Organic Matter and Generation Potential of Paleozoic Deposits in the Tal’bei Block of the Chernyshev Ridge (Timan–Pechora Petroleum Province)

Abstract

––The study area is located within the Chernyshev Ridge, a fold–thrust structure, which is a promising area for oil and gas exploration in the Timan–Pechora province. Petroleum source rocks of Paleozoic (from Upper Ordovician to lower Carboniferous) deposits stripped by the Vorgamusyurskaya-1 well in the Tal’bei block of the Chernyshev Ridge were studied by lithological, petrographic, organic-petrology, and organic-geochemistry methods. Most of the section is characterized by low values of Corg (<0.5%), genetic potential (S1 + S2 < 0.5 mg HC/g rock), and hydrogen index (HI < 100 mg HC/g Corg). Petroleum source rocks with elevated values of Corg (up to 0.9%), S1 + S2 (up to 2.1 mg HC/g rock), and HI (up to 277 mg HC/g Corg) were identified at different stratigraphic levels of the section: Upper Devonian (D3tm–sr), upper Silurian (S2gj), and Upper Ordovician (O3mt). The maceral composition of organic matter (OM) and the distribution of hydrocarbons in the saturated fraction of bitumens indicate that petroleum source rocks include only marine OM (type II kerogen). The degree of catagenesis of OM was estimated based on the bituminite reflectance (RVeq), Rock-Eval pyrolysis (Tmax), and conodont color alteration index (CAI). The available RVeq (0.63–0.84%), Tmax (430–443 °C), and CAI (1.5–2.0) data indicate that the entire Paleozoic well section is in the oil window (MC1–MC3). The new data refined the catagenetic zoning of the sedimentary section, according to which the OM reached the following gradations: MC1 in the lower Carboniferous and Famennian deposits, MC2 in the interval from the Frasnian to the upper part of the lower Silurian, and MC3 in the lower part of the lower Silurian and in the Upper Ordovician. The results of the study of petroleum source rocks and the type and maturity of OM will be the basis for basin modeling, which will increase the reliability of reconstructions of oil and gas formation at the Chernyshev Ridge.