Ketch and Schooner gas fields are located in the Southern Basin of the UK Continental Shelf (UKCS) in licence blocks 44/28a and 44/26a, respectively, 26km away from the Murdoch installation in the North Sea.
The Ketch and Schooner gas fields, comprising 20 platform wells and a subsea well, are owned by the operator DNO North Sea, a wholly-owned subsidiary of Norwegian oil and gas company DNO, along with the partner Tullow Oil SK, an oil and gas company based in the UK.
The companies decided to decommission the fields as they could not find a feasible solution to extend their economic life after considering several technical and commercial solutions.
The companies ceased production from the fields in August 2018, following the termination of operations at the onshore Theddlethorpe Gas Terminal, which was owned and operated by ConocoPhillips on the Lincolnshire coast, England.
The decommissioning programmes for the fields were submitted to the Department for Business, Energy and Industrial Strategy (BEIS) for approval in July 2019.
Hague and London Oil (HALO) was awarded the Schooner field in licence block 44/26a in December 2020. It plans to reactivate Schooner, with the production planned to be re-directed to the Western Gas Transmission system and the Den Helder processing facilities (WGT) in the Netherlands.
Details of Ketch and Schooner gas fields
The Ketch platform is a normally unattended installation (NUI), which was installed at a water depth of 54m in 1998. The platform used to export gas to the Murdoch platform via an 18in diameter export pipeline, while a trunk line was transporting gas from the Murdoch platform to the Theddlethorpe Gas Terminal.
The topsides of the Ketch installation weigh 2,179t while the jacket and the piles weigh 1,550t and 690t, respectively. The topside is made of a conventional carbon steel structure, featuring a sub-cellar deck, cellar deck, a mezzanine deck and a top deck with a helideck situated above it.
The field has 12 well slots of which nine were drilled. The jacket is a conventional four-legged skirt piled steel structure with overall base dimensions measuring 20m long and 22m wide.
The Schooner platform is also a NUI installed at a water depth of 71m in 1996. It used to export gas to the Murdoch platform through a 16in line, from where a trunk line was transporting gas to the Theddlethorpe Gas Terminal.
The topsides of the Schooner installation weigh 2,375t while the jacket and the piles weigh 2,021t and 694t, respectively.
The Schooner platform also has 12 well slots, of which 11 were drilled. Both platforms have an accommodation capacity of 12 personnel plus two flight crew and feature a temporary overnight shelter.
Ketch and Schooner gas fields decommissioning details
The decommissioning programmes of the two fields will be implemented under a six-year project.
The Ketch decommissioning plan includes the decommissioning of an installation and two pipelines while the programme for the Schooner field includes the decommissioning of two installations, comprising one platform and one subsea wellhead, and two pipelines.
The wells will be plugged and abandoned in accordance with the regulatory standards of the UK Government’s Health and Safety Executive (HSE). The programmes will also meet the regulatory requirements of Oil & Gas UK, a trade association, and the Oil and Gas Authority (OGA), a regulatory body of the government.
The pipelines will be flushed and left buried in situ. The topsides, jackets, and subsea installations will be removed and transported onshore for proper disposal and will be re-used or up to 97% of the infrastructure will be recycled.
Heerema Marine Contractors received a decommissioning contract for the Ketch and Schooner platforms in January 2022. The company is responsible for the integrated engineering, preparation, removal and disposal (EPRD) of the Ketch and Schooner installations.
Well-Safe Solutions, a well-decommissioning services provider based in the UK, was appointed to provide engineering, contractor management and logistics for the decommissioning project.