Patent ID: 6325159
Filing Date: 2001-12-04
Classification: E21B,F04B,Y10T

Abstract:
A system for drilling a subsea well from a rig through a subsea wellhead below the rig, comprising:a wellhead stack mounted on the subsea wellhead, the wellhead stack comprising at least a subsea blowout preventer stack and a subsea diverter;a drill string extending from the rig through the wellhead stack into the well, the drill string for conducting drilling fluid from the rig to a drill bit in the well;a riser having one end coupled to the wellhead stack and another end coupled to the rig, the riser internally receiving the drill string such that a riser annulus is defined between the drill string and the riser;a well annulus extending from the bottom of the well to the subsea diverter, the well annulus being separated from the riser annulus by the subsea diverter and adapted to conduct fluid away from the drill bit; anda pump having a suction side in communication with the well annulus and a discharge side in communication with the rig, the pump being operable such that a selected pressure gradient is maintained in the well annulus, the pump comprising a first chamber in communication with the well annulus, the first chamber being provided to selectively receive fluid from and dispense fluid to the well annulus wherein the first chamber is defined in a vessel having a second chamber defined therein and a movable member disposed between the first and second chambers, the movable member being arranged to move within the vessel in response to pressure differential between the first and second chambers.