(88c) SAFT Model for Upstream Applications

The increasing incidence of flow assurance problems caused by asphaltene deposition during oil production has motivated the development of numerous theoretical models and experimental methods to analyze this complex phenomenon. Even more challenging are the prediction of the occurrence and the magnitude of asphaltene deposition. It is normally well accepted that precipitation of asphaltenes is a necessary but not a sufficient condition for deposition. Hence, a significant amount of work has been devoted to the understanding of the conditions at which asphaltenes precipitate from the crude oil. Although, several models seem to work well for correlating available data of onsets of asphaltene precipitation, we have found that they usually lack good prediction capabilities.

In this article, we review the properties of asphaltene and present a thermodynamic model based on the Perturbed Chain version of the Statistical Associating Fluid Theory (PC-SAFT) equation of state, which has been proven to provide excellent prediction capabilities for both the asphaltene onset pressure and the bubble point of the crude oil, in a wide range of temperatures, pressures and compositions. Furthermore, several case studies are presented where we analyze the effect of gas injection, commingling of oils, and contamination with oil based mud, as well as the effect of asphaltene polydispersity. Finally, the asphaltene compositional grading that can lead in some cases to the formation of tar-mats is studied using the same thermodynamic model. In all the cases, very good agreement with experimental data and field observations is obtained. From the results presented in this work, we are confident that the PC-SAFT equation of state is an excellent tool to understand the phase behavior of asphaltenes in crude oil.