Bundles and towed installation

Bundles and towed installation

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DEEP-WATER BUNDLES

DEEP-WATERBUNDLES

DEEP-WATER BUNDLES

ƒ Conflicting requirements

ƒ Carrier imploding in deep water ƒ HSE nitrogen pressure – onshore construction risks ƒ Alternative methods proposed: ƒ Pressurise conventional bundle in trimming area before tow – to depths of 800 m (2600 ft) ƒ Pressurise conventional bundle at pre-determined temporary parking areas during tow ƒ Decant nitrogen from flowlines into carrier during tow For deep-water bundles, the carrier cannot be safely filled with nitrogen onshore to resist the hydrostatic pressure at the field. The options available are: 1 Pressurise in trimming area to 80 bar (1160 psi): This overcomes onshore safety issues – the risks of explosive impact with cranes and construction vehicles, and proximity to personnel It is suitable for a water depth of up to 800 m (2600 ft) 2 Re-pressurise at selected offshore parking areas at around 250 m (820 ft) to match seabed: Difficulties arise in transporting and transferring of nitrogen at sea There is a need to re-trim the bundle to counteract the additional weight of pressurised nitrogen. This is limited by diving depths or requires a ROV If bundle rises too high during the remainder of the tow, it could explode 3 Decanting nitrogen into the carrier pipe from the flowlines: Valve technology exists which can automatically release nitrogen into a carrier at various depths The effectiveness is dependent upon ratio of flowline volume to carrier volume No additional mass need be added, therefore there is no need for re-trimming It can be effective in water depths of up to 1200 m (4000 ft)

DEEP-WATERBUNDLES