Located around 225 kilometres west of Jutland, the Tyra field has been supplying Denmark with natural gas since 1984 – and right now, great changes are under way at the field.
Production of gas from the field has resulted in the seabed subsiding by more than 5 metres. This has naturally resulted in the production facilities subsiding as well, and this subsidence – combined with new knowledge about the effects of waves on the platforms – may have consequences for safety. All the facilities on the Tyra field therefore need to be removed. New facilities are installed, and some of the jackets are reused in the new design. This allow production to continue safely.
The Tyra field is one of the fields in the Sole Concession Area managed by the Danish Underground Consortium (DUC), a joint venture involving Total, Noreco and Nordsøfonden. Total is operator of the field with a share of 43.2%, while Noreco holds a share of 36.8% and Nordsøfonden 20%. In 2017, the DUC decided to invest DKK 21 billion in redeveloping the Tyra field facilities. This constitutes the largest single investment ever made in the Danish area of the North Sea, and the total investment is comparable with that made in the Cityringen phase of the Copenhagen Metro, which amounted to DKK 25 billion.
Production of gas from the Tyra field was suspended in September 2019. Most of the installations at the field were dismantled in June 2020, and the two giant process facilities are scheduled for removal in August. This will mark a major milestone in the project. The plan is to install new facilities at the Tyra field in 2021, which would allow production to resume in 2022.
A great deal of work was required to prepare the removal of installations from the field. The project involved closing more than 50 wells and rerouting a number of pipelines. Following shut-down of production, all installations were completely emptied of gas and oil. The equipment and systems were then readied for removal. As a part of this work, pipes and cables had to be disconnected to make it possible to lift large modules, bridge connections and entire well-head modules off their substructures. It was also necessary to attach pad-eyes to the installation sections.
The work to lift the giant facilities required bringing in Sleipnir, the biggest floating crane in the world. The crane, which is owned by the Dutch company Heerema Marine Contractors, entered into service in 2019. The barge is a massive 220 metres long and 102 metres wide, giving it a total surface area larger than three football pitches. Sleipnir is equipped with two cranes, each with the capacity to lift 10,000 tonnes. The elements that Sleipnir is to lift at the Tyra field comprise bridges, bridge modules and wellhead topsides weighing up to around 3,600 tonnes.
The two biggest integrated accommodation and process modules are scheduled for removal in August 2020. Pioneering Spirit, the largest construction vessel in the world, has been booked for the assignment. This is a twin-hull ship measuring 382 metres long and 124 metres wide. Owned by Allseas, Pioneering Spirit was commissioned in 2016 and can lift loads of up to 48,000 tonnes. The two units at the Tyra field that Pioneering Spirit is to help remove weigh 7,500 tonnes and 14,000 tonnes, respectively.
The decision was made to remove the old installations in large “chunks”, and then dismantle them onshore. This will make it possible to perform the disassembly work more efficiently. Performing the operation on land will also ensure that the work can be carried out under conditions that are easier to control than if the work were done at sea.
The installations removed by the Sleipnir crane will be sailed to the Netherlands for disassembly. The two process and accommodation modules will be sailed to the port of Frederikshavn in Denmark for disassembly.
It will be possible to recycle the vast majority of the materials from the old installations. Metal parts will be melted down and reused as scrap steel, while other materials will be recycled and reused as far as possible.