New data for a model update of the Waiwera geothermal reservoir in New Zealand

Abstract. Waiwera is a small coastal village located on New Zealand's North Island above a geothermal reservoir. The origin of the hot water is not well understood. An inferred fault zone at the base of the reservoir is thought to channelise the uprising thermal water. The most recent geological model of Waiwera integrates the depositional environment, mineralogical composition and stratigraphic structures. Coupled numerical fluid flow, heat and transport simulations indicated that further model revisions are required, with support by additional field campaigns, to increase the knowledge of the complex reservoir geology. In this study, gravity data were acquired around the greater Waiwera area. Its interpretation shows a potential fault downthrow in the basement. This feature was tested using a revised geological model in view of a focus for the hot water to rise upwards. The observed characteristic cold and hot water distribution in the system was simulated and the temperature profiles show an improved agreement in the near field around the centre of the reservoir.