Asphaltene phase behavior: prediction at a crossroads

Recent results from SAXS, X-ray transmission, and differential scanning and other calorimetry experiments with neat asphaltenes and asphaltene + hydrocarbon mixtures highlight the structural and behavioral complexity of asphaltenes, however defined, at diverse length scales. Much of this complexity spans the temperature range of importance for reservoir fluid applications, and calls into question many aspects of existing thermodynamic models for them. Apparent heat capacities, for neat asphaltenes, can drop below those of rigid organic crystals revealing the presence of significant exotherms. Of equal importance, typical molecular and submolecular analysis techniques: C13NMR, fluorescence, elemental analysis, ‘molar mass’ do not appear to correlate with asphaltene behaviors in their native oils or in solvent solutions at infinite dilution. Maya and athabasca asphaltenes provide an excellent illustration of this phenomenon. Our understanding of the phase behavior of neat asphaltenes and the behavior of asphaltenes in fluids is at a crossroads.