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This floating drilling unit has pontoons and columns that, when flooded with seawater, cause the pontoons to submerge to a predetermined depth. Although it is moved by wave action, it sits low with a large part of its structure under water. This, combined with eight huge mooring anchors, make it a very stable installation and the preferred choice for exploring the North Sea and the new wells west of Scotland.

There can be over one hundred people on board and although smaller than a platform, conditions are usually good.

This type of rig makes its money by drilling a hole in the seabed then it moves to the next location. There is often an urgency to get things done quickly. With advancing technology some semi submersibles can drill in water depths over five thousand feet.

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This immobile structure can be built from concrete or steel and rests on the seabed. When oil or gas is located a platform may be constructed to drill further wells at that site and also to produce the hydrocarbon. Although some platforms can be small, most are massive compared to the other types of installations.

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This is a mobile drilling rig, different to the semi submersible. Instead of floating over its drilling location the Jackup has long leg structures, which it lowers to and into the seabed raising the rig out of the water. The obvious limitation with this type of installation is the depth of water it can operate in. The maximum being five hundred feet. Surprisingly, many areas of the North Sea are not too deep for this type of installation to operate.

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As the name suggests this is a ship shaped drilling vessel. Unlike the semi submersible and the Jackup, it does not require tugboats to tow it to location. Although they are not as stable as semi submersibles they also drill in very deep waters.

This is usually a converted semi submersible. It is attached to a platform by a long gangway to provide extra accommodation. This, along with the usual leisure and catering facilities, is their only task. They do have a marine crew in charge of stabilizing the installation.

They are usually converted takers or purpose built units although semi submersibles have also been used. They are attached to a seabed well head and they produce and store the oil until another tanker takes it from them. They are used to produce from small wells where it would be too expensive to build a platform.