| Abstract |
An extensive low temperature geothermal system underlies the Tauranga Harbour in the Bay of Plenty, New Zealand. Temperatures in wells range from cool to warm groundwater, between 18 and 67 °C. The resource is freshwater, with minimal saltwater intrusion and no mineralisation. There are no active geothermal surface features. The resource is tapped by direct use bores that cover a range of applications including: municipal supply, irrigation, commercial pools, and domestic space and water heating. Management of the groundwater-geothermal resource is complex, with several hundred individual users. In addition, New Zealand legislation stipulates that water 30°C and above is geothermal. This means that parts of the aquifer are managed as a groundwater system, while other parts are managed as geothermal water despite the fact that they can impact on each other. Monitoring of production is not widespread, with data collected from only a small fraction of wells. In this paper, we present details of a numerical model used to simulate heat and mass flow through the system. A TOUGH2 model was created, using downhole temperature profiles and water level changes due to seasonal production changes for calibration. Seasonal changes in production data were estimated from a selection of metered production wells. Simulations of possible future use patterns of the resource were performed to understand the likely impact of continued abstraction of geothermal groundwater on pressure and temperature in the Tauranga low-temperature geothermal system. |