Home – Home – Jornals – Russian Geology and Geophysics 2017 number 3-4

Asphaltenes and asphaltogene acids of organic matter (OM) of lacustrine sediments in the Novosibirsk and Tomsk Regions of West Siberia have been investigated by physical and physicochemical methods(elemental and X-ray diffraction analyses, IR, NMR, and EPR spectroscopy, Rock-Eval pyrolysis, and electron microscopy). Compared with asphaltenes of dispersed OM at the early catagenesis stages, asphaltenes of OM at the diagenesis stage have a high number of hydrogen atoms and heteroatoms, a low degree of aromaticity, a low concentration of paramagnetic centers, a large number of carbon atoms in the long paraffin chains and oxygen-containing groups. Tetravalent vanadium is absent from asphaltenes of recent lacustrine sediments, and only complex compounds of copper have been identified. The sediments contain not asphaltenes but their precursors, protoasphaltenes. These are less condensed compounds with a looser nongraphite structure but a rather high petroleum potential. At the diagenesis stage, protoasphaltenes are immature protokerogen blocks.

The author determines the conditions under which lateral migration of primary oil accumulations in the near-roof reservoir zone leads to their Pareto distribution by mass. It is shown that this power-series distribution is preserved in a wide range of the values of bed porosity, permeability, and slope angle, i.e., does not depend on the individual parameters of the petroliferous basin.

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.

Samples of Triassic sediments were collected fr om cores of parametric boreholes drilled on the Admiralteiskii Rise, Franz Josef Land Archipelago, and Fersman structure in the northeastern part of the Barents Sea sedimentary basin. The composition and distribution of hydrocarbon biomarkers (n-alkanes, isoprenoids, cyclic alkanes, and polyaromatic hydrocarbons) were studied using the GC-MS method and provided information about the genesis, facies conditions of sedimentation, and catagenetic maturity stage of dispersed organic matter (DOM). The Late Mesozoic-Cenozoic uplifting of the region and active magmatic processes significantly influenced the thermal transformation of sediments. The revealed trend is best observed in the sediment section of the Franz Josef Land archipelago, wh ere the thermal effects led to a radical increase in DOM transformation, up to the AC1 stage.

The composition of biomarkers and aromatic hydrocarbons of Late Devonian oils of the- Timan-Pechora petroliferous basin has been studied. It shows that the organic matter of oil-generating deposits is at the close stages of thermal maturity, which are within the early and middle stages of the oil window. Five groups of oils have been recognized, three of which were generated by organic matter of Domanik deposits and the other two formed from organic matter of another source. Most of the studied oil samples contain derivates of isorenieratene indicating that the organic matter of oil source rocks formed in the photic-zone anoxia of the paleobasin.

The paper deals with the South Kara regional depression covering the southern part of the Kara Sea. A comparative analysis of the geologic structure of major petroleum-promising sedimentary complexes in the water area and on the land is carried out. Regional tectonic processes are considered, and the main stages of the formation of large tectonic elements are reconstructed. A brief comparative analysis of the anticline traps on the land of the study area and in the Kara Sea is made.

We have analyzed the predictions of the petroleum potential of West Siberia made by Academician I.M. Gubkin in his public reports and scientific works. We outline the strategy of oil exploration in the area east of the Urals, set up in the early postwar period, and the current state of research into the petroleum potential of the province. Special attention is focused on Jurassic deposits, which were regarded by I.M. Gubkin as oil-promising. At present, the largest volumes of predicted oil and gas resources of the province are concentrated in Jurassic and Neocomian plays.

Results of regional seismic exploration and drilling testify to the occurrence of moderately dislocated thick Upper Proterozoic and Lower Paleozoic deposits of subplatform type west of the Yenisei River. The deposits are buried beneath the Meso-Cenozoic sedimentary cover in the east of the West Siberian geosyneclise and form the Cis-Yenisei sedimentary basin. A comprehensive analysis of the new geological and geophysical data has refined the seismogeological model of sedimentary complexes, including 2D sections, structural and geological maps, and tectonic scheme. The Neoproterozoic and Paleozoic geodynamic evolution of the western margin of the Siberian craton is discussed.

The paper presents new paleotectonic data on the Bovanenkovo, Taz, and Gubkin arch uplifts and the Novyi Port, Urengoi, Kharampur, and Medvezh’e swells, with implications for the history of zone J2 and the Jurassic reservoir as a whole. Most of the large uplifts originated in the Early-Middle Jurassic and completed their evolution in the early Late Cretaceous (latest Cenomanian), generally (Bovanenkovo, Novyi Port, Kharamp, and Taz) or to a large extent (Urengoi and Gubkin), except for the much younger Medvezh’e swell, which formed in the Paleogene-Quaternary interval. The conditions for oil storage and retention in anticlinal traps of Jurassic zones J1 and J2 were the most favorable between the middle Late Cretaceous and the Eocene, inclusive. Gas accumulation lasted for a much longer time, from the Late Jurassic to the Present, and was especially rapid in the Late Cretaceous-Paleogene.

It is proposed to separate a regionally persistent member of fine-dispersed mudstones as the individual Kogalym Member within the Lower Vasyugan Subhorizon (Uppermost Bathonian-Lowermost Oxfordian). We present data on the lithologic composition, geophysical characteristics, and geochemical properties of the organic matter and depositional environments of the member. The Tyumenskaya SDB-6 well is proposed as a type section of the Kogalym Member, where a biostratigraphic approach has yielded the Middle-Upper Callovian volume of the member. We also discuss the aspects of specification and detalization of the Callovain-Oxfordian part of the Callovian and Upper Jurassic regional scheme of West Siberia.

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 ^o_Vt) 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 total organic carbon and presence of expelled oil found for logged zones in the Bazhenov section allows allocation and quantifying oil resources in unlogged beds.

The petroleum potential of the Bazhenov Formation reservoir has been assessed on the regional scale using several criteria inferred from published evidence, available geological and geophysical data, and well logging results from Upper Jurassic reservoirs.

Based on results of comprehensive lithological and geochemical analysis, we have established the regularities of the spatial distribution of major rock-forming components of the Bazhenov Formation in the West Siberian Basin (WSB), namely, siliceous, argillaceous, and carbonate material. According to the SiO2/Al2O3 ratio, the most siliceous rocks of the Bazhenov Formation are biomorphic siliceous mudstones (radiolarites) (>20), cryptocrystalline siliceous mudstones (8-20), and the most argillaceous rocks are argillaceous mudstones (<3). Intermediate SiO2/Al2O3 values (3-8) are observed in mudstones of different types. North-south distribution profiles of the SiO2/Al2O3 ratio and CaO content in different areas of the WSB were constructed. The areas of occurrence of radiolarites (potential reservoirs) and a “coccolith” member with the highest content of organic matter have been clarified. The thickest radiolarite bed (3-4 m) has been found in the Salym area. In some sections of the North Surgut area, a “coccolith” member is 2 m thick and is carbonatized. In most of the sections of the North Surgut, South Tomsk, and West Tomsk regions, rocks of this type are observed as 1 cm thick intercalates, and in the Novosibirsk region they are virtually lacking. We have established that a “coccolith” member, localized mostly in the upper part of the Bazhenov Formation, occurs not only in the Salym and Krasnoleninsk regions but also in the North Surgut region. It was also found in the Northern region in the southern and central parts of the South Nadym megamonoclise. Coccolithophorid relics are occasional in the South and West Tomsk regions and are lacking in the Novosibirsk region and in the Northern region of the South Nadym megamonoclise.

The composition of saturated and aromatic hydrocarbons and the structural-group characteristics of resins and asphaltenes of four oils of northern West Siberia have been studied. As follows from the distribution of hydrocarbons, the Cenomanian oils (pools in the beds PK and K2c) of the Russkoe, Barsukovskoe, and Pangodinskoe fields are naphthenic and the Pangodinskoe oil sample from the Lower Cretaceous pool (bed BN9) is paraffinic. The hydrocarbon composition pattern of the saturated fraction and the characteristics of the heterocyclic components of these oils point to their formation from dispersed organic matter of mixed genesis in the oil window. Hence, the oil source rocks are localized at depths much greater than the present-day level of the oil pools. Secondary (cryptohypergene) alterations (oxidation and biodegradation) in the shallow-depth oils determined their current predominantly naphthenic composition and considerably hamper the reconstruction of the types of dispersed organic matter. We assume that the mixed genetic type of the studied oils is not only due to their heterogeneous source but also due to the reorganization of primary oil pools at the Cenozoic stage of tectogenesis. The Cenomanian Russkoe and Pangodinskoe naphthenic oils are saturated with adamantoids, which can selectively accumulate during biodegradation.

Results of comprehensive geochemical studies of dispersed organic matter of the Bazhenov Formation are presented. The maximum contents of total organic carbon are found in the areas of the Surgut arch and South Nadym megamonoclise. The contents of organic matter are high (up to 24%) at the top of the formation section and gradually decrease to its bottom. By pyrolysis parameters and the composition of hydrocarbon biomarkers, the organic matter is referred to as type II kerogen (sapropelic organic matter) and is localized in the oil window.

More than 1500 measurements of vitrinite reflectance ( R 0Vt), along with mathematical modeling and computing, have been used to map the uppermost Middle Jurassic sediments of the West Siberian basin according to thermal maturity (catagenesis). The thermal maturity varies within the grades PC3 to AC2. Sediments are the least mature along the margins of the basin, and the maturity grade increases progressively toward its central and northern parts (grades MC21-MC2). It reaches a maximum in the north (AC2), where the sediments which subsided to large depths became exposed to high temperatures and pressures. The maturity zones of Jurassic sediments in the West Siberian basin form a typical pattern of regional catagenesis.

The structure of the junction between the Turukhan zone of deformation and the Kureika Basin was studied using regional reflection profiling data acquired along the Lower Tunguska River, with reference to well logs and land-based geological surveys. The western flank of the line comprises four large blocks separated by faults, which produce different patterns in seismic sections. The eastern part of the line covers the margin of the Kureika Basin filled with plane-bedded sediments and its border with the Turukhan Uplift and the Turukhan tectonic zone with thrust sheets.

We analyze geologic and geophysical factors enhancing the prerequisites for the high petroleum potential of East Siberia that were formulated by A.A. Trofimuk in 1960. The main updates concern the northern Siberian Platform, where it is indeed possible to significantly increase its petroleum potential and to refine the localization of large and giant, mostly oil accumulations.

We present results of lithological and geochemical studies of Paleozoic deposits stripped by drilling within the Ledyanskaya area in the north of the Tunguska syneclise. The studied section has a terrigenous sulfate-carbonate composition and is complicated by trap intrusions. We have established that the Ordovician-Devonian sedimentation proceeded within an epicontinental basin, with its depth varying from supralittoral to lower sublittoral zones. In the Carboniferous and Permian, coastal-continental sedimentation was predominant; in the Late Permian it was accompanied by volcanic activity. Analysis of the poroperm properties of rocks has distinguished three potential oil reservoirs: Silurian reef carbonate deposits and Ordovician and Carboniferous sand horizons. The Lower Silurian argillaceous-carbonate rocks and Devonian carbonate-sulfate-clay members, halite beds, dolerite bodies, and tuffaceous rocks are probably confining beds of these reservoirs. Geochemical study of organic matter has shown several possible sources of hydrocarbons: Upper Proterozoic deposits, Lower and Middle Cambrian Kuonamka complex, Middle Devonian Yukta Formation, and Upper Paleozoic coal-bearing deposits.

The Yurubchen-Kuyumba petroleum production center is being formed in the central part of Krasnoyarsk Territory, in the middle reaches of the Podkamennaya Tunguska River. It comprises the Kamo arch, the most elevated area of the Baikit anteclise, and its slopes. The main hydrocarbon (HC) resources (app. 820 mln tons) occur in the unique Riphean petroleum fields (Yurubchen and Kuyumba) of the Yurubchen-Tokhomo petroleum accumulation zone (YuT PAZ). The first commercial gas inflow was obtained from the Kuyumbinskaya-1 well in 1973, and that of oil, from the Kuyumbinskaya-2 and 9 wells in 1976. The Yurubchen-Tokhomo petropeum accumulation zone was originally established in 1986 under the ‘Complex Plan for Optimization of Regional, Prospecting, and Exploration Works in the Yurubchen-Tokhomo Petroleum Accumulation Zone’. Nowadays the main resources and reserves of oil, gas, and condensate are located in two petroliferous complexes, Riphean (main) and Vendian (supplementary). The extension, structure, and petroleum potential of the reservoirs of these complexes are discussed in the paper. To facilitate continuation of the prospecting and exploration works of the new oil fields and reservoirs, it is proposed to include the adjacent territories of the YuT PAZ (Omoro PAZ, Vaivida and Taimba petroleum prospects, Turama and Mutorai underexplored prospects) into the Yurubchen-Kuyumba petroleum production center. We propose support of stable annual oil production in the Yurubchen-Kuyumba petroleum production center as the main purpose of the petroleum exploration works.

Riphean and Vendian terrigenous complexes are not affected by trap injections within the South-Tunguska petroliferous region and thus can be considered a priority for further prospecting for hydrocarbon accumulations. Although these strata are not exposed with wells and are not characterized by core samples, their wide distribution is proved by seismic data. The obtained data and previous paleogeographic reconstructions show similar depositional environments of terrigenous sediments for the South-Tunguska and Baikit petroliferous regions. These facts substantiate criteria for the prediction of sand reservoirs within the study area. Taking into account the complex geologic structure of the South-Tunguska petroliferous region, ambiguity of seismic-data interpretation, and problems of deep-drilling technology, we provide recommendations for the geological exploration.

Large gas reserves have been discovered in the Vendian terrigenous rock complex of the Angara-Lena step in the southern Siberian Platform. In recent years, regional and areal exploration has yielded substantial data on the structure of gas-promising sedimentary strata and their reservoir properties. The author has analyzed the main structural features of Vendian gas-producing deposits and has made deterministic and probabilistic evaluation of initial hydrocarbon resources with regard to the discovered-field reserves.

Organic matter (OM) and rocks of the upper member of the Mesoproterozoic Malgin Formation in the southeastern Siberian Platform have been studied by modern research methods. Analysis has revealed homologous series of alkanes, tricyclanes, and hopanes in the bitumens. Leiosphaeridia crassa, L. Minutissima, cf. Leiosphaeridia tenuissima, cf. Glomovertella, and Oscillatoriopsis sp. have been identified among the rare microfossils preserved in mudstones. Geochemical, lithological, and paleontological studies have shown that bacterial microcommunities and, to a lesser extent, eukaryotic microorganisms were the main source of OM. Based on results of sedimentological analysis and study of biomarkers, the depositional environment has been reconstructed. A model for the accumulation of black shales and carbonate rocks of the Malgin Formation is considered. The hypothesis that the highly carbonaceous rocks formed in uncompensated depressions of shallow epicontinental marine suboxidation environments is substantiated. The petroleum potential and degree of OM catagenesis of the Malgin Formation rocks are evaluated. Pyrolysis, bitumen analysis, and hydrocarbon composition study have revealed autochthonous and parautochthonous bitumens in the oil shales, mudstones, and carbonate rocks. The obtained data show that the Malgin Formation rocks might have participated in petroleum generation in the Uchur-Maya region.

The Vendian-Riphean section of the Ust’-Maiskaya-366 parametric well was studied. The well is the first deep well drilled in the central part of the Aldan-Maya depression, in the southeast of the Siberian Platform. New probable oil source rocks within the Upper and Middle Riphean deposits have been identified based on core analysis supported by geological-survey data. We make a geochemical description of organic matter from these deposits and report the composition of abundant migrated bitumens discovered in the Ust’-Maiskaya-366 well section. The petroleum content in the Aldan-Maya depression has been predicted with regard to the new geological and geochemical data.