Decommissioning and abandonment

Decommissioning and abandonment

33

REFLOAT PIPELINE AND TOW TO SHORE

ƒ Use of divers to attach buoyancy to line ƒ In deeper water, pull back onto barge and relaunch ƒ Bottom tow or CDT to shore Converted recovery vessel Pipe-lift davits

Hold-back winch

Sea level

Flotation bags

Seabed Abandoned pipeline Unburied pipeline

Stingers fore and aft

Cut and install end cap

Offshore tow tug

Flotation bags

Tow head

Seabed

An alternative would be to attach buoys to long sections of the pipeline – perhaps up to 4 km (2½ miles) and then tow it to shore, where it can be cut up. In shallower water, divers could undertake this. An alternative would be to pull it up onto a specially-designed barge, where buoyancy could be added. A pair of stingers would be required to be fitted to the specially-designed laybarge for support. It is likely that a flat- bottomed anchor barge could be adapted. Once ashore, the steel and concrete could be recovered.

BUNDLERECOVERY

BUNDLE RECOVERY

ƒ Bundle recovery by off-bottom towing ƒ Use ballast to raise bundle off the seabed ƒ Fill bundle with air ƒ Use ballast chains to stabilise ƒ Tow to an onshore facility ƒ Advantage ƒ No offshore cutting of pipeline ƒ Disadvantages ƒ Depends on structural integrity of bundle ƒ Extensive preparatory work

This method is intended to recover continuous lengths of bundles that are lying on the seabed with minimal rock dump protection.