Dual gradient drilling system and method

A distributed riser-less dual gradient drilling system comprising:

• a subsea blowout preventer disposed above a wellhead, the subsea blowout preventer comprising a central lumen configured to provide access to a wellbore;
• an annular sealing system fluidly connected to the subsea blowout preventer;
• a closed-hydraulic positive displacement subsea pump system fluidly connected to a fluid diversion port of the annular sealing system;
• and
• an independent mud return line fluidly connecting one or more pump heads of the closed-hydraulic positive displacement subsea pump system to a rig without use of an additional pump system,
• wherein a pump speed of the closed-hydraulic positive displacement subsea pump system is adjusted to achieve a target amount of fluid mass in a fluidly connected system upstream of the closed-hydraulic positive displacement subsea pump to achieve a target inlet pressure of the closed-hydraulic positive displacement subsea pump.