OFFSHORE SPAR PLATFORM

Abstract

A floating, unmanned wellhead or production facility includes a topside configured to process a hydrocarbon fluid, and a spar hull supporting the topside. The spar hull is designed to minimize maintenance and thus does not include many of the systems commonly found in the hull of a floating offshore facility. Systems that are not present within the spar hull include an active ballast system, a bilge system, a drainage system, an active zone isolation system, a fire detection and suppression system, and an internal lighting system.

Claims

1. A floating offshore facility comprising: a topside configured to receive a hydrocarbon fluid, process the hydrocarbon fluid to produce one or more processed hydrocarbon fluid, and output the one or more processed hydrocarbon fluid; and a spar hull supporting the topside, wherein the spar hull does not comprise at least one of: an active ballast system, a bilge system, and a drainage system.

2. A floating offshore facility according to claim 1, wherein the spar hull does not comprise any of an active ballast system, a bilge system, and a drainage system.

3. A floating offshore facility according to claim 1, wherein the spar hull does not comprise an active zone isolation system.

4. A floating offshore facility according to claim 1, wherein the spar hull does not comprise one or both of a fire suppression system and a fire detection system.

5. A floating offshore facility according to claim 1, wherein the spar hull does not comprise an internal lighting system.

6. A floating offshore facility according to claim 1, wherein the spar hull is designed not to permit internal access to the spar hull whilst deployed.

7. A floating offshore facility according to claim 1, wherein the spar hull defines one or more cofferdam located at a waterline following deployment.

8. A floating offshore facility according to claim 1, wherein the spar hull is formed from concrete, metal or a combination thereof.

9. A floating offshore facility according to claim 1, wherein the spar hull comprises a concrete hull defining a primary, air-filled chamber comprising at least 80% of the internal volume of the spar hull.

10. A floating offshore facility according to claim 1, wherein the spar hull comprises a metal hull defining a plurality of air-filled chambers.

11. A floating offshore facility according to claim 1, wherein the floating offshore facility is a wellhead platform.

12. A floating offshore facility according to claim 1, wherein the floating offshore facility is a production platform.

13. A floating offshore facility according to claim 1, wherein the floating offshore facility is an unmanned platform.

Description

[0032] Preferred embodiments of the present disclosure will now be described in greater detail, by way of example only and with reference to the accompanying drawings, in which:

[0033] FIG. 1 shows a topside of an unmanned wellhead platform whilst connected to a service vessel via a “Walk to Work” system;

[0034] FIG. 2 shows an underwater configuration of the unmanned wellhead platform;

[0035] FIG. 3 shows a first embodiment of a spar hull for use with the unmanned wellhead platform; and

[0036] FIG. 4 shows a second embodiment of a spar hull for use with the unmanned wellhead platform.

[0037] FIG. 1 shows an unmanned wellhead platform 1.

[0038] The platform 1 comprises a topside 2 and a spar hull 3. The topside includes all necessary processing equipment to perform the functions required by the platform 1. The spar hull 3 provides the necessary buoyancy to support the topside 2.

[0039] The platform 1 is an unmanned platform, and as such has been designed with the intent that it will require no permanent personnel to carry out its normal function, and will only be occupied for particular operations such as maintenance and/or installation of equipment. Thus, the platform 1 has no provision of facilities for personnel to stay on the platform for a prolonged period of time, such as overnight. Such platforms are typically much cheaper to install and maintain than manned platforms, making them particularly useful for extraction of hydrocarbons from marginal wells, which might otherwise not be commercially viable.

[0040] The unmanned platform 1 does not include a heli-deck or lifeboats, and is designed to be accessed in normal use solely by a bridge 5, known as a Walk to Work (W2W) system. The gangway 5 connects the topside 2 of the platform 1 to a service vessel 4 in the illustrated embodiment. However, in other implementations, the bridge 5 may connect to another, manned platform. The length of the bridge is typically about 100 m long.

[0041] Referring the FIG. 2, the illustrated platform 1 is an unmanned wellhead platform 1. Thus, the platform 1 is connected to a plurality of production risers 6, which receive wellstream fluid from a plurality of manifolds 7 connected to wellheads on the seabed. The wellstream fluid received via the production risers 6 is processed by equipment on the topside 2, which may perform processes such as separation, dehydration, acid gas removal, and the like. The processed hydrocarbons are then output via export risers 8, which carry the processed hydrocarbons back to the seabed for supply to a subsea pipelines 9 for onward transport, for example back to shore or to a further offshore processing facility.

[0042] As the platform 1 is designed to be unmanned during normal operation, it is important to minimise the maintenance requirements of the facility. Typically, an unmanned facility such as that illustrated may be designed to have fewer than 3000 maintenance hours per year. This may, for example, facilitate maintenance to be carried out twice per yet in two one-week maintenance visits. Whilst additional or longer maintenance visits can be carried out, each visit significantly increases the costs associated with operation of the platform 1, and thus reduce the viability of marginal hydrocarbon reservoirs.

[0043] The inventors have recognised that a large number of systems typically incorporated within the spar hull 3 of the platform 1 do not provide significant advantages within the context of an unmanned facility. However, such systems are often quite complex and must still be regularly maintained. The maintenance of the spar hull systems adds a significant number of annual maintenance hours to the overall annual maintenance hours of the platform 1. It is therefore proposed to significantly simplify the construction of the spar hull 3.

[0044] FIG. 3 illustrates a first embodiment of a spar hull 3a for use with the offshore platform 1.

[0045] The spar hull 3a is a metal spar hull and comprises a hollow, cylindrical outer hull 10, which in this embodiment is formed from steel. In order to minimise the weight of the hull 10a, annular ribs are formed on the inside of the hull 10a to improve structural stability.

[0046] The spar hull 3a comprises a plurality of annular chambers 11 that provide buoyancy for the platform, and define a central passageway 12 through the spar hull 3a for risers 6, 8 or umbilicals to be run to the seabed. This arrangement protects any risers 6, 8 or umbilicals from collisions, as well as from wear due to exposure to the splash zone of the platform 1.

[0047] In the illustrated embodiment, the spar hull 3a comprises four annular compartments 11a-11d. These are each filled with air and are fluidly isolated from one another. In some embodiments, each of these annular compartments may be further subdivided into segments, for example into four equal chamber sectors.

[0048] The chamber 11b that is at sea level acts as a cofferdam. Thus, in the event that the hull 10 is breached by a ship impact, this chamber 11b (or one sector thereof) will fill with water. However, the other chambers 11a, 11c, 11d are fluidly isolated and thus continue to provide buoyancy to the platform 1.

[0049] The hull 10 extends beyond these annular chambers 11a-d and defines a water-filled chamber 12 which provides damping against sea movements. At the bottom of the hull 10 is a ballast chamber 13. As above, this chamber 13 maybe subdivided into segments, for example into four equal chamber sectors. The ballast chamber 13 may be filled with a permanent ballast, typically iron ore.

[0050] FIG. 4 illustrates a second embodiment of a spar hull 3b for use with the offshore platform 1.

[0051] The spar hull 3b is a substantially concrete spar hull and comprises a hollow, approximately cylindrical outer hull 10, which in this embodiment is formed from concrete. In the illustrated embodiment, the spar hull 3b defines a single, primary chamber 15, which accounts for most of the volume within the hull 14. The primary chamber 15 is filled with air and is completely sealed. This chamber 15 provides the buoyancy for the platform 1. Risers 6, 8 or umbilicals that need to run to the seabed are run along the outside of the hull 14.

[0052] The spar hull 3b further comprises an annual cofferdam 16 that is positioned at sea level between the hull 14 and the primary chamber 15. Thus, in the event that the hull 14 is breached by a ship impact, this chamber 14 will fill with water. However, the primary chamber 15 remains fluidly isolated and thus will continue to provide buoyancy to the platform 1. In the illustrated embodiment, the cofferdam 16 is isolated from the primary chamber by a steel wall coupled to the concrete hull 14.

[0053] Whilst not shown, permanent ballast may also be provided at the bottom of the concrete spar hull 3b.

[0054] As will be appreciated, the spar hulls 3a, 3b described above are designed with the intention that they do not contain any machinery requiring maintenance. Thus, the spar hulls 3a, 3b do not comprise any of an active ballast system, a bilge system, and a drainage system, which would normally be expected to be found within the spar hull 3 of an offshore platform 1.

[0055] Indeed the spar hulls 3a, 3b are not designed with the intention of permitting internal access to the spar hull whilst deployed. Therefore, systems associated with occupancy of the spar hulls 3a, 3b are also not required. Thus, the spar hulls 3a, 3b also do not comprise a zone isolation system, a fire suppression and/or detection system, an internal lighting system, or access passageways.