This paper deals with the observation that in most equilibrium systems of petroleum mixtures, the molar distribution shape of heavier fractions such as C7+ are very similar. This observation is verified for a wide range of equilibrium pressure-temperature conditions for a wide range of petroleum reservoir mixtures. The states of equilibrium studied include saturation pressure, two-phase flash within the phase envelope, and isothermal systems under the influence of gravitational segregation. The gamma distribution model is used to quantify molar distribution. The gamma distribution parameter a defines the distribution shape which provides a quantitative measure of similarity between equilibrium phases.

The Hoffman, Crump and Hocott(1953) source of reservoir fluids for a saturated gas-oil system (containing only hydrocarbons) has been used in this study. The SRK EOS with zero binary interaction coefficients is used as the thermodynamic model to describe phase behavior of the Hoffman et al fluid system.

A number of applications are given related to the similarity of equilibrium phase molar distributions.

Keywords:
psia, saturation pressure, gamma distribution model, composition, PVT measurement, calculation, fraction, best-fit gamma model, molecular weight, EOS calculation
Subjects:
Fluid Characterization, Phase behavior and PVT measurements
Copyright 2018, Society of Petroleum Engineers
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