Results obtained with flocculation threshold experiments and with inverse gas chromatography were used to validate the use of the solubility parameter approach to asphaltene flocculation phenomena. It was found that values of solubility parameters obtained with both methods are in good agreement. The global solubility parameter of the crude oils was factorized in terms of Linear Solvation Energy Relationship (LSER) coefficients corresponding to a given fluid. Results confirm the validity of the three-dimensional solubility parameter proposed by Hansen to deal with petroleum fluids.

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The microstructure of the crude oils is very sensitive to temperature and composition changes. Differential scanning calorimetry (DSC) is a suitable technique to detect changes of the oil microstructure as a function of temperature. It was observed that thermal curves of certain crude oils confirmed the existence of these phenomena. However, due to the very slow kinetics of processes occurring in the oil, results depend on the sample history. Mixtures of crude oils with toluene, n-alkanes, and mixed solvent exhibit characteristic calorimetric peaks corresponding to aggregation−dissociation phenomena occurring in the asphaltene-containing oil. The size of endotherms observed with mixtures probably can be correlated with the propensity of asphaltenes to flocculate.

Aggregation phenomena involved in asphaltene precipitation under ambient conditions are studied in an effort to correlate them with the asphaltene deposition. The effects of compositional changes on the aggregation and the flocculation onset of asphaltene have been investigated for different crude oils. Density measurements of the system fcrude oil þ toluene þ n-heptaneg were used to assess changes of aggregation occurring in a crude oil under influence of the chemical or physical factors. Obtained results made it possible to determine the asphaltene flocculation onset of several crude oils. Density changes of mixtures were used to quantify the changes of the molecular packing of the oil components. It was found that n-heptane increase the molecular packing of crude oils but also of deasphalted crude oils. Toluene increases the molecular packing also. Therefore, aggregation phenomena occurring in crude oils concern not only asphaltenes but also other components of the oil.

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