Much of the team’s energy and effort was put into finding the best engineering solution to refloat the platform in the safest way possible. There were two main engineering challenges: one was to ensure a controlled extraction from the seabed and the other was to ensure an even distribution of weight on the topsides so that the platform would rise vertically.
The plan was to pump seawater beneath each of the three tanks and build up the pressure so that the bases would be freed gradually from the seabed. Simultaneously, the three tanks would be deballasted to lighten the platform (as the water was pumped out, nitrogen was pumped in to maintain structural integrity). Before the refloat operations began, a surcharge of gravel and rock was placed around each of the bases to prevent the seabed soil eroding and allowing the water being pumped beneath the bases to escape, thereby reducing the pressure.
The refloat operations for the platform began on 18 June 2001 with the deballasting of the tanks at a very slow rate during the following five days. The deballasting continued until neutral buoyancy had been reached. The under-base pumping then began and the skirts around the bases began to rise from the seabed. After two hours of careful deballasting and pumping, the tops of the three tank domes broke the surface of the water. On 26 June the platform reached a towing draft of 63 metres and was then towed by six tugs to Stord on the West coast of Norway.
The ALC was similarly refloated on 3 July 2001 and towed to Stord in Norway where it was moored near to shore. Although the operation was much less complex, the same care and attention was given to detailed engineering plans to refloat the column. At 10,000 tonnes the ALC is the heaviest structure, apart from the Maureen platform, to be decommissioned in the North Sea to date.
The Moira wellhead cage and infrastructure were recovered in sections from the seabed and brought to shore in Scotland for recycling or disposal as were the pipelines and umbilical