I'm sure readers recall the grounding, refloating and salvage of the cruise liner Costa Concordia a few years ago. It was one of the most complex and difficult marine salvage jobs in history, and success was far from a foregone conclusion.
Whilst the ship is no more, the technologies developed and used to salvage her wreck are now being applied in a new and innovative way.
Scottish marine salvage group Ardent is adapting the tanks it used to refloat the Costa Concordia, the cruise ship wrecked off the Italian coast in 2012, to decommission North Sea oil platforms.
Costa Concordia with caissons (tanks) attached to its sideIt is one of several companies trying new ideas to win business in the market for dismantling disused oil platforms.
In Britain’s ageing oil fields alone, the opportunities could be worth up to 17 billion pounds ($21.85 billion) before 2025, according to industry body Oil and Gas UK. The ideas could then be deployed to other maturing fields such as in the Gulf of Mexico and southeast Asia.
. . .
Oil platforms are usually removed piece by piece and taken to the shore using complex vessels. The floating tanks that Ardent used to lift the Costa Concordia, are much cheaper to use, industry experts say.
There's more at the link.
It's an interesting approach, very different from the more complex techniques used up until now. Here, for example, is the removal of a 14,000 ton rig from the North Sea by lifting it with a ship after cutting its legs.
Caissons (a.k.a. tanks or sponsons) are nothing new, of course: they've been used for centuries to assist with underwater construction in building bridges and digging tunnels, and also in more recent years to refloat grounded vessels. However, to use them to float a big oil rig off its base, or lift the base off the ocean floor and then tow it to shallower water, is new. I presume they'd be attached to the legs, which would then have to be cut off quite deep beneath the water. One wonders whether caissons can provide adequate stability to such a tall object, as well as buoyancy.
It's going to be interesting to watch this, and find out if it can be made to work.
Peter
2 comments:
Peter,
for stability and structural strength, it makes no sense to mount the caissons to the bottom of the legs. No need to. They will be mounted as close to the surface as possible, leaving the legs dangling for balance purposes. I suspect that they may even mount additional weight near the feet, to dampen any rolling movement from wave, wind, and towing inputs. That may not be necessary in all cases, though, as some have built-in ballast tanks that were used during the tow and positioning/installation process.
Each oil rig tends to be a unique, or very small production run item, so there will be a bit of custom work done to each one to make this happen.
If this can reduce dismantling costs, I'm all for it. There's a reason why the Peter Schulte (or whatever they call it now, it was sold recently), the world's largest ship, is designed ONLY for dismantling old rigs.
One of the harder parts to explain to folks is the enormous diversity of offshore oil rigs. Most people think of MODU units when they think of this at all, and yet MODU rigs make up less than 1% of offshore oil structures.
Navigating through the oil patch in the US Gulf of Mexico is actually pretty damn stressful. There are traffic lanes, which can mean congestion, which sometimes forces ships into the patch to slalom between rigs. Many are unmanned and unlit, except for small flashing lights. Some abandoned smaller platforms have been damaged by hurricanes and the wreckage lies under the surface. Plus the active rigs have their own support vessels like ticks on a hound.
Really, anything that can keep companies afloat while they deal with the hugely expensive costs of dismantling is good. Awful lot of companies go under because of ballooning dismantling costs.
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