Systems and methods for managing pressure in a wellbore

A method for drilling a subsea well from a rig through a subsea wellhead below the rig, the method comprising:

• (a) providing a drill string having drilling fluid therein, the drill string extending from the rig into the well;
• (b) providing 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 a drill bit in the well and operating at a surface mud pump rate;
• (c) providing 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 one end coupled to the rig and another end coupled to a subsea rotating device located in the riser for sealing the riser annulus and separating a riser fluid above the subsea rotating device and the drilling fluid below the subsea rotating device;
• (d) providing 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;
• (e) providing 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 is isolated from the pressure in the riser annulus;
• (f) providing a subsea pump located below the subsea rotating device, the subsea pump having an inlet adapted to receive drilling fluid emerging from the well and operating at a subsea pump rate;
• wherein during times of drilling, the surface mud pump adjacent the rig delivers drilling fluid into the well, resulting in a dynamic bottom hole pressure;
• and during times that drilling is not occurring, the surface mud pump adjacent the rig is not delivering drilling fluid into the well, resulting in a static bottom hole pressure, the static bottom hole pressure being less than the dynamic bottom hole pressure;
• wherein the surface mud pump and the subsea pump operate together to circulate drilling fluid in the drill string in the well;
• and
• (g) selectively decreasing pressure below the subsea rotating device by increasing the subsea pump rate relative to the surface mud pump rate thereby achieving a desired pressure reduction in the well annulus below the subsea rotating device.