RECENT ADVANCES IN THE COMPUTER MODELLING OF THE OHAAKI GEOTHERMAL SYSTEM

Abstract

A sequence of three-dimensional numerical models of the Ohaaki geothermal system has been developed at the University of Auckland (UoA) in collaboration with Contact Energy Ltd (CEL) to assist with the sustainable development of the geothermal resource. This paper describes the latest computer model of the Ohaaki Geothermal System (called here Model 35446) made up of 35446 blocks and using an irregular numerical grid. Model 35446 has a simplified permeability structure based on the geological model provided by CEL which includes nine geological units and discrete vertical structural features (i.e. faults). This paper considers a more holistic approach of reservoir modelling by focusing on the interactions between the different hydrological units and presents the collaborative efforts of UoA and CEL to replicate the overall field behaviour. It was found that permeable faults are paramount for representing some aspects of the behaviour of Ohaaki including the deep pressure recovery recorded in the last few years. The paper also discusses the benefits and limitations of using either a pure water or a water plus carbon dioxide equation of state.