Fairfield Betula has filed a decommissioning programme draft to support decommissioning of the Dunlin Alpha to Cormorant Alpha pipeline (PL5) and associated infrastructure which is part of a wider suite of decommissioning programmes for the Greater Dunlin Area.
The Greater Dunlin Area consists of the Dunlin, Dunlin South West, Osprey and Merlin Fields, located in the Shetland Basin of the northern North Sea. The Dunlin Alpha platform served as the production facility for the Greater Dunlin Area and is located in block 211/23a, approximately 137 km north east of Shetland and 11 km from the UK / Norwegian median line, in a water depth of 151 meters.
Termination of Production from the Greater Dunlin Area was announced in May 2015, having Maximised Economic Recovery (MER) from these oilfields. Termination of Production was agreed with the Oil & Gas Authority (OGA) on 9th July 2015, with Cessation of Production (COP) on 15th June 2015, confirmed by letter dated 15th January 2016.
Pipeline PL5 is a rigid 34.2 km concrete-clad 24” diameter pipeline installed in 1975. PL5 historically transported stabilised production fluids from Thistle Alpha, Murchison and the Dunlin cluster into the Brent Pipeline System. It now only transports fluids from Thistle Alpha and this arrangement will be terminated in 2019.
The recommendation from the comparative assessment is for the surface laid ends of the pipeline to be cut and removed for recycling, leaving the remainder largely trenched below mean seabed level. In order to mitigate against potential snagging hazards, rock cover will be applied at the cut locations of the exposed pipeline ends and identified areas of spanning. Partially buried concrete mattresses will also be removed, together with the anode skids and spools at the Dunlin Alpha platform and the spools at the Cormorant Alpha platform.
Buried deposits (concrete mattresses and grout bags) and grout bags that continue to provide pipeline stability to protect against movement and spans will be decommissioned in situ and rock coverage will be applied to prevent snagging hazards. Any oilfield debris within the pipeline corridor will be recovered as part of debris clearance operations. Once complete, seabed clearance surveys will be conducted and used to initiate a monitoring regime with the regulator and its consultees.
PL5 is owned by three joint venture groups: Dunlin Field Group, Thistle Field Group, Murchison Field Group.