A Noncubic Equation of State for the Treatment of Hydrocarbon Fluids at Reservoir Conditions

Abstract

A modified version of the Benedict-Webb-Rubin equation of state (EOS) has been developed. Attention was focused on near-critical conditions, where good behavior was obtained by forcing a tight fit to the experimental critical isotherms, including the critical density. The new model requires component critical constants T{sub c} and P{sub c} and acentric factor {omega}. Generalized expressions have been developed for the calculation of the EOS parameters from the reduced temperature and the acentric factor. Pure-component vapor-pressure and density data were reproduced accurately in a wide range of conditions (reduced temperatures down to 0.4 and pressures up to 1,000 bar, both for liquids and gases, including the critical region) and {omega} values up to 0.6. Mixtures are treated like pure compounds. Their T{sub c}, P{sub c}, and {omega} are calculated by new mixing rules derived from those of cubic EOS`s. With these rules, experimental VLE data were reproduced accurately, with no need of binary interaction constants for alkane-alkane pairs and one constant for the other pairs. Procedures were developed for a fast and safe solution of the equation of state.