Source: Offshoreenergytoday - The Semisubmersible Transocean Barents. Introduction: Drilling for oil and natural gas Worldwide is an important and growing business despite a slowdown due to the recent oil crash. The Offshore drilling is a type of oil extraction in which wellbores are drilled through the seabed, either by shallow water drilling ( 25m-150m of water depth ) or deep water drilling (500m-3,650m of water depth). The total drilling depth depends on the location of the reservoirs and the type of drilling facilities being used. Different types of drilling rigs used for offshore drilling are jackup rigs, barges, platform rigs, submersible rigs, semi-submersible rigs, and drillships. However, the most common types are the Jackups and the floaters, which comprised the semi-submersibles and the drillships. Source: Maersk drilling.