Decommissioning Insight 2019

DECOMMISSIONING INSIGHT 2019

CNR INTERNATIONAL – NINIAN NORTHERN PLATFORM (NNP)

NNP ceased production in May 2017 and was permanently down-manned in April 2018. The topsides and jacket are planned to be removed by the single lift vessel Pioneering Spirit in 2020 and 2021 respectively, with the NNP jacket being one of the first users of its new Jacket Lift System. To that end, a gangway-linked construction support vessel (CSV) campaign in summer 2019 achieved separation of NNP topsides and made the jacket ready for topsides removal and transport to Dales Voe for disposal.

Personnel with prior experience of Murchison decommissioning and understanding of the steps to achieve ‘hydrocarbon safe’ and down-manning were transferred into the NNP offshore operations team to augment their intimate knowledge of the installation with decommissioning ‘savvy’. The decommissioning of the 24 platform wells was particularly efficient thanks to a number of factors. Geological evaluation of the potential to flow justified a single reservoir barrier with no requirement for intermediate barrier, hence none of the casing cutting, milling and cementing that characterises other field abandonment requirements with intermediate flow potential. Moreover, the NNP rig had drilled as recently as 2015 and had been maintained in warm stack thereafter, so rig reactivation was not onerous. The rig operating contractor, together with deck crew, tubular handling and cutting specialists collaborated in cross-training their operatives to bring about a reduced rig crew that had all the necessary competencies for 24-hour well decommissioning work. A small coiled tubing campaign to de-risk three wells with known problems was followed by through-tubing reservoir abandonment of the 24 wells. Following 28-day pressure monitoring of each cemented well, subsequent activities such as Xmas tree removals, tubular cutting and pulling ahead of conductor recovery could be performed ‘open hole’ without any need for BOP or lubricator. Simultaneous operations with both the rig and wireline activities with the use of a platform crane instead of a mast further contributed to efficient execution. Weather downtime was almost completely mitigated by performing cementing, rig skidding and cutting activities when adverse weather precluded tubular handling. Finally, the conductor recovery was achieved with two cutting and pinning locations on the rig floor and in the well bay.

Production continues at Ninian field from the Central and Southern platforms.

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