Systems and methods for managing pressure in a wellbore

Abstract

A method for drilling a subsea well from a rig through a subsea wellhead below the rig includes employing a single gradient or dual gradient drilling system that includes a drill string that extends from the rig into the well and surface mud pumps for pumping drilling fluid through the drill string and into a well annulus of the well. The drilling system includes a subsea rotating device for conducting the drilling fluid from the well annulus and through a solids processing unit. A subsea pump then conducts the drilling fluid from the solids processing unit to a return line back to the rig. The surface mud pump and subsea pump are staged in coordination to trap pressure and/or remove pressure in the well annulus to maintain a selected pressure gradient in the well annulus.

What is claimed is: 
     
         1 . A system for drilling a subsea well from a rig through a subsea wellhead below the rig, the system comprising:
 (a) a drill string adapted to convey drilling fluid therein and having a drill bit at an end of the drill string, the drill string extending from the rig into the well;   (b) a surface mud pump positioned adjacent the rig, the surface mud pump configured for conducting drilling fluid through the drill string from the rig to the drill bit in the well;   (c) a riser for internally receiving the drill string such that a riser annulus is defined between the drill string and the riser, wherein the riser has a first end coupled to the rig;   (d) a subsea rotating device located in the riser and coupled to a second end of the riser for sealing the riser annulus and separating riser fluid above the subsea rotating device and drilling fluid below the subsea rotating device;   (e) the well annulus on the exterior of the drill string, the well annulus extending from the bottom of the well to the subsea rotating device, wherein the well annulus is isolated from the riser annulus by the subsea rotating device such that the pressure in the well annulus can be isolated from the pressure in the riser annulus; and   (f) a subsea pump located below the subsea rotating device, the subsea pump having an inlet adapted to receive drilling fluid emerging from the well;   wherein the surface mud pump and the subsea pump can be cooperatively operated to circulate drilling fluid in the drill string in the well and control the pressure in the well annulus below the subsea rotating device during drilling.   
     
     
         2 . The system of  claim 1 , further comprising a solids processing unit adapted to reduce the size of cuttings contained in drilling fluid and conduct drilling fluid away from the well annulus; and a return line for conducting drilling fluid from the solids processing unit to the surface mud pump, wherein the subsea pump has an inlet operably coupled to the solids processing unit and an outlet operably coupled to the return line. 
     
     
         3 . The system of  claim 1 , further comprising a check valve positioned within an inner diameter of the drill string in the well located around the subsea rotating device configured to close when the surface mud pump stops or slows thereby preventing free fall of the drilling fluid in the drill string and providing isolation between the subsea pump and surface mud pump during times that drilling fluid flow is static.