OFFSHORE DRILLING SYSTEM

摘要

A system (10) for drilling a subsea well (30) from a rig (20) through a subs ea wellhead below the rig (20) includes a wellhead stack (37) which is mounted on the subsea wellhead. The wellhead stack (37) comprises at least a subsea blowout preventer stack and a subsea diverter (106, 108). A drill string extends from the rig (20) through the wellhead stack (37) into the well (30) to conduct drilling fluid from the rig (20) to a drill bit in the well (30). A riser (52) which has one end coupled to the wellhead stack (37) and another end coupled to the rig (20) internally receives the drill string such that a riser annulus is defined between the drill string and the riser (52). A well annulus (66) extends from the bottom of the well (30) to the subsea diverter (106, 108) to conduct fluid away from the drill bit. A pump has a suction si de in communication with the well annulus (66) and a discharge side in communication with the rig (20) and is operable to maintain a selected pressure gradient in the well annulus (66).