An Updated Computer Model of Rotorua Geothermal Field

Abstract

The Rotorua geothermal field is situated at the southern margin of the Rotorua Caldera in the Taupo Volcanic Zone, New Zealand. The Rotorua system lies beneath a major city and has an abundance of natural features utilised as tourist attractions. Over 900 shallow wells have been drilled into the shallow reservoir producing hot fluid (up to 215°C) at an average depth of 200m for private, commercial and industrial bathing and heating purposes. A 3-dimensional numerical model of the Rotorua system has been developed – UOA Model 3. UOA Model 3 includes information from an IRL model1, and a previous University of Auckland model2. UOA Model 3 differs from previous models by having a much finer layer structure in the shallow zone, which allows for better representation of near-surface mass and heat flow behaviour. UOA Model 3 also includes the complex structural and lithological structures associated with Rotorua’s asymmetrical caldera collapse setting. These changes resulted in a more accurate representation of the geological formations and have influenced the boundary conditions used for the model. Both manual and inverse modelling methods have been used for calibration of UOA Model 3, and a good match to surface activity and shallow temperatures has been obtained. 1. Burnell, J., & Kissling, W.: Rotorua geothermal reservoir modelling part 1: Model update 2004. Industrial Research Limited Report to Environment Bay of Plenty. February, 2005 (2005) 2. Ridwan Febrianto, Peter Johnson, Zhi Yang Wong, Michael O’Sullivan and John O’Sullivan: A Computer Model of Rotorua Geothermal Field. New Zealand Geothermal Workshop 2013 Proceedings. 17 -20 November 2013 (2013)