A drillship is a maritime vessel 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 company and/or investors, but can also be a modified tanker hull outfitted with a dynamic positioning system to maintain its position over the well.
The greatest advantages these modern drillships have is their ability to drill in water depths of more than 2500 m and the time saved sailing between oilfields worldwide. Drillships are completely independent, in contrast to semi-submersibles and jackup barges.
Drillships are just one way to perform exploratory drilling. This function can also be performed by semi-submersibles, jackup barges, barges, or platform rigs.
The first drillship was the Cuss 1, and the fleet size has been growing ever since. By 2013 the worldwide fleet of drillships is expected to top 80 ships, more than double its size in 2009. Drillships are not only growing in size but also in capability with new technology assisting operations from academic research to ice drilling. U.S. President Barack Obama's decision in late March 2010 to expand U.S. domestic exploratory drilling seems likely to increase further developments of drillship technology.
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