Middle Ordovician - Early Devonian carbonate deposits of Timan-Pechora petroleum province: criteria of oil and gas occurrence

At present, petroleum potential of Middle Ordovician - Early Devonian carbonate deposits in the Timan-Pechora province is poorly understood and still underestimated. The paper presents the analysis of geological and geophysical data in accordance with the identified criteria of oil and gas occurrence in Middle Ordovician - Early Devonian deposits within the Khoreiversky Depression (Bol’shezemel’sky paleo-arch), Varandey-Adz’vinsky structural and tectonic zone (Sorokina swell), and Denisovsky Depression (Laisky-Lodminsky paleohigh). The authors discuss structural and tectonic, lithological and facies, geochemical and hydrogeological criteria of oil and gas occurrence in the considered deposits. Main factors of reservoir properties formation in Middle Ordovician - Early Devonian carbonate deposits are: depositional environment (littoral, sublittoral, lagoon, tectonics) and postsedimentary transformations of the deposits (dilomitization, recrystallization, leaching, and fracture formation). Silurian, Lower Devonian source rocks undergone phases of oil and gas generation. High oil and gas generation potential of Middle Ordovician - Lower Devonian deposits, commercial oil inflows are indicative of high potential of these deposits. Accumulations are discovered in the Silurian and Early Devonian formations. They are associated with carbonate deposits that were subject to supergene processes related to long hiatus. According to hydrogeological criteria, the considered territories belong to zones with difficult water exchange conditions. In conclusion, the authors propose to create a geological model of Middle Ordovician-Lower Devonian series formation and determine exploration targets