The decommissioning of the Buchan and Hannay fields in the North Sea, UK, has been underway since 2017 and is expected to be completed in 2024. Repsol Sinopec Resources UK is the operator and holds 100% interest in the infrastructure of both the fields.
Repsol Sinopec Resources UK is a joint venture between Talisman Colombia Holdco (51%), a subsidiary of Spanish oil and gas company Repsol, and Addax Petroleum UK (49%), a subsidiary of Chinese state-owned Sinopec. Talisman Sinopec Energy UK was renamed Repsol Sinopec Resources UK following Repsol’s acquisition of Talisman Energy in May 2015.
The Buchan oil field, discovered in 1974, commenced production in May 1981 and ceased operations in May 2017, whereas the Hannay field, discovered in 1996, remained productive for 11 years from 2002 to 2013.
The decommissioning of the Buchan Alpha floating production unit (FPU) was completed in January 2021, while the contract to decommission the Buchan and Hannay subsea wells was awarded in September 2021.
Buchan and Hannay field location
The Buchan field spans blocks 20/5a and 21/1 in the Central North Sea, UK, approximately 154km northeast of Aberdeen, Scotland, UK. The water depth in the field area is 115m.
The Hannay field is located in 123m-deep waters in block 20/5c of the UK North Sea, approximately 13.5km northwest of the Buchan field.
Buchan and Hannay field development details
The Buchan field comprised 12 wells including seven production wells, two water injection wells, two appraisal wells, and one exploration well, while the Hannay field was developed with two production wells.
The Buchan and Hannay fields were tied back to the Buchan Alpha FPU through 18 risers that included seven production risers, eight gas lift risers, one water injection riser, and two umbilical risers.
A 56.3km-long export pipeline transported oil from the Buchan Alpha FPU to the Forties Charlie platform. Oil from the Forties Charlie platform is transported to the shore through the Forties Pipeline System.
The subsea installations across the fields included the Buchan template, Hannay manifold, Hannay subsea isolation valve, a pipeline end manifold (PLEM), as well as pipelines and umbilicals.
Buchan Alpha FPU details
The Buchan Alpha semi-submersible FPU, weighing 12,000t, was originally constructed as a drilling rig in 1973, but later converted to an oil production unit between 1978 and 1980.
The FPU started operations at the Buchan field in May 1981, while the Hannay field was tied back to it in 2002.
A gas lift compression system was installed on the FPU in 1984. It was also fitted with a flexible riser system in 1999.
The pentagon-shaped Buchan Alpha FPU cumulatively produced 150 million barrels (Mbl) of oil until it ceased operations in May 2017.
The Buchan Alpha FPU was removed and brought to the Dales Voe decommissioning facility in the deepwater Lerwick Harbour, Shetland, Scotland, in August 2017.
Contractors involved in Buchan and Hannay fields decommissioning
Well-Safe Solutions, a company specialised in well plug and abandon services and based in Aberdeen, Scotland, was contracted for decommissioning 14 subsea wells of the Buchan and Hannay fields in September 2021.
It will execute the contract by deploying Well-Safe Guardian, a semi-submersible well-plugging rig, in 2022.
Veolia UK, a subsidiary of French-based environment and waste recovery conglomerate Veolia Group, received the Buchan Alpha FPU decommissioning contract in June 2017.
Peterson, a global risk management and logistic solutions provider, also partnered with Veolia in decommissioning the FPU.
The Buchan Alpha FPU, while undergoing decommissioning at the Dales Voe facility operated by Veolia and Peterson, was hit by a heavy storm in November 2019, which caused the FPU to break free and drift across the water.
Ocean Kinetics was contracted by Veolia to remove and recycle the remains of the Buchan Alpha FPU from water in July 2020. Ocean Kinetics lifted the Buchan Alpha pontoons to the decommissioning pads at the Greenhead Base decommissioning facility in the Lerwick Harbour.
John Lawrie Decom, a subsidiary of metal recycling and industrial decommissioning specialist John Lawrie Metals, was sub-contracted by Ocean Kinetics to downsize four Buchan Alpha FPU pontoon structures and associated steelwork.