US contractor McDermott is making its return to the North Sea market with the contract for key facilities for the Total-operated Danish Underground Consortium’s (DUC) Dkr21 billion ($3.21 billion) Tyra redevelopment project off Denmark.

Total and its DUC co-venturers embarked on the Tyra redevelopment after seabed subsidence threatened the integrity, and potentially the future safety, of the facilities at the field that processes more than 90% of Denmark’s gas production.

“The key challenge that the redevelopment of Tyra is overcoming is seabed subsidence,” Morten Hesselager Pedersen, Total vice president and head of the Tyra redevelopment project, says.

“Ever since we started extracting the gas, which started more than 30 years ago back in 1984, the production of gas has essentially impacted the underground and, at this point in time, the total compaction is between five and six metres at Tyra,” says Pedersen, who headed up the project at Maersk Oil prior to the company's acquisition by Total earlier this year.

“This means the platforms are essentially sitting five to six metres lower than they did when they were initially installed. It is subsiding relatively evenly across the main Tyra area. [However], the reduced distance between the sea level and the platform is a challenge that we have obviously known about for many years.

“We have done a lot of work, a lot of investments to mitigate the subsidence, but a couple of years ago we decided that now actually it would be necessary to completely redevelop these [platforms] to increase distance to the seabed,” he says.

Main centres

The Tyra field today has two main centres, Tyra East and Tyra West, that also produce from the Tyra Southeast, Harald, Valdemar, Svend and Roar satellites.

The existing gas processing and accommodation platforms on Tyra East and Tyra West will be replaced by one new processing platform and one new accommodation platform.

Meanwhile, the four wellhead platforms and two riser platforms will have their jackets extended by 10 metres and the existing topsides will be replaced with new facilities, extending the life of Tyra by at least another 25 years.

McDermott’s workscope comprises the engineering, procurement, construction and commissioning of two packages.

The first EPCC contract is for gas processing topsides for the Tyra East G (TEG) platform, two connecting bridges and a flare.

Package two involves wellhead topsides for the Tyra East B and C platforms, a riser topsides for the Tyra East E platform, four connecting bridges and six module support frames.

The unmanned satellite platforms in the area have not been affected by subsidence and will therefore not be redeveloped.

However, production from the satellite fields will be temporarily shut-in during the redevelopment work.

Production from Tyra is expected to be temporarily stopped in November 2019 to enable the removal, renovation and redevelopment of the facilities.

“The decommissioning scope has been split into two different contracts. Essentially we will be removing approximately 50,000 tonnes of steel from the North Sea, equivalent to seven Eiffel Towers in weight,” says Pedersen.

“A major piece of this work is the existing process and accommodation platforms on Tyra East and West. They will be removed by Allseas utilising Pioneering Spirit,” he says, referring to the world’s largest construction vessel.

The vessel, which can remove large decommissioned platforms in a single lift, is set to arrive in 2020, remove the existing platforms and sail the structures to a disposal yard in a city in the north of Denmark.

Up to 97% of the materials from the removed Tyra structures are expected to be recycled and reused, according to Pedersen.

“We will be monitoring this very, very closely to make sure we understand where the materials are moving, and making sure that they are disposed of in compliance with legislation,” he says.

First steel for this project, for which McDermott will deliver structures totalling 33,000 tonnes, was cut in October at the company’s Batam Island yard in Indonesia.

Riser platforms

The wellhead and riser platforms are due for delivery from McDermott in February 2020 and the TEG facilities in February 2021.

The new jacket is being constructed in Spain by Dragados, while Heerema has been awarded the contract to install the structures at Tyra, located around 220 kilometres west of Esbjerg, Denmark.

The new facilities are intended to have an average 28-metre clearance between the sea level and the lowest part of the platforms’ topsides.

Dutch contractor Royal Boskalis Westminster in October won the Tyra redevelopment subsea installation phase two contract.

This includes subsea engineering, procurement, fabrication and installation work.

Boskalis will provide a range of specialist subsea contracting activities for relocating and connecting subsea pipelines, as well as the installation of manifolds, vertical platform production risers and umbilicals.

Engineering and procurement will be carried out from the contractor’s offices in Papendrecht and Aberdeen, as well as in Esbjerg, Denmark prior to the project's execution.

The high-end diving support vessel Boka Atlantis, which was recently added to Boskalis’ fleet, will carry out most of the offshore workscope.

Once the new facilities are installed and operational, Tyra’s production capacity will be 300 million cubic feet per day of gas.

It will have an oil treatment capacity of 40,000 barrels per day, which will be fully utilised at start-up.

At its peak production of 60,000 barrels of oil equivalent per day, Tyra will produce natural gas corresponding to the needs of 1.5 million Danish homes.

Partners’ current equity in the DUC is operator Total on 31.2%, Shell on 36.8%, Chevron on 12% and Danish state-owned Nordsofonden on 20%, although Total announced in September it is acquiring US supermajor Chevron’s stake.

“The announcement to buy Chevron’s 12% stake is a demonstration of our commitment to Denmark,” says Goffart.

Anglo-Dutch supermajor Shell the following month revealed its exit from Denmark, with Norway’s Noreco the purchaser of all its assets, including the Tyra interest.

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Total picks up pace on Tyra redevelopment