Assessment of technical safety for the selected platform concept

The concept recommended and chosen for Goliat is an FPSO with subsea wells tied back to it. The surface installation is a circular, permanently moored floater with integrated storage and offloading systems. This type of production facility is in use on the UK continental shelf, but has not previously been adopted on the NCS.

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A permanently moored floating platform has been chosen instead of the ship-shaped solution more traditionally seen on the NCS. Such a unit makes it simpler to pull in an electricity transmission cable from land. The platform is powered partly from shore and partly from a gas/liquid-fuelled turbine. That reduces the need for local power generation on the facility compared with a solution based solely on gas turbines. See also appendix C.

The platform is specially tailored to the cold climate in the Barents Sea, with extensive weather protection/winterisation. Account has been taken of special requirements for these waters, in that no produced water will be discharged to the sea during normal operation.

The platform is designed to provide oil storage in its hull, with the process plant and living quarters above. The hull is built in steel with double bottom and sides.

Figure 3-12. Offshore loading on the Goliat field. (Source: Eni)

Oil is landed via shuttle tankers. Direct loading from a geostationary, permanently moored facility is new for the NCS. The tanker stays on station with the aid of a dynamic positioning system which ensures that the minimum distance between platform and vessel always exceeds 150 metres. During loading operations, the tanker will not normally lie bows-on to the platform. See Figure 3-12. The platform incorporates a large oil store and generally has great flexibility for adding new risers and umbilicals. This opportunity to attach more risers makes the facility suitable for functioning as a future field centre.

The topsides are constructed of modules installed on a circular steel hull, with the process deck having a diameter of 107 metres. See Figure 3-13. This deck was originally intended to be placed five metres above the main deck, which forms the top of the hull structure. After the PDO had been submitted, however, the need to increase the height required substantial changes. The process deck is supported by the radial support frames in the hull, and this load distribution principal has been implemented on all process deck levels. There are two levels above the process deck.

The process deck is divided by an explosion-proof wall running east-west.

Area north is the safe side, with cranes, quarters, lifeboat stations, generators, space for electrics/instrumentation/telecommunications, workshops, stores and so forth.

Area south is covered by a steel structure for protection against wind and weather, and contains five modules – flowlines, separation, gas recompression, gas compression and water injection, produced water and chemical injection. In addition come the primary/

secondary loading station and bunkering station, flare boom and escape chute (the secondary loading station has later been removed).

The flare boom and related equipment are placed as far as possible from the quarters and the safe area.

Pursuant to the PDO documentation, two areas would be provided on the platform for offloading oil. The primary station is positioned to the north-east of the topsides, with the secondary station on the western side. This was intended to permit offloading to continue regardless of wind direction while simultaneously maintaining high regularity should one

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station be out of operation. However, it was decided at a later stage to the remove the secondary station.

The utilities area on the west side is dedicated to electrical equipment at various levels, with the heaviest components on the process deck. A number of safety functions related to fires and emergencies are on the east side, along with stores and the workshop area. The primary and secondary areas for material handling are located in the centre of the process deck. Cranes are positioned on the north-west and north-east sides.

The living quarters are dimensioned for a crew of 120 people, with single cabins and all necessary facilities. The helideck is placed above the top storey of the living quarters and cantilevered towards the north in order to achieve a direct view down to the sea surface.

Figure 3-13. Illustrations of the Goliat topsides layout. (Source: Acona)

The hull is a circular cylindrical structure with a diameter of 90 metres. Twenty ballast tanks are arranged around the periphery of the hull to provide the latter with double sides and bottom. That reduces the possibility of damage to the oil storage tanks.

Two separate machinery rooms are provided in the hull for the installation of small items of operating equipment. See Figure 3-14. These areas are placed in the central shaft and in the forward machinery room beneath the living quarters. They contain such equipment as pumps, heat exchangers and other utilities. The shaft is divided vertically, with an internal quadrangular section in the centre which functions as a safe zone, while the external section is an unclassified zone. Stairs and personnel lifts are among the facilities in the safe zone.

The shaft is outfitted for safe transport of equipment which will require maintenance or replacement during production. Located at the north side of the platform, beneath the living quarters, the forward machinery room primarily contains utility systems for the living

quarters like sewage and waste water systems. Equipment such as coolant pumps for seawater, firewater pumps at the lowest level, and liquid supply is found here. A personnel lift rises to the process deck.

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Figure 3-14. Goliat FPSO with listing of safety-related topics. (Source: Acona)