First came a loud bang, and then a leak which simply increased in scope. We were checking that the concrete shafts and pumps functioned as they should. We had reached the critical trial deballasting of the GBS when it happened. Dag Halstensen, who was NC’s operations manager on the Sleipner A GBS, recalled the fateful events in the local press: A Norwegian Contractors worker seems to remember that a concrete structure stood here. Sleipner East was scheduled to start gas deliveries on 1 October 1993 – but the sinking put the whole schedule under threat. The latter were also ready and waiting nearby to be joined to the GBS, with subsequent assembly hook-up work. Casting the last of these concrete structures had finished and it lay out in the Gands Fjord to be prepared for mating with the steel topsides. Work on Troll A had begun, Draugen was under construction, and Sleipner A was nearing completion. Fotnote: Steen, Øyvind, 1993, På dypt vann: Norwegian Contractors 1973-1993, Norwegian Contractors, Oslo.Īctivity at and off the Hinnavågen GBS construction site in Stavanger was in full swing during the summer of 1991. Work began the following spring on what was described as “a relatively straightforward structure with several challenging production solutions”. The job of building the GBS was awarded to Norwegian Contractors (NC) in June 1988. Sleipner A was the first – and smaller – of two large platforms (the other was Troll A) scheduled to deliver gas under a big sales contract signed in 1986 with European buyers. Photo: Norwegian Contractors/Norwegian Petroleum Museum Unexpected descent The Sleipner A GBS photographed shortly before it sank – and after it had disappeared. Remains were spread over a wide area in water depths ranging from 170 to 220 metres. Fotnote: Ī subsequent survey showed that the GBS was completely smashed and had probably imploded on the way down. Seismic shock waves were registered by several seismological stations around the time of the sinking. The whole mass hit the seabed with great force just under 200 metres down. On its way down, the concrete structure collapsed completely and all the air in its storage cells was forced out – creating a tsunami effect so great that two nearby tugs lost sight of each other. That was enough time to evacuate all the 22 people who had been on board without injury. About 18 minutes later, the Sleipner A GBS went to the bottom. Although the ballast pumps were started immediately, the volume flooding in was much greater than they were designed to handle. The control room recorded almost 1 000 tonnes of water flowing into the drilling shaft. It was quickly established that a substantial leak had occurred. The platform support unit had been almost wholly submerged for its final pressure tests when a loud bang was heard from within by those on board and alongside at 05.49.
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