Dnieper-Donets Basin Research Articles

Seismic lithospheric model across Ukrainian Shield from the Carpathians to the Dnieper-Donets Basin and its tectonic interpretation

The SW-NE directed wide-angle reflection-refraction (WARR) SHIELD’21 profile crosses entire width of Ukraine. It targeted the structure of the crust and uppermost mantle in the southwestern part of the East European Craton (EEC), between Carpathians and Voronezh Massif, across Ukrainian Shield and Dnieper-Donets Basin. The ∼660 km-long profile is an extension of the RomUkrSeis profile in Romania and Ukraine. SHIELD’21 experiment, using TEXAN and DATA-CUBE short-period seismic stations, provided high-quality seismic sections from 10 shot points. This allowed construction of a ray-tracing P-wave velocity model, supplemented by Vp/Vs ratio, for the upper part of the lithosphere in the Sarmatia segment of the EEC and constraining geodynamic processes that led to the formation of the Ukrainian Shield and its margins since Archean times.The velocity distribution in the crystalline crust indicates a rather uniform structure, with velocity changing from 6.0 km/s near the surface to 6.8 km/s at the Moho. The entire section shows the lack of a high-velocity lower crust (Vp > 6.8 km/s), presumably resulting from delamination of the primitive mafic lower crust during early evolution of a juvenile continental crust. The seismic boundaries in the upper crust reflect a Paleoproterozoic extensional detachment system below the SW flank of Dnieper-Donets rift basin, initiated in the Devonian. At larger depths, a wide dome of the lower crust with velocities of 6.5–6.8 km/s in the SW-central segment of the profile, probably represents an enormous Palaeoproterozoic(?) granitoid batholith. In the southwesternmost part of the profile, the crystalline crust shows exclusively low velocities. The prominent Moho is undulating and varies in depth between 32 and 50 km. It is underlain by high-velocity bodies (Vp: 8.36–8.40 km/s), against the background of 8.16–8.25 km/s in the mantle. The velocity model corresponds with the anomalies of potential fields and zones of high electric conductivity.

STUDY OF THE EFFECTIVENESS OF THE APPLICATION OF COMPLEX GEOLOGICAL AND TECHNOLOGICAL MEASURES ON THE EXAMPLE OF GAS-CONDENSATE GENERATION IN THE CENTRAL PART OF THE PRIAXIAL ZONE OF THE DNIPROV-DNETZ BASIN

The field development system is the basis of hydrocarbon production, as it ensures the achievement of the necessary technical and economic indicators. Therefore, a high-perfor- mance development system is necessary to ensure maximum profit in the shortest possible time. Empirical studies, analysis and assessment of the effect of implementing a complex of geological and technological measures on the operational facility of a gas condensate field in the central part of the peri-axial zone of the Dnieper-Donets Basin were carried out in order to find methods for improving the existing gas and gas condensate field development systems and increasing gas extraction rates. It is shown that due to hydraulic fracturing, drilling and transfer of wells to the production facility during the five years of production of the produced gas, it is 7.8 % more than in the previous 21 hours, the rate of development of the field from 2015 to 2019 increased from 2.52 %. to 7.9 %, the average well yield increased by 83 % with an increase in the operational fund by 55 %. The results of studies of the effect of the application of geo- logical-technological measures are shown in the form of graphical dependences of the change in the rate of sampling on the number of production wells over time, the rate of daily gas sampling on the number of conducted geological-technological measures on the researched operational object over time. It has been determined that the main driver of the increase in gas production is the hydraulic fracturing of the formation in most of the operational wells, thanks to which the average increase in the output of the wells is 425 %. According to the results of geological and industrial data processing and analysis of changes in the rate of daily gas extraction over time, the effect of the performed operations is divided into three time segments lasting 15–18 months. The decrease in the duration of the effect from the increase in the fund of production wells and the conduct of hydraulic fracturing of the reservoir is due to the decrease in the volume of reservoir energy, therefore the investigated complex of measures will have the greatest effect when implemented at the initial stage of the development of a reservoir with similar geological parameters.

Sources of Neogene Rare Metal–Titanium Placers of the Northeastern Wall of the Dnieper–Donets Basin: First Results of U–Pb Geochronological Studies of Detrital Zircon

Sources of Neogene Rare Metal–Titanium Placers of the Northeastern Wall of the Dnieper–Donets Basin: First Results of U–Pb Geochronological Studies of Detrital Zircon

The SHIELD’21 deep seismic experiment

The wide-angle reflection and refraction (WARR) SHIELD’21 profile carried out in 2021 crosses from SW to NE the main tectonic of Ukraine. The SHIELD’21 targeted the structure of the Earth’s crust and upper mantle of the southwestern margin of the East European Craton with overlying Neogene Carpathian Foredeep and Vendian-Paleozoic Volyn-Podolian Monocline, Archaean and Paleoproterozoic segments of Ukrainian Shield and Late Paleozoic Dnieper-Donets Basin. The ~650 km long profile is an extension of realized in 2014 RomUkrSeis line in Romania and Ukraine from Apuseni Mountains to southwestern Ukrainian Shield. The field work performed in 2021, included the deployment of autonomous seismic stations and drilling-explosive works. A total of 264 seismic receivers were deployed (160 DATA-CUBE and 104 TEXAN stations) with the average spacing between the observation points about 2.65 km. The sampling interval for all stations was 0.01 s. Seismic energy was generated by 10 shot points with ~50 km of distance between them and total charge in all wells 5775 kg. The SHIELD’21 experiment using TEXAN and DATA-CUBE short-period seismic stations provided high-quality seismic records. The main recorded seismic waves are the refractions of P- and S-waves in sediments, basement, crust and upper-most mantle, and reflections from crustal boundaries, Moho interface and boundaries in the uppermost mantle. Correlation of travel time arrivals of seismic waves provides calculation of the velocity model for both P- and S-waves. The main objective of the SHIELD’21 project is to get new seismic data that increase our knowledge on the lithosphere structure as well as geodynamics of the oil-and-gas-bearing and ore regions of Ukraine.

Donbas conductivity anomaly in the Karpinsky Swell

Donbas Foldbelt (DF) and Karpinsky Swell (KS) are contiguous parts of a system of elongated sedimentary basins forming lineament from Poland through Pripyat Trough in Belarus, the Dnieper-Donets Basin (DDB) and DF in Ukraine, KS in Russia, across the Caspian Sea, through Mangyshlak in Turanian plate in Asia. In DF, the Mesozoic-Cenozoic sediments were raised, and subsequent erosion exposed the Carboniferous coal-bearing strata. In contrast to DF, the Paleozoic rocks in KS are covered by 1—3 km thick sediments of Mesozoic-Cenozoic age; productive structures of the earlier age cannot be confidently studied in KS by geological methods. So, geophysical methods are the promising approach for the KS deep structure studies. This work is devoted to electromagnetic (EM) studies of the electrical conductivity of rocks by the methods of magnetic variation profiling (MVP) and magnetotelluric sounding (MTS). Previously [Rokityansky, Tereshyn, 2022], we described the results of the EM research on DF in detail. MVP reveals the intense Donbas electrical Conductivity Anomaly (DCA) running along the main anticline of the folded Donbas. DCA parameters: maximum possible depth of the anomalous currents center h=18±2 km. Frequency response maximum Т0≈3600 s yields the total longitudinal conductance G=(8±2)∙108 S∙m. 70 MTS at periods 0.1—3000 s yield two conductive stripes, with the upper edge varying from 0.3 to 5 km. The stripes are parallel to the DCA axis and are considered as part of DCA. A very large value of G suggests that the anomalous body extends to some considerable depth. The DCA axis spatially coincides with an intense (up to 90 mW/m2) deep heat flow anomaly. Thus, the nature of the DCA lower part can be a partial melting. Theoretical estimates show that intense anomalous fields of geomagnetic variations arise over highly elongated conductors. Therefore, there is reason to expect that the anomaly continues eastward. We found two MTS profiles crossing the Karpinsky swell, and under both profiles strong conductivity anomalies are clearly seen. We re-interpreted original data and presented parameters of all 3 anomalies in an identical style. The main conclusion: the anomaly parameters on the three profiles are approximately the same, and one can assume with a high probability the existence of a single anomaly of electrical conductivity in the Donbas and Karpinsky Swell with a common length of more than 500 km and longitudinal conductance G≈8×108 S×m.

Middle Eocene cartilaginous fishes (Vertebrata: Chondrichthyes) of the Dnieper-Donets Basin, northern Ukraine.

Marine basins that existed in present-day Ukraine during the Eocene harboured various groups of cartilaginous and bony fishes, reptiles, aquatic birds, and marine mammals. Fish remains from Paleogene deposits of Kyiv and its vicinities were first collected and described by O.S. Rogovich in the mid-19th century. Here we have carried out a re-examination of chondrichthyan fossils from Rogovich's collection and evaluated several later records, all of which were recovered from middle Eocene deposits. In total, 88 specimens represented by teeth, vertebrae, and other skeletal elements were analysed and described. As a result, the sample revealed to a single chimaeriform species (Edaphodon bucklandi), and 12 shark and two ray taxa, respectively. Ten sharks were identified to species level, whereas the rays could be identified only at higher systematic ranks (Myliobatidae, Myliobatiformes). Several nomenclatural changes are proposed here, including the synonimisation of Carcharodon megalotis, C. lanceolatus, C. productus, Lamna cuspidata, L. denticulata, L. compressa, L. (Odontaspis) hispida, L. lata, Oxyrhina brevidens, and O. biflena with more recently proposed taxa. Seven species erected by Rogovich (Galeocerdo paradoxus, Otodus microtus, Lamna elegans, Oxyrhina falcata, Oxyrhina leptodon, Chomatodus dubius, and Hybodus helophorus) are suggested to most likely be nomina dubia. Many identified taxa represent the epi- and mesopelagic fishes and only a relatively small number of them belong to benthopelagic, demersal, and bathydemersal forms. The studied sample is of important historical and scientific value and substantially contribute to the understanding of the palaeodiversity of Eocene marine ecosystems that existed in present-day Ukraine and generally in Eastern Europe.

Carapaces of the Dnieper-Donets Basin as a New Exploration Target for significant hydrocarbon deposits

New geological structures — displaced blocks of salt overburden — were identified in the axial part of the Dnieper-Donets basin (DDB) beside one of the largest salt domes due to modern high-precision gravity and magnetic surveys and their joint 3D inversion with seismic and well log data.
 Superposition of gravity lineaments and wells penetrating Middle and Lower Carboniferous below Permian and Upper Carboniferous sediments in proximity to salt allowed proposing halokinetic model of displaced salt overburden, assuming Upper Carboniferoussalt reactivation.
 As an analogy todescribed halokinetic deformationswe consider rafts and carapaces of the US Gulf of Mexicobasin.
 Density of Carboniferous rocks within the displaced blocks evidence a high probability of hydrocarbon saturation. Possible traps include uplifted parts of the displaced blocks, abutting Upper Carboniferous reservoirs, and underlying Carboniferous sequence. Play elements (reservoir type and quality, seals, hydrocarbon generation) are analyzed using analogues from the Dnieper-Donets basin and the Gulf of Mexico basin.
 Hydrocarbon reserves of the displacedblocks within the study area are estimated to exceed Q50 (Р50)=150 million cubic meters of oil equivalent.

Oil and gas bearing potential of crystalline basement in Dnieper-Donets Basin – unbiased view

Purpose. Based on the analysis of existing information on the exertions of oil and gas in crystalline rocks of the Dnieper-Donets Basin (DDB), assess the presence of hydrocarbon deposits in certain fields and assess the prospects for the discovery of new ones. Methodology. The study on oil and gas bearing capacity of the crystalline basement was based on the analysis of stock material on oil and gas fields of the Dnieper-Donets Basin, the study on petrographic composition of rocks in sections, analysis of results of well logging, petrophysical studies on rock samples from promising intervals of wells. The peculiarities of the structure of structural-tectonic models of hydrocarbon deposits with oil and gas exertions in the upper parts of the crystalline basement were also taken into account. Findings. A significant number of drilling and well testing results, lithological-petrographic and petrophysical studies were analyzed, which allowed making objective conclusions about the existence of independent oil or gas deposits in the weathering crust of the crystalline basement at already known deposits. The conclusions also concerned the assessment of the industrial (commercial) attractiveness of the discovered deposits or oil and gas exertions in the upper parts of the crystalline basement of the DDB fields. Originality. At the current level of study, it can be argued that within the Eastern Ukrainian oil and gas basin in the Archean-Proterozoic traps apart from the basal horizons of the cover, oil deposits were found in only three fields: Yuliivske, Ulianivske and Hannivske. Undoubtedly, there are hydrocarbon deposits in the Precambrian formations of DDB, but the most extensive discoveries in this direction of exploration and involvement in the development of already discovered accumulations seem to be still ahead. The geological situation should be realistically assessed for the presence of potential areas where the existence of common hydrocarbon deposits in the weathering crust of the foundation and the lower horizons of the sedimentary cover in the DDB is possible. Practical value. The main value of this study is the real assessment of the existence of industrial accumulations of hydrocarbons in already discovered oil and gas fields in DDB. The myth of the presence of many oil and gas deposits in DDB in crystalline rocks of the crystalline basement, which without proper justification has repeatedly been found in the professional literature and in scientific reports at specialized conferences of various levels, has been debunked. Certain prospects for the discovery of oil and gas deposits in the crystalline basement of the Dnieper-Donets Basin are unmarked.

ГЕОДИНАМІКА

The article focuses on the formation mechanisms of fold’s diversity of sedimentary basin inversion. They are investigated on the example of structures of the Dnieper-Donets paleorift system. To achieve this aim we systematized structural and lithofacial data of the Dnieper-Donets basin and Donbas; used numerical modelling to establish the regularities of deformations within lithosphere and sedimentary cover in collisional compression setting. It is shown that the formation of main folding styles as discontinuous (intermittent), transitional and continuous (full) is accompanied by characteristic features of the cover. In this respect, we formulated the basic dependence principle of folding from lithofacial and lithogenic factors, which defined different mechanical properties of sedimentary cover complexes (the lithomechanics principle). Modelling results confirm prime significance of horizontal compressional conditions of basin’s folds development. Moreover, the sedimentary basin plays the role of independent deformation attractor in the lithosphere. The main conclusion is that the transitional fold paragenesis of Donbas with crest-like Main anticline may be the result of particular strength’s distribution, i.e. axial weak zone and competent layer of variable thickness with central minimum. Main anticline formation mechanism is complex. It includes vertical, axial-parallel viscous-plastical flow with distant bending. It is shown that intermittent folds (uplifts) of the Dnieper-Donets basin may be a result of sedimentary cover compression with a random combination of weakened and strengthened zones. On the contrary, full folding of East Donbas and the Karpinsky ridge corresponds to a bending mechanism of competent layer compression of constant thickness. For the first time we obtained the evidence for the folding inversion mechanisms within Dnieper-Donets aulagogen (including Main anticline), which was problematic for many years. Folding is directly related to peculiarities of sedimentary basin infilling within formulated principle of lithofacial mechanics. With necessary caution, the study offers the results of modelling and conclusions for explanations of fold development within intracontinental basins and marginal folded belts. Practical significance. Numerical modelling and elaborated principles of analysis may be used in reconstructions, numerical investigations of fold structures (uplift) within inverted basins, as well as in prognosis of ore, oil-and-gas deposits.

ГЕОДИНАМІКА

The purpose of the research is to analyze the impact of the region's geodynamics on the formation of hydrocarbon reservoirs in the carbonate Lower Visean-Tournaisian stratum. The paper is focused on the substantiation of hydrocarbon traps within the Machukhy-Tyshchenky area of the southern zone of the Dnieper-Donets basin, as well as oil and gas exploratory drilling and new effective methods of stimulating gas inflows to boreholes. Methodology. The study applies the stratigraphic, lithological, tectonic, paleotectonic methods of studying geology and oil potential, as well as the method of geological analogies. Results. Gas-bearing carbonate rocks of the Early Visean-Tournaisian age in the Machuhy-Tyshchenky area have been studied. A comparison with other oil and gas regions has shown that they are the domes of carbonate platforms (Wаulsoгtiаn facies). Three echelons of bioherm limestones have been identified within the the area. The research helped to describe the stages of their formation and determine the dependence of reservoir properties of limestones on their biofacial types. The role of tectonic fracture in the formation of reservoir rocks is shown. As a rule, tectonic fractures are cemented by calcite under the action of formation waters. An assumption is made about the formation of microfractures in dense limestones due to the action of plumectonic. It consists in the intrusion of high-energy fluids from the depths of the earth, the natural fluid fracturing of rocks and the formation of non-anticlinal hydrocarbon accumulations in them. Probable places of fluid breakthrough may be zones of deep faults: the Ingulets-Kryvorizhzhya-Krupetsk fault zone crosses Machuhy-Tyshchenky area. Filling microfractures with hydrocarbons prevents their cementation. The paper gives examples of microfracturing in the cores of boreholes and establishes reduced core from microfracture intervals. To identify microfracturing intervals in carbonate rocks, it is proposed to use information on the reduction of core, as well as the speed drilling of rocks. The study suggests using multistage hydrofracturing and acid hydrofracturing in order to stabilize and increase gas influxes from carbonate reservoirs to the boreholes. Such technology should provide the connection between the borehole and oil-saturated reservoirs. Probable factors of negative impact on the environment during hydrofracturing have been identified. Originality. Adiabatic microfracturing of dense lithotypes of rocks is possible at considerable depths, in addition to tectonic fracturing. It is due to natural fluid fracturing of sedimentary strata by hydrocarbon gases. This gives hope for the discovery of new types of hydrocarbon deposits that are not associated with anticline traps. Practical significance. Geophysical surveys and the location of six boreholes are recommended in order to search for hydrocarbon deposits in the Machuhy-Tyshchenky area. The study suggests effective methods for increasing gas influxes to boreholes from low-permeability carbonate rocks.

ГЕОДИНАМІКА

The article studies the system organization of inversion tectonic deformations of the Dnieper-Donetsk Basin which covered the territory of the Western Donetsk Graben. The research uses the kinematic and structural-paragenetic analysis of inversion structural transformation of the folded floors of the sedimentary cover of the Graben. The original model of tectonic inversion of the Dnieper-Donets Basin was completed from the previous models. The tectonic inversion of the Dnieper-Donets Paleorift rift-like structures began at the late Hercynian stage in the geodynamic environment of the territory of the Eastern European Platform general collision. Tectonophysical analysis shows that the inversion folding was formed by the mechanism of sedimentary horizons longitudinal bending in the environment of the interference of the intraplate submeridional collision compression and the regional strike-slip stress field. At the Mesozoic-Cenozoic stage, tectonic inversion continued in the field of right-hand strike-slip deformations with a variable compressive component. This caused the formation of folded covers of tectonic plates and scales in the uplift-thrust mode. They, Hercynian neo-autochthonous formations and further the weakly located syneclise autochthon of the South-east of the Basin. The pressure of the "tectonic stamp" geoblock of the Donetsk Foldbelt contributed to the formationof the Segment body of geomass Tectonic Wedging. It was diagnosed with a structural orocline of transverse extension of the sliding type. Large linear throw-folded zones were formed within geodynamic bands of injection and displacement of geomass along the front of the orocline. The tectonic compression fan, characteristic of geodynamic compression zones, was formed in the foreland of the orocline, on the ends of the main thrusts. They served as “tectonic rails”of the allochthon invasion within the rift-like structure. There are the transverse zones of tectonic sutures formed on the roots of the folding covers of the Hercynian neo-autochthon thrusting, which are located in the hinterland of the orocline in the Foldbelt Western slope. The study completed an original kinematic model of tectonic inversion of the transition zone between the Dnieper-Donets Basin and Donets Foldbelt. According to the model, the pressure of the “tectonic stamp” geoblock initiated the invasion of the Segment of Tectonic Wedging which consists of the intensively dislocated allochthonous geomass. The Segment destroyed the rift-like structure and formed the Western Donetsk Cover-Folded Region in the South-eastern part of the Basin. The system organization model of inversion complications of the rift-like structure in the territory of the Western Donetsk Graben will allow to improve the regional geological schemes of tectonic oil and gas zoning.

Tectono-magmatogenering structures in zones of increased geodynamic instability as priority objects for exploration of hydrogen fields

Based on comparison of the migration activity of hydrocarbons, helium and hydrogen, the paper substantiates the types of cap rocks for hydrogen accumulations (pools), which most of all contributes to its partial shieldingat steady feed. Such cap rocks are represented by predominantly smectite clay, pure (without inclusions) salt at depths over 1—2 km, non-fractured quartz sandstone at depths over 4 km, effusive and hypabissal intrusive rocks, as well as basement rocks undisturbed by metamorphic decomposition processes. Endogenous hydrogen isconsidered as the main factor of dissipative structures formation. Occurrence of hydrogen, hydrocarbon and ore macro accumulations is a kind of energy, information-geochemical fluctuations, which are intermediate states of dissipative structures subordinated to the planetary heat and mass transfer processes caused by the deep Earth degassing. In this context, the nature of geodynamic instability (activation of vertical movements, shifts, tensile and compressive stresses) can be considered as a growing sequence of dissipative processes associated with the energy percolation role of endogenous hydrogen. In the hierarchy of ring structures (RS) (from minor depressions to large structures of dozens kilometres in diameter) special attention should be paid to Sribne RS within the Dnieper-Donets Basin and Kaluga RS within the SW part of the Voronezh anteclisepericline. These ring structuresare genetically related to explosion or volcanic calderas, and characterized by ancient origin (Proterozoic) and long-term development, including neo- and actuotectonic stages. Intensity of hydrogen degassing in the Sribne RSis confirmed by micro- and nano-inclusions in the black-shale domanicoid rocks of the productive horizons in the form of particles of native metals(including oxyphile elements Al, Zn, W and others), natural alloys and intermetallids, which are tracers of ascending flows of deep reduced fluids. It is reasonable to assume the occurrence of a large hydrogen or helium-hydrogen field (group of fields) within the Sribne RS in the Lower Visean, Lower Bashkirian and Lower Permian aged rocks, which are shielded by the Lower Permian salt deposits.

ГЕОДИНАМІКА

The second part of the article studies the tectonic conditions and natural mechanisms of tectonic inversion of the Dnieper-Donets Basin and the Western Donets Graben. Method. The research uses the original method of reconstruction of fields of tectonic stresses and deformations. It also makes tectonophysical analysis of geostructures was used. The analytical base of the research consisted of the latest materials of geo-mapping, numerical modeling of deformations of the southern edge of the Eastern European platform and comparison of model and reconstructed stress fields. Results. In the geodynamic environment of the interference of the intraplate submeridional collision compression with the regional strike-slip stress field, the inversion deformations of the rift-like geostructure took place in the uplift-thrust and strike-slip modes. This led to significant horizontal movements of geomass of sedimentary rocks, deformation folding with the formation of three inversion floors - Late Hercynian (Saal-Pfalz), Early Alpine (Laramian) and Late Alpine (Attic). They formed structural ensembles of scaly tectonic covers of transverse displacement of geomass a from axial to onboard zones, folded covers of longitudinal approach from the Donbas Foldbelt and long linear anti- and synforms, the axes of which are oriented orthogonally to the direction of geomass advancement. Together they form the body of the Segment of Tectonic Wedging of geomass, which is distinguished as part of the Cover-Folded System of Tectonic Thrusting of regional scale. A feature of the tectonic framework of the Segment is the curvature of the planes of the main thrusts, which limit it, and smaller plumage thrusts, which control the folded covers of the thrust. It is associated with a change in the extension of the thrusts from the north-west in the territory of the Western Donets Graben to the western direction in the extreme south-east of the Basin. This causes the corresponding bending of the axes of the fracture anti- and synforms. Structural patterns of folding with a tendency to adapt the axes of folds to the extension of thrusts indicate significant horizontal displacements of geomas of the sedimentary stratum, which in conditions of limited geological space cause secondary deformations of linear folded forms. Due to the displacement of geomas from the zones of maximum compression in the axial part of the Graben to the zones of geodynamic shadow - in the direction of the Oryl depression and Graben boards, the West Donets Cover-Folded Tectonic Region was formed within the transition zone. Scientific novelty. The study completed an original kinematic model of tectonic inversion of the Western Donets Graben was completed. The mechanism of inversion, due to which the riftogenic structure is completely destroyed by folded deformations of platform orogeneses, is caused by the pressure of the "tectonic stamp" of the Donbas Foldbelt. Under its influence, a segment of tectonic wedge was formed in the Graben, which was diagnosed with oroclin of transverse extension of the sliding type. The body of the Oroclin is formed by echeloned, rock-articulated ensembles of anticlinal uplift -folds, synclines and scaly plates-covers of pushing. A geodynamic injection band was formed in the foreland of the Tectonic Orocline extension, where folded zones of geomas displacement were formed, which consist of coulisse articulated uplift-anticlines. At the top of the Orocline, at the ends of dynamically conjugate main thrusts, an advanced tectonic compression fan is formed. In the rear of the Oroclin – hinterland are tectonic sutures – the roots of the folding covers of the approach. Practical significance. Development of a structural-kinematic model of tectonic inversion of the Western Donets Graben will allow to improve the geodynamic model of tectonic inversion of the Dnieper-Donets paleorift, on the basis of which regional schemes of tectonic and oil-gas-geological zoning will be adjusted.

Possibilities of attrtribute analysis of seismic data to clarify the structural features of geological section

Seismic attributes are used for qualitative estimation of changes in the wave field performed within the analysis of seismic response characteristics. Related changes can be associated with sedimentation characteristics and structural features of the geological section. Subject of the study is Kovalivka field in the northern pre-flank zone of the western part of Dnieper-Donets basin. The aim of the study was to specify geological structure of the sub-salt Devonian sediments by means of attribute analysis of the wave field dynamic characteristics. It should be mentioned that Devonian sediments in Dnieper-Donets depression are very poorly studied by seismic and well drilling. New attempts to study Devonian formation here were caused by obtained inflows from similar Devonian reservoirs in Prypiat depression and by finding new prospects within the investigated area. The results of old seismic data re-processing have been analyzed as well as recent seismic and well data. Basing on the obtained data, the attribute analysis has been conducted and madden a prognosis of the geological section by wave field dynamic characteristics using Petrel software (Sсhlumberger). Due to performed interpretation procedures, we have specified location of faults, stratigraphic boundaries and distribution of sub-salt Devonian sediments. Also, we predicted a zone of development sub-salt carbonate sediments with possible a rifogenic origin. Significant increase of a total thickness of sub-salt formation and presence of quite thick relatively pure low-density organogenic carbonate sediments take place in Kovalivka field. It significantly increases the prospect potential of the area.

Density heterogeneity of the Earth’s crust of Ukraine and adjacent territories from three-dimensional gravity modelling

The work was performed to study the density heterogeneity of the crust of Ukraine and adjacent regions analyzing detailed 3D gravity models of the following tectonic regions and separate structures: Dnieper-Donets Basin and Donbas, Ingulsky megablock, Golovanivska suture zone, latitudinal zones of fractures of the Ukrainian Shield, Black Sea megadepression and surrounding areas. The models are constructed on the basis of geological, petrophysical and seismic data along geotravers, DSS profiles, the modern WARR methodsand are calculated using the automated software complex for interpretation of potential fields GMT-Auto. As a result, new information was obtained for the density distribution in the whole Earth’s crust.The density distributions construct for the entire crust of Ukraine and adjacent regions at certain depths (surface of the basement, 10, 20, 30 km, Moho discontinuity). The thickness was determined for conditionally distinguished «granite», «diorite», «basalt» layers of the Earth’s crust and crust-mantle mixture within the whole region of the study. Its values are graphically represented by isolines on the respective schematical maps. The resulting density inhomogeneity became the basis for constructing, for the first time in a three-dimensional version, a scheme for the predictive composition of the Earth’s crust with typification according to the power ratios of its constituent layers. The heterogeneity of the present-day consolidated crust of the whole study area is characterized by granitic, granitic-dioritic, dioritic and basaltoid types. To clearly identify the dismemberment of the lower layer of the crust which is considered inseparable by the classification of the DSS method the basaltoid type is divided into 3 subtypes. The subtype 1 with a content of 40—70 % of basalt, subtype 2, where concent-ration of basalt increases to 70—90 % and subtype 3, which is composed only of basalt.It has been established that the basicity of the Earth’s crust of the USh changes from west to east, respectively, from basalt to diorite type. Decrease in crustal basicity is also observed in suture zones, namely from diorite and basaltoid typein Golovanivskii suture to basaltoid and diorite type in the Inguletsko-Kryvorizckii suture and diorite type in the Orikhivsko-Pavlogradskii suture. In the DDB the crustal basicity increases from northwest to southeast in accordance with the segmentation of this feature. The basaltoid type of the crust is predominant in the Black Sea megadepression and adjacent territories. For the first time, a type of crust was identified that does not coincide with the known ones and is characterized by the presence in the section of the «basalt» and «granite» layers (with a zero or very low «diorite» thickness). A similar type of bark is present in the Ingul megablock of the USh, in the northern side zone of the DDB, as well as in the Black Sea megadepression.

On the question of geological prerequisites of Dnieper-Donets depression hydrodynamic traps formation

Formulation of the problem. Hydrocarbon pools in hydrodynamic traps are known within many oil and gas provinces. The Dnieper-Donets basin is one of the regions where non-vault traps of almost all types and associated with them hydrocarbon pools are widespread, while HT in DDD are not yet typical, although the geological structure of the region indicates the possibility of their formation. Thus, substantiation of the role of geological preconditions in the processes of hydrodynamic type traps formation is the main task of the work. Analysis of recent research and publications. In the monograph of O. Plotnikov (2001) among the promising regions for the search for HT defined DDD. The reason for this was the data on the presence in some productive horizons, in particular in the Sorochinsky and Rudenkivsky fields, of formation waters that lie above gas-bearing deposits. It is believed by some researchers, that the leading role in the formation of gas accumulations at these fields belongs to formation waters. According to the results of geological and geophysical study of the southern slope of the Kalmius-Torets depression and the Krasnoarmijska monocline in the south-eastern part of the DDD (A. Terdovidov (2000), S. Pavlov (2004), favorable geological prerequisites for the formation of HT in Paleozoic sediments established. Selection of previously unsolved parts of the overall problem. The general problem of searching for HT in the DDD as a whole task has not been solved so far. Formulation of the purpose of the article. Estimation of possibilities of a new direction of search and reconnaissance works in DDD, namely on non-traditional non-vault traps of hydrodynamic type substantiation. Results. The Visean dominant productive complex, regionally extended on the monocline slopes of the northern and southern sides of the depression and lithologically represented mainly by sandy horizons, was selected for priority research. The significant content of alluvial sandstones in Visean sediments section allowed the authors to consider them as special reservoirs of fluids, and paleoalluvial systems to study in the rank of independent search objects. Their territorial location is logically related to the existing deflections of the surface of the crystalline basement, most of which are associated with modern river systems, which indicates the current functioning of their relationship. The authors made an attempt to substantiate within the northern side of the DDD the following forecast water exchange systems: 1) expultional overflowing; 2) docking regime (both in the terminology of O. Plotnikov) in Paleozoic sediments; 3) infiltration water exchange in Mesozoic sediments, as necessary conditions for catching migrating upward hydrocarbons. The decrease in the infiltration waters velocity to insignificant values is interpreted by the authors as a typical phenomenon for "closed" monoclines, within which there was an equilibrium between the pressure of infiltrative waters and the resistance of expultional fluids. This equilibrium is seen as a term of creating conditions for hydrodynamic trapping. The conclusions emphasize the need for comprehensive research to confirm the predictive models of water exchange and obtain data for mapping piezometric minimums, where there is an presumable accumulation of hydrocarbons.

Detection of intervals / layers in sections of the wells with anomalous areas of drilling mud filtrate contamination according to the well logging (with negative test results of horizons)

The zone of infiltration of the drilling fluid filtrate into the reservoir rock creates significant difficulties for the study by logging methods and during further testing of the formation. Due to the penetration of filtrate, significant contamination of the near-wellbore zone occurs. The porosity and filtration characteristics of reservoir rocks are changing. There is a possibility of blockage by filtrate in the invaded zone of oil or gas flow from the formation to the well. As a result of the studies carried out using well logging data, it was found that the presence and distribution of a mud cake on the borehole wall opposite the reservoir is an important factor influencing the process of filtration of the drilling fluid into the layers. On the examples of the Yablunivske oil and gas and Kolomatske gas fields of the Dnieper-Donets basin, it is shown that the absence of a mud cake on the borehole walls leads to the formation of maximum, anomalous zones of filtrate invasion. The determining of the diameter of the invaded zone was carried out according to the data of electrical logging methods. In addition, the diameter of the invaded zone was calculated as a solution direct task equation for the case of direct filtration without blocking by the mud cake. Comparison of the results of determining the diameter of the invaded zone by two methods made it possible to draw certain conclusions. An important conclusion is that even partial absence of mud cake on the reservoir wall in the well leads to horizontal and vertical filtration of the drilling fluid from the well into the formation. As a result, the invaded zone may be so deep, that the gas flow rate is absent even at high values of porosity, permeability and gas saturation

Differentiation of Rudov Beds based on the statistical methods on geological and geophysical data

Purpose. To perform the lithological-facies dismemberment of the Rudov Beds using geological and well-logging data to clarify the formation genesis of the hydrocarbon sources deposits within the Yablunivska structure of the Dnieper-Donets basin. Methodology. Cluster and factor analysis methods were used as well as Q.Passys method of well logging data interpretation for estimating the content of organic carbon (TOC). Findings. Regularities of geological structure, lithological heterogeneities, distribution of separate lithotypes and content of organic carbon in the Rudov Beds within Yablunivske oil and gas condensate field are established. The spatial distribution of separate facies types of rocks, thicknesses of their radioactivity layers and content of organic carbon (organic matter) within a single structure of the Dnieper-Donets depression is studied. Originality. For the first time according to geophysical data with the use of statistical methods, the lithological-facies dismemberment of the petroleum bearing strata, which have a regional distribution within the Dnieper-Donetsk basin, has been performed. It is found that there is no close correlation between natural radioactivity and the content of organic carbon in the Rudov Beds of the Lower Carboniferous. Certain conclusions have been made concerning the confirmation of the hypothesis about the formation of the Rudov beds in the conditions of shallow water desalinated sea gulf. Practical value. The proposed approach to lithological-facies dismemberment of the Rudov Beds by the well-logging data allows clarifying conditions for petroleum bearing stratum formation in order to assess its real oil and gas generation potential.

ГЕОДИНАМІКА

Aim of the work is tectonophysical identify the totality of the deformation structures of the collisional evolutionary stage, which determine the tectonic style of the Transition Zone between Dnieper-Donets Basin and the Donbas Foldbelt. Methods. For the research, we used the author's technique for reconstructing the fields of tectonic deformations and tectonophysical analysis of geostructures. The analytical base of the research was made up of new materials of geological mapping of the territory of the transition zone between the Basin and the Foldbelt. Results. Inversion deformations of the Dnieper-Donets Paleorift were controlled by lattices of tectonites of regionally stable submeridional directions of movements. An analysis of structural patterns of tectonites indicates over the riftogenic faults of the basement in the sedimentary cover of the transition zone, echeloned stages of plumage are formed, composed of thrusts with a significant component of horizontal displacement. The tectonic style of the Transition Zone is determined by the pushing on the low dislocation autochthonous of the Basin of the repeatedly deformed, crumpled into the folds of sedimentary geomas from the Foldbelt. The allochthon structural and tectonic framework consists of thrusts, coulisse-jointed structural ensembles of thrusts, folded covers of transverse extrusion of geomas from axial to side zones, and folded covers of longitudinal thrust towards the depression. All together its form the Western Donets Cover-folded Region, the main structural element of which is the Segment of the Tectonic Wedging of geomass. The north-eastern flank of the Segment is formed by linear anticlinal zones - Torsky-Drobishivska, North-Donets, Matrossko-Toshkovska, south-western - Petrovsko-Novotroitska. The structural apex of the Segment is a tectonic junction at the ends of dynamically conjugated thrusts in the area of the joint of the salt-dome shafts of the axial part of the Basin. Scientific novelty. The tectonic inversion is responsible for the formation of three folded structural floors - the Herzinian, Laramian and Attic. According to the dynamically coupled lattice, a cover-folding system of tectonic thrusting was formed in them, which was first diagnosed as a Segment of Tectonic Wedging of geomas by the Donbas Foldbelt. On the basis of this, within the Transtition Zone, a Western-Donetsk cover-folded Region was separated, covering two tectonic areas in intensity and style of deformation of the sedimentary cover - Kalmius-Toretsky area of scaly covering in the southwestern part, which is limited to the South Donbass Melange Zone in the south, and the Lugansk-Kamyshuvakhsky area of the coulisse-jointed uplift-folding on the northeastern part, which from the north is limited by the low-folded Mesozoic-Cenozoic cover. They are separated by the Central Zone of Strike-slip control along the axial folded zone of large stage-jointed uplift-folds, which include Great-Kamyshuvakhska, Novotroitska, Druzhkovsko-Konstantinovska and Main anticlines. Practical significance. Based on the actual geo-mapping data, it is proved the riftogenic structure in the southeast of the Dnieper-Donets Paleorift is destroyed by folding at the stages of platform activation. Allocation of territory of the Western Donetsk Сover-folded Region allow to correct the scheme of tectonic zoning of the Dnieper-Donets Basin, which is the basis for modeling the geodynamics of the Transition Zone formation.

Pripyat trough as a possible channel of mantle degassing: deep structure and position in the junction zone of Sarmatia and Fennoscandia

The Pripyat Trough, representing the northwestern end of the Pripyat-Dnieper-Donetsk Basin, is located in the junction zone of the Precambrian terrains of Fennoscandia and Sarmatia, controlled by the Osnitsk-Mikashevichy Igneous Belt. The ancient tectonic suture was reactivated during subsequent episodes of Meso-Neoproterozoic and Devonian rifting. The lithosphere structure of the Pripyat Trough is generalized according to published geophysical data and new interpretation of the velocity-density model of the lithosphere structure on Eurobridge-97 profile is given. The structure of the lithosphere at the southern flank of the Pripyat Trough and the Korosten pluton, consisting of rapakivi granites — gabbro-anorthosites, is associated with the existence of a mantle magma chamber, inflow of mantle melts into the crust, partial melting, magmatic differentiation and transformation of the substance throughout the crust under the pluton. Within the Pripyat Trough, a special role belongs to the South Pripyat fault, which limits the Pripyat Trough from the south, and the Korosten pluton from the north, and is associated with an inclined seismic boundary (reflector) in the mantle. The South Pripyat fault, being a deep fault zone, controlled the intrusion of magmatic melts and mantle fluids throughout its evolution. At present it controls seismicity and, obviously, is a conduit for hydrocarbons and a mantle degassing channel. Significant features of the structure and evolution of Pripyat Trough are: (I) origination in an ancient zone of weakness that undergone repeated tectonic and magmatic activations, (II) position at the intersection of four major zones of heterogeneity: Osnitsk-Mikashevichy Igneous Belt of NE strike, N-S-trending Odessa—Gomel zone, W-E-oriented Brest—Pripyat, and the Dnieper—Donets Basin of the NW orientation, (III) the spatial relationship of the limiting listric faults with mantle heterogeneities; (IV) recent activation and confinement of hydrocarbon deposits to it. These criteria make it possible to consider the Pripyat Trough as a possible channel of mantle degassing.