Different adsorption/occlusion properties of asphaltenes associated with their secondary evolution processes in oil reservoirs

In this work, two asphaltenes derived from the same set of source rocks, C1 from a crude oil and C2 from an oil sand, were studied, concerning their adsorption/occlusion properties. From the adsorbed components, saturated and aromatic hydrocarbon distributions are distinctly different for these two asphaltenes. For example, some n-alkanes and alkyl-branched alkanes were found adsorbed in C2 asphaltenes, whereas only some cyclic compounds, particularly terpanes were detected from C1 asphaltenes. This difference is due to their different evolution processes in oil reservoirs, and the exchangeability between asphaltene-sorption compounds and those from outside of the bulk phase is different for these two asphaltenes. However, from the asphaltene-occlusion compounds, saturated hydrocarbons show almost the same distribution features. This is consistent with the fact that these two asphaltenes were derived from the same set of source rocks, therefore, occluded almost the same original oils from the source rocks. The experimental results suggest that substantial microporous units exist inside the macromolecular structures of asphaltenes and the asphaltene-derived adsorption/occlusion phenomena extensively occur in oil reservoirs. It seems that asphaltene occlusion should have taken place before asphaltene was detached from kerogen.