Long-term oil exploration activities in Kustanaisky saddle of Southern Trans-Urals turned out to be unsuccessful. Nevertheless, hydrocarbon potential of the Palaeozoic sediments of this region is assessed as highly promising in a number of recent publications. The argumentation is: presence of oil shows; insufficient seismic exploration maturity; similarity of Southern Trans-Urals and Pre-Urals Palaeozoic sections; existence of oil accumulations in West Siberian Palaeozoic formations. On the basis of a comprehensive analysis of the accumulated materials, the authors show the weakness of these views. Oil and gas shows were observed in Famennian-Lower Carboniferous deposits of Borovsky and Vagai-Ishimsky zones (areas of 15 and 10 thousand km²). Both zones are situated in a large backarc basin on the active margin of the Kazakhstan microcontinent to the rear of the Valer’yanovsky volcanic arc. In this basin, there were conditions favourable for early oil and gas accumulation in a shelf settings. However, the subsequent “active life” of the region caused destruction of hypothetic accumulations. Collision processes accompanied by orogenesis, magmatism, and subsequent intensive denudation occurred during Middle Carboniferous – Early Permian up to Turonian. Palaeozoic rocks of Borovsky and Vagai-Ishimsky zones are bent into narrow linear folds dipping at high angles. Potential oil and gas bearing beds were brought to the pre-Cretaceous erosion surface and were broken by numerous faults. Reservoirs and reliable seals are lacking because of the processes of secondary mineral formation. A fractured oil accumulation was observed in Novonezhinsky area. This oil show is referred to as a field in some works. Oil is sealed in separate nests with secondary calcite. Testing of two wells showed that oil recovery is possible only by rock destruction or acid treatment. It should be noted that oil accumulations in Palaeozoic uplifts of Western Siberia and Southern Turgai owe their existence to the overlying Jurassic source rocks. Palaeozoic uplifts in Southern Trans-Urals are overlapped by variegated Upper Cretaceous rocks having very low gas saturation coefficient. Thus, the Palaeozoic deposits of Southern Trans-Urals cannot be classified as oil and gas promising objects.

Vitalii A. Bykadorov  ORCiD  Scopus
Candidate of Geological and Mineralogical Sciences,
Senior Researcher
Geological Institute of Russian Academy of Sciences,
7, Pyzhevskiy per., Moscow, 119017, Russia
e-mail: vbykadorov@yandex.ru
ORCID ID: 0000-0002-7011-7728

Mikhail P. Antipov Scopus
Candidate of Geological and Mineralogical Sciences,
Senior Researcher
Geological Institute of Russian Academy of Sciences,
7, Pyzhevskiy per., Moscow, 119017, Russia
e-mail: mpantipov@yandex.ru

Tkacheva Anastasiya Aleksandrovna
Researcher
Geological Institute of Russian Academy of Sciences,
7, Pyzhevskiy per., Moscow, 119017, Russia
e-mail: a.a.tkacheva1@yandex.ru

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