Downhole pressure maintenance system using reference pressure

A method 400 of maintaining an isolated portion of an external region of a completion string within a predetermined pressure range, the method comprising: positioning a completion string that has an internal surface that at least partially defines an internal region and an external surface that at least partially defines an external region within a wellbore; pressurizing a pressurized fluid source located within a pressure maintenance device that is located within a wall of the completion string to a reference pressure that is associated with a wellbore hydrostatic pressure within the external region; isolating a portion of the external region from the wellbore hydrostatic pressure to form the isolated portion of the external region; and allowing a first fluid within the internal region to flow through a first flow path within the pressure maintenance device to the isolated portion of the external region when a pressure differential between the external region and the reference pressure is less than a first pressure differential threshold that is associated with the predetermined pressure range.