Murchison was one of the biggest steel jacket platforms in the North Sea with its topside weighing 24,500t and jacket weighing 24,600t excluding piles
Image: Waves Group - Murchison Decommissioning Project. Photo: courtesy of Waves Group.
The Murchison field was originally discovered in 1975 and started producing oil in 1980. It is situated in the northern North Sea approximately 240km northeast of the Shetland Islands and 2km west of the UK/Norway median line in a water depth of 156m. Murchison was one of the biggest steel jacket platforms in the North Sea with its topside weighing 24,500t and jacket weighing 24,600t excluding piles. A Cessation of Production application was submitted by CNR International (UK) Ltd, as operator, in 2011 and approved in 2012. Permanent Cessation of Production took place on 31 March 2014 following a period of one month’s notice given to DECC (now part of the Department for Business, Energy & Industrial Strategy).
Waves Group were pleased to be awarded the Marine Warranty Services contract by CNR International (UK) Ltd back in 2015. The Removal Services Contract for the platform had already been awarded to a consortium formed by Heerema Marine Contractors and AF Decom Offshore (HAF) and the topsides removal campaign took place in the summer of 2016. The removal method used was ‘Reverse Installation’ and was carried out by separating the topsides into its original modular components and lifting them back one by one onto the massive decks of the Semi-Submersible Crane Vessels (SSCVs) Thialf (four trips) and Hermod (one trip). This amounted to twenty-six lifts in total and at the end of each trip, the SSCVs offloaded the structures to the decommissioning yard in Vats, Norway.
The jacket removal campaign was carried out the following year in the summer of 2017 and required the splitting of the substructure into four removable sections that again utilised the SSCVs Thialf (two trips) and Hermod (two trips). This required extensive underwater cutting using a range of diamond wire cutting frames that were fabricated specifically for the Murchison jacket with leg members up to 6m in diameter. An estimated 2400t of marine growth was present below water and this had to be partly removed where the cuts were to be made.
Waves Group’s scope included vessel suitability surveys, engineering procedure and document reviews, attendance for interface meetings including HAZID/HAZOP and readiness review, and attendance on the SSCVs throughout the offshore campaigns. An impressive 97% of the removed structures was either re-used or recycled at the AF Decom yard in Vats.
Source: Company Press Release