Occlusion inside Asphaltene Aggregates: Insights into the Structural Characteristics of Asphaltenes and its Geochemical Significance
Résumé
Asphaltene molecules are characterized by aromatic ring units attached to plenty of aliphatic chains and some heteroatoms, and they have the capacity to fold upon themselves into a complex three-dimensional globular configuration with internal structures. This kind of structural features enable asphaltenes to form substantial microporous units, and thus liable to adsorb and occlude the other fractions in the crude oil. The occluded compounds inside asphaltene aggregates can be released through mild degradation processes oxidized by H2O2/CH3COOH system. The occlusion results indicate that asphaltene aggregates are the stable species even in toluene, and then they can stabily exist in the oil reservoir underground to survive the long geological timescale on a much more extensive scale with larger sizes. These occluded compounds are realized as the original oil from kerogen, which were generated from kerogen at a low matured level and then occluded inside asphaltenes and have survived the long geological timescale owing to the effective protection from asphaltene macromolecular structures. Some biogenic compounds have been detected from the occluded fraction inside asphaltenes, which were not detected directly from the maltenes. The geochemical significance of these occluded compounds deserves some more efforts to probe its application into the field of oil reservoir geochemistry, especially for the heavily altered oils such as biodegraded oils from which it is difficult to obtain useful geochemical information directly from the maltenes because in which the hydrocarbons have been heavily depleted.