Draugen oil platform3/10/2024 ![]() Since it made people nervous and had no practical significance, the plumb was eventually removed and the workforce became used to the motion. “A plumb line hung from the ceiling there, and moved in big figures of eight,” Jenssen relates. It had been known that skyscrapers could oscillate many metres in strong winds, and the Draugen structure was expected to behave similarly in response to wind and waves.īut this platform was the first design of its kind, with only a single shaft, and the swaying created a good deal of concern among control room staff. Installed in 250 metres of water, the platform ended up 0.3 degrees out of true – which added up to a horizontal offset of 1.5 metres at the topside height of 300 metres.Īlthough this was a very small deviation, it was enough to create a few problems for guiding the ROVs through the narrow aperture in the various intermediate decks.Īnother issue was that the platform started to sway once it was finally in place. ![]() The mini-cell contained piping positioned beneath the other storage cells for pumping out grout in order to fill the spaces beneath the GBS and stabilise the ground. This extended upwards from a depth of 250 metres to 180 metres. The latter contained about 70 metres of water during towout, while a big tank also held ballast water.Ī concrete pipe with a square cross-section ran down the centre of the shaft to a “mini-cell” at the base of the platform. Like the other Condeep concrete platforms, the Draugen GBS had cylindrical storage tanks clustered around the central shaft. The view was great while deballasting the platform in calm and beautiful weather.” “We Subsea Dolphin operators were on board during the towout ,” recalls Jenssen. The ROV pilots wanted to insert wooden wedges in the holes to prevent the slamming, but the engineers from builder Norwegian Contractors maintained that this motion was as it should be. This in turn generated vibrations and a “bong, bong” sound almost like church bells. ![]() That meant the tubing which ran from the base of the structure through holes in the intermediate decks banged against the sides of these apertures. Preparing for internal ROV work while readying the platform for tow-out proved a special experience because of the motion in the shaft, which was several hundred metres tall. These devices were used inside the GBS because the shaft was filled with seawater once the platform had been installed on the field, and they could therefore move around as required. Fotnote: Arild Jenssen in conversation with Kristin Øye Gjerde, 31 March 2016. Arild Jenssen, one of the company’s ROV pilots, remembers this phase well. Subsea Dolphin was involved as early as the latter stage. The lower part of the GBS had been cast at Hinnavågen in Stavanger, while slipforming of the tall monotower shaft took place in the deep fjord at Vats further north. Finally, the spar was laid down in the dock for further dismantling.All the hatches at the bottom of the Condeep concrete gravity base (GBS) structure were to be opened with the aid of remotely operated vehicles (ROVs). After completion of the down ending into the horizontal floating position, the spar was transported to the Kvaerner dry-dock, suspended in the Rambiz cranes. Subsequently, the Rambiz lifted the bottom end, while a tug controlled the heading of the top of the spar coming down. A subsea lifting frame was installed at the bottom end of the spar. First the Rambiz lifted the helideck and topside from the spar. Eager.one positively assessed Scaldis’ plan which included our previous recommendations. Decommissioning of the Draugen FLPĪfter a contractor switch, Scaldis got the job with its HLV Rambiz. One of the ideas was a lifting frame, like a bucket, at the bottom end of the spar. We produced a full report with notes, comments and possible solutions to Shell. The contractor’s plan did not take into account the structural integrity, how the spar was installed originally and the damage in the spar-middle. After this research we concluded that reverse installation wasn’t possible as the plan suggested.”Įager.one handed over a comprehensive report advising against the proposed plan. By climbing the spar I noticed damage, which we certainly had to include in our calculations. We have extensively studied the Draugen FLPs’ history: how the FLP was filled with ballast water and iron ore and how the FLP was constructed. The fjords are incredibly deep and the spar looked like a little bobber in the big fjord. Hubert: “It was a great decommissioning project to support. For a total insight our senior project engineer Hubert Boter visited the FLP.
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