A Heat Transfer and Solute Transport Model as a Tool for Sustainable Management of the Thermal Water Resource, Waiwera, New Zealand

Abstract

Waiwera is a small east coastal township, north of Auckland, New Zealand. Geothermal fluid of approximately 50?C is entering the well fractured Waiwera aquifer. The proximity to the sea is an important feature of the Waiwera geothermal aquifer. Due to the threat of seawater intrusion and the varying temperatures present in geothermal reservoirs, only a numerical coupled flow, heat transfer and solute transport model can represent the complex processes in the Waiwera geothermal aquifer. SHEMAT, a numerical simulation code, especially designed to simulate geothermal reservoirs, is used to set up a model of the aquifer. Two simulations are performed: one to define a natural state of the Waiwera geothermal aquifer and one to show the influences of exploitation on hydraulic heads, salt concentrations, and temperatures. The simulation of the Waiwera geothermal aquifer leads to acceptable results. It succeeds in simulating many observed processes. Temperature and NaCl concentrations coincide with observed data at Waiwera. The simulations suggest that the inflowing geothermal water at the bottom of the aquifer prevents saltwater intrusion. Further, the simulation shows that seawater intrusion into the Waiwera aquifer occurs only due to exploitation.