Rising gas

Smit Heavy Lift’s 1,600 tonne capacity floating sheerlegs Taklift 4 played a major role in the recently completed offshore phase of the decommissioning of a gas platform in the Dutch sector of the North Sea.

The removal project involved the P14-A satellite gas platform operated by Wintershall Noordzee BV. P14-A was installed in 1993. It consisted of a four-leg jacket, secured by four main foundation piles, together with a drill deck and topsides. The contract was awarded to Smit Marine Projects in December 2007 and work began in May 2008.

With the removal offshore completed in early July, the onshore scrapping of the drill deck and jacket is scheduled to conclude in November. Meanwhile, the topsides are to be refurbished, for continued service offshore.

The offshore work programme, including the cutting of piles 6 m below the seabed, was completed with minimal weather downtime, due to the fact that Taklift 4 was equipped with the newly-developed Ampelmann access system.

Despite repeated episodes of bad weather, the decommissioning team was able to complete on schedule, thanks to the Ampelmann unit. The P14-A project marks the first commercial use of this system, which allowed safe access from Taklift 4 to P14-A in conditions that would have been unworkable with conventional access equipment.

Development

The Ampelmann system was developed in a joint project involving Smit, offshore contractors Heerema and the University of Delft in the Netherlands. Operational trials offshore were judged a complete success and the Smit tender for the P14-A contract was based on its use.

The topsides, with a total weight of 650 tonnes, included a heli deck, drill deck and cellar deck, mezzanine and main deck, together with the emergency crew quarters. The 500 tonne jacket consisted of four-piled legs, complete with the pre-installed conductors, caissons, boat landing and riser tubes. The four foundation piles each weighed in at 65 tonnes.

During the removal works Taklift 4 was also used to accommodate the crew and project personnel, together with the storage of project equipment and materials. The sheerlegs was manoeuvred close to the platform with the assistance of the anchor handler Smit Bronco.

The project team prepared the platform for removal and transport ashore. In the case of the topsides and drill deck, a new pad eye was installed and a further pad eye reinforced. Existing pad eyes under the heli deck were checked, tested and made accessible for connecting up.

Separation

The jacket foundation piles were severed by means of an internal pile-cutting device. The topsides removal had been completed by the beginning of June, with delivery at the NAMI offshore fabrication yard, Ridderkerk.

The drill deck was separated from the topsides on the deck of the Smit flat-top barge E3505, following loading by Taklift 4. Subsequently, the drill deck, jacket and substructure were taken, by barge, from Rotterdam to a scrapping facility at Heerenhoek, near Vlissingen, the Netherlands.

The topsides lift was the more complex of the main lifting tasks for Taklift 4. In this instance, the major lift was performed with the 30 m jib rigged. During this and all other principal lifting tasks, the weather conditions offshore remained excellent.

There were, however, successive periods of poor weather, beginning with the first weekend of mobilisation. A summer storm hit the Dutch coast, but the Smit team continued operating despite winds of up to BF 7 and significant wave heights up to 3 m. In this period the team recorded three hours of downtime, rather than the four days that would have been lost, had a traditional gangway been used.