Fluid transfer device usable in managed pressure and dual-gradient drilling

A fluid transfer device for use in wellbore drilling, comprising:

• at least one pressure vessel having a fluid port proximate a bottom thereof for entry and discharge of a working fluid into and out of the at least one pressure vessel and a fluid port proximate a top thereof for entry and discharge of a power fluid into and out of the at least one pressure vessel;
• wherein the at least one pressure vessel has no physical barrier between the power fluid and the working fluid, wherein dimensions of the at least one pressure vessel are selected with respect to a rate of movement of the power fluid into and out of the at least one pressure vessel to substantially prevent mixing of the power fluid and the working fluid;
• valves coupled to the fluid port proximate the top of the at least one pressure vessel for selective introduction and removal of the power fluid into and out of the at least one pressure vessel;
• and
• valves coupled to the fluid port proximate the bottom of the at least one pressure vessel and arranged such that the working fluid is constrained to flow in only one direction through an inlet line and an outlet line in hydraulic communication with a respective one of the valves coupled to the fluid port proximate the bottom of the at least one pressure vessel.