Design and Operating Features of the SEDCO 135-F Floating Drilling Vessel

This paper describes the design of one of the largest semi-submersible drilling vessels ever constructed. The arrangement and operating features of the drilling machinery and auxiliary underwater drilling equipment are also reviewed. The SEDCO 135-F is presently under construction at Victoria Machinery Depot in Victoria, B.C. Sister vessels have been completed and are in operation in the Gulf of Mexico, off Borneo, in the North Sea and off Nigeria. The physical layout of the vessel is presented in terms of its unusual shape, size and arrangement of equipment and accommodations. The diesel-electric power plant provides D.C. power for the heavy machinery and A.C. power for miscellaneous ship service. Electrically driven deep-well pumps are used to deballast the vessel and to move water and fuel from the lower compartments to the operating deck level. Other mechanical features include three large cranes, pneumatic storage tanks and other special equipment required to handle the underwater drilling equipment. Due to the severe oceanographic conditions off the west coast of Canada, a special mooring system was designed to secure the rig under adverse conditions. The design criteria, hardware and operation of this system are reviewed. The vessel will be equipped with specialized underwater equipment to enable it to drill exploratory wells in water depths of up to 800 feet. The hydraulically operated well control equipment is situated on the ocean floor during normal operations. This "diverless" equipment is described, along with its handling and operating procedures.