Asphaltene precipitation modeling using PC-SAFT and Flory-Huggins theory considering polydisperse asphaltene description

To find an asphaltene thermodynamic model that can predict phase behavior and precipitation at reservoir and surface conditions and can consider mixing and titration with intermediate hydrocarbons is a challenge for design of petroleum production systems. In addition, regression of equation of state (EOS) to describe the precipitated solid can lead to non-physical and inconsistent parameters during model preparation. In this study, Flory-Huggins (FH) solution theory is combined with two EOSs, Peng-Robinson (PR) and perturbed chain statistical associating fluid theory (PC-SAFT) for fluid phase behavior modeling and asphaltene precipitation prediction. In this modeling, pseudo-liquid asphaltene-rich phase is considered and based on the different natures of asphaltene molecules, polydisperse (PD) approach is implemented for characterization to provide a physically consistent model in addition to a monodisperse (MD) approach. For evaluation of the suggested modeling approach, two samples of laboratory data published by Buenrostro-Gonzalez et al. (AIChE J 50:2552-2570, 2004) are studied. Several combinations of models are used including PC-SAFT + FH + MD, PC-SAFT + FH + PD, PR + FH + MD and PR + FH + PD for these samples. The accuracy of the predictions for fluid C1 and Y3 are 2.7, 5.2 (PC-SAFT + FH + MD, bubble pressure), 3.4, 2.6 (PC-SAFT + FH + MD, titration), 0.08, 6.3 (PC-SAFT + FH + MD, onset pressure), 2.4, 6.3 (PR + FH + MD, bubble pressure), 3.4, 2.5 (PR + FH + MD, titration), 1.2, 5.7 (PR + FH + MD, onset pressure) respectively compared to 4.53, 6.3 (bubble pressure), 7.39, 6.9 (titration), 4.57, 7.008 (onset pressure) for SAFT-VR from the literature. In addition, the deviations are 2.7, 5.2 (PC-SAFT + FH + PD, bubble pressure), 2.3, 1.8 (PC-SAFT + FH + PD, titration), 0.4, 0.8 (PC-SAFT + FH + PD, onset pressure), 2.4, 6.2 (PR + FH + PD, bubble pressure), 2.6, 2.3 (PR + FH + PD, titration), 1.3, 2.4(PR + FH + PD, onset pressure).

Automated summary

This study combines Flory-Huggins (FH) solution theory with two equations of state (Peng-Robinson (PR) and perturbed chain statistical associating fluid theory (PC-SAFT)) for modeling phase behavior and predicting asphaltene precipitation. The modeling considers the pseudo-liquid asphaltene-rich phase and uses a polydisperse (PD) approach for characterization. The accuracy of the predictions for different fluid properties is compared to literature values, showing good performance of the proposed models.