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The paper presents new thickness and sandiness maps of the Visean terrigenous strata (Radayevkian and Bobrikian regional stages, Lower Carboniferous) of the South Tatar Arch, constructed using the “Natural Neighbour” spatial interpolation method in ArcGIS Pro software based on the analysis of geophysical survey data for more than 30,000 boreholes.The interpretation of the maps in combination with the results of sedimentological, ichnotextural and petrophysical core studies, supplemented by the analysis of archival and published materials, provided an opportunity to update the approach to modelling the sedimentation of the terrigenous Lower Carboniferous of the South Tatar Arch. The proposed sedimentation models of terrigenous and coal-bearing sediments take into account the chronostratigraphic data, the karstification of isolated carbonate platforms, the sediment accumulation rates and the ichnotextural characteristics of the sediments. It is concluded that the accumulation and preservation of terrigenous and peat (coal-bearing) sediments differ in duration (0.1 million years vs. 1.5–2 million years) and are consequently associated with transgressive and regressive phases.The accumulation of terrigenous sediments includes: (a) transgressive eustatic episodes – short-term incursions of a marine basin onto the eroded surface of an isolated carbonate platform, during which silty and sandy, wellsorted bioturbated sediments were accumulated, often with a variety of ichnofossils of marine benthic organisms; (b) the regressive eustatic phase resulted in the predominant erosion of sediments on the arch; whereas sediments in the incisions were largely preserved.The accumulation of peat (coal-bearing) deposits includes (a) the regressive eustatic phase, during which the vast area of the eastern Volga-Urals region was covered with flourishing vegetation and stable swamp environments were forming in the incisions of the Tournaisian surface; (b) the transgressive phase – the peat was overlaid and buried by transgressive marine silt-sand sediments; then it was compacted and transformed into coal. The alternation of coal-bearing and transgressive intervals indicates the cyclicity of these processes.The proposed sedimentation models extend the concepts of previous studies and are consistent with the developed maps of thickness and sandiness of the Lower Carboniferous terrigenous sediments, explaining the complex, covering and mosaic distribution of sand bodies over the area, as well as the filling of incisions with sediments of different lithological types.

The method of acid hydraulic fracturing has been actively used in recent years, for the deposits of the Vereysky horizon of the Moscowian strata in the south-east of Tatarstan. Design development and the use of hydraulic fracturing requires full-fledged studies of the geomechanical characteristics of rocks, including the prediction of the propagation of emerging fractures. It is considered the main geomechanical characteristics for reservoir rocks and dense rocks involved in the structure of the sections, on the example of the study of polyfacial reservoirs of the Vereysky horizon of the Ivinskoye oil field. It was revealed that the carbonate reservoir rocks of the middle and upper parts of the Vereysky horizon (C2 vr3 and C2 vr5) have the least strength properties and a greater susceptibility to fracturing. More durable were sandstones of the upper part of the horizon, marls and mudstones of the middle and upper parts of the horizon, as well as mudstone and dense packstone, typical for the lower part of the Vereysky horizon. The presented data can be valid for most of the sections of the Vereysky horizon of the southeast of Tatarstan and are used for the choice of optimal solutions when applying the hydraulic fracturing technology.

Formulation of the problem. In the world's oil and gas-bearing basins, there are known examples of an increase in the reserves of hydrocarbon deposits as a result of inflow of fluids from the deep subsoil. Recently, the theory of the Earth degassing is gaining popularity. There are more and more arguments in favor of the fact that in many oil- and gas-bearing provinces of the world, oil and gas deposits are constantly replenished due to the migration of hydrocarbons through degassing pipes. Certain prospects for maintaining oil and gas production are possible as a result of the natural recovery of depleted deposits in Ukraine as well. However, this issue has not been sufficiently studied and requires further research. The purpose of the article is to argue with actual materials for the regeneration of hydrocarbon deposits, to estimate the probable volumes of their replenishment, to determine the methods of geological research to outline the zones of nourishment of hydrocarbon deposits. Materials and methods. Research materials are actual materials from the development and permanent assessment of hydrocarbon reserves of Ukrainian deposits. The research methodology consists in the analysis of the facts of the replenishment of hydrocarbon deposits from the point of view of new scientific concepts of the supply of hydrocarbons from the deep subsoil. Results. Based on the results of the increase in reservoir pressures of spent gas condensate deposits and repeated calculations of hydrocarbon reserves of the Shebelynka, Chornukhy, Bilousivka and Proletarka deposits of the Dnipro-Donets Basin, a conclusion was made about the replenishment of deposits due to the vertical migration of oil and gas, the probable scales of deposit regeneration were estimated. The results of industrial development of the East Kazantyp and North Bulganak gas fields of the Indolo-Kuban depression also testify to their probable feeding from the depths. Adiabatic fracture formation associated with seismotectonic impulses and phenomena of natural rupture of rocks by deep fluids plays a significant role in the formation of unconventional deposits. The result of fluid fracturing of rocks is specific matrix microcracking. It is well manifested in well cores from depths of more than 5.5 km (Semyrenky, Machushy deposits of the Dnipro-Donets Basin). Hydrocarbon deposits at these depths have a zonal character and are not controlled by the structural factor. Scientific novelty, practical significance and recommendations. Actual materials have proven that some hydrocarbon deposits in Ukraine are constantly being replenished as a result of seepage of deep fluids. It is likely that the main channels of hydrocarbon supply to deposits are deep faults. To determine the degassing channels it is advisable to use the methods of field geophysics and geochemical studies. We can state that the replenishment of gas reserves of some Dnipro-Donets Basin fields according to confirmed facts ranges from 14 to 1800 million m3 annually. It is necessary to monitor the spent deposits, therefore it is advisable not to liquidate decommissioned wells, but to preserve them or transfer to the fund of observation wells, periodically measuring reservoir pressures and determining the character of fluid saturation of spent deposits. It is necessary to manage the process of extraction of hydrocarbons, applying a policy of balanced economical production.

The multi-scale study of rock properties is a necessary step in the planning of oil and gas reservoir developments. The amount of core samples available for research is usually limited, and some of the samples can be distracted. The investigation of core reconstruction possibilities is an important task. An approach to the real-size reconstruction of porous media with a given (target) porosity and permeability by controlling the parameters of FFF 3D printing using CT images of the original core is proposed. Real-size synthetic core specimens based on CT images were manufactured using FFF 3D printing. The possibility of reconstructing the reservoir properties of a sandstone core sample was proven. The results of gas porometry measurements showed that the porosity of specimens No.32 and No.46 was 13.5% and 12.8%, and the permeability was 442.3 mD and 337.8 mD, respectively. The porosity of the original core was 14% and permeability was 271 mD. It was found that changing the layer height and nozzle diameter, as well as the retract and restart distances, has a direct effect on the porosity and permeability of synthetic specimens. This study shows that porosity and permeability of synthetic specimens depend on the flow of the material and the percentage of overlap between the infill and the outer wall.

The article discusses the prospects of oil and gas in the Paleozoic, Mesozoic and Neogene sediments in under thrust uplifts in the outer zone of Precarpathian trough, within the Carpathian graben and southwest of the graben, that is, within Folded Carpathians. It is assumed that most of these uplifts are composed of Mesozoic terrigenous-carbonate rocks, partly Neogene and Paleogene non-flysch rocks, which have reservoir properties, and are overlain by Neogene molasses and a thrust complex of flysch rocks. In the conditions of the Carpathian Orogen, seismic prospecting is not always possible to determine the location of the dome of the structures due to insufficient traceability of the reflection horizons. Search drilling is often unsuccessful. Therefore, the development of new inexpensive additional methods for forecasting oil and gas promising uplifts is relevant. A technique for interpreting geological and gravimetric materials is presented. These uplifts are identified as a result of the analysis of geological and geophysical materials, in particular geologic-tectonic maps, drilling data, gravity anomaly maps and geologic-gravimetric modeling data along profiles that, as a rule, cross the vault of uplifts. Geological-gravimetric modeling is based on solving of the gravity inversion. The geological and tectonic characteristics of promising areas are illustrated by structural maps and geo-density cross-sections, which were built by the authors. Geo-density models of geological cross-sections are consistent with gravity anomalies. The number of detected uplifts is more than 50. A number of uplifts, except for those under the Carpathian bed, are located at relatively shallow depths, more accessible for drilling. The location of prospecting boreholes is recommended.

The relevance of the study is caused by the need to develop the oil and gas industry in Western Siberia by identifying unconventional (including low-permeability) reservoirs and assessing their prospects for development. The aim: to increase the efficiency of gas production by studying the influence of the structure of the mineral substance of rocks on the pore space and identifying unconventional reservoirs. Objects: Senonian deposits, the commissioning of which is planned to support production in the gas industry. Methods: optical and electron scanning microscopy, X-ray spectral and X-ray fluorescence analysis, Infrared spectroscopy, X-ray diffraction, analysis of filtration-capacitive properties by the GRI–SMP-200 method. Results. The features of the mineral composition of low-permeable siliceous-clay reservoir rocks of the Berezovskaya formation in the north of Western Siberia are studied on the example of the Medvezhye deposit. The chemogenic-biogenic origin of these sedimentary rocks is confirmed by the remnants of organic material: sponge spicules, radiolarian shells, mollusks, etc. The rock structure reveals small pores filled with kaolinite and quartz, and individual grains of montmorillonite. Also, there are numerous spherical aggregates of framboid pyrite (FeS2), which is an autigenic early-diagenetic biomineral and characterizes the reduction zone of diagenesis. It is shown that the «crystallinity index» which characterizes the degree of transformation of the opal-cristobalite-tridimite phase (OCT-phase) of silica can be chosen as a lithological and mineralogical criterion for identifying productive zones in unconventional reservoirs of the Medvezhye deposit. The appearance of the crystalline phase of quartz from unstable chemogenic-biogenic amorphous silica causes the appearance of larger voids, increasing gas saturation and gas permeability.

The Lower Berezovskaya subformation in the Upper Cretaceous is a complex reservoir with unconventional reservoir rocks located in the north of Western Siberia. The clay–siliceous deposits in the Lower Berezovskaya subformation are represented by various types of silicites that have unique petrophysical and mineralogical characteristics that cause significant difficulties in the development of associated productive layers. The aim of the research is to study their mineral composition, the parameters of the void space structure, and the conditions of formation, as well as to determine the sources of silica and perform a detailed study on the structure of nanoquartz. To study the mineral composition, the structure of the void space, and the genesis, special methodological techniques were applied, and a comprehensive analysis of the results using a wide range of laboratory studies, including optical micro- and stereoscopy, scanning electron microscopy, X-ray diffraction analysis, and microtomography, was performed. Silicites in the Lower Berezovskaya subformation are caused by the complex structure of the void space, which includes a wide range of genetic types of voids ranging from micron and submicron dimensions to fractions of a millimeter (voids confined to the burrowing organisms, intraform voids, interform voids, lenticular voids, cellular voids, and voids confined to microstylolite seams). The most widespread type of void is the interaggregate (lenticular and cellular) void, which is formed by clay (montmorillonite) scales, on the surface of which numerous α-quartz nanocrystals ranging in size from 0.05 to 0.5 microns are noted. The content of such quartz reaches up to 80% of the total volume of the rock in individual samples. The source of siliceous material for nanoquartz crystals was most likely volcanic processes, since the revealed mineral paragenesis of montmorillonite, cristobalite, and zeolites indicates the active transformation of ash material that entered the basin from volcanic formations.

Compressional and shear wave velocities (Vp and Vs respectively) are essential reservoir parameters that can be used to delineate lithology, calculate porosity, identify reservoir fluids, evaluate fracture and calculate mechanical properties of rocks. In this study, the potential application of intelligent systems in predicting Vp and Vs of reservoir rocks is presented. To date, considerable efforts are being carried out to obtain the best set of parameters capable of predicting Vp and Vs with a high degree of accuracy. Three intelligent models namely artificial neural network (ANN), adaptive neuro-fuzzy inference system (ANFIS) and least square support vector machine (LSSVM) were used in this study. The different models were based on the available information sourced from wireline log data. Parametric studies showed that measured depth, neutron porosity, gamma-ray, and density log data are vital in predicting both Vp and Vs. In developing the models, a comprehensive dataset available from one of the oil fields in the Norwegian North Basin was used. In evaluating the different models, two different statistical parameters namely Pearson’s correlation coefficient (R2) and root mean square error (RMSE) were considered. It was found that the LSSVM model is the most accurate technique for predicting both Vp and Vs. LSSVM model predicted the Vp with R2 and RSME of 0.9706 and 0.0893 respectively. In addition, the model showed an excellent accuracy level in the prediction of Vs with R2 and RMSE of 0.9991 and 0.0457 respectively. The proposed approach, if implemented, is crucial for geoscientists, reservoir and drilling engineers working on reservoir characterization and drilling operations.

With significant increase of tomographic equipment power, demand for Prediction relative permeability prediction Predicting in porous media from digital image data. In this work, it is predicted three -phase relative permeabilities with co-applying Darcy’s and Stokes equations in two case studies, namely Bentheimer sandstone and Estaillades limestone which their micro-CT data files were downloaded from Imperial College website. In order to perform calculations firstly we extracted pore connected network from the micro-CT data and it is estimated fluids distribution within pore channels during two-phase flow. Then we calculated pressure distribution of each phase solving its continuity and momentum equations within the obtained connected phase network. Pressure distribution and fixed volumetric flow rate ( that flows through all cross-sections perpendicular to the supposed flow direction), then were applied to solve for effective permeabilities. Effective permeabilities were then related to the relevant saturation and curves of two -phase relative permeabilities were derived in this manner. Stone’s equation was finally applied to estimate three phase permeability ternary curves. Results showed that application of correlations for determining fluid distributions is accurate enough for multiphase relative permeability estimation in real case studies. This paper also shows that performing calculations on the segmented REVs is more accurate than work on simplified pore network models extracted from micro-CT data.

Abstract An overview and integration of key petroleum exploration findings in the onshore Central Sarawak Basin, NW Borneo in the last 2 decades is presented. Findings revealed that critical moments for the generation and preservation of hydrocarbon may be found in the Early Oligocene, Early Miocene, and Late Miocene times. Geochemical data of ninety-five (95) source rocks suggest TOC values of 1.54 wt% (Miri Formation) to 70.00 wt% (Nyalau Formation) with promising S 2 and S 2/S 3 ratios. T Max fell below the 435 °C maturation threshold. Reservoir facies of the Nyalau, Belait, and Lambir formations and their subsurface equivalents have moderate-to-poor poro-perm properties. Reservoir plays in the area are the Oligocene–Miocene clastics and limestones of Cycles I, II, III, and IV. Significant diagenetic modification is evident in analogue reservoir sandstones, and could constitute major poro-perm control in subsurface reservoir units. Observed predominance of structural related traps gleaned from seismic data is a reflection of the paleotectonic (Sarawak orogenic) event (ca. 40 − 36 Ma) associated with the region. Shale rocks overlying possible reservoirs and observed juxtaposition of reservoir units against impermeable beds provide seal integrity. Deeply seated faults are potential conduits, in addition to buoyancy. Concentration of future research efforts on petroleum/basin modeling and subsurface reservoir assessment was to further improve current understanding of the under-explored onshore Central Sarawak.

The productive capacity of the Guarani Aquifer System is subject to variations along its length, due to its complex structural and compositional heterogeneity. Several parameters may influence the quality of this reservoir rock, such as its mineralogical and textural constitution, as well as the physicochemical processes, since its diagenesis is not the same throughout the aquifer, influencing the water productivity in wells in different locations. Such parameters are useful in the geoscience studies for the elaboration of diagenetic models for the prediction of the reservoir quality. In this work, several properties of the sandstone rock from Botucatu Formation were determined using different techniques, such as geotechnical tests, optical microscopy (MO), electron scanning microscopy (SEM), X-ray Fluorescence and X-ray diffraction. The results indicate that the studied sandstones have characteristics of the reservoir rocks, with potential for water storage.

Tortuosity is an important geometrical parameter of the pore or grain network in a porous medium. Here we present and discuss an implementation of a plugin to estimate the pore/grain network tortuosity of a porous medium sample. The tortuosity is estimated according to the geometric reconstruction algorithm that can be applied to 2D or 3D μCT image samples. To illustrate the tortuosity plugin features, applications are given i) for the 2D case: three synthetic image samples being one horizontal straight line, one diagonal straight line and a curved line, and additionally it is considered a Dolomite Silurian rock sample, ii) for the 3D case: the pore network of a Berea and Fontainebleau sandstone and a Grosmont carbonte reservoir core samples; the grain network of a distal-radius trabecular bone sample and, finally, the pore network of a Rhodic Ferralsol soil sample. Some comments and discussions about the tortuosity estimated with the current algorithm are also addressed.

Complexly constructed low-permeability reservoirs are still poorly understood. This slows down the development of oil and gas resources of the Jurassic and deeply submerged pre-Jurassic deposits of the West Siberian oil and gas basin. There is also no consensus among the geological community on the prospects of these deposits from the perspective of the oil generation in them and subsequent emigration. There are many questions on the structure and oil and gas content of the deposits of the Bazhenov formation, whose oil resources amount to tens of billions of tons. The problems of oil and gas content and mapping of heterogeneous structure of massive rocks, including the basement formations, are considered in the article. In addition, the prospects of the oil and gas potential of the Jurassic and pre-Jurassic deposits of the northern regions of Western Siberia with geological and geochemical data were estimated. The revealed zones of highly transformed organic matter (OM) in the sediments of the Bazhenov formation and a number of other facts allow us to re-argue the prospects of the oil and gas bearing of the underlying deposits.

The deposits of the Bazhenov formation are a unique reservoir of unconventional oil reserves in Western Siberia. They contain both solid organic matter (kerogen) and liquid light oil. The successful development of these hydrocarbons is largely determined by the adequacy of the void space models. The aim of the study is to identify the types of void space in the sediments of the Bazhenov formation and to identify the distribution patterns across the section of the researched wells. The void space was studied by electron and optical microscopy, and the mineral composition of the rocks was determined by X-ray diffraction analysis. The deposits of the Bazhenov productive formation in the territory of Western Siberia are represented by a wide complex of lithotypes, including various kinds of silicites, carbonate, clay rocks, and mixtites. The reservoir space in the reservoir rocks of the Bazhenov formation is a complex and hierarchically subordinated system, which includes voids and fractures of various sizes, configurations, and genesis. The void space of the Bazhenov formation is characterized by a fairly high degree of spatial heterogeneity, which is controlled by lithological, facies, and tectonic factors, as well as the direction of catagenetic processes.

The article presents a lithogenetic typification of the rocks of the Ust-Kutskian horizon of the Teterian formation in the central part of the Nepa-Botuobin anteclise. A generalized scheme-model of their formation is drawn up. Granular dolomites have been identified as the most promising lithogenetic type to allocate zones with improved reservoir properties. The structure of the void space of the Ust-Kutskian horizon is characterized. Based on the quantitative assessment of pores and caverns, the presence of salts in them, a correlation was established between these parameters and the reservoir properties of the rocks. The connection with post-sedimentation processes is shown. The conditions for the formation of the Ust-Kutskian depositsare reconstructed with the use of geochemical indicators for element-impurities. As a result of the studies, a set of criteria for local forecasting of reservoirs for setting up the first stage of exploration and development has been developed.

The petrophysical properties of a well selected from among the onshore oil fields in the Niger Delta Basin, Nigeria was evaluated using gamma ray log, resistivity log and neutron-density overlay log to analyze for the hydrocarbon potential of the well. Some petrophysical properties of the reservoir rocks and fluid characters such as porosity, shale volume, effective porosity, permeability, and formation resistivity factor, resistivity of water, hydrocarbon saturation, water saturation, and net pay thickness were evaluated. The results show that the volume of shale in each reservoir zone directly affects the effective porosity and the zones. The volume of shale is inversely proportional to the effective porosity, as an increase in the volume of shale will bring about a decrease in effective porosity. On the other hand, permeability is dependent on the effective porosity. Facies type identification of the reservoir sands were also carried out using the wireline log - Gamma Ray Log. Results of the work revealed the presence of hydrocarbon in 10 reservoirs across the well, and the hydrocarbon type was observed to be only oil. Oil/Water contacts occurred at 2288m, 2518mm, and 2989m, and the Net Pay Thickness was calculated to be 238m, that is the total thickness of the hydrocarbon reservoirs. Keywords: Petrophysics, Wireline logs, Facies, Reservoir rocks, Pay thickness.

A variation of temperature produces a change in the microstructure of the rock due to the mineral thermal expansion and its residual strain. Depending on the temperature cycle and texture, microstresses may lead to the development of preexistent cracks or the creation of a new and irreversible cracking. The effect of temperature on reservoir rocks is an important topic since it conditions the permeability and the fluid flow. Two main questions arise from this: the first is if an irreversible cracking threshold is attained in the reservoir rocks at low temperature geothermal systems (around 100 °C); the second one is about the influence of thermal fatigue by the repetition of heating–cooling cycles on the different rock types. To answer these questions, four reservoir rocks (chalk, sandstone, fresh granite, and weathered granite) were submitted to two different thermal regimes. The first test was conceived to detect the irreversible cracking threshold, and for that, the rocks were submitted to progressive heating (90°, 100°, 110°, 120°, and 130 °C). The second test consisted of doing cycles of fast heating of the samples up to 200 °C. The microstructure variation was assessed by means of a scanning electron microscope, mercury porosimetry, and capillary water uptake combined with passive infrared thermography. Infrared thermography is an emerging tool in the field of rock study, used to detect water masses or determine thermal properties. The water transfer during the capillary tests of the rocks, before and after the tests, was monitored with this technique. In addition, the cooling rate index, a non-destructive parameter to detect cracking development, was calculated. The results made it possible to differentiate the behaviours in relation to the rock type, with a chalk and a weathered granite less susceptible to thermal stresses than a fresh granite and sandstone. In addition, infrared thermography resulted in being a very useful indirect technique to detect the changes on the surface, although they do not always correlate to the bulk microstructural changes.

The assessment of the geothermal potential should always take an accurate identification of the geological conditions into account. Petrographic and petrophysical investigations of the aquifers allow to estimate their productivity and infectivity. The area of the Mogilno-Łódź Trough is next to the Podhale basin, one of the most prospective regions in terms of geothermal potential in Poland. The Lower Jurassic aquifers are characterized by the largest dispositional resources among geothermal aquifers in the Polish Lowlands. The Lower Jurassic geothermal reservoir consist of fine and mixed grain-size sands and sandstones layers from 10-650 m thick, depending on the depth. The water within the reservoir exhibits mineralization ranging from 2 to over 250 g/L and its temperature ranges from 30 to 100°C. Boreholes profiles selected for study consist Lower Jurassic formations of the Polish Lowlands, which are perspective for the heat production in Poland. Sandstones are represent mainly by quartz arenites and subordinate by quartz wackes. Parameters measured include among others porosity, permeability and surface area. The results of the petrographic and mineralogical studies of core samples confirmed the presence of rock with favorable parameters for geothermal water accumulation.

This study is focused on two structures in the Baltic offshore region (E6 and E7 structures in Latvia) prospective for the geological storage of carbon dioxide (CO 2 ). Their CO 2 storage capacities were estimated recently with different levels of reliability. Petrophysical, geophysical, mineralogical and geochemical parameters of reservoir rocks represented by quartz sandstones of the Deimena Formation of Middle Cambrian in two wells and properties of Silurian and Ordovician cap rocks were additionally studied and interpreted in the present contribution. Extended methodology on rock measurements and estimation of conservative and optimistic storage capacity are presented. Uncertainties and risks of CO2 storage in the offshore structure E6 estimated as the most prospective for CO2 geological storage in the Baltic Region, and the largest among all onshore and offshore structures studied in Latvia, were discussed. We re-estimated the previous optimistic capacity of the E6 structure (265–630 Mt) to 251–602 Mt. Considering fault system within the E6 structure we estimated capacity of two compartments of the reservoir separately (E6-A and E6-B). Estimated by the optimistic approach CO2 storage capacity of the E6-A part was 243–582 Mt (mean 365 Mt) and E6-B part 8–20 Mt (mean 12 Mt). Conservative capacity was 97–233 Mt (mean 146 Mt) in the E6-A, and 4–10 Mt (mean 6 Mt) in the E6-B. The conservative average capacity of the E6-B part was in the same range as this capacity in the E7 structure (6 and 7 Mt respectively). The total capacity of the two structures E6 and E7, estimated using the optimistic approach was on average 411 Mt, and using the conservative approach, 159 Mt.

In the Slovenian part of the Pannonian basin the oil-gas field Petišovci, the gas fields Dolina and Gančani, and the oil fields Filovci, Bakovci and Bukovci were discovered. With the exception of Petišovci, the mentioned fields arecurrently not productive. On this basis, and as a consequence of recent results of oil geological investigations, the lithostratigraphic description of the Neogene beds of this part of the Pannonian basin is presented, together with occurrences or source rocks in the given stratigraphic horizons, as well as the structural charactcristics or the territory. The results highlight the somewhat higher potential of certain areas, which is also of importanceeconomically.

Baltic countries are located in the limits of the Baltic sedimentary basin, a 700 km long and 500 km wide synclinal structure. The axis of the syneclise plunges to the southwest. In Poland the Precambrian basement occurs at a depth of 5 km. The Baltic Basin includes the Neoproterozoic Ediacaran (Vendian) at the base and all Phanerozoic systems. Two aquifers, the lower Devonian and Cambrian reservoirs, meet the basic requirements for CO2 storage. The porosity and permeability of sandstone decrease with depth. The average porosity of Cambrian sandstone at depths of 80–800, 800–1800, and 1800–2300 m is 18.6, 14.2, and 5.5%, respectively. The average permeability is, respectively, 311, 251, and 12 mD. Devonian sandstone has an average porosity of 26% and permeability in the range of 0.5–2 D. Prospective Cambrian structural traps occur only in Latvia. The 16 largest ones have CO2 storage capacity in the range of 2–74 Mt, with total capacity exceeding 400 Mt. The structural trapping is not an option for Lithuania as the uplifts there are too small. Another option is utilization of CO2 for enhanced oil recovery (EOR). The estimated total EOR net volume of CO2 (part of CO2 remaining in the formation) in Lithuania is 5.6 Mt. Solubility and mineral trapping are a long-term option. The calculated total solubility trapping capacity of the Cambrian reservoir is as high as 11 Gt of CO2 within the area of the supercritical state of carbon dioxide.

The sand control by consolidation involves the process of injecting chemicals into the naturally unconsolidated formation to provide an in situ grain-to-grain cementation. The sand consolidation chemicals are available for some 30 years. Several types of consolidating material were tried. Presently available systems utilize solidified plastics to provide the cementation. These systems include phenol resin, phenol-formaldehyde, epoxy, furan and phenolic-furfuryl.The sand consolidation with the steam injection is a novel technique. This process provides a highly alkaline liquid phase and temperatures to 300 °C to geochemically create cements by interacting with the dirty sand.While the formation consolidation has widely applied, our experience has proved a high level of success.