Thermodynamics of petroleum mixtures containing heavy hydrocarbons. 1. Phase envelope calculations by use of the Soave-Redlich-Kwong equation of state

Abstract

Analytical data for various North Sea oils and gas condensates have been measured. The data include compositional measurements, TBP analyses, molecular weights, PNA analyses and specific gravities of most fractions. In addition, some dew and bubble points have been measured for each mixture establishing a few points on the phase envelopes. The corresponding phase envelopes are computed with the SRK (Soave-Redlich-Kwong) equation of state. Different methods of representing the heavy components by subfractions and different methods for computing the properties of the subfractions (T /SUB c'/ P /SUB c'/ and ..omega..) are compared. It is found that the phase envelopes can be accurately represented if the TBP residue (C/sub 21/+) is split into approximately 20 subfractions and the C/sub 6/-C/sub 20/ interval is treated as one subfraction for each carbon number. A logarithmic dependence of the mole fraction against carbon number may be assumed for the residue. The best results are obtained by using the Cavett relations for T /SUB c/ and P /SUB c/ of the subfractions and the Lee-Kesler relations for ..omega... The results are improved when the paraffinic, naphthenic, and aromatic parts of each subfraction are treated separately rather than lumped. No ''matching'' or ''tuning'' to experimentalmore » phase equilibrium data is needed.« less