In this paper we analyze the geological structure and prospects of hydrocarbon potential of the Paleozoic deposits in southeastern regions of West Siberia, including the Tomsk, Novosibirsk, Omsk regions and the southwest of the Krasnoyarsk Territory in the left -bank part of the Yenisei River. In the process of our studies, we analyzed the tectonic structure of the basement and made a conclusion that most of the studied area is occupied by the Central West Siberian zone of Late Hercynides. In the northeast of the Tomsk region and the adjacent area of the Krasnoyarsk Territory, the cis -Yenisei Upper Protezoic-Paleozoic sedimentary subbasin, lying on the pre -Baikal basement, developed. We constructed regional -zonal models of the Riphean-Cambrian deposits of the cis -Yenisei subprovince and Paleozoic deposits in the area of distribution of Hercynides and analyzed the material composition and age of the rocks of the pre -Jurassic basement. We assessed hydrocarbon potential of the Upper Proterozoic-Paleozoic deposits, identified prospective blocks and objects, developed seismogeological criteria to identify and map in detail the Paleozoic oil and gas prospective reservoirs and constructed seismogeological models of reference fields.

Bazhenov horizon is the main source rock stratum of the West Siberian petroleum province, which possesses significant resources of hard -to -recover hydrocarbons, making it a unique exploration target. The study summarizes geochemical data on crude oils (39 samples) collected from pools within the Bazhenov and Tutleima formations. A comparative analysis of the carbon isotope composition and geochemical parameters calculated from the composition of the identified saturated and aromatic compounds (pristane/phytane, C29/C27 steranes, C35/C34 homohopanes, tricyclane index, relative concentrations of dibenzothiophenes) confirm a common aquatic genotype of the studied oils and their genetic affinity to the organic matter of the same age. At the same time, significant variations in the main physical and chemical characteristics of the studied Bazhenov oils may be caused their fractionation during migration processes.

Статья посвящена анализу геологического строения и перспективам нефтегазоносности палеозойских отложений юго-восточных районов Западной Сибири, включающих Томскую, Новосибирскую, Омскую области и юго-запад Красноярского края в левобережной части Енисея. В процессе проведенных исследований проанализировано тектоническое строение фундамента, сделан вывод о том, что большую часть исследуемой территории занимает Центрально-Западно-Сибирская зона поздних герцинид, на северо-востоке Томской области и прилегающей территории Красноярского края развит Предъенисейский верхнепротезойско-палеозойский осадочный суббасейн, залегающий на добайкальском фундаменте; построены регионально-зональные модели рифей-кембрийских отложений Предъенисейской субпровинции и палеозойских отложений в зоне распространения герцинид; проанализирован вещественный состав и возраст пород доюрского основания; выполнен анализ перспектив нефтегазоносности верхнепротерозойско-палеозойских отложений, выделены нефтегазоперспективные блоки и объекты; разработаны сейсмогеологические критерии выявления и детального картирования палеозойских нефтегазоперспективных объектов; построены сейсмогеологические модели эталонных месторождений. In this paper we analyze the geological structure and prospects of hydrocarbon potential of the Paleozoic deposits in southeastern regions of West Siberia, including the Tomsk, Novosibirsk, Omsk regions and the southwest of the Krasnoyarsk Territory in the left-bank part of the Yenisei River. In the process of our studies, we analyzed the tectonic structure of the basement and made a conclusion that most of the studied area is occupied by the Central West Siberian zone of Late Hercynides. In the northeast of the Tomsk region and the adjacent area of the Krasnoyarsk Territory, the cis-Yenisei Upper Protezoic–Paleozoic sedimentary subbasin, lying on the pre-Baikal basement, developed. We constructed regional-zonal models of the Riphean–Cambrian deposits of the cis-Yenisei subprovince and Paleozoic deposits in the area of distribution of Hercynides and analyzed the material composition and age of the rocks of the pre-Jurassic basement. We assessed hydrocarbon potential of the Upper Proterozoic–Paleozoic deposits, identified prospective blocks and objects, developed seismogeological criteria to identify and map in detail the Paleozoic oil and gas prospective reservoirs and constructed seismogeological models of reference fields.

-The work is devoted to the analysis of the geological structure and assessment of the oil and gas potential of the Anabar-Khatanga and Lena-Anabar oil and gas areas (OGA) of the Lena-Tunguska oil and gas province, which are located on the continental margin of the Siberian Platform, on the coast of the Laptev Sea. Administratively, the study area includes the northeastern regions of the Krasnoyarsk Territory, the northwest of the Republic of Sakha (Yakutia), the offshore of the Khatanga Bay and the southern, transit part of the Laptev Sea (Khatanga-Lena interfluve). Based on integrated interpretation of geological and geophysical materials, we present regional-zonal models of the geology of the upper Proterozoic-Phanerozoic deposits of the Arctic regions of the Siberian Platform, sets of seismogeological sections, structural and parametric maps, results of structural-tectonic analysis, potential estimates of oil-producing formations; analysis of reservoir properties and types of oil and gas promising objects, and a quantitative assessment of hydrocarbon resources. The study area is of interest in terms of oil and gas potential. In this region, the Central Olgin field was discovered, numerous bitumen, oil and gas shows were noted. A series of oil-producing formations enriched in organic matter occurs in the sedimentary cover, and in the sections of all sedimentary complexes, high-capacity reservoirs are distinguished. There are prerequisites for the formation of both anticlinal and complex oil and gas promising objects. The prospects for the oil and gas potential of the Anabar-Khatanga OGA are mainly associated with Permian terrigenous deposits and Cambrian-Devonian carbonates. In the Lena-Anabar OGA, all upper Proterozoic-Paleozoic sedimentary complexes from the Riphean to the Permian level are of interest in terms of oil and gas potential.

Баженовский горизонт является основной нефтепроизводящей толщей Западно-Сибирской нефтегазоносной провинции, в которой одновременно аккумулированы значительные ресурсы трудноизвлекаемого углеводородного сырья, что делает эту толщу уникальным объектом для исследований. В работе обобщена геохимическая информация о нефтях (39 проб) из залежей в баженовской и тутлеймской свитах. Сравнительный анализ изотопного состава углерода и геохимических показателей, рассчитанных по составу идентифицированных насыщенных и ароматических соединений (пристан/ фитан, стераны С29/С27, гомогопаны С35/С34, трициклановый индекс, относительные концентрации дибензтиофенов), подтверждают единый аквагенный генотип исследованных нефтей и их генетическое родство с одновозрастным органическим веществом. Вместе с тем, отмечается широкий диапазон изменения базовых физико-химических характеристик исследованных баженовских нефтей, которые обусловлены влиянием их фракционирования в ходе миграционных процессов. The Bazhenov horizon is the main source rock stratum of the West Siberian petroleum province, which possesses significant resources of hard-to-recover hydrocarbons, making it a unique exploration target. The study summarizes geochemical data on crude oils (39 samples) collected from pools within the Bazhenov and Tutleima formations. A comparative analysis of the carbon isotope composition and geochemical parameters calculated from the composition of the identified saturated and aromatic compounds (pristane/phytane, C29/C27 steranes, C35/C34 homohopanes, tricyclane index, relative concentrations of dibenzothiophenes) confirm a common aquatic genotype of the studied oils and their genetic affinity to the organic matter of the same age. At the same time, significant variations in the main physical and chemical characteristics of the studied Bazhenov oils may be caused their fractionation during migration processes.

Баженовская свита Западно-Сибирской нефтегазоносной провинции в настоящее время выступает в качестве одного из ключевых объектов потенциального прироста запасов и добычи нефти. В статье представлены результаты исследования геохимии органического вещества баженовской свиты по методике, разработанной в ИНГГ СО РАН для высокообогащенных органическим веществом пород. Рассмотрены особенности группового и углеводородного состава битумоидов открытых и закрытых пор баженовской свиты Северо-Сургутского района. Установлено, что основная часть новообразованных нафтидов находится в свободном (фазово-обособленном) и сорбированном состояниях в закрытом поровом пространстве пород. В открытых порах находятся наиболее подвижные компоненты битумоидов, перераспределенные из закрытых пор в ходе первичной миграции и оставшиеся после эмиграции нафтидов из баженовской свиты в берриас-нижнеаптские (пласты групп А и Б) резервуары. Используемая в работе методика позволила по объему порового пространства, занимаемому битумоидами открытых пор, выделить интервалы с повышенной открытой пористостью и нефтенасыщенностью в разрезе баженовской свиты (силициты и карбонаты). The Bazhenov Formation of the Western Siberian oil-and-gas province is currently one of the key objects of potential growth in oil reserves and production. Here we present results of a geochemical study of the Bazhenov Formation according to the methodology developed at Trofimuk Institute of Petroleum Geology and Geophysics, Novosibirsk (IPGG SB RAS) for rocks highly enriched in organic matter. The features of the group and hydrocarbon compositions of the bitumoids that are filling open and closed pores of the Bazhenov Formation rocks from the North-Surgut region were considered. It has been established that most of the naphthides are in a free (phase-segregated) or sorbed state in a closed pore space. The open pores contain the most mobile components of bitumoids, redistributed from closed pores during the primary migration and remained after the secondary migration of naphtides from the Bazhenov Formation to the Berriasian-lower Aptian reservoirs (A and B strata groups). The methodology used in this work allows determining intervals with increased open porosity and oil saturation in the section of the Bazhenov Formation (silicites and carbonates) by the volume of pore space occupied by open-pore bitumoids.

The study considers the distribution of organic carbon in different formations and facies of Cambrian age identified in the cis-Yenisei subbasin. Two groups of depositional environments were recognized in the deepwater perioceanic and epicontinental basins, which accumulated sediments with elevated and sometimes anomalously high concentrations of planktonic and benthic organic matter. These are 1) local centers in the Tommotian (Oksym Formation) and Botomian stages of the lower Cambrian, Mayan (Elogui and Pudzhelga formations) and Ayusokkanian (Kondes Formation) stages of the middle Cambrian; 2) regional Kuonamka horizon, which is composed of Toyonian and Amgian deposits and occurs along the margins of the Siberian Platform; it is represented by the Inikan and Kuonamka formations in the east of the Siberian Platform and by the Paidugina Formation in the study area. The study shows that the organic matter has undergone a high degree of transformation and reached the apocatagenesis grade. The results of the study assume that the hydrocarbon generation intensity was high in the Cambrian formations of the cis-Yenisei subbasin in the geological past.

Катагенез органического вещества юрско-меловых отложений юго-запада Енисей-Хатангского регионального прогиба1 Институт нефтегазовой геологии и

We analyzed the organic matter composition of bottom sediments from Lake Baikal, sampled in the areas near Cape Gorevoi Utes and the mouth of the Bolshaya Zelenovskaya River, using a set of geochemical methods (extraction, column chromatography, gas-liquid chromatography, and chromatography-mass spectrometry). We have established that the organic matter of Baikal’s fresh-water sediments from these areas is predominantly of terrestrial, but differs both in the initial biota and in the degree of maturity and biodegradation. In contrast to the sediments of the Bolshaya Zelenovskaya River, whose autochthonous organic matter is immature and nondegraded, the sediments of Cape Gorevoy Utes are enriched in more mature and allochthonous organic matter, which is biodegraded to varying degrees depending on the depth of occurrence.

The article discusses the concept of Bazhenov reservoir rocks exemplified by a oil productive interval of the Bazhenov Formation cross-section in the West-Kvenzer area, southeastern Western Siberia. Characteristics of the analyzed interval are derived from the interpretation of the results obtained by the geophysics, lithology, rock physics and organic geochemistry integrating methods. It has been shown that the studied oil saturated interval is represented by kerogen-siliceous and siliceous mixtites. The studied rocks are found to be identical in terms of the lithological composition, organic matter geochemistry, geophysical and petrophysical characteristics. Most of the mobile (allochthonous) bitumoids (chloroform extractable bitumens) generated by the Bazhenov Formation within the West-Kvenzer area are concentrated in open pore space, rather than being fracture-filling type.

—The homologous series of high-molecular weight dimethylalkanes (HMWDMAs) with either odd- or even-numbered carbon chains in the range from C19–20 to C30–31 have been identified in organic matter from recent and partially lithified deposits of Siberia and the Russian Platform by chromatography–mass spectrometry. The first homologous series is represented by even-numbered 3,4-HMWDMAs followed by the alternation of odd-numbered 3,5-HMWDMAs, even-numbered 3,6-HMWDMAs, and odd-numbered 3,7-HMWDMAs. The most abundant are 3,7-dimethylalkanes. The microbial origin of high-molecular weight dimethylalkanes is the most likely explanation for their presence in the fossil organic matter. The precursors of HMWDMAs might have been tetra- and diether lipids of archaea and bacteria. It is assumed that HMWDMAs and other immature hydrocarbons from great depths (SV-27 and SG-6 superdeep boreholes) result from the decomposition of asphaltenes, which occluded the related compounds inside their structure during the early stages of generation and carried them unchanged throughout the “oil window”.

Summary In the east part of the West Siberian sedimentary basin the Bazhenov Formation has the Tarkosale, Vakh, and Nyurolka types of section. We have studied the lithology and geophysical characteristics of its rocks and the geochemistry of its organic matter and described the obtained characteristics of the sections. The greatest attention is paid to the geochemistry of organic matter. The results of the investigation indicate that the aquatic organic matter of the studied section types of the Bazhenov Formation was concluded to differ in content and composition of bitumoids primarily due its different maturity degree. The electrical resistivity and gamma activity of the studied section changes with proportion ratio of clay and carbonate components in the composition of their rocks. That can be preliminary explained by the position of the sections relative to the paleodepth and regional provenance.

Conceptual models are formulated and quantitative predictive functions of reservoir porosity, fluid saturation, effective thickness rate of the Bazhenov Formation and its geological and geochemical characteristics are obtained. These parameters were used to predict oil and gas potential and quantitative assessment of oil resources in the Bazhenov Formation in the southeastern regions of the Western Siberian Basin.

The main features of the geochemistry of individual aromatic compounds (phenanthrenes, dibenzothiophenes, mono- and triaromatic steroids) in chloroform extracts (bitumoids) from the open (regular form and coarse-crushed (≥0.5 cm) samples) and closed (fine-crushed (0.25 mm) samples) pore space of the Bazhenov Formation have been determined. The differences in the aromatic compounds distribution of organic matter of the Bazhenov Formation in the North of the Khantey hemiantheclise (Surgut region, Khanty-Mansiysk Autonomous District, Western Siberia) are mainly related to its stage of thermal maturity which decreases in the south-west direction within the studying area. The most sensitive to maturity variations at the same catagenesis gradation are the parameters: CPI, Ts/Tm, 1/Ki ((n-C17 + n-C18)/(Pr + Ph)), MDR (4-MDBT/1-MDBT), DBTI ((2+3-MDBT)/DBT) and TASI (TAS I/(TAS I + TAS II)). Based on some indicators (PI, MPI, PP-1, MDR, DBTI etc.), it is possible to notice the decrease and equalization of its values in bitumoids from closed pores compared with those from open ones. It seems to be associated with the removal of the most transformed, light and migratory-capable part of bitumoids during their extraction from the open pore space of rocks.

—The gradual transition of the Bazhenov Formation top into the overlying deposits makes it difficult to establish its upper boundary. The problem is aggravated by the lack of core material when the formation is recognized according to the results of geophysical well studies. A comprehensive analysis of geochemical and lithological data and the results of geophysical well surveys enabled us not only to determine the specific structure of the transitional zone from the Bazhenov Formation top to the rocks of the sub-Achimov member, but also to propose the criteria for delineating the upper boundary in the central regions of the West Siberian sedimentary basin within the Khentei hemianteclise, the South Nadym megamonoclise and the Mansi syneclise. Four members are distinguished in the transitional zone of the studied well sections (from bottom to top), which differ in lithological, geochemical and geophysical characteristics: (I) the “coccolithic” upper part of the Bazhenov Formation; (II) transitional member from the upper part of the Bazhenov Formation to the bottom of the sub-Achimov member; (III) transitional member from the bottom of the sub-Achimov member to its lower part; and (IV) the lower part of the sub-Achimov member. Member II is virtually not distinguished within the Khentei hemianteclise and the South Nadym megamonoclise. Member III contains the boundary between zones with different redox conditions. In case member II is distinguished, the upper boundary of the Bazhenov Formation corresponds to its top. To recognize the Bazhenov Formation top, it is necessary to use the integrated analysis results of the lithological and geochemical studies of the well core, and logging data (gamma-ray logging, neutron gamma-ray logging and its variations, lateral logging, and induction logging) when focusing attention mainly on radioactivity.

There are six sedimentary seismic sequences overlying pre-Mesozoic basement in the Mesozoic-Cenozoic sedimentary cover of the Arctic regions of West Siberia and the Kara Sea shelf. The paper describes the seismic markers characteristics and the seismic-facial features of the Paleozoic, Triassic, Jurassic, Neocomian, Apt-Cenomanian and TuronianCenozoic seismic sequences. It was concluded that the features of large Cenomanian gas pools are seismic markers associated with gas-water contacts; Apt-Albian pools are displayed on time sections by a bright spot seismic anomaly.

The West Siberian marine basin of the Volgian–initial Berriasian ages is described. It is shown that a marginal filter (according to A.P. Lisitsyn) functioned in the basin. The main mass of terrigenous sediments was deposited within the eastern margin of the sea. The central part of the basin only received a small amount of the terrigenous material. Water area of the West Siberian Sea was 2 mln 530 thou km2; eastern marginal filter, 535 thou km2; and open epicontinental marine basin, 1 mln 994 thou km2. Depth of the Volgian Sea was 500 m. Mass of sediments in the West Siberian Sea by the end of late diagenesis was 228.4 Tt (recalculated to the anhydrous material), with sediments in the eastern marginal filter accounting for 121.7 Tt. Bioproductivity of the Volgian–Berriasian West Siberian Sea was extremely high. The mass of living matter was composed of archaea, bacteria, and protozoan unicellular eucaryotes (organic-walled), as well as organisms with the siliceous (radiolarians) and carbonate skeleton (foraminifers and others). The rock mass formed from sediments of the central deep-water part of the basin at the stage of diagenesis was 106.7 Tt (recalculated to the anhydrous material), including the mass of organic matter (OM) accounting for 15.8 Tt; mineral (siliceous and carbonate) relicts of organisms, 67.8 Tt; and allothigenic components (clay minerals and iron hydroxides), 23.1 Tt. Analysis of the composition of kerogen (polymerlipids) revealed that the amount of OM transported to sediments was 15–20 times higher than the present-day amount in rocks of the Bazhenov Formation. At the stage of early diagenesis, the OM mass in sediments was as high as 235–320 Tt (recalculated to the anhydrous material). The Bazhenov Sea represented a huge natural ecosystem favorable for the generation, reworking, and accumulation of living matter relicts. At the stage of catagenesis, unique oil-and-gas resources were generated from OM masses deposited in this system.