This paper presents and discusses a complete phase behavior package for determining PVT properties of mixtures of hydrocarbon and non-hydrocarbon species commonly encountered in the Petroleum Industry. All calculations are performed using a generalized Equation Of State, which upon selection of appropriate parameters, can be used to represent any of five Equations Of State commonly employed in the Petroleum Industry; i.e., Redlich - Kwong, Zudkevitch - Joffe - Redlich - Kwong, Soave - Redlich - Kwong, Peng - Robinson and Schmidt -Wenzel.

A robust algorithm, which utilizes a combination of the modified successive substitution and Minimum Variable Newton-Raphson methods, is used to calculate flash composition and saturation points. The algorithm is optimized to facilitate convergence near the critical point. The modified successive substitution method is used to determine the number of phases present at a given pressure and temperature. A new simple method is used to ascertain whether the system temperature is greater or less than the critical temperature. The method does not require estimation of the critical temperature for the specified mixture. Straight forward application of a method proposed by Baker and Luks allows the user to efficiently compute all saturation points (i.e., a bubble point and a dew point, or, an upper dew point and a lower dew point) at a given value of temperature. This latter unique feature enables the user to define the two-phase envelope without having to perform a multitude of time consuming flash calculations. Finally, results from our phase package are compared to those presented previously in the literature in order to verify the accuracy and efficiency of the computational procedure.

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