Bundles and towed installation

Bundles and towed installation

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Where the water depth is too great to safely allow this use of pressurised nitrogen, the flowlines may be towed without the use of a carrier. This is known as a ‘flat-pack bundle’.

TYPICALBUNDLECONTENTS

TYPICAL BUNDLE CONTENTS

ƒ Carrier

ƒ Thin wall – pressurised ƒ Production/ flowline ƒ Co-mingled flow ƒ Test line/pigging loop ƒ Methanol, glycol and chemical injection ƒ Water or gas injection ƒ Gas lift at well

ƒ Hot water – constant or following shutdown ƒ Umbilical cables – control lines to valves

The carrier provides the buoyancy for the bundle, but also some protection against dropped objects and trawling activities. Nevertheless, although of a large diameter – around 1 m (40 in), it is a thin wall – typically 10 mm (0.5 in). It requires nitrogen pressure within to prevent collapse when submerged. The other lines which may be carried are listed above. These are kept some 70 mm (3 in) from the wall of the carrier to allow some deformation of its wall (should it suffer impact from dropped objects) and provide space to fit the internal clamps. Production lines or flowlines carry the product (oil/gas mix) as co-mingled flow from a number of wells – typical size 323.8 mm (12¾ in). A smaller diameter test line of around 168.3 mm (6⅝ in) can be used to prove individual down hole conditions. Sometimes the test line is sized to enable round trip pigging. Some flows need injection from the platform to the well in order either to improve flow or prevent corrosion. Some fields require water to be injected to improve the recovery of oil and gas from the reservoir. This is injected through a separate well from the recovery well, driving the product ahead. Similarly, gas may be abstracted and re-injected into an oil reservoir to aid recovery. Or gas may be needed just at the well to aid lift heavy oil up through the production tubing. With sluggish oil flows, we may use the bundle to maintain heat or recover from a shut-down situation. This can be done by including a hot water line perhaps in combination with warm water returning through the annulus of the carrier. Control of the valves and manifolds at the field is usually accomplished with a separate umbilical cable laid adjacent to flowlines. With bundles, these can be incorporated within the carrier. They do not require the heavy armour normally used for cables. The advantage of bundles is that all these can be incorporated within a single flowline corridor.