Scottish firms Ocean Kinetics and Green Marine (UK) have formed a JV to decommission OpenHydro’s tidal energy platform in the Orkney Islands.
Work is rapidly advancing to remove the steel superstructure installed in 2006 at EMEC’s Fall of Warness test site which OpenHydro used to streamline its tidal turbine technology development.
EMEC awarded the decommissioning contract in early April.
The OpenHydro test rig consisted of two steel piles drilled and grouted into the seabed, with a steel superstructure attached to the piles to provide a working area.
The turbine component was previously fixed to the piles using two steel collars, which allowed the unit to be raised and lowered into the tide using two 15 tonne hydraulic winches.
The decommissioning work scope involves the entire removal of the steel superstructure, Diamond Wire Cutting of the piles, along with cable disconnection and termination.
For the task Ocean Kinetics is providing divers, riggers, welders & ROV services, while Green Marine is providing offshore management, the Green Isle vessel, moorings & operational cable experience.
Both firms are sharing responsibilities for operational engineering, cutting and heavy lift operations, where they benefit from significant experience managing a wide range of marine works – including subsea servers, port gates, aquaculture equipment and sunken barges (reaching 1000 tonnes in weight) and decommissioning of the Buchan Alpha platform.
To date, the OpenHydro superstructure has been broken down into a series of smaller components for removal from its static base following a series of lifts performed by the Green Isle.
Green Marine operations manager Terry Norquay said the entire topside infrastructure has now been successfully removed with work imminently progressing to the pile removal and cable termination.
He added: “The OpenHydro project has demanded a strong understanding of operations within harsh marine environments combined with solid preparation and execution.
“While Green Marine and Ocean Kinetics offer a broad range of marine services, this particular job demonstrates the turnkey solution we offer specifically for subsea superstructure removal projects.”
Work is currently being undertaken during Neap tides with water speeds approaching 6 knots (3 metres per second).
Engineering teams are aiming to capitalise on slack tide windows, when the water changes direction and flows at a much slower speed (0.5 metres per second), allowing operation in calmer conditions.
Ocean Kinetics marine projects manager Roger Goudie said: “This project cements Ocean Kinetic’s status as a leader of offshore decommissioning works.
“Our experienced rope-access-trained decommissioning team have worked alongside the Green Marine crew to safely deconstruct the topside structures and prepare the piles for removal.
“We have also had our dive team working onsite which proves the skills offered by Ocean Kinetics given the tidal nature of the site.”
In order to complete the final elements of the decommissioning project, the Green Isle will be spread moored, in a four-point mooring configuration – requiring significant planning – in order to remain stationary in the tide and allow divers to safely enter the water.
Under the marine licence which allowed OpenHydro to operate, the seabed must be returned to its original condition, which means cutting each pile foundation flush to the seabed.
To achieve this result diamond wire cutting machines will be turned upside-down to create an optimal finish.
OpenHydro was the first developer to use the tidal test site at the Fall of Warness off the island of Eday when its test rig and 250kW open centred turbine were installed in 2006.
The device was the first tidal turbine to be grid-connected in Scotland and subsequently the first to successfully generate electricity to the national grid in the UK.