Thermodynamics of Geothermal Fluids: a Benchmark Between Thermodynamic Models, from Henry’s Approach to Advanced EoS (GECO Project)

Abstract

In the context of the Castelnuovo non condensable gas reinjection project (EU Geothermal Gas Emission Control (GECO) project), relevant and rigorous tools to describe the thermodynamic behavior of fluids composed of water, salt (NaCl), CO2 and other impurities such as H2S, methane are needed. These tools will allow to represent and predict accurately the phase equilibrium and thermodynamic properties such as density, viscosity, compressibility, heat capacity and enthalpy, under the different conditions encountered in the process. Within this study, starting with a state of art, we propose a comparison between several thermodynamic models, different in nature and complexity, from Henry’s approach to advanced Equation of State taking into account association (such as CPA, Cubic Plus Association EoS). To evaluate the thermodynamic models, we will use not only experimental data from the laboratory but also data generated by molecular simulations. These advanced methods of statistical thermodynamics make possible to obtain pseudo-experimental data even under tough conditions, difficult to reach in laboratories such as high temperature, high pressure, presence of toxic compounds.... The different thermodynamic approaches considered in this study will be compared and their advantage and drawback will be discussed. The aim of this work is to present a global assessment of thermodynamic approaches for different contexts of water – salt – CO2 + impurities systems : the results of this study will be relevant and exploitable not only for the Castelnuovo context but also for many other geothermal contexts, including reservoir and surface conditions.