Hydrocarbon Deposits Research Articles

Prospects of early Jurassic deposits within the Khapchagay megaswell of the Vilyuy syneclise

The study of terrigenous Jurassic deposits in the Vilyuy syneclise has become increasingly important. This is because the fields contains shallow gas reserves and were first discovered in anticline traps during the 1960s. Renewed geological exploration in this region is now providing valuable new geological and geophysical data. The aim of research is to select exploration criteria for locating hydrocarbon deposits in the territory. Seismic exploration is a leading method of research. Based on this, an analysis is conducted on the characteristics of hydrocarbon gas deposit formation and distribution within the early Jurassic stratigraphic complex of the Vilyuy oil and gas Vilyuy oil and gas bearing region. In particular, the Khapchagay megaswell has been analyzed. The study has identified the Nedzhelinskoye local uplift as an inversion structure. A dynamic anomaly of the "bright spot" type is observed at the roof of the productive lower Jurassic deposits of the Kyzylsyr suite in the central block. Well tests confirmed the difference in hydrocarbon fluid saturation between the western and eastern parts of the Nedzhelinskaya structure. The presence of dynamic anomalies of inversion type can be seen as an exploration indicator for hydrocarbon accumulation zones in the terrigenous deposits of the Vilyuy syneclise. This is a practical significance of the work.

Prospects of productive strata of the pre-Jurassic complex of Western Siberia for the discovery and involvement in the development

The article discusses the prospects of productive strata of deposits of the pre-Jurassic complex of Western Siberia for searching, forecasting and involving in the development. Some features of the geological structure of Triassic volcanic-sedimentary deposits and formations of the Paleozoic basement have been identified within the pre-Jurassic complex. The construction of digital geological models of Triassic and Paleozoic formations, which are fundamentally different in the geometry of the internal structure of the hydrocarbon deposits discovered in them, is based on 3D seismic information and its interpretation. In deposits of Triassic and Paleozoic sediments, significant differences in the composition and filtration-capacitive properties of rock reservoirs have been recorded; the principles for creating the structural frameworks of their digital models are also different. 3D seismic data makes it possible to correlate the Triassic strata and identify individual cycles, the boundaries and geometry of which are used to create digital three-dimensional geological models. When creating models of hydrocarbon deposits in Paleozoic formations confined to basement high areas, based on the interpretation of 3D seismic survey materials and analysis of seismic attributes, in combination with information on core, petrophysics and well testing, a forecast is made for the development of areas and strata of increased fracturing of rocks, which are the main inflow strata in production wells. Using the example of individual developed deposits confined to the pre-Jurassic complex in the fields of Western Siberia, the actual results of integrating geological and geophysical information with 3D seismic data are shown. Based on these results not only an assessment of the geological reserves of hydrocarbons was carried out, but also hydrodynamic calculations were conducted to perform history matching, as well as recommendations were made for the locations for drilling wells, their geometry and test strata. The accumulated experience in exploration and development of productive deposits of the pre-Jurassic complex allows us to assess the geometry and features of objects of interest in this interval, select the most informative methods for their mapping and methods for creating digital geological models that are the basis for designing the development.

Hygienic assessment of heavy metal and organic compounds pollution in snow cover of a multi-industrial city

Introduction. One of the leading health risk factors is atmospheric air pollution, the state of which can be indirectly assessed by the content of a wide range of pollutants in snow and soil cover. Materials and methods. The study analyzed data on deposits of polycyclic aromatic compounds (PAHs), heavy metals (HMs) and petroleum hydrocarbons (PHs) in the snow of different functional zones of the agglomeration. Physicochemical research methods were used. Results. The content of ΣPAHs was found to range from 412.8 to 2843.7 ng/L. The highest concentrations of ∑PAHs were observed in the residential area in the square (point 10) – 2843.7 ng/L; and on the border of the sanitary protection and residential zones in the area of the Yuzhnaya station (point 3) – 1758.2 ng/L. The share of benzo(a)pyrene (B(a)P) from ∑PAH ranged from 2.9 to 9.7%. PHs levels ranged from 51.0–117.0 μg/L. The difference in the range of fluctuations in values was most evident in the content of individual PAHs: B(a)P (16.13 times), Ant (12.05 times) and B(g,h,i)P (11.56 times ), mercury (17.53 times), zinc (9 times) and manganese (8.58 times); metals: cadmium (1.89 times), copper (1.75 times), and lead (1.47 times). Limitations. Sampling and features of snow cover contamination by atmospheric precipitation in the dynamics of the winter season. Conclusion. Concentrations of PAHs and HM varied in different ranges of values and had a non-uniform spatial distribution over the territory. Direct links were found between the content of B(a)P and other polyarenes in the snow cover.

Определение литологического состава осадочных пород для построения объемной модели по данным ГИС

The features of the lithological composition of productive sediments and their consideration in the petrophysical modeling of a volumetric model based on a GIS complex are considered. It is noted that on the basis of X-ray spectral and granulometric analysis, it is possible to obtain reliable information about the structure, texture, component and mineral composition in order to clarify the petrophysical characteristics of the rocks under study. Using the example of two hydrocarbon deposits “K” and “N” the results of determining the lithological composition of sedimentary rocks from core from different age terrigenous deposits are discussed in order to build a petrophysical model of the entire well section, taking into account the areas of lack of information from direct studies (sludge and core). Electron microscopy and X-ray diffraction analysis are used to study finely dispersed (clay, siliceous, carbonate, etc.) rocks, which are especially important for accurate diagnosis of the mineral composition of rocks. In addition to the features of the geological structure of the deposit, the quantity and quality of the initial information largely determine the methods of constructing the model and the results obtained. The results of X-ray spectral analysis made it possible to determine the composition of chemical elements and the amount of each element in the sample. Information about the mineral composition of rocks and the lithological differences identified at the first stage are distributed to the part of the section where there is no or insufficient information on the core or sludge. The information obtained on the lithological composition of sediments gives the most complete picture of the geological structure of the section opened by the well and is further used as the basis of a volumetric model based on the data of geophysical surveys of GIS wells.

Deciphering origins of hydrocarbon deposits by means of intramolecular carbon isotopes of propane adsorbed on sediments

Hydrocarbons are one of the important fluids within the Earth’s crust, and different biotic and abitoic processes can generate hydrocarbon during geological periods. Tracing the sources and sinks of hydrocarbons can help us better understand the carbon cycle of the earth. In this study, an improved approach of adsorbed hydrocarbons extraction from sediments was established. The improved thermal desorption approach, compound-specific isotope analysis and position-specific isotope analysis were integrated to investigate the molecular and intramolecular isotope fractionation between trace hydrocarbon gases within sediments and geological hydrocarbon deposits. The isotopic compositions of the terminal position carbon of propane (δ13Cterminal) serves as a correlation indicator between trace hydrocarbon gases within sediments and geological hydrocarbon deposits. The tight sandstone gas from the Turpan-Hami Basin is a first case study for the application of this novel method to trace hydrocarbon origins. The results showed that the hydrocarbons in the tight sandstone gases in the study area most likely originated from humic organic matter (type III kerogen) at an early mature stage. δ13Cterminal values of the thermally desorbed propane gases from different source rocks were distinguishable and the values of the tight sandstone gases significantly overlap with those of the Lower Jurassic Sangonghe source rocks, suggesting their genetic relationship. Overall, the results provided novel position-specific carbon isotopic constraints on origins of hydrocarbons.

Magnetostratigraphy of the upper Jurassic and Lower Cretaceous deposits of the Bolshekhetskaya structural terrace

Relevance. The confinement of hydrocarbon deposits to certain stratigraphic horizons, poor knowledge of the northeast of Western Siberia and adjacent territories, including the magnetostratigraphic method, with their oil and gas potential (over the past 10 years, four unique hydrocarbon deposits have been discovered here), the boreal nature of the deposits, and the need for remote magnetostratigraphic correlations. Aim. To create a magnetostratigraphic reference section of the northeast of Western Siberia. Objects. Sections of deep wells of the Pendomayakhskaya, Vostochno Suzunskaya, Vostochno Lodochnaya and Gorchinskaya areas of the Bolshekhetskaya structural terrace, which exposed the Lower Cretaceous and upper parts of the Upper Jurassic (Yanovstan Formation) deposits. Methods. Paleomagnetic studies were carried out according to standard methods and included sampling of core samples with an "up-down" orientation, sample preparation (kappametry, marking of samples, photographing, sawing), measurement of magnetic susceptibility, temporary cleaning (the samples were located along the field during a week, then a week-against the field with determination of residual magnetization), complete demagnetization by alternating magnetic field, plotting of complete demagnetization, mass cleaning, determination of components of natural residual magnetization, assessment of paleomagnetic stability, identification of forward and reverse polarity zones, construction of paleomagnetic sections. To construct the magnetostratigraphic sections given in this article, the paleomagnetic and biostratigraphic data are linked. For this purpose, magnetochrons were identified using biostratigraphic analysis. Results. The authors have compiled a composite magnetostratigraphic section of the boundary Jurassic-Cretaceous deposits of the Bolshekhetskaya structural terrace and identified four magnetozones with subzones of direct and reverse polarity, compared with the Berriasian ammonite scale. The high information content of the results of magnetostratigraphy research under boreal conditions was noted.

РЕЗУЛЬТАТЫ ПРИМЕНЕНИЯ СТАТИСТИЧЕСКОГО МЕТОДА ДЛЯ ПРОГНОЗА НЕФТЕГАЗОНОСНОСТИ ТЕКТОНО-КОНЦЕНТРИЧЕСКИХ СТРУКТУР ДАЛЬНЕГО ВОСТОКА РОССИИ С ИСПОЛЬЗОВАНИЕМ ЭТАЛОННЫХ ТЕРРИТОРИЙ

he paper presents the results of using the statistical method to analyze geological and geophysical data measured within several tectonic-concentric structures in oil and gas-bearing regions in the Far East of the Russian Federation (depth of the Mohorovichi surface, depth of the the lithosphere bottom, values of geothermal energy). The distribution and values of some statistical parameters (histograms, distribution densities, probabilities, median and mean values) used for forecasting zones of hydrocarbon deposits location have been calculated. It was found that the most informative initial data used for statistical prediction of areas of location of oil and gas deposits are the presence of concentric zones at the depth of the Mohorovichich surface, and concentric inhomogeneites at the lower boundary of the lithosphere associated with the «root» structures of paleo-mantle plumes. Based on the calculated statistical parameters, four local tectonic-concentric structures promising for prospecting new oil and gas fields were identified.

Флюидный режим образования вторичных доломитов в палеозойских карбонатных коллекторах Хасырейского месторождения (вал Гамбурцева)

The search for hydrocarbon deposits in the sediments of the Lower Paleozoic complex of the Timan-Pechora oil and gas province, which are associated with the main prospects for increasing reserves, is a relevant topic for research. It is necessary to understand the formation processes of carbonate reservoirs within the complex under consideration to develop a strategy for predicting the structure of the complex reservoirs. Obtaining data on the parameters of the fluid regime of the formation of secondary dolomites in the Paleozoic carbonate reservoirs of the Khasyrey field (Gamburtsev swell) was the aim of the study. We studied primary fluid inclusions in dolomite and anhydrite cements filling vuggy voids in reservoir rocks. We showed that the inclusions contained up to 10 vol. % of the gas phase, which was represented by methane and water vapor. The liquid phase was characterized by a substantially chloride-calcium composition, the salinity is 13.5–23.5 wt. % NaCl-eq. These data might indicate the formation of cavities and cements of secondary dolomites from moderate-temperature solutions of high salinity, which were formed as a result of mixing sedimentation (primary marine) waters and brines of hydrothermal vents. The products of evaporite dissolution in the presence of hydrocarbons and sulfate reduction processes were the most likely source and supplier of the fluids, both the formation of leaching caverns in the rock and the cements performing them. Fluids could enter the upper floors of the section from hydrothermal sources in the basement zones and lower horizons of the sedimentary cover through a system of faults and cracks during tectonic activation.

Sediment bypass in a marl-dominated margin of a turbidite system in a narrow basin setting

Submarine sediment density flows play a pivotal role in transporting clastic material to the deep sea. The volume of sediment they transport, which bypasses a specific point or geographical location, shapes the stratigraphic record of the entire turbidite systems. Hence, recognition of bypass-dominated zones is crucial in facies prediction and understanding the architecture of turbidite systems. This understanding is linked to the economic aspects of exploring hydrocarbon deposits, the occurrence of geohazards that impact submarine infrastructure, the distribution of pollutants, and carbon sequestration.In the western part of the Ropianka Fm (Skole Nappe, Polish Outer Carpathians), three bed types showing evidence of sediment bypass were identified in the channel-mouth setting of marl-dominated slope and base-of-slope successions. The varying proportions of these bed types in studied successions and relationship with adjacent facies associations led to the identification of two channel-mouth zones. This study provides insights into deposits with characteristics differing from the previously described channel-mouth setting, evidenced by a significantly lower sand-to-mud ratio and smaller scale of erosional and depositional structures. The reported channel-mouth zones are interpreted as the marginal parts of a channel mouth, formed by subcritical flows. This study broadens the understanding of the channel-mouth setting by introducing dynamic and mud-dominated zones that experience sediment bypass and weak erosion. The identified bed types and typical characteristics of Marginal channel-mouth zones 1 and 2 can serve as a reference for interpreting marginal areas of channel-mouth settings in mud-dominated successions with scattered thin-bedded and coarse-grained deposits in other deep-water basins.

Effect of secondary processes on the petrophysical properties of sand rock of the tanopchin formation of the Tambey field (Yamalo-Nenets autonomous okrug)

Relevance. Finding the correlation between filtration-capacitive properties and secondary processes helps to identify missed oil and gas deposits. Traditional methods of processing geophysical information are becoming less and less effective, and accordingly there is a need to introduce new techniques for detecting missed hydrocarbon deposits. Aim. To study the effect of secondary processes on the filtration and reservoir properties of rocks in the productive lower strata of the tanopchin formation of the North Tambey license area, located within the Tambey field, using materials from geophysical surveys of wells and core data. Methods. The statistical-correlation interpretation method represents a significant breakthrough in the field of interpretation of well logging data. It allows for a more accurate interpretation of data from existing reservoir studies, which makes it possible to identify productive sections of wells where hydrocarbons could not be detected by traditional methods. Statistical correlation interpretation is carried out on the basis of data from secondary geochemical processes occurring in the formation. The scientific novelty. Identification of the relationship between the intensity of secondary processes and the petrophysical properties of the rocks of the Lower Cretaceous productive horizon of the Tambey field (Yamalo-Nenets autonomous okrug). Results and conclusions. The author has determined the dependence of the filtration-capacitive properties of rocks on the intensity of secondary geochemical processes. It was established that secondary geochemical processes such as carbonatization and pyritization worsen reservoir properties, while kaolinization and pelitization lead to an improvement in the filtration and reservoir properties of reservoir rocks. The paper explains the mechanism of effect of secondary processes on filtration-capacitive properties. Pelitization of potassium feldspars leads to the formation of three-layer clay minerals, which have the largest sorption surface area and cation exchange capacity; as a result, the reservoir capacity increases, which leads to an increase in permeability several times.

Discoverers of Siberian oil and gas: from Raul-Yuri G. Ervier to Farman K. Salmanov. Sabit A. Orudzhev, Igor S. Gramberg and others — discoverers of gas and oil in the arctic shelf

The work perpetuates the names of scientists and discoverers of hydrocarbon deposits who have contributed to the development of the oil and gas industry. These figures are the finest examples of service to the Motherland, Society, and Science. The article is based on the results of a report at the plenary section of the international scientific conference entitled “Formation and development of the oil and gas industry — the contribution of Russian and Azerbaijani scientists and specialists”.

IMPACT OF REAL-LIFE ENVIRONMENTAL EXPOSURES ON REPRODUCTION: Evidence for reproductive health effects following exposure to hydraulic fracturing chemical mixtures.

Unconventional oil and natural gas (UOG) operations, particularly hydraulic fracturing, have revolutionized oil and gas production, using and containing complex mixtures of chemicals that may impact reproductive health. While there is growing evidence for effects on births in hydraulic fracturing/UOG regions and good mechanistic evidence for potential reproductive toxicity, there is much research still needed to make firm conclusions about these practices and reproductive health. Unconventional oil and natural gas (UOG) operations have emerged over the last four decades to transform oil and gas production in the United States and globally by unlocking previously inaccessible hydrocarbon deposits. UOG development utilizes many compounds associated with conventional oil and gas, as well as some specific to UOG extraction, particularly during hydraulic fracturing (HF). While research is increasing on UOG chemicals and their mixtures, this review discusses the current evidence for reproductive toxicity following exposures to UOG/HF mixtures. These complex chemical mixtures have been demonstrated to interact with numerous mechanisms known to influence reproductive health. A growing number of environmental and controlled laboratory testing studies have reported adverse reproductive health effects in animals exposed to various UOG chemical mixtures. An expanding body of epidemiological literature has assessed adverse birth outcomes, although none has directly examined reproductive measures such as time to pregnancy, semen quality, and other direct measures of fertility. The existing literature provides moderate evidence for decreased birth weights, increased risk of small for gestational age and/or preterm birth, increased congenital abnormalities, and increased infant mortality, though importantly, studies are widely variable in methods used. Most studies utilized distance from UOG operations as an exposure proxy and did not measure actual chemical exposures experienced by those living near these operations. As such, while there is growing evidence for effects on births in these regions and good mechanistic evidence for potential reproductive toxicity, there is much research still needed to make firm conclusions about UOG development and reproductive health.

ECONOMIC, ORGANIZATIONAL AND TECHNICAL PROBLEMS OF OIL AND GAS FIELD ABANDONMENT

More and more mature fields in the old oil-producing regions are now in the stages of declining production, and their operation is close to completion, therefore, the upcoming liquidation work is of particular relevance and importance. Decommissioning of developed or inactive oil and gas wells is associated with a number of environmental, economic and legal problems. Liquidation of oil and gas facilities can become a significant expense for companies, especially if the budget deficit does not fully pay off during operation. At the same time, the negative impact of field development on the environment is not limited to the period of active production. With the onset of liquidation work, subsoil users may have obligations to government agencies in the form of taxes, licenses and other payments, which also increases their financial burden. Interaction between the state and subsoil users in the process of development and decommissioning of oil and gas fields becomes an important factor in the rational use of natural resources. Often, control over the liquidation of abandoned or decommissioned fields is entrusted to the state, although companies also have obligations to report on planned and implemented related activities. Since liquidation measures are a rather labor-intensive process that requires careful planning and financial resources, subsoil users sometimes evade responsibility, citing the lack of the necessary amount of financial resources to carry out these works. The article provides an overview of international experience in approaches to financing liquidation work. Mechanisms of legal regulation of relations between state management bodies and subsoil users, organizational, technical and economic problems of liquidation of oil and gas fields, as well as a number of approaches to effective financial support for the decommissioning of oil and gas facilities are considered. In conclusion, based on the presented analysis of the problems of the industry and international experience in organizing liquidation measures, the authors give several of their proposals, the implementation of which can be considered necessary preparatory work for effectively solving the problems of eliminating the consequences of the operation of hydrocarbon deposits with the onset of the desired economic stability.

Comparative analysis of the effectiveness of inhibitors preventing the formation of high molecular hydrocarbon deposits

Comparative analysis of the effectiveness of inhibitors preventing the formation of high molecular hydrocarbon deposits

Pre-Jurassic weathering crust of the Kalinovoe hydrocarbon deposit, Tomsk region: composition and structure characteristics

Abstract. The study of pre-Jurassic deposits in the southwestern part of Western Siberia is highly relevant due to their potential of increasing hydrocarbon resources. These deposits are considered prospective targets for the discovery of hydrocarbon accumulations. Weathering crusts developed on the upper part of the Paleozoic rocks in the Tomsk region exhibit a complex composition and structure, reflecting the interplay of various factors, including primary sedimentary processes and later alteration processes, including fracture-controlled fluid flow and metasomatism. Aim. To establish the characteristics of the mineralogical composition and structure of the Paleozoic weathering crust formations developed at the Kalinovoe oil-gas-condensate field. Methods. Optical microscopy, X-ray diffraction, scanning electron microscopy. Results and conclusions. The composition and structure of the deposits at the boundary zone between the Paleozoic and Mesozoic successions have been studied in detail in the section of one of the wells at the Kalinovoe oil-gas-condensate field. The factual material is represented by core and thin sections of weathering crust deposits. The primary rock-forming minerals are silica minerals (quartz, chalcedony and opal) and clay minerals, with a lesser amount of carbonate minerals (siderite). Different lithological units were identified based on the content of minerals and bioclast (radiolarians and sponge spicules), indicating their formation under marine conditions. The protoliths of the altered rocks were carbonate-siliceous rocks, argillaceous limestones, and radiolarian cherts, which as a result of multiple stages of hydrothermal alteration and metasomatic processes were transformed into argillaceous-silicified rocks. In these rocks, with intense post-alteration overprinting, good reservoir quality porosity can develop. This porosity includes biogenic voids, microcavities, micropores, and open fractures.

PARAGENETIC RELATIONS OF COAL-BEARING AND OIL- AND GAS-BEARING FORMATIONS (EXAMPLE OF THE DON-DNIEPER TROUGH)

The relationship between coal-bearing and oil-and-gas-bearing formations is a fundamental problem in geology. The aim of this study is to determine the paragenetic relationships between hydrocarbons with coal-bearing sediments. This is achieved through the analysis of hydrocarbon composition, hydrocarbons deposits distribution, connection with petrographic types and degree of coalification of the coal in the Don-Dnieper trough. It provides various examples of the coexistence and palaeogeographic connectivity of coal, oil, and gas-bearing formations, which is a widespread occurrence in many basins worldwide. During both peat accumulation and the transformation of organic matter from peat to coal, the Don-Dnieper trough was located in the equatorial range of paleo-latitudes. This observation is significant because it sheds light on the conditions that existed during the formation of coal in this region. This text describes the petrographic composition and degree of coalification of the concentrated and scattered organic matter in the Don-Dnieper trough. These characteristics determine the formation of liquid and gaseous hydrocarbons. Based on the distribution of hydrocarbon deposits in the Don-Dnieper trough, and their consistency with petrographic coal types and degree of coalification, carboniferous deposits are classified into several categories: coal-bearing, gas-carbon-bearing, coal-gas-bearing, gas-bearing, oil-gas-bearing, gas-oil-bearing, and oil-bearing. The distribution of coal deposits of a certain age, the degree of coalification, and the composition of organic matter are consistent with the presence of liquid or gaseous hydrocarbons. The additional data obtained strongly support the concept of a paragenetic connection between coal-bearing and hydrocarbon-containing formations.

Clarification of the geological structure of hydrocarbon deposits when creating a digital geological 3D model

Clarification of the geological structure of hydrocarbon deposits when creating a digital geological 3D model

Coal in the 21st century: Industry transformation and transition justice in the phaseout of coal-as-fuel and the phase-in of coal as multi-asset resource platforms

The coal industry is enjoying long-term investments in new coal-fired power generation even as coal mining and production have been declining. Recent conflict in Europe has disrupted energy supplies and reinvigorated coal use. The duration of the retrenchment to coal may be short lived, but the end point of “short lived” remains uncertain. The present state of the coal industry and the investment community that underpins its growth obviates any meaningful acceleration in coal's phaseout as a core fuel resource. However, coal can be recast as a catalyst for achieving clean energy and economy futures. This can be done by seeing coal hydrocarbon deposits and byproducts of coal processing as long-term multi-asset resource platforms (MARPS), which integrate multiple new revenue streams on coal lands other than just mining coal as a fuel. New value comes from repurposing and leveraging mining lands, harvesting minor and trace elements from coal, and creating new revenue from harvesting hydrogen and carbon materials from coal bed methane, raw coal, coal tailings, and fly ash residues. We make the case that Coal Mining Enterprise (CME) value can be enhanced by ending the use of coal-as-fuel and creating new value streams serving existing and emerging markets by fully assessing, evaluating, and utilizing the portfolio of natural resources that are collocated within a typical coalfield. Coal sector investors tend not to see undervaluation in coal assets because CMEs focus predominantly on mining, processing, and shipping coal-as-fuel for electricity production and industrial processes. Formulating and asking the correct questions about how much value is being left on the table may bring innovation into a new frontier of coal as multi-asset resource platforms. Co-benefits of the approach include job creation across many viable emerging markets where “refining” coal is a competitive source of factor inputs. Moreover, it aids governments in aggressive support of coal industry transformations, through which lasting coal transition justice can be achieved. Ironically, despite all the technological and market uncertainties, coal in the 21st century can be, and should be, a critical success factor in achieving clean energy and economy futures.

Информативность геоморфологических и изотопно-геохимических методов при оценке газоносности территории (на примере Ангаро-Ленской нефтегазоносной области)

The paper examines the geochemical method's effectiveness for assessing the gas potential of territories and prospecting for natural gas fields in combination with data on a territory's neotectonic activity obtained from the digital elevation model analysis in the Eastern Siberia area. Geochemical data include the content of methane and its homologues (C1 – C6), determined by gas chromatography in subsoil samples, as well as the carbon isotope ratio (δ 13C) of the detected methane, measured on an isotope mass spectrometer. The reconstruction of neotectonic activity areas was carried out using a modified morphometric method of digital elevation model analysis. Estimates of the macroscopic fracturing of the sedimentary cover, also caused by neotectonic activity, were obtained from the digital elevation model as the density of lines – primary linear objects expressed in relief, identified using the method of A. A. Zlatopolsky. The information obtained from the digital elevation model allows to identify areas where the probability of gas fields destruction is the highest. A joint analysis of isotope-geochemical data and information on the probable hydrocarbon deposits destruction makes it possible to assess the prospects for the territory's gas content, as well as identify promising areas.

Formation mechanism of the small-angle X-type strike-slip faults in deep basin and its controlling on hydrocarbon accumulation: a case study from the Tabei Uplift, Tarim Basin, NW China

In the central Tarim Basin, numerous hydrocarbon deposits were found along ultra-deep strike-slip faults, and its evolving progress and formation mechanism are research hotspots. The Paleozoic small-angle X-type strike-slip fault in the Tabei Uplift is the research subject in this article. Based on high-precision three-dimensional seismic data, three structural deformation layers were revealed: the rift system, weak strike-slip deformation and salt tectonics in the deep structural layer (Sinian–Middle Cambrian), the strong strike-slip deformation and karst-dissolution structure in the middle structural layer (Upper Cambrian–Middle Ordovician), and echelon normal faults in the shallow structural layer (Upper Ordovician–Carboniferous). The formation and evolution of strike-slip faults is jointly controlled by the distribution pattern of basement rift and the activities of surrounding orogenic belts, which can be divided into three stages. In the Middle to Late Cambrian, the initial subduction of the Paleo-Asian and Proto-Tethyan oceans precipitated the emergence of two sets of small-angle X-type strike-slip faults, striking NW and NE above the grooves of Precambrian rifts, influenced by local weak compressive stress. Affected by the closure of peripheral paleo-ocean, strike-slip faults deformed considerably in the Middle–Late Ordovician and were reactivated in the Silurian–Carboniferous, forming en-echelon normal faults in the shallow layer. The layered deformation structure of the strike-slip faults significantly affects the accumulation of hydrocarbons. The differential hydrocarbon enrichment of faults in the Tabei Uplift is collectively influenced by the distribution of source rocks and the migration of oil and gas. The topographical features of the Tabei Uplift, along with the distribution of strike-slip faults across tectonic units, have rendered the NE direction the preferential pathway for hydrocarbon migration. Additionally, impacted by the development of en echelon faults, the NE-trending faults offer superior conditions for hydrocarbon preservation and charging condition, compared to the NW-trending faults.