Terrigenous Rocks Research Articles

ЕЛЕКТРИЧНІ ТА ПРУЖНІ ВЛАСТИВОСТІ ГЛИБОКОЗАНУРЕНИХ УЩІЛЬНЕНИХ ПОРІД КАРБОНУ ЦЕНТРАЛЬНОГО ГРАБЕНА ДДЗ

Paper concerned the research of elastic and electric properties of deep-seated consolidated terrigenous rocks of Carboniferous period of the Central graben of the Dnieper-Donetsk depression (DDD). The purpose of the research was to study the petrophysical parameters of the consolidated reservoir rocks, as the basis of the integrated analysis of their physical properties. Such electric and elastic parameters of rock samples as resistivity and formation resistivity factor, formation resistivity enlargement factor, velocities of the P-waves and interval (transit) time have been studied. The correlation analysis has allowed establishing a series of empirical relationships between resistivity and formation resistivity factor, and between porosity and formation resistivity factor in atmospheric and reservoir conditions. The correlation relationships of the resistivity with formation resistivity factor manifest itself in linear function. Physical modeling of reservoir conditions allows adapting the values of electrical parameters obtained in atmospheric conditions to parameters of rocks in reservoir conditions. Laboratory acoustic study of siltstones and sandstones managed to establish correlation relationships of: velocities of the P-waves and interval (transit) time with density and porosity in atmospheric conditions; velocities of the P-waves in atmospheric and reservoir conditions; velocities with porosity in reservoir conditions. The dependence of the velocities of the P-waves in atmospheric and reservoir conditions for the studied rocks manifest itself in linear function. Physical modeling of reservoir conditions allows adapting the values of elastic parameters obtained in atmospheric conditions, to parameters of rocks in reservoir conditions. The correlation relationships of the electric and elastic properties with reservoir properties of siltstones and consolidated sandstones which were obtained in laboratory petrophysical research should be at the basis of preliminary interpretation of geophysical data on new areas of the Central graben of DDD.

Application of seismic attribute analysis in Lower Miocene reservoir characterization, northeast Bach Ho field, Vietnam

The Cuu Long basin is an Early Tertiary rift basin of southern Vietnam, and the most potential basin in the country with high productive for oil and gas. Special interest in the Lower Miocene reservoir in the Cuu Long basin is caused by the gradual depletion of unique oil-bearing in the fractured basement and the possibility of transferring production wells to overlying deposits in the terrigenous rocks of the sedimentary cover and entering new deposits into development. In recent years, seismic attributes analysis has emerged as an effective tool to predict ancient riverbeds where sand bodies may exist in nonstructural traps. Understanding the distribution of these sand bodies will be of great significance in the orientation of oil and gas exploration activities. The paper applied seismic attribute analysis method combined with artificial neural network (ANN) and well data to predict the distribution of sandstones reservoirs of Lower Miocene sediments in the Northeastern Bach Ho oil field. Seismic attributes selected as input for ANN training including Relative Acoustic Impedance, Root Mean Square, Sweetness. The attributes provide the most obvious opportunity to display geological features with varying seismic amplitude characteristics as well as predict lithofacies, petrology and the distribution of sand bodies. The research results have identified the potential reservoirs in the Northeastern area of Bach Ho field, which are deposited in the fluvial, marginal lacustrine and deltaic environments.

Determining factors of the unconsolidated rocks of Cenomanian reservoir on the Bolshekhetskaya depression

The relevance of the article is associated with the importance of the object of the research. Dozens of unique and giant oil and gas fields, such as Urengoyskoye, Medvezhye, Yamburgskoye, Vyngapurovskoye, Messoyakhskoye, Nakhodkinskoye, Russkoye, have been identified within the Cenomanian complex. The main feature of Cenomanian rocks is their slow rock cementation. This leads to significant difficulties in core sampling and the following studies of it; that is the direct and most informative source of data on the composition and properties of rocks that create a geological section.The identification of the factors, which determine the slow rock cementation of reservoir rocks, allows establishing a certain order in sampling and laboratory core studies. Consequently, reliable data on the reservoir and estimation of hydrocarbon reserves both of discovered and exploited fields and newly discovered fields that are being developed on the territory of the Gydan peninsula and the Bolshekhetskaya depression will be obtained. This study is also important for the exploration and development of hydrocarbon resources of the continental shelf in the waters of the Arctic seas of Russia as one of the most promising areas.As a result of the analysis, it was found that the formation of rocks of the PK1-3 Cenomanian age of the Bolshekhetskaya depression happened under conditions of normal compaction of terrigenous sedimentary rocks that are located in the West Siberian basin. Slow rock cementation of reservoir rocks is associated with relatively low thermobaric conditions of their occurrence, as well as the low content of clay and absence of carbonate cements. Their lithological and petrophysical characteristics are close to the analogous Cenomanian deposits of the northern fields of Western Siberia and can be applied to other unconsolidated rocks studied areas.

Geomechanical parameters of sedimentary rocks of Southern Sakhalin

The samples of terrigenous rocks of the Sakhalin were selected for geomechanical studies: the rocks of the Nevelskaya and Kholmskaya Formations from the Petropavlovsk quarry; ones of the Kholmskaya Formation on the west coast of the south of Sakhalin, rocks of the Junonskaya Formation on the east coast. The Kholmskaya Formation N1hl is represented by siltstones and interlayers of fine-grained sandstone. The Nevelskaya Formation N1nv is represented by siltstones with inclusions of tufogenic material. The Junonskaya Formation T2-Jun is represented by variegated greyish-green jaspers. Their static and dynamic parameters (strength limits, static Young’s modulus and Poisson’s ratio, cohesion and angle of internal friction) were determined. The obtained results are characterized by a significant spread of values, which is likely explained by the significant fracturing of the initial samples and the effect of anisotropy.

Multistages mineralization and transformation of terrigenous rocks in the Vyun ore field, Yana-Kolyma metallogenic belt, Northeast Asia: insight from the sedimentary, diagenetic and hydrothermal sulfides and geochemistry of ore-hosting rocks

The article presents the results of studying the sulfidization zone of the Charky-Indigirka thrust fault within the Vyun ore field in the Upper Adycha sector of the Yana-Kolyma metallogenic belt. The purpose of the research is to study the composition and distribution of basic and trace elements in terrigenous rocks of the Upper Triassic and Middle Jurassic, as well as in distal metasomatites on the territory of the Vyun ore field. The petrochemical features of weakly altered terrigenous rocks, conditions of their formation and changes of composition during epigenetic processes were analyzed. Three generations of pyrite were identified: diagenetic Py1, metamorphogenic Py2 and metasomatic Py3. Typomorphic trace elements and variations of their distribution in pyrites were determined. Composition analyses of weakly altered sedimentary rocks of the Upper Triassic (V/(V+Ni)=0.5-0.8, V/Cr=0.1-2.9 and Ni/Co=2.5-10.3) and Middle Jurassic (V/(V+Ni)=0.7-0.9, V/Cr=0.2-2.0 and Ni/Co=1.3-8.8) yielded the conclusion that changes in oxygen conditions to disoxic and anoxic, as well as the enrichment of terrigenous material with ore elements, lead to the formation of authigenic sulfide mineralization at the early stages of the sedimentary strata formation. The subsequent multistage development of the territory was accompanied by an active migration of chemical elements, their input and redistribution.

Diagenesis and reservoir space types of alkaline lake-type shale in Fengcheng Formation of Mahu Sag, Junggar Basin, China

Using observations and descriptions of drilling cores, image logging, microscopic section, argon ion polishing field emission scanning electron microscopy, X-ray diffraction, and whole-rock trace element analysis, the study of shale reservoir diagenesis and space types in the Fengcheng Formation of the Mahu Sag was conducted. Considering the trace element contents and their ratios (Sr/Ba, V/Ni, Th/U, V/(V + Ni), U/Mo, and Sr/Cu), the Fengcheng Formation is formed in a dry and hot continental lacustrine basin with a paleoenvironment of saltwater and anoxic/lean oxygen conditions. The shale reservoirs of the Fengcheng Formation with the characteristic of multisource mixed sedimentation include terrigenous clastic, volcaniclastics, and carbonate rocks. Currently, the Fengcheng reservoir of the Mahu Sag is in the middle of diagenetic-stage B. The principal factors for reservoir densification are compaction, dissolution, carbonate mineral cementation, and clay mineral cementation. The Fengcheng Formation develops multiple reservoir storage space types, such as rock fractures, stylolites, and micro–nanoscale pore-throat systems. The macroreservoir space types include tectonic, induced, bedding, and dissolution–expansion fracture types. The microreservoir space types include microfractures, stylolites, and micro–nanoscale pore throats. The research showed that the Fengcheng Formation has tectonic fracture-pore systems (tectonic fracture-type reservoirs) and stylolite-matrix pore-tectonic microfracture systems (shale oil reservoirs), forming the shale oil preponderant charging channel network. Reservoir space type and its spatial distribution are the principal factors for shale oil accumulation of the Fengcheng Formation in the Mahu Sag.

Digital core modeling technology for determining the reservoir-capacitive properties of terrigenous reservoirs

For today digital core modelling technology is demanded and developing instrument in conducting the main reservoir-capacitive properties of terrigenous rocks. This technology is becoming more widespread in connection with the development of computer and nanotechnologies. The main attempts to apply the digital core model in practice have been undertaken in the last decade, although the first examples of its use for the analysis of reservoir rocks date back to the 80s of the last century. Improvement of digital core modeling technology will allow to cope with the problem of lack or absence of core material, as well as to solve the problems of studying loose, weakly cemented and other rocks, "problematic" of conducting physical experiments. In addition, it seems relevant to create a digital core block that fits into the general digitalization platform of technologies related to reservoir-capacitive properties in the development of hydrocarbon fields. With the use of a digital core model, it also becomes possible to effectively refine and supplement the calculated parameters in laboratory core studies, reducing the likelihood of errors in the obtained results.

Depositional Environments and Paleogeographic Evolution during the Formation of Upper Paleozoic Terrigenous Rocks in Taimyr

Depositional Environments and Paleogeographic Evolution during the Formation of Upper Paleozoic Terrigenous Rocks in Taimyr

Gravity Anomalies And Crustal Structure Of The Eastern Part Of The Verkhoyansk Fold-And-Thrust Belt, NE Russia: Evidence From The Junction Area Of The Adycha-Elga And Allakh-Yun Tectonic Zones

The results of geophysical studies of the junction area of the Adycha-Elga and Allakh-Yun tectonic zones of the Verkhoyansk fold-and-thrust belt located on the submerged eastern margin of the Siberian craton are presented. Three structural-mineral complexes are recognized: Archean-Paleoproterozoic, Mesoproterozoic-Middle Carboniferous, and Upper Carboniferous-Early Mesozoic. The Early Jurassic plume-related basaltic volcanism and suprasubduction Late Jurassic-Early Cretaceous granitoids, regional Brungadin and Suntar faults are identified. The goal of the research is to identify deep heterogeneities and clarify the structure of the Earth’s crust in the junction area of the Adycha-Elga and Allakh-Yun tectonic zones of the Verkhoyansk fold-and-thrust belt. The analysis of gravitational anomalies is carried out, their transformations are performed – distinguishing the medium and low-frequency components, the vertical derivative Vzz, and calculating the equivalent distribution of sources of density masses at depth. It is determined that the hidden granitoids of the Adycha-Elga tectonic zone are located mainly in linear zones of decompaction at a depth of about 3.5 km. In the Allakh-Yun zone, a large gravitational minimum has been identified, where it is assumed that there is a magma granitoid chamber occurring at a depth of about 9 km. The model of the deep structure of the territory is based on the analysis of materials on the reference seismic profile 3-DV with the use of gravimetric data and the regional structure of the territory. According to the results of the wave pattern interpretation, the thickness of the lithosphere varies from 41 to 44 km. The thickness of the Upper Carboniferous-Triassic terrigenous rocks is 8-12 km, Mesoproterozoic - Middle Carboniferous carbonate-terrigenous complex is up to 12 km. The Archean-Paleoproterozoic crystalline basement occurs at a depth of 19-21 km. The Conrad discontinuity is assumed at a depth of about 30 km. Intense deformations of the crystalline basement are recognized, and trans-crust faults are identified.

A new straton in the Late Devonian sedimentation in the Tsil’ma river basin of the Middle Timan

Research subject. Terrigenous rocks of the Sargaevo stage of sedimentation in various structural-facies settings within the Tsilma area (Middle Timan). Material and methods. The composition, structural features of rocks, and the species diversity of spores of higher plants were studied in the most complete natural outcrops proposed as a stratotype of the Paladinskaya Formation – a new straton of the Sargaevo age in the Middle Timan. Over a large area of the region, the deposits contain very few remains of fossil fauna, often indifferent. As a result, palynostratigraphy was selected as the main biostratigraphic method. Results. In the Middle Timan, a new straton, the Paladinskaya Formation, is described, which characterizes the Sargaevo stage of sedimentation in various structural-facies settings within the Tsil’ma area. The new straton has clear lithological and detailed palynological characteristics; a description of the limitotypes was performed.At present, the Paladinskaya Formation is the most complete sequence of Early Frasnian sedimentation in the European North-East of Russia, where it was possible to record regional responses to the global Frasnes event and to determine the position of the controversial level of the boundary between the Middle and Upper Devonian. Conclusions. The name “Ust’e Yarega” Formation in the Middle Timan cannot be considered valid, since it is a homonym of the sediments of the same age in the South Timan. The section is represented mainly by continental, rather than marine, deposits. A new name for the identifed formation is proposed – “Paladinskaya” with a description of the stratum section and limitotype.The Paladinskaya Formation is characterized by subcomplexes of spores (А and Б) of the regional miospore zone Cristatisporites pseudodeliquescens, which made it possible to correlate the marine and continental deposits of the Early Frasnian on the territory of the entire Timan-Pechora region and establish its exact position in the stratigraphic scheme of the Devonian.

The Ludicovian of the Raahe–Ladoga Zone of the Fennoscandian Shield (Isotope-Geochemical Composition and Geodynamic Nature)

Abstract —In the northern Ladoga area, the age of the Sortavala Group rocks in the southeast of the Raahe–Ladoga zone of junction of the epi-Archean Fenno-Karelian Craton and the Paleoproterozoic Svecofennian province, their relationship with dome granitoids, the age of the provenances, and the time of metamorphic processes were estimated. The study was focused on the Nd isotope composition of rocks, the geochemical and isotope-geochronological parameters of zircon from the granite-gneisses of the Kirjavalakhti dome, the basal graywackes of the lower unit and the trachytes of the middle unit of the Sortavala Group, and the plagio- and diorite-porphyry dikes cutting the volcanosedimentary units of this group. The new isotope-geochemical data show a Neoarchean age of the granitoids of the Kirjavalakhti dome (2695 ± 13 Ma) and their juvenile nature (εNd(T) = +1.5). The granitoids underwent tectonometamorphic transformations (rheomorphism) in the Paleoproterozoic (Sumian) (2.50–2.45 Ga), which are recorded in the U–Th–Pb isotope system of the rims of the ancient cores of zircon crystals. The volcanosedimentary complex of the Sortavala Group formed on the heterogeneous polychronous (3.10–2.46 Ga) continental crust of the epi-Archean Fenno-Karelian Craton. With regard to the errors in determination of the age of clastic zircon, the minimum concordant U–Th–Pb ages of 1940–1990 Ma of detrital zircon from volcanomictic graywackes of the Pitkyaranta Formation can be taken as the upper age bound of terrigenous rocks, which agrees with the maximum age of the Sortavala Group rocks estimated from the U–Th–Pb (SIMS) age of 1922 ± 11 Ma of the Tervaoya diorites (Matrenichev et al., 2006). According to the proposed new tectonic model, the accumulation of the volcanosedimentary complex of the Sortavala Group, its metamorphism, erosion, and overlapping by the Ladoga Group turbidites had already occurred in the pericratonic part of the epi-Archean Fenno-Karelian Craton by the time of the Svecofennian continent–island arc collision, subduction, and formation of bimodal volcanoplutonic complexes of the young Pyhäsalmi island arcs and felsic volcanics of the Savo schist belt (1920–1890 Ma).

Lithogenetic preconditions of reservoirs and reservoir rocks formation in the Middle Devonian sediments of the Skhidnosaratske deposit (Dobrudja Foredeep)

The lithological features of the Middle Devonian sediments of the Skhidnosaratska structure of the Dobrudja Foredeep in the aspect of their influence on the formation of reservoir rocks and hydrocarbon reservoirs have been considered. Nine lithocycles of regressive nature (e-1 – e-5; g-1 – g-4), characterized by a two-membered structure have been identified in the section. Each lithocycle represents a separate productive horizon. The lower parts of the latter are composed of porous and fractured reservoir rocks (limestones, dolomites, siltstones, sandstones), and the upper parts are composed of fluid-resistant packs (marls, anhydrites).Features of cyclic sedimentation conditions caused spatial-age variability of trap localization and morphology, nature of distribution of reservoir rocks of various types, and post-sedimentation processes caused spatial heterogeneity of petrophysical properties of rocks, which entailed different prospects for individual areas of the Skhidnosaratske deposit. The vaulted traps of the productive horizons of the Eifelian deposits tend to the area of borehole 2, and the Zhivetian deposits to the borehole 1. Consequently, in the first case, the most perspective horizons are e-2 and e-3, in the second – g-2 – g-4. Often more powerful packs of better-quality reservoir rocks are developed outside the vault, which leads to the formation of lithological traps in the e-1 and e-2 horizons. It has been shown that the complex structure (presence of layers of carbonate and terrigenous rocks) of fluid-resistant marl-sulfate packs could cause dispersion of hydrocarbons and thus reduce the prospects of individual horizons, in particular, e-2 and e-3. The established heterogeneity of the structure of the productive horizons, the pinching out of individual packs of both pore and fractured reservoirs, the spatial uneven development of the limestones anhydritization and dolomitization processes give possibilities to suggest the formation of separate deposits with different hypsometry of water-oil contacts.

LITHOLOGICAL AND FACIAL FEATURES, COMPOSITION, AND SEDIMENTATION CONDITIONS OF TERRIGENOUS-CARBONATE ROCKS OF THE MOTY GROUP (SHAMAN CLIFF, IRKUTSK REGION)

We have studied terrigenous-carbonate rocks in the area near the Sayan mountains in the Irkutsk Region (Russia), specifically at the Shaman Cliff, being the stratotype area of rocks that belong to the Moty group. The cliff’s lower part is composed of sandstones, which fragments gradually decrease in size upward the cross-section. The middle and upper parts are composed of sandy dolomites and dolomites, respectively. In terms of material characteristics, the terrigenous rocks correspond to arkoses. According to the genetic typification, the arkoses are composed of destructed primary igneous rocks. The terrigenous-carbonate rocks contain a carbonate component that gradually increases in the upper part of the cross-section. In the Shaman Cliff cross-section, we distinguish 32 lithological units and eight lithologicalgenetic types of deposits. Paleogeodynamic conditions are reconstructed for the formation of the sedimentation basin. Our study of the Shaman formation reveals specific features of the lithological facies, which suggest that these rocks accumulated in a coastal environment affected by tides. In the study area, clastic materials were mainly removed from an orogen that formed due to the Vendian accretion-collision events in the southern folded frame of the Siberian platform. Dolomites composing the upper part of the cliff are attributed to the Irkutsk formation of the Moty group. Their lithological features give evidence of shallow-marine conditions of their formation, without any supply of clastic material, which contributed to mass dispersal of the Cambrian biota described in [Marusin et al., 2021]. It is our first initiative to draw a boundary between the Shaman and Irkutsk formations of the Moty Group along the base of the carbonate eluvial breccia unit that marks the stratigraphic break. In the cross-section, this boundary represents the border between the Upper Vendian and Lower Cambrian.Our conclusions are generally consistent with the ideas of most researchers about the Late Vendian evolution of the southern margin of the Siberian platform. The results of our study can be used in further investigation of this area and provide a basis for correlating the studied strata with the same-age reference cross-sections of other regions in Siberia.

Precambrian and Early Palaeozoic metamorphic complexes in the SW part of the Central Asian Orogenic Belt: Ages, compositions, regional correlations and tectonic affinities

Precambrian metamagmatic complexes of the Zhingeldy and Kendyktas blocks of the Zheltau and Chu-Kendyktas terranes of the SW part of the Central Asian Orogenic Belt (CAOB) consist of predominant Neoproterozoic orthogneisses with the estimated protolith ages of ca. 790–800 Ma, and subordinate epidote and garnet amphibolites, metabasalts and metadolerites of the lower metamorphic grades. The orthogneisses are characterized by negative εNd(t) values of −12 to −4 with Nd model ages of 2.3–1.7 Ga, indicating their protoliths could have formed by a reworking of the Palaeoproterozoic crustal materials. Precambrian metavolcanic rocks in the studied region are rhyolites with the estimated crystallization ages of ca. 800–830 Ma, and are associated with metabasalts. Metasedimentary complexes in the studied region consist of intensively retrogressed garnet-mica schists interlayered with marmorized limestones, metasilicic rocks, epidote and garnet amphibolites and strongly altered eclogites. The inferred protoliths of the garnet-mica schists are terrigenous rocks accumulated during the latest Ediacaran – middle Cambrian and formed from Mesoproterozoic (ca. 1.0 Ga) and to a lesser extent Palaeoproterozoic felsic source rocks (ca. 1.6–1.7 Ga and ca. 2.5 Ga). The garnet-mica schists of the Kendyktas block have negative εNd(t) of −13.4 and a model age tNd(DM) of 2.2 Ga, implying formation of their protolith from Palaeoproterozoic crustal source. The studied Zheltau and Chu-Kendyktas terranes from the SW part of the CAOB have much in common in terms of Precambrian and Early Palaeozoic evolution and chemical compositions of the key rock types. The presence of the Early Precambrian rocks (Zheltau terrane), an abundance of the Late Mesoproterozoic (1000–1100 Ma) detrital zircons in the Ediacaran-Cambrian metasedimentary complexes and a wide distribution of the Late Neoproterozoic magmatism, are distinctive features of the studied terranes. We refer such Precambrian terranes of the western CAOB to the Ulutau-Moyunkum group where tectono-magmatic evolution is consistent with that observed from the northern part of the Tarim craton. Our results also aid comprehensive correlation of metamorphic complexes of the Precambrian terranes from the SW CAOB.

DEVELOPMENT OF SELECTIVE GROUTING COMPOSITIONS BASED ON BITUMINOUS EMULSIONS FOR WATER INSULATION WORKS

To increase the efficiency of water inflow isolation in oil wells, selective grouting compositions are preferred. The use of selective isolation methods provides for selective clogging of water inflow channels while maintaining the permeability of oil-saturated reservoir intervals. The mechanism of selectivity realization for different groups of grouting compositions is shown. It is noted that the selectivity of the action of these compositions is significantly affected by the permeability heterogeneity of the formation. In this case, the water primarily flows through the high-permeable interlayers, where the grouting composition will be pumped in a larger volume than in the low-permeable interlayer during water insulation works. In this paper, we continue to study selective grouting compositions that clog the pore space with a material that is subsequently soluble in oil and insoluble in water. The possibility of using bitumen emulsions, including commercially available road emulsions, is analyzed. The use of bituminous emulsions as water-insulating compositions has a number of advantages: due to the low viscosity of the direct emulsion, it easily penetrates into the porous medium. At the same time, bituminous emulsions have high thermal stability. The resulting bitumen film is impervious to water and is sufficiently resistant to aggressive media (acids and alkalis). The objects of the study were used bitumen road emulsion cationic grade EBDK B-52 and acrylic dispersions, which were intended to increase the adhesion of bitumen to the surface of rock and metal. Commercially produced reagents of the Lacroten brands (E-081, E-31, E-082, E-43), Lacryl 4443 were used as acrylic dispersions. Studies of bituminous emulsions and acrylic dispersions for adhesion to the surface of metal, carbonate and terrigenous rocks have been carried out, from which it follows that acrylic dispersions with a low pH (3.0-3.6) are an effective means of processing samples. Filtration studies indicate the selective properties of the bitumen emulsion. When injecting B-52 bitumen emulsion for both the bulk model and the ideal crack model, there is a general tendency to reduce water permeability: 32.8 % for the bulk model and 33.6 % for the ideal crack model. When conducting filtration studies with the initial injection of acrylic dispersion followed by injection of the emulsion, in all experiments, filtration attenuation is observed in both the water-saturated and oil-saturated reservoir models. According to the results of the conducted studies, for the isolation of water-saturated interlayers, it is proposed to carry out works according to the scheme of selective isolation using bituminous emulsion B-52; and when carrying out works on the elimination of behind-the-casing flows, disconnecting water-filled layers and eliminating the leakage of production columns in the coupling joints, sequential injection of acrylic dispersion and bituminous emulsion is provided.

Recycling of drainage brines by means of re-injection in Udachny Mine

The permafrost zone in Levoberezhny 2 Site, represented by the Upper Cambrian carbonate–terrigenous rock strata up to 270 m thick, is studied. It is found that during injection, brines first flow along fractures and pores, and dissolve ice fill in them. The permafrost rocks degenerate as a result, and extra porosity is generated together with formation of a manmade aquifer. The analytical flow model of brine disposal in permafrost rocks in Udachny Mine represents the analytical flow model in dry soil, with rock permeability varied from zero to maximum values to describe frozen and thawed zones. The hydrogeological research of permeation by the numerical modeling method used GMS MODFLOW environment. The key complexity of the permeation problem consists in the fact that permeability coefficient and storage capacity of permafrost rocks greatly increase with time of injection. The highest degradation of ice takes place in the injection site; brines are displaced deeper in rock mass at the front velocity governed by density of joints, ice content, injection flow rate, mineralization of brines, temperature of rock mass and brines, etc. The permeation problem was solved using the method of alternation of quasi-stationary states in conformity with the modern hydrogeology and frost in the permafrost rock mass, and in accord with experience of drainage brine re-injection in Udachny Mine, subject to the key requirement of free flow of drainage brine into the permafrost rock zone at the eliminated discharge of water into local stream flows.

О геологическом и изотопном возрасте золоторудных месторождений на примере золото-серебряного месторождения Кубака (Северо-Восток России)

Information on the geological and isotopic age of the Kubaka gold-silver deposit in the Omolon middle massif in the North-East of Russia is presented. It has been established that the Kubaka deposit geological age lies in between the Late Devonian age of the Kedon series volcanites, containing the gold-silver mineralization, and the Early Carboniferous age of the Korbinsky suite terrigenous rocks, overlapping the volcanites and the mineralization. The post-ore nature of the Omolon complex dykes, which produce no significant impact on the distribution of gold mineralization in ore bodies, is shown. According to isotope dating, the following stages of the Kubaka deposit formation are distinguished: the accumulation of the Kubaka suite tuffs (369 Ma); the introduction of subvolcanic intrusions (344 and 337 Ma); the formation of ore metasomatites (335±5 Ma); the formation of gold-silver mineralization (330 and 334 - 324 Ma); the introduction of post-ore dikes (179±8 - 176±10 Ma).

Formation of the Neoproterozoic Continental Crust in the Structures of the Central Segment of the Central Asian Fold Belt

The paper considers the results of geochronological (U-Pb method, ID-TIMS), geochemical, and Sm-Nd isotopic studies of granitoids, volcanics, and terrigenous rocks of the eastern Dzabkhan terrane, as well as felsic volcanics of the Dzabkhan Formation in its southern part. It is established that the post-kinematic granitoids of the Dzabhan–Mandal Zone, Erdenekhairkhan, and Bogdoingol blocks were formed in the range of 813 ± 9–772 ± 3 and ca. 720 Ma, and the rhyolites of the Dzabkhan Formation were formed at 790 ± 3 Ma. The rock sources in the southern part of the terrane and in the Bogdoingol Block were mainly ancient crustal complexes. Nd isotopic data on the rocks of the Dzabkhan–Mandal Zone and the Erdenekhairkhan Block demonstrate the mixed nature of their sources and suggest a significant contribution of Early Neoproterozoic juvenile material. Based on obtained and previous data, it is shown that the Dzabkhan terrane is not a homogeneous block of the Early Precambrian continental crust, but represents a Neoproterozoic composite terrane consisting of rocks of island arc and continental margin complexes, and reworked Early Precambrian continental crust. The correlation of the Precambrian complexes of the Dzabkhan terrane with those of the Songino, Baidarik, and Tarbagatai terranes is discussed, and features of the formation of the Neoproterozoic continental crust in the central segment of the Central Asian fold belt are considered. It is established that the Khangay group terranes comprise widespread oceanic, island arc, continental margin, and riftogenic complexes formed at ca. 960–930, 880–850, and 810–790 Ma. Based on the data obtained, a model of the formation and evolution of the Neoproterozoic crust of the Central Asian fold belt is proposed by the example of paleoreconstructions for 925 and 825 Ma. It is assumed that the extensive growth of the Neoproterozoic continental crust of the region was related to the subduction processes in the framing of the Rodinia supercontinent at about 960–860 Ma ago and continental rifting that initiated the breakup of the supercontinent in the middle Tonian at about 860 and 800 Ma ago.

Age of volcanic-sedimentary complex from Сape Svyatoi Nos (Eastern Arctic)

Geological structure and age of the volcanogenic-sedimentary complex of the Cape Svyatoi Nos (Svyatonosskaya formation) are presented. The rocks of Cape Svyatoi Nos are located on the border of the Novosibirsk-Chukotka and Verkhoyansk–Kolyma fold belts, on the coast of the Laptev and East- Siberian Seas. Field studies indicate that the rocks belong to a single volcanogenic-sedimentary complex. The maximum thickness of individual sections reaches up 700 m. Coarse-grained pyroclastic rocks with rare lava flows prevail on the north (on the coast of Laptev Sea). The proportion and dimension of volcanics and pyroclastic rocks decrease in the south, terrigenous rocks appear. In the modern structure, the rocks are deformed.Zircons of several populations were separated from the flow of basalts. Two, the most representative zircon populations are characterized by close subconcordant ages. The structure and U-Pb ages of zircons from the first population suggest their formation during magmatic crystallization with a superimposed postmagmatic thermal event. Zircons of the second population have a xenomorphic appearance, which is typical of zircons formed at the late or postmagmatic phases. The weighted average age (MSWD = 3) of the first two populations is 149.3 ± 1.2 Ma (Tithonian age). It corresponds to the age of crystallization of basalts and the superimposed (close in time) postmagmatic thermal event.The third population of zircons is represented by two rounded grains with Archean U-Pb ages. It is assumed that these grains were trapped by magmatic melt from pre-Jurassic clastic rocks.Late Jurassic-Early Cretaceous radiolarians were identified from different horizons of tuff-terrigenous and terrigenous rocks. This is confirm the obtained U-Pb ages and the coeval of all the studied sections. The Titonian age of volcanic-sedimentary rocks allows us to classify them as suprasubduction complexes of the Late Jurassic - Early Cretaceous, widespread in the Verkhoyansk-Chukotka Mesozoids.

FEATURES OF PHYSICAL AND MATHEMATICAL MODELING OF OIL AND WATER FILTRATION AT DIFFERENT CRIMPING PRESSURES

The article discusses the features and results of physical and mathematical modeling of filtration experiments on terrigenous and carbonate rock core samples at different crimping pressures. Such studies are necessary to understand the effect of rock pressure on the reservoir properties and relative phase permeability (RP) of reservoir rocks, including from the standpoint of the Digital Core technology, since core tomography is usually performed under atmospheric conditions and data on rock properties are required for reservoir conditions. The article discusses the features and results of physical and mathematical modeling of filtration experiments on terrigenous and carbonate rock core samples at different crimping pressures. Such studies are necessary to understand the effect of rock pressure on the reservoir properties and relative phase permeability (RP) of reservoir rocks, including from the standpoint of the Digital Core technology, since core tomography is usually performed under atmospheric conditions and data on rock properties are required for reservoir conditions. The laboratory study of the relative permeability was carried out on composite core models by the method of stationary filtration at crimping pressures of 10 and 20 MPa. Mathematical modeling of filtration experiments was performed in the Eclipse simulator. The distribution of porosity in the hydrodynamic models of the core was set based on data from computed tomography of the core. The distribution of other rock properties (permeability, residual saturations, RPP values at residual saturations) was calculated using generalized dependencies. It is shown that for terrigenous and carbonate rocks, an increase in pressure leads to different behavior of the RPP functions and fluid mobility. The results of laboratory studies are interpreted from the point of view of processes at the micro level, based on the formation of the nature of the flow and the associated water saturation during deformation of the void space. It is also shown that filtration experiments on core at different rock pressures can be simulated on a hydrodynamic simulator, but at the same time, the study of patterns in the change in model parameters with a change in pressure depends on the presence of patterns in the behavior of rock properties based on the results of physical modeling.