Heavy oil characteristics

The high viscosity of heavy crude oils is essentially due to the high levels of asphaltene content. Asphaltene is the highest MW component of crude oil, is a friable, amorphous dark solid, which is colloidally dispersed, in the oily portion of the crude. Asphaltenes are considered to be heavily condensed aromatic molecules with aliphatic side chains and with high heteroatom content (S, N, and O) as well as high-metal content. The asphaltene fraction is physically defined as that fraction insoluble in n-alkanes, but soluble in toluene and is the most polar fraction of oil. 

The covalent nature of the asphaltene molecules and the complex nature of the corresponding environment results in agglomeration. Based on the formulated structural models, asphaltenes are seen as an aromatic core which aggregates in concentrated solutions, 1 %, comprising high-MW covalent molecules, which are surrounded by varying numbers of smaller ones held together by various intermolecular bonds [408], Such molecules are considered to be overlapped/stacked over each other in oil mainly due to 

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