Chemical Changes in Natural Features and Well Discharges at Wairakei New Zealand

Abstract

Development of the Wairakei geothermal resource has resulted in changes to the chemistry of the discharged fluids. The output of hot chloride springs declined rapidly and eventually ceased 10 years after of commencement of drilling. Deep pressures were drawn down by well discharge resulting in the increase in size and pressure of the shallow steam zone. Natural heat flow in the steam discharge at Karapiti area increased from 40MW in 1950 to 420MW in 1964. Lower reservoir pressures also caused cool and lower mineralised water to enter the main production reservoir. This reduced the average chloride concentration in the well discharges from 1580 g/t in 1960 to 1375 g/t in 1997. By this time 27% of the well discharge was from cool inflow water. "Dry" steam wells in the Te Mihi sector, with gas concentrations up to 3.2 wt%, were brought into service in 1989. This increased the gas flow to the station from 1700 to over 7000 kg/hr.