Decommissioning Insight 2018

There are many subsea structures installed on the UKCS, including manifolds, wellhead protection structures, subsea isolation valves, drilling templates, riser base structures and many more. These structures vary in size depending on their purpose and may be piled to the seabed, or gravity-based. They are typically made of steel, concrete or a mixture of the two. Althoughnot specificallymentioned in theOSPAR98/3decision, BEIS GuidanceNotes state that these subsea structures fall under the definition of a steel installation. This means that upon decommissioning they should be fully removed. Subsea structures can normally be lifted onto a construction support vessel (CSV) using the vessel crane. In some cases, structures with piles will need to have them internally or externally cut to be released from the seabed, which will cause some level of seabed disturbance. Due to the weight of some larger structures, it may be necessary to cut the infrastructure into sections for removal. 54,217 tonnes of subsea structures are due to be decommissioned by the end of 2027. Subsea infrastructure removal accounts for £1.7 billion of the forecast expenditure on decommissioning over the next ten years, or 11.3 per cent of forecast expenditure.

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PRACTITIONER PROFILE

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Rever Offshore Rever Offshore, formerly known as Bibby Offshore, is a leading Aberdeen-based offshore construction contractor and has been at the forefront of decommissioning in the North Sea since themid 2000s. Rever has a fleet of construction vessels, diving support vessels and ROVs which it can utilise in all aspects of offshore construction, maintenance and decommissioning activities. Typically working for oil and gas operating companies, the decommissioning services performed by Rever ranges from pre- and post-decommissioning surveys, through cleaning and isolation of subsea systems and cutting and lifting materials for disposal onshore.

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Decommissioning projects often span more than one season but can typically represent between 10% to 35% of Rever’s business in any one year.

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The skills to perform decommissioning activities come from Rever’s in-house Project Management, Engineering and Offshore Operations teams, including a full saturation diving capability. These teams have been established over many years and provide the planning, preparation and mobilisation support for the fleet operations as well as executing the offshore operations themselves. Their experience and capability are built from executing many offshore campaigns from new-build projects, inspection-repair-maintenance activities as well as decommissioning. Rever also has strong relationships with its supply chain partners and uses those links to gain access to the latest technologies to continually improve the efficiency of their offshore operations. Rever Offshore sees decommissioning as a key part of its future business and is seeking to build on its decommissioning track record as the pace of decommissioning increases in coming years. In meeting this increasing demand for their services, Rever continues to invest in its engineering teams through recruitment and graduate training, as well as the potential to add new vessels to its fleet and investing in new technologies and equipment to enhance its capabilities.

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