Revised and improved geological model of the Waiwera geothermal reservoir, New Zealand

Following a thermal and photogrammetric outcrop mapping campaign undertaken at the Waiwera geothermal reservoir in 2019, a pre-existing 3D hydrogeological model was revised in the present study to assess the impact of the updated structural and lithological interpretation on the existing numerical model calibration. For the latter, well data comprising measured temperature and salinity profiles were employed to reconstruct the reservoir’s natural thermal state and spatial distribution of salinity, supported by numerical simulations of density-driven fluid flow coupled with the transport of heat and sodium chloride. In this context, the previously applied fluid equations of state were extended to consider all relevant parameters as functions of temperature and salinity. Our simulation results demonstrate that the undertaken revisions of the static model and fluid properties substantially improve the agreement between the simulated and observed temperature profiles in the monitoring wells, while the achieved match of the simulation results with early recordings on seawater intrusion emphasizes the general model validity. Ongoing work focusses on applying the newly calibrated numerical model to support the sustainable management of the reservoir and to investigate the reappearance of natural seeps at the Waiwera beach, triggered by a decrease in the past excessive groundwater abstraction.