Comparative characteristics of resins, asphaltenes, and
low polar
components of heavy oils from the Ashalchinskoye (I) and Nurlatskoye
(II) oil fields (Republic of Tatarstan, Russia) are given. These oils
differ in the age of host rocks (Permian and Devonian, respectively)
and the content of their components and heteroatoms. An X-ray phase
analysis and scanning and transmission electron microscopy reveal
that, in contrast to smooth surface asphaltenes of oil I, asphaltenes
of oil II are characterized by a loose and porous surface and smaller
sizes of nanoaggregates. Nanoaggregates form a disorderly tangled
structure because of the alkyl side-chain configuration, which makes
it difficult to stack aromatic sheets. The crystallites of nanoaggregates
of asphaltenes of oil II are smaller than the crystallites of nanoaggregates
of asphaltenes of oil I. The application of the method of structural-group
analysis based on the use of the measured indicators of the elemental
composition, average molecular weights, and the results of 1H NMR spectroscopy made it possible to establish that overall sizes
of mean molecules of resins and asphaltenes of heavy oil I are larger
due to the increased content of aromatic and naphthenic cycles in
the naphthenoaromatic system. A feature of the structure of the resin–asphaltene
components of oil II is a greater number of alkyl substituents in
the side chains. According to gas chromatography–mass spectrometry
(GC–MS) analysis, the low polar components under study are
characterized by a similar set of saturated hydrocarbons (n-alkanes, mono-, and polycycloalkanes) but differ in the
composition of identified aromatic hydrocarbons and heteroorganic
compounds. A feature of the low polar components of oil II is the
presence of a wider range of n-alkyl- and phenylalkyl-substituted
benzenes and nitrogen- and oxygen-organic compounds in their composition.
