The structure and conditions of formation of oil-bearing depression Domanic and Late Frasnian deposits of the Upper Grubeshor oilfield (Timan-Pechora oil and gas province)

In tectonic terms, the Upper Grubeshor oil field is located in the southern part of the Shapkin-Yuryakhin swell of Denisov trough of the Pechora-Kolva aulaco- gen (PKA). The investigated deposits are part of the Upper Devonian litholog- ic-stratigraphic complex in which the Frasnian and Famennian stages are distin- guished. The Frasnian stage which with the oil reservoir in the depression sedi- ments is connected, is divided into the middle one that includes the Domanic and Vetlasyan horizons, and the upper substage represented by the Sirachoy, Evlan and Livonian horizons.A typical Domanic horizon within the PKA was not drilled. The cross-sections of this type are confined to the head trough of the aulacogen, where drilling was not carried out. In the Timan-Pechora oil and gas province the Domanic horizon is represented by the Domanic suite. In outcrops and the core, the suite is represented by dark gray and black, fine-grained, bituminous, silicified limes- tones turning into organogenic, pteropodal limestones with interlayers of black, bituminous, platy marls with inclusions and interlayers of black silicide and bi- tuminous shale. Organogenic residues are represented by pteropods, radiola- rians. The thickness of the Domanic suite is 10-30 m. It is established that the Domanic horizon within the Upper Grubeshor deposit is represented by strati- graphically complete (wells 2 and 4-Upper Grubeshor are opened) and strati- graphically reduced types of the section (well 1-Upper Grubeshor). In time sec- tions, the wedging is clearly seen.The formation of the Domanic horizon and the Upper Frasnian substage (the Grubeshor and Upper Grubeshor suites) occurred within the elevation confined to the head trough of the aulacogen, which is classified as rising subject to ab- rasion with a slow lowering. As a result of the research, the structure of the Domanic horizon and the Upper Frasnian substage was clarified. It is established that the age of the oil pool in the Upper Devonian complex is Sirachoy-Evlan time. The material obtained allows us to assume the presence of new deposits in the Frasnian part of the Upper Devonian complex at the Upper Grubeshor field.