Fabrication of Pipe Bundles Offshore

Abstract

A pipeline bundle for a riser tower or tie-back is manufactured offshore by suspending the bundle from an installation vessel, adding structural core sections successively to an upper end of the suspended bundle, lowering the bundle after adding each successive core section, and feeding one or more lengths of flowline pipe beside the core sections for incorporation into the bundle. The flowline pipe is coiled on a reel or carousel as a full-length piece before being uncoiled progressively as core sections are added to the lengthening bundle. The flowline pipe is then engaged with guide frames and/or buoyancy blocks supported by the core sections, by movement in a radially-inward direction through a radially-outer opening in a retainer formation. The opening is then closed to hold the flowline pipe in the retainer formation.

Claims

1-29. (canceled)

30. A method of assembling an elongate pipeline bundle offshore aboard an installation vessel, the method comprising: suspending the bundle from the vessel so that the bundle hangs in an upright orientation underwater beneath the vessel; successively attaching pre-fabricated elongate structural core sections to a corresponding uppermost core section already incorporated into the bundle, in each instance to become a newly-uppermost core section of the bundle; each pre-fabricated elongate structural core section comprising a core pipe and at least one of: a guide frame, and a buoyancy block; and, after attaching each core section, lowering the bundle in a downward launch direction to suspend the bundle from the newly-uppermost core section; wherein the method further comprises incorporating a length of flowline pipe into the bundle aboard the vessel, a portion of that pipe already incorporated into the bundle extending along the bundle beside the successive core sections, that pipe being a flexible pipe, a composite pipe or a rigid pipe as herein defined.

31. The method of claim 30, comprising uncoiling the flowline pipe from coiled storage for incorporation into the bundle.

32. The method of claim 30, comprising feeding the flowline pipe on a feed path converging with the launch direction.

33. The method of claim 32, comprising bending the flowline pipe along its length to follow the feed path.

34. The method of claim 30, comprising effecting relative movement of the flowline pipe in a radially-inward direction with respect to a core section for incorporation into the bundle.

35. The method of claim 34, wherein said relative movement of the flowline pipe takes place as the bundle is lowered in the launch direction.

36. The method of claim 35, wherein said relative movement of the flowline pipe is at least partially effected by movement of a core section in the launch direction.

37. The method of claim 36, wherein said movement of the core section takes place after incorporation of that core section into the bundle.

38. The method of claim 34, comprising inserting the flowline pipe into a longitudinally-extending retainer formation of the bundle through a radially-outer opening of the retainer formation.

39. The method of claim 38, comprising inserting the flowline pipe into the retainer formation progressively in a longitudinal direction.

40. The method of claim 39, comprising inserting the flowline pipe first into a lower part of the retainer formation and then into an upper part of the retainer formation.

41. The method of claim 38, further comprising closing the radially-outer opening of the retainer formations to hold the flowline pipe in the retainer formation.

42. The method of claim 41, comprising pressing the flowline pipe into the retainer formation by applying a closure that closes the radially-outer opening of the retainer formation.

43. The method of claim 30, wherein the flowline pipe extends along successive core sections of the bundle as a continuous piece.

44. The method of claim 30, comprising storing the flowline pipe offshore as a full-length piece before incorporation into the bundle.

45. The method of claim 30, comprising engaging the flowline pipe with the guide frames, the guide frames extending radially outwardly from the core sections of the bundle.

46. The method of claim 45, comprising suspending the bundle from successive ones of the guide frames after lowering the bundle in the launch direction.

47. The method of claim 45, further comprising engaging the flowline pipe with the buoyancy blocks supported by core sections of the bundle.

48. The method of claim 30, wherein the bundle is incorporated into a riser tower or a subsea tie-back.

49. An apparatus for assembling an elongate pipeline bundle offshore comprises: hang-off equipment for suspending the bundle from the vessel; a connection workstation for adding prefabricated structural core sections successively to an upper end of the suspended bundle, each pre-fabricated elongate structural core section comprising a core pipe and at least one of: a guide frame, and a buoyancy block; lowering equipment for lowering the bundle in a downward launch direction after adding each successive core section; and pipe feed equipment for feeding a length of flowline pipe beside the core sections for incorporation into the bundle by engaging with the at least one of the guide frames and/or buoyancy blocks.

50. The apparatus of claim 49, further comprising lifting equipment for lifting the structural core sections to the upper end of the suspended bundle.

51. The apparatus of claim 49, further comprising pipe storage upstream of the pipe feed equipment.

52. The apparatus of claim 51, wherein the pipe storage is arranged to store the flowline pipe in a coiled configuration.

53. The apparatus of claim 49, wherein the pipe feed equipment defines a feed path converging downwardly with the launch direction.

54. The apparatus of claim 53, further comprising guide equipment for bending the flowline pipe along its length to follow the feed path.

55. The apparatus of claim 53, wherein the feed path is arranged to divert the flowline pipe in a radially-inward direction with respect to a core section incorporated into the bundle.

56. The apparatus of claim 53, wherein the feed path is disposed above the hang-off equipment.

57. An installation vessel comprising the apparatus of claim 49.

Description

[0067] In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings, in which:

[0068] FIG. 1 is a partial sectional side view of an installation vessel adapted in accordance with a first embodiment of the invention, taken on line A-A of FIG. 3, in the process of fabricating a riser tower that is launched through a moonpool of the vessel;

[0069] FIG. 2 is a plan view of the installation vessel shown in FIG. 1;

[0070] FIG. 3 is an enlarged detail view corresponding to Detail B of FIG. 2;

[0071] FIG. 4 is a schematic part-sectional side view of a second embodiment of the invention, in which an installation vessel employs a J-lay tower to fabricate a riser tower and launches the riser tower over a side of the vessel;

[0072] FIG. 5 is a schematic plan view showing how riser pipes may be inserted into recesses in a guide frame of the riser tower of FIG. 4; and

[0073] FIG. 6 is a schematic plan view corresponding to FIG. 5 but showing two ways in which the riser pipes may be retained in the guide frame after insertion.

[0074] Referring firstly to FIGS. 1 to 3 of the drawings, these show a first embodiment of the invention in its context of use. Here, an installation vessel 10 is shown fabricating a riser tower 12 at an offshore location that may be directly over, or conveniently close to, a subsea installation site for the riser tower 12 upon completion.

[0075] The riser tower 12 is shown partially constructed in FIG. 1. The riser tower 12 hangs freely in a substantially vertical orientation in the water column beneath the surface of the sea 14, represented here by a dashed line. The lower or distal end of the riser tower 12 has a pivot formation 16 for anchoring the riser tower 12, when completed, to a seabed foundation (not shown), as is well understood by those skilled in the art. However, this lower end of the riser tower 12 remains clear of the seabed during fabrication and is only brought to the seabed for installation after fabrication of the riser tower 12 has been completed.

[0076] It will be apparent that the riser tower 12 remains upright under the tension of its own weight during construction, installation and use. This effectively avoids or resists bending fatigue that arises during the towing and upending operations that are required to install conventionally-manufactured riser towers. It will also be apparent that the riser tower 12 can be fabricated wherever there is deep enough water, without relying upon the limited availability of coastal fabrication yards as used in the prior art.

[0077] FIGS. 1 to 3 show that the vessel 10 comprises a moonpool 18 that extends through a working deck 20 of the vessel 10 and into the sea 14. A crane 22 atop the working deck 20 beside the moonpool 18 serves as a hoisting apparatus in this embodiment. The crane 22 has a jib 24 whose lateral reach extends over the moonpool 18.

[0078] Other embodiments of the invention may use other hoisting apparatus, such as an erector arm or a travelling clamp of a J-lay tower, as will be explained later with reference to FIG. 4.

[0079] FIG. 1 shows that the riser tower 12 comprises a series of modules attached together end-to-end in longitudinal succession as a pipe string. The modules in this example are prefabricated structural core sections 26, each of which comprises a core pipe 28 whose central longitudinal axis 30 coincides with, and defines part of the length of, a central longitudinal axis of the riser tower 12. The core pipe 28, in turn, may comprise a single pipe joint or two or more pipe joints welded end-to-end.

[0080] In this example, the length of each structural core section 26, determined by the length of the core pipe 28, is no greater than the lifting height of the crane 22 when its jib 24 is positioned centrally over the moonpool 18.

[0081] Each structural core section 26 further comprises a laterally-extending guide frame 32 attached to the core pipe 28 near its upper end. The guide frame 32 in this example extends in a plane substantially orthogonal to the central longitudinal axis 30. The guide frame 32 may be welded or clamped to the core pipe 28. In the latter instance, stop formations on the core pipe 28 suitably provide a back-up to restrain any tendency of the guide frame 32 to slide along the core pipe 28 in use. Such stop formations are well known in the artsee, for example, the discussion in WO 2013/114211and so need not elaboration here.

[0082] Buoyancy blocks 34 of syntactic foam are assembled circumferentially around the core pipe 28 under each guide frame 32. In this way, buoyant upthrust loads are transferred via the guide frames 32 from the buoyancy blocks 34 to the core pipes 28 of the riser tower 12.

[0083] In this example, the buoyancy blocks 34 are not required to contribute thermal insulation and so are spaced longitudinally to distribute their buoyancy along the riser tower 12. However, if required for thermal insulation, the buoyancy blocks 34 could abut in longitudinal succession to provide substantially continuous thermal insulation along the riser tower 12.

[0084] The buoyancy blocks 34 are preferably pre-installed around the core pipe 28 of each structural core section 26 as shown in FIG. 1. Alternatively the buoyancy blocks 34 could be installed around the core pipe 28 after each structural core section 26 has been added to the string of structural core sections 26 that make up the riser tower 12. In some examples, the buoyancy blocks 34 may be secured by temporary means to allow sliding or locking relative to the structural core section 26.

[0085] Short end portions of the core pipe 28 protrude longitudinally beyond the guide frame 32 at an upper end of the structural core section 26 and beyond the buoyancy blocks 34 at an opposed lower end of the structural core section 26. This provides ample longitudinal clearance for access to the core pipe 28 for weld preparation, followed by welding, weld testing and protective coating. Optionally, if continuous thermal insulation is required along the length of the riser tower 12, additional foam blocks could then be placed around the welded and coated joint region.

[0086] FIG. 1 shows the partially-completed riser tower 12 at an early stage of construction. The riser tower 12 currently comprises just two structural core sections 26 that have been fixed to each other end-to-end by butt welding between abutting, protruding ends of their core pipes 28. When welded together end-to-end, these core pipes 28 form the principal tensile member of the riser tower 12.

[0087] The upper one of the two structural core sections 26 of the riser tower 12 is supported by a hang-off bushing 36 that lies centrally over the moonpool 18. The hang-off bushing 36 closes under the guide frame 32 of that structural core section 26. In this way, that guide frame 32 serves as a hang-off formation to transmit the weight load of the partially-completed riser tower 12 to the vessel 10 via the hang-off bushing 36.

[0088] In accordance with the invention, the riser tower 12 further comprises riser pipes 38 that extend continuously from one structural core section 26 to the next along the length of the riser tower 12. The riser pipes 38 are supported by the guide frames 32 spaced longitudinally along the riser tower 12 so as to extend substantially parallel to the successive core pipes 28.

[0089] In this embodiment, there are four riser pipes 38 spaced equiangularly in plan view around and outside the core pipes 28 of the structural core sections 26. Other embodiments could have more or fewer riser pipes, from just one riser pipe to more than four riser pipes.

[0090] The bottom ends of the riser pipes 38 are suitably anchored to the lowermost structural core section 26 of the riser tower 12. Those ends are suitably provided with bottom end fittings for fluid communication with pipework of a seabed installation to which the riser tower 12 will be connected for use.

[0091] The riser pipes 38 are fed from onboard storage apparatus that holds the riser pipes 38 in a compact curved configuration until required. In this example, the storage apparatus comprises respective reels 40 mounted on the working deck 20 of the vessel 10. The 35 reels 40 turn about substantially horizontal axes in respective intersecting or parallel upright planes that converge on, and substantially align with, the common central longitudinal axis 30 of the core pipes 28 that together form the riser tower 12.

[0092] The riser pipes 38 may be flexible pipes, composite pipes or rigid pipes. In this example, the riser pipes 38 are composite pipes that are bent elastically around the reels 40. Thus, the riser pipes 38 tend to straighten by elastic recovery as they come off the reels 40.

[0093] Guide structures 42 spaced above the hang-off bushing 36 guide the riser pipes 38 from the top of the reels 40 into substantially vertical alignment with the core pipes 28 of the riser tower 12. The MBR appropriate to the particular riser pipes 38 is observed throughout.

[0094] As the riser pipes 38 are guided downwardly and laterally into vertical alignment with the core pipes 28, the riser pipes 38 enter, and are retained within, longitudinally-extending retainer formations of the guide frames 32 and the buoyancy blocks 34. As will be explained in more detail in the second embodiment illustrated in FIGS. 4 to 6 of the drawings, this keeps the riser pipes 38 substantially parallel to the core pipes 28.

[0095] Several more structural core sections 26 must now be added to complete the riser tower 12. The next such structural core section 26 is shown here having been lifted by the crane 22 from the working deck 20 of the vessel 10 to a central position over the moonpool 18. The downwardly-protruding end of its core pipe 28 is shown in lateral alignment with the opposed upwardly-protruding end of the core pipe 28 of the structural core section 26 at the top of the riser tower 12.

[0096] Once the next structural core section 26 has been upended and aligned with the partially-completed riser tower 12 in this way, the opposed core pipes 28 are butt-welded to each other to incorporate the structural core section 26 into the lengthening riser tower 12. The crane 22 can then support the weight of the riser tower 12 through the uppermost structural core section 26, lifting from the hang-off bushing 36 the guide frame 32 that previously bore the weight of the riser tower 12.

[0097] With the crane 22 continuing to support the weight of the riser tower 12, the hang-off bushing 36 may then be opened to provide clearance for the guide frame 32 that previously bore the weight of the riser tower 12. This allows the riser tower 12 to be lowered into the sea 14 by the length of the newly-added structural core section 26.

[0098] Simultaneously, the riser pipes 38 pay out from their respective reels 40, being drawn from the reels 40, or driven off the reels 40, to an extent required by the downward longitudinal movement of the riser tower 12. Thus, the riser pipes 38 advance from the reels 40 in a stepwise movement synchronised with the stepwise launch movement of the riser tower 12. The reels 40 suitably maintain some back-tension in the riser pipes 38, which encourages the riser pipes 38 to straighten and to stay substantially straight.

[0099] Next, the hang-off bushing 36 is closed so that the guide frame 32 of the uppermost structural core section 26 can rest on the hang-off bushing 36, which then again supports the weight of the riser tower 12 suspended beneath the vessel. As the downward launch movement of the riser tower 12 consequently pauses, the reels 40 also pause their dispensing of the riser pipes 38.

[0100] The crane 22 is then free to disconnect from the uppermost structural core section 26 and to slew around to pick up another structural core section 26, for example from the working deck 20 of the vessel 10. The fabrication cycle then repeats, whereupon further lengths of the riser pipes 38 are dispensed from the reels 40 to match the lengthening riser tower 12.

[0101] Eventually the full length of the riser tower 12 is completed, whereupon the riser pipes 38 may be cut and terminated by suitable top end fittings. Also, a buoyancy module may be added to the top of the uppermost structural core section 26. The riser tower 12 can then be suspended by the crane 22 through the moonpool 18 for installation, when the pivot formation 16 at the lower end of the riser tower 12 is used to anchor the riser tower 12 to a seabed foundation.

[0102] The apparent weight load on the crane 22 and the hang-off bushing 36 during fabrication and installation of the riser tower 12 is reduced by the buoyant upthrust of the buoyancy blocks 34 and any additional buoyancy module, when submerged. The weight load and orientation of the riser tower 12 may also be controlled by ballasting or deballasting operations. This may, for example, be achieved by attaching temporary buoyancy to, or removing temporary buoyancy from, the riser tower 12 or by flooding or purging the core pipes 28, the buoyancy module or other such other buoyancy tanks as may be attached permanently or temporarily to the riser tower 12.

[0103] Turning next to the second embodiment shown in FIGS. 4 to 6, like numerals are used for like features. In this example, which is not shown to scale, the hoisting apparatus that lifts and lowers the successive structural core sections 26 comprises a lifting arm 44 and a travelling clamp 46 of a J-lay tower 48. This is distinguished from the crane 22 that serves as hoisting apparatus in the first embodiment. Also, the J-lay tower 48 is supported by an outrigger structure to launch a riser tower 50 over the side or stern of an installation vessel 52 rather than through a moonpool 18.

[0104] For ease of illustration, the riser tower 50 in FIGS. 4 to 6 is shown as having two riser pipes 54 that are diametrically opposed about a central core pipe 28. Also, the riser pipes 54 are exemplified as flexible pipes that permit a relatively small MBR. The riser pipes 54 extend from reels 40 and around guide wheels 56 at a level above the hang-off bushing 36. The guide wheels 56 guide the riser pipes 54 into parallel vertical alignment with the core pipes 28 and with each other.

[0105] The foregoing description of the first embodiment shown in FIGS. 1 to 3 makes reference to riser pipes being held in longitudinally-extending retainer formations of the guide frames 32 and the buoyancy blocks 34. Examples of such retainer formations are illustrated in the second embodiment shown in FIGS. 4 to 6 and will now be described.

[0106] Specifically, the guide frames 32 of the structural core sections 26 and the associated buoyancy blocks 34 have circumferentially-aligned, longitudinally-extending, full-length grooves, cut-outs or recesses 58. As best appreciated in FIGS. 5 and 6, the recesses 58 are open to their radially outer side with respect to the central longitudinal axis 30 of the associated core pipe 28.

[0107] As the riser pipes 54 are guided or diverted downwardly and laterally into vertical parallel alignment with the core pipes 28, the riser pipes 54 enter the respective recesses 58 in a radially-inward direction toward the central longitudinal axis 30. A similar effect may arise from downward movement of the structural core sections 26 as they are lowered by the travelling clamp 46 of the J-lay tower 48. The riser pipes 54 will then enter the respective recesses 58 progressively from the bottom of the recesses 58 to the top. This can also occur in the first embodiment as shown in FIG. 1, when the structural core sections 26 are lowered by the crane 22 relative to the converging riser pipes 38.

[0108] In each case, the structural core sections 26 move in a downward launch direction and the riser pipes 54 bend as they move along downwardly and radially-inwardly on feed paths that converge with the launch direction. The feed paths end at the recesses 58, where the riser pipes 54 eventually reach parallel relation with the core pipes 28 and hence with the launch direction that coincides with the vertical central longitudinal axis 30.

[0109] The radially outer open sides of the recesses 58 are then closed with closures such as clamps 60 or straps 62 to retain the riser pipes 54 in the recesses 58. Clamps 60 or straps 62 may, for example, be applied to the guide frames 32 at a welding station 64 that also houses a hang-off bushing 36. This prevents radially-outward movement of the riser pipes 54 out of the recesses 58 and so keeps the riser pipes 54 substantially parallel to the core pipes 28. Applying clamps 60 or straps 62 may also help to align the riser pipes 54 with the recesses 58 and to press the riser pipes 54 radially inwardly into the recesses 58.

[0110] In FIG. 6, an example of a bolted clamp 60 is shown on the left side of the guide frame 32 and an example of a strap 62 is shown on the right side of the guide frame 32. Clamps 60 and straps 62 are also shown schematically in FIG. 4. Here, clamps 60 are shown being applied to the guide frames 32 with radially-inward movement in a welding station 64 immediately above the hang-off-bushing 36. Straps 62 are, optionally, also applied to the buoyancy blocks 34 to provide extra security.

[0111] Many variations are possible without departing from the inventive concept. For example, other storage apparatus could be used instead of reels, such as carousels that turn about substantially vertical axes. Also, the riser pipes may be stored on, and supplied from, offboard storage apparatus that is not on board the installation vessel, for example on a supply barge that is tied to the installation vessel.

[0112] Retainers such as clamps or straps may be applied to the riser tower at a further station downstream of, or below, the welding station.

[0113] Guide frames need not be incorporated into the structural core sections during pre-fabrication but could instead be fitted to the core pipes at any stage before the riser tower is launched into the sea. This could even be after the core pipes have been incorporated into the top of the riser tower above the level of suspension.

[0114] The techniques of the invention are apt to install elongate elements other than riser pipes on the riser tower in addition to the riser pipes themselves. Such elements may be umbilicals for conveying power or service fluids along the riser tower, in parallel to the riser pipes.

[0115] There may be more than one core pipe, the core pipes being in concentric or mutually parallel relation.

[0116] Pipe joints forming the core pipe may be single-walled or of double-walled pipe-in-pipe construction. The core pipe may serve as a flowline for production fluids and/or as a protective carrier pipe for power or data cables or for other pipes, such as may carry service fluids.

[0117] Similar principles could be used to fabricate a pipeline bundle for use in a substantially horizontal orientation as a tie-back structure, in which case the completed bundle can be tipped from a vertical orientation, when underwater, for installation on the seabed. In that application, there will be no need for a top buoyancy module and there may be less need for buoyancy blocks along the bundle, although some removable or floodable buoyancy modules may be used instead or additionally.

[0118] If it may be desirable for the lay angle, departure angle or launch angle of the pipe bundle into water to diverge from the vertical while still remaining upright, a J-lay tower may gimbal and tilt to modify that angle, for example by up to 15 from the vertical.