Hydrocarbon Composition of Products Formed by Transformation of the Organic Matter of Rocks from Tatarstan Domanik Deposits in Supercritical Water

The composition of hydrocarbons (HCs) generated in the course of transformation of the organic matter (OM) of domanik rocks from high-carbon siliceous–carbonate–clay deposits of the Romashkino (Соrg 7.07%) and Taveli (Соrg 1.90%) fields and from low-carbon carbonate deposits of the Bavly field (Соrg 0.33%) in supercritical water (SCW) at 374°С and pressures of up to 24.6 MPa was determined. The rock samples differ in the mineral composition, OM (including kerogen) content, and composition of bituminoids being recovered. The effect of SCW on the degradation of the polymer structure of kerogen and high-molecular-mass bituminous components of domanik rocks of different lithological and facial types with the formation of petroleum fractions was demonstrated. The content of saturated HCs in extracts from high-carbon rocks of the Romashkino and Taveli fields increases after the treatment in SCW, whereas the content of aromatic compounds, resins, and asphaltenes decreases. The fraction of resins in the extract from the carbonate low-carbon rocks of the Bavly field, transformed under similar conditions, appreciably increases, whereas the content of saturated and aromatic HCs and of asphaltenes decreases. The extract from the rock of the Romashkino field, characterized by the highest content of OM and kerogen, contains, along with liquid fractions, also solid substances of carbene/carboid type. The content of n-alkanes and isoprenoids in the saturated fractions increases irrespective of the type of domanik rocks, whereas the content of polycyclic steranes, triterpanes, arylisoprenoids, and monoaromatic steroids decreases. A common trend is observed for aromatic fractions: the content of dibenzothiophenes and phenanthrenes increases, whereas the content of arylisoprenoids, naphthalenes, and benzothiophenes decreases. The main differences in the composition of HC fractions generated from rocks of different types are manifested in the molecular-mass distribution of n-alkanes С10–С36. The role of SCW in the formation of HC (СH4, C2H4, C2H6, C3H8, n-C4H10, and n-C5H12) and inorganic (H2, O2, and CO2) gases was demonstrated. The yield and composition of the gases, as well as of С10–С36 HC fractions, depend on the mineral composition of the rocks, on the content and composition of OM in the rocks, and on the heat resistance of the OM in SCW medium.