Dense Sandstone Research Articles

Research and application of the low-damage temperature-controlled phase change temporary plugging agent

Ultra-deep dense sandstone reservoirs are characterized by high stress, large stress difference, high temperature, etc. Compared with conventional fracturing techniques, temporary plugging fracturing techniques are more capable of increasing fracture complexity and improving the stimulation reservoir volume (SRV). Phase-change temporary plugging agent has received wide attention due to its easy injection and return characteristics, etc. However, the temporary plugging mechanism of phase-change temporary plugging agent on shot-holes and fractures is still unclear. Therefore, this study aimed to develop a temperature-controlled phase change temporary plugging agent (STPA). The main properties of STPA, such as gel formation time and plugging capacity, are studied. The results show that STPA completes the transition behavior of solution-gel-solution at different temperatures; the gel formation time and gel breaking time of STPA decrease with increasing temperature; the pressure-bearing capacity of the plugging increases with the width of the fracture; the pressure-bearing capacity of STPA is more than 20 MPa in the fracture, and more than 18 MPa in the “shot-hole + fracture”; the rate of injury to core permeability by STPA is about 1.2%. In addition, STPA was successfully applied in fracturing field practice, and the maximum injection pressure increment was about 12.08 MPa, with remarkable temporary plugging effect. These results help to reveal the plugging mechanism of phase change plugging agent, which is of guiding significance for the field application of STPA.

Study of rock-breaking performance of V-axe-shaped PDC cutter in tight sandstone formation

In the field of oil and gas drilling engineering, tight sandstone strata are one of the strata that are difficult to drill. The V-axe-shaped cutter has a good effect in crushing tight sandstone strata. However, there were few studies on its specific structural parameters and rock-breaking performance in tight sandstone formations. To further explore its structural parameters and rock-breaking performance, this paper studies the rock-breaking performance of a V-axe-shaped PDC cutter in tight sandstone formation by combining experiments with finite element simulation. Mechanical tests show that the compressive strength is high, with values of 130.3 MPa, 223.3 MPa, and 271.6 MPa under confining pressures of 0/15/30 (MPa), respectively, with the condition of 0.02 mm/min loading rate. Rock lithology tests that the sandstone in this formation has strong abrasiveness. The penetration ability should be considered when evaluating the rock-breaking performance of cutting cutters. The results show that the V-axe-shaped PDC cutter mainly uses shear, extrusion, and point load to break rock together. It has a stronger ability and stability to attack the rock. With a 100° V-shaped angle (α) and 140° Axe-shaped angle(β) has the best rock-breaking property. The back-rake angle of the cutter can reduce cutter vibration and significantly improve PDC bit rock-breaking efficiency. The optimal rock-breaking back-rake angle of the V-axe-shaped cutter is 20° in dense sandstone formations. With the increase of wear height(0–3 mm), the synthetical mechanical specific energy (MSE) is reduced by 11.53%, 6.30%, 10.30%, and 33.28%, respectively, compared with the conventional cutter. The tests indicate that the rock-breaking efficiency of the V-axe-shaped PDC cutter is 12.9% higher than that of the conventional PDC cutter. The application of V-axe-shaped cutters on the bit is expected to improve the rock-breaking efficiency and footage of PDC bit in tight sandstone formations and realize the development of low-cost and high-benefit oil and gas resources.

Different Fracture Liquids under the Action of Enclosure of Dense Sandstone Reservoir Micro-Damage Characteristics Study

The sandstone reservoir in the Lule River group of Mahai East District is strong, densely dense, and the expansion of clay material is very easy to block the pores. Therefore, the new pressure cracks and cationic cluster stabilizers with double-season ammonium salt clay stabilizers are used. Experimental analysis is performed under the circumstances of the perimeter. Use nuclear magnetic real-time testing different fracture liquids to drive the pore structure structure changes before and after the sandstone, combined with differential theory to calculate the fractal dimensions of sandstone. As a result, under the condition of water full, as the perimeter pressure increases, the rocks are increased, and the rocks are increased, and the rocks are increased. The matrix occurs under the common action of the fence and the fracture fluid to prevent the inflation of clay minerals under the combined action of the fence and the fracture fluid, which causes a significant reduction in large holes and increased micropores and medium holes. Exploring different fracture liquids to reservoirs is of great significance to the development of dense sandstone reservoirs.

Three-Dimensional Spatial Microscopic Characteristics and Developmental Influencing Factors of Tight Gas Layers in Hangjinqi Prospect Area, Ordos Basin, China

The unconventional tight oil and gas resources in the Xinzhao East belt of the Hangjinqi Prospect area in the Ordos Basin of China are abundant. However, the reservoir’s internal storage space is complex, and the microscopic pore throat structural features are not well recognized, which has led to some trouble in the deployment of oil and gas exploration. To reveal the microscopic characteristics of the dense sandstone gas layer in the first member of the Lower Stone Box Formation of the D-well Zone in the Xinzhao East belt of the Hangjinqi Prospect area, a three-dimensional space digital core was built, and the stored set spatial data were extracted, based on rock sheet and coring data and X-CT scanning technology. Quartz grain size was segmented and analyzed based on an adaptive approach. The microscopic characteristics of the gas layer in the studied section and the factors influencing its development were studied, combining the use of a field emission scanning electron microscope, helium porosimeter, and gas permeability meter. We found that in the studied section, the porosity is relatively high, the pore throat size is large, and the pore permeability correlation is good. The reservoir space, which consists of intergranular pores, intragranular pores, and microcracks at the grain edges in the study area, is characterized by a complex distribution pattern. Within the gas layer, isolated pores are connected by microcracks to form a network of reservoir spaces, which increases the pore throat size, enhances the connectivity of the pore throat, and makes the microscopic characteristics of the reservoir space better. The first member of the Lower Stone Box Formation could be an advantageous reservoir. Hole–throat connectivity is poor because of the gas layer having underdeveloped primary pores, the blockage of pores by unstable minerals (kaolinite, etc.), and poorly connected pore throats based on insoluble mud cementation. The high content of quartz brittle minerals and the development of natural microcracks within the gas formation are favorable conditions for fracking development. The quartz grain size within the gas layer is positively correlated with the pore throat size, which suggests that the quartz grain size somewhat influences the microscopic characteristics of the reservoir space. This comprehensive study shows that the methodology of the study is more advantageous than traditional methods in the fine and three-dimensional spatial characterization of the microstructure of dense sandstone reservoirs. The research results of this paper have certain guiding significance for further reservoir evaluation and advantageous reservoir prediction in the Hangjinqi Prospect area in the Ordos Basin. We also provide the basis for the subsequent efficient development of the gas reservoir.

Study on the seepage characteristics and influencing factors of low permeability reservoir based on microscopic seepage experiments in real sandstones-taking Dongsheng gas field in Hangjinqi area as an example

Taking the dense sandstone gas reservoirs of Shibang Group and Shanxi Group in Dongsheng area of Ordos Basin as an example, based on the characterization of the dense sandstone reservoirs in the study area in terms of petrological features, pore structure and diagenesis, we carried out real sandstone microscopic seepage experiments to analyze the gas-water seepage law and fluid storage state of different types of reservoirs, and systematically evaluated the efficiency of gas-water repulsion from the dense sandstone reservoirs and the microscopic influencing factors. The results show that the study area has strong non-homogeneity and different degrees of pore density, so a variety of fluid transportation channels are formed, and different transportation channels represent different types of evacuation. When the residual pore space and dense sandstone microporous space exist at the same time, gas and water are mainly transported along the residual pore space, and the microporous space of the dense particles almost does not enter; gas and water transport is very much affected by permeability, and the transport resistance will increase with the decrease of permeability; the pressure has a certain effect on the efficiency of the replacement, but it can only improve the efficiency of the replacement to a certain extent; the fluids in the process of rock transport, there will be varying degrees of bubbles stuck off In the process of fluid transport in the rock, there will be different degrees of bubble jamming phenomenon, resulting in the transport needs to overcome a large capillary resistance, which greatly increases the replacement pressure; for the low-permeability sandstones in Hangjinqi area, the good homogeneity of the pore structure of the conductor does not mean that the transport effect is good, in the area of the conductor pore space is strongly developed, the gas-water transport will form an advantageous channel, and its transport effect is better.

A case study of petrophysical prediction using machine learning integrated with interval inversion in a tight sand reservoir in Egypt

This study presents a new algorithm for reservoir characterization using borehole logging data, which integrates unsupervised machine learning techniques and interval inversion to automatically determine layers’ boundaries and petrophysical parameters. The research aims to reduce the time and manual input required for borehole inversion to estimate petrophysical parameters. The algorithm was used to predict different layer boundaries of sand-shale intercalations for both synthetic and field wireline log data. Field well logging measurements were obtained from an oil and gas field in Egypt, specifically the Jurassic reservoir. The reservoir is composed of a dense sandstone layer with significant heterogeneity due to diagenesis, which converts kaolinite into illite. The algorithm was used to predict petrophysical parameters, resulting in a decrease in porosity and permeability. The field data from the well reveals that the reservoir is made up of varying-quality sandstone, impacting storage capacity and hydrocarbon saturation. The algorithm demonstrates consistent convergence of the data at 7.5%. Overall, the integration of the new cluster technique and interval inversion can improve the time-intensive and laborious process of borehole data inversion to estimate petrophysical parameters.

Characteristics and control factors of tectonic fractures of ultra-deep tight sandstone: Case study of the Lower Cretaceous reservoir in Bozi-Dabei area, Kuqa Depression, Tarim Basin, China

The Bozi-Dabei area in the Kuqa Depression host high-quality reservoirs in the Bashijiqike Formation and Baxigai Formation sandstones of the Lower Cretaceous, in which reservoirs yield significant industrial gas flow despite being situated at a considerable burial depth of 8200 m. The geological history of the target formation involves multiple phases of tectonic movements, resulting in the development of multi-genetic fractures that enhance the reservoir's storage and seepage capacity. Based on the results of the drilling core, field profile survey, imaging logging, and experimental analysis, this study presents an analysis of fractures in the Lower Cretaceous dense sandstone reservoir of the Bozi-Dabei area, andclarifies the characteristics and controlling factors of the multi-genesis and multi-period fractures. Additionally, it proposes an effective fracture development model that accounts for geo-stress control. In the Bozi-Dabei area, the prevailing high extrusion stress environment has led to the development of predominantly regional tectonic fractures and fault-related fractures, with relatively gentle deformation-related fractures. The results of a combination of multi-attribute data determination techniques, including fracture filling, inter-cutting relationship, fracture filling isotope, inclusions, and cathode luminescence tests, this study reveals that the reservoir fractures have experienced three major periods of tectonic movement. The regional tectonic fracture development is mainly controlled by stratigraphic lithology and thickness, while the proximity influences fault co-derived fractures to the fault and the relative positions of the upper and lower plates of the fault. The shift in the direction of the late horizontal maximum principal stress leads to the opening or closing of early fractures under different conditions in the Bozi-Dabei area, consequently affecting the degree of fracture opening and effectiveness. Notably, when the horizontal maximum principal stress is deflected to intersect with early fractures at a smaller angle or even superimpose, the fracture effectiveness of the related group system in the deflection direction improves, resulting in an overall coordination. The distribution characteristics of the fracture system in this highly productive reservoir are the result of dominant configurations from multi-phases of geological activities.

Experimental study on equilibrium initiation and extension of multiple clusters of fractures based on true triaxial physical simulation

In the context of tight sandstone reservoirs in the Ordos Basin characterized by compact and heterogeneous rock formations, conventional fracturing techniques yield monolithic fracture shapes, rendering 3D reservoir reconstruction unattainable. This study investigates the principles governing balanced initiation and propagation of fractures in multi-cluster fracturing within unconventional fracturing technology. Employing a large-scale true triaxial simulation experiment system, we utilize the dimensional analysis method (π theorem) to design a physical simulation experiment similarity criterion. Through various experimental adjustments involving proportioning, curing, and mechanical testing, we generate an artificially cured rock mass with mechanical parameters akin to the target layer. The rock mass is maintained at a size of 30 cm × 30 cm × 30 cm. Systematic physical simulation experiments on unconventional volume fracturing are carried out using the 30 cm-sized dense sandstone outcrop rock mass. Taking the conventional fracturing technology as a reference and manipulating experimental conditions and design parameters, we simulate the non-equilibrium initiation and extension behaviors of fracturing fractures under five unconventional volume fracturing technologies, namely hydraulic pulse pretreatment, temporary plugging between clusters, flow-limiting method, cyclic loading and unloading, and pulse intermittent fracturing. Through this, we elucidate the non-equilibrium initiation and extension laws governing multi-cluster fractures. Comparative analysis with conventional fracturing, known for inducing stress interference on fractures and inhibiting their expansion, revels that the five unconventional volume fracturing techniques mitigate stress interference in multi-cluster fracturing. This promotes uniform fracture initiation and expansion, facilitating the creation of complex fractures and larger reconstructed volumes. Among these techniques, inter-cluster block fracturing stands out for its exceptional ability to generate complex fracture networks. The research culminates in the development and refinement of a balanced fracture and extension control technique tailored for multiple cluster fractures in bulk fracturing. This technique significantly contributes to enhancing the degree of 3D reconstruction achievable in unconventional tight oil and gas reservoirs.

A new method for the characterization of microcracks based on seepage characteristics

Microcracks are the main seepage channels and reservoir space for oil and gas in dense sandstone reservoirs, and the degree of development dominates the reservoir’s high and stable production capacity. A new method has been devised to address the lack of quantitative identification and characterization methods for microcrack networks. The method is based on core stress sensitivity, permeability anisotropy, and two-phase seepage rule testing. By improving upon the traditional black oil model, this method can accurately calculate the impact that microcracks of varying degrees of development have on the capacity of tight oil reservoirs. The study shows that 1) the higher the degree of microcrack development, the stronger the reservoir stress sensitivity and the greater the permeability anisotropy. As the degree of microcrack development increases, the irreducible water saturation decreases, the residual oil saturation gradually increases, and the oil–water two-phase co-infiltration zone becomes more extensive and smaller. The degree of microcrack development in tight reservoirs can be characterized based on the seepage characteristic parameters; 2) a microcrack characterization method and classification criteria have been established. It is based on stress sensitivity coefficients, permeability anisotropy parameters, and phase seepage characteristics in cores with different microcrack development degrees. For the first time, the method enables a macroscopic-level description of microcrack seepage; 3) numerical calculations show that the degree of microcrack development significantly affects the reservoir’s oil production and water production. The higher the degree of microcrack development, the higher the reservoir’s initial oil production and cumulative oil production. However, when the degree of microcrack development is too high, the microcracks are connected, thus exhibiting the nature of large fractures. This strengthens the bypassing communication effect and causes the microscopic inhomogeneity to strengthen, the oil production decreases rapidly, and water production increases quickly at the later stage. This research result enriches the reservoir microcrack characterization and evaluation system, which has essential theoretical guidance and practical significance for the rational and effective development of tight oil and tight sandstone gas.

Numerical simulation on the re-injection capacity of drainage water in Area H of E gas field

The E gas field is a typical dense sandstone gas reservoir. It faces the problem of sewage treatment during production and development due to the influence of water formation. The H area with weak production capacity is selected for sewage re-injection and evaluating its re-injection capacity is a significant step before sewage treatment. In this paper, geological modeling and numerical simulation are carried out to evaluate the re-injection of the drainage water in Area H of the East E gas field, to maximize the amount of water injection within the acceptable range of the reservoir, and to analyze the leakage simulation of the two main possible leaky layers. The results show that: the formation rupture pressure in the study area is 42 MPa; the injection flow rate should be controlled at 60-80 m3/d, and the recommended injection wellhead pressure is 16-20 MPa; the leakage problem in He 7 sections should be considered in the subsequent wastewater re-injection.

Study on the development options of tight sandstone oil reservoirs and their influencing factors

The research area of tight sandstone oil reservoirs was selected, a numerical model of the oil reservoir was developed, and a study of the development options and influencing factors was carried out to analyze the influence of different development methods, physical and engineering parameters on the development dynamics. Study shows that the two main factors limiting the efficient development of tight sandstone reservoirs are reservoir properties and formation energy. Fractured horizontal well injection huff and puff development can effectively improve reservoir physical properties and timely replenish formation energy, which is suitable for the development of such oil reservoirs. In dense sandstone reservoirs, its impact on production capacity is also relatively small when the permeability ratio is small. Due to both gravity and reservoir physical properties, the permeability ratio increases, the cumulative oil production of positive rhythm reservoirs decreases and that of reverse rhythm reservoirs increases, and the location of high-quality reservoirs in the upper part of producing wells is conducive to increasing the final recovery rate. A lower oil to water viscosity ratio can significantly increase the swept volume and improve development effect. Hydrophilic reservoirs can reduce the injection pressure and increase the spread range, effectively improving the problem of inability to inject, and improving reservoir hydrophilicity through surface activators can increase reservoir recovery. The water injection rate determines the recovery rate of formation energy. Generally, the faster the rate, the higher the cumulative oil production. Therefore, the rate of water injection should be increased as much as possible, taking into account construction conditions and economic evaluation. Additionally, the effect of water injection on the development effect is different at different stages, so the appropriate timing of water injection is very important to the water injection huff and puff development effect, and the use of early water injection in this research area is not conducive. Soaking can promote pressure and fluid redistribution and improve water injection huff and puff development effect, but soaking for a long time can lead to reservoir contamination and reduce crude oil production, so the preferred time for a soaking is about 20 days.

Methodology for dissolution of sediment and calcareous deposits for paleontological specimen collection and identification

The Lance Creek Formation (Late Cretaceous) is significant in the study of late dinosaurs and is a diverse formation containing both terrestrial and aquatic macrofossils. To study this important ecosystem, all of the fossils present must be uncovered and examined from Lance Creek sedimentary rocks, which exhibit variable degrees of lithification. In order to liberate the fossils, a dissolution methodology was designed to determine which solution was most effective at uncovering specimens and dissolving/disaggregating sediment. Different solutions were tested including water, a 50% Calgon© solution, and a 5% acetic acid solution. The control was a sedimentary rock sample not subjected to any solutions prior to rinsing and sieving. A small-scale dissolution (10 g of loose sediment) was performed using each solution and examined for fossils. Acetic acid was deemed the most effective solution for the dissolution of dense sandstones, and indurated sediment from the Lance Creek Formation. Large-scale disaggregation (800 g of consolidated sedimentary rock) yielded abundant terrestrial, fluvial, and marine macrofossils. Macrofossil disaggregation using these methods has the potential to yield a more diverse assemblage of contemporaneous fossils than macrofossils alone, and can therefore provide substantial insight into ecological reconstructions.•A small-scale study was done to determine which solution was the most efficient at dissolution of sediment. Acetic acid was deemed the most effective.•A large-scale experiment was done on dense sandstones using 5% acetic acid and a shaking incubator.•A large-scale experiment of indurated sediment was performed using 5% acetic acid.

Optimization of Key Parameters of Tight Cut Fracturing Cracks for Horizontal Well Development of Tight Sandstone Gas Reservoirs

The permeability of dense sandstone gas deposit substation is very low, and it is often developed by horizontal well-tight cutting fracturing. The pressure crack network determines the production capacity of the gas well, so the optimization of the seam mesh parameters is the key problem in the efficient development of dense sandstone gas deposit. In order to solve the problem of multi-parameter comprehensive optimization of fracking horizontal wells, based on the principle of unstable seepage, a model for predicting the yield of fracking gas storage horizontal wells considering crack interference is established, and different crack conductivity, crack length, different crack patterns, crack spacing and number of crack clusters are designed in the model to simulate production, and the optimal fracking crack parameters are compared. Using numerical simulation method to analyze the main control factors of horizontal well fracturing effect, obtain the optimal parameters of fracking cracks, and provide ideas and reference for horizontal well fracturing construction in dense sandstone gas storage sites, which has certain theoretical guidance significance.

A new potentially large uranium district in Russia (Far East)

Research subject. The aim was to justify the prospects of uranium deposits in the Tyrminsk area of the Far East, which were briefly studied over 60 years ago. These deposits are highly similar to those located in the Streltsovsk mega uranium district. Materials and methods. The materials were geological data on uranium deposits in the promising Tyrminsk district and in the largest Streltsovsky district in the Far East. The research method was a comparison of the available information about the geological features of uranium deposits and ore areas as a whole. Results. The uranium ore regions under study are localized in Mesozoic volcanogenic calderas, within Paleozoic granites. Specific uranium deposits are formed at intersections of multidirectional faults, most frequently in the vicinity of volcanic caldera boundaries. The deposits formed within a contrasting geological section are represented by steep vein-like and stock-like bodies, as well as by gently sloping formation-like bodies under the screens of layers of dense sandstones and siltstones. In addition, deposits are found in favourable layers of conglomerates and effusives breccia. The length and thickness of ore bodies comprise 0.2–1 km and 1–80 m, respectively. Uranium ores belong to the fluorine-molybdenum-uranium type; near-ore rocks are represented by mudstones and hydrosludites. Some fields in the Tyrminsk district are opened by wells to a depth of 80– 160 m from the surface, while the fields in the Streltsovsk district are explored by wells and underground mine workings to a depth of 1.5 km from the surface. Conclusion. The extent of uranium deposits in the Tyrminsk district is predicted to reach a depth of 500–700 m, with their resources being estimated as “large” based on the high similarity of localities in the areas under study. As the most promising uranium area in the south Far East, the Tyrminsk district is recommended as a priority exploration site for uranium.

ПЕРСПЕКТИВЫ НЕФТЕГАЗОНОСНОСТИ И ИЗУЧЕНИЕ КОЛЛЕКТОРСКИХ СВОЙСТВ МЕЛОВЫХ ОТЛОЖЕНИЙ ЕВЛАХ-АГДЖАБЕДИНСКОГО ПРОГИБА

The aim of the study is to substantiate the prospects for the oil and gas content of the Upper Cretaceous effusive and carbonate deposits by studying their reservoir parameters. Previous studies have established that a sedimentary complex, present in the geological structure of the Muradkhanly field, is lithologically represented by clays, siltstones, sands and sandstones, dolomites, limestones, tuffs, Upper Cretaceous porphyrites. Since this lithofacies composition of the section is of great importance as a reservoir rock, volcanic sandy tuffs, mudstones and dense sandstones of the Upper Cretaceous age have been comprehensively investigated throughout the territory. We studied carbonates of this age and found that they have compaction of varying extent and are divided into 3 groups: weakly, moderately and strongly compacted and this, in turn, has considerable effect upon the rock porosity. At the beginning of the study, the reservoir features of Meso-Cenozoic sediments in the Yevlakh-Agdjabedi depression [YAD] were studied mainly on the basis of terrigenous rocks that refer to the Cenozoic. In our studies, Cretaceous deposits were studied, which are represented by effusive, carbonate rocks with secondary reservoir properties. The reservoir properties of chalk deposits in the YAD areas were investigated on the basis of studies of core samples in laboratories. It was found that the reservoir rocks of the area under investigation are volcanic, volcanic-sedimentary and carbonate, that is, they mainly consist of fractured limestones, marls and dolomites. Studies have shown that the oil and gas content of the depression is associated mainly with carbonate and effusive reservoirs. To assess the prospects for the oil-bearing capacity of the YAD, geological sections were studied in terms of the reservoir properties of a number of structures, and on the basis of the obtained core samples data. Trend maps were compiled using the "Surfer" software. Analysis of the maps allows identifying the corresponding zones of carbonate content, permeability, porosity, characterized by high, medium and low values. According to the carbonate readings, the studied territory does not have a strict distribution pattern and, according to the permeability distribution data, it is divided into two zones: the northern zone with average and the southern one with low values. There is, to a certain extent, pattern for variation of the values of carbonate content and permeability, and this can be explained by the secondary transformation of the reservoir properties of carbonate rocks, as a result of which permeability and porosity changed. Porosity distribution, to some extent, is aligned with permeability. Inverse relationship between the values of porosity and permeability can be explained with the filling of voids with cement material in the rock formation environment. Currently, in order to continue exploration and drilling works, comprehensive geological and geophysical studies are being carried out, as a result of which comparison of data obtained will make it possible to assess the prospects of each structure in more detail.

THE GROSS CHEMICAL COMPOSITION OF INITIAL SOILS OF VERKHOVYNA’S WATERSHED RIDGE OF THE UKRAINIAN CARPATHIANS

Problem Statement and Purpose. The intrasonal initial organogenic soils are formed with in the Verkhovyna’s watershed ridge of the Ukrainian Carpathians. They are dated to the access to the daily surface of dense sandstones of the Krosno zone. The aim of research is to establish the features of the gross chemical composition of the initial soils of the Verkhovyna’s watershed ridge of the Ukrainian Carpathians at differents tages of evolutionary development have been defined in this work. The investigate the impact of the major cenosis-forming species on the change of their gross chemical composition and morphological features has been investigated. Data & Methods. The analysis of references, source materials, the results of personal field studies based on morphological characteristics and consideration of succession of vegetation changes allowed to form an evolutionary series of initial soils within the area of research:embryonic soils-soil-like bodies-initial (primary) soils - primitive (young) soils. Within the study area, The morphological features of the initial soils were studied and samples were taken for laboratory-analytical studies. Results. The characteristic feature of gross chemical composition of initial soils at different stages of development is the accumulation of one and a half oxids of silica, Aluminum and Iron compounds, which is caused by the introduction of these elements from plant precipitation and atmospheric sediments. This is confirmed by them formation of the elemental composition of leaf lichens and mosses, where tlie accumulation of compounds of Aluminum and Fenun, as well as Calcium and Magnesium due to biological cycling is noted .The calculated eluvial-accumulative coefficients attested the total removal of oxides at all stages of evolution of the initial soils. Them formation of the gross chemical composition of the initial soils made it possible to diagnose file main EGP, which form the morphological features of the initial soils at different stages of development. Decarbonisation of soil-forming rocks is a prerequisite for the beginning of embryonic soil formation and formation of embryonic soil; fersialization - the process of accumulation of movable forms of iron is based on decarbonisation, which is inherent in the soil-like body; humus - socialization - transformation of mineral mass under the action of neutral and slightly acidic humus substances, which contributes to the partial removal of bases and the formation of sod-humus ( peaty ) horizon; peat formation, which is characteristic of all stages (except the embryonic one) and is determined mainly by the climatic conditions of thestudying area.

A laboratory experiment on salt weathering by humidity change: salt damage induced by deliquescence and hydration

A laboratory experiment on salt weathering was carried out under changing humidity conditions. Three types of rock (tuff and dense and porous sandstone) with sodium chloride, sodium sulfate, or magnesium sulfate were subjected to humidity oscillations from 20%RH to 98%RH during 6 h periods at 20 °C. Prior to the weathering experiment, the rock specimens were oven-dried, and the water supply was restricted to only that from the air during the experiment. Salt on the rock specimens was deliquesced/hydrated at almost 100%RH during the high-humidity period and crystallized/dehydrated during the low-humidity period. Sodium chloride, which has high deliquescence ability, caused the most intensive weathering. Porous sandstone with sodium chloride was completely broken down after 100 cycles of humidity changes. The other two types of rock with sodium chloride showed flaking or swelling on their surfaces. For dense sandstone with sodium chloride, the Equotip rebound value decreased as the humidity cycles increased. Sodium chloride has a high susceptibility of deliquescence at humidities of more than 80%RH. Weathering by sodium chloride would occur extensively on the surfaces of stone heritages and geoheritages in humid coastal spray zones. Magnesium sulfate induced a weight loss in porous sandstone, flaking from the surface of tuff, and cracks on the surface of dense sandstone. Sodium sulfate had almost no effect in the humidity-change experiment, although salt efflorescence was obvious. The results for magnesium sulfate, salt deliquescence, hydration, and crystallization in the humidity-change experiment were easily repeated. Magnesium sulfate might have more influence than sodium sulfate when air humidity fluctuates in a short period.

Стадії ґрунтотворення підвісних ґрунтів Верховинського вододільного хребта Українських Карпат

It was found out that suspended soils in Verkhovyna Dividing Range in Ukrainian Carpathians are intrazonal ones and are formed near dense sandstones outcrops in Krosnenska zone provided excess moisture of flushing type of water regime. Suspended soils are located within the mountain-forest and subalpine zones under moss lichen communities. They form habitats ranging from 0.1 to 1.0 square meter, oval and oblong shaped with the highest capacity of organic horizon in the central part with gradual reduction to the periphery. Suspended soils in Ukrainian Carpathians were mentioned for the first time in writings of Professor A. Zrazhevskyi. Formation of suspended soils in dense sandstones within Verkhovyna Dividing Range can occur in two ways: initial (primary) soil development and settlement of moss lichen communities from adjacent soil areas. Main stages of formation of soils under research are detected analyzing the succession of plant communities and morphological features of each section. Initial stage begins with the settlement of alga, bacteria, fungi, actinomyces, lichens (crustose and foliose) in centres of soil formation and formation of humified layer of dark gray colour up to 2 cm thick. Moss settlement on the developed organo-mineral layer and formation of organic (peat) horizon marks the beginning of development stage. Soils under research with formed organic horizon up to 10 cm thick are to be classified as initial suspended soils. The development stage is accompanied by accumulation of defunct organic remains (peat formation) and expansion of organic horizon (Td+T). Soils formed in Krosnenska zone in mild wind-blown sandstones with organic horizon more than 10 cm thick are at the stage of equilibrium functioning. It is advisable to define these soils as peat-suspended soils. Suspended soils are not represented in the nomenclature list of soils of Ukraine, that encourages conducting more detailed research on their classification. Patterns of distribution of soils under research and stages of soil formation were found out. Key words: Verkhovyna Diving range, suspended soils, the formation of peat, genesis, stages of soil formation.

Evaluation of geotechnical properties of Cretaceous sandstone, Western Desert, Egypt

The Western Desert, Egypt, mostly covered by clastic sedimentary rocks ranging in age from Lower Cretaceous to the Quaternary. Taref Formation of Nubian Group constitutes one of Cretaceous succession; it consists mainly of yellowish, pale red, pink, and white massive and cross-bedded sandstone in fining-upward cyclic manner. The petrographical parameters and mechanical properties of these clastic rocks must be integrated to better understand their geotechnical behavior. Mineralogically, it composes quartz, feldspars, and rock fragments, with an average value of 97.9, 1.2, and 0.9 %, respectively. Accordingly, Taref Sandstone can be classified as quartz arenite. The roundness of grains are dominated by sub-angular, sub-rounded, angular, rounded, very angular, and well rounded with an average value of 36, 25, 17, 9, 7, and 6 %. Its dry density (γd, g/cm3) varies from 1.65 to 1.87 g/cm3 that indicates Taref Sandstone classified as dense-very dense sandstone. Porosity (n%) ranges from 9.41 to 13.59 % that means that it ranges from medium to high porous sandstone. The dry uniaxial unconfined compressive strength (UCSdry) and point load strength index (IS50) values indicated that its compressive strength rages from moderately strength to very high strength and both of them are closely related. The porosity (n%) of Taref Sandstone has a significant correlation with mostly its physical and mechanical properties of the studied sandstone. Through matching correlation data among these parameters, it was clearly indicated that both porosity (n%) and dry density (γd) had been considered as the major parameters influencing other physical and mechanical properties of the studied Cretaceous sandstone samples.

Saturated Hydraulic Conductivities and High Yield Zones in the Phreatic Aquiferous Formations in Kumba – Cameroon: Determined From Slug-In Tests in Dug Wells

Kumba (latitudes: 4°36’-4°40’, longitudes: 9°23’- 9°29’), the economic capital of the Southwest Region- Cameroon, is located along the Cameroon Line at northwestern edge of the Douala Basin. This study aimed at determining the saturated hydraulic conductivities and high yield zones of the phreatic aquiferous formations in Kumba using slug-in tests in hand-dug wells, to guide the design and selection of sites for construction of wells capable of yielding pumping rates compatible with the users’ needs. A field geological mapping exercise was carried out in Kumba. There are over 4500 dug wells in Kumba. The wells are dug and completed according to the owner’s budget. Some have lids, other do not have collars, some have aprons, while others are inclined. Slugin tests were carried out at 11 sites using a 30 liters, 35 kg (45cm long 30cm diameter high pressure non deformable PVC round edged cylindrical water filled) slug. The quasisteady model of wellaquifer interaction for slug-in testing was adopted and spreadsheet interpretation by the Bouwer and Rice and Vivier methods gave minimum hydraulic conductivity values range from 2.88E-08m/d at Lawyer Enow to 1.60 E-06 m/d at New Quarters; and maximum values range from 1.81E-08 m/d at Lawyer Enow to 2.96E-06 m/d at New Quarters with an average of 2.41E-07 m/d. First estimates of dug well yields range from 2.36 m3 /d (at Akale Street) to 17.36 m3 /d (at New Quarters) with an average of 7.64 m3 /d with the relative high well yields zones at New Quarters, CCAS and Nkamlikum. The phreatic aquiferous formations in Kumba have averagely low saturated hydraulic conductivities with the lowest values at Lawyer Enow and the highest at New Quarters. The first estimations of well yields were lowest at Mile 1, Anglican, GS and Akale Street and highest at New Quarters, CCAS and Nkamlikum. These aquiferous formations are made up of dense clays, dense sandstones, dense limestones, dolomites, fractured gneisses, vesicular basalts, dense basalts and claystones layers with different permeabilities.