Condensate Formation and Cold Water Incursion in the Poihipi Sector, Wairakei Geothermal System

Abstract

The chemical and isotopic compositions of water and gas discharges and the hydrothermal mineralogy and fluid inclusion characteristics of altered rocks from the Poihipi wells bear the hallmarks of a hydrothermal system located at the very edge of the Wairakei upflow. In Poihipi, most wells produce dry steam and one discharges an immature water produced by mixing of a shallow, low temperature with a high-temperature component during well tests. Petrological evidences, corroborated by chemical compositions of well discharges, indicate that Poihipi is a liquid-, rather than a vapour-dominated system. It consists of a shallow bicarbonate condensate layer with maximum temperatures of containing sporadic vapour pockets high in overlying a dilute Cl zone with maximum temperatures of 200-230?C. The deepening of the bicarbonate condensate layer towards the follows the trend of increased dissolved within the deeper Cl zone. Temperatures in this sector are further lowered by cold water influx along faults, down to elevation.