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By Alastair HamiltonAugust 30th 2020
Alastair Hamilton

The decommissioning of the many North Sea oil production platforms presents a challenge. They’re huge, heavy structures, so how is it done? People in Shetland have just had an opportunity to find out the answer to that question.

The port of Lerwick has identified oil platform decommissioning as a business opportunity and some work has already been undertaken. However, the project now under way, which involves dealing with the redundant Ninian North platform, represents a step change in scale.

On Friday, 28 August, local residents and visitors were greeted by the sight of the world’s largest construction vessel, Pioneering Spirit. The huge ship can install or remove oil platforms with astonishing speed and efficiency.

Earlier in the week, the vessel had sailed to the Ninian field, about 100 miles north-east of Shetland. Its equipment allowed the topsides of the platform – essentially, everything above the supporting legs – to be cut free and lifted aboard, which is no small task given that the platform weighs 14,200 tonnes.

In what was its first visit to a British port, the ship then made for the Dales Voe base in the north of Lerwick’s harbour. Overnight, the platform was lowered onto a very large barge, Iron Lady and then transferred to a new, heavy-duty decommissioning pad developed by Lerwick Port Authority. By then, the Pioneering Spirit was well on her way back to the Netherlands.

The new facilities expand the capability to keep UK sector decommissioning projects in the UK. In Lerwick, the dismantling will be undertaken by leading contractors, Veolia/Peterson, creating and sustaining jobs and investment in the local economy. The aim is that 97% of the platform will be recycled.

Lerwick Port Authority were understandably very pleased to have brought their decommissioning capacity to this level. Its Chief Executive, Captain Calum Grains, said: "The arrival of the Ninian Northern topside at our Dales Voe Base is a welcome boost to activity in Shetland amidst the Covid-19 downturn and another very important stage in the development of Lerwick's reputation as an active, leading centre for decommissioning.

"The pad is a significant addition to our unique quayside infrastructure, not only as a catalyst for handling larger offshore structures, but also in attracting the interest of the renewables sector for future projects, particularly floating offshore wind developments.

“The scale of the topside, the single-lift delivery and the infrastructure already in place adds weight to the widely-accepted case for Lerwick to be the location of an Ultra-Deep-Water Quay in the UK for even bigger projects in the competitive international decommissioning and renewables industries. The proposal has strong Government and industry support."

The Port Authority’s vision for the future includes enabling bigger, deeper-draft vessels to berth, includes further dredging at Dales Voe to complement the planned Ultra-Deep-Water Quay.

Investment by the Port Authority has been backed by the Scottish Government, Highlands and Islands Enterprise and Bank of Scotland who have provided financial assistance for the quay development at the base, as well as the decommissioning pad.

Audrey MacIver, Director of Energy and Low Carbon for Highlands and Islands Enterprise, said: “The foresight and commitment by Lerwick Port Authority to invest in critical infrastructure continues to bring benefits to Shetland and the wider Scottish supply chain. This latest arrival is particularly timely given current challenges being faced by the oil and gas industry and the associated supply chain.

“Building on existing strengths and expertise, Dales Voe is firmly establishing itself as a key UK facility for serial, large scale offshore decommissioning, ensuring Shetland continues to play an ever increasing role in the country’s energy transition.“

The decommissioning pad, designed and project-managed by Arch Henderson and constructed by local company, Tulloch Developments, has an impermeable surface and a 60 tonne per square metre load which matches the quayside capacity. Unique to the quayside design is an 800 tonne per metre line loading for transfer of the topsides from the barge across the quayside.

The twin-hulled Pioneering Spirit is a very impressive vessel. Built in South Korea, and 382 metres long and 124 metres wide, she displaces 365,000 tonnes and has a maximum draft of 27 metres. The cost of construction was €2.6 billion (£2.3 billion). When seen from the front, she resembles a catamaran. Between the two hulls, there is a space that’s 122 metres long and 59 metres wide, which enables her to sail in and straddle the platform. Eight sets of horizontal lifting beams then enable the platform topsides to be lifted clear of the platform’s legs.

In the case of Ninian Northern, it took two hours to connect the beams to the platform in preparation for the lift, which took only seven seconds. At the destination, the topsides are lowered onto a barge, from which they are transferred ashore.

However, the vessel has many other capabilities. There is a 5,000 tonne special-purpose crane that can be used lighter lifts and she can also install and remove jackets and lay deep-water pipelines. Over this season, she has removed 57,000 tonnes of redundant platform, the equivalent of eight Eiffel Towers.

You can read more about the vessel and the Ninian Northern removal project here and you can find out about Lerwick Port Authority here.