Modeling of Asphaltene Phase Behavior with the SAFT Equation of State

Abstract

The SAFT equation of state was used to model asphaltene phase behavior in a model live oil and a recombined oil under reservoir conditions. The equation of state parameters for the asphaltenes were fit to precipitation data from oil titrations with n-alkanes at ambient conditions. The SAFT model was then used to predict the asphaltene stability boundaries in the live oils. A lumping scheme that divides the recombined oil into six pseudo-components based on composition, saturates–aromatics–resins–asphaltenes fractionation, and gas–oil-ratio data was introduced. Using this lumping scheme, SAFT predicted stock-tank oil and recombined oil densities that are in excellent agreement with experiment data. For both the model and the recombined oil systems, SAFT predicted asphaltene instability and bubble points agree well with experimental measurements.

Acknowledgments

We would like to thank ChevronTexaco, D. B. Robinson, DeepStar, ExxonMobil, Marathon, Norsk Hydro, Phillips, Schlumberger, Shell, and Department of Energy for their financial and technical support. We also thank Jill Buckley and Jianxin Wang at New Mexico Institute of Mining and Technology for performing the ambient condition titration studies and for many fruitful discussions.