A rigorous approach to the solution of phase equilibrium of geothermal fluids

The phase-split problem for fora geothermal multicompanent mixture is considered. The mixture is mainly composed by water (or brine) and other gas species. Solving the phase-split problem require the minimization of the Gibbs free energy of the system. This is addressed by means of an iterative procedure which is stopped whenever the equality of chemical potentials (i.e. the thermodynamic equilibrium. condition) is met within some fixed tolerance. At any iteration, the mole fraction of each phase is evaluated according to the Rachford-Rice equation and excess chemical potentials are calculated from Peng-Robinson equation of state. Results from numerical simulations are shown.