This paper presents the aggregation of asphaltenic materials in three dead crude oils, including two heavy samples from Hokkaido (Japan) and an extra heavy sample from Canada. In this study, a modified ASTM D3279 method and PVT test were used to estimate the amount of precipitated asphaltene and the experimental bubble-point pressures of the samples, respectively. Upon which, a crude oil characterization was performed following pseudocomponent approach with the use of molecular weight and specific gravity of single carbon number from oil assay data as distribution variables. A simplified thermodynamic model, derived from the solubility model, was used to correlate the maximum asphaltene soluble with the aggregated amount. This study has highlighted that oil precipitation, during its titration, occurs as a function of both the molecular weight of the titrant and the carbon-to-hydrogen ratio in the asphaltene phase. Furthermore, the kinetics and the stability of intermolecular forces, developed during the miscibility process, are believed to alter oil polarity and gas solubility. More specifically, pressurization of the system [oil-supercritical gas] decreases the solubility parameters of the asphaltene fraction and increases the solvating strength of gas. Both effects were found to occur concurrently. This study has also demonstrated that asphaltenes are less soluble in impure gases compared to the pure one. At/near the bubble-point pressure, the supercritical gas, in contact with the oil, develops a potential as either a flocculant or coagulant. The increase in pseudo equilibrium temperature attained after gas injection was found also to alter asphaltene aggregation.

Presented paper, herein, is on phase equilibrium of light and heavy crudes known to be closely related to enhanced oil recovery (EOR). In miscible gas injection, the advancing gas (or injecting fluid) develops with petroleum fluids a miscibility front in the reservoir fluids that further reduces the viscous forces holding crudes stranded. The present work presents a phase equilibrium scheme upon which heavy oil swelling and light crude vaporization were found when carbon dioxide (or methane) was used as advancing gas. Heavy crude swelling was observed to be not only dependent on gas solubility but also on the chemical composition of the crude oil. Although a small fraction of injecting gas was distributed in the reservoir water, the initial water-oil ratio was seen to alter the bubble-point pressure from 10 to 30 % depending of the injected gas. In order to mimic miscible-like behavior during gas injection, a dynamic description of methane and carbon dioxide was proposed. Alteration of PVT parameters below and beyond the bubble-point pressure was highlighted therefrom.

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