Role of strike-slips and graben-rifts in controlling oil and gas reservoirs in deep horizons of the Russko-Chaselsky Ridge (West Siberian Province)

The study of the geological setting features of the West Siberian Oil-and-Gas Province (OGP) is relevant for establishing the relationship between the spatial distribution of local strike-slip dislocations (Russko-Chaselsky Ridge) and the structure of the regional Pai-Khoi-Altai shearing zone. The work aims to identify the regularities of hydrocarbon accumulations location associated with fault systems of this zone. The paper presents the results of studies aimed at assessing the nature of the Earth crust disturbance within the regional Pai-Khoi–Altai shearing zone and the prerequisites for the occurrence of hydrocarbon accumulations within it. A complex set of regional and detailed geophysical data, including 2D and 3D seismic surveys and digital models of gravity and magnetic fields, was used as a factual basis. Based on these materials, cross-sections and maps were drawn showing the structural features of the sedimentary cover and consolidated basement, and an analysis of the nature of the Earth crust disturbance within the shearing zone was performed. It was revealed that the disjunctive dislocations of the regional Pai-Khoi–Altai shearing zone have a characteristic morphology described by a right-lateral strike-slip (dextral) fault strain ellipsoid. Within the Russko-Chaselsky Ridge, patterns were identified in the manifestation of strike-slips and graben-rifts systems caused by the tectonic activity of the regional Pai-Khoi–Altai shear. The shearing zone, en echelon faulting, and associated Riedel shears constitute a single, hierarchically subordinate system of the upper Earth crust disturbance. It is characterized by the development of en echelon system of disturbance zones in the platform cover and the upper part of the consolidated basement, interpreted as Riedel shears of prevailing submeridional strike. Based on the interpretation of seismic cross-sections along the Riedel shears, "flower structures" extending from the Lower Cretaceous to the top of the Paleozoic were distinguished. Structures of this type, located within the West Siberian Oil-and-Gas Province and represented by dislocation systems, may act as drainage in further substantiation of the mechanisms of migration and accumulation of hydrocarbons.