High Pressure Acid Gas Viscosity Correlation
Résumé
Acid gases containing H2S are often encountered in the petroleum industry. However, reliable experiments on their thermophysical properties in reservoir conditions, in particular viscosity, are very scarce. From a modeling point of view H2S (and CO2) are polar compounds and are so often considered as rather difficult to model accurately. In this work, we propose a correlation based on a corresponding states approach in order to predict the viscosity of acid gas mixtures, among others, with a strong physical background. This correlation is based on the Lennard-Jones fluid model, which has been studied extensively thanks to molecular dynamics simulations over a wide range of thermodynamic conditions. This fluid model can be extended to deal with polar molecules such as CO2 or H2S without a loss of accuracy. In a first part, we demonstrate that the proposed physically based correlation is able to provide an excellent estimation of the viscosity (with average absolute deviations below 5 %) of pure compounds including normal-alkanes, CO2 or even H2S whatever the thermodynamic conditions, gas, liquid or supercritical. Then, using a one-fluid approximation and a set of combining rules, the correlation is applied to various mixtures in a fully predictive way, i.e. without any additional fitted parameters. Using this scheme, the deviations between predictions and measurements are as low as on pure fluids. The viscosity of natural and acid gas mixtures in reservoir conditions is shown to be very well predicted by the proposed scheme. In addition, it is shown that this correlation can also be applied to predict reasonably the viscosity of asymmetric high pressures mixtures even in the liquid phase. This physically based approach is easy to plug in any simulation software as long as the only inputs, the molecular parameters, are directly related to the critical temperature and volume.