Twin-hull offshore structure comprising an interconnecting central deck

Abstract

A floating hydrocarbon processing/storage structure with a first and second assembly, each including a hull having side walls, one or more storage tanks and a deck structure, a connection structure interconnecting the hulls, processing equipment situated on the deck structures, at least one riser connected to a subsea hydrocarbon well and to the processing equipment and/or storage tanks, with a mooring system connecting the processing/storage structure to the sea bed, each hull including a hull deck structure bridging the side walls, the connection structure including a central deck extending at or near the height of the hull deck structures along at least 70% of the length of the hulls, the central deck supporting at least one of: risers vertically extending from the central deck between the hulls to the sea bed, fluid ducts horizontally supported on the central deck, and at least one drilling/work-over rig or crane.

Claims

1. A floating hydrocarbon processing and storage structure comprising: a first assembly and a second assembly each comprising a hull having spaced-apart side walls, a main hull deck structure bridging the side walls and having a width corresponding with a width of each of the hulls, and one or more storage tanks accommodated therein; an interconnection structure interconnecting the first and second hulls and comprising a central deck extending at or near a height of the main hull deck structures along at least 70% of a length of the hulls, the central deck having a width corresponding with a distance between the hulls, the central deck supporting one or more of the following: a plurality of vertically-extending risers vertically extending from the central deck between the hulls to the sea bed, along a length of at least one third of the length of the central deck, a plurality of fluid ducts horizontally supported on the central deck along at least one third of the length of the central deck, and at least one drilling or work-over rig or crane; processing equipment situated on the hull deck structures; at least one hydrocarbon riser extending from the processing equipment or from the storage tanks of the processing and storage structure to a subsea hydrocarbon well; and a mooring system connecting the hydrocarbon processing and storage structure to the sea bed, wherein the central deck supports one or more of a plurality of horizontally-supported risers and pipe elements horizontally supported on the central deck along at least one third of the length of the central deck, and the plurality of vertically-supporting risers vertically extending from the central deck between the hulls to the sea bed, and the processing and storage structure further comprises a track along an outer side of each hull, movable supports displaceable along each track, and a lifting member extending between the supports and being displaceable over a central area, for lifting of one or more of the risers and the pipe elements.

2. The floating hydrocarbon processing and storage structure according to claim 1, further comprising: between the hulls, an intermediate bottom hull part, a bow hull part, an aft hull part, and at least one fluid storage tank comprised within a space between the two hulls underlying the central deck.

3. The floating hydrocarbon processing and storage structure according to claim 1, wherein the central deck has a width between 0.2 and 0.5 of the width of the hulls.

4. The floating hydrocarbon processing and storage structure according to claim 1, wherein at least one of the hulls is provided along an outer wall thereof with an outboard riser supporting structure, supporting the plurality of risers.

5. The floating hydrocarbon processing and storage structure according to claim 1, wherein the plurality of vertically-extending risers vertically extends from the central deck between the hulls to the sea bed, along half of the length of the central deck.

6. The floating hydrocarbon processing and storage structure according to claim 1, wherein the plurality of fluid ducts is horizontally supported on the central deck along half of the length of the central deck.

7. The floating hydrocarbon processing and storage structure according to claim 1, wherein the mooring system comprises a turret carrying the risers, and connected to mooring lines that are moored to the sea bed, and the interconnection structure comprising a bow deck structure rotatably connected to the turret and connected to the hull deck structures and to the central deck at or near the height of the hull deck structures.

8. The floating hydrocarbon processing and storage structure according to claim 7, wherein the bow deck structure is connected to the hull deck structures along a combined width of the first and second hulls and the central deck.

9. The floating hydrocarbon processing and storage structure according to claim 1, further comprising a bow structure extending from the bow deck structure to below the water line, and interconnecting with outer side walls of the hulls to form a substantially closed bow.

10. A method of constructing a floating hydrocarbon processing and storage structure comprising: providing a first assembly and a second assembly each comprising a hull having spaced-apart side walls, a main hull deck structure bridging the side walls and having a width corresponding with a width of each of the hulls, and one or more storage tanks accommodated therein; interconnecting the first and second assemblies via an interconnection structure that comprises a central deck extending at or near a height of the main hull deck structures along a length of at least 70% of a length of the hulls; providing a bow module having a turret configured to carry a plurality of risers, connectors for mooring lines that are configured to be moored to the sea bed, and a bow deck structure rotatably connected to the turret; and connecting the bow module to the main hull deck structures and to the central deck at or near the height of the main hull deck structures and the central deck, wherein the central deck supports one or more of a plurality of horizontally-supported risers and pipe elements horizontally supported on the central deck along at least one third of the length of the central deck, and the plurality of vertically-supporting risers vertically extending from the central deck between the hulls to the sea bed, and the method further comprises providing a track along an outer side of each hull, movable supports displaceable along each track, and a lifting member extending between the supports and being displaceable over the central area, for lifting of one or more of the risers and the pipe elements.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Some embodiments of a floating hydrocarbon processing and storage structure according to the invention will by way of example be explained in detail with reference to the accompanying drawings. In the drawings:

(2) FIG. 1 shows a side view of a floating LNG plant according to the invention,

(3) FIG. 2 shows a top view of the floating LNG plant of FIG. 1,

(4) FIG. 3 shows a schematic transverse cross-sectional view of a floating structure according to the invention, along the line in FIG. 2,

(5) FIG. 4 shows a schematic cross-sectional view of a floating structure of the type shown in FIG. 3 including a traveling crane supported on a central pipe rack,

(6) FIG. 5 shows a top view of a spread moored floating structure comprising a riser balcony and a gantry crane,

(7) FIG. 6 shows a top view of a structure of the type of FIG. 5 comprising two gantry cranes,

(8) FIG. 7 shows a side view of the floating structure of FIGS. 5 and 6,

(9) FIG. 8 shows a top view of a spread moored floating structure comprising a central deck, supporting risers and cranes,

(10) FIG. 9 shows a schematic lay out of the riser configuration of the spread moored structure of FIG. 8

(11) FIG. 10 shows a top view of a floating structure comprising a turret mooring system,

(12) FIG. 11 shows a modular construction of a floating structure according to the invention,

(13) FIG. 12 shows a side view of an embodiment of a floating structure comprising a drilling rig supported on the central deck structure, and

(14) FIG. 13 shows a schematic top view of the embodiment of FIG. 13.

DETAILED DESCRIPTION OF THE DRAWINGS

(15) FIG. 1 shows a floating liquefied natural gas (LNG) vessel 1 comprising first and second assemblies 2, 2 each having a hull 3, 3 and a deck structure 4, 4. The deck structures 4, 4 bridge the width W (see FIG. 2) of the hulls, that is defined by side walls 5, 6;5, 6. The hulls 3, 3 accommodate cryogenic spherical LNG tanks 7, 7 that partly extend above deck level. Processing equipment 10, 10 such as liquefaction equipment including air compressors, steam turbine electrical generators, a liquefied petroleum gas (LNG) export system, a LPG extraction facility, flare drums and the like is situated on the deck structures 4, 4. The vessel 1 is moored to the sea bed 12 via a mooring system, comprising mooring lines 8 anchored to the sea bed and a turret 13, around which the hulls 3, 3 can jointly weathervane. Risers 19 extend from a subsea hydrocarbon well to a swivel 16 on the turret and are at the swivel 16 connected via schematically indicated piping 17, 18 to the processing equipment 10, 10 and to the storage tanks 7, 7.

(16) In FIG. 2, the central deck 20 can be seen to extend along at least 70% of the length of the hulls 3, 3 at or near the height of the deck structures 4, 4. At the central deck 20, additional processing equipment, vertical risers, horizontal risers or other pipe segments and/or one or more cranes may be supported.

(17) In FIG. 3 an embodiment of a twin hull structure is shown comprising hulls 3, 3 having double walls 27, 28 and the tanks 25, 25, the deck structures 4, 4 being supported by bulkheads and by the sidewalls 5, 6; 5, 6. A central tank 26 is provided between the hulls 3, 3 and is delimited by an intermediate bottom hull part 32, an aft hull part 33 and a bow hull part 34 (see FIG. 2). The hulls 3, 3 are moored via a spread mooring configuration 35, 35. On the central deck 20, that extends substantially flush with the deck structures 4, 4, a pipe rack 30 is provided, storing pipe segments for forming hydrocarbon transport ducts 31, the pipe segments extending in the length direction of the twin hulls between various tanks and processing equipment.

(18) FIG. 4 shows an alternative embodiment in which a travelling crane 36 is supported via wheels or slide members 37 on tracks 38 running on top of the pipe rack 30 to be displaceable along the central deck 20 in the length direction. In this case, the pipe rack 30 may store pipe segments 31 such as drill string sections or riser pipe sections (steel or flexible), which may be transported via the crane 36 along the tracks 38 to a drilling or work-over rig on the vessel to be interconnected and lowered to the sea bed.

(19) As shown in FIG. 5, a single gantry crane 42 can be provided with supports 44, 44 movable along tracks 43, 43 that extend in the length direction along the outward sides of the hulls 3, 3. A number of risers 41 is pending from a riser balcony 40. Riser segments can be picked up from their horizontal transport position on the central deck 20 by the gantry crane 42 and can be connected in a vertical orientation to the riser parts that are supported from the riser balcony 40 for installation purposes or for increasing hydrocarbon production.

(20) In FIG. 6, two independently movable gantry cranes 42, 45 are shown, each spanning the width of a single hull 3, 3. Gantry crane 42 is mounted on supports 46, 46 which run approximately alongside the sidewall positions of hull 3. Gantry crane 45 is mounted on supports 47, 47 and can be displaced in the length direction independently from crane 42 for picking up process equipment modules on deck of the vessel during operations or during construction.

(21) FIG. 7 shows the side view of the spread-moored structures of FIGS. 5 and 6.

(22) In FIG. 8 two fixed rotating cranes 51, 52 are provided on the central deck 20, risers 50, 54, 54 being suspended from the central deck 20. The cranes 51, 52 are used for riser installation. The construction in FIG. 8 can optionally be combined with riser balconies 53, 53 such that a large number of risers (e.g. 200 risers or more) can be accommodated.

(23) FIG. 9 shows a top view of the spread of the risers 54, 54 extending from the hulls 3, 3 to the sea bed.

(24) FIG. 10 shows a turret moored vessel 15 in which the hulls 3, 3 are connected to a bow module 55 comprising a bow deck structure 56 and a rotatable turret 57 connected to the bow deck structure, which turret is anchored to the sea bed via groups of anchor lines 58, 59, 60. As can be seen from FIG. 11, the vessel 15 is composed of modules comprising hull-deck assemblies 3, 4; 3; 4 supporting respective processing equipment 10, 10, which modules are interconnected via central deck 20 and bow module 55.

(25) In the embodiment of FIGS. 12 and 13, a drilling or work-over rig 70 is placed on the central deck 20, a drill string or risers 71 being installed via the rig 70. Travelling gantry cranes 42, 45 may transport riser parts or pipe sections from a storage position on deck to the rig 70, and may be operated for lifting processing modules or equipment 72, 73 on the deck structures 4, 4 of the hulls 3, 3.