional views of FIGS. 14A to 14C, actuation of the centraliser assemblies will now be described.

[0147] FIG. 14A shows the centraliser assembly 250 in its fully retracted condition, FIG. 14B shows the centraliser assembly 250 in its partially expanded condition, and FIG. 14C shows the centraliser assembly 250 in its fully expanded condition.

[0148] In FIG. 14A, the hydraulically actuated centraliser members 252 of the centraliser assembly 250 are fully retracted, such that the outer surfaces of the pads 254 are flush with the body 251 of the centraliser assembly 250. It can be seen that the centraliser members 252 comprise an assembly of pins and other additional components, such as spring 262. In its retracted state, no hydraulic fluid is present in the auxiliary fluid transmission path 260.

[0149] FIG. 14B shows the centraliser assembly 250 in its partially expanded condition. In this condition, the auxiliary fluid transmission path 260 is becoming filled with hydraulic fluid (i.e. water) in the direction indicated by the arrow, simultaneously as the annular volume between the seal assemblies of the swage tool and the liner is filled with low pressure water (not shown). The water which fills the auxiliary fluid transmission path 260 and the annular volume is the same water from the same source. The force which is provided by the water in the auxiliary fluid transmission path 260 begins to overcome the force of the spring 262, to push the centraliser members 252 and thus the centraliser pads 254 outward from the body 251 of the centraliser assembly, towards the liner 202. In doing so, the water moves into the space 260a which is created by the outward movement of the centraliser members 252.

[0150] FIG. 14C shows the centraliser assembly 250 in its fully expanded condition. The pads 254 expand (nearly fully) to touch, or almost touch, the liner 202 when the annular volume between the seal assemblies of the swage tool and the liner is full of the low pressure water, before operation of the high pressure pump is initiated to reach swaging pressure within the annular volume.

[0151] When the swaging operation commences, operation of the high pressure pump to pump water into the annular volume also results in the a higher pressure in the auxiliary fluid transmission path 260, such that the centraliser members 252 and pads 254 reach their maximum expanded condition, and contact the liner 202 sufficiently to centralise the swage tool therein. Full expansion of the centralisers occurs before the liner is deformed as a result of the swaging operation.

[0152] The centraliser members 252 are all only permitted to expand by a certain maximum distance. This distance corresponds to the small clearance area which exists between the swage tool and the liner. Therefore, controlling the actuation and retraction of centraliser members in applications in which only a small travel distance for the centraliser exists (i.e. between the tool and the liner) is particularly beneficial.

[0153] On completion of a swaging operation, normal draining of the swage tool results in draining of the auxiliary fluid transmission path 260. With hydraulic fluid no longer present in the transmission path 260 for the centraliser members 252, the spring 262 moves the centraliser members 252 of the centraliser assembly 250 back into their retracted condition.

[0154] Centralising the swage tool within the liner facilitates the application of a uniform pressure over the length and/or circumference of the liner, which can be challenging when using such a large tool. This is especially difficult when such a large-scale application, such as that described herein in relation to caissons, is combined with the increased pressure requirements and common inconsistencies and inaccuracies associated with the thickness and ovality of rolled tubulars (such as liners).

[0155] It is therefore important that pivoting of the swage tool about its longitudinal axis during swaging is reduced, not only to ensure that the pressure which is applied is uniform, but also to ensure that the seals are not damaged during the swaging process. For example, if the swage tool is able to pivot about its longitudinal axis during swaging, the annular clearance between the cup seal assemblies and the liner may be uneven. At points where the annular clearance gap is larger, there may not be sufficient reinforcement for the seal spring, causing the seal spring and seal to extrude through the clearance gap, thus damaging the seal.

[0156] For at least the reasons outlined above, it is beneficial to centralise the swage tool within the liner during pressure application. However, it is important that the swage tool is able to be centralised within the liner by a mechanism which does not otherwise pose an obstacle to the movement of the swage tool (for example, when the swage tool is being raised or lowered within the liner). This is of particular significance when the liner is of non-uniform cross section and/or wall thickness.

[0157] The invention in one aspect provides an apparatus and method for forming a connection between an inner tubular and a caisson of an offshore structure. The apparatus comprises a mandrel, and a seal arrangement disposed on the mandrel and configured to create a seal between the mandrel and an inner surface of an inner tubular in which the apparatus is located. The seal arrangement comprises first and second cup seals, axially separated on the mandrel, and configured to define a substantially annular volume between the mandrel and the inner tubular in use. A pressure transmission path delivers a pressurised fluid to the annular volume, and the apparatus is configured to pressurise the annular volume and thereby expand the inner tubular in a radial direction and into contact with the caisson to form a connection between the inner tubular and the caisson.

[0158] Various modifications to the above-described embodiments may be made within the scope of the invention, and the invention extends to combinations of features other than those expressly claimed herein.