The Severo-Varyoganskoye oil and gas condensate field is located on the territory of the Nizhnevartovsk region of the Khanty-Mansiysk Autonomous District. The results of well drilling in the Severo-Varyoganskoye field prove high potential for hydrocarbon production in the upper part of the Pre-Jurassic sequence (Devonian-Carboniferous), but, on the other hand, indicate extremely complex geological architecture of the target, which considerably impairs the effectiveness of seismic predictions. Structural and compositional characteristics of rocks by core, well section layering and correlation allow suggesting of an optional stratification for the upper section of the Pre-Jurassic sequence. The section with the core is divided into six strata of different lithologic composition. Now there are two most common points of view on the mechanism of formation of promising deposits of the Devonian-Carboniferous: a) weathering crust and, b) hydrothermal-metasomatic formations. Silicites and argillaceo-siliceous rocks were interpreted by the authors as primarily sedimentary, mainly of biogenic (planktonic) type, rarely mixed bio-chemogenic type. Mutual arrangement, close age and rock composition, common genesis features allow the West-Siberian silicites to be considered as the age and facial analogue of Domanic shales of the Russian platform. On the other hand, unlike the Russian platform Domanic, the West-Siberian platform “Domanic” was subjected to intensive hydrothermal – metasomatic impact as a result of activated volcanic processes, which could have probably resulted in organic matter decomposition and acid re-working of rocks.
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