Subsalt Deposits Research Articles

Generalization of regional seismic results within the Central Tunguska prospective petroleum region

The results of regional geological exploration at the expense of the federal budget on the territory of the Central Tunguska prospective petroleum region located in the Republic of Sakha (Yakutia) over the past 17 years are analyzed. To date, the territory of the Yakut part of the Central Tunguska PPR is closed by modern regional geological exploration by 77.9 %, which allows us to speak about the completion of the regional stage of geological exploration here. It was shown that Vendian terrigenous deposits and Vendian carbonate, subsalt deposits of the Lower Cambrian, as well as carbonates of intersalt deposits of the Cambrian have the greatest prospects for oil and gas potential. Riphean deposits have a limited distribution. Based on the results of these works, promising objects for prospecting work were identified.

Evaluating tectonic dislocations formation under the action of stresses at the Upper Kama potassium salt deposits

Introduction. The studies of the tectonic structure, dynamic behavior and prediction of the areas of the most probable manifestation of hazardous dynamic events at the Upper Kama potassium salt deposits (VKMKS) revealed that active faults, nodal structures, fracture zones and individual fractures in the oversalt, salt and subsalt rocks exercise a decisive influence on the violation of the steady state of geological structure. The regional stress field and a large number of local factors caused by folding, basement tectonics (catagenetic and supergene leaching), exogenous (weathering and unloading) and endogenous (halokinesis) processes in the oversalt strata, the growth of dome structures, etc. cause tectonic dislocations in the VKMKS. Cracks and fissure zones have currently been incidentally mapped and quantitatively studied mainly in mine workings in the productive part of the deposit, to a lesser extent in the oversalt rock, and scarcely in subsalt deposits. A detailed high-precision gravity prospecting along with other geophysical methods is currently the only effective method for tectonic dislocations mapping in the rock mass of the VKMKS. Methods for the widespread and systematic mapping of tectonic dislocations both in plan and in section within the VKMKS have not been developed yet. However, the evaluation of kinematic tectonic dislocations development in bulk can be obtained to some extent by analyzing the qualitative and quantitative characteristics of the natural stress field. It is due to the fact that dislocations are formed only when the acting stress exceeds the limit of the corresponding longterm strength of rocks forming the object under study. Methods of research. Tectonic dislocations of various kinematic types are formed under the action of stresses. Kinematic dislocations depend on the relationships between the stress principal values. Therefore, to solve the problem of kinematic type in the Solikamsk depression (SD) and VKMKS, the data of natural stress field components measurement in Ural mine workings were analyzed, the regularities of its behavior in plan and depth were determined, which served as the basis for two mathematical models, regional and local. Research results. Mathematical modeling was carried out, giving a quantification of stress components behavior regularities with the depth for the tectonic and physical-geological conditions of SD and VKMKS. Conclusions. The data on the change in stress components, obtained from mathematical modeling for two models of the geological environment, made it possible to predict the regularities in formation of tectonic dislocations of various kinematic types at different depths in SD and VKMKS at the regional and detailed scale levels.

Fluid Geodynamics of Deeply Buried Zones of Oil and Gas Accumulation in Sedimentary Basins

Abstract —We substantiate certain ideas concerning the key role of fluid-geodynamic processes in the evolvement of hydrocarbon accumulations at great depths, in the Earth’s crust. The presented geodynamic model of oil and gas accumulation is based on updated ideas of the structure of the Earth’s tectosphere, which includes plate, preplate, and folded complexes, and the model makes clearer the spatial scale of the organic matter transformation into hydrocarbons of the oil series. In the bottom layers of the Earth’s crust, we predict the existence of a special stagnation type of water-drive systems with the following distinguishing features: (a) different scales of manifestation, from local to regional; (b) a limited nature of processes of water exchange with the external environment; (c) absence of persistent drainage horizons (beds and interbeds); (d) alignment of hydrodynamic potentials in terms of depths and laterals; and (e) increasing importance of lithohydrochemical and organic-chemistry factors in the development of the void space of the fluid host medium. In their inner space, systems with difficult water exchange can exercise control over the evolvement and preservation of autoclave hydrocarbon systems for a long time, the key feature of the autoclave systems being spatial coincidence (localization) of the processes of oil and gas generation and accumulation. We assume that, in the settings of all-round compression, hydrodynamic instability, and no drainage, occurrence of productive zones is controlled by foci of low pore (reservoir) pressures rather than by local hypsometric highs. We present results of prediction of the development of water-drive stagnation systems occurring in the subsalt deposits of the Caspian depression within the unpenetrated areas of the subsalt profile. For the sedimentary cover at large (and ultralarge) depths, a prediction of reservoir pressures was made, which can be regarded as a necessary component in any prediction of oil and gas potential, since it makes it possible to contour some new (previously unknown) industrially significant zones of hydrocarbon accumulation.

Evolution of Hydrocarbon Systems in the Tersk-Caspian Trough

The article analyzes the evolution of hydrocarbon systems in the Tersk-Caspian trough. In general, the modeling results confirmed the existing distribution of oil and gas content across the sedimentary cover of the region. Thus, according to modeling data, confirmed hydrocarbon deposits are located in reservoirs of upper Cretaceous chemogenic limestones in the areas: Andreevsk, Starogroznensk, Khayan-Kort, Pravoberezhsk, etc. The degree of reservoir saturation, excluding field development, is high – up to 80-90%. Subsalt bundles of the upper Jurassic may become promising objects for searching for hydrocarbons. According to the results of geological and geochemical modeling, there are significant volumes of hydrocarbons in the advanced anticline folds in the upper Jurassic subsalt deposits. The oil saturation here can reach 80% or more

К МЕТОДИКЕ ПОИСКОВ НЕФТЕГАЗОВЫХ ЗАЛЕЖЕЙ В ПОДСОЛЕВЫХ ОТЛОЖЕНИЯХ ПРИКАСПИЙСКОЙ ВПАДИНЫ

The Caspian Basin is a unique geological object, the most notable features of which are the anomalously large thickness of the sedimentary cover and its enormous hydrocarbon potential. It is generally known that the main reserves in the identified fields and the prospects for discovering new large deposits of oil, gas and gas condensate here are associated with a subsalt complex of terrigenous and carbonate strata, submerged in the central part of the basin to depths of over 10 km. To date, this complex has been most studied in the edges of the depression at depths of 4-5 km. Confident forecasting of oil prospecting operations for deeper-lying objects is constrained by low researched of their structural, lithological, thermobaric and other parameters. In the debate about these very complex problems, one rarely recalls such a simple and at the same time crucial fact as direct signs of oil and gas potential. Indeed, every year we receive more and more new data on the “breathing of resources”, on the hydrocarbons migration from subsalt sediments into post-salt reservoirs, but we do not give them due attention. The article provides convincing, in the author's opinion, examples of the formation of post-salt deposits on salt domes due to the vertical migration of hydrocarbons. Taking this process into account, recommendations were made both НЕФТЬ И ГАЗ 2020 6 (120) 21 ГЕОЛОГИЯ on the general method of oil prospecting in subsalt deposits, and specific proposals for the search for subsalt and post-salt deposits of oil and gas.

Upper Jurassic subsalt complex of the Terek-Caspian trough due to oil and gas content

The article considers a complex of factors determining the oil and gas content of the Upper Jurassic subsalt deposits of the Terek-Caspian trough. The potential resources of hydrocarbons are associated primarily with the zones of the Nazran and Harbizhsk saddles, the western end of the Terek and Sunzhensk and Soviet-Right-Bank anticlinal zones. Synclinal and near-side zones are assigned to zones with unexplained oil and gas potential, where it is recommended to conduct regional geophysical studies in conjunction with parametric drilling.

Sedimentation-capacity model of the subsalt deposits of the Southern Urals and adjoining territories

The junction zone of the Caspian syneclise, the Russian Plate and the Pre-Ural trough is characterized by a complex structure. It has been studied in some detail during large-scale geological, geophysical, and drilling operations in the search for mineral deposits. Subsalt deposits are associated with the main prospects for the growth of hydrocarbon reserves in this region. This makes it important to rethink the available data and conduct scientific analysis to identify patterns of formation of sedimentary complexes and an integrated assessment of their possible hydrocarbon productivity by means of sedimentation modeling. The structure and history of the formation of five large sedimentary complexes: the Ordovician-Lower Devonian, the Central Middle Devonian, the Frasnian-Tournaisian, the Visean-Upper Carboniferous, and the Permian are considered in detail. For each complex, a structural-formational position and sedimentation conditions are determined, which should determine the hydrocarbon productivity of local objects. The revealed relationship between the conditions of carbonate sediments accumulation and their potential reservoir properties served as the basis for forecasting the productivity of regional natural reservoirs. The paper presents a generalized model of the formation of subsalt strata and the forecast of the spatial distribution of different facies deposits, which play the role of accumulating and preserving strata. The results obtained are applicable in the practice of oil and gas exploration in the region

Карбонатные резервуары подсолевых отложений Прикаспийской синеклизы

Карбонатные резервуары подсолевых отложений Прикаспийской синеклизы

PETROLEUM POTENTIAL PERSPECTIVES OF THE DEVONIAN SUBSALT DEPOSITS WITHIN THE NORTH-WEST DNIEPER-DONETSK DEPRESSION

Petroleum potential of subsalt deposits of Dnieper-Donetsk depression was observed. The presence of two different age generations of hydrocarbons is discovered. Generations of hydrocarbons have different supply sources. The type of the original organic matter for the early bitumen generation was composed mainly of association of reef-building algae. Dispersive organic matter was a source of supply for the second generation of “easy oil”. Hydrochemical features of formation waters indicate that interaction of hydrocarbons with subsalt Devonian deposits took place with the active participation of the vertical migration of highly mineralized aqueous solutions. Brings to the bitumen accumulations of methane, under favourable thermobaric conditions (abrupt removing of geostatic and fluid pressures) led to their destabilization and the formation of more mobile, less viscous oil.

Pripyat Trough: Tectonics, geodynamics, and evolution

The Pripyat Trough is situated in the East-European Platform and is a part of the more extensive system of the Sarmatian-Turanian lineament. It is one of the most thoroughly drilled and seismically investigated oil-bearing basins of the paleorift type that are known in the ancient platforms. Its geological structure reflects the typical features of ancient rift basins and can be interpreted as the tectonic type of an oil-bearing paleorift. The tectonic style of the paleorift can be reconstructed from the structure of some markers, such as the surfaces of the basement, of the subsalt deposits, of the intersalt rocks, of the upper salt-bearing rock sequence, and of some other rocks residing in the upper parts of the sequence. The Pripyat Trough is characterized by the block tectonics of its subsalt deposits, by the block-fold tectonics of its intersalt deposits, and by the essentially fold tectonics of its upper salt-bearing and overlying deposits. The specific styles of the tectonic deformation of the subsalt, intrasalt, and suprasalt deposits suggest three structural zones, namely, the Northern, Central, and Southern zones. Proceeding from the results of deep seismic sounding, the Pripyat rift is interpreted as a zone of listric breaking which had enveloped not only the Pripyat Graben but also the adjacent areas of the Ukrainian Shield and Belorussian Anteclise, forming its shoulders.

Microelements in petroleums of West Kazakhstan

Fe, Ni, Co, Zn, Sc, Sb, Hf and Hg content in petroleums and gas-condensates of 22 beds of West Kazakhstan is determined by neutron-activation. The average concentration of these microelements is minimum in petroleums obtained from layers adjacent to salt-bearing deposits of Upper Permian age and increases in persalt petroleums with a reduction and in subsalt petroleums - with increasing depth of occurrence and age of the holding reservoirs. Fe, Ni, Co, Sc and Sb content in petroleums subjected to catagenic transformations from subsalt deposits increases in proportion to the extent of their metamorphic change. Gas-condensates contain on average the same metal microimpurities, which indicates a fairly high volatility of organometallic complexes under conditions of retrograde evaporation of mineral resources. 5 references, 1 figure, 3 tables.

Types of carbonate structures in the subsalt deposits of the Caspian Basin and their petroleum capacity

Types of carbonate structures in the subsalt deposits of the Caspian Basin and their petroleum capacity

Conditions of formation of petroleum accumulation in the subsalt deposits of the Caspian Basin

Conditions of formation of petroleum accumulation in the subsalt deposits of the Caspian Basin

Petroleum Occurrences in Subsalt Deposits of the Caspian Depression and the Mid-European Basin

The high productivity of the subsalt deposits of the Caspian and Mid-European salt-bearing basins demonstrably results from features of their structure and development: long and intense downwarping, the presence of a thick salt-sulfate caprock, the distribution of petroleum-generating and reservoir sequences, etc. The distribution patterns of the major zones of petroleum accumulation are primarily determined by paleotectonic and tectonic factors and are controlled by major basement rises of ancient origin. The distribution of petroleum occurrences through the section within the zones of petroleum accumulation has been associated with the lithologic-facies composition of the rocks. The predominant gas or oil-and-gas capcity is determined by the original type of disseminated organic matter, the grade of its catagenic transformation, and the features of formation of the segregations.

Prediction of temperature conditions at great depths

The effects of temperature and pressure on the heat conductivity of dry, and water- and oil-saturated rocks, which form the upper part of the Earth's crust were examined: carbonates, sulfates, clastic rocks (siltstones), and also granites and andesite-basalts. Using the data on the intensity of heat flow and changes in the heat-conductivity of rocks, as exemplified by the Front Ranges of Eastern Ciscaucasia, the predicted temperatures through the sequence of oil fields were calculated and a sketch map of the distribution of temperatures along the top of the Jurassic subsalt deposits was constructed. It has been established that neglect of the temperature and pressure effects on the heat-conductivity of rocks will lead to distortion of the heat-flow assessment, and for the conditions under discussion, its over-estimate is 20 to 25%. When determining the intensity of heat flow, distortion factors, such as surface, hydrogeologic, and sedimentation conditions, were accounted for. (JMT)

Role of salt-bearing associations in catagenetic transformation of dispersed organic matter (as in the supra- and subsalt deposits of the Near-Caspian Depression)

Role of salt-bearing associations in catagenetic transformation of dispersed organic matter (as in the supra- and subsalt deposits of the Near-Caspian Depression)

Problems of utilizing subsalt deposits of the Near-Caspian Depression

Problems of utilizing subsalt deposits of the Near-Caspian Depression

Formation and distribution of gas-oil accumulations in the Paleozoic subsalt deposits of the northern marginal zone of the Caspian depression

We consider the formation and distribution of the gas--oil (gas-condensate) accumulations in the upper Paleozoic subsalt deposits of the northern marginal zone of the Caspian depression. On the basis of a detailed analysis of the geological, geochemical, and other conditions of preservation and conversion of the disseminated organic matter (DOM), we conclude that the principal sources of the hydrocarbons (HC) are the Devonian--Middle Carboniferous oil-source sequences. A result of the complex (stepped) migration of the hydrocarbons from these deposits, accumulations of oil and gas (gas-condensate) were formed in the Middle Carboniferous--Lower Permian deposits. From factual geological--geophysical and geochemical data, and also the results of sampling deep exploratory wells (the West Teplovo area), there is a possibility of discovering tectonically screened deposits of oil and gas in the marginal sectors of the basin, confined to the sunken blocks of structures and associated with faults in the subsalt Paleozoic sequence.