ABSTRACT
To drill an oil/gas well in the middle of sea or ocean, it is essential to have some platform on which necessary drilling equipment and other accessories and ancilliaries can be placed. The economics which vary globally from place to place, offshore platforms can be broadly categorised into three types: Fixed platform, compliant platform and mobile platform/units. Fixed type platforms are those whose leg or base is fixed at the seabed forever either by way of penetration to the seabed or by its own weight. Compliant platforms are those structures that extend from the surface to the ocean bottom and directly anchored to the seafloor by piles and/or guidelines. The last type of mobile drilling unit is the drillship. As the name implies, it is simply a shipshape vessel used for drilling purposes. Drillships similar to the semisubmersibles are held on location either by conventional mooring system or by dynamic positioning.
