DeepOcean has completed a contract to provide maintenance to a tidal stream facility and has finished a subsea decommissioning project, both offshore Scotland
Siem Offshore’s 2013-built Siem Day offshore subsea construction vessel has reinstalled an Andritz Hydro Hammerfest tidal turbine generator at SAE’s MeyGen project in Pentland Firth, offshore Scotland under DeepOcean’s management.
The offshore workscope, undertaken 23-28 June, included installing connection components on the subsea foundation, cable rerouteing works and installing the turbine.
In addition, DeepOcean provided subsea services using a remotely operated vehicle after it was mobilised from the Nigg Energy Park. It helped to execute the offshore work, then managed the demobilisation back to the park.
Siem Day, a 121-m, STX OSCV 11L design vessel, installed the turbine in slack tidal conditions in water depths of 35-42 m.
DeepOcean delivered the project as a subcontractor to Normandie Hydroliennes, which used Proteus Marine Renewables offshore service staff on secondment.
The MeyGen tidal stream project is located between Scotland’s northernmost coast and the island of Stroma, producing power from the water flowing between the North Sea and the Atlantic Ocean.
“We performed the work in an area with heavy currents, which our vessels and subsea equipment are fit to handle,” said DeepOcean project manager Per Thuestad.
“Compared with offshore wind, tidal power has largely gone under the radar. However, the global potential for tidal power is huge – as it is a highly predictable renewable energy source.”
In the central North Sea, DeepOcean completed a significant decommissioning project for an unnamed client, reaching a 98% recycling rate for the removed subsea infrastructure.
During a six-month campaign, DeepOcean recovered 9,000 tonnes of subsea equipment from three oil and gas fields and recycled or re-used this through its key waste management provider for the project.
As part of this decommissioning, DeepOcean removed a nine-leg mooring system of a floating production storage and offloading (FPSO) vessel and recovered flexible risers, umbilicals and a mid-water arch release and tow.
It also removed various piled and non-piled structures, including production manifolds and a subsea safety isolation valve module, concrete mattresses, general debris and subsea rock installation.
Several vessels within DeepOcean’s fleet were used during the six-month campaign, although most of the work was completed by Normand Jarstein and hybrid battery-powered vessel, Edda Freya.
This work included recovering more than 700 concrete mattresses to Normand Jarstein using the UTROV mattress recovery system, with no dropped objects.
To remove the FPSO mooring system, DeepOcean performed the pump-out and recovery of three 7-m diameter suction anchors, weighing around 110 tonnes, onto Edda Freya.
More than 3-km of studless mooring chain and around 8-km of spiral strand wire were also recovered. DeepOcean conducted the external dredge and cut of the remaining six 5-m suction anchors at a depth of 3 m below the seabed.
The campaign was project managed and engineered from DeepOcean’s Aberdeen office, with further support from the company’s Haugesund and Stavanger offices in Norway.
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