Development Strategy for Ngawha

Abstract

Ngawha geothermal field in Northland differs from the explored fields of the Taupo Volcanic Zone in a number of ways. It has a capped reservoir, and it appears that there could be little or no recharge laterally from groundwater. The reservoir rock is fractured greywacke, and has low porosity. These factors mean that the large heat store in the reservoir might not be fully producible, for lack of water to carry the heat to surface. Delineation by drilling will not of itself determine the extent to which the reservoir's electric power potential may be limited by its fluid reserves. A substantial discharge will. It is proposed that a pressure turbine be installed in the next year. Provided that over 100 t/h of steam is withdrawn from the reservoir for three or more years, reservoir properties should be fully defined when it is time to design a power station.