Abstract: Methods and systems for drilling subsea wells bores with dual-gradient mud systems include drilling the subsea well bore while employing a subsea pumping system, a subsea choke manifold and one or more mud return risers to implement the dual gradient mud system. When a well bore influx is detected, the well bore is shut in, and components determine if pressure control may be used to circulate the influx out of the well bore, the size of the influx, and how much the mud system weight will need to be reduced to match the dual gradient hydrostatic head before the influx reaches the subsea pump take point. The subsea pumping system, subsea choke manifold, and mud risers are isolated while the influx is circulated up one or more fluid passages in the drilling riser package using the surface pump, through the wellhead, and out the surface choke manifold.

Abstract: Methods and systems for drilling subsea wells bores with dual-gradient mud systems include drilling the subsea well bore while employing a subsea pumping system, a subsea choke manifold and one or more mud return risers to implement the dual gradient mud system. When a well bore influx is detected, the well bore is shut in, and components determine if pressure control may be used to circulate the influx out of the well bore, the size of the influx, and how much the mud system weight will need to be reduced to match the dual gradient hydrostatic head before the influx reaches the subsea pump take point. The subsea pumping system, subsea choke manifold, and mud risers are isolated while the influx is circulated up one or more fluid passages in the drilling riser package using the surface pump, through the wellhead, and out the surface choke manifold.