Conventional, carbon number compositional analysis techniques provide the weight or mole fraction of pure components up to Cg-and carbon number pseudo-components that represent the C7+ fraction. These typically reported carbon number oil compositions cannot be used with asphaltene and/or wax phase behavior models and are not suitable for interpretation of experimental asphaltene and wax studies, because they do not provide direct phase compositional information on the waxes, resins, and asphaltenes. Waxes, resins, and asphaltenes are usually distributed among the heavier carbon number pseudo-components in these carbon number-type compositional analyses. Hence, new techniques and methodologies are required for analyzing hydrocarbon fluids for the amount and type of waxes, resins, and asphaltenes and for developing EOS oil characterizations suitable for predicting PVT, wax, and asphaltene phenomena. This will eliminate the traditional guess-work that is involved in the development of EOS oil characterizations of asphaltenic and/or waxy fluids.
A new, efficient, and more accurate technique for analyzing crude oil and its fractions to determine hydrocarbon group types, i.e., paraffins (including paraffin waxes), aromatics, resins, and asphaltenes is the PARA analysis. Distillation, solvent extraction, high performance liquid chromatography (HPLC), gel permeation chromatography (GPC), and other techniques are used to perform the oil analyses and obtain the compositional and structural data required for characterizing each hydrocarbon group with its individual pseudo-components. The analyses, in addition to providing weight and/or mole percent for each fraction, provides a starting a priori oil characterization suitable for EOS type modeling methods. The starting oil characterization includes an experimentally assisted selection of pseudo-components for each hydrocarbon group type together with an initial estimate of their critical properties, molecular weight, and acentric factor. This paper discusses the PARA-Based (Paraffin-Aromatic-Resin-Asphaltene) EOS reservoir fluid characterization technique and presents an example application of PVT and wax phase behavior modeling.