Computer Modelling of the Chemistry of the Rotorua Geothermal System

Abstract

The Rotorua Geothermal System is located in the southern margin of Rotorua caldera in the Taupo Volcanic Zone, New Zealand. The system has a hot temperature aquifer (220°C) at very shallow depth (50 – 300m). In 1986, a wellbore closure program was deployed due to a pressure decline caused by a large increase in production from the 1950’s onwards. According to monitoring reports the activity of some geysers and geothermal hot springs has recently been rejuvenated. A new computational model of Rotorua Geothermal System is presented which includes chloride and carbon dioxide. The simulator used is the EWSG version of AUTOUGH2, the University of Auckland’s extended version of TOUGH2. The permeability structure and mass and heat inflows used are adopted from the latest computer model of the Rotorua Geothermal System developed at the University of Auckland, named UOA model III (Ratouis et al., 2014). Adjustments of the deep inflows of chloride and CO2 are made to calibrate the model against the available chloride data, CO2 emission data, and the location of natural geothermal features.