THERE ARE THREE basic ultra deepwater (over 5,000 ft) subsea drilling systems available to the industry. The conventional 21-inch riser/18-in. BOP stack used with 5th Generation MODUs; surface BOP (SBOP) located directly under the rotary with high pressure casing riser to the seafloor; and the Slim Riser Concept (SRC) using a 16-in. standard riser with a 3rd or 4th generation semi-submersible and 18-in. BOP. The SBOP has an option to use a Subsea Disconnect System (SDS) at the ocean floor consisting of two hydraulic connectors and two shear rams. The author provides a detailed description of the three systems and provides guidance to which of the three concepts for drilling ultra deepwater wells is best suited for a given well and situation.
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