Chemical Structure and Biomarker Content of Jinghan Asphaltenes and Kerogens

The compound classes and biomarker compositions of immature Jinghan crude oil asphaltenes and their potential respective source rock kerogens have been investigated by chemolysis. The C−S-, C−O-, and Carom−C-bound appendages have been liberated by Ni2B reduction, BBr3 hydrolysis, and ruthenium-ions-catalyzed oxidation. Measured were the saturate, aromatic, and polar (+ asphaltene) compound classes and the homologous series of hydrocarbon biomarkers: n-alkanes, regular isoprenoids, steranes, 4-methylsteranes, hopanes, gammacerane, their monocarboxylic acid derivatives, and α,ω-di-n-alkanoic acids. The nature and distribution of the biomarkers in shallower depths reveals a good correlation between the crude oil asphaltene and the kerogen, manifesting a crude oil−source rock relationship. In deeper strata, the correlation is less convincing but there is no indication of incompatibility. The biomarker composition confirms the immaturity of this deposit, and the huge (53%) yields of C−S plus C−O bond cleavage products from the high-sulfur asphaltene set this type of asphaltene aside from mature crude oil asphaltenes. Also, the biomarker composition points to a strongly reducing, lacustrine depositional environment for this deposit.