Seaway develops lower-cost platform removal concept

Offshore staff

ROTHBURY, UK – Seaways Engineering International has appointed marine engineer Joe Glass as managing director (UK).

His goal is to develop an alternate solution for decommissioning platforms in the North Sea.

Glass has worked since the early 1980s with San Diego-based Craig Lang, the owner of Seaways, whose inventions are said to include the reelship Apache and steel catenary risers.

They have now developed the novel extended semisubmersible (Nessie), based on the Shell-approved multi-purpose semisubmersible (MPSS).

Nessie is a box section semi with six columns and a gate at the aft end, similar to a giant floating dry-dock. Once the vessel approaches the structure, it ballasts down, opens the gate and moves over the structure.

Using laser-based positioning, the topsides unit is lifted clear and secured at the forward end. Nessie then positions itself until the jacket is located amidships, after which rigging is attached and the jacket is rotated underwater to the horizontal position, where it is secured for transport to shore.

The full-size version of Nessie measures 220 x 120 m (722 x 394 ft) and is said to be capable of handling the largest North Sea structures.

A smaller version, 60 x 60 m (197 x 197 ft) is designed for single lifts of the smaller structures typically deployed in the southern North Sea gas basin.

Glass claims the semi’s construction costs would be less than 10% of the new giant heavy-lift decommissioning vessels and would also operate at a correspondingly lower day rate.

OGIC (Oil and Gas Innovation Centre) in Aberdeen has commissioned Strathclyde University in central Scotland to conduct further research. This will include a desktop study to prove the vessel’s stability; analysis of the lifting arrangement for a jacket; a detailed animation showing the procedure; and fabrication and tank testing of a 4-m (13-ft) long model.

Glass hopes to secure more funds from the UK government or an oil company to develop a full-size prototype.


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