A Tension-leg platform
or Extended Tension Leg Platform (ETLP)
is a vertically moored floating structure
normally used for the offshore production of oil
, and is particularly suited for water depths greater than 300 metres (about 1000 ft) and less than 1500 meters (about 4900 ft). Use of tension-leg platforms has also been proposed for wind turbines.
The platform is permanently moored by means of tethers or tendons grouped at each of the structure's corners. A group of tethers is called a tension leg. A feature of the design of the tethers is that they have relatively high axial stiffness
), such that virtually all vertical motion of the platform is eliminated. This allows the platform to have the production wellheads
on deck (connected directly to the subsea wells by rigid risers), instead of on the seafloor
. This allows a simpler well completion
and gives better control over the production from the oil
or gas reservoir
, and easier access for downhole intervention operations.
TLP's have been in use since the early 1980s. The first Tension Leg Platform was built for Conoco's Hutton field
in the North Sea in the early 1980s. The hull was built in the dry-dock at Highland Fabricator's Nigg yard in the north of Scotland, with the deck section built nearby at McDermott's yard at Ardersier. The two parts were mated in the Moray Firth in 1984.
Larger TLP's will normally have a full drilling rig on the platform with which to drill and intervene on the wells. The... Read More