Bazhenov Formation Research Articles

Tectonic–Hydrothermal Processes and their Relationship with the Petroleum Potential of the Bazhenov-Abalak Complex of Western Siberia

Abstract —The main types of reservoir rocks have been identified within the Bazhenov-Abalak complex. To assess the geological resources of hydrocarbons, it is proposed to formally divide the entire set of lithological rock types comprising the Bazhenov-Abalak complex into two main varieties: fluid seals and reservoirs. We argue that it is possibile to distinguish between potentially productive and productive rocks, represented by siliceous and carbonate varieties, according to logging data. A possible mechanism for the formation of reservoir rocks within the Bazhenov-Abalak complex as a result of the tectonic-hydrothermal impact on these deposits has been reconstructed. An original methodology for identifying perspective zones of various categories of hydrocarbon accumulation in the Bazhenov-Abalak complex through integrating seismic data and tectonophysical modeling carried out on their basis has been proposed. For example, an assessment of the predicted geological resources of hydrocarbons contained in the Bazhenov-Abalak complex within the limits of 3D seismic exploration of the Yem-Yegovskaya area has been carried out. The necessity of assessing the prospects for oil content and calculating the predicted geological resources of hydrocarbons in the whole Bazhenov-Abalak complex, and not only in the Bazhenov Formation, is substantiated, based on a single mechanism of formation of reservoir rocks of tectonic-hydrothermal origin in them.

STRUCTURAL-FACIES TYPIZATIONS OF YHE BAZHENOV HIGH-CARBON FORMATION OF THE WEST SIBERIAN BASIN

The Bazhenov high-carbon formation is a part of the Bazhenov formation, characterized by a high content of aquagenic organic matter. Formation is a perspective source for expanding the hydrocarbon resource base. The article presents a combination of the results of core studies, interpretation of well logging and seismic data. A multi-faceted approach to the study of rocks made it possible to divide the West Siberian basin into 13 structur- al-facies zones, each of which has its own structural features of the bazhenov high-carbon formation section. This typification of the section will make it possible in the future to simplify the modeling of the properties of bazhenov high-carbon formation and predicting the most prospective areas.

Impact and implications of hydrothermal fluids migration in the Frolov hydrocarbon province in West Siberia

Both the prolific source rocks of the Bazhenov Formation and the reservoir-prone units of the Abalak Formation cover most of the West Siberian region. Hydrothermal fluids circulation has been suggested to affect hydrocarbon potential and reservoir properties at some localities of this vast hydrocarbon province. However, integrated studies are currently lacking. Here we present an extensive multidisciplinary study combining regional studies with core logging properties and sample analyses (i.e. geochemistry, petrography, organic geochemistry) to reveal processes related to the hydrothermal activity that affected both formations. We also focus on the factors and implications for secondary unconventional reservoir formation within the deposits from the Kamennaya summit of the Frolov oil and gas region. Three boreholes corresponding to type sections located in different parts of the study area (elevated, transitional and deep) were investigated. The elevated and transitional parts of the basin are adjacent to the weakened contact zones of a granite massif. These tectonic discontinuities acted as conductors for hydrothermal fluids circulation on the area. Lithological and stable isotope studies revealed the presence of intensive hydrothermal secondary alterations in various types in rocks, including massive metasomatic carbonatization, sulfatization, sulfide mineralization and leaching processes. This hydrothermal fluid activity resulted in reservoir formation within siliceous radiolarite layers, while in the deep part of the basin potential reservoirs were completely healed. Organic matter maturity varies in different parts of the basin. We identify several mechanisms related to the various hydrothermal processes that influenced rocks composition, structure and organic matter maturity: (1) A weakened zone located on the periphery of the granite massif in the basin basement is characterized by extensive fault damage zones facilitating the migration of high temperature fluids along deposits during post-sedimentation stages; (2) The thickness, mineral composition of the rocks overlying the basement control fault attenuation and fluid workflow; (3) The fluids composition, their acidity/alkalinity, prompted various changes in rock structure, especially in secondary porosity formation. The identification of various hydrothermal processes and their influence on pore space allowed to determine the approach for the spatial distribution prediction of unconventional reservoirs in the studied formations, and subsequently improve the efficiency and effectivity of the exploration process not only at the Kamennaya summit, but also on the other similar West Siberian basin areas.

Идентификация компонентного состава твердой углеводородной фазы в пласте и оценка ее влияния на поведение подвижного флюида баженовской свиты в процессе разработки залежи

The purpose of the work is to identify the composition of the initial reservoir hydrocarbon (HC) system of the Bazhenov formation, as well as to assess the influence of the presence of a heavy solid hydrocarbon phase (bitumen) in the formation on the production of mobile fluids using PVT modeling methods. The article describes the necessary experiments to determine the component composition of the C81+ fraction and the PVT properties of the formation mobile fluid taken from the well and the bitumen extract from the rock, and also presents their results. In addition, the properties of fractions up to C81+ were calculated depending on the molecular weight for PVT modeling (extension of the Katz-Firuzabadi table). One of the important parts of the article is the assessment of the ratio of bound and free oil in the original reservoir system. Based on geochemical research data, an analysis was performed to assess the component composition of the original system (using the example of the Bazhenov Formation) using rock pyrolysis and studying formation fluid and bitumen. Using the results of studies of reservoir fluid samples, a PVT model was built and tuned. This PVT model was used to assess the properties of the initial reservoir hydrocarbon system and was adjusted to the fraction of the solid phase in the reservoir at the initial reservoir conditions. After this, based on the PVT model, an assessment was made of the influence of the presence of a solid phase in the composition of the reservoir system on the behavior of a mobile hydrocarbon fluid during reservoir development for depletion, as well as on the use of enhanced oil recovery methods (injection of associated petroleum gas and thermal methods of influencing the reservoir).

Comparative analysis of the application of the Lichtenecker and Lichtenecker – Asaad models for the theoretical assessment of the rocks effective thermal conductivity

The analysis of the conditions and limitations of using the Lichtenecker and Lichtenecker – Asaad models for predictive assessment of the effective thermal conductivity of rocks have been carried out. For a comparative assessment, experimental data on the thermal conductivity of carbonate rocks (limestone, dolomite) from the South-West German Molasse basin, the Chicxulub impact structure (Yucatan Peninsula, Mexico) and the Bazhenov Formation (Western Siberia, Russia) have been considered. Comparative assessments were carried out based on the use of correlation relationships obtained by the authors of experimental works as a result of regression analysis of the petrophysical properties of carbonate rocks. The results of the computational and analytical assessment have shown that the highest accuracy of thermal conductivity prediction using the Lichtenecker – Asaad model can be achieved if experimental data are available that provide a highly accurate determination of the structure factor. The features of the influence of various parameters of the Lichtenecker – Asaad model on the error in estimating the effective thermal conductivity of the rock have been studied. It has been established that at the stage of pre-design research, the Lichtenecker model can be used for a fairly correct theoretical assessment of the thermal conductivity of water-saturated, slightly porous rocks.

Results of Quantitative Estimation of Unconventional Oil Resources of the Russian Federation

Abstract —The estimation results of the initial total unconventional resources of hydrocarbon in Domanik type sediments, the Khadum and Bazhenov formations are provided. The reasonability of estimating hydrocarbon resources in these deposits by the volumetric method is substantiated. The stratigraphic interval of their distribution is given. The technique of oil and gas geological zoning based on the mapping of structural and facies zones, the degree of catagenetic transformation of organic matter, and the boundary values of the thickness of carbonaceous rocks in the section is described. The criteria for the allocation of pay intervals that make up the effective part of the section are determined. The choice of parameters such as porosity coefficient, oil recovery coefficient, oil saturation coefficient, correction factor and oil density is justified. For each complex of deposits, adjustments related to the features of the geological structure of the estimation targets, the conditions of their occurrence and the degree of geological and geophysical study have been introduced into the estimation of total geological resources. The volumes of total geological and recoverable resources of unconventional hydrocarbon sources for the Volga– Ural, Timan–Pechora, Black Sea–North Caucasus, West Siberian and Lena–Tunguska oil and gas provinces are given. The conducted research has rationalized extensive resources, the recovery of which can compensate for the decrease in oil volumes from traditional deposits.

Geochemistry of Crude Oils from the Bazhenov Horizon (West Siberia)

Abstract —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.

Особенности разработки нефтяных залежей Западной Сибири с недонасыщенными коллекторами

The article is devoted to the urgent problem of designing and developing undersaturated reservoirs with hard-to-recover reserves, with an assessment of efficiency and improvement of methods for increasing oil recovery. Using the example of one of the objects of the Achimov deposits of Western Siberia, an algorithm of actions for choosing the optimal technology for developing a reservoir with a two-element structure characterized by homogeneous filtration and capacitance properties with high vertical anisotropy and the development of undersaturated zones in the plantar part is presented. The paper reflects information on design solutions using an areal combined well system and the use of multistage hydraulic fracturing. The article presents approaches to the development of oil deposits with undersaturated reservoirs, as well as describes in detail the geological structure of a number of fields in Western Siberia, and considering the correlation of production wells, various features of the occurrence of the Achimov strata were established. Using the example of specific deposits, the features of the formation of rocks of the Achimov strata are shown, based on the idea of the clinoform occurrence of the Neocomian rock strata in the interval between the roof of the Bazhenov formation and the sole of the Uriev pack. Two methodological techniques are proposed that allow us to reveal the main features of the macrostructure of geological objects, regardless of what kind of geological processes caused the sedimentation of complex objects: plicative or discontinuous tectonics, differentiating them unmistakably.

ANALYSIS OF DISSOLVING ABILITY OF LOWER ALCOHOLS AND ESTERS AQUEOUS AND HYDROCARBON SOLUTIONS TO ORGANIC MATTER OF BAZHENOV FORMATION ROCKS

This work is devoted to studying the characteristics of treatments with organic solvents on bazhenov formation rock samples, which contains a large amount of unconverted organic matter (kerogen, bitumen). This article contains the results of studying the dissolving abilities of individual low-molecular alcohols and esters, and solutions of these compounds in water and in a non-polar aromatic solvent (petroleum solvent). Among the individual solvents studied, esters of acetic acid showed the greatest dissolving ability; alcohols are less active. Petroleum solvent slightly dissolves the rock’s organic matter and needs the addition of more polar organic compounds. The dependences of dissolving ability of alcohols’ hydrocarbon solutions on alcohol concentration is extreme, with a maximum of 10 wt.%. Based on the obtained results, the mutual influence of solvents in the hydrocarbon fluid was additionally evaluated. It has been established that solutions of isopropanol and aromatic solvent show a synergistic effect to the dissolution of rock organic matter more than hydrocarbon solutions of esters. For the compositions that showed the greatest dissolving ability, a qualitative and semi-quantitative analysis was made for establishing changes in the composition of rock samples after extraction using X-Ray diffraction and Fourier-transform infrared spectroscopy. It is shown that mixtures of polar and non-polar solvents provide a more regular extraction of aliphatic and aromatic components of rock organic matter. Systems containing petroleum solvent, isopropanol and isopropyl acetate have been identified as the basis for the development of process fluids for increasing oil recovery in organic-rich reservoirs.

Lithology and oil content of the Bazhenov Formation in the central part of the Mansi Syneclise (Russia)

The article presents the results of studying four sections of the Bazhenov Formation and the overlying sediments in the central part of the Mansi syneclise, which are based on a comprehensive analysis of the results laboratory lithological and geochemical studies of core material and data from a wide range of geophysical studies of wells. For lithological characteristics, the section of the Bazhenov Formation was divided into five members, which differ in the ratio of carbonaceous, clayey, siliceous contents and carbonate component of rocks. The boundaries of the units were determined by their lithological composition, and then the velocity rectified taking into account GIS. The first two members are characterized by high contents of siliceous and clayey material, the third – a significant increase in the siliceous component, the fourth – increased concentrations of organic matter, which indicates its higher compared to the lower part section oil generation potential. In the fifth member, the content of carbonate material increases, the “coccolithic” interval is divided, and numerous fragments of bivalves are noted. Throughout the section minerals (strontianite, witherite) were discovered in the Bazhenov Formation, indicating that they occurred in diagenesis hydrothermal processes. In the section of one of the studied wells in the middle part of the Bazhenov formation, a reservoir interval was identified. High variability of reservoir properties of Bazhenov rocks was noted even within one oil-field, which is associated with their secondary transformations of rocks in dia- and catagenesis. It is substantiated, that materials of geophysical studies of wells that does not contain nuclear magnetic resonance data can only be used to identify possible productive intervals, the study of which by laboratory methods will allow establish the presence or absence of collectors in them.

Calculated and model profile of reservoir temperature during in-formation oxidation on the example of an oil field

The article describes physical and mathematical models of reservoir oxidation in oil deposits, the development of which is impossible with known technologies. In-formation oxidation is realized in the form of oil oxidation. A laboratory experiment on the core for the formation of combustion is presented, and the problems arising during the initiation of combustion in the rocks of the Bazhenov formation are described. It was revealed that the temperature gradient at the front and the rate of movement of the oxidation front are influenced by the volume of injected oxygen and the amount of kerogen per unit volume of the formation. The well-known Thomas model has been adapted for the analytical solution of the radial problem of in-situ combustion to the conditions of the implementation of oxidation processes in bituminous formations. The results of analytical calculations of the dynamics of changes in the formation temperature profile depending on the content of coking material and the flow rate of the injected air are presented. It was found that the temperature gradient at the front reaches 1,573 K/m, and that the rate of oxidation movement is influenced by the volume of oxygen and the density of kerogen reserves in the formation. Recommendations are made for further study of the advance of the front of intra-layer combustion in order to clarify the dependencies of the influence of other parameters (permeability, water saturation, etc.) on the speed of the front advance.

Experimental Data on Organic Matter Maturation in a Sample of Bazhenov Shale Formation (Western Siberia)

Experimental Data on Organic Matter Maturation in a Sample of Bazhenov Shale Formation (Western Siberia)

The Evolution of Bioclasts during Catagenesis in Rocks of the Bazhenov Formation in the Territory of the Frolov Oil and Gas Region

The Evolution of Bioclasts during Catagenesis in Rocks of the Bazhenov Formation in the Territory of the Frolov Oil and Gas Region

ROLE OF ELECTROMAGNETIC FIELDS IN DEVELOPMENT OF OIL AND GAS GENERATION PROCESSES IN UNCONVENTIONAL RESERVOIR ROCKS

The specifics of the Bazhenov Formation sediments, which are fundamentally different from traditional Green River oil shales, is that the processes of organic matter (kerogen) transformation into hydrocarbons have not yet been completed in them. The achieved paleotemperatures allowed the studied sediments to enter the main phase of oil formation during the regional catagenetic transformation of kerogen, but they failed to realize their oil-maternal potential to the full extent. At present, there are several unsolved problems for these rocks, related both to the genesis of oil and to the search for commercial hydrocarbon deposits in them and the development of technologies for their further development. The processes of «proto-oil» formation in the Bazhenov Formation sediments are still poorly understood. In fact, these processes are a system of equations with many unknowns, the correct solution of which is still impossible at the current stage of study. In our opinion, an important role in the development of oil formation processes in the Earth’s subsurface is played by magnetic fields formed under the action of a number of reasons (in particular, during the development of numerous tectonic disturbances). Our laboratory experiments by gas chromatography showed that in bitumoids of the studied samples there is a progressive shift of the «naphthenic hump» associated with internal transformations in the magnetic field. As a result of these studies, a decrease in the naphthenic fraction of hydrocarbons in samples heated in a magnetic field was recorded compared to samples without exposure to a magnetic field. Significant differences were found in paired samples of most geochemical characteristics - n-C23/24, n-C25/26, n-C26/27, n-C29/30, OEP, CPI, naphthene sum. Taking into account the influence of electromagnetic fields on the development of oil and gas generation processes allows us to create a completely new technology of «maturation» of hydrocarbon compounds (proto-oil) directly in the oil-maternal sediments and the formation of «artificial/technogenic» oil deposits.

Sequence Stratigraphy of the Jurassic Strata and Occurrences of Potential Sandstone Reservoirs in the ST Gas Field, Northern West Siberia Basin

Jurassic strata in the ST gas field of the northern West Siberia Basin have been regarded as a potential exploration target with undiscovered hydrocarbon resources. However limited research has been performed on the sequence stratigraphy of the Jurassic strata, as well as its sandstone distribution controlled by variable sea level change and sediment input. In this paper, four third-order sequences (SQ1, SQ2, SQ3, and SQ4) and nine fourth-order sequences for the Jurassic strata are interpreted based on seismic facies analysis and the lithology stacking patterns of seven wells. SQ1 is characterized by the special Bazhenov Formation which is featured by regionally distributed deep marine shales. SQ2 (J1) is composed of a coarsening upward sequence, the base of which is an unconformable surface that can be recognizable in both seismic profiles and well logging data. SQ3 (J2-J8) is composed of a complete fining-upward and coarsening-upward sequence, showing a series of transgressive and regressive successions. A complete SQ4 has not been drilled through by all the seven wells, only showing a coarsening upward succession on its top (J9) which evolves into a fining upward succession at the base of SQ3. Combined with the seismic inversion result, which predicts sandstone distribution, a sequence evolution model was built for SQ3 showing a full unit of transgressive system tract and highstand system tract (TST-HST) which often occurs in shallow marine shelves. During sequence development, most reservoir sandstones are deposited in the shelf and tidal delta environment at the bottom of the TST and the top of HST, and mudstones are deposited as shelf mudstones, especially at maximum flooding surface. That is controlled by both accommodation and sediment input. Generally, under this sequence framework, the depositional architecture can be further analyzed with implications for source rock, reservoir sandstones, and sealing rock, which may guide future gas exploration and exploitation in this area.

Features of Using the Lithogeochemical Indicators for the Reconstruction of Paleoclimate and Composition of Demolition Sources in the Late Jurassic-Lower Cretaceous West Siberian Sedimentary Basin

For the rocks of the Upper Jurassic-Lower Cretaceous Bazhenov formation, a significant positive linear dependence of the Th, Hf, Sc, La content on the Al2O3 content was revealed, and their terrigenous genesis was confirmed. It has been determined that the samples in which the distribution of the values of the Sc/Al2O3 and La/Al2O3 ratios does not satisfy the linear dependence are mixed clayey-siliceous rocks with a P2O5 content 1 mas. % or substantially pyritized (in which the content of pyrite exceeds the content of S and C/S ≤ 1), as well as siliceous mudstones with a SiO2 content 70 mas. % by weight. It is concluded that before analyzing geochemical indicators for reconstructing the conditions of formation of the Bazhenov formation, in addition to carbonated rocks, rocks of the above types, as well as rocks that have undergone late diagenetic kaolinization, should be excluded from the analysis. The conditions of formation of the studied deposits were reconstructed based on the analysis of the values of a number of geochemical modules and indicators. As a result of the study of CIA, CIW variations, it was confirmed that the climate in the Late Jurassic-Early Cretaceous period in the West Siberian sedimentary basin was warm, semiarid. It was revealed that during the entire period under review, it did not change significantly. For the deposits of the Bazhenov formation, a number of indicators such as (La/Yb)N, Eu/Eu*, as well as the distribution of trace element content values on the triangular diagram Th‒La‒Sc, suggest that in the central and southeastern regions of the formation distribution area, the sources of demolition of the mafic composition prevailed.

ЗАКОНОМЕРНОСТИ РАСПРОСТРАНЕНИЯ ОСНОВНЫХ КОМПОНЕНТОВ И ТИПОВ ПОРОД БАЖЕНОВСКОЙ СВИТЫ ЗАПАДНОЙ СИБИРИ

The distribution regularities of the main components and types of rocks of the Bazhenov Formation are investigated. It is one of the largest black shale formations in the world. The results of the lithological and geochemical study revealed that the brittlest rocks of the formation are widely distributed in the Central region and are considered as potential reservoirs: siliceous mudstones, kerogenic siliceous mudstones, carbonated radiolarites (limestones and dolomites). In the South-Eastern region, thicknesses of silicites are noticeably reduced; kerogen-clay-siliceous mudstones (similar in silica content to siliceous mudstones) prevail, which are also reservoirs in a number of areas. These types of rocks are practically not typical for the Northern and Southern regions. Detailed distribution maps of the main components of rocks for the lower, middle and upper parts, as well as for the Formation as a whole, were constructed. It was revealed that the highest concentrations of siliceous material are observed in the lower and to a lesser extent in the middle parts of the Bazhenov Formation section in the Central region. By the nature of distribution, composition and thickness of potential reservoirs, the Central region can be considered as a highly promising region in terms of development for hydrocarbon raw materials, the South-Eastern is medium-promising one, the Northern and Southern are low-promising ones.

FIRST RESULTS OF U−Th/He DATING OF EPIGENETIC PYRITE FROM ROCKS OF THE BAZHENOV FORMATION, WESTERN SIBERIA

U–Th/He method was applied to determine the age of epigenetic pyrite from the oil source rocks of the Bazhenov Formation, Western Siberia. Results indicate the possibility to date the post-sedimentation processes in a sedimentary basin by authigenic pyrite U–Th/He dating. The U–Th/He isochron age of pyrite (n = 7) from the dolomites of the Bazhenov Formation within the Frolovskaya megadepression is much younger than the age of sedimentation and corresponds to the Santonian-Cenomanian stages of the Upper Cretaceous (90 ± 8 Ma).

Experimental data on organic matter maturation investigation in one sample of the Bazhenov shale formations (Western Siberia)

The paper presents the results of the closed system hydrous pyrolysis isothermal kinetic experiment on a source rock sample from the Bazhenov shale formation. After 48 hours of thermal exposure at a temperature of 350 °С 80% of the kerogen generation potential relative to the original sample was transformed into hydrocarbons. Organic matter changes during laboratory modeling of maturation, controlled by pyrolytic parameters, follow the same trends as in natural source rocks. The kinetic spectra of kerogen activation energy destruction show a heterogeneity of organic matter inside the rock. At the constant frequency factor, a decrease in low-energy bonds and an increase in the release of hydrocarbon compounds from 53 to 54 kcal/mol are observed. Calculated changes in hydrocarbon compounds formation at different activation energies depending on maturity level are different from experimental ones, which indicates the influence of maceral composition and necessity to take into account a variability of individual components in basin modeling.

Evolution of bioclasts during catagenesis in rocks of Bazhenov formation on the territory of the Frolov oil and gas region

The paper presents the results of the Bazhenov formation rocks organic matter on the territory of the Frolov oil and gas region of the West Siberian basin investigations. The maceral composition of the sediments is represented by bituminite and alginite, removed vitrinite, as well as bioclasts: onychites and calcespheres organic matter. The investigation is focused on bioclasts. The petrographic characteristics, their change in the process of maturation evolution are described, qualitative parameters to access the degree of bioclasts maturity are established, and the initial formula for converting the onychites reflection index to the equivalent of vitrinite reflection index is proposed.