FLOATING STRUCTURE

Description

TECHNICAL FIELD

The invention relates to a Floating Production Storage and Offloading, FPSO-, or Floating Production Storage, FSO-, structure comprising a hull with sidewalls of a length L extending in a longitudinal direction, a bottom structure and an upper deck, the hull having a breadth B, a process unit support structure overlying the upper deck, hydrocarbon processing equipment units mounted on the process unit support structure and piping connecting the processing units to at least one hydrocarbon storage tank for storage of processed hydrocarbons.

BACKGROUND

Large floating structures, such as FPSO's or FSO's are moored offshore, for instance near offshore hydrocarbon production wells, in a spread-moored or weathervaning configuration. An FPSO comprises a number of risers that extend from riser balconies, or from an internal or external turret to one or more wellheads. The upper deck structure carries processing units for the treatment of the produced hydrocarbons, which are stored in tanks located within the hull. As an example, a known floating structure may have a topside having a weight of up to 50.000 tons and can have a length of 330 m, a width of 60 m, a draught of 25 m, a height above water level of 40 m and may comprise 19 crude oil tanks. It is an object of the invention to provide a floating structure that can support large top sides and that provides improved safety and protection of the hydrocarbon tanks under conditions of a collision. It is also an object to provide a large floating structure of a relatively simple construction, in which the number of hydrocarbon tanks can be reduced, resulting in less pumps, less maintenance and reduced access. It is also an object to provide a floating structure in which the offloading sequence of hydrocarbons is improved.

SUMMARY

According to the invention, a floating structure is provided, comprising Floating structure comprising a hull adapted to support a weight of at least 50.000 tons, preferably at least 70.000 tons, with sidewalls of a length L extending in a longitudinal direction, a bottom structure and an upper deck, the hull having a breadth B, a process unit support structure overlying the upper deck, hydrocarbon processing units mounted on the process unit support structure and at least one hydrocarbon storage tank for storage of hydrocarbons,

• • side spaces being bounded by the bottom structure, the upper deck, a respective side wall and an adjacent longitudinal sidewall, the adjacent longitudinal sidewalls being situated at a distance Wt from the side walls, Wt being at least equal to the smallest of 0.2 B or 11.5 m,
  • the at least one hydrocarbon storage tank being situated between the bottom structure, the upper deck and the adjacent longitudinal walls.

The floating structure according to the invention provides large side spaces, or wing tanks, between the sidewalls and the hydrocarbon storage tanks, so that in case of collision, the deformations are contained in the zone of the wing tanks, in accordance with the MARPOI definition of damage, and the hydrocarbon storage tanks are protected. The side spaces, or wing tanks, may be filled with ballast water, or can contain equipment or may be void.

The design may comprise either a single bottom or a double bottom.

The vessel may comprise a centre line bulkhead and a number of hydrocarbon storage tanks (of substantially the same size, between 1 and 4 tanks extending, in a transverse direction, between an adjacent longitudinal sidewall and the centreline bulkhead.

The design provides a reduced number of equally sized hydrocarbon storage tanks, such as crude oil tanks, resulting in improved offloading, as less time is required for switching between tanks, and since for all tanks the offloading times are similar.

The storage tanks may be situated between front and aft transverse walls extending in a transverse direction from an adjacent longitudinal sidewall to the centreline bulkhead.

The floating structure according to the invention may in addition to the centreline bulkhead comprise 1 or more longitudinal bulkheads between which the crude oil tanks are situated.

Because in a preferred embodiment, a relatively small number of bulkheads is provided, the construction of the floating structure according to the invention is simplified.

The processing units can be placed on the upper deck structure, overlying the longitudinal bulkheads and the transverse bulkheads for a strong support construction. The processing units can be mounted on an upper deck structure at positions overlying the side spaces for optimal utilisation of the available decks space. The process unit support structure may form integrated parts of the topside modules that are mounted on the upper deck through supports or legs.

The floating structure may comprise hydrocarbon risers extending from the floating structure to a subsea well, piping connecting the risers to the processing units. The risers may extend through the side spaces.

The side spaces may be provided with special internal reinforcement structures for a riser balcony and/or a mooring structure. Depending on the specific requirements of the design, riser balconies and/or mooring connectors may be attached to the reinforcement structures.

In an embodiment, the side spaces comprise water tanks, the floating structure comprising pumps adapted for filling and emptying the water tanks.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of a floating structure according to the invention will by way of non-limiting example, be explained in detail with reference to the accompanying drawings. In the drawings:

FIG. 1 shows a schematic plan view of a floating structure according to the invention,

FIG. 2 shows a schematic transverse cross-sectional view of the floating structure of FIG. 1,

FIG. 3 shows a detailed transverse cross-sectional view of the hull of the floating structure of FIG. 1, and

FIG. 4 shows a perspective view of the hull section of FIG. 3.

DETAILED DESCRIPTION

FIG. 1 shows a plan view of a floating structure 1, having a hull 2 with sidewalls 3, 4, a bow 6 and a stern 8. The length L of the structure 1 is at least about 380 m, the breadth B being at least about 64 m. The structure 1 comprises longitudinal bulkheads 10, 11 and a centreline bulkhead 12, extending from the stern 8 to the bow 6. The transverse distance Wt of the longitudinal bulkheads 10, 11 from the sidewalls 3, 4 is at least 0.2 B or 11.5 m, whichever is less, in this example 11.5 m. Transverse bulkheads 15, 16, 17, 18 extend in a transverse direction between the sidewalls 3, 4, so that spaces, or wing tanks 20,21,22,23,24,25 are formed by the spaces bounded by a sidewall 3,4; a longitudinal bulkhead 10, 11 and adjacent transverse bulkheads 15,16; 17,18. Crude oil tanks 30,31,32,33,34,35 are situated on each side of the centreline bulkhead 12 between the longitudinal bulkheads 10, 11. The twelve crude oil tanks 30-35 are of substantially the same size. Other lay outs with a different number and a configuration of the cargo tanks may be provided.

FIG. 2 shows a schematic transverse cross-section of the floating structure 1, with a bottom 7 and an upper deck 9. The bottom 7 may be formed by a single plate or can be formed by a double wall bottom structure. The height H may be about 34 m. A process unit support structure 40 in the form of an integral deck, or a number of individual process unit support structures, is placed on supports 41, 42 and carries processing units 43, 44, the total weight of the top structure being about 50.000-100.000 tons. Risers 50 may be supported on riser balconies 51, connected to a well head 52 on the seabed 53. Via piping 54, 56 and pumps 55, the risers 50 are connected to the processing units 43, 44 for the separation of gas and water from the produced oil, and for storage of the processed oil in the crude oil tanks 30-35.

FIG. 3 shows a cross-sectional view of the hull 2 and a transverse bulkhead.

FIG. 4 shows a perspective view of the part of the hull 2 shown in FIG. 3.