The tendency of asphaltene, the heaviest and most polarizable component of crude oil, to deposit and block wellbores and pipelines can potentially lead to production loss and significant cost of remediation. Asphaltenes constitute a particular interest in oil production because of the lack of understanding of their molecular structure and the mechanisms by which they precipitate and deposit. Because prevention is far less expensive than removal, a better understanding of asphaltene precipitation and deposition phenomena is of great importance for the oil industry. Precipitation, which is a necessary but not sufficient condition for deposition, requires accurate modeling of asphaltene phase behavior with respect to variations in the temperature, pressure, and composition. Over the past decade, cubic-plus-association (CPA) and perturbed-chain statistical associating fluid theory (PC-SAFT) equations of state (EOSs) have been proposed for modeling complex systems, such as asphaltenic crude oils. In this work, a comparison between CPA and PC-SAFT EOSs is presented to illustrate their potential and limitations on the prediction of asphaltene phase behavior and pressure–volume–temperature (PVT) properties of crude oils over a range of pressures and temperatures. With an optimized characterization, both EOSs are able to give acceptable predictions of the phase behavior and asphaltene precipitation tendency. However, PC-SAFT is superior in the prediction of derivative thermodynamic properties, especially at high pressures.

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Crude oils consist of tens of thousands of components belonging to various hydrocarbon families, including n-alkanes, cyclo-alkanes, and aromatics. Because the experimental determination of the composition and molecular structure of each component is an infeasible task, it is common to use characterization factors that describe the nature of the pseudo fractions based on their bulk thermophysical properties. In this work, a new characterization factor, called the aromatic ring index (ARI), is developed based on measurements of molecular weight and refractive index. Unlike other popular characterization factors (e.g., Watson's K w ), ARI can clearly distinguish between various hydrocarbon families. Additionally, and most importantly, ARI can provide a quantitative measure of the aromaticity of the hydrocarbon of interest as it provides a rough indication of the number of aromatic rings contained within the molecular structure. Applications of the new ARI concept to well-defined mixtures of hydrocarbons as well as true boiling point (TBP) distillation data of bitumen and heavy oils indicate that ARI shows reasonable trends consistent with the current understanding of the nature of petroleum fractions. Additionally, the concept of ARI can be used to explain some of the apparent discrepancies in the reported results from popular characterization methodologies for asphaltenic systems. Unlike other measures of aromaticity, ARI shows a clear monotonic trend in the aromaticity of the saturates-aromaticsresins-asphaltenes fractions with asphaltenes as most aromatic, which is consistent with the current understanding of asphaltenes.