This paper is designed to present the challenges and obstacles faced in the use of a new technology for the plugging and de oiling of sections of unpiggable flowlines prior to decommissioning.

Conventional methods of decommissioning subsea pipeline infrastructure are inherently very expensive with the mobilization and operation of DSV (Dive Support Vessel), equipment and personnel.

In this case the only other viable option was to mobilise a DSV to hot tap the flowlines and circulate fluid from the platform before filling the line with cement. This operation would have incurred considerable expenditure so the operator sought a more cost effective solution.

The solution deployed utilised an ultra lightweight, minaturised coiled tubing system which was deployable from the platform lower decks with minimal laydown area required. The system had the ability to traverse multiple bends (360° total), de-oil the line and deliver an expandable cement to plug the pipeline in a single operation. This paper will outline this new approach and will identify how this new technology can positively impact project economics as well as environmental and safety implications. It will also highlight the engineering problems encountered and resolved during this project.

The innovative, unconventional approach to this project in the North Sea provides an alternative solution for operators to consider when planning pipeline decommissiong. The result of the operation will be outlined as well as the future of this new technology within the decommissioning sector.

Cost reduction is an important topic in the current economic climate and this paper will conclude that this technology provided a suitable solution to the operator and at a reduced cost when compared to conventional solutions. It will also demonstrate how collaboration between companies within the industry has paid dividends to all involved during this project in line with Oil & Gas UK Economic Report 2014.

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