Pipeline laying vessel and method for laying a pipeline in a marine environment

Background of the invention

Field of the invention

This invention relates to a pipeline laying vessel and a method for laying a pipeline in a marine environment, in particular for laying a pipeline on a bottom of a seabed. The invention further relates to a reel for use in the pipeline laying vessel and the method. The invention also relates to the laying of a pipeline which extends from a seabed to a target location at or near the water level, which pipeline is also known as a riser.

Description of the related art

Offshore oil and gas production has increased strongly over the recent years, due to a growing demand for oil and gas. New oil and -' ^" gas fields are being explored and made ready for production.

Therefore, a strong demand exists for undersea pipelines which connect oil and gas fields to production and storage facilities. A general need in the field of the art exists to lay these pipelines with a high quality in a fast and cost-effective way. Different methods of laying pipelines at sea are known. One method is to connect consecutive pipe sections to a free end of a pipeline supported by a pipeline laying vessel. As the pipeline is gradually paid out from the vessel, the vessel moves forward. Hereinafter, this type of laying a pipeline is referred to as a connecting method.

Several subtypes of the connecting method exist. Depending on the form of the pipeline on board the vessel and in the area between the seabed and the vessel, known subtypes of this method are J-lay, S-lay and G-lay. An example of a J-lay vessel is disclosed in US 5 464 307. An example of an S-lay vessel is disclosed in US 3 685 305. An example of a G-lay vessel is disclosed in GB 2 287 517.

A different method of laying a pipeline is known as reeling, or reel-lay. In the reeling method, a relatively long section of pipeline is wound onto a reel positioned on board the pipeline-laying vessel prior to a pipeline laying operation. At the time of laying, the pipeline is unreeled from the reel and launched from the vessel. An example of a reeling vessel is disclosed in GB 2 025 566 A.

The choice whether to perform J-lay, S-lay, G-lay or reeling in a given situation depends on a number of factors such as: water depth, diameter of the pipeline, wall thickness of the pipeline, a target position and a target orientation of the pipeline, a maximal allowed plastic deformation of the pipeline and other factors.

Of these methods, the J-lay method is often preferred as being more suitable for large water depths. The J-lay method is also generally employed for a situation in which the quality of the pipeline is very important, such as for a riser, and for a situation in which a substantial plastic deformation of the pipeline is not acceptable. Also, J-lay is generally performed for pipes having thick walls, which render the pipe very rigid and difficult to wind onto a reel . Typically, a pipeline is laid by reeling when a substantial length of pipeline is to be laid on the seabed. In the reeling method a certain amount of plastic deformation is accepted.

In order to be able to alternate between the reeling method and the J-lay method in dependence on the circumstances, pipeline-laying vessels have been developed which are equipped with both a J-lay system and a reeling system. Such a vessel is for instance known from US 6 371 694. The vessel of US 6 371 694 has two reels on board which are mounted for rotation about a horizontal axis. The two reels are referred to as ^λ vertical reels' , because the width of the reels is relatively small in comparison with their height.

The vessel of US 6 371 694 comprises a launching ramp which is used both in the J-lay method and in the reeling method.

In operation, the pipeline may be unreeled from either of the reels. When one reel is empty, a reeling operation may be continued by switching to the other reel.

A problem associated with the vessel of US 6 371 694 occurs when both the reels are empty. Then, the empty reels must each be reloaded with a new pipeline section before the reeling operation can

be continued. This reloading is to be performed at the quayside by- winding a pipeline section onto the reels. For this reloading operation, the vessel must leave a location where the pipeline is laid and sail back to shore. The journey to shore, the winding of the pipeline onto the reels and the return journey to the laying location require a considerable amount of time (also called downtime) , which slows down the pipeline laying operation.

There is a general need to reduce the downtime of pipeline laying vessels caused by reloading of a reel with a new pipeline section.

A further problem associated with the vessel of US 6 371 694 is that the launching ramp needs to be movable with respect to the vessel. For the reeling operation, it is necessary that the launching ramp be substantially aligned with the reel, which is in use. The pipeline from both reels is unreeled via the same launching ramp.

Because the position of the reels is fixed relative to the hull, the launching ramp itself must be moved relative to the hull in order to substantially align it with one of the two reels. Pivoting the launching ramp about a vertical axis relative to the hull effects this movement.

The launching ramp however is a large, heavy and complex structure. Mounting the launching ramp pivotably about a vertical axis relative to the hull is very cumbersome. It is preferable to configure the pipeline laying vessel such that the launching ramp does not need to be pivoted relative to the vessel about a vertical axis .

Summary of the invention

It is an object of the present invention to provide a pipeline- laying vessel, which has a substantially reduced downtime between the unwinding of pipeline from two consecutive reels.

It is a further object of the invention to provide a pipeline laying vessel which can lay a substantially longer length of pipeline with the reeling method than known vessels without having to return to shore.

It is another object of the invention to provide a pipeline- laying vessel capable of performing both the J-lay method and the

reeling method, having a shared launching ramp which can ^' be fixed about a vertical axis relative to the hull assembly.

In a first aspect, the invention relates to a pipeline-laying vessel comprising: - a connecting assembly configured for laying a pipeline by connecting consecutive pipe sections to a free end of the pipeline; - a reeling assembly configured for laying a pipeline by unreeling a pipe section from a reel; wherein the connecting assembly and the reeling assembly share at least a part of a support assembly for supporting the pipeline and/or pipe section, wherein the pipeline laying vessel further comprises an active reel position in which a reel is to be positioned during the unreeling of the pipe section from the reel, and wherein the pipeline laying vessel is configured to allow a reel to be moved to the active reel position and to be removed from the active reel position.

With the pipeline-laying vessel according to the invention, an empty reel may be removed from the active reel position and be replaced by a full reel so that the required downtime between the unreeling of two reels is substantially reduced. The exchanging of the reels may be performed at sea, obviating the need for the vessel to return to shore for reloading of the reels .

Because the reels are movable relative to the hull assembly, the support assembly need not rotate about a vertical axis relative to the hull assembly in order to be aligned with a reel in the active reel position.

The connecting assembly and the reeling assembly are capable of laying what is known in the field of the art as a rigid pipeline, e.g. a steel pipeline having a substantial rigidity. Other metals or materials may also be used.

The connecting assembly generally comprises a support assembly for supporting a pipe section in an abutting position with the free end of the pipeline. The support assembly has the form of a launching ramp or tower assembly. The free end of the pipeline is supported on the vessel by a hang-off table. The connecting assembly further typically comprises a welding station for welding pipe sections to the pipeline.

The reeling assembly generally comprises a pulling device for pulling the pipeline section from the reel, an aligner for giving the pipe an universal bending radius and for aligning the pipeline section with the firing line, a straightener for straightening the pipeline, and a support assembly for supporting the pipeline as it is advanced along the firing line on board.

The support assembly may be pivotable relative to the hull assembly about a substantially horizontal axis.

The pipeline-laying vessel may be configured such that the pipeline is advanced along a same trajectory on board the pipeline- laying vessel in the connecting method and in the reeling method. This trajectory is also known as ^firing line' or ^λ lay path' in the field of the art.

In one aspect, the connecting assembly comprises a J-lay assembly configured for connecting pipe sections to the pipeline in a J-lay method. The combination of the J-lay method with the reeling method is found to be very advantageous, because the J-lay method is very advantageous for risers, whereas the reeling method is very suitable for pipelines which are to rest on the seabed. Both types of pipeline may thus be laid with a single vessel.

In one aspect, the invention relates to a pipeline laying vessel comprising a reel coupling configured to allow a reel in the active reel position to be coupled to and uncoupled from the pipeline laying vessel. With the reel coupling, a rapid exchanging of an empty reel with a full reel may be performed in the active reel position.

In a further aspect, the connecting assembly and the reeling assembly share a pipeline advancing device configured for unreeling a pipeline from a reel in the reeling method, wherein said pipeline advancing device is also configured for lowering the pipeline in the J-lay method.

Advantageously, only a single pipeline advancing device needs to be provided. The pipeline advancing device may comprise a moving clamp, one or more pairs of endless tracks or belts, or another device suitable for advancing the pipeline and/or pipe section.

In a further aspect, the pipeline laying vessel comprises at least one inactive reel position for at least temporarily storing a

reel, wherein the pipeline laying vessel is configured to allow a reel to be moved to and removed from the inactive reel position.

This provides the advantage that at least one empty reel may be stored on board, thereby obviating the need for an auxiliary vessel or a return journey to shore each time an empty reel needs to be replaced.

In a further aspect, the pipeline-laying vessel comprises a moving device for moving a reel to and from the active reel position, in particular for moving the reel between the active reel position and the inactive reel position.

Advantageously, a full reel can be positioned in the active reel position by the moving device by moving it from the inactive reel position to the active reel position. A crane is a simple and effective way of moving a reel to and from the active reel position. In a further aspect, the pipeline-laying vessel comprises a guiding device, in particular a track, for guiding a reel to and from the active reel position. This allows the exchanging of the reels with a minimal effort. The reels comprise sliding means or wheels via which the reels can move along the guiding device. In a further aspect, the pipeline-laying vessel comprises a moving device for transferring a reel between the pipeline-laying vessel and an auxiliary vessel. Advantageously, an empty reel can be transferred from the pipeline-laying vessel to the auxiliary vessel and be replaced by a full reel. The transfer may be performed by the same moving device as the moving device used for moving the reel to and/or from the active position to the inactive position. Alternatively, a separate moving device may be provided.

In a further aspect, the reeling assembly is configured for laying a pipeline when the connecting assembly is not in use. A known method exists wherein a reeled pipeline is provided merely as a piggyback pipeline on a pipeline laid with the connecting method . In this known method, the reeling method can not be performed independently from the connecting method. However, in the present invention the reeling assembly is capable of laying a pipeline independent from a pipeline laid with the connecting assembly.

In the known method, the reeling assembly is only capable of reeling pipeline with a diameter which is substantially smaller than the diameter of the pipeline that can be laid with the connecting

assembly. In the present invention, the reeling assembly and the connecting assembly can lay pipeline having the same diameter.

In an aspect of the present invention, the moving device is positioned between the active reel position and the inactive reel position.

In a further aspect, the pipeline laying vessel comprises:

- a pipeline construction location for connecting pipe sections to one another for forming a pipeline section, and

- winding means for winding the formed pipeline section onto a reel, in particular onto a reel which is positioned in the inactive reel position.

Advantageously, an empty reel may be reloaded with new pipeline on board the vessel. After reloading, the full reel may again be used for unreeling. During the reloading of a first reel, a second reel may be used in the reeling method in order to perform the reeling method continuously.

In one aspect, the pipeline laying vessel comprises a plurality of inactive reel positions. This allows a substantial flexibility of the reeling operation. For instance, a substantial number of empty or full reels may be stored on board. Also, in combination with a pipeline construction location a reel may be reloaded during a movement of another reel to or from an inactive position.

The invention further relates to a reel configured for use in a pipeline-laying vessel according to the invention. The reel may comprise a pipeline wound on the reel. The reel may be adapted for being coupled to and from the pipeline-laying vessel in order to allow a swift exchange of the reel when it is empty by a full reel.

The reel may also comprise sliding means or rolling means for moving the reel on board the pipeline-laying vessel. Alternatively, the reel may be equipped with a lift coupling for coupling the reel to the crane, in order to lift the reel to and from the active reel position.

The invention further relates to a method of laying a pipeline, the method comprising: (a) providing a pipeline laying vessel comprising:

- a connecting assembly configured for laying a pipeline by connecting consecutive pipe sections to a free end of a pipeline which is supported by the vessel;

- a reeling assembly configured for laying a pipeline by unreeling a pipe section from a reel; wherein the connecting assembly and the reeling assembly share at least a part of a support assembly for supporting the pipeline and/or pipe section, wherein the pipeline laying vessel further comprises an active reel position in which a reel is to be positioned during the unreeling of the pipe section from the reel, and wherein the pipeline laying vessel is configured to allow a reel to be moved to the active reel position and to be removed from the active reel position; (b) positioning a first reel in the active reel position;

(c) unreeling a pipe section from the first reel, wherein the pipe section is supported by the shared part of the support assembly;

(d) removing the first reel from the active reel position; and (c) positioning a second reel in the active reel position. In a further aspect the present invention relates to a method of loading a reel with pipeline, the method comprising:

- connecting consecutive pipe sections to one another for forming a pipeline; and

- winding said pipeline onto said reel, wherein said reel is adapted to be unreeled by the reeling assembly of the pipeline laying vessel.

The claims and advantages will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts, or parts with the same or similar function.

Brief Description of the Drawings

Fig.l shows a schematic side view of a pipeline laying vessel according to the invention performing the reeling method;

Fig. 2 shows a schematic side view of a pipeline laying vessel according to the invention performing the J-lay method; and

Fig. 3 shows a schematic top view of the pipeline laying vessel according to the invention. With reference to Figures 1 and 2, a pipeline laying vessel 10 according to the invention is shown. The vessel 10 comprises a hull 12, a deck 14, a connecting assembly 16 in the form of a J-lay

assembly, and a reeling assembly 18. The water-line is indicated with reference number 20.

The J-lay assembly 16 and the reeling assembly 18 share a tower assembly 26. The tower assembly 26 extends upwards from the deck 14, and is pivotably connected to the hull 12 about a horizontal axis 28 and adjustable struts 30. The tower assembly 26 is not pivotable about a vertical axis relative to the hull 12. A firing line 24 (or lay path) is defined along which a pipeline 22 is advanced during the laying thereof. A part of the firing line 24 extends through the tower assembly 26.

Turning to Fig. 2, the J-lay assembly 16 comprises a welding station 32 for welding a lower end 33 of a pipe section 35 to a free end 34 of a pipeline 22 suspended from the vessel 10. A pipeline support device in the form of a hang-off clamp 36 supports the free end 34. The hang-off clamp 36 may operate on the pipeline 22 via friction forces. Other means of supporting the pipeline 22 are also possible .

The tower assembly 26 further comprises a pipe section support means 38 configured for supporting a pipe section 35 (shown in Fig. 2) which is to be welded to the free end 34 of the pipeline 22. The pipe section support means 38 can have the form of a friction clamp which is movable along the firing line 24 in the direction of arrow 40.

Other pipe section support means 38 are also possible, such as endless belts (not shown) which operate on the pipeline 22 via friction.

Further, support means 63 which are substantially fixed, for instance rollers, may be provided along the tower assembly 26 for laterally supporting the pipe section 22 at the firing line 24, which support means 63 may also be used in the reeling method.

The J-lay assembly 16 further comprises a pipe storage (not shown) for storing pipe sections 35. The pipe sections 35 may be pre- assembled from a number of shorter pipes, e.g. from four or six pipes, which pre-assembling may be performed on board. The movable clamp 38 on the tower assembly 26 is configured for roughly positioning a pipe section 35 along the firing line 24 in an end-to-end relationship with the pipeline 22 and for handing the pipe section 35 over to the line-up means 61. After the pipe section 35

has been. connected to the pipeline 22, the movable clamp 38 is used for lowering the upper end of the pipe section 35 plus the pipeline 22 to the hang-off clamp 36. The line-up means 61 is a controllable tool for precisely aligning the pipe section 35 with the pipeline 22 prior to welding, by laterally and axially moving the pipe section 35 relative to the pipeline 22 and/or by rotating the pipe section 35 relative to the pipeline 22.

The reeling assembly 18 comprises an active reel position 42 configured for supporting a reel 44. The reel 44 is rotatable about a rotation axis 49. A drive 48 for rotating a reel 44 about the horizontal rotation axis 49 is provided, which drive 48 may be integrated with reel support means 50 for supporting the reel 44. The active reel position 42 is substantially aligned with the firing line 24, when viewed from above. A reel coupling 52 is provided which allows a reel 44 to be coupled to and uncoupled from the vessel 10.

The reeling assembly 18 further comprises an aligner 54 mounted for rotation at an upper end 56 of the tower assembly 26. The reeling assembly 18 further comprises a straightener 60 and a pulling device 38 which are known in the field of the art. Further, support means 63 along the tower assembly may be provided for laterally supporting the pipeline 22 at the firing line 24, which support means 63 may also be part of the J-lay assembly 16.

The active reel position 42 is provided on a reel support module 62 positioned on the vessel 10 and coupled to the vessel via module coupling means 80. The reel support module 62 may be uncoupled and integrally removed from the vessel 10.

As can be seen in Figure 1, a number of components of the reeling assembly 18, i.e. the aligner 54, the straightener 60 and the pulling device 38 are mounted on the tower assembly 26. The J-lay assembly 16 and the reeling assembly 18 share a number of components, i.e. the tower assembly 26 and the support means 63 for supporting the pipeline on the tower assembly 26.

The reeling method and the J-lay method also share a part of the firing line 24 or lay path 24. In operation, there are two modes (or methods) of pipeline laying. In the J-lay mode, which is well known in the field of the art, pipe sections 35 are taken one by one from the pipe section storage and positioned end-to-end with the pipeline 22. The pipe

section is then aligned with the pipeline 22, and welded to the pipeline 22.

Then, the pipeline 22 is lowered by lowering the moving friction clamp 38 relative to the tower assembly 26 until the upper end 34 of the pipeline 22 is in a position in- which it can be supported by the hang-off clamp 36. At the same time, the vessel 10 moves forward in the direction of arrow 64. By successively- connecting pipe sections 35 to the free end 34 of the pipeline 22, the pipeline 22 is laid. In the reeling method, the pipeline 22 is unwound from the reel 44, advanced in the direction of arrow 66 over the aligner 54 and down into the tower assembly 26 along the firing line 24. The pipeline 22 is straightened by the straightener 60, because the pipeline 22 has previously been plastically deformed due to being wound onto the reel 44.

In the reeling mode, the pipeline 22 is lowered by repetitiously lowering the moving friction clamp 38 relative to the tower assembly 26 until the upper end 34 of the pipeline 22 is in a position in which it can be supported by the hang-off clamp 36. At the same time, the vessel 10 moves forward in the direction of arrow 64. When the moving friction clamp 38 is at the hang-off clamp 36, the hang-off clamp 36 is engaged to the pipeline 22 and the moving friction clamp 38 retrieved to its uppermost position. In this position, the moving friction clamp 38 is engaged to the pipeline 22 and the hang-off clamp released. By successively lowering the moving friction clamp 38 over the height of the tower and holding the pipeline 22 in the hang-off friction clamp 36 when the moving friction clamp 38 is retrieved, the pipeline 22 is laid.

When the reel 44 is empty, it will be replaced by a full reel 44. The reel 44 is uncoupled from the reel coupling 52, and removed from the active reel position 42. The empty reel 44 may be removed from the vessel 10, or moved to an inactive reel position on board the vessel 10, as will be discussed with reference to Figure 3.

With reference to Figure 2, the vessel 10 is shown wherein a top section 68 of the tower assembly 24 is removed and replaced by a different top section 68. In this configuration, the vessel 10 is capable of laying pipeline in J-lay mode, wherein the pipe sections 35 which are to be connected to the free end of the pipeline are pre-

assembled from six shorter pipes. The pipe sections 35 may have a length of 73 meter. Other lengths are also possible. With reference to Figure 1, the vessel 10 is shown wherein a top section 68 of the tower assembly 24 is configured for reeling. In this configuration, the vessel 10 is capable of laying pipeline in J- lay mode, wherein the pipe sections 35 which are to be connected to the free end of the pipeline are pre-assembled from four shorter pipes. The pipe sections 35 may have a length of 49 meter. Other lengths are also possible. With reference to Figure 3, the pipeline laying vessel 10 is shown, comprising an active reel position 42 and two inactive reel positions 43.

It is also possible to provide a single inactive reel position 43, or more than two inactive/storage reel positions 43. In an alternative embodiment, no inactive reel positions 43 are provided. The tower assembly 26 is positioned at a side 46 of the vessel 10. A crane 70 having a working range 72 is provided on the vessel 10 for moving a reel 44 from the active reel position 42 to the inactive reel position 43 and back. The working range 72 overlaps the active and inactive reel positions 42, 43. Instead of a crane 70, other means of moving the reels 42 may be provided, such as a track (not shown) extending between the active reel position 42 and the inactive reel positions 43, on which track a reel 44 can roll or slide.

The vessel 10 further comprises a pipe section construction ramp 74, comprising two assembly lines 76. Each assembly line 76 comprises a number of working stations 78, which depending on the type of pipeline to be welded, are configured for welding, weld inspection or coating.. The assembly lines are used for manufacturing a pipeline from respective pipe sections. Further a tensioning device 84 is provided at each assembly line 76 configured for giving back- tension when winding an assembled pipeline section 22 onto a reel 44.

Drive means 48 are provided for rotating each reel 44 in the inactive position 43 about a rotation axis 85 as the pipeline 22 is wound onto the reel 44. In operation, one inactive reel position 43 may be kept empty so that a reel 44 in the active reel position 42 can be moved by the crane 70 to that empty inactive reel position 43. The inactive reel positions 43 thus may have the function of storage of a full reel 44,

storage of an empty reel 44 or for reloading an empty reel with a new pipeline 22. An inactive reel position 43 may be selected and a reel 44 may be moved from the active reel position 42 to a selected inactive reel position 43. Different methods of providing a full reel 44 on board the vessel 10 are possible. One way is to assemble a pipeline section 22 on board an auxiliary vessel, and to wind the pipeline section onto the reel 44 on board the auxiliary vessel. Then, the full reel 44 can be transferred to the pipeline laying vessel 10 from the auxiliary vessel. Another way is to assemble a pipeline section on shore, and to wind the pipeline section onto a reel 44 on shore. When the vessel 10 is positioned at the quayside, the full reel 44 can be transferred to the vessel. Alternatively, the full reel may be transferred from the shore to the vessel 10 by an auxiliary vessel. Other possibilities also exist.

The present combination of a reeling method and a connecting method is disclosed with respect to the J-lay method, but may also be embodied as a combination of reeling and S-lay or a combination of reeling and G-lay. It will be obvious to a person skilled in the art that numerous other changes in the details and the arrangement of the parts may be varied over considerable range without departing from the spirit of the invention and the scope of the claims.