(422b) Evaluation of the Phase Equilibria of Gas Condensates and Light Petroleum Fractions Using the Saft-Vr Approach

The phase behavior and
thermoynamic properties of gas condensates and petroleum fractions are
important in process simulation, design and operation.  These systems are unique in that the precise
composition of gas condensates and petroleum fractions are undefined, being
complex mixtures of paraffinic, naphthenic and aromatic compounds. Before
theoretical calculations to predict or correlate thermodynamic data can be
performed these fluids need to be characterized.  Several methods have been proposed to characterize petroleum
fractions into pseudocomponents from the available physical property
information such as the density, molecular weight, viscosity and normal boiling
point temperature. However these trial-and-error methods require significant
time to implement, and do not have a rigorous basis.  A semicontinous thermodynamics approach was proposed by Cotterman
et al.¹ for polymer and petroleum
systems, and later extended by Behrens and Sandler² to model C₇₊
fractions.  In this work, we combine the
semicontinous thermodynamics method with the SAFT-VR³ equation of state to model
gas condensates and petroleum fractions. 
In earlier work we demonstrated that simple relations for the model
parameters are easily obtained⁴, these are used to
characterize the defined components for the systems studied, taking either
molecular weight or carbon number as inputs. Good agreement is obtained for
between the SAFT-VR calculations and experimental data for dew-bubble curves of
several gas condensates and composition data for reservoir fluids.

References:

¹              R. L. Cotterman, R. Bender,
and J. M. Prausnitz, Industrial & Engineering Chemistry Process Design and
Development 24 (1), 194 (1985); R.
L. Cotterman and J. M. Prausnitz, Industrial & Engineering Chemistry
Process Design and Development 24
(2), 434 (1985).

²              R. A. Behrens and S. I.
Sandler, SPE Reservoir Engineering, 1041 (1988).

³              A. Gil-Villegas, A. Galindo,
P. J. Whitehead, S. J. Mills, and G. Jackson, J. Chem. Phys. 106 (10), 4168 (1997); A. Galindo, L.
A. Davies, A. Gil-Villegas, and G. Jackson, Molecular Physics 93 (2), 241 (1998).

⁴              C. McCabe and G. Jackson,
Phys. Chem. Chem. Phys. 1, 2057
(1999).