A MOLECULAR THERMODYNAMIC APPROACH TO THE PREDICTION OF PHASE-EQUILIBRIA IN RESERVOIR SIMULATION

Highly asymmetric molecules interacting during miscible-gas processes of oil recovery are responsible for the form of the reservoir fluid phase diagrams, from which feasible displacement conditions can be chosen. In order to fit the expermental fluid phase behavior, current reservoir models employ classical equations of state which cannot easily account for the polydisperse and asymmetric nature of such systems. Using a continuous thermodynamics extension of the Simplified Perturbed Hard-Chain Theory (SPHCT) equation of state of Kim et al. (1986), an alternative molecular method for representing these equilibria in reservoir-fluid systems is presented. The approach yields results which compare well with both experimental data and classical calculation procedures.