In-depth | RIG DESIGN


COSCO extols benefits of cylindrical design


Having built the world’s first cylindrical ultra-deepwater semisubmersible drilling rig –Sevan Driller– in less than 30 months, COSCO Nantong Shipyard has started to construct a sister rig named Sevan Brasil. Sandra Tsui reports.


S


evan Driller reported for duty to charterer Petrobras SA in the pre salt area off the Brazilian coastline


in March 2010, four months aſter it was delivered to its owner Sevan Marine. In addition to the cutting-edge


cylindrical design, Sevan Driller has a maximum operating water depth of 3810m (12,500ſt) and a capacity of drilling wells of up to 12,192m (40,000ſt). Te unit has an oil storage capacity of 150,000bopd


TECHNICAL PARTICULARS Launch barge used in building of Sevan Driller


Length, oa ............................................122m Beam, oa ................................................60m Depth ........................................................7m Draught, maximum ...............................13m Lifting capacity .......................20,000tonnes Inboard length .....................................104m Inboard beam ....................................50.2m


Sevan Driller


Length, oa ..............................................85m Beam, wl .................................................75m Variable deck load ................15,000tonnes Deck area .........................................5700m² Accommodation ......................150 persons Thrusters ...................................................... 8 Transit speed ........................................7-9kts Oil storage capacity ..................150,000bbl Drilling lifting capacity ..............1000tonnes Set back load ............................1000tonnes Riser tensioning system ........ DAT – 3200kips Max operating water depth ..........12,500ft Blow out preventer .......... 15,000psi – 18 ¾” Choke and kill manifold ................15,000psi HP mud pumps ...........................4 x 2200hp Mud storage ......................................2850m³ Parallel operation .................stand building while drilling


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Sevan Driller cylindrical ultra-deepwater semisubmersible from COSCO Nantong Shipyard (Credit: COSCO Nantong Shipyard/Sevan Marine).


and its variable deck load amounts to 15,000tonnes. Te lightship weight of the Sevan Driller amounts to 28,180tonnes. Te living cabin is as quiet as 45dB and can accommodate 150 persons. COSCO has participated in the basic


design of the Sevan Driller, and handled the detailed and production designs of the rig, according to Xu Xiulong, deputy general manager of COSCO’s technical centre in Dalian.


Why cylindrical? “Te idea of a cylindrical shape rig is from Sevan and we helped make it possible,” Xu said. Xu explained some of the advantages


of the innovative cylindrical shape of the Sevan Driller. Traditionally, there are two types of drilling vessels. Te first type is the drillship


where a drilling unit is installed onto a ship. Drillships are typically of rectangular shape. Tey usually have a higher variable deck load but are less stable when operating in the sea because its rectangular ship-like shape makes it more susceptible to wind and current, according to Xu. Te second type is the semisubmersible


drilling unit which is usually square in shape. Semisubmersible drilling units in general have lower variable deck loads compared to drill ships and are more stable in the ocean because of the square shape. With similar level of variable deck load, a round-shape rig is even more stable than the traditional square semisubmersible drilling unit, Xu explained. Moreover, when the unit has to sail


to a certain location, the effect of wind direction and current is minimised if the unit is cylindrical. In the case of a drill ship,


Offshore Marine Technology 3rd Quarter 2010


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