A drillship is a ship that has been fitted with drilling apparatus. It is most often used for exploratory offshore drilling of new oil or gas wells in deep water or for scientific drilling. The drillship can also be used as a platform to carry out well maintenance or completion work such as casing and tubing installation or subsea tree installations. It is often built to the design specification of the oil production companyor investors, but can also be a modified tanker hull outfitted with a dynamic positioning system to maintain its position over the well....