Oil shale of the Middle Volga region: Composition, structure, energy properties

The article presents the results of the Volga oil shale study in the territory of Tatarstan and the Ulyanovsk region. It is shown that shales are polymineral rocks of complex composition. The main valuable component is organic matter (kerogen), formed from the products of aquabionts fossilization. Ash components are represented by clay minerals, clastic fragments of mineral grains, calcareous fragments of organic residues, and diagenetic pyrite. Organic matter has a complex structure. The predominant fractions are light and medium hydrocarbons boiling out in the temperature range 150-560°C. In smaller amounts, heavy fractions are present, which are released at temperatures of 560-620°C. The heat capacitance of oil shale ranges from 1607 to 9052 J/g. Loss of shale mass can range from 18.0 to 25.0% of the original sample. According to the summary valuable and genetic indicators, the Volga oil shale belongs to the humus-sapropel type; low-calorie in heat of combustion terms; polysulphide in terms of sulfur content; aluminosilicate-carbonate in terms of the prevalence of oxides in ash

Sedimentary-diagenetic ore formation in the Jurassic system terrigenous deposits of the Tatarstan Republic

© 2020 IOP Publishing Ltd. All rights reserved. Authigenic ore mineralization of the Jurassic terrigenous complexes rocks, widespread in the Tatarstan, is considered. It has been established that the ore minerals associations' composition is determined by geochemical conditions of mineral formation environment. In rocks of oxide geochemical facies (sandstones, siltstones), iron, manganese and titanium oxides predominate. Pyrite framboids and copper-nickel intermetallide compounds predominate in rocks of neutral geochemical facies (green clays). The rocks of anoxic geochemical facies (black clay, oil shale) contain only pyrite framboids. The main factor determining the authigenic ore minerals associations composition is redox potential of environment

Hydrogeological systems of landslides in central part of the Volga-Ural region

© 2020 IOP Publishing Ltd. All rights reserved. The study of landslide massifs made it possible to identify two types of hydrogeological systems that differ by feeding area structure and transit zone. In landslide bodies of Urzhuminan stage, composed by dolomites and marls, hydrogeological systems are simple stratal. The aquifers are localized in fractured marls, which, under the influence of infiltration water seeping through them, have turned into a poorly structured gruss-rock cover, which lies on dense dolomites - water-resistant. The inclined bedding of dolomite layers creates the prerequisites for directed filtration of groundwater towards natural lowering. Here forming areas of ground water discharge as low-water springs. In landslides composed of the Upper Jurassic series clays and marls, hydrogeological systems are distinguished by the prevailing vertical groundwater infiltration in transit zone. Theirs's water source is shallow lakes formed on the surfaces of landslide terraces. Under water pressure influence of in the lake basins and gravity, infiltration groundwaters leaking through the systems of cracks in clays penetrate to a more dense clay layers which are fluid trap. Here, directly under the lake basin, a dome of groundwater is formed. The flow of groundwater from the dome towards inclined depressions leads to creation of unloading areas. They are presented by permanently wet land (flarks) or low-water infiltration springs that come to the surface at the same hypsometric level

The influence of lithofacies features of the Permian natural bitumen-saturated reservoir rocks on groundwater formation conditions

© 2020 IOP Publishing Ltd. All rights reserved. The reservoirs rocks of natural bitumen deposits of the Lower Permian system and the Kazanian stage of the Tatarstan territory are considered. The relationship of groundwater composition in bitumen reservoirs with lithologic features of water-saturated rocks is shown. Rocks compositions contribute to formation of three water classes in oil deposits: hydrocarbonate, sulfate and chloride. Hydrocarbonate waters lie over erosion downcutting of rivers in the most elevated territory part. Their origin is associated with hydrolysis and carbon-dioxide leaching of the Permian terrigenous rocks. Inland waters of hydrocarbonate-sodium (soda) composition of bitumen deposits are located above local drainage basis. They are formed as a result of sulfate reduction processes in deposits. The inland waters of sulfate composition of calcium and sodium groups are characteristic of deposits located below the drainage basis. Their origin is associated with dissolution of gypsum and anhydrites, as well as with ion exchange reactions between the calcium of the solution and the sodium which absorbed by rock complex. Chloride waters associated within the eastern side of the Melekess Depression, where there is an active hydrodynamic relationship between the Permian system aquifers and chloride-calcium salt brines of the Carboniferous rocks. The nature of the distribution and presence of aquifers in deposits is determined by the lithological features of reservoir formation

Geological and hydrogeological features of the lower Permian carbonate locally bituminous complex of the Tatarstan

© 2020 IOP Publishing Ltd. All rights reserved. The Lower Permian bituminous complex is characterized by complex hydrogeological conditions. The predominant type of reservoir is mixed porous-fractured-cavernous. Water layers lateral prevalence is directly related to the degree of fracturing and cavernous of dolomites and limestones. Regional hydrogeological studies have shown that at the dividing ranges the Lower Perm sedimentary stratum is anhydrous, and in the river valleys it is water-rich. The center parts of such areas are erosive incisions of river valleys. From the periphery to karst regions center, a consistent increase in well flow rates and a decrease in piezometric groundwater levels from the slopes of dividing ranges to the river valleys are observed. In the domed sections of the South Tatar Arch in the Asselian - Sakmarian sediments, calcium-sulphate waters with a total salinity of 1.5 to 3.5-4.0 g/dm3 are prevalent. Sodium sulfate waters appear within the western slope of the arch. Within the eastern part of the Melekess Depression, the Asselian-Sakmarian stage groundwater deposits are already completely sulphate-sodium. The predominance of sodium components over calcium in groundwater is observed during total salinity of 4.5-5.5 g/dm3. In the areas of the Melekess Depression, where the Lower Permian sediments are drowning, groundwater acquires to sodium-chloride composition

Influence of technological parameters of the Volga oil shale on the efficiency of heat release during combustion

Volga oil shale in the Middle Volga region is a promising energy raw material for regional factories. Their heat of combustion varies from 1.6 to 9.0 MJ/kg, averaging 4.2-4.5 MJ/kg. The low calorific value of the fuel can be compensated by the proximity of the consumption sources and the cheapness of supplies. Oil shale is a high-ash energy feedstock with high sulfur content. The share of the organic component (kerogen) is 15-25%. During the combustion of oil shale, kerogen undergoes a multistage transformation due to the reactions of organic molecules hydrogenization. Experimental modeling has shown that the heat of combustion of the Volga oil shale is determined not only by their composition, but also by the organization of the combustion process. When burning lump shale, the heat release from rocks is 15-20% less than similar fuel in the form of fine dust. When using the technology of coal-water combustion (in the form of suspensions), the heat release of rocks is reduced in comparison with the combustion of dry finely dispersed oil shale by 10%. Although it remains higher, compared to the heat release during combustion of lump oil shale using boiling bed technology

Manifestation of infiltration-metasomatic processes in the Kazanian stage sediments of the Lobach Mountain in Tatarstan

© 2020 IOP Publishing Ltd. All rights reserved. For the first time in the Kazanian stage evaporate sediments of the Kama-Ustyinsky structure, metasomatites were identified confined to bituminous accumulations zones. metasomatites develops in microgranular sedimentary-diagenetic dolomites. The main dense core of metasotatic bodies is composed of marble-like calcite, along periphery of which there is ferriferous goethite-hydrogetite edge. Numerous calcite veins extend from carbonate core to sides, their thickness decreases with distance from metasotatic bodies. In the zone of metasomatites development, processes of gypsum lenses recrystallization and siliceous nodules dissolution, originally found in micrograin dolomites, are observed. The small size siliceous nodules are completely leached and replaced by calcite aggregates. Larger flints partially pass into translucent chalcedony and aggregates, consisting of large quartz crystals - clear rock crystal. The formation of metasomatites is due to aggressive hydrocarbon-containing fluids introduction into the rocks, as indicated by their spatial confinement to bituminous accumulations

Assessment of the geological factors influence on the oil-productive of terrigenous reservoirs of the Vereyian horizon of the Melekess depression

The article presents study results of terrigenous reservoirs of the Vereiskian horizon of Tatarstan. The sandstones and silty sandstones are composed by grains of quartz, feldspars, clay minerals and organic remains cemented with calcite. Rocks were formed under the conditions of marine paleobasin coastal part with normal salinity. The migrated aggressive solutions partially leached out the carbonate cement from sediment, realizing the reservoir-filtration potential inherent in rocks. The oil fluids that filled the pore space practically did not interact in any way with the mineral skeleton of terrigenous reservoirs at the chemical level. Thus, the influence of the rocks mineral component on the properties of oils is completely excluded. In oil-saturated reservoirs, from which good oil inflows are obtained, light fractions of hydrocarbons prevail, boiling away at temperatures of 200-320°C. In the reservoir rocks, from where the watered oils are obtained, there are medium and heavy fractions of hydrocarbons, boiling at temperatures of 320-450°C. In unproductive sandy reservoirs with immobile viscous oil, only heavy fractions of hydrocarbons, which boiling at temperatures above 450°C, prevail. Thus, the oil recovery of terrigenous reservoirs is determined not by the composition of host rocks, but by the degree of oils oxidation contained in them

Features of the transformation of visean quartz sandstones under the influence of water-oil fluids

Research subject. This article analyses specific features of secondary transformations of quartz grains under the influence of water-oil fluids on the example of the Tulsky and Bobrikovsky oil-saturated quartz sandstones of the Demkinskoye oil deposit in the south-east of Tatarstan. Materials and methods. The research was carried out using the methods of optical microscopy, x-ray diffraction and electron paramagnetic resonance (EPR). Results. On the example of the Tulsky and Bo-brikovsky oil-saturated Visean quartz sandstones, we analysed the influence of water-oil fluids on rocks and features of the secondary transformations of quartz grains in the Demkinsky oil field in the southeast of Tatarstan Republic. In the oil-charge stage, the spatial redistribution of silica was realized. Quartz grains dissolved in the sole and middle part of the re-servoir, precipitating in the form of chalcedony in the top part of the reservoir. The dissolution of quartz grains was promo-ted by micro defects concentrated on their periphery. The dissolution was triggered by both plastic deformations of minerals at the contacts and an increase in the alkalinity in the pore space up to pH = 9–10. Chalcedony aggregates were formed in the intergranular space of oil-saturated sandstones. Depending on the nucleation point of the siliceous substance and silica concentration in pore fluids, either single spherulitic or agate-type aggregates were formed. According to EPR, the studied chalcedony aggregates have a high content of paramagnetic E’-centres. This was caused by a deficiency of oxygen in the mineral-forming fluid during chalcedony precipitation. Conclusions. Chalcedony precipitation underwent in acidic con-ditions, which led to silica-type metasomatism in the top part of the reservoir followed by substitution of muscovite grains by morphological fibrous chalcedony. Metasomatism affected the grains of both detrital muscovite and muscovite present as inclusions inside quartz grains. This process indicates the manifestation of surface and bulk diffusion of silica, affecting all clastic components