A theoretically modified PC-SAFT equation of state for predicting asphaltene onset pressures at low temperatures

Abstract

This paper presents a modified perturbed chain-statistical association fluid theory (mod-PC-SAFT EoS) obtained by including into PC-SAFT the second-order dispersion term developed originally by Zhang [Fluid Phase Equilibria, 154 (1999) 1–10] for pure components. This version of PC-SAFT was then used to predict asphaltene onset pressures (AOPs) for nine petroleum reservoir fluids with asphaltene contents, based on saturates-aromatics-resins-asphaltenes (SARA) analyses, varying from 0.80 to 16 wt%. In all modeled cases, this new version predicted less accelerated AOPs at low temperatures than the original PC-SAFT, and then the well-known and widely discussed tendency of PC-SAFT of predicting very high AOPs at these conditions was corrected. The new model also reduced or eliminated the crossover temperatures predicted by PC-SAFT when a reservoir fluid, prone to precipitate asphaltenes, was enriched with CO2.