RE: Thistle6 Feb 2020 21:07
Kraken,
Neil and others are right in this case
The tanks are ~1,100t each, empty and in air.
Full of water they are pushing 3,500t
They are not large empty voids and in reality contain a series of chambers and pipe work. There will ha e been an operation to empty them of what’s known as “attic oil”. That is, oil which will have risen to the highest dome element of the tank by virtue of being less dense than seawater.
The tanks will like have been flushed and then the tops of the tanks will likely have been drilled now and emptied of attic oil to get out the last the mobile oil
I would imagine at this stage in the life cycle the tanks may well have holes in them so a lot of structural assurance and inspection will need to be conducted by divers before any lift. Although I heard the steel on these is several inches thick so pretty sturdy
Cutting them is likely to be a complete non starter. They will likely have inaccessible hydrocarbons, oily sand and other nasties in there (such as NORM) which you really don’t want to release to the environment.
It’s likely ENQ will have considered filling them with Nitrogen or using flotation devices before they found the supports to the central nodes were corroded/unstable.
I would imagine a single lift is the safest way to do. They’ll likely use some sort of simultaneous shaped charges, delivered by ROV to simultaneously cut all supports or maybe timed to swing each tank away from the jacket.
Will certainly be a fascinating project to work on and will require some precise engineering to safely deliver. Remember of BP’s decomm money is being spent, they will likely have some of their best engineering bods involved for assurance. More importantly that money and cost is minor wanting to be attached to a bad job either safety wise or environmentally, especially given today’s BP protests.
Cheers
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