Structural features of asphaltenes in heavy oils from the sediments of the Paleozoic complex of the Volga-Ural and Timan-Pechora oil and gas provinces
E. YU. KOVALENKO1, T. V. CHESHKOVA1, K. A. CHEREDNICHENKO2, T. A. SAGACHENKO1, R. S. MIN1
1Institute of Petroleum Chemistry, Siberian Branch of the Russian Academy of Sciences, Tomsk, Russia
2Gubkin Russian State University of Oil and Gas (National Research University), Moscow, Russia
Keywords: heavy oils, asphaltenes, morphology, structural-group characteristics, chemical destruction
Abstract
The structural organisation and chemical composition of asphaltenes of heavy oils from the sediments of the Paleozoic complex of the Volga-Ural and Timan-Pechora oil and gas provinces are studied using a mix of physicochemical research methods (electron microscopy, proton magnetic resonance spectroscopy, X-ray diffraction, chemical destruction, and combined gas chromatography-mass spectrometry). It is shown that the asphaltenes of oils from the Permian-Carboniferous and Devonian sediments, unlike the asphaltenes of Permian oil with their smooth surface, are characterised by a loose and porous surface, and smaller sizes of nanoaggregates forming a disordered tangled structure caused by the presence of a branched alkyl chain configuration, which hinders aromatic sheets stacking. The crystallites of asphaltene nanoaggregates of heavy oils are characterised by similar thickness, average diameter, and number of aromatic layers in their cluster core, as well as the distance between the aromatic layers and saturated fragments. It has also been determined that the mean molecule of asphaltenes of the Permian oil is larger in size due to the high content of aromatic and naphthenic cycles in the naphthenoaromatic system. A structural feature of the asphaltene components of Devonian oils is a more branched alkyl chain configuration. The structure of the asphaltenes of heavy oils includes fragments linked through sulphide, ether, methylene and polymethylene bridges. Among them, acyclic, mono- and polycyclic naphthenic and aromatic hydrocarbons, as well as sulphur- and oxygen-containing compounds have been identified. The same representatives of sulphur-bound and ether-bound saturated and aromatic hydrocarbons in the structure of asphaltene molecules of heavy oils are similar in composition, but differ from each other in molecular mass distribution. The results of the investigation expand our understanding of the structure of asphaltenes of heavy oils, which may be used to model their structure for developing new controlled methods for processing hydrocarbon raw materials.
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