Decompression to fill pressure

A system for pumping mud subsea comprising:

• a water supply line;
• a series of mud pumps, each mud pump comprising,
• a housing having an attached manifold,
• a selectively opened and closed water inlet valve having an end in communication with the manifold and an end in communication with the water supply line,
• a water space in the housing in communication with the manifold,
• a selectively opened and closed water exit valve having an end in communication with the manifold and an end in communication with a water discharge line;
• a mud space in the housing that is in pressure communication with the water space,
• a bladder mounted in the housing having a side in contact with the water space and an opposing side in contact with the mud space, and that defines a flow barrier between the water and mud space;
• and
• a pressure control circuit having a pressurization line at an upstream end in communication with the water supply line and a bypass line at a downstream end selectively switchable between communication to ambient of the pressure control circuit and communication with the water discharge line.

A system for lifting mud from a subsea wellbore to above the sea surface comprising:

• a series of pump modules that each comprise mud pumps with a housing in communication with a water supply line, a water discharge line, a mud supply line, and a mud discharge line, and a bladder that selectively pushes mud from the housing in response to flowing water into the housing, and pushes water from the housing in response to mud flowing into the housing;
• a means for resisting an influx of mud into the housing when a pressure of the mud exceeds a threshold value by creating a backpressure in the water discharge line;
• and
• a means for equalizing pressure across a water inlet valve of each of the pump modules disposed in water lead lines that connect the water supply line to each of the housings.