Decommissioning Insight 2017

For a pipeline to be decommissioned it must be hydrocarbon-free. Making safe of pipelines involves depressurising them and removing any hydrocarbons. Then the pipelines are cleaned and purged, with the cleaning programme based on the specific needs of the system. This may involve the use of pigs, which are maintenance tools used to clean or inspect the insides. Making safe is often carried out several years prior to the next phase of decommissioning. In some cases, pipelines can be brought back into use after making safe, reflecting the importance of the infrastructure and the drive to maximise economic recovery of reserves where possible. In the UKCS, for example, there has been an influx of investment in key pieces of upstream and midstream infrastructure as private equity firms see that opportunities are still available to recover the significant resources that remain in the basin. Antin Infrastructure Partners has taken on operatorship and invested in a major export route called the Central Area Transmission System (CATS), while Arclight is investing in the Shetland Islands Regional Gas Evacuation System (SIRGES) and Frigg UK pipeline (FUKA). Further deals this year included the sale of the Forties pipeline, which INEOS bought from BP, and purchase of the decommissioned Thames pipeline from Perenco by Independent Oil & Gas. The latter was with a view to using the pipeline as the export route for its southern North Sea infrastructure. Mattresses and Other Subsea Infrastructure Mattresses are concrete structures that are usually used to protect or support subsea pipelines. Mattress decommissioning typically involves recovery from the seabed. This is a diver and vessel-intensive operation, with duration of the work dependent on the mattress age and condition. In some cases where mattresses are badly degraded, regulatory approval may be sought to decommission in situ .

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Other subsea infrastructure includes manifolds, Christmas trees, risers, spools, jumpers, anchors and subsea isolation valves, which are removed as part of the decommissioning programme.

Operators forecast that over 15,200 mattresses will be decommissioned across the UK, Norwegian and Danish Continental Shelves from 2017 to 2025. Information on mattresses was not available for The Netherlands. Around 54,000 tonnes of other subsea infrastructure are also expected to be removed from the North Sea.

Figure 11: Forecast for Mattresses and Other Subsea Infrastructure Decommissioning, 2017 to 2025

Other Subsea Infrastructure (tonnes)

Number of Mattresses

CNS

7,975 2,433 4,670

31,015 13,586

NNS and WoS

Southern North Sea and Irish Sea Norwegian Continental Shelf

4,772 2,555

186

Danish Continental Shelf Dutch Continental Shelf 14

9

590

-

1,385

14

14 The number of mattresses forecast to be decommissioned was not available for the Dutch Continental Shelf.

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