Geology, geography and global energy

Scientific and Technical Journal

Features of geological structure and formation of hydrocarbon deposits at the juncture of the south-western pre-Ural marginal foredeep and Caspian depression

2014. №2, pp. 32-41

Navrotskiy Oleg K. - D.Sc. in Geology and Mineralogy Professor, Lower Volga Research Institute of Geology and Geophysics, 70 Moskovskaya st., Saratov, 410012, Russian Federation,

Zozyrev Nikolay Yu. - C.Sc. in Geology and Mineralogy, Lower Volga Research Institute of Geology and Geophysics, 70 Moskovskaya st., Saratov, 410012, Russian Federation,

Navrotskiy Aleksandr O. - C.Sc. in Geology and Mineralogy, JSC “SibGeoTehServis”, 29 Novogireevskaya st., Moscow, 111397, Russian Federation,

The article discusses structural and tectonic characteristics of the salt domes, intersalt troughs and possible causes of the hydrocarbon deposit destruction in subsalt complexes at the junction of the southwestern Pre-Ural foredeep and the caspian depression. Remarkably, the axial parts of the salt domes are oriented to the west, while the sedimentary complex is regionally uplifted eastward towards the Ural Hercynides. Geochemical studies of core samples with methods of thermal mass spectrometry and chemical and bituminologic analysis, including IR-spectroscopy, demonstrated that the generated liquid hydrocarbons have not been preserved during the geological history and were subjected to mechanical destruction. The intense gypsum dehydration from a thick salt-bearing formation resulted in the development of a huge amount of water. The water served not just as a powerful “hydrogeological cushion”, but also as a salt solvent. The caspian depression has abundant conditions for halokinesis (autonomous movement of salt), in which differential thickness of the salt formations generated conditions for salt fluidity and salt mass redistribution thus creating potent salt dome “nuclei”. The final stage of Hercynian folding was accompanied with the tangential forces display from the Urals in the western direction, leading to the Permian and Triassic “lithoplate” sliding over subsalt Paleozoic “lithoplate” to the west. At this stage, the structural correlation of salt bodies with their westerly slope and regional rise of the harder terrigenous Permian and Triassic rocks to the east was completed. The upper “lithoplate” sliding led to the deposit destruction in the subsalt sediments. Authors of the article believe that search of deposits of oil and gas in such complex geological settings necessary to carry out in integration of geophysical and geochemical research, such as seismic and geochemical modeling, construction of energy-dynamic models.

Key words: соляная тектоника, дегидратация гипсов, движение «литопластин», геохимические исследования керна, разрушение залежей углеводородов, сейсмогеохимическое моделирование, поиски залежей, герцинский этап, salt tectonics, gypsum dehydration, “lithoplate” moveme