are four basic types of off shore drilling rigs for exploration:
- These are not used often. They can be in
shallow water locations then ballasted to sit on the bed of the
- Usually used in waters around 160 metres deep. They are
almost always towed to their location an lowered and setup in
ship. These locations look like regular ships but
have a derrick on the top which drills through a hole in the
hole. They are anchored at a certain position and uses
it's computer controlled propellers to continually correct the
ships drift. Often used to drill 'wildcat' wells in deep waters
submersible - These are mobile structures. Their
superstructures are supported by columns sitting on hulls or
pontoons which are ballasted below the water surface. They
provide excellent stability in rough, deep seas.
moveable offshore rigs are mostly used for exploratory purposes because
they are less expensive to use than the permanent platforms.
Once oil or gas is discovered, the drilling rig is generally replaced by
a production platform, assembled at the site using a barge equipped with
heavy lift cranes.
Platforms vary in size, shape and type depending on the size of the
field, the water depth