WO1996036528A1

WO1996036528A1 - Device for transferring a fluid

Info

Publication number: WO1996036528A1
Application number: PCT/NO1996/000121
Authority: WO
Inventors: Kristian Haslum
Original assignee: Marotec A/S
Priority date: 1995-05-16
Filing date: 1996-05-20
Publication date: 1996-11-21
Also published as: AU5781996A; NO303533B1; NO951924L; NO951924D0

Abstract

In an assembly for transferring a fluid, comprising a fluid carrying pipeline (31) from a point in a water mass (22) up towards the surface (21) of the water mass, where the pipeline is attached to a floating body (25) which is moored to the bed (23) of the sea mass with an elongate mooring member (26), the fluid carrying pipeline (31) is conducted in a spiral around the mooring member. The pipeline (31) may extend upwards around the mooring member (26) with varying pitch (33, 34, 35).

Description

DEVICE FOR TRANSFERRING A FLUID

The invention relates to an assembly for transferring a fluid, comprising a fluid carrying pipeline which runs in a spiral from a point in a water mass up towards the surface of the water mass, where the pipeline is attached to a floating body which is moored to the bed of the water mass by means of an elongate member.

The invention has been developed in connection with the need during the production of oil/gas at sea to be able to transfer oil and/or gas, for example, from a floating production plant to a surface vessel.

In connection with oil/gas production at sea, it is known to conduct a riser, rigid or flexible as such, from the seabed to a moored ship which can turn windwards.

A known solution in this connection is that the ship has a through-going well wherein there is located a rotatable mooring plug which is connected to the ship by means of a rotary bearing. The mooring plug is attached to anchor cables which extend to the seabed, and is also attached to one or more risers. The mooring plug is thus in principle anchored with a fixed orientation relative to the seabed. However, the ship can turn about the mooring plug, so that it can assume an optimal direction relative to the weather. The mooring forces are transferred between the mooring plug and the ship via the rotary bearing. The flow of oil/gas can be transferred between ship and mooring plug via a vertical pipe swivel or devices and pipelines of different design which give from a half revolution to a few revolutions turning freedom in both directions, for example as taught in Norwegian Patent No. 162 011. If a vertical pipe swivel is used, the maximum number of revolutions will be indefinite.

Solutions are also known where the mooring plug is fixedly secured to the ship and the anchor cables are attached to a ring or similar which is attached to the mooring plug via a rotary bearing. In a construction of this kind, the riser is attached to the mooring plug by means of a swivel coupling or a swivel link. A solution of this kind is used both during so-called offshore loading and in connection with floating production plants.

The above-mentioned solutions are relatively complex and costly. Thus, there is a real need for simpler and cheaper solutions, inter alia on smaller production fields. A particular objective of the invention is to provide the possibility of eliminating the rotary bearing in connection with a mooring plug, whilst retaining the strongly preferred possibility of the ship being able to lie against the weather.

The said mooring plug is in practice designed in the form of a floating body, i.e., in the form of a buoy. It is an objective of the invention to allow a floating body of this kind a rotational movement in the horizontal plane.

More specifically, it is an objective of the invention to make possible attachment to a vessel without a swivel connection, so that the vessel can lie against the weather.

It is also an objective of the invention to provide a combined loading/unloading and mooring assembly, where loading/unloading of, for example, oil can take place whilst the vessel is anchored.

These objectives are achieved according to the invention by means of an assembly for transferring a fluid, comprising a fluid carrying pipeline which runs in a spiral from a point in a water mass up towards the surface of the water mass, where the pipeline is attached to a floating body which is moored to the bed of the water mass by means of an elongate member, that which characterises the assembly according to the invention being that the fluid carrying pipeline passes in a spiral around the elongate mooring member.

It is especially expedient if the pipeline can extend upwards around the mooring member with varying pitch. This provides the possibility of adjusting the pitch to the local needs along the mooring member.

Thus, according to the invention it is advantageous if the pipeline can extend upwards around the mooring member, a first length having a first pitch, a second length having a second pitch which is greater than the said first pitch and with a third subsequent length having a third pitch which is less than the said second pitch.

With an embodiment of this kind, it is possible to take into account the motional needs which exist at the point where the pipeline begins to run around the elongate mooring member, and at the point where the pipeline leaves the mooring member and passes into the floating body, whilst in the second or intermediate length a greater pitch can be used because the motional needs there are not as great, and it is then also possible to save pipeline length.

According to the invention, the mooring can to advantage comprise slack anchor cables, preferably anchor chains, which meet and are attached to the elongate mooring member.

A rigid member, i.e., a tension stay, may be used as mooring member, but the mooring member may also to advantage be a flexible member such as a line, a wire or a chain, the last-mentioned advantageously having floating bodies to make the chain lighter.

It is especially advantageous if the pipeline is connected to the elongate mooring member with the aid of connecting means extending between the pipelines and the mooring member, especially in the form of rungs, which in the horizontal projection will look like spokes in a hub sprocket.

In an especially preferred embodiment, where a combined loading/unloading and mooring system is realised, the elongate mooring member can to advantage be attached to a mooring plug designed for positioning in a docking bay in or attached to a vessel.

A mooring and fluid transfer system of this kind will enable the vessel to assume positions independent of the weather, without any need for the known rotary bearing and the known swivel coupling.

The mooring plug can in a known way be in the form of a truncated cone. It is constructed having a passage for the pipeline and may, for example, be in the form of a spatial tubular structure having buoyancy means. In an embodiment of this kind the pipeline will extend in a spiral up through the mooring plug. An embodiment that is considered to be especially advantageous is one wherein a preferably flexible mooring member is used, and this is surrounded by a tubular structure comprising an upper portion attached to the floating body and a lower portion attached to slack anchor cables.

The invention will now be described in more detail with reference to the drawings, wherein:

Fig. 1 illustrates an assembly according to the invention, with the floating buoy in an inoperative position; Fig. 2 illustrates the assembly with the floating body in an operative position in the sea surface; Fig. 3 shows a modified embodiment wherein a rigid mooring member is used;

Fig. 4 shows yet another modified embodiment wherein an articulated tower located on the seabed in used;

Fig. 5 shows a modified embodiment with an elongate mooring member which is attached to slack anchor cables on the seabed; Fig. 6 shows an embodiment of an assembly wherein the pipeline has variable pitch around the mooring member as it passes up through the water mass;

Fig. 7 shows a combined loading/unloading and mooring arrangement according to the invention; Fig. 8 shows the arrangement according to Fig. 7 in a possible position of use, and the same applies to Fig. 9;

Fig. 10 shows the arrangement in Figs. 7, 8 and 9 in an inoperative position; and

Fig. 11 illustrates an arrangement with more than one pipeline.

Fig. 1 illustrates a water mass 1 whose surface is designated 2 and whose bed is designated 3. A floating body 4 is moored to the seabed 3 by means of an elongate flexible mooring member 5. This elongate mooring member 5 may, for example, be a wire or a chain. A fluid carrying pipeline 6 passes from the seabed in an upward direction in the water mass in a spiral around the mooring member 5 and runs up to the floating body 4. The floating body 4 is in an inoperative position, i.e., it is submerged in the water mass so that it is not disturbed by and does not disturb shipping traffic. It shall in this connection be noted that "inoperative" here must not preclude the possibility that the floating body can be operative in the position shown in Fig. 1, but normally it will be preferred to have the floating body in surface position when the fluid transfer is to take place, a position which is shown in Fig. 2.

In a known way, the pipeline 6 is conducted in an S-shape and is attached to buoyancy means 7. As mentioned, the pipeline 6 extends upwards in a spiral in the water mass 1 , around the mooring member 5. The term "spiral" is here intended to convey a twining and turning form, which may follow a helical line or deviate from the ideal helical line, both with a view to pitch and radius. In Fig. 2, as already mentioned, the floating body 4 has been put in a position in the water surface 2 by deballasting. The mooring member is now relatively straight and taut. It is not shown in detail, but the floating body 4 in Figs. 1 and 2, and also in the subsequent figures, is intended to be made in the form of a type of cage body with buoyancy potential, so that the pipeline can as shown extend in coils up through the floating body and preferably open horizontally uppermost in the floating body.

It will be understood that with the illustrated and described arrangement the floating body 4 will be able to move relatively freely, the mooring and the pipeline being capable of withstanding the relative movements the floating body makes in relation to the seabed.

The embodiment in Fig. 3 is in principle constructed in the same way as the embodiment in Figs. 1 and 2, with the difference that here a rigid elongate mooring member 5' is used between the floating body 4 and the seabed 3. The mooring member 5', thus acting as a tension stay, is swivel mounted at 8.

The embodiment in Fig. 4 also uses the same inventive principle, with the difference that an articulated tower 9 is located on the seabed 3, which tower uppermost at 10 is attached to the elongate mooring member 5". This mooring member 5" may be a flexible member or a rigid member. If it is in the form of a rigid member, the connection 10 is made in the form of a swivel link in the same way as in Fig. 3.

The embodiment in Fig. 5 is also constructed in a similar manner as the assemblies described above, with the difference that the elongate mooring member 5'" here is connected to slack anchor cables 11, 12 which extend to respective anchors 13, 14 on the seabed 3. The anchor cables 11 and 12, there are preferably more than two anchor cables, meet at point 15 where the mooring member 5'" is attached. The mooring member 5'" may be a flexible member or a rigid member. If it is constructed in the form of a rigid member the link 15 is expediently made in the form of a swivel link.

The embodiment in Fig. 6 is as in Fig. 2 with the alteration that the pipeline 6 is conducted in coils around the mooring member with varying pitch and that the pipeline in this case runs out horizontally at the bottom of the spiral, so that the S-shape is not used here. Thus, it can be seen that the pipeline 6 passes in around the mooring member 5 in a first length of a certain pitch. After this first length, there follows a second length of a second pitch which is markedly greater than the pitch of the first length. The pipeline 6 ends by continuing up towards the floating body 4 in a third length of a third pitch which is less than the pitch of the middle or second length. With an embodiment of this kind, the pipeline in intermediate length is run up straighter so that pipeline length is saved.

Figs. 7 to 10 show an especially preferred embodiment of the invention. In Fig. 7 a vessel 20 is shown floating on the surface 21 of a water mass 22, whose bed is designated 23.

The ship 20 has a through-going well 24 wherein there is secured a mooring plug 25. The mooring plug is secured in the well 24 in a rotation-prevented manner. From the underside of the mooring plug 25 a flexible mooring member runs down in the form of a wire 26, which extends down to a coupling loop 27 from where anchor chains 28, 29 pass out to a respective anchor 30. In Fig. 7 only two anchor chains and two anchors are shown, but of course the number of anchor chains will as a rule be greater than two.

It will be understood that in a simpler embodiment the bed anchoring system in Fig. 7 could be modified so that there is only one anchoring point, for example in the form of a submerged anchor or a pile as, for example, is assumed in Figs. 1 and 2.

The mooring plug 25 is designed as a buoyant body or floating body, and in an inoperative position it can be detached from the vessel 20 and anchored in a submerged position as shown in Fig. 10. This part of buoy technique is well-known to experts in the field.

To be able to transfer oil and/or gas from a non-illustrated production site to a vessel 20 there is provided a flexible pipeline 31 which extends from the production site along the seabed 23, and with the aid of buoyancy means 32 is held in a floating S-shape in the water mass 22. This pipeline 31 passes from the floating means 32 in towards mooring member 26 and is wound around this upwards in the direction of the mooring plug 25. In the illustrated embodiment, the pipeline 31 first runs in a spiral of small pitch 33 around the lower portion of the mooring member 26, and then continues across the mid- portion of the mooring member at a steeper pitch 34, and then passes into a portion of smaller pitch 35 around the upper portion of the mooring member 26, in order then to continue as a rigid or flexible pipe through the mooring plug 25. The mooring plug 25 may be designed to have a passage for guiding the pipeline, or it may for example be designed as a cage body, with buoyancy means, the pipeline then passing through the cage body in a spiral as is indicated schematically in the figures.

Under the stress of wind, current or waves, the vessel 20 will move, for example as shown in Figs. 8 and 9. In the upper region, the spiral form 35 of the pipeline 31 will ensure that the pipeline can adapt to the angular deflection of the mooring member 26. In the lower region, the S-shape 32 of the pipeline will ensure that the pipeline can adapt to the angular deflection and displacement of the mooring member.

To enable the pipeline 31 to remain in the illustrated and described form around the mooring member, some structural components will be necessary to guide the pipeline spiral. Two tubular bodies 36 and 37 are provided on the outside of the mooring member 26. These tubular bodies form attachments for radial stays 38, 39, 40 and 41 or spokes which form a part of the suspension of the pipeline coil. The uppermost tubular body 37 is attached to the upper end of the mooring member, i.e., the wire 26. This upper tubular body 37 will therefore rotate with the vessel 20 when it turns. The lowermost tubular body 36 is secured to the coupling loop or shackle 27 which connects the mooring wire 26 to the anchor chains 28, 29. This tubular body 36 will therefore not rotate about its own axis when the vessel 20 turns with the weather. Rigid stays or rigid spokes 38, 39, 40, 41 are secured to each of the tubular bodies 36,37 for the support of the pipeline coil. The uppermost rigid stay 41 ensures that the upper portion of the pipeline coil rotates with the vessel. A lowermost, rigid stay 38 ensures that the pipeline does not develop any significant changes in direction in the horizontal plane relative to the fixed pipe 31 located along the seabed.

The rotation is absorbed at the mid-portion in that reduced pitch and radius compensate for the increase in turning. The mid-portion of the pipe may be centralised relative to the mooring member by means of two or more resilient spokes 42, 43.

The flexible buoyancy means, which are indicated purely schematically at 32, cause the pipeline at this point to have a slack catenary S-shape which is highly suited to cope with the change in shape required when the vessel 20 is moved on the surface 21. The associated change of angle between the vessel and the mooring member at the upper end is absorbed by the closed spiral form that the pipeline has at that point. When the ship 20 turns, the mooring member 26 and the portion of the pipeline spiral which is between the rigid stays 39 and 40 will absorb the rotation. Figs. 1 to 10 show one fluid carrying pipeline only, but of course more are conceivable which then extend upwards in the water mass, grouped in a bundle, or individually.

An example of an arrangement with more than one pipeline is shown in Fig. 11 , where two fluid carrying pipelines run in turns around the mooring member.

The invention can be implemented both with real flexible pipelines and also with so- called rigid pipelines or pipes. A rigid pipeline may, for example, to advantage be of titanium, a highly suitable material in this connection because of the favourable modulus of elasticity .

Claims

P a t e n t c l a i m s

1.

An assembly for transferring a fluid, comprising a fluid carrying pipeline which passes in a spiral from a point in a water mass and up towards the surface of the water mass, where the pipeline is attached to a floating body which is moored to the bed of the sea mass with an elongate mooring member, characterised in that the fluid carrying pipeline passes in a spiral around the mooring member.

2.

An assembly as disclosed in Claim 1 , characterised in that the pipeline extends upwards around the mooring member with varying pitch.

3.

An assembly as disclosed in Claim 2, characterised in that the pipeline extends upwards around the mooring member in a first length at a first pitch, a second length at a second pitch, which is greater than first said pitch, and in a third subsequent length at a third pitch which is less than said second pitch.

4. An assembly according to one of the preceding claims, characterised in that the mooring consists of slack anchor cables which meet and are connected to the elongate mooring member.

5.

An assembly according to one of the preceding claims, characterised in that the mooring member is a rigid member.

6.

An assembly according to one of preceding claims 1-4, characterised in that the mooring member is a flexible member.

7.

An assembly according to one of the preceding claims, characterised in that the pipeline is connected to the elongate mooring member.

8.

An assembly according to one of the preceding claims, characterised in that the elongate mooring member is attached to a mooring plug designed to be secured in a docking bay in or attached to a vessel.

9.

An assembly according to Claim 8, characterised in that the pipeline extends in a spiral upwards through the mooring plug.

10.

An assembly according to one of the preceding claims, characterised in that the mooring member is surrounded by a tubular structure comprising an upper portion attached to the floating body, a lower portion attached to the anchor and an intermediate portion, free relative to the upper and lower portion, and which is connected to the mooring member.

11.

An assembly according to one of the preceding claims, characterised in that a plurality of single pipelines or parallel pipelines run around the elongate mooring member.

12.

An assembly according to one of the preceding claims, characterised in that the pipeline or pipelines from the seabed follow one of the slack anchor cables in order then to adopt a spiral form around the mooring member.

13.

An assembly according to one of the preceding claims, characterised in that the pipeline or pipelines from the seabed run directly into a spiral form around the mooring member.