WO2005056379A1

WO2005056379A1 - Modular offshore hydrocarbon storage and/or processing structure

Info

Publication number: WO2005056379A1
Application number: PCT/NL2004/000872
Authority: WO
Inventors: Willem Cornelis Van Wijngaarden; Theodorus Johannes Bernardus Brinkel
Original assignee: Single Buoy Moorings Inc.
Priority date: 2003-12-15
Filing date: 2004-12-15
Publication date: 2005-06-23

Abstract

Floating storage and/or processing structure (1) for hydrocarbons, such as cryogenic fluids, comprising a vessel (2) moored to the sea bed, a tank member (7)for containment of the hydrocarbons, a processing unit (6), and an interconnecting fluid duct connecting the processing unit (6) and the tank member (7), characterised in that the tank member comprises at least a first and a second tank unit, the first tank unit (12, 13) being attached to the vessel (2) via a first support (41) and being connected to the processing unit via the interconnecting fluid duct (16, 16', 16'), the vessel comprising at least a second support position (38) and support (40) for receiving the second tank unit (11) fastenable to said support (40) and interconnectable to the processing unit (6) via a fluid interconnection member (31', 33, 49, 34'), the second tank unit (11) not being connected at the second support position (38) to the second support (40) and not being connected to the processing unit (6).

Description

Modular offshore hydrocarbon storage and/or processing structure.

The present invention relates to a floating storage and/or processing structure for hydrocarbons, such as cryogenic fluids, comprising a vessel moored to the sea bed, a tank member for containment of the hydrocarbons, a processing unit and an interconnecting fluid duct connecting the processing unit and the tank member.

The invention also relates to a method of constructing such a storage and/or processing structure and to a tank unit for use in such a structure.

Such floating storage and/or processing structures for cryogenic fluids are known from: "Floating LNG Solutions. From the drawing Board to Reality, F. Faber et al, Offshore Technology Conference 14100, 6-9 May 2002, pp 1-10.

Herein Floating Liquid Natural Gas (FLNG) and Floating Oil and Natural Gas (FONG) production structures are described comprising a turret-moored barge equipped with oil and gas swivels, oil tanks and isolated LNG storage tanks, and a Nitrogen refrigerant-based LNG liquefaction plant including water and CO2 separation units.

The known storage and/or production structures require a relatively large capital expenditure when assembled on shore and are laid out for a capacity which may not be completely utilised off-shore, or at least during the early stages of a project. Also, the integrated construction of the vessel and the cryogenic storage structures require a relatively complex building process, placing special demands on building skills required from the shipyard, and a relatively long construction time. Furthermore, repair of the vessel may need to be carried out while the production process is interrupted, resulting in a loss of useful operating hours.

It therefore is an object of the present invention to provide a floating storage and/or production structure and construction method thereof for hydrocarbons, in particular for relatively cold fluids such as LNG or LPG, which can be built at reduced initial capital expenditure, and which can be completed relatively rapidly. It is another object of the present invention to provide a floating storage and/or production structure and construction method thereof for hydrocarbons, in particular for cryogenic fluids, which can be built at a marine yard without the requirement of complex construction facilities and which can be repaired at reduced down time. It is again an object of the present invention to provide a floating storage and/or production structure which has a flexible production and/or storage capacity.

Hereto the structure according to the present invention is characterised in that the tank member comprises at least a first and a second tank unit, the first tank unit being attached to the vessel via a first support at a first support position and being connected to the processing unit via an interconnecting fluid duct, the vessel comprising at least a second support position and support for receiving the second tank unit fastenable to said support and interconnectable to the processing unit via a fluid interconnection member, the second tank unit not being connected at the second support position to the second support and not being connected to the processing unit.

The storage and/or processing structure according to the present invention can be built at low initial costs, within a relatively short time by installing a smaller number of tank units on the vessel on shore, and subsequently mooring the assembly of vessel and tank unit at an offshore production site and starting operation. The operator of the production and/or processing structure can decide to start out the project on a small scale at low initial costs within a short time. When more capacity is required, a gradual expansion to more capacity can be achieved when demand increases. Additional tank units can be constructed while operation continues, and can be transported to the offshore location, be installed on the vessel and be interconnected to the processing equipment.

Furthermore, the tank units can be built at a separate yard, in a reduced overall building time as complex integration of tanks and floating structures is not required. The barge or vessel may be of conventional shape, such as for instance a simple rectangular barge, which may be built on regular shipyards. Repair or change/out of tank units can be carried out without interruption of operations. New or additional tank units may be connected to the vessel while the removed tank unit may be transported to shore for repair, dock inspection or redeployment.

The vessel according to the present invention may for instance be a floating LNG import terminal (FRSU) with a regasification unit or can be a floating export terminal (LNG FSO), or an FLNG or FONG production system. The vessel may be turret moored in a weathervaning manner or may be spread moored to the sea bed.

It should be noted that a modular cargo vessel is known from US 2,406,084. In this patent, a vessel is shown having a hull devoid of cargo space. The cargo compartments are formed by tank members of rectangular cross section, which can be floated above the cargo deck of the vessel. The cargo deck is ballasted such that it is submerged. After being positioned above the vessel in their proper position, the vessel is deballasted such that the containers come to rest on the deck of the vessel, and are attached by rigid fasteners to secure the tanks against relative movements. The known publication fails to disclose to place each tank unit individually in fluid connection with a processing unit, such as a cryogenic fluid processing unit and to allow for optional incremental increase in storage and processing capacity.

In one embodiment, each tank unit comprises attached thereto a processing unit for processing hydrocarbons, in particular cryogenic fluids. In this way tank/processing modules are formed. The vessel or barge for receiving the tank/processing modules does not comprise any complicated systems other than regular marine systems, which implies building times can be short and the construction process can be straight forward and can be carried out on a regular ship yard. The floating structure allows for construction in sizable blocks which may be sub-contracted and constructed at different locations to shorten dock time. Furthermore, the modular construction of the processing equipment allows the capacity of this equipment to match the storage capacity on the vessel. A further advantage of integration of the processing equipment in the tank units or modules is that downtime of the whole system upon exchange or repair of the processing equipment of one tank unit is avoided. The processing unit forming with the tank unit a storage/processing module can comprise a regasification/ boil off handling system, CO2 separators, water separators, compressors and cooling/refrigeration units.

The tank units may be substantially rectangular and placed side by side on the vessel, each tank unit comprising at a side the fluid interconnection member connectable to the interconnecting fluid duct, the interconnecting fluid duct extending along the sides of the tank units. The tank units may for instance be containerized LNG tanks, which in themselves may be of spherical shape and may comprise regular LNG containment systems such as Moss-Rosenberg's storage systems, GTT, IHI-SPB, or, depending on the product, be formed by regular steel tanks.

Upon installation, the additional containers are transported to the offshore location of the production and/or storage structure and are connected to the deck of the vessel. The containers may be sailed to location on a barge, and lifted to their deck position by a crane, upon which they are fastened on their supports which are situated at reinforced deck positions on the vessel. Alternatively, the containers may be floated and towed to location, and may be placed on the vessel by ballasting the vessel such that deck level is submerged by several meters below water level, after which the containers are floated over their proper position and the vessel is raised by deballasting. Once the tank units are secured, connections can be made to the interconnection members to attach product piping and interconnecting ducts to the processing equipment.

Preferably the interconnecting ducts and product piping extend along the side of the containers for easy access. In a preferred embodiment the ducts and product piping extend along the top surface of the containers, such that easy access is provided and the piping does not interfere with mooring of vessels alongside the production and/or storage vessel. At the top surfaces of the tank units, working decks may be provided for access to the product piping, valves and interconnection members.

In one embodiment, the interconnection members of the tank units comprise a flexible joint for accommodating thermal expansion and contraction. In particular in case of cryogenic fluids being stored, the flexible joints, such as for instance steel bellows or jumper hoses allow thermally induced expansion and contraction of the product piping. The tank units are connected to the vessel via the supports, which may comprise stools placed at the strong positions of the vessel, such as over the bulk heads, the stools having a degree of flexibility to allow for flexing of the tank unit due to wave actions. The supports furthermore comprise positioning means for allowing movement of the tank units relative to the vessel prior to being connected to the supports. The positioning means may be formed by rollers on the tank unit and/or on deck, by slide bearings and hydraulic actuators, drive motors and the like. After placing a tank unit on deck in a first, global positioning step, the displacement means are operated to move the tank unit relative to the vessel to assume its proper position on the supports, after which the tank unit can be fastened on its supports.

Some embodiments of a floating storage and/or processing structure according to the present invention will, by way of non-limiting example, be described in detail with reference to the accompanying drawings. In the drawings:

Figure 1 discloses a side view of a cryogenic storage and/or production vessel according to the present invention,

Figure 2 shows a top view of the vessel of figure 1,

Figures 3-5 show different embodiments of interconnection of the tank units to the processing unit,

Figure 6 shows a cryogenic tank unit comprised in a rectangular container ;

Figure 7 shows a cryogenic tank unit which together with a modular processing unit forms a tank-processing module; and

Figure 8 and 9 show a side view and a top view respectively of a cryogenic and/or production vessel with a midship offloading facility. Figure 1 shows a floating energy import or export terrninal 1 with a barge 2 which is anchored to the sea bed 3 via anchor lines 4 and 5. The vessel 1 comprises a processing unit 6 such as a regasification unit, refrigerating equipment, gas and water separators and compressors. The vessel comprises a tank member 7 comprised of tank units 8, 9, 10, 11, 12 and 13. The tank units 8-13 are generally rectangular in cross section and comprise a cryogenic fluid such as liquefied LNG gas. The tank units 8-13 are connected to the deck of the vessel via supports or stools 15. The tank units 8-13 are each connected to the processing unit 6 via an interconnecting fluid duct 16 (see fig. 2). The interconnecting fluid duct 16 extends along a top side of the tank units 8-13, and is connected to fluid interconnection members 17, 18 at the top of each tank unit 8- 13. A deck structure 24 for supporting equipment may be supported on the top side of the tank units 8-13. The processing unit 6 is connected to a cryogenic swivel 20 of a turret 21. The turret 21 is moored to the sea bed 3 via the anchor lines 4, 5 that are attached to a chain table near keel level 22 of the vessel 2 (such that the vessel 2 can weathervane around the turret 21). The processing unit 6 may comprise a (modular) boil-off handling and regasification plant, or e.g. a refrigeration or liquefaction facility.

The vessel 2 carries at the stern a crane 25 with a cryogenic fluid transfer arm 26 which is in fluid connection with the tank units 8-13 via hard piping or flexible ducts which have been schematically indicated at reference numeral 27. Its is also possible to have a configuration with midship placed LNG stations 25', 25" for offloading on one or both sides of the FSRU for midships fluid transfer, such as shown in Figs. 8 and 9. Via the transfer arm 26, cryogenic fluid might be transferred to shuttle tankers or may be loaded from the shuttle tankers into the tank units for processing in the processing unit 6. Since the interconnecting fluid duct 16 extends along the top side of the tank units 8- 13, free access to fluid interconnection members 17, 18 which may comprise mechanical and fluid coupling valves and the like, at the top of the tank units 8-13 is possible for inspection and for maintenance or installation and free access to the sides of the vessel 2 for mooring a vessel 28 alongside is possible. At the front of the vessel 2 personnel quarters 29 and a helideck 30 are provided.

In figure 3 an embodiment is shown in which the vessel 2 is moored in a spread moored configuration and is connected to the sea bed 3 in a non-weamervaning manner via anchor lines 4, 5. In this embodiment, the interconnecting fluid ducts 16, 16' form a series interconnections between the tank units 12, 13 and the processing units 6. The fluid connection members are in this case formed by couplings and valves 31, 31', 32, 33 and 34 located at the vertical sides of the tank units 12, 13. Flexible joints 35 such as steel bellows or jumper hoses (not shown) may be comprised in the duct 16 to allow for flexing and bending due to movements of the vessel and due to thermal expansion and contraction The entire duct 16 could be a jumper hose as well.

The tank units 12, 13 are situated at a first support position 37 on the vessel 2 and may be installed on shore prior to sailing the vessel to its offshore production site. A second support position 38 on deck of the vessel on which one or more tank units may be placed, is not occupied by any tank unit and can receive a tank unit when the production capacity needs to be increased. The tank units 8-13 are supported on supports 40, 41 which are situated on deck of the vessel 2 at a strong position, for instance at the position of the vertical bulk heads 42, 43. For increasing the production capacity, an additional tank unit may be placed on the supports 40 for instance via a crane on a lifting barge on which tank unit is sailed to the production site. After being lowered on the supports 40, for a fine positioning, the tank units 12, 13 or the support stools 40, 41 may be provided with displacement means such as rollers or slide bearings. After placing a tank unit on the support 40, a displacement actuator may be installed such a drive motor45 and an actuator 46. The actuator 46 may be formed by a rack and pinion construction, or may be formed by a hydraulic displacement cylinder and the like. By actuating the motor drive 45, a fine adjustment of the exact position of the tank unit over the support stools 40, 41 can be achieved after which the tank units 12, 13 are permanently fixed to the stools for instance via bolts, welding or combinations thereof. Thereafter, an interconnecting fluid duct 16 to the processing unit 6 is provided in this case extending to the interconnection member 31' of the adjacent tank unit 12. Operations of the processing unit 6 may be continued at increased capacity. After installation of the tank units, the motor drive 45 and actuator 46 may be removed.

As shown in figure 4, the interconnecting fluid duct 16 extends along the top of tank units 12, 13, each tank unit at the top being provided with a connector and valve 31", 32. After placing an additional tank unit on the second support position 38, interconnecting fluid duct parts may be connected to termination coupling 49 on the interconnecting fluid duct 16. In the embodiment shown in figure 4, the motor drive 45 and hydraulic actuator 46 are shown for a positional adjustment of the container unit 12 in the length direction of the vessel 2.

In the embodiment shown in figure 5, the tank units 11, 12 or 13 are connected to the processing unit 6 via a respective interconnecting fluid duct 16, 16', 16" and a respective coupling 34, 34', 34" on the processing unit 6. The number of couplings 34- 34" corresponds to the number of tank units that can be placed on the deck of the vessel

2.

Figure 6 shows a tank unit 50 for use in the present invention comprising a rectangular container 51 which has a rectangular cross-sectional shape and which is provided at the bottom thereof with positioning means such as rollers or slide bearings 52 and which comprises at its upper surface lifting members 53 for lifting of the container to a support position on deck of the vessel via a crane. Inside the container 51, a cryogenic tank 54 is placed for containing for instance LNG. The space between the tank 54 and the walls of container 51 is filled with a temperature-insulating material 55 which also may provide extra buoyancy and/or stability to the container 51. In case of a buoyant container 51, the container may be towed to the offshore production location prior to installation on the vessel 2. At the top surface 56 of the container 51, the fluid interconnection member 57 is placed for interconnecting the tank 54 to a processing unit. The interconnection member 57 may comprise one or more valves and a flange for receiving interconnecting bolts for attachment to an interconnecting fluid duct 16.

In the embodiment of figure 7, a tank unit 50 is combined with a processing unit 60 to form a tank-processing module. The processing unit 60 may for instance comprise a compressor 61, a refrigerating unit 62 and a gas and water separating unit 63. The tank/processing module can be connected to the interconnecting fluid duct 16, 16', 16" via interconnecting flange/valve units 65', 65". Via a supply duct 65, the gas may be introduced into the processing unit 60 for liquefaction and be stored in the cryogenic tank 54. Through outlet duct 66, the LNG might be transported to a regasification unit 67, which forms part of the processing unit 60 and from thereon to an outlet duct 68 for supplying the gas to for instance an offshore power plant or to other parts of the processing unit on the vessel 2.

Claims

1. Floating storage and/or processing structure (1) for hydrocarbons, such as cryogenic fluids, comprising a vessel (2) moored to the sea bed, a tank member (7)for containment of the hydrocarbons, a processing unit (6), and an interconnecting fluid duct (16, 16', 16")connecting the processing unit (6) and the tank member (7), characterised in that the tank member comprises at least a first (12, 13)and a second (8, 9, 10, 11) tank unit, the first tank unit (12, 13) being attached to the vessel (2) via a first support (41) at a first support position (37) and being connected to the processing unit via the interconnecting fluid duct (16, 16', 16"), the vessel comprising at least a second support position (38) and a second support (40) for receiving the second tank unit (8, 9, 10, 11) fastenable to said second support (40) and interconnectable to the processing unit (6) via a fluid interconnection member (31', 33, 34", 49), the second tank unit (8, 9, 10, 11) not being connected at the second support position (38) to the second support (40) and not being connected to the processing unit (6).

2. Floating storage and/or processing structure (1) according to claim 1 comprising a predetermined number, larger than two, of tank units (8, 9, 10, 11, 12, 13), the number of support positions (37, 38), supports (40, 41) and interconnection members (31', 34, 34', 34") on the vessel corresponding to said predetermined number of tank units, at least one support position (37, 38) and support (40, 41) not being occupied, and at least one interconnection member (31', 34, 34', 34") not being interconnected to a tank unit.

3. Floating storage and/or processing structure (1) according to claim 1, wherein the tank units are substantially rectangular and placed side by side on the vessel (2), each tank unit comprising at a side the fluid interconnection member (31, 31', 32, 33) connectable to the interconnecting fluid duct (16, 16', 16"), the interconnecting fluid duct (16, 16', 16") extending along the sides of the tank units.

4. Floating storage and/or processing structure (1) according to claim 3, wherein the interconnection members (31, 32, 33) and the interconnecting fluid duct (16, 16', 16") are situated at a top side of the tank units (8-13).

5. Floating storage and or processing structure (11) for hydrocarbons, such as cryogenic fluids, comprising a vessel (2) moored to the sea bed (3), a tank member (7) for containment of the hydrocarbons, a processing unit (6), and an interconnecting fluid duct (16, 16', 16"), connecting the processing unit and the tank member, characterised in that the tank member (7) comprises at least a first and a second tank unit (8, 9, 10, 11, 12, 13), each releasably attached to the vessel via a respective support (40, 41), the tank units being connected to the processing unit (6) via the interconnecting fluid duct (16, 16', 16") and an interconnection member (31, 31', 31") each provided at a side of the tank unit, the interconnecting fluid duct extending along the sides of the tank units.

6. Floating storage and/or processing structure (1) according to claim 5, wherein the interconnection members (31, 31', 31") and the interconnecting fluid duct (16, 16', 16") are situated at along the top side of the tank units (8-13).

7. Floating storage and/or processing structure (1) according to claims 5 or 6, wherein the tank units comprise at their top sides a deck structure (24) for supporting equipment.

8. Floating storage and/or processing structure according to any of the preceding claims, wherein the interconnection members (31 , 31', 31 ") and/or the interconnecting fluid duct (16, 16', 16") comprise a flexible joint for accommodating thermal expansion and contraction.

9. Floating storage and/or processing structure (1) according to claim 8, wherein the flexible joint comprises a bellow (35, 35', 35").

10. Floating storage and/or processing structure (1) according to any of the preceding claims, wherein the vessel comprises positioning means (45, 46) for allowing movement of the tank units relative to the vessel when the tank units are being supported on the supports (40, 41).

11. Floating storage and/or processing structure (1) for hydrocarbons, such as cryogenic fluids, comprising a vessel moored to the sea bed (2), a tank member (7) for containment of the hydrocarbons, a processing unit (6), and a interconnecting fluid duct (16, 16', 16"), connecting the processing unit (6) and the tank member, characterised in that the tank member (7) comprises at least a first and a second tank unit (8, 9, 10, 11, 12, 13), each attached to the vessel via a respective support (40, 41), the vessel comprising positioning means (45, 46)for allowing movement of the tank units relative to the vessel when the tank units are being supported on the supports (40, 41).

12. Floating storage and or processing structure (1) for hydrocarbons, such as cryogenic fluids, comprising a vessel (2) moored to the sea bed (3), a tank member (7) for containment of the fluids, characterised in that the tank member (7) comprises at least a first and a second tank unit (8, 9, 10, 11, 12, 13), the first unit being attached to the vessel via a first support (41) and being connected to the processing unit via an interconnecting fluid duct (16, 16', 16"), the vessel (2) comprising at least a second support position (38) and support (40) for receiving the second tank unit fastenable to said support, wherein each tank unit comprises attached thereto a respective processing unit (60) for processing cryogenic fluids to form a tank/processing module.

13. Floating storage and/or processing structure (1) according to claim 12, wherein the tank/processing modules each comprise an interconnection member (65'), the tank/processing modules being connectible to an interconnecting fluid duct via the interconnection members (65, 65').

14. Method of installing a storage and/or processing structure for hydrocarbons, such as cryogenic fluids, comprising the steps of: - providing a vessel (2) comprising a tank member (7) for containment of the hydrocarbons, a processing unit (6), and an interconnecting fluid duct connecting the processing unit and the tank member, the tank member comprising at least a first and a second tank unit (8, 9, 10, 11, 12, 13), - installing the first tank unit on the vessel on or near shore, the first tank unit being attached to the vessel via a first support (41) and being connected to the processing unit (6) via the interconnecting fluid duct (31', 33, 34", 39), - providing a second support position (38) and second support (40) on the vessel for receiving the second tank unit fastenable to said support and interconnectable to the processing unit (6) via a fluid interconnection member (16, 16', 16"), - mooring the vessel at an offshore location, - transporting the second tank unit to the vessel, and - placing me second tank unit on the second support, and attaching the second tank unit to the processing unit.

15. Method according to claim 14, wherein the second tank unit is connected to the processing unit (6) via a second interconnection member (34, 34', 34", 49)wbich is provided on the interconnecting fluid duct (16, 16', 16") or on the processing unit (16).

16. Tank unit (50) for use in a hydrocarbon processing and/or storage unit according to any of claims 1 to 12, the tank unit being of generally rectangular cross-section and having an interconnection member (65', 65") for attaching to the processing unit (6), and a support member (52) for attaching to the support on the vessel.

17. Tank unit according to claim 16, comprising buoyancy and temperature isolation along its walls.