Geochemical Evolution of Occluded Hydrocarbons inside Geomacromolecules: A Review

Within geomacromolecules, such as kerogen, asphaltene, and solid bitumen, other compounds can be adsorbed and even occluded as free molecules. The occluded components have been well preserved by the macromolecular structure, and retain some of the primary geochemical information. In this work we try to probe the geochemical evolution of occluded hydrocarbons inside geomacromolecules associated with the geomacromolecule evolution from kerogen -> asphaltene -> solid bitumen. The results show that occluded hydrocarbons can be transferred steadily from kerogen -> asphaltene -> solid bitumen. Later-evolved geomacromolecules not only inherit the occluded hydrocarbons from the former ones, but can also occlude some new free molecules. Occluded hydrocarbons are subject to a relatively independent thermal evolution, whereas the evolution of adsorbed molecules is constrained by other factors besides thermal stress. Elucidation of the geochemical evolution of occluded hydrocarbons inside geomacromolecules will be helpful in oil (bitumen) source correlation, identification of mixed-source reservoirs, and characterization of hydrocarbon accumulation and evolution.