Methods and systems are provided for selectively displacing water from a hydraulically continuous water zone in a porous geological formation. The target zone to be displaced is defined by a hydrodynamically maintained pressure differential, which has been shown to be capable of confining an expanding injected gas zone. One or more gas injection wells and water production wells are located within the zone. During pressurized gas injection within the zone, the gas displaces water downward within the confined zone such that water is selectively produced from the target zone and the injected gas zone is confined within the hydraulically continuous water zone.