Equation of State Phase Equilibria Calculations

Mixtures of carbon dioxide and some hydrocarbons will form liquid-liquid-vapor equilibrium at temperatures and pressures considered reservoir conditions. So that carbon dioxide miscible flooding may be properly simulated, accurate modeling of the phase behavior is necessary. An algorithm has been developed which is capable of predicting the two-phase and liquid-liquid-vapor equilibrium shown by C02-hydrocarbon mixtures. The algorithm conducts phase stability analysis calculations in series with flash calculations using the Peng-Robinson equation of state to model fluid behavior of all phases present. Example calculations were made of CO2 mixtures with normal alkanes which show liquid-vapor, liquid-liquid, and also liquid-liquid-vapor behavior. An example calculation was also made for a mixture of CO2 with a reservoir oil.Petroleum and Geosystems Engineerin