Cette etude fournit egalement une nouvelle methode pour estimer la tension interfaciale et la miscibilite dynamiques en introduisant des diffusivites contre-directionnelles dans le modele de Parachor traditionnel.

Keywords: interfacial tension, solubility, miscibility, mass transfer, diffusivity, vanishing interfacial tension (VIT) technique, mechanistic Parachor model

Ayirala and Rao (2004a) proposed a diffusivity incorporated mechanistic Parachor model to predict dynamic gas-oil interfacial tension in several crude oil-gas systems.

Our previously developed mechanistic Parachor model (Ayirala and Rao, 2004a) has been utilized to characterize the mass transfer mechanisms from interfacial tension measurements.

The Parachor model (Macleod, 1923; Sudgen, 1924; Weinaug and Katz, 1943) is the oldest among all the IFT prediction models and is still widely used in petroleum industry to estimate the interfacial tension between fluids.

Where [sigma] is the surface tension in mN/m, [[rho].sup.L.sub.M] and [[rho].sup.V.sub.M]are the molar densities of the liquid and vapour phases, respectively, in gmole/[cm/sup.3], [x.sub.i] and [y.sub.i] are the mole fractions of component i in the liquid and vapour phases, respectively and [P.sub.i] is the Parachor value of the component i.

In the Parachor model, Parachor values of pure components were used while calculating the interfacial tensions with an assumption that the Parachor value of a component in a mixture is the same as that when pure.

Recently, Ayirala and Rao (2004a) proposed a mechanistic Parachor model for reliable prediction of dynamic gas-oil interfacial tensions in multicomponent crude oil-gas mixtures by introducing the ratio of diffusivity coefficients between the fluid phases raised to an exponent (n) for mass transfer effects into the original Parachor model.

This condition of equal mass transfer in both the directions of vaporization and condensation appears to be most common in binary mixtures where the conventional Parachor model has shown to result in reasonably accurate interfacial tension predictions (n = 0 in the mechanistic Parachor model).

The value of the exponent (n) in the proposed mechanistic model was obtained by equating the mass transfer enhancement parameter (k), the correction factor to the original Parachor model at which the objective function (the sum of weighted squared deviations between the original Parachor model predictions and experimental IFT values) becomes minimum, to the ratio of diffusivity coefficients between the fluid phases.

The measured densities of the equilibrated fluid phases and the pure component Parachor values reported by Danesh (1998) were used during gas-oil IFT calculations.

The comparison between IFT predictions from the Parachor model and the experiments at various pressures is given in Table 2.