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Jotun 09/11/2016

Bentley Systems 10/11/16

Damen introduces decom design

Offshore Marine Technology: 3rd Quarter 2016

Decommissioning’ may well become the next big buzzword for the offshore oil and gas sector, as it seeks new escape routes from the current market doldrums.

According to a recent survey commissioned by industry association Oil and Gas UK, an estimated £17 billion (US$25 billion) will be spent on decommissioning in the North Sea over the next 10 years – a programme that will cover around 80 ageing fixed/floating installations and require the plugging of approximately 1,200 wells, not to mention associated pipelines.

Some industry players are now hoping that vessels previously used to install offshore platforms and structures can also be utilised for decommissioning purposes, performing similar roles in ‘reverse motion’. However, unlike with installations, it is important that decommissioning operations take into account factors such as structural integrity and removal loads acting on structures.

Damen Shipyards Group has now thrown its hat into the ring with the unveiling of its latest vessel concept, dubbed the Damen Decommissioning Series. Reflecting on the genesis of this venture, Lucas Zaat, manager for design and proposal in Damen’s Offshore & Transport division, says: “We initiated this project because we felt that we can make a difference in this sector – and it has certainly generated some significant ideas. The decommissioning market is close to our current activities…we are therefore planning to continue with this project and assign specialised personnel to implement it.”

Undergraduate assistance
The basic concept for this new ship type has been developed in-house by Damen undergraduate intern Justin Rietveld; the group is now evaluating the concept before its team of engineers begins to tweak and shape it, in earnest, into an official vessel design. Forthcoming areas of development will cover the vessel’s seakeeping attributes, hull form, DP system, propulsion systems and topside/jacket lift-related equipment – in addition to green ship credentials. Importantly, the group stresses, the finalised design should prove “catchy”, in order to attract players in the decommissioning sector.

Damen has also joined the DECOM UK industry association, to expand its knowledge and build up contacts within the European offshore decommissioning market.

“The research started off with the idea of developing a decommissioning vessel based on Damen’s existing portfolio,” says Rietveld. “However, we soon found out that the market needs more; for example, there are many different activities within the decommissioning sector. This vessel can support a vast number of those. [Our concept will] cover the bigger part of this new and exciting market.”

What could we be looking at, then? Damen hints that the forthcoming class will feature a 60-person complement, although an ‘accommodation version’ of the vessel, capable of housing up to 150 people and featuring an offshore access system and helideck, is also an option. Damen says: “Initially, it was the intention to keep the vessel as small as possible, preferably less than 85m rule length. However, [following] market analysis, we ascertained that a deck space of approximately 1,000m² was required.”

Ultimately, the goal is to ensure that the new series is capable of undertaking the decommissioning of fixed platforms of up to 1,600tonnes in weight. This should be sufficient to handle more than 50% of existing North Sea fixed platforms, as well as a significant number of offshore installations around the globe, Damen estimates.

“Modular add-ons”
Rietveld, who is currently studying maritime technology at Rotterdam Mainport University of Applied Sciences, has specified a split stern design in order to facilitate platform removal operations. He adds: “This ship will be able to reverse up to a jacket, where it will be ballasted to sink below the platform. Upon deballasting, the vessel will rise up to pick up the platform.”

Damen adds: “Jacket removal remains challenging. However, at this stage, it is anticipated that the recess will also be used for that purpose, possibly in combination with a kind of modular hoisting tower.” This will obviously be progressed further as the group assesses the options and takes into account customer and manufacturer considerations.

To widen the vessel’s window for charter opportunities, the Damen Decommissioning Series will also include a number of “modular add-ons”, Damen says, making the vessel suitable for non-decommissioning-related tasks. As well as the aforementioned accommodation modules and helideck, these will include a mixture of fixed and temporary cranes of varying sizes and lifting capacities.

The stern could also be modified with a temporary platform to create a ‘solid’ shape, should the operator wish to increase aft deck space for the carriage of heavy-duty offshore equipment or components.

For instance, the vessel could use the temporary platform to transport monopiles to an under-construction offshore wind turbine park, before removing the platform and committing the ship to decommissioning work at a nearby fixed oil and gas platform, thereby keeping the vessel in full occupancy.

In terms of propulsion systems, Damen is currently assessing various options. One method would rely on diesel engines and a 6-point anchoring system; an alternative would be a diesel-electric arrangement, running alongside a DP2 system. Alternatively, the new series might adopt LNG power, Damen hints – a move that should confer additional green kudos on the class. In this scenario, the vessel would incorporate deck-stored modular LNG tanks.

In Damen’s own words, “a great deal of work still needs to be done”, but this ambitious project should prove to be well worth keeping an eye on.

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