Modeling the properties of two-phase, multi-component geothermal fluid for use in wellbore simulation

Abstract

The thermophysical properties of geothermal fluids play an important role for designing the energy conversion system. Geothermal fluid is a multiphase, multicomponent brine, which can be generalized as the system H2O – salt (Na–Ca–K–Mg–Cl-HCO3) – gas (CO2–N2–CH4–H2S). While modeling the phase behavior is crucial . In this work, a three-zone Equation of State model of geothermal fluids is presented with pressure and enthalpy as independent variables. Hence, it is appropriate for two-phase simulation in geothermal reservoirs, wellbores and heat exchangers. Improved gas activity coefficientsare presentedbased on the extension of neutralinteractions of the dissolved gases. The model can be applied to other multi- salt and gas composition which has been achieved through the fusion of binary systems. The validity of the model presented here has been evaluated by using the experimental data from literature and online field-measurements applying pressure, temperature, and ionic-strength range of 0.5 – 50 MPa, 32 – 177 °C, and 0 – 8.1 mol/kgw, respectively. As shown by the validation, the new model can properly reproduce mutual gas solubility of ternary, quaternary mixtures; density, specific heat capacity, and dynamic viscosity of geothermal brine, and show a benefit compared to VLE of geochemical solvers. The developed model can be coupled to any geochemical solvers useful for two-phase, reactive flow simulation of geothermal fluids.