Chemical Structure of Kerogen of Shale Formations. (By the Example of the Shale Formations of the East European Platform)

The article deals with the chemical structure of kerogen and its transformation in catagenesis in shale formations by the example of the Middle Volga shale formations and the Domanic carbonaceous deposits of the East European Platform. The studies allowed identifying the main distinctive features in the structure of individual structural components of these types of kerogen and refining the models of the fragment of their chemical structure. Some of the oxygen-containing structures are found to be present in the Middle Volga kerogen as carbohydrate moieties and algaenan components, the alkyl chains in which are interlinked by ether bonds, and the structure of the sulfur-containing components can be represented as sulfide (polysulfide) bound n-alkyl structures, in pyrolysis of which low-molecular and high-molecular alkyl-substituted thiophenes, thienyl- and phenylthiophenes are formed. The average S/C value exceeding 0.04 classifies the Upper Jurassic kerogen as Type II-S. The predominant components constituent in the composition of kerogen of Domanic rocks are lipid components, however, its lower aliphaticity is probably due to the higher maturity of organic matter (OM) and to the low ratio of n-alkyl structures to polyaromatic moieties, the formation of which is connected with the rearrangement of polyene and heteroatomic structures in catagenesis.