The Troll A platform is a condeep offshore natural gas platform in the Troll gas field off the west coast of Norway. It is the tallest construction that has ever been moved to another position, relative to the surface of the Earth, and is among the largest and most complex engineering projects in history. The platform was a televised sensation when it was towed into the North Sea in 1996, where it is now operated by Statoil.
The Troll A platform has an overall height of 472 metres, weighs 683,600 tons (1,2 million tons with ballast)and has the distinction of being the tallest structure ever moved by mankind. The platform stands on the sea floor 303 metres (994 feet) below the surface of the sea and each of the continuous-slip-formed concrete cylindrical legs has an elevator that takes over nine minutes to travelfrom the platform above the waves to the sea floor. The legs use groups of six 40 metres (130 ft) tall vacuum-anchors holding it fixed in the muck of the sea floor.
The walls of Troll A’s legs are over 1 metre thick made of steel reinforced concrete formed in one continuous pour (See Slip forming) and each is a mathematically joined composite of several conical cylinders that flares out smoothly to greater diameters at both the top and bottom, so each support is somewhat wasp-waisted viewed in profile and circular in any cross-section (see picture at right). The concrete legs must be able to withstand intense pressure so are built using a continuous flow of concrete, a lengthy process that takes 20 minutes per 5 cm laid.
Troll A was built by Norwegian Contractors for Norske Shell, with base construction beginning in July 1991.The base and the deck were built separately, and were joined in 1995 while the base was partially submerged. The base is a Condeep gravity base structure built from reinforced concrete.
The Troll platform was towed over 200 kilometres (120 mi) from Vats, in the northern part of Rogaland, to the Troll field, 80 kilometres (50 mi) north-west ofBergen. The tow took seven days.
In the fall of 2010 the Troll A platform was expanded with a new module. This module contains living quarters and a new control room. The new control room and expanded facilities are needed to support the new compressors (a 4th and 5th are planned). These compressors are needed due to the dropping reservoir pressure in the wells.
Gas rises from 40 wells, and is exported through a number of pipes. Troll A is scheduled to receive two additional gas compressors to increase production volume and compensate for dropping reservoir pressure in the wells.
In 1996 the platform set the Guinness World Record for ‘largest offshore gas platform’.
In 2006, the 10th anniversary of Statoil’s operatorship of Troll gas production was celebrated with a concert by Katie Melua held at the base of the Troll A platform. As well as entertaining the workers on the rig, the concert set a new world record for the deepest underwater concert at 303 metres below sea level.