A type of mobile offshore drilling rig that floats and is not secured to the sea floor. Floaters include drillships and semisubmersible rigs.
Drillship rigs are maritime vessels that have been outfitted with drilling apparatus. Most often used for exploratory drilling of new oil and gas wells in deep water, drillships can also be used as platforms to carry out well maintenance or completion work such as casing and tubing installation or subsea tree installations. Ensco’s dynamically positioned drillships are equipped with advanced capabilities to meet the demands of ultra-deepwater drilling in depths of up to 10,000 feet with a total vertical drilling depth of 40,000 feet. The rigs’ design and capabilities include numerous features that increase operating efficiency. Primary to these capabilities are offline tubular stand building features and a 160-ton automated heave compensating construction crane, allowing for the deployment of subsea production equipment without interference with ongoing drilling operations.
Semisubmersible rigs are floating offshore drilling units with pontoons and columns that, when sea water is permitted to enter, cause the units to be partially submerged to a predetermined depth. Dynamically-positioned semisubmersible rigs are held in a fixed location over the ocean floor by computer-controlled propellers or "thrusters." ENSCO 8500 Series® semis, which is capable of driling in water depths up to 8,500 feet, is a dynamically-positioned rig that can be adapted for moored operations (anchored to the seafloor with mooring chains). Additional enhancements include a 2 million-pound quad derrick, offline pipe handling capability, automatic station-keeping ability and 150-people living quarters. These features make the ENSCO 8500 Series® rigs especially well-suited for ultra-deepwater development drilling.
Jackup rigs stand on the ocean floor with their hull and drilling equipment elevated above the water on connected leg supports. Jackup rigs are generally preferred over other rig types in water depths of 400 feet or less, primarily because jackup rigs provide a more stable drilling platform with above water blowout prevention equipment. Premium jackup rigs are generally defined as rigs capable of drilling in water depths of 250 feet and greater and are of independent leg design. All of our jackup rigs are considered premium jackups. All but one of our jackup rigs are equipped with cantilevers that allow the drilling equipment to extend outward from the hull over fixed platforms enabling drilling of both exploratory and development wells. The jackup rig hull supports the drilling equipment, jacking system, crew quarters, storage and loading facilities, helicopter landing pad and related equipment.
There is no universally accepted classification of water depths for offshore drilling. We use the following terms to describe our capabilities: