Depositional Environments and Petroleum Generation Potential of Lower Devonian Rocks in the Chernyshev Ridge, Timan–Pechora Petroleum Province

Abstract

Results of the study of Lower Devonian rocks in the Chernyshev Ridge to determine their hydrocarbon (HC) generation potential are presented. Assessment of the organic matter (OM) content in Lower Devonian rocks showed that most of the studied section is characterized by low C_org concentrations (<0.3%). Elevated OM contents were determined only in Unit III rocks of the Ovinparma regional stage, which are considered as potential petroleum source rocks: C_org 0.13–0.35 and 0.54–1.44%, respectively, in the carbonate and clayey–carbonate rocks. Based on the Rock-Eval pyrolysis data, S₁ + S₂ (0.04–6.20 mg HC/g rock) and hydrogen index (HI) value (19–430 mg HC/g C_org), they are characterized as poor and moderate petroleum source rocks. These source rocks were deposited under open-marine outer ramp conditions during the marine transgression. The OM maturity of the petroleum source rocks, determined based on the bituminite reflectance value, RV_eq (0.75–0.81%), maximum HC yield temperature, T_max (437–449°C), and conodont color alteration index, CAI (1.5), corresponds to the middle of the main oil generation zone (catagenesis grade MC₂). Thus, the presence of rocks with the HC generation capacity and sufficient OM maturity for oil generation indicates that unit III source rocks of the Ovinparma regional stage represent an effective element of the Lower Devonian petroleum system.