WATCH: Allseas vessel on decom quest carries out this year’s largest single lift in North Sea

August 14, 2025, by Melisa Cavcic

EnQuest, a London Stock Exchange-listed energy firm, has tucked a new decommissioning milestone under its belt in the UK sector of the North Sea, thanks to the assistance received from a heavy lift vessel owned by Allseas, an offshore pipeline installation, heavy lift, and subsea construction contractor.

Allseas' Pioneering Spirit removes Heather Alpha topside; Source: EnQuest

Following regulatory approval in May 2020, the firm awarded the Heather topsides removal contract in September 2022 with a single lift operation scheduled for 2025. The Heather jacket removal scope was subject to a separate process.

After AquaTerra was hired by Allseas last year to support an engineering, preparation, removal, and disposal (EPRD) project on EnQuest’s Heather Alpha platform, the firm’s scope of work entailed providing engineering, fabrication, access, and construction teams to carry out underdeck preparation for topside removal.

According to the North Sea operator, the completion of the topsides heavy lift represents “a major decommissioning milestone.” This removal of the Heather Alpha topsides was carried out on August 11, 2025, with the Allseas-owned Pioneering Spirit heavy lift vessel, which removed the 15,300 tonne topsides in a single lift, the largest single lift planned in the North Sea this year.

The topside was part of the Heather oil field’s infrastructure in the UK sector of the northern North Sea, 458 km north-northeast of Aberdeen, where production of oil started in 1978 and ceased in 2019 to undergo decommissioning. This builds on EnQuest’s decommissioning history, encompassing the plugging and abandonment of over 80 North Sea wells in the past three years.

The UK player describes the heavy lift operation as the culmination of significant planning, engineering, and offshore preparation work undertaken by its in-house decommissioning team, working alongside Allseas and other specialist contractors. The Heather topsides are currently in transit to Frederikshavn in Denmark, where dismantling will take place with a continued focus on safe operations.

John Allan, EnQuest Decommissioning Director, highlighted: “The removal of the Heather Alpha topsides is a tremendous accomplishment for the EnQuest team, as well as our colleagues at Allseas and across the project support network.

“The Pioneering Spirit completed the lift in around 14 seconds, but that astonishing reality was only made possible by three years of meticulous planning, engineering and preparation works.”

According to EnQuest, more than 95% of the structure is expected to be recycled and repurposed, ensuring maximum material recovery and minimizing the carbon footprint of the project.

“After almost 50 years of operations in the North Sea, Heather Alpha’s legacy is to be an exemplar of a best-in-class decommissioning project, from inception to the responsible recycling of its materials,” emphasized Allan.