Structural Organization of Asphaltenes and Resins and Composition of Low Polar Components of Heavy Oils

Abstract

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.