ИСТИНА

Investigation of 200 core samples from Tol`kinskiy through was conducted in order to identify source rock potential.Generally all the samples were from Jurassic clastic section.Five potential source rocks were identified as a result of a number of pyrolysis analyses: Koutukhin(J1h-J2t), Tyumen (J2a-J2bt), Vasyugan (J3kv-ox), Georgiev (J3km) and Bashenov(J3t). For determine the level of catagenetic maturity vitrinite reflectance (Ro) and Tmax were used. Positive correlation between these two parameters is observed, especially in the interval of Tmax values 430-446°С (catagenetic maturity level МК1-МК2). According to this correlation catagenetic maturity of Mesozoic deposits within Tol`kinskiy trough was indicated. Jurassic deposits within the study area are now in the main zone of oil generation, mainly МК1-МК2. The boundaries of the main zone of oil generation are found at depth 2,4-3,8 км; MK1 zone is widely spread. Thickness of catagenetic zones decreases with depth, which is characteristic for many oil and gas bearing basins. According to coal petrographic investigations in some of the studied samples vitrinite is presented by parenchynite from leafs material and is closely connected with cutinite included in the leptynite group. Leptynite components are characterized by high content of hydrogen in elemental composition, which leads to decrease of such parameters as vitrinite reflectance and Tmax. Generation of oil by Jurassic rocks is proved by presence of migrational (often trace migrational) bitumoids and hydrocarbons within sandy-silty layers. Migrational bitumoids are also found in mudstones, that breaks the negative correlation between concentrations of organic carbon and its bituminous, including hydrocarbon content (“Uspenskyi – Vassoevich” regularity). Break of this correlation is usually observed within the main zone of oil generation, where is not only generation, but also the most reduced bitumoids and hydrocarbons are emigrated into the pores and cracks. Presence of migrational hydrocarbons is observed according to pyrolysis data. High values of S1 peak (higher than S2) and PI index (S1/S1+S2) and low values of Tmax are characteristic for this type of hydrocarbons, which are on the same level of transformation as syngenetic organic matter; often migrational hydrocarbons are found in rocks of Tyumen and Vasyugan suits.