AU739843B2

AU739843B2 - Device for connecting an offloading buoy and an offshore petroleum products production installation

Info

Publication number: AU739843B2
Application number: AU86119/98A
Authority: AU
Inventors: Daniel Didier Paul De La Cruz; Jean-Christophe Le Gal; Jean Francois Marie Pepin-Lehalleur; Francois Eugene Paul Thiebaud
Original assignee: STOLT COMEX SEAWAY
Current assignee: STOLT COMEX SEAWAY
Priority date: 1997-09-26
Filing date: 1998-09-22
Publication date: 2001-10-18
Anticipated expiration: 2018-09-22
Also published as: FR2768993A1; FR2768993B1; EA199800763A2; OA10886A; EA001337B1; EA199800763A3; AU8611998A; BR9803365A

Description

I "W

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: Name of Applicant: Doris Engineering, Stolt Comex Seaway Actual Inventor(s): SJean-Christophe Le Gal Jean Francois Marie Pepin-Lehalleur Francois Eugene Paul Thiebaud Daniel Didier Paul De La Cruz Address for Service: PHILLIPS ORMONDE FITZPATRICK J. Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: DEVICE FOR CONNECTING AN OFFLOADING BUOY AND AN OFFSHORE PETROLEUM PRODUCTS PRODUCTION INSTALLATION Our Ref 551401 POF Code: 1149/80072,346329 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): 0 1 p~~Oi0s8 Device for connecting an offloading buoy and an offshore petroleum products production installation The present invention relates to a device for connecting an offloading buoy and an offshore petroleum products production installation equipped with its own mooring means, the device comprising at least one underwater line for transferring said products between said installation and said buoy.

For offloading petroleum products stored on production structures such as an offshore platform or an FPSO (Floating, Production, Storage and Offloading) vessel, i.e. a vessel equipped with means for production, storage and 10 offloading of said products, offloading buoys are currently used such as those known as SPM (Single Point Mooring) and CALM (Catenary Anchor Leg Mooring) buoys. Conventionally such buoys are permanently moored by means of catenary anchor lines at a distance from the FPSO vessel or the platform with **which they communicate via petroleum product transfer lines that are also 15 permanently installed for offloading the stored products, the transfer lines ordinarily running on the sea floor between the vessel or the platform and the buoy. The mooring lines and the transfer lines employed make this solution costly or even prohibitively expensive in deep water.

.i :At such depths, where the water is very cold, the cost of the transfer .i 20 lines is further increased by the necessity to insulate them thermally using costly materials and to increase the lines thickness in order to resist the high pressure of the water.

In another solution the transfer line is supported by floating arches maintained at a substantially constant depth by tension lines anchored to the sea floor. Anchoring the arches makes this solution costly, especially in deep water, with depths of a few hundred metres or more, for example.

The aim of the present invention is to provide a device for connecting an offloading buoy and an offshore petroleum product production installation which satisfies the security conditions that apply in particular when the device is installed in a severe environment but which is nevertheless economic to manufacture and install, especially in deep water.

The above aims of the invention, and others that will become apparent on reading the following description, are achieved by a connecting device of the type described in the preamble to this description which is noteworthy in that it includes a substantially horizontal tension line for coupling excursions of the petroleum product production installation and the buoy to limit the amplitude of relative displacement of said installation and said buoy.

By limiting the amplitude of relative displacement in this way a sufficient safe distance is maintained between the buoy and the installation to be offloaded, a safe distance in the order of one nautical mile, for example.

10 In accordance with the invention, the tension line supports the petroleum product transfer line or lines. The tension line supporting said transfer line are below the surface, at a predetermined depth. By maintaining the tension line at a depth of 30 m, for example, surface vessels can sail freely obetween the installation and the buoy. As a result such transfer lines have a total length that is much less than the length of a line running along the sea floor, especially in deep water. The connecting device of the invention is then particularly economic.

Other features and advantages of the present invention will become apparent on reading the following description and from the accompanying 20 drawings in which: -figure 1 is a general elevation view of the connecting device of the invention, figures 2 and 3 are respectively elevation and plan views of part of the device of the invention in the proximity of the offloading buoy, and -figure 4 is a cross-section view of a connecting member that can be used in the device of the invention.

Figure 1 of the accompanying drawing shows that the device of the invention is designed to connect an offshore petroleum product production and storage installation 1 such as a floating platform or an FPSO vessel as defined in the preamble to the present description to a buoy 2 for offloading petroleum 7 products treated and stored by said offshore installation 1. The body of the buoy is of one of the types mentioned in the preamble, for example.

Lines 3, conventionally catenary lines, anchored to the sea floor 4 moor the installation 1. At least two lines 51, 52 contribute to the mooring of the buoy 2 (see figure 3).

In accordance with the present invention the device includes means 6 for coupling excursions of the floating installation 1 and of the buoy 2, taking the form of a tension line between the installation 1 and the mooring lines 51, 52 of the buoy 2, and for supporting one or more transfer lines 71, 72 for petroleum products shipped from the installation 1 to the offloading buoy 2 from which :i 10 they are then transferred to a tanker (not shown) for shipping said products moored to the buoy.

In a preferred embodiment of the invention the tension line comprises a tube 6, possibly a compartmented tube, full of air or some other fluid lighter than water, so as to have positive buoyancy distributed all along the tube, the 15 floating tube 6 being adapted to support the transfer lines (71, 72) by means of spacers 9 i The distributed buoyancy of the tube improves the dynamic behaviour of the system comprising the tube and the lines 71, 72 that it supports. The spacers 2 9 i (see figure distributed along the floating tube 6, have holes 7'1, 7'2 .i 20 through which the tube 6 and the transfer lines 71, 72 respectively pass to group them into a bundle running below the surface at a predetermined depth, as shown in figure 1. This depth is typically about 30 m or more, to enable very large surface vessels to sail over the bundle 71, 72). Thus, advantageously, the maritime traffic is not impeded in the area around the installation 1.

As shown in figures 2 and 3, the end of the floating tube 6 near the buoy 2 is connected to the mooring lines 51, 52 of the buoy by at least two tension lines 81, 82 the other ends 101, 102 of which are fixed to the mooring lines 51, 52 of the buoy. A substantially horizontal spreader bar 11 perpendicular to the tube 6 is installed between the ends 101, 102. Between these ends the lines 51 or 52 (or other lines consisting of cables and chains in a different embodiment) ascend to the buoy 2 where the are fixed to points 4 disposed substantially in a vertical plane P passing through the vertical axis X of the buoy 2. This minimises horizontal forces transmitted to the buoy 2 by the lines 51, 52.

The other end of the tube 6 is connected to the installation 1 via a rigid body 15 fixed to the installation to transmit tension forces from the tube 6 to the mooring lines 3. The buoyancy of the tube 6 and the tension applied to it when it is installed are adjusted to support the transfer lines 7 1, 72 and to assure the overall stability of the device under all operating conditions.

Flexible lines 121, 122 connect compliantly the respective transfer lines 10 7 1, 7 2 to the buoy 2. Similar lines 131, 13 2 connect the other ends of the lines 71, 72 to the installation 1.

According to another embodiment of the device of the invention, where the additional buoyancy provided by the tube 6 is not required, the coupling means can comprise a tension cable between the installation 1 and the 15 offloading buoy 2, this cable being substituted for the tube 6 shown in figure 4.

The cable then supports the transfer lines 71, 72 by appropriate means (similar to the spacers 9i).

The device described above connects petroleum fluid transfer lines directly from the production installation to the offloading buoy along an arc with .i 20 a small deflection. This is a highly economic solution, especially in deep water, compared to that consisting in having the lines running along the sea floor. It is also more economic than the solution in which the transfer lines run along floating arches requiring complex and bulky anchorages on the sea floor.

According to one important feature of the present invention the means 6 supporting the lines 71, 72 ensure the coupling of displacements of the installation 1 and of the buoy 2. Thus an excursion of the installation 1 in any direction, due to winds or currents, for example, leads to an excursion of the buoy of substantially the same amplitude. The mooring lines 3, on the one hand, and 51, 52 on the other hand, return the installation and the buoy to their respective equilibrium positions. The distance between the buoy and the installation 1 is therefore maintained at a substantially constant value, dependent on the length of the coupling means, which is highly favourable to the safety of the floating units and ships sailing near them.

The means 6 (tube or cable) also serves as a mooring line for the buoy 2.

A buoy of this kind is conventionally anchored by means of three mooring lines or groups of mooring lines distributed circumferentially around them. Figure 3 shows that the tube or cable 6 lies in a plane of symmetry of the mooring lines 51, 52 of the buoy 2 to serve as a third mooring line of the buoy. This reduces the cost of the anchor system for the buoy.

A safety cable 14 can be provided in the bundle 10 71 72) to support said bundle in the event of rupture of the tube or cable 6 (see figure 4).

It is now apparent that, by virtue of the coupling procured by the means 6, the invention achieves the stated safety and economy objectives for a connecting device to be installed in deep water.

15 Of course, the invention is not limited to the embodiment described and shown which has been given by way of example only. For example the •invention is not limited to connecting a production and storage installation and an offloading buoy. The installation could have no storage means, the transfer lines then operating permanently. Similarly, the invention is not limited to 20 connecting an installation of the above kind to an offloading buoy in the strict sense of the term, an FSO (Floating, Storage, Offloading) vessel possibly taking the place of the buoy of the device as described. Likewise, the invention is not limited to the use of spacers for assembling the tube or cable 6 and the transfer lines into a bundle, the skilled person being free to choose any other type of connecting member.

Claims

1. A device for connecting an offloading buoy and an offshore petroleum products production installation equipped with mooring means, including at least one underwater line for transferring said petroleum products between said installation and said buoy and a substantially horizontal tension line for coupling excursions of the installation and the buoy to limit the amplitude of relative displacement of said installation and said buoy.

2. A device according to claim 1 wherein said tension line supports the petroleum product transfer line at a predetermined depth below the surface. •o A device according to claim 2 wherein said tension line is made up of a cable. 5 4. A device according to claim 2 wherein said tension line has positive buoyancy to support said transfer line.

5. A device according to claim 4 wherein said positive buoyancy of said tension line is distributed along the entire length of said transfer line. O.

6. A device according to claim 5 wherein said distributed buoyancy tension line is in the form of a floating tube.

7. A device according to any one of claims 1 to 6 wherein said tension line constitutes a mooring line of the buoy.

8. A device according to any one of claims 2 to 7 including distributed connecting members for grouping said tension line and said transfer line into a bundle.

9. A device according to any one of claims 2 to 8 wherein the end of the tension line in the proximity of the buoy is connected to at least two mooring lines of the buoy by at least two other tension lines. XALvioleo delete6119-98.doc kFN X'lltN 7 A device according to claim 9 including a spreader bar installed between said other tension lines connecting the tension line to the mooring lines of the buoy, said bar being suspended from the buoy in a substantially vertical plane passing through the vertical axis of the buoy.

11. A device according to any one of claims 2 to 10 including flexible lines for connecting the ends of the transfer line beyond the length of said transfer line supported by said tension line to the offshore installation, on the one hand, and to the buoy, on the other hand.

12. A device according to any one of claims 8 to 11 wherein said bundle includes a safety cable for supporting the transfer line.

13. A device for connecting an offloading buoy and an offshore petroleum product production installation substantially as herein before described with reference to the illustrations. DATED: 8 September 2000 PHILLIPS ORMONDE FITZPATRICK 20 Attorneys for: DORIS ENGINEERING AND STOLT COMEX SEAWAY 00 W:tona'BFRSpeci861 19-98.doc