The Ngawha geothermal system is atypical of New Zealand geothermal systems, being located outside the Taupo Volcanic Zone, and contained in tight sedimentary structures. Early geochemical surveys of surface discharges indicated a high gas,, high borate fluid, discharging in small quantities, to the surface. An initial well (drilled in the early 1960's, to 500111) produced a very gassy fluid before calciting. Deeper wells drilled and discharged in the early 1980's produced large flows of high gas fluid (up to 3wt%), at enthalpies around 1000 kj/kg. These low energy contents coupled with a low water to rock ratio, a very fractured structure, and consequent expected changes in the production fluid following exploitation, led to large scale exploitation plans being scrapped in 1982. The close attention to geochemical studies before and during the drilling operations enabled predictions of fluid type, physical conditions at depth, fluid disposal problems, and hydrologic reservoir models that have proved to be correct. The project served to indicate the value of comprehensive exploration strategies which preceed the drilling phase, and the further value of, in particular, geochemical studies as an integral part of well testing procedures, for the updating of reservoir models. The close and open cooperation amongst the scientists and engineers involved was also of great value.

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