A GENERALIZED-APPROACH TO PREDICTION OF 2 AND 3-PHASE CO2-HYDROCARBONEQUILIBRIA

A generalized form of the Peng-Robinson equation of state is used to c alculate two and three phase equilibria in systems containing dense CO 2 in contact with both well defined hydrocarbons and with reservoir oi ls. The thermodynamic model combines completely generalized interactio n parameters and critical property correlations with a truncated form of a gamma distribution model for describing the hexane plus fraction of a reservoir oil in a semi-continuous manner. Predictions of phase b ehaviour in well defined systems are used to demonstrate the accuracy of the method and are compared to regressed fits of the data. Characte rization of the C6+ fraction of the reservoir oil requires specificati on of the nature of the oil (paraffinic, olefinic, naphthenic, or arom atic), the average molecular weight of the C6+ fraction, and a single parameter describing the skew of the gamma distribution model. Sensiti vity of phase behaviour predictions to the above parameters is found t o be reasonably limited and surprisingly good fits of the data are obt ained over a wide range of parameter values.