Nepa-Botuoba Anteclise Research Articles

Gneisses and granitoids of the basement of the Nepa-Botuoba anteclise: constraints for relation of the archean and paleoproterozoic crust in the boundary zone between Tungus superterrane and Magan terrane (South Siberian craton)

Gneisses and granitoids of the basement of the Nepa-Botuoba anteclise: constraints for relation of the archean and paleoproterozoic crust in the boundary zone between Tungus superterrane and Magan terrane (South Siberian craton)

Gneisses and Granitoids of the Basement of the Nepa-Botuoba Anteclise: Constraints for Relation of the Archean and Paleoproterozoic Crust in the Boundary Zone between the Tungus Superterrane and Magan Terrane (South Siberian Craton)

Gneisses and Granitoids of the Basement of the Nepa-Botuoba Anteclise: Constraints for Relation of the Archean and Paleoproterozoic Crust in the Boundary Zone between the Tungus Superterrane and Magan Terrane (South Siberian Craton)

Osinskaya subformation of the Usolsky formation of the Lower Cambrian of the central and southern parts of the Nepa-Botuoba anteclise: structure, formation conditions and biostratigraphical characteristics

Relevance. Geological prospecting carried out recently throughout the Lena-Tunguska oil-and-gas province makes studies of carbonates of the Osinskaya subformation particularly relevant, as they make it possible to establish the patterns of hydrocarbon trap formation. Aim. To present the results of the lithological and facial, biostratigraphic and petrophysical studies of the Osinskaya subformation in the southern and central part of the Nepa-Botuoba anteclise. Objects. Carbonate rocks of the middle Osinskaya subformation of the Usolskiy Formation of the Lower Cambrian Tommotian Stage, studied from well cores. Methods. GIS complex, detailed lithological and sedimentological description of the core, sequential stratigraphic analysis, petrographic analysis of 300 samples and examination of paleontological remains taken from the core; analysis. Results. Based on these studies, three sedimentation zones were identified, traced, and described for the first time: deep-water, marginal, and shallow-water. The deep-water zone is characterized by uncompensated sedimentation, the presence of single reefs, and confinement to depressions and troughs. It was flanked by an edge zone of carbonate platform associated with elevated thicknesses of the subformation and distribution of reefs over the area. It was followed by a shallow-water zone, represented by medium and reduced thicknesses of the Osinskaya subformation, its sediments are composed of carbonate grained and clayey rocks with small single reefs. The localized marginal zone of the extended carbonate platform agrees with the previously identified Chambinsko-Altybsko-Mirninskaya and Verkhnetokhomsko-Katsko-Pilyudinskaya zones of distribution of reef-like organogenic structures. On the basis of the studied wells, the structure of three formations according to the lithologic-facial profile was described. The paper introduces the authors’ variant of conducting the boundaries of the members. It was revealed that in the deep-water zone the prospects of searching for reservoir rocks are associated with single carbonate structures, in the marginal zone with area bioherms, and in the shallow-water zone with detrital deposits and shallow bioherms. The paleontological finds are shown to be confined to the selected sedimentation zones and beds. It was determined that algae diagnosed in the boudstones (autochthonous) were involved in the formation of the second and third strata, the edge zone of the carbonate platform. Archaeocyaths were diagnosed in detrital carbonate rocks of the second pack (allochthonous) in well no. 7 and autochthonous in boudstones of well no. 2X. Cribriciates were diagnosed in the boudstones of the third member (autochthonous). Archaeocyaths, cribriciates, namacalatusses, and calcareous algae studied from the cores of wells West Yaractinian no. 45, 361, Bolshetyrskaya no. 7, 3X, 2X, 4X, 5X, 6X were major edificators of Early Cambrian organogenic structures (biostromes, bioherms, bioherms massifs, reef formations).

Вторичные изменения карбонатных пород Непско-Ботуобинской антеклизы юга Сибирской платформы и их влияние на коллекторские свойства продуктивных горизонтов

Nepa-Botuoba anteclise is one of the most promising territories in Eastern Siberia, within which more than a half of the hydrocarbon resources are connected with carbonate reservoirs. One of the main tasks in the development of oil and gas resources in this region is associated with the forecast of the localization of reservoir rocks, which is largely determined by the degree of knowledge of the post-sedimentation proc-esses which have occurred. The article is dedicated to the influence of secondary processes on the capacitive and filtration properties of productive carbonate rocks of the Nepa-Botuoba anteclise. One of the wells drilled within its northeastern section has been taken as an example. The features of each of the post-sedimentation processes manifestation which took place were examined in detail and their influence on the filtration-capacitive properties of rocks of various lithotypes was assessed for all carbonate horizons penetrated by the well. The results of the research will help to increase the reliability of the forecast for the localization of carbonate rocks with improved capacitive and filtration properties, and therefore increase the efficiency of development of oil and gas resources in the considered region

Seismogeological model of the terrigenous vendian deposits on the north–eastern slope of the Nepa-Botuoba anteclise

A seismogeological model of the junction zone of the Nepa-Botuoba anteclise and the Ygyattinskaya depression was built based on the results of a comprehensive interpretation of deep drilling and seismic data. The position and propagation of regional high-rank faults have been specified, and a model of tectonic faults of the study area has been constructed. All faults of the study area were divided into three classes: those that cut the entire sedimentary cover; developed in the lower part of the sedimentary section, fading in the Cambrian salt pack; complicating the upper post-salt complex of rocks. Criteria for identifying thinning zones were developed and were made use of to identify oil and gas perspective objects within the Talakh, Ulakhan and Kharystan productive horizons.

Влияние факторов литогенеза на фильтрационно-емкостные свойства пород-коллекторов Ботуобинского горизонта Восточного склона Непско-Ботуобинской антеклизы

Влияние факторов литогенеза на фильтрационно-емкостные свойства пород-коллекторов Ботуобинского горизонта Восточного склона Непско-Ботуобинской антеклизы

Выражение Марковско-Ичерской зоны дислокаций Непско-Батуобинской антеклизы в геологическом строении района Дулисьминского НГКМ

In the Nepa-Botuoba anteclise of the Siberian Platform, the Sosninsky swell-like fold-thrust structure is described that was formed, presumably, since the Late Devonian – Early Carboniferous under conditions of episodic displaying of significant tangential stresses from the southeast – i.e. from the structural heterogeneity of the Baikal-Patom highlands, which has formed in the Late Riphean. The effect of shear deformations occurred also. It is shown that tectonic displacements that were recognized along thick plastic layers of salt, caused a significant difference in the geological structure of the deformed lower-middle (supra-salt and saline) and undeformed lower (sub-salt) structural complexes of the Dulisma oil and gas condensate field.

Features of high-density transient electromagnetic sounding data inversion under oil and gas prospecting in the Nepa-Botuoba anteclise area

The data of near-field transient electromagnetic sounding, which are widely used for the purposes of oil and gas exploration within the Nepa-Botuoba anteclise, are typically interpreted in terms of quasi-horizontally-layered models of media. The purpose of this study is to develop an approach to the inversion of transient electromagnetic sounding curves obtained via high-density 3D observation networks. The study was based on mathematical modeling, whose results allowed to estimate the lateral spatial parameters of a non-stationary electromagnetic field as well as to understand the differences between the results of one-dimensional inversion of the transient electromagnetic sounding data and the true parameters of the target horizon. As a result, the characteristic of the electromagnetic field described by an exponential function and used in the lateral-constraint inversion of high-density electromagnetic sounding was obtained. The proposed approach was tested on the practical data within the site under investigation located on the slope of the Nepa-Botuobа anteclise. It is shown that the use of spatial discrepancy under TEM sounding data inversion makes it possible to obtain geoelectric models characterized by lateral consistency of section geoelectric parameters. The application of the spatial stacking-based approach in the inversion process allows to increase the solution stability of the inverse problem of the near-field TEM sounding data.

Lithofacies variability of the Yarakta horizon as a complex result of geodynamic processes of tectonogenesis and sedimentogenesis

The purpose of the research is to analyze the lithological and facies conditions of formation and the causes of lithological composition variability of the Yarakta horizon deposits as well as formation and distribution features of reservoir rocks in the horizon. The paper uses the data on drilling and geophysical work results and research materials from the public sources. The Yarakta horizon is commercially productive in the deposits of the southeastern slope and the central part of the Nepa-Botuoba anteclise: Dulisminskoe, Yaraktinskoe, Ayanskoe, Danilovskoe deposits, etc. The deposits of the Yarakta horizon were formed during the initial transgressive stage of the Vendian sedimentation cycle and are characterized by extreme lithological irregularity of rock composition and thickness. Investigations of a number of scientists testify that in the early formation of the Yarakta horizon its territory in geomorphological terms was predominantly presented by a coastal plain, which was occasionally flooded by the sea. The rocks in the area are represented by the facies of temporary proluvial-deluvial flows of the coastal plain replaced by coastal shallow sediments. The change in the lithological composition of rocks and thicknesses of the Yarakta horizon is a result of changes in the nature of oscillatory movements, while its structural and textural features are determined mainly by the dynamics of water flows of the sedimentation medium and the paleorelief nature of the underlying surface. The conducted research allows to conclude that lithological heterogeneity of the Yarakta horizon in sections (vertically) and along the strike (laterally) is determined by the frequent alternation of various lithotypes, the formation of which is determined by the complex nature of tectonic movements and irregularity features of sedimentary layer facies.

Cyclicity, sedimentation environments and the influence of post-sedimentary processes on the structure and formation of the Vanavara Formation reservoir (based on the analysis results of core material of the Novo-Yudokon field)

The Lower Vendian oil and gas bearing play is one of the main ones in the Siberian platform and dominant within large tectonic elements (Nepa-Botuoba anteclise, Sayan-Yenisei syneclise, etc.). The oil and gas content of the complex is determined both by the conditions of its formation and by post-sedimentation processes, which are largely associated with the stages of formation and reformation of hydrocarbon pool. All these features of Vanavara reservoir were explored in a detailed lithofacies analysis of the core material of the Novo-Yudokon field and adjacent territories.

About the Influence of the Neotectonic Movements on the Placement of Oil and Gas Deposits in the Difficult Mining and Geological Conditions of the Nepa-Botuoba Anteclise

The Nepa-Botuoba anteclise is one of the unique territories within the ancient Siberian platform. At present, after more than half a century of oil and gas exploration, the territory of the Nepa-Botuoba petroleum area under consideration, with a comparative assessment of the oil and gas potential of the sedimentary cover of the Lena-Tunguska petroleum province, which covers the predominant part of the Siberian platform, is unambiguously distinguished as one of the petroleum region richest in hydrocarbons raw materials. This article examines the neotectonics of the territory of the Nepa-Botuoba anteclise, provides information on the structure of the sedimentary cover. A brief description of the methodological approach is given, aimed at optimizing the methodology of oil and gas exploration in the conditions of the study area.

Sequence stratigraphy of the Upper Vendian of the North-East of the Nepk-Botubinskaya anteclise of the Siberian platform (based on studyng boreholes core and Aliza gis)

The results of the analysis of core and logs of the upper vendian sediments (vilyuchansky, nepsky, tirsky and danilovsky horizons) of the northeast of the Nepa-Botuoba anteclise are presented. Regional sequence-stratigraphic analysis made it possible to identify six third-order sequences and stratigraphic unconformities confined to their boundaries. The systemic tracts are represented by proluvial, alluvial, lagoon and shallow-water-marine sediments, successively replacing each other, which is typical for the passive continental margin and the general subsidence of the Siberian platform in the vendian time.

Seismogravimetric Methodology: Specifics and Applicability to the Siberian Platform

Abstract —The paper presents a new seismogravimetric method for estimating static corrections used in processing of seismic data and in construction of time and depth sections. The method efficiency is demonstrated by comparison of the results of industrial and new experimental processing of data for the western slope of the Nepa–Botuoba anteclise.

A Sequence-Stratigraphic Analysis of the Upper Vendian of the Northeastern Part of the Nepa–Botuoba Anteclise of the Siberian Platform Based on the Study of Cores and Analysis of the GWL Data

A Sequence-Stratigraphic Analysis of the Upper Vendian of the Northeastern Part of the Nepa–Botuoba Anteclise of the Siberian Platform Based on the Study of Cores and Analysis of the GWL Data

Identification of Osinsky horizon organogenic structures by 2D and 3D seismic survey data in the north-eastern part of the Nepa-Botuoba anteclise

The fields of Eastern Siberia belong to the one of the main centers of hydrocarbon production in the eastern part of Russia. The main part of hydrocarbon reserves is located in the area within the Nepa-Botuoba anteclise, where the Lower Cambrian deposits are major production objects. The main purpose of this research is to provide a detailed study of the inner space and features of organogenic structures of the Cambrian period, as well as to determine the procedures for detecting reef structures by seismic research methods. Statistical processing of the available factual material on reservoir properties has shown a very uneven distribution of cavernosity (porosity). It is found that pores were formed as a result of leaching of shaped formations in loose packing locations of epigenetic dolomite grains, along the cementing substance in the intergranular spaces, along cracks and stylolite seams. To identify organogenic structures in the Osinsky horizon of the Nepa-Botuoba anteclise on the basis of seismic studies some additional methodologies have been selected. Identification of single reef structures in the Osinsky horizon of the Lower Cambrian based on the analysis of seismic amplitudes was carried out by means of a 2D and 3D seismic survey. According to the data of seismic studies, the Nepa-Botuoba anteclise features the development zones of both linear and single carbonate structures. It is also revealed that there is an increase in effective thicknesses in wells located in the annular anomaly. Summing up the results and analyzing the compared materials, it can be concluded that the main identification method of ring zones in wells is the method of longitudinal wave slowness measurement. A comprehensive analysis of 2D and 3D seismic survey data by the common depth point method as well as by a number of other methods using a specific algorithm allowed us to identify individual formations of organogenic (riphogenic) structures in the carbonate section of the north-eastern part of the Nepa-Botuoba anteclise.

Formation of Hydrocarbon Deposits in the Riphean-Lower- Paleozoic Sedimentary Basin in the Southern Siberian Platform

In fluidodynamic theories activated deep faults with a key characteristic "activated" are an important and integral part of the oil and gas basins. The influence of fault tectonics on the processes of oil and gas formation is generally recognized and reflected in a variety of publications, but the mechanism of influence that is associated with the activation parameters: cyclicity of manifestation, generation redirection, time and the period of activation of fault systems, remains insufficiently studied [10, 11, 12, 13, 14].Previously, in the marginal depressions of the east of the Siberian platform (Viluy Syneclise), carried out by several sedimentary basins (OPB), periodic processes of different ages activation of previously laid deep fault systems with various directions and generations were established.It’s argued that the formation of hydrocarbon deposits in the synchronous sediments of the same Riphean-lower Paleozoic OPB on-site of Nepa-Botuoba anteclise was due to subvertical fluid flows from underfoundation sources and processes of reformation of hydrocarbon deposits between productive layers under the influence of the periodic re-activation of fault systems with different spatial orientation. Deposits in productive formations of the terrigenous Vendian complex form under the influence of fault activation of early North-East, North of the North-East and submeridional generations. But in productive carbonate horizons of Wend-Cambrian and Lower Cambrian deposits form at the cost of reformation of deposits in the vendian deposits as affected by late north-west generation faults in the zones of overlaying on earlier generation. Oil exploration in the carbonates is recommended in the areas adjacent to the selected fault systems.

НОВЫЕ РЕЗУЛЬТАТЫ КОМПЛЕКСНОГО ЛИТОЛОГО-ФАЦИАЛЬНОГО И БИОСТРАТИГРАФИЧЕСКОГО ИЗУЧЕНИЯ ОСИНСКОГО ГОРИЗОНТА НИЖНЕГО КЕМБРИЯ ЮГА СИБИРСКОЙ ПЛАТФОРМЫ (БОЛЬШЕТИРСКАЯ СКВ. 7)

The section of the Osa Subformation of the Usolka Formation of the Lower Cambrian Tommotian stage penetrated by the Bolshetirskaya 7 well in the south of the Nepa-Botuoba anteclise has been studied. As a result of lithological-facies investigations, seven lithological types of rocks were identified, they are regularly replaced by each other along the section. Facies environments of the reef complex were dеtected: bar bank, rear part of the reef, organogenic bioherm bildup, reef rear bars, reef buildup, core of reef buildup. In the section of the subformation, three fourth-order sequences are identified. The sequence boundaries are fixed by subaerial hiatuses represented in the core by sedimentation breccias, karst zones. The largest lowering of sea level, in terms of amplitude and duration, is confined to the border of the second and third sequences. The conducted biostratigraphic analysis confirms the Lower Cambrian age. Remains of calcareous algae Renalcis polymorphum, R. gelatinosum, R. granosum, Botomaella zelenovi were found. Small shell fauna of the genus of Namacalathus Grotzinger, Watt ers et Knoll. also was found. It has global distribution in the Lower Vendian (Ediacaran) deposits in Namibia, Brazil, Canada, Oman, Spain, China, Russia, etc.

THE NEPSKY-1 IMPACT CRATER AND ITS FILL DEPOSITS ON THE BASEMENT ROOF OF THE SIBERIAN PLATFORM

In the Earth studies, discoveries and investigations of impact craters buried beneath thick sediments are sporadic so far and may still remain inefficient, unless geophysical surveys of the areas of interest are initiated. Such studies can provide useful data to develop the knowledge about cosmic events of the past geological eras, as well as contribute to industrial development of the areas. It is known that an impact crater is filled with layered deposits that create specific sequences and are generally thicker that deposits outside the crater. We have investigated a Precambrian crater located in the southern part of the Nepa-Botuoba anteclise of the Siberian platform. This impact crater called Nepsky-1 was discovered by seismic surveys using the common depth point method (CDPM). In our study, we used the geological and geophysical deep-drilling data of three wells, including gamma-ray and neutron logs and lithological core descriptions. With reference to the concepts of regional geological conditions, we reconstructed the conditions of sedimentation in the study area based on a comprehensive analysis of the structural and textural features of the rocks, and logging and seismic survey data. By processing and interpretation of the CDPM 3D seismic survey data, we obtained the structural images and cross-sections of the impact crater and analysed the thickness of its fill deposits. The Nepsky-1 crater is a bowl-shaped structure with a rim composed of allogenic breccia. In the area around the crater, fault systems are detected. Based on the core sample analysis, we identified the lithological members of the crater and its rim and described them in detail. Active compensation with lacustrine-delta sediments took place in the Nepa period of the late Vendian. By the end of the Tira time, the crater was completely leveled up. In our study, we obtained the first data on the structure of the crater section of the Vendian deposits. Sedimentation in the study area was controlled by the sea level changes. The main terrigenous productive horizons are confined to sandstones that accumulated during the sea level low stand, and found at the bottoms of the lower and upper Nepa subsuites, as well as at the bottoms of the lower and upper Tira subsuites. It is established that the study area was tectonically active in the late Tira time. As a result, the sediments filling the crater were removed to subaerial conditions, and the edges of the allogenic breccia rim were partially destroyed and formed granite breccia outgrowths observed in the rim’s cross-section. We conclude that in the Nepa and Tira times, tectonic vertical movements initiated relatively fast weathering and transportation of the terrigenous material from the adjacent hills into the sedimentation basin. The Nepsky-1 crater gives evidence of meteorite bombing of the Siberian paleocontinent in Precambrian. Finding similar crater structures can be reasonably expected in the study region. Considering the increased thicknesses of crater fill deposits, buried craters are promising potential for discovering oil-source and overlying seal rocks, which is important for petroleum industry.

Facies and Paleogeographic Reconstructions of Vendian Postglacial Deposits in the Southeastern Nepa–Botuoba Anteclise

The work is based on extensive factual material, including a core collection and GIS data on 84 deep wells drilled in the southeastern Nepa–Botuoba anteclise (Siberian Platform). Lithological studies of the Vendian basal deposits formed in the postglacial epoch were carried out. These deposits characterized by significant vertical lithological heterogeneity include layers of highly radioactive coarse-grained monazite-containing rocks. Therefore, it was necessary to check the clay content and combine the chosen lithological types into paragenetic rock associations that compose relatively thick intervals of the section and can be recognized using the geophysical research methods. The results of cyclostratigraphic analysis made it possible to indentify three ranks of binomial sedimentary cyclites and a basal acyclic unit of pudding conglomerates. The population of detritus zircons from pudding conglomerates (66 grains) contains the youngest grains with an age of 600–900 Ma. Minimum age of zircons is 631 ± 14 Ma. Taking into account the presence of diamictites and pudding conglomerates in the Vendian basal deposits, the results of studying the quartz grain surface and mineralogy of the heavy fraction from the sedimentary cover base and basement rocks suggested that their formation coincided with late glacial and postglacial stages of the Gaskier glacioperiod (584–582 Ma). Structural and textural features of postglacial deposits were determined based on the hydrodynamic parameters of fluvioglacial flows, features of the postglacial relief, the distance to provenances, and the mineral composition of eroded rocks. The Vendian cyclical deposits (Nepa and Tira formations) were formed during climate changes from the glacial to arid conditions in the course of transition from the continental to coastal-marine type.

Особенности геологического строения и перспективы нефтегазоносности зоны сочленения Анабарской, Непско-Ботуобинской антеклиз и Вилюйской синеклизы

Особенности геологического строения и перспективы нефтегазоносности зоны сочленения Анабарской, Непско-Ботуобинской антеклиз и Вилюйской синеклизы