The AFGlobal Corporation has developed a mid-riser pump system targeted toward managed pressure drilling (MPD) wells that maintains a full riser fluid column and statically overbalanced well at all times while excluding the need for rig and riser modifications or multiple interconnected manifolds at topside. The optimized configuration of this system is envisioned to permit rapid deployment on any deepwater floating drilling vessel to serve as one method of controlling equivalent circulating density. Ultimately, the PRS will serve as a stepping stone to full dual gradient drilling.
Wellbore pressure is controlled by utilizing a subsea pump system to reduce the amount of riser annulus pressure exerted on the formation. The subsea pump system is operated in conjunction with an MPD wellbore seal permitting a configuration where the pump system can take suction from the riser below the MPD wellbore seal and discharge back into the riser above the MPD wellbore seal. As such, all riser flow is returned to the rig via the main flow line which also permits the option for conventional or advanced kick detection techniques. Since there is no independent mud return line out of the riser, the riser is always full of drilling mud. The topside footprint consists of a combined hydraulic power unit and pump controller skid and umbilical reel permitting 1-2 weeks of rig up time. The pump system and MPD wellbore seal are packaged as single unit which can be deployed through the rotary table in the same manner as a conventional joint of riser. By utilizing a positive displacement pump, the power requirement is low enough for installation across a broad range of drilling vessels.