Precursory Changes to Natural Thermal Features During Testing of the Wairakei and Broadlands-Ohaaki Fields

Abstract

Exploitation of geothermal fields in New Zealand has led to moderate to severe, but localised, effects on natural thermal features, such as geysers and hot springs. These effects have been caused primarily by decreases in reservoir pressure associated with mass withdrawal and net mass loss. ' Small, but now clearly identifiable, precursors for some of these effects were observed during pre-production testhg at Wairakei and Broadlands fields, but their significance was not recognised at that time. Precursors of changes to ~tural t h e m features were: decline in flow rate from springs, decline in chloride content and temperature of emerging fluids, and an increase in the eruption period of geysers.