A Numerical model of Rotorua Geothermal Field

A three-dimensional numerical model of the Rotorua system, called here UOA Model 4a, has been developed to study the response of surface features to production and reinjection. It differs from previous models by featuring a higher level of refinement and complexity. The model includes the vadose zone and has a fine layer structure in the shallow zone, which enables a better representation of near-surface mass and heat flows. Natural state and production simulation runs were carried out using the EWASG equation of state (non-isothermal mixtures of water, sodium chloride and a non-condensible gas) in the numerical simulator AUTOUGH2, the University of Auckland's version of TOUGH2. UOA Model 4a was calibrated using the available chloride and CO2 data in addition to temperatures, pressure transients and surface heat and mass flows. The results show that the model provides a valuable tool for representing and understanding the behaviour of the Rotorua system and assisting with future management of the resource.