Decommissioning Insight 2018

DECOMMISSIONING INSIGHT 2018

8.9 Subsea Infrastructure Over 30,000 kilometres of pipelines, cables and umbilicals related to oil and gas have been installed in the UKCS. This number continues to grow as new discoveries are developed and more infrastructure is installed. When a pipeline, cable or umbilical has reached the end of its useful economic life, itmustbedecommissioned. IntheUK,pipelinedecommissioning is regulated by OPRED under national regulations. To determine the optimum pipeline decommissioning option, owners are required to carry out a Comparative

Assessment, taking account of the safety, environmental impact, societal impact, technical feasibility and economics of each feasible option. There are currently no international regulations for decommissioning disused pipelines.

Decommissioning options available for pipelines are as follows:

• Leave in place • Full removal • Trench and bury • Rock cover • Hybrid options encompassing elements of the above

Outcomes from the CA are embodied in the Decommissioning Programme, which undergoes public consultation before approval by the Secretary of State for Business, Energy and Industrial Strategy. Once the Decommissioning Programme is approved, it is up to the owner to determine the optimumway of delivering the agreed scope. Offshore decommissioning activities are performed by offshore construction contractors with specialist equipment to safely carry out the required activities.

5,724 km of pipelines are to be included in decommissioning programmes over the next ten years.

Protective structures called mattresses are placed over pipelines for stabilisation and protection. Mattress design has changed over time, with a number of materials and methods of manufacture being utilised. In most cases mattresses are concrete blocks joined together with rope. The BEIS Decommissioning Guidance Notes 11 provide clarity on the decommissioning of concrete mattresses and other protective structures. The overarching principal is that mattresses, grout bags, or other systems which have been installed to protect pipelines throughout their operational life should be removed during decommissioning, for disposal onshore.

In some situations, removal may not be considered the optimal decommissioning solution and an owner may propose to leave mattresses in situ. Such proposals must be supported by Comparative Assessment.

Removal methods for mattresses can include the use of speed loaders — small handling structures which are normally used during installation—or mattresses can be connected to a crane and lifted directly from the seabed onto a vessel.

There are 18,136 mattresses forecast to be decommissioned over the next ten years. Industry has recognised that this is an area where efficiency gains can be made, and there are various technologies in use or being developed to ensure efficient and safe removal.

10 BEIS — Guidance Notes for Decommissioning of Offshore Oil and Gas Installations and Pipelines

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