Thermolysis of Asphaltenes of Timan-Pechora Heavy Oils

The hydrocarbon composition of the thermolysis products of asphaltenes from biodegraded oils of the Labagan and Usa oilfields and non-biodegraded oil of the Salyukinskoe oilfield of the Timan-Pechora sedimentary basin has been studied. The IR spectra of the asphaltenes are identical, indicating their similar structural group composition. The thermolysis of the asphaltenes has been carried out in an argon flow successively at 300 and 350 degrees C. It has been shown that desorption of saturated and aromatic components from the pores of the asphaltenes predominantly occurs at 300 degrees C. For the initial biodegraded oils and the oil that did not undergo biochemical oxidation, a number of geochemical parameters calculated in terms of acyclic hydrocarbons (HCs) and polycyclic biomarkers turns out to be similar to those obtained for the thermolysis products of the asphaltenes heated at 350 degrees C. The values of the methylphenanthrene index are similar for the thermolysis products of asphaltenes and the parent oils. This similarity, in turn, allows the genetic identification of oils and evaluation of their catagenetic maturity by asphaltene thermolysis products in the case when biomarkers of the aliphatic fraction are lost during biodegradation. An analysis of the supermolecular structure of the asphaltenes of the oils under study has shown a general trend of its change by heating at 350 degrees C, which consists in a sharp decrease in the particle size and loosening of the particle packing due to the appearance of pronounced porosity.