The ESSI decommissioning system is designed to access, characterise and safely remove contaminated fluids from within subsea concrete gravity base structures.
After the cell cap has been cleared of debris and cleaned, the Location Plate Assembly is positioned onto the cell cap using ROV. Once secured using 3x ROV anchor pegs, it provides lateral stability and centralised positioning for all tooling. The ROV then positions the Core Drilling Tool onto the Location Plate and latches in place.The Core Drilling Tool removes core section of reinforced concrete approximately 3" dia x 24" deep and is recovered to the surface.
The Anchor Hub Installation Tool then sets and seals the Anchor within the concrete bore. The Anchor Hub internal anvil teeth are mechanically actuated into the concrete and back filled with epoxy resin. An Isolation Valve Block is lowered into position and locked into the anchor hub before the Thru Drilling Tool is positioned on top. A 3.5" hole is drilled through the remaining cell cap material.A range of sampling tools are deployed to scan, test and extract the cell contents. Samples are returned to the platform for further analysis.
If contaminated contents are present they are pumped to a single holding cell for safe disposal. When the contents have been fully characterised in accordance with OSPAR, Annex III, the remaining clean contents can be left in situ. A mechanically set sealing plug is installed into the Anchor Hub and tested before removing the Isolation Valve Block. This plug can be left in situ permanently.
An ROV debris cap is installed onto the anchor hub to provide protection against mechanical damage and to enable continued access for legacy monitoring.