The article is devoted to the variation of generation potential of the Lower-Middle Jurassic organic matter in the Karabash area (South-Western part of the West Siberian basin) depending on facies and sedimentary cyclisity. Based on geochemical and lithological core studies, specific geochemical features of organic matter established for main facies groups of Early-Middle Jurassic in the study area. The best generation potential inherent in deposits of swamps, swampy floodplains and tidal plains. These facies groups characterized by predominance of the continental organic matter and considered to gas source rocks. However, macerals composition, kinetic spectra and biomarker analysis show the presence also of marine organic matter. Some facies groups, such as flooded swamps and swampy floodplains has potential to generate hydrocarbons due to preservation of liptinites with high hydrogen index. Cyclic analysis with basics of sequence stratigraphy of the continental deposits allow tracing the correlation between generation potential and relative sea level changes.

Today there is no verified methodology to calculate oil reserves in the Bazhenov Formation, which makes it impossible to identify any references for the initial oil reserves. Therefore, the analog approach that is usually applied for quantitative assessment of petroleum potential becomes inapplicable. The paper considers different approaches to assessment of the petroleum potential of the Bazhenov Formation in West Siberia. Since oil distribution in the formation is determined by the initial content and catagenetic maturity of organic matter in the rock and controls the formation of an effective reservoir, it becomes apparent that estimating the oil resources and reserves requires geochemical studies. The proposed methodological approaches consider separation of net oil pays using the Rock-Eval data, well log data, and results of oil-promising objects survey and the principles of differentiated assessment of oil resources and territory ranking by the compositions of saturating hydrocarbons.

The paper presents approaches to characterization of shale source rocks using geochemical data for the case of the Bazhenov petroleum system in West Siberia. Regional patterns of oil distribution in the Bazhenov shale are shown to depend on their original total organic carbon (TOC) content and thermal maturity. The existing thermal maturity model for the Bazhenov Formation based on vitrinite reflectance (R-vt(o)) of nearby beds has been updated using parameters measured by Rock-Eval pyrolysis (T-max, HI, PC, and RC) for the shale itself. The results were used to quantify hydrocarbon resources in different maturity zones. The relationship between TOC and the presence of para-autochthonous oil found for logged zones in the Bazhenov section allows allocating and quantifying oil resources in unlogged beds. (C) 2017, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

The results of genetic typification of oils and bitumens from oil source rocks (OSR) of the Buzuluk depression are presented. Crude oils within the study area were divided into five genetic types, which differ both in organic-matter composition and in the conditions of its accumulation. Characteristic of the potential source rock was given for each oil type. Oil-to-source rock bitumen correlation studies were performed using biomarker distribution. The studies have shown that only oils from the Upper Devonian-Middle Carboniferous deposits (oils of Types I and II) were generated by Domanik rocks. Middle Devonian oils (Types III-V) are not related to the Domanik strata. The identified relationships between oils and organic matter of different facies-genetic types of Domanikoid-Domanikite OSR can be used to refine the stratigraphic volume and geographic distribution boundaries of Domanik deposits in the study area. (C) 2017, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

The distribution of biomarkers in bitumens of source rocks of different ages in the southern Siberian Platform is studied to elucidate the correlation between oils and their sources. It is shown that the bitumens of Riphean, Vendian, and Lower-Middle Cambrian source rocks are different in some parameters reflecting the type of primary biogenic material, first of all, in the distribution of n-alkanes and acyclic isoprenoids and in the portions of steranes and triterpanes among polycyclic naphthenes. The revealed difference in the composition and distribution of biomarkers in bitumens of source rocks of different ages can be used to identify the sources of hydrocarbons in discovered pools.

Some 36 oilfields, all producing from Middle Cambrian (Deimena Group) sandstones, are located in the central Baltic Basin in an area covering onshore Lithuania and Kaliningrad (Russia) and the adjacent offshore. This paper presents new data on the composition of crude oils from fields in this area and reviews the reservoir properties of the Deimena Group sandstones.Twenty‐one crude oil samples from fields in Lithuania and Kaliningrad were analysed by standard techniques including GC and GC‐MS. The oils had densities of 790.5 to 870.0 kg/m3, and had low asphaltene (<2.2%) and sulphur (<0.44%) contents. The gasoline fraction (b.p. >200°C) ranged from 12–34%. The saturated hydrocarbon content was 35.3 to 77.8%, and the ratio of saturate to aromatic hydrocarbons was 2.1–5.2, indicating long‐distance migration or high thermal maturities. GC analyses of saturate fractions indicated a composition dominated by n‐alkanes with a maximum at C13–C15 and reduced abundance in the C20–C35 range. The analysed crude oil samples are characterized by relatively low concentrations of steranes and triterpanes.Biomarker data indicated an algal origin for the precursor organic matter and a clastic‐dominated source rock. Sterane isomerization ratios imply that the oils are in general relatively mature. Exceptions are samples from the Juzno Olempijskoye and Deiminskoye fields, Kaliningrad, which were early mature. Oil from well Gondinga‐l (Lithuania) was lightly fractionally evaporated and has a relatively higher density, higher viscosity, higher asphaltene content and lower content of saturated fractions.Stable carbon isotope ratios of crude oils and saturated and aromatic fractions were analysed. Whole oils showed little carbon isotope variation, but there were significant differences in δ13C ratios for saturated and aromatic fractions. The geochemical data show differences in oil sourcing and indicate the possible existence of different kitchen areas in the Kaliningrad region.Vertical and lateral variations in Deimena Group reservoir properties are controlled by variations in quartz cementation. In fields in western Lithuania, sandstone porosity ranges from 0.7 to 20% and permeability from 20 mD to 300 mD; in fields onshore Kaliningrad, porosity is up to 34% and gas permeability up to 4.8 D. Wide variations in porosity and permeability occur at a field scale.

The isotopic criteria used to predict the hydrocarbon phase composition were justified by a comparison of regional trends in the delta(13)C values for hydrocarbon liquids and gases from Riphean and Vendian-Cambrian deposits of the Lena-Tunguska petroleum province. The delta(13)C ratios for liquid hydrocarbons and gases, which are defined by kinetic isotope effects due to kerogen cracking during petroleum generation, were used as a criterion for establishing a genetic relationship between different hydrocarbon phases.The study has revealed that oil-versus gas-prone areas exhibit significant differences in the delta(13)C values and the reverse isotope distributions in the liquids and gases. In the oil-prone areas, methane becomes progressively enriched in (12)C compared to oils and condensates, which is the normal trend of carbon isotopic compositions of liquid hydrocarbons and gases generated by organic matter of the same type and same maturity level. In the gas-prone areas, the delta(13)C values for methane either overlap with those of liquids or methane may show a general trend of enrichment in (13)C relative to liquids. This relationship suggests that gases were probably generated and migrated later than oils, which may provide explanation for predominant gas accumulation in the study areas.The results of the isotopic studies and analysis of the geologic history of the region allowed the recognition of hydrocarbon kitchen areas that were potentially expelling late-stage gas to mostly gas-prone areas.The proposed isotopic method, i.e., a comparison of variations in carbon isotopic compositions of hydrocarbon liquids and gases, allowed us to establish a genetic relationship and discriminate between different hydrocarbon phases on the basis of the delta(13)C ratios. This can provide additional information about the timing of liquid hydrocarbons and gases generation and help to establish the likely locations of hydrocarbon kitchen areas and the history of hydrocarbon accumulations, thus improving the reliability of predictions for the hydrocarbon resource potential in the study areas and the phase composition of accumulated hydrocarbons. (C) 2011, V. S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B. V. All rights reserved.

This report presents new geochemical data on the initial hydrocarbon potential of coal-bearing complexes in South Sakhalin. By the results of pyrolytic analysis, the yield of hydrocarbons (HCs) from the rocks amounts to 0.8–240 mg HC/g of rock. It is shown that lipoid coals and coaly rocks of Paleogene age may be considered as mother rocks of oil (HI of 263–619 mg HC/g Corg). The rocks of Early-Miocene age (HI of 70–247 mg HC/g Corg) are mainly gas sources. The hydrocarbon potential of organic matter in Paleogene coals and coaly rocks of South Sakhalin is higher then that of similar rocks of West Kamchatka considered as oil sources for several oil fields. The data obtained are important for characterization of the prospects of the oil-and-gas content in sedimentary basins of the Sea of Okhotsk.

The trends in composition of higher biomarker hydrocarbons (steranes and tri-, tetra-, and pentacyclic terpanes) in crude oils from diachronous producing complexes of deposits of the Romashkino oil field, which occurs in the central part of the South Tatarian arch, were studied. On the basis of variations in molecular biomarker parameters that reflect the type of source organic matter and the facies conditions of its accumulation and early diagenesis, the oils are classified with three groups.

Hydrothermal alterations in the composition of heavy petroleum and organic matter of rocks from producing carbonate reservoirs of the Middle-Carboniferous Bashkirian stage upon heat treatment at 360 degrees C in the presence of water and hydrogen were studied. It was shown that the soluble portion of organic matter remaining in the rocks after thermal treatment became prevalent as a result of intense degradation of the insoluble organic part of kerogen. This leads to an increase in the production index of these rocks. In the group composition of petroleum and rock extracts, the amount of saturated and aromatic hydrocarbons increases and that of resinous-asphaltic components and solid n-alkanes decreases. Among biomarker hydrocarbons, the relative amount of tricyclic terpanes increases with a simultaneous decrease in the proportion of steranes and pentacyclic triterpanes; the amount of pregnane relative to C-27 alpha-sterane (20R) and the amount of rearranged steranes relative to regular steranes also increase. The results of investigations suggest that, by the action of hydrothermal processes, hydrocarbons of petroleum and organic matter from carbonate collectors undergo structural transformations and isomerization, along with thermal degradation, characteristic of natural catagenetic processes catalyzed by clay materials. Thus, it was concluded that the heat treatment may facilitate oil recovery from carbonate rocks and improve the quality of heavy petroleum.

С применением методов жидкостно-адсорбционного разделения, газовой хроматографии и хромато -масс-спектрометрии выявлены особенности состава нефтей и битумов из отложений осадочного чехла и пород фундамента Бавлинской площади и проведена дифференциация углеводородных флюидов по молекулярному составу их биомаркерных параметров. Показано, что битумы фундамента имеют органическую природу подобно нефтям и битумам осадочной толщи. Установлено генетическое сходство битумов фундамента и рифей-вендских отложений, а также тех и других с нефтью из живетских отложений среднедевонского возраста. Сделаны заключения о геохимических типах исследованных флюидов в пределах изучаемой площади и об их вероятных источниках.

Specific features of the composition of oils and bitumens from deposits of the sedimentary cover and basement rocks of the Bavlinskaya area were revealed using liquid adsorption separation, gas chromatography, and chromatography coupled with mass spectrometry. Hydrocarbon fluids were differentiated in terms of the molecular composition of their biomarkers. Basement bitumens were shown to be organic in nature, as were oils and bitumens from the sedimentary strata. A genetic similarity between bitumens from the basement and Riphean-Vendian deposits, as well as a similarity between bitumens and oil from the Givetian deposits of the Middle Devonian age, was established. Conclusions were drawn about the geochemical types of the fluids in this area and about their probable sources.