Equation of state modules for Waiwera including water, chloride and non-condensible gas

Abstract

In some geothermal systems there are high concentrations of chloride and some non-condensible gas (mainly CO2). For reservoir modelling, equation of state (EOS) modules that can handle non-isothermal mixtures of water, chloride and NCGs are required. In the TOUGH2 simulator, EWASG provides a suitable EOS.
In this paper we describe a set of new EOS modules for modelling chloride-rich systems using the parallel, opensource geothermal flow simulator Waiwera. EOS modules for water & chloride, water, chloride & CO2 and water,chloride & air are provided. Shared code is used to give consistency between results from different EOS modules. The main physical properties of chloride are computed using the updated thermodynamic formulation of Driesner (2007) which also removes the low-temperature limitations of EWASG. As in the pure water and water & NCG EOS modules for Waiwera, primary variable interpolation gives improved phase transition performance and hence faster convergence of natural state simulations.
Some results for theoretical test problems and real high- and low-temperature geothermal fields are presented.