Sand Deposits Research Articles

Evidence that siltation aggravated by climate change can shift the dominance of two globally invasive freshwater macrophytes

Siltation has been aggravated by climate changes due more frequent and intense rain events, resulting in greater amounts of sediment in water bodies. These changes have impacted drastically submerged macrophytes growth by light limitations. Despite biological invasions are among the major threats to freshwater biodiversity and invasive submerged aquatic plants also has been impacted by these changes. The main aim of this study was to investigate through an experimental study as two globally invasive freshwater macrophytes, Hydrilla verticillata and Egeria densa, respond to the changes in water transparency caused by siltation. We performed a factorial experiment to test the effect of turbidity increase caused by siltation on growth of these two species. For this, we included sand or mud sediment in containers to obtain without and with siltation treatments. Then both species were planted at the two treatments and grown for 30 days. The main results of our study were that there was a shift in the dominance at the performance of some biological traits between the species, where H. verticillata showed better development of these biological traits than E. densa at treatment with siltation, and the reverse was also true, where E. densa had better performance in without siltation treatment. In summary, our results demonstrated that if the increase in water siltation continues at the current rate, a greater performance of H. verticillata can also be expected and, consequently, the impacts on aquatic biodiversity will also increased. These results may be helpful in predicting the effects of siltation on the development of two globally invasive freshwater submerged macrophytes. Moreover, could increase the ability of managers environmental to predict the future development of ecosystems in relation to invasions by non-native species.

Data-based models to investigate protective piles effects on the scour depth about oblong-shaped bridge pier

The primary objective of this study is to examine the suitability of employing a machine learning models (MLMs) comprising Support Vector Machine (SVM), Gene Expression Programming (GEP), and Artificial Neural Network (ANN) algorithms to emulate the influence of geometric and geotechnical parameters of the piles on the scour depth reduction about the oblong-shaped bridge pier. A dataset consisting of 90 laboratory observations was utilized, allocating 70 % of the data for the training and 30 % for the testing the MLMs. An oblong-shaped bridge pier of diameter D, was positioned and subjected to a rectangular flume featuring an erodible bed comprising sand sediment particles of D50 = 1.7 mm under clear water and subcritical flow conditions. The spacing between the piles, LD, the angle of pile orientation with respect to the flow, θ, and the Froude number, Fr, were identified as independent parameters through the dimensional analysis and Buckingham-Π theory. The MLMs’ performance were assessed employing root mean square error (RMSE), mean absolute error (MAE), coefficient of determination (R2), and developed discrepancy ratio (DDR). The outcomes, affirming the predictive capacity of all MLMs included, revealed that the GEP model employing a three-gene configuration exhibited superior accuracy compared to the other two MLMs. Specifically, the performance indicators (RMSE, MAE, R2, DDR) during the training and testing phases were (0.0433, 0.033, 0.981, 6.8) and (0.054, 0.045, 0.958, 4.81) respectively. The sensitivity analysis elucidated the hierarchy of influential variables as follows: Fr, LD and θ.

Microfossil and geochemical evidence for the Storegga tsunami at Budle Bay, Northumberland, UK

Evidence for the Storegga tsunami, which was generated by one of the world’s largest submarine slides, is well documented in Scotland, but the southerly extent of tsunami inundation in the UK is far more uncertain. Here, we combine new sedimentological, geochemical, microfossil, and ground-penetrating radar datasets to investigate the origins of two sand beds at Budle Bay, Northumberland. The lower of these two sand deposits is a fine- to medium-grained sand that fines upwards, is dominated by fragmented marine diatom taxa, and is characterised by elevated calcium concentrations. Two radiocarbon dated samples provide minimum age constraints on the timing of the deposition of the lower sand at around 8120–8380 cal yr BP. It is tentatively interpreted as being deposited by the Storegga tsunami. The upper sand bed is generally finer grained than the lower sand, and the calcium concentrations are considerably lower. One hypothesis is that the upper sand was deposited by the 1953 CE storm surge, but additional chronological control is required to test this interpretation. Our findings highlight the challenges associated with differentiating between storm and tsunami deposits and confirm the localised nature of preservation of Storegga tsunami deposits.

Assessing The Impact of Lithological and Geological Features on Electrical Resistivity Tomography (ERT) at Kelantan River Basin, Malaysia

The relationship between lithological and geological features, as assessed through Electrical Resistivity Tomography (ERT), is crucial for exploring subsurface characteristics. ERT is non-invasive and provides high-resolution images of subsurface electrical resistivity, closely linked to lithologyand geological formations. This study aims to accurately delineate lithology, geological formations, and aquifer presence, whether in alluvial layers or bedrock. ERT measurements, employing Pole-dipole and Gradient-XL protocols, were conducted at At-Taqwa Mosque in Gua Musang, Mini Zoo in Kuala Krai, Kampung Sedar, and Kuala Jambu in Tumpat, Kelantan. Results indicated regions with high clay content exhibited low electrical resistivity (<100Ωm), whereas areas with sand and gravel deposits showed high resistivity (>500Ωm). Faults and fractures within hard layers significantly influenced resistivity values, revealing intricate connections between survey lines. Algorithmic analysis integrated with topographical data enhanced the identification of mineral exploration potential, paving the way for real-time monitoring. The Kelantan River Basin was selected due to its environmental importance, facilitating insights into groundwater dynamics, economic significance, and sustainable development practices. This study underscores ERT's role in ground management strategies, mineral exploration, and advancing ground exploration technologies.

Identifying topographic changes at the beach using multiple years of permanent laser scanning

Sandy beach-dune systems make up a large part of coastal areas world wide. Their function as an eco-system as well as a protective barrier for human and natural habitat is under increased threat due to climate change. A thorough understanding of change processes at the sediment surface is essential to facilitate prediction of future development and management strategies to maintain their function. Especially slow and small scale processes happening over several days up to weeks at cm level, such as aeolian sand transport are difficult to identify and analyse. Permanent laser scanning (PLS) is a useful tool in the study and analysis of coastal processes as it captures a data representation of the evolution of the sediment surface over extended periods of time (up to several years) with high detail (at cm-dm level). The PLS data set considered for this study, consists of hourly acquired 3D point clouds representing the surface evolution of a section of the Dutch coast during three years. However, it is challenging to extract concrete information on specific change processes from the large and complex PLS data set. We use multiple hypothesis testing in order to reduce the PLS data set to a so-called inventory of trends, consisting of 12.8 million partial time series with associated rate of change and elevation. The inventory of trends proofs to be a suitable tool to identify natural processes such as storms and aeolian sand transport in our test area in the aeolian zone of a sandy beach-dune system on the Dutch coast. We identify these processes and provide a tool to derive summarising data from the complex PLS data set. We find that all partial time series identified as most likely representing aeolian sand transport, result in 1354 m3 of sand deposition in our study area over the course of three years. We also show a comparison with transects from JarKus data and find a correlation between anthropogenic activities and erosion in our test area with a correlation coefficient of 0.3.

Grain-size distribution characteristics of sediments in coastal shallow waters from Van Don to Tien Yen - Ha Coi, Northwest Gulf of Tonkin, Vietnam, according to End-member modelling analysis

The study involved the collection of eighteen surface sediment samples from the coastal shallow water area from Van Don to Tien Yen - Ha Coi in the Northwestern section of the Gulf of Tonkin to analyze their particle size composition. Utilizing the EMMAgeo end-member analysis model, four characteristic particle sizes (4EM) of 0.34, 7.7, 130, and 230 µm, corresponding to clay, fine silt, and fine sand of varying sizes were identified. In conjunction with the sedimentary environment, the spatial distribution analysis of these end members allowed a detailed determination of the formation conditions and distribution of the sediment components. Clay deposits (EM1) are primarily intercalated between the islands. At the same time, fine silt (EM2) is concentrated in the northern part of the study area, transported by flows, and deposited in a low-energy environment. Fine sand sediments (EM3 and EM4) are distributed along the coast of the Van Don peninsula in the Southern part of the study area and likely formed in association with tidal-wave processes under higher energy conditions compared to the North.

Laboratory study into engineering characteristics of siliciclastic sedimentary sand

Diverse applications and tremendous usefulness of siliciclastic sedimentary sands make investigation into their mechanics of behaviour very essential globally. This study examines the convergence or otherwise of the specimens in compression; physical, fabric, chemical and mineralogical characteristics and their relationships with compression behaviour; shape characteristics, possible particle breakage and their overall effect on the behaviour of siliciclastic sedimentary sands obtained from two locations. The findings are as follows; (a) Siliciclastic sedimentary sands are poorly graded and coarse in nature. (b) The fabrics are characterized by aggregation of sub rounded particles and smaller particles tend to combine with fines to form coatings around bigger particles. (c) Chemical compositions are predominantly silica and alumina and heamatite are significant. (d) Quartz dominates the mineralogy and the other minerals are muscovite, albite, orthoclase and chlorite. (e) The samples have convergent behaviour and the compressibility is not significantly different but lower than the related materials. (f) The original particle is sub round in shape and the particles become sub angular after the test with no relationship between particle shape and compression behaviour. (g) The particle breakage is linked to coarser nature of the specimens and the overall effect of particle breakage on the compression behaviour of siliciclastic sedimentary sand is small.

Spatial Distribution of Water Quality Classes of Rawa Pening Lake

Abstract Rawa Pening Lake is a source of water for irrigation and clean water for the people around the lake. The quality of water is the primary concern for sustainable functioning. This study aims to examine the water quality status of the lake under government regulations. The variables are temperature, total dissolved solid (TDS), total suspended solid (TSS), Escherichia coli (E. coli), dissolved oxygen (DO), biological oxygen demand (BOD), chemical oxygen demand, phosphate, nitrate, and oil. The study was conducted during the rainy season, from September to November 2020. It’s because of the season that farmers and the community use more of the lake water. The method used is purposive sampling, where a total of 12 locations represent each village, inlet, and outlet. The data analysis used is Storet to determine the water quality class and Inverse Distance Weighted (IDW) for the spatial distribution of water quality classes. The results showed that the water quality class of the lake suffered mild pollution. TSS and DO were variables that influenced that condition. It can be concluded that the lake has sucked sedimentation as a result of the deposits of mud and sand, which can damage the ecosystem of the lake.

Geochemical and Radiogenic Sr‐Nd Isotope Characterization of Widespread Sandy Surface Sediments in the Great Indian Desert, Thar: Implications for Provenance Studies

AbstractUnderstanding large desert formation/evolution contributing to regional‐to‐global dust cycles remains a challenge. This study presents the geochemical and Sr‐Nd isotope compositions of 51 surface sediment samples collected from the widespread hyper‐arid Thar Desert in northwestern India. The major objective is to determine sediment provenance for a better understanding of the formation/evolution mechanism of this Great Indian Desert as well as downwind dust contributions toward the Himalayas. The compositionally immature sandy Thar sediments (CIA ∼50 ± 4, WIP ∼49 ± 12, and EuN/Eu* ∼0.80 ± 0.13) are recycled materials derived from the Himalayan orogen and later modified by quartz addition and heavy mineral depletion/sorting processes. The 87Sr/86Sr (0.7259 ± 0.0012 and εNd (−12.5 ± 2.7) in the bulk of these Thar sediments are different from the earlier published compositions of the eolian sand deposits in northwestern India. The subcategories of Thar materials collected from different dune types exposed over different lithologies (Quaternary alluvium vs. Tertiary and Mesozoic sedimentary formations) are geochemically and isotopically indistinguishable, which indicates their cogenetic sources and/or sediment reworking. Thar sediments collected in this study have a predominant Indus origin along with significant contributions from the upwind Ghaggar‐Hakra paleochannels. The Indus sediments are most likely wind‐eroded from the shelf region exposed during the low sea stand of LGM and afterward deglaciation. Considering the new and published data sets, the Sr‐Nd isotope budget of dust deposited in the Himalayan frontal glaciers indicates that atmospheric mineral dust contribution from the upwind Indo‐Gangetic Plain proximal to the Himalayas is at par with dust parcels from distant natural deserts.

The genus Maracarus (Acari: Halacaridae), description of three new species and one new record from Türkiye

Three new and one previously known species belonging to the halacarid mite genus Maracarus Bartsch, 2016 are described on the basis of the specimens collected from fine and medium coarse sand sediment from Muğla and Antalya, Türkiye. The new species, Maracarus almiri n. sp., Maracarus pedroi n. sp., and Maracarus terueae n. sp., are found to belong to the gracilipes group. Additionally, previously known species Maracarus gracilipes (Trouessart 1888) is reported for the first time from Turkish coast.

Penanganan Rembesan dan Perkuatan Tanah Menggunakan Metode Insitu Test (Pressure Meter Test) Studi Kasus : Proyek Bendungan Margatiga

The bearing capacity of the soil is the support of the foundation, where the foundation transmits the loads derived from the weight of the building itself and the loads acting on the building to the surrounding soil. The purpose of this paper is to determine the handling of seepage and soil reinforcement needed in the case study of the Margatiga Dam Project, East Lampung. Based on the results of geological investigations, the Margatiga Dam is composed of a quarter-aged rock layer with a fragment composition of fine sand - gravel, with a soft - hard hardness level and the need for foundation repair. Based on the lithological conditions of the Margatiga Dam Extraction Gate foundation and the Spillway building which are composed of relatively deep and quite porous alluvial sand deposits, this causes the curtain grouting results to be ineffective, therefore it is necessary to change the seepage control design from the Grouting Curtain to the boundary wall. Based on the simulation check in Plaxis Software for Seepage and Excavation Staging, processing was carried out using Secant Pile and Soldier Pile with a depth of 30 meters with a stretch of 140 m and overlapping with Curtain Grouting of Embankment Dam on the left side and 5 m right side. Field PMT results showed that the maximum stress of the rock layer under the spillway foundation was 0.016 MPa and 0.630 MPa.

Channel evolution in the lower reach of palaeo Fen River: evidence from detrital apatite petrochronology and zircon geochronology

This study provides a comprehensive analysis combining multi-element (Sr, Y, Th, U and REE) geochemistry and U–Pb geochronology of single-grain apatite with zircon U–Pb ages from channel sand deposits of the palaeo Fen River, collected at the Chaizhuang and Weijiazhuang sites, corresponding to sediments from the Late Pleistocene and late Middle Pleistocene, respectively. The results unveil that the analysed apatites originated from a varied assemblage of source rocks, encompassing mafic–ultramafic rocks, intermediate to felsic I-type plutons, highly fractionated S-type granites and pegmatites, as well as assorted metamorphic rocks. U–Pb age dating of detrital zircons and apatites identifies three predominant age peaks at 2.4, 2.2 and 1.8 Ga, consistent with known tectonothermal episodes within the North China Craton (NCC). The similarity in U–Pb age spectra for both zircon and apatite, along with comparable apatite geochemical characteristics across both the Chaizhuang and Weijiazhuang sections, indicates stable provenance with little to no change from the late Middle Pleistocene to the Late Pleistocene. This continuity in provenance signatures suggests an absence of shift in drainage patterns or sediment sources, indicating that the current location and pattern of Fen River lower reach drainage was not formed at least by then. Consequently, it is inferred that the detrital material composing the palaeo Fen River sediments during this period predominantly originated from the NCC.

Absolute dating of sediments forming the Lena river terraces (Northeastern Siberia)

Sediments of the Lena River represent an important environmental archive for understanding the Quaternary history of North-Eastern Siberia. However, at present, the structure, origin and age of the Lena River terraces are poorly known. This article presents results of lithofacies analysis and absolute dating of the Ust’-Buotama section exposing the fourth (Bestyakh) terrace of the Lena River. We report the first quartz and K-feldspar luminescence ages, the reliability of which was argued by age relations and standard tests. Three stratigraphic units have been recognized in the section (depths from the top): lacustrine-alluvial deposits (85–120 m) of the Mavrinka Formation; aeolian sand deposits of the Dolkuma Formation (23–85 m), and Holocene aeolian dune sediments (0–23 m). The resulting chronology suggests that the sediments of the Mavrinka Formation were deposited no later than 300 ka (MIS 9 or later). Deposition of the Dolkuma Formation occurred from ∼30 ka to ∼15 ka (late MIS 3 - late MIS 2). Holocene aeolian dune formed during initial Neoglacial cooling post climatic optimum (c. 5.5 cal ka BP). More extensive Late Holocene dune sediments which formed ∼400 years ago are coeval with Little Ice Age (11th-19th centuries).

Grain Size Distribution and Provenance of Holocene Sand from the Sava River (Zagreb, Croatia)

This study involves an investigation into the grain size distribution and provenance of the sand deposited near Zagreb (Croatia) in the riverbed of the regionally important, almost 1000 km long Sava River, which connects several SE European countries. Recent research in the study area has mainly focused on the deposits forming the Zagreb alluvial aquifer system, rather on the Sava River sediment deposited in its riverbed, which is the focus of this study. The grain size distribution results obtained by dry sieving and laser granulometry showed a predominately fine and medium sand deposition at riverbanks and sand point bars. Medium sand increased downstream towards the east, within the artificially more channelized riverbed in the urban area. Fine sand prevailed 50 km further downstream in a more meandering low-relief area, near the city of Sisak and Lonjsko Polje Nature Park. Provenance analysis showed predominately carbonate sand in the western part of the city of Zagreb, originating from distant (Alpine) and local (Medvednica Mt. and Samobor Hills) sources. More siliciclastic sand was deposited in the Sava riverbed in the middle and eastern parts of Zagreb, originating mainly from the Medvednica Mt. The prevailing siliciclastic sand further downstream of the Sava River is probably sourced from the Kupa River tributary. Although various studies of the Zagreb alluvial aquifer system have been conducted so far, this study represents a novelty in its investigation into the grain size distribution of the Sava riverbed sand itself, setting the foundations for investigations in the future.

Estimating relative density from shallow depth CPTs in normally consolidated and overconsolidated siliceous sand

Current interpretation of relative density (<i>D<sub>r</sub></i>) based on CPT end resistance (<i>q<sub>c</sub></i>) data in sand relies on empirical expressions established from calibration chamber studies for which a deep failure penetration mechanism is attained. These expressions are mainly based on stress normalised <i>q<sub>c</sub></i> data. Previous studies have highlighted the importance of performing the normalisation procedure with respect to the mean effective stress (<i>p'</i>) in overconsolidated (OC) sand deposits instead of the vertical effective stress (<i>σ'<sub>v</sub></i>) that has been used in normally consolidated (NC) deposits. Due to a large variation in the coefficient of earth pressure at rest (<i>K<sub>0</sub></i>), on which <i>p'</i> depends, in the uppermost (3-5) m of OC sand, a recent study has demonstrated a rigorous unified approach for estimating a varying <i>K<sub>0</sub></i> with depth. However, the surficial shallow failure penetration effects are not accounted for, and consequently, interpretation of the upper (0.5-1.5) m of sand is still erroneous. This depth range is very important for low stress geotechnical applications such as offshore flowlines and mudmats. With a reinterpretation of previously published data, a new global model is presented that enables estimation of <i>D<sub>r</sub></i> from shallow CPTs in siliceous sand by taking into account both the shallow failure penetration effects (important in the uppermost 0.5-1.5 m) as well as the varying <i>K<sub>0</sub></i> with depth for OC sand (important in the uppermost 3-5 m).

Progress in Research on Microplastic Prevalence in Tropical Coastal Environments: A Case Study of the Johor and Singapore Straits

Microplastics are contaminants in marine ecosystems, posing great threats to biota and human health. In this work, we provide an overview of the progress made in understanding microplastic prevalence in tropical coastal environments, focusing on the Johor and the Singapore Straits as a case study. We examine the sources, distribution, transport, and ecological impact of microplastic pollution in this region through a systematic review. All papers relating to marine microplastics in Singapore’s sand and benthic sediments, seawater, and marine biota were used for analysis, from 2004 to 2023. In addition, we discuss the influence of envi-ronmental factors such as coastal morphology and anthropogenic activities on patterns of microplastic accumulation. We emphasize that microplastic pollution is more prevalent along the eutrophic Johor Strait compared to the Singapore Strait due to hydrological conditions. Rainfall is also a key factor that influences mi-croplastic abundance during the monsoon seasons. Furthermore, the bacterial and plankton assemblages of organisms on microplastic surfaces are diverse, with eutrophic waters enhancing the diversity of organisms on microplastic surfaces. Novel harmful cyanobacteria and bloom species of phytoplankton were also found on microplastic surfaces. By synthesizing existing research findings and highlighting regional characteristics, this paper contributes to ongoing efforts to mitigate microplastic pollution in tropical regions.

Study on the hydrate growth characteristics and rheology of silica-containing sand water-in-oil emulsion system

Understanding the transportability of silica-sand-containing hydrate slurries is crucial for production safety of non-consolidated natural gas hydrate reservoirs, especially when solid-state fluidization technology is utilized. Despite some research on silica sand and marine sediments’ influence on hydrate formation kinetics, rheological studies are scarce for systems with silica sands. The formation process of cyclopentane hydrates under the coexistence of hydrophilic silica particles and surfactants were observed. The effects of the concentration and particle size of silica sands as well as the water cut and surfactant concentration of emulsion on the rheological properties of hydrate slurries were investigated using a rheometer. The results indicated: (1) Hydrophilic sand aggregates were entrapped in water droplets, indirectly affecting the oil–water contact area due to the increase in water droplet volume, which was conducive to the combination of alkanes and water molecules to form a hydrate shell; silica particles provided nucleation sites at the oil–water interface to promote the adsorption and aggregation of cyclopentane molecules. (2) The synergistic effect of silica sand and surfactants significantly shortened the induction time of hydrates and increased the viscosity of the slurry. As the concentration of silica sand (1 wt%, 5 wt%, 10 wt%) increased, the induction time of hydrate formation decreased by 44.8 min. Within the concentration range below 5 wt%, the viscosity of the slurry increased as the concentration increased, with an amplitude of 13830.7 mPa·s. The induction time of hydrate formation decreased with increasing silica sand particle size (2 μm, 6.5 μm, 12 μm), but the size of silica sand particles had no significant effect on the viscosity of the slurry. (3) Hydrate slurries in all systems exhibited shear-thinning behavior. There was no obvious relationship between the yield stress of slurry under different silica sand concentrations. However, the yield stress of the slurry was inversely proportional to the size of silica sand particles. The yield stress decreased by 141.13 Pa when the size of silica sand particles increased from 2 μm to 12 μm. Overall, this study highlighted the influence of silica sand presence on flow safety assurance in solid-state fluidization technology.

Spatially and Temporally Variable Impacts of Hurricanes on Shallow Sediment Structure

AbstractSediment dynamics are fundamental to understanding coastal resiliency to climate change in the coming decades. Tropical cyclones can radically alter shallow sediment properties; however, the uncertain and destructive nature of tropical cyclones make understanding and predicting their impacts on sediments challenging. Here, grain size sampling in conjunction with continuous hydrodynamic data provided an unprecedented perspective of the impacts of two tropical cyclones, including Hurricane Sally (2020), in which the inner core of the storm passed directly over the field sites, on shallow coastal sediments in Alabama (USA). Sampling directly before and after Sally as well as out to ∼7 months after the second storm event, Hurricane Zeta, showed that the changes in sediments following storm events exhibited notable site‐to‐site variability. This variability during the first storm event was consistent with low sand supply and flow interactions driven by local bathymetry that led to sand transport and deposition at some previously‐muddy sites, near‐surface mud loss at some sandy sites, or little change at others. Post‐Sally impacts to grain size were well preserved 8 months after the storm, despite passage of Zeta as well as seasonal winds and riverine inputs during winter and spring. Overall, high temporal‐resolution sampling over a relatively large area (<500 km2) revealed relatively small‐scale spatial variability (on the order of 5–10 km) of hurricane impacts to sediment structure. These observations demonstrate a critical limitation for accurately predicting changes to coastal sediment dynamics in the face of a changing climate and its impact on tropical cyclones.

Leaching Efficiency of 238U and 232Th series from Granitic Soils

Granitic soil, a uranium (U) and thorium (Th)-bearing soil body, can be sourced to extract fissionable nuclides through leaching using acidic solutions. Limited research indicates the feasibility of extracting U and Th from granitic sources, necessitating further studies to optimize leaching efficiency and its potential as a fissionable fuel. This study investigates the leaching efficiency of the uranium 238U and thorium 232Th series, as well as 40K, in granitic soil samples. The study utilized a high-purity germanium detector (HPGe) to quantify the activity levels of the 238U and 232Th series and 40K in the studied samples. The black sand deposit and tin-tailing samples were also utilized to benchmark the finding of the leaching efficiency of the uranium 238U and thorium 232Th in granitic samples. The study found that the leaching samples contained low radioactivity levels that were a few to tenth times lower compared to the original samples, with tin-tailing samples exhibiting the highest leaching activity for 238U (630.05 Bq l-1) and 232Th (512.17 Bq l-1) and comparable to granitic soil samples 238U (437.7 Bq l-1) and 232Th (23.9 Bq l-1). Sulfuric acid showed the most efficient leaching reagent ~ up to 23% and 32% for 232Th and 238U, respectively. In comparison, nitric and hydrochloric acids exhibited low leaching efficiencies, ~ 1 – 13%. Overall, granitic soil shows comparable leaching rates to conventional sources of natural uranium nuclear fuel, making it a potential secondary and alternative nuclear fuel source.

Operation of downhole pumps under sanding conditions

One of the unfavourable factors of downhole pumping equipment operation at the fields at the final stage of development is high content of mechanical impurities in the pumped fluid. Similar problems are observed in fields with friable, weakly cemented formations, the fracture products of which flow downhole, resulting in lower extraction rates, equipment damage and higher operating costs. In oil production practice various technological measures and technical means are used to reduce the negative impact of sand penetration - regulation and optimisation of pumping equipment operation mode to ensure a rational rate of fluid withdrawal, application of technical devices in the form of sand filters and sand anchors and others. However, these measures and recommendations, for the most part, work successfully in the modes of continuous operation of wells. With the growing number of oil fields at the final stage of development, the issue of sanding becomes more and more urgent, as due to low flow rate wells at such fields are often switched to the mode of periodic operation, which favours the formation of sand plugs in tubing above the pump due to sufficient time for sedimentation of mechanical impurities. This can lead to pump jamming or rod breakage during subsequent well pump start-up. The experience of using sand filters (frame, slotted and others) in the arrangement of downhole pumps has shown that it does not always effectively solve the problem of sand penetration due to clogging of their cells with mechanical impurities and increased hydraulic resistance. This negatively affects the pumping equipment operation due to the shift of characteristics into the zone of suboptimal modes with associated problems for the electric drive. This makes it necessary to carry out underground well workover with removal of deep well pumping equipment for replacement or washing of the filter in surface conditions, as due to their peculiarities in the well pump layout (the filter is located at the intake of the pumping section), washing in well conditions is not always possible. These problems require not only the creation of effective downhole devices to prevent sand ingress to the pump intake or devices to prevent sand plugs above it, but also acceptable in practice calculation methods for predicting the sedimentation time of mechanical impurities in tubing or determining the minimum required speed of upward oil flow for stable sand removal. These calculation methods would also allow to reasonably regulate the time of technological interruptions while waiting for the wells to start up in periodic operation modes or to predict the time of activation of sand control devices for discharging the sand accumulated above the pump. This is the subject of this article. As a result of calculation analysis it was established that the main factors affecting the sedimentation process of mechanical impurities in the well are the speed and mode of fluid movement, its viscosity, density and size of the impurities themselves. Moreover, the most sensitive for the calculation accuracy is to take into account the change of fluid viscosity as it moves along the tubing as a result of heat exchange and the change of dissolved gas content due to pressure drop. Although at this stage the proposed methodology does not take into account some factors that can make additional adjustments to the process of sand sedimentation, however, it allows to predict with acceptable accuracy the time of technological interruptions in the well operation to prevent the formation of sand plugs, or the rational mode of operation of pumping equipment, providing the necessary speed of upward flow in the pipe for sand removal.