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The onset of brittle failure in rocks includes dilatancy and strain localization. To better understand this nucleation process, we analyze the evolution of the local three‐dimensional strain tensor using X‐ray tomograms acquired during triaxial compression experiments on granite and sandstone. The onset of the localization of the compaction, dilation, and shear strain occurs when ∼65% of the rock volume experiences dilation. Tracking the locations of the high strains throughout loading suggests that the deformation that occurs early in loading influences the location of the system‐sized fracture network that produces macroscopic failure. This influence is larger in the sandstone experiments than the granite experiments, likely due to the microstructure of the sandstone. These results have important implications for detecting precursors to catastrophic failure. Plain Language Summary: We investigate the fundamental processes that lead to brittle failure in rocks. We deform two common types of crustal rocks, granite and sandstone, under upper crustal stress conditions. As the stress applied to the rock increases, the rock tends to expand (dilate) more than compact, particularly as it approaches catastrophic, macroscopic failure. A larger portion of the rock undergoes dilation when the strain field starts to localize, indicating that accelerating dilation is a precursor to macroscopic failure. We observe different localization patterns in the rocks: in sandstone, strain localization progresses monotonically with increasing stress, whereas phases of delocalization can occur in the granite. Two competing models describe the development of the system‐sized fracture network that produces macroscopic failure: the network develops from (a) the coalescence of fractures that form early in loading, or from (b) the propagation of a process zone of interacting fractures through relatively intact rock. We find that the high strain events persist at the same location throughout the experiments more than expected by chance, particularly in experiments on sandstone. The results provide perhaps the most robust experimental confirmation yet that the fracture network that causes macroscopic failure evolves from the deformation that occurs earlier in loading. Key Points: X‐ray tomography quantifies the evolving spatial evolution of high strain events during brittle failureAt the onset of strain localization, on average 65% of the volume of the rock cores undergo dilationLocalized zones of high strain events persist in space from the onset of loading [ABSTRACT FROM AUTHOR]

Understanding the petrographic and geochemical characteristics of different tectonic settings is essential to improving traditional methods of identifying the provenance of palaeo-sedimentary environments. This research focuses on the K2b unit, which consists of mixed carbonate and volcanic lithic sandstones located in Iran with the age of the Turonian-Early Campanian period. Five sedimentary lithotypes with distinct petrographic and geochemical signatures were identified in the Turonian/Lower Campanian K2b unit, which consists of coarse-grained fan-delta strata. Carbonate and volcanic lithic fragments are the most characteristic components of mostly quartzo-lithic to felspatho-litho-quartzose sandstone layers, documenting a unidirectional paleocurrent pattern with the north-eastward direction. The original composition has undergone diagenesis, resulting in the precipitation of authigenic carbonates and depleting Rare Earth Elements (REE) except for Eu, which shows a positive anomaly. The K2b fan delta was situated on the margin of the proto-south Caspian back-arc basin, and the sediments were sourced from the undissected magmatic arc. The gravity flow deposits in the K2b unit were likely triggered by tectonic activity in the catchment area of the fan delta, leading to uplift and formation of relief associated with the regional Mosha Fault and, on a larger palaeogeographic scale, with subduction of the Arabian plate beneath the Iranian plate during Turonian-Early Campanian. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the possibility of predicting the yield curves of sandstones considering only a few key mechanical parameters, and more importantly microstructural properties. Porous rocks are modeled as a set of 2D circular grains subjected to radial and axial stresses that reflect the external forces applied on the material. The contact between individual grains define local planes. The sample is assumed to yield at the inception of nonlinear response on one of these planes, when local stresses reach either shear, tensile, or compressive limit values. A Mohr–Coulomb criterion is considered, with a tensile cutoff and a limitation on the maximum allowable shear stress. The parameters of the developed yield equations are then divided into two groups. The first category relates to the microstructure of the material: porosity, grain radius, intergranular contacts radius, and intensification factor. The second category contains a set of four mechanical properties: the cohesion, the friction angle, the maximum shear, and the compressive limit. While the first set differs from one sandstone to another, the second one is assumed to be the same for all sandstones showing similar mineral compositions. The experimental data for five sandstones, Berea, Boise, Darley Dale, Diemelstadt, and Rothbach, are gathered from the literature. The mechanical parameters are calculated based on Rothbach sandstone experimental data. Satisfactory predictions of the yield limits for the remaining sandstones are obtained from their microstructural characteristics. [ABSTRACT FROM AUTHOR]

Hydrogen (H 2) storage in porous reservoirs has been explored as a promising solution to support large-scale H 2 storage and maintain the energy supply and demand balance in future low-carbon economy. Despite its potential, the impact of different injection and withdrawal methods on H 2 distribution, trapping, and recovery efficiency in geological porous media has not been experimentally studied. This research utilized nuclear magnetic resonance (NMR) technique combined with core flooding experiments to explore how varying injection and withdrawal rates affect the H 2 /water two phase flow in sandstone. The results show that changes in fluid saturation primarily occurred in macropores with pore sizes corresponding to T 2 relaxation times ranging from 10 to 1000 ms. When H 2 was injected and extracted at low flow rates, nearly half of the pore volume was occupied by H 2 after drainage, while 19.2% of the H 2 remained trapped in the pores at the end of the imbibition. In contrast, at high flow rates, the initial H 2 saturation decreased to 26.6%, and residual trapping significantly decreased. The approach of low-rate injection and high-rate extraction was proven to achieve high pore space utilization and high H 2 recovery, making this scenario optimal for H 2 storage in porous geological structures. • NMR is used to monitor hydrogen/water two phase flow in sandstone. •Effect of injection and withdrawal rates on hydrogen distribution is investigated. •Hydrogen saturation changes primarily occur within macropores. •Low-rate injection combined with high-rate withdrawal is optimal for hydrogen storage. [ABSTRACT FROM AUTHOR]

IntroductionMethodsKey results and conclusionsLocated on the extreme edge of its range, Didymodon cordatus is exceptionally rare in Britain and is considered a priority for conservation. In the present study, its current population status and ecology were investigated.All previously known locations for the species were surveyed, plus other potential locations nearby. Abundance was measured in terms of ‘individual-equivalents’, defined as an occupied 1  m grid cell. Geographical coordinates of each individual-equivalent were recorded with a GPS unit. Habitat and community composition were recorded by relevés.Didymodon cordatus continues to survive at its only location in Britain, at Saunton Down, North Devon, including a length of nearby coastal cliff from where it has been known since 1916 and an adjacent roadside bank from where it has been known since 1962. No other locations were found. It occupies open, dry, calcareous and thermophilous habitat, together with a diverse assemblage of other acrocarpous mosses. While the species is particularly associated with loess soils in continental Europe, at Saunton Down it is closely associated with soft, calcareous sandstone and thin, overlying sandy soil. Natural erosion is an important part of the occupied habitat, maintaining early successional habitat patches suitable for colonisation. A total of 102 individual-equivalents were found, and it is estimated that the entire population at Saunton Down comprises 250–1000 individual-equivalents. The habitat is generally in favourable condition and the population appears to be secure, although the species will remain vulnerable to extinction in Britain because of its extreme rarity. [ABSTRACT FROM AUTHOR]

Tensile and shear failure are the main damage modes of rocks in geotechnical engineering. To investigate the energy evolution and failure characteristics of coarse-grained sandstone during pure mode I/II loading, loading-unloading tests were performed on cracked straight-through Brazilian discs (CSTBD) with different unloading levels (i), and its acoustic emission (AE) signals and microstructure were monitored. The results show that the AE signals of the CSTBD are negligible before the peak load (Mode I), or appear when the axial load exceeds a stress threshold and then increases significantly before the peak load (Mode II), and the Kaiser effect was observed in the second loading stage. The specimens’ input, elastic and dissipative energies varied quadratically with i. The elastic energy is always greater than the dissipative energy (Mode I), whereas the dissipative energy exceeds the elastic energy at i < 0.5 (Mode II). The crack propagation paths start from the crack tip and extend rapidly and straightly (Mode I) or slowly in the form of wing crack (Mode II) to the loading point. The microstructures of the specimens are mainly intergranular fracture (mode I) and transgranular fracture (mode II). The results provide references for studying energy evolution and failure mechanisms of rocks under mixed modes I+II/I+III loading. [ABSTRACT FROM AUTHOR]

This study addressed the need for a more comprehensive inventory of pit and quarry operations in Tetouan province and M’diq-Fnideq prefecture. It employed a Geographic Information System (GIS) approach, integrating various spatial remote sensing (RS) and field data to identify suitable areas for extracting alluvial, rocky, and clay materials. The used data includes quarry inventory, geological information, hydrographic networks, slope, and land use. The finding revealed 72 quarries and assessed their suitability for resource extraction. Alluvial deposits, approximately 127 million m³, were identified mainly in the primary wadis (river valley), including Oued Laou, Oued Amsa, Oued Mhajrate, and Oued Khemis. Massive rock deposits, consisting of limestone and sandstone, were estimated at 3.4 billion m³ . Clay deposits, suitable for various industrial applications, were also identified in significant quantities. In addition to confirming potential quarry deposits, our field surveys indicate that exploitation activities contribute to deforestation, and quarry waste often invades agricultural lands and forests. This information can facilitate sustainable resource management, environmental conservation, and informed policy and planning. The results highlighted the economic significance of geological resources in the study areas, contributing to various industries. Furthermore, by examining the relationship between quarries and the environment, including hydrographic networks, the study provides insights into eco-friendly quarrying practices. This methodology is expected to offer valuable insights into geological resources, guide sustainable resource management, and inform decision-making processes for regional development. [ABSTRACT FROM AUTHOR]

Since the Paleozoic, the tectonic evolution of northeastern Eurasia has been dominated by the Paleo-Asian Ocean and the Paleo-Pacific Ocean tectonic domains. However, the spatiotemporal framework and the timing of tectonic transition between these two oceanic domains remain enigmatic. To address this issue, we report petrological, geochronological, and geochemical data for eight sandstone samples deposited along the convergent margin between the Northeast China terranes and the North China craton in central Jilin Province, China. The results show that these sandstones are immature graywackes with a maximum depositional age of Early Triassic (248 ± 1 Ma), and their sediments were largely derived from coeval magmatic rocks in a juvenile continental arc. According to our new results and previous studies, we identified a sedimentary basin (most likely an intraarc or forearc basin) intimately associated with one or more continental arcs along the northeastern edge of the North China craton, and we suggest that the southwestward subduction of the Jilin-Heilongjiang Ocean in the early Mesozoic accounts for this continental arc setting. There is a distinct temporal gap between the closure of the Paleo-Asian Ocean (ca. 260 Ma) and the onset of Paleo-Pacific plate subduction (234-220 Ma), which is essentially coeval with the southwestward subduction of the Jilin-Heilongjiang Ocean between 256 Ma and 239 Ma, meaning the latter is a key link that marks the transition between these two tectonic domains. [ABSTRACT FROM AUTHOR]

Water plays a crucial role in underground engineering, significantly influencing the short-term and long-term strength and deformation behavior of rocks. Understanding the mechanics of rock deformation under water–rock coupling is vital for assessing the stability of underground structures. In this study, short-term strength compression and creep experiments were conducted on sandstone samples with varying water contents. Critical water contents (0%, 0.8%, 1.6%, 2.4%, and 3.3%) were determined through water absorption experiments, with corresponding tests performed under confining pressures of 0 MPa, 6 MPa, 9 MPa, and 12 MPa. Results revealed an exponential decrease in uniaxial compressive strength and elastic modulus with increasing water content, while confining pressure influenced radial deformation, leading to a linear increase in compressive strength. Water content also significantly impacted micro-cohesion and internal friction angle, with cohesion being more sensitive to water. The creep experiment demonstrated a deformation trend similar to compressive strength, with analysis revealing three stages of creep deformation: viscoelastic, plastic, and nonlinear acceleration. Critical strengths entering different stages were identified, with their ratio to compressive strength stabilizing between 0.44–0.59 and 0.59–0.74. A strain parameter εac, related to steady-state and accelerated creep failure time, showed little correlation with water content but exhibited a linear relationship with confining pressure. Short-term and long-term failure modes of sandstone were analyzed, indicating a transition from "X-shaped" conjugate shear failure to single oblique shear failure with changing confining pressure and water content. Mitigation measures, such as groundwater isolation and the application of high confining pressure, were identified as effective means to mitigate long-term rock deformation's adverse effects on structural integrity in onsite engineering projects, ensuring structural stability throughout construction. The study's findings and data are crucial for informing the long-term stability of engineering structures. Highlights: Water content significantly affects the short-term and long-term strength and deformation behavior of rocks. The creep behavior of rocks is influenced by water content, confining pressure, and shear stress. The water content and confining pressure affect the formation and evolution of cracks in rocks during creep. Different failure modes are observed in rocks, depending on water content and confining pressure. [ABSTRACT FROM AUTHOR]

Siliceous sandstone (including quartzites), petrified wood, and agates located in Alabama and Mississippi were utilized as a toolstone resource during every recognized cultural period in the Lower Mississippi Valley region of the Southeastern United States. Regrettably, these materials have not been the focus of many provenance‐related investigations. Recent analyses of quartzite and sandstone from other regions in North America and from the Pyrenees were successful in discriminating sources using petrographic techniques. The current study examines the application of visible/near‐infrared reflectance and Fourier transform infrared reflectance (FTIR) spectroscopy on sourcing siliceous materials besides chert, particularly sandstones, orthoquartzites (quartz sandstone), petrified woods, and agates. This source characterization investigation focuses on a case study involving materials gathered from eight distinct collection sites, encompassing nine different siliceous resources collected in Alabama and Mississippi. These materials were sourced from two distinct geological formations: the Hattiesburg and Tallahatta. Results demonstrate the ability of non‐destructive reflectance spectroscopy and introduces a new outlier modeling method that detects, clusters, and separately models outliers with their own set of basis vectors. Principal component analyses, least absolute shrinkage and selection operator regression, linear discriminant function analysis (LDA), and random forest classification are used in this paper to better identify outlier elements as well as discriminate for stone materials accurately (between 67% and 100%). Although this is the first reflectance spectroscopy investigation used to characterize these materials for provenance applications, the preliminary results compare favorably with other provenance techniques whose aim is to quantify between‐formation (inter) and within‐formation (intra) outcrop variation. The quantified and differentiated sources, based on the hyperspectral signatures of the material, will provide a better understanding of prehistoric reliance on these lithic resources and produces a proxy to determine mobility, social interaction, and other past behavior. [ABSTRACT FROM AUTHOR]

Relationships between drilling parameters and the uniaxial compressive strength (UCS) of rocks are typically established through measurement while drilling (MWD) by analyzing either drilling speed or specific energy. This study enhances the commonly utilized specific energy formula by considering the frictional dissipation energy of the drill bit, along with the initial thrust and torque exerted by the drilling machines. A novel specific energy index, ηp, optimized for rotary drilling applications, was introduced. The modified expressions significantly mitigate the impact of variations in drilling parameters on the specific energy. Employing the concept of a minimum specific energy coefficient, a model was developed that directly relates drilling parameters to the UCS of rocks. An iterative solution method for determining the minimum specific energy coefficient was provided. Extensive MWD tests on intact granite samples, conducted on a specially developed indoor drilling test platform, facilitated the calibration of the minimum specific energy coefficient. The model's efficacy in UCS estimation was further validated through additional MWD tests on sandstone and limestone. For sandstone, the model's estimated UCS showed a relative error (RE) ranging from 0.62% to 21.22%, a mean relative error of 11.7%, and a maximum absolute error of 9.75 MPa. Limestone tests revealed an RE range of 1.99%–12.86%, with absolute errors between 2.53 and 16.4 MPa. The UCSs of sandstone and limestone were estimated to lie between 39.65 and 55.71 MPa and 113.29 and 143.90 MPa, respectively, demonstrating close alignment with the results of uniaxial compressive strength tests and confirming the model's accuracy and reliability for UCS prediction using MWD data. [ABSTRACT FROM AUTHOR]

With the development of large-scale tunnel construction and green energy mining toward the depths of the Earth, the study of the mechanical properties and the deformation, and fracture characteristics of the surrounding rock mass under high confining pressures and high temperatures has become an urgent requirement. Therefore, we compare and study the effects of different high temperatures and confining pressures on the mechanical behavior and fracture characteristics of rock samples under loading and unloading conditions. In this paper, uniaxial and triaxial compression tests of sandstone at high temperature, and the stress–strain curves of red sandstone under different temperatures and confining pressures, are obtained. On this basis, the characteristics of energy conversion in the process of rock deformation and failure are studied. The research results indicate that the high-temperature effect weakens the brittle characteristics and enhances the plasticity of red sandstone, and there is a certain lag in the time of rock failure relative to the stress reaching peak strength. The high confining pressure weakens the brittleness and enhances the plastic properties of red sandstone, enhancing the overall resistance of the rock to deformation and enhancing its ability to store elastic deformation energy. According to the law of energy evolution, a new strength criterion is established to describe the three-dimensional spatial critical state surface of macrofailure caused by rock fracture coalescence. The study of the mechanical properties and failure criteria of rocks under high temperatures and pressures from the perspective of energy not only has important value for deep resource extraction but also has important theoretical significance for deep underground engineering construction. [ABSTRACT FROM AUTHOR]

Due to excavation disturbances and the coupled hydro-mechanical effects, deep rock masses experience nonlinear large deformations in the surrounding rock, necessitating an urgent exploration of the rock damage and failure mechanisms from the perspectives of hydro-mechanical coupling and mechanical properties. Therefore, this study conducted uniaxial cyclic loading-unloading tests on sandstone samples with different water contents (0%, 0.26%, 0.52%, 0.78%, and 1.04%) to investigate the microstructural evolution, energy evolution laws, and failure characteristics under varying water contents and cyclic loading conditions. The main conclusions are as follows:(1) Concerning micro-pore structures, as the water content increases, the porosity and maximum pore size of the sandstone first decrease and then increase. At 0% water content, the porosity is 4.82% and the maximum pore size is 31.94 µm. At 0.26% water content, both porosity and maximum pore size decrease to 3.03% and 16.15 µm, respectively. When the water content reaches 1.04%, the porosity and maximum pore size increase to 14.34% and 45.99 µm, respectively. (2) Regarding energy evolution laws, the energy evolution of the specimens during cyclic loading-unloading mainly converts to elastic energy, showing a step-wise increase in energy. Further analysis reveals that the water content has a significant impact on the dissipation energy coefficient of the sandstone. At lower stress levels (<0.4σmax), the water content has a negligible effect, while at higher stress levels (>0.85σmax), an increase in water content leads to increased fluctuations in the dissipation energy coefficient. (3) In terms of failure characteristics, with increasing water content, the failure mode of the specimens shifts from primary crack failure to microcrack failure, corresponding to the energy evolution during cyclic loading-unloading processes. [ABSTRACT FROM AUTHOR]

The pore space characteristics of geological materials are closely related to their mechanical, transport and hydraulic properties. In geomorphology, pore size distribution (PSD) is an important characteristic in rock weathering, evaporation and other studies. In an effort to find novel methods to determine the PSD, perhaps to bypass the disadvantages of the current techniques, there has been a growing interest in the use of non‐Newtonian fluids. In this contribution, we are particularly interested in the method recently introduced by Abou Najm and Atallah (the ANA method), which exploits the way in which the flow of different shear‐thinning fluids distributes differently in the pore space to compute the functional PSD estimation. We performed a set of saturated flow experiments with aqueous xanthan gum solutions of different concentrations, using as simple as possible laboratory settings, and we implemented a modified version of the previously introduced numerical model to obtain the PSDs of four sandstone and one tuff samples. The results are compared with conventional mercury intrusion porosimetry, showing a good agreement regarding the dominant pore size and a notable similarity in the distributions. Several limitations were identified as well, such as the lack of information on relatively small pores (<5–10 μm for the samples studied) and the potential issues in obtaining a more detailed distribution. We conclude that the ANA method is promising for geomorphological evaporation and rock durability studies, particularly for coarser materials such as sandstone, but it also encounters challenges for certain applications, especially for fine‐grained rocks. It must be acknowledged that the ANA method has been tested on a limited range of materials and further investigation is required to fully explore its capabilities and limitations. [ABSTRACT FROM AUTHOR]

The causes of the size effect (SE) and loading rate effect (LR) for rocks remain unclear. Based on this, a gypsum-mixed material was used to simulate sandstone, where the dosing ratio was 7.5% river sand, 17.5% quartz, 58.3% α -high-strength gypsum, and 16.7% water. The specimens were designed to have a height-to-diameter ratio (HDR) of 0.6~2, and three strain rates (SRs)—static, quasi-dynamic, and dynamic—were used to perform single-factor rotational uniaxial compression experiments. PFC2D was used to numerically simulate the damage pattern of a sandstone-like specimen. The results showed that the physical parameters did not change monotonically, as was previously found. The main reason for this is that the end-face friction effect (EFE) is generated when the dynamic SR or the HDR is 0.6~1, with a damage pattern of "X". Under mechanical analysis, the power consumed by the EFE was inversely proportional to the HDR and directly proportional to the LR, and it can reduce the actual amount of energy transferred inside the specimen. This paper may provide a foundation for the study of non-linear hazards in coal and rock. [ABSTRACT FROM AUTHOR]

ABSTRACT In the complex geological environment of deep mining area, water‐bearing soft rock is more prone to damage and destruction by low‐frequency disturbance. In this paper, the dynamic–static combination test was conducted on the basis of uniaxial compression test by using creep dynamic disturbance impact loading system and acoustic emission technique. The test results show that with the increase of the initial value of disturbance loading, the fracture morphology of sandstone gradually changes from a single major crack to multiple cracks coexisting, and some saturated sandstones lose the bearing capacity in the process of disturbance, presenting a cone‐shaped fracture surface. The increase of the initial value of the disturbance changes the bearing capacity of the sandstone, and the peak energy of acoustic emission reaches the maximum value when the initial value of the disturbance is 80% UCS. The results of the study can provide some reference for the stability analysis of deep water‐rich soft rock mines. [ABSTRACT FROM AUTHOR]

Tritaxis kurnoolensis, a small tree of the Euphorbiaceae family, is endemic to a valley within the Sullavai Sandstone plateau in close proximity to the Paleru Reservoir (Owk dam). The species is a narrow endemic. No documented sightings of this species have been recorded beyond the type locality since its description in 1994 by Venkataraju & Pullaiah as Dimorphocalyx kurnoolensis from the Nandyal District of Andhra Pradesh. In this study, the authors applied the grid method for quantification and subjected the species to a meticulous analysis aligning with IUCN Red List Criteria. The distribution was found to be restricted due to habitat (valley) fragmentation, reservoir which is arresting seed dispersal, and destruction caused by tunnel construction civil works. The area of occupancy (AOO) at 16 km² and the extent of occurrence (EOO) at 0.474 km², were systematically computed using GeoCAT. The species is assessed here using the Red List methodology for evaluating extinction risk. Based on its AOO, EOO, and population size, it has been classified as Critically Endangered. [ABSTRACT FROM AUTHOR]

In view of the characteristics of low permeability, strong heterogeneity, small effective sand scale and poor connectivity of tight gas reservoir, well pattern infilling optimization is the main method to improve gas recovery. Taking Sulige gas field as an example, based on the study of sedimentary facies, effective sand-body distribution, combined with production performance and engineering parameters, the well control drainage was obtained. Meanwhile, the interwell connectivity and interference probability was qualitatively analyzed by interference well test, and the critical well spacing density was determined. In order to quantitatively reveal the gas grabbing degree at different well spacing density and determine whether the final cumulative gas production of gas wells with interference is economical and feasible, the evaluation index of "gas well production interference ratio (GWPIR)" was defined specifically, and the intersection plot of GWPIR relating to gas reserve abundance and well spacing density was draw. Different from the traditional method of well number interference probability, through the combination of GWPIR plot and economic evaluation, well pattern optimization from both two perspectives of pursuing higher economic benefits and recovery degree can be realized, providing technical support for improving gas recovery and long-term stable production of gas field. [ABSTRACT FROM AUTHOR]

This document introduces a novel equivalent algorithm for forecasting gas content within deep coal seams, which is subject to constraints stemming from the advancements and precision achieved in well and roadway engineering endeavors. This algorithm meticulously acknowledges that coal seam gas content comprises three fundamental components: the inherent gas emission rate of the equivalent stratum, the residual gas content retained within the coal seam itself, and the influence imparted by the gas content within the coal seam. Furthermore, the approach thoroughly considers variations in the level of porosity development within the coal seam and its surrounding rock formations, as well as the occurrence of gas within these structures. The equivalent layer is classified into two distinct groups: the sandstone zone and the clay zone. The sandstone zone utilizes pertinent parameters pertaining to fine sandstone, whereas the clay zone distinguishes between clay rock and thick mudstone. The influencing factor considerations solely encompass natural elements, such as the coal seam's occurrence and geological structure. The residual gas content employs either existing measured parameters or acknowledged experimental parameters specific to the coal seam. Based on this predictive approach, an intelligent auxiliary software (V1.0) for mine gas forecasting was devised. The software calculates the gas content of deep coal seams within the mine at intervals of 100 m × 100 m, subsequently fitting the contour lines of gas content across the entire area. The gas content predictions derived from this equivalent algorithm demonstrate robust adaptability to variations in gas content caused by construction activities, and the prediction results exhibit an acceptable level of error on-site. Notably, the prediction process is not constrained by the progress of tunnel engineering, ensuring that the prediction outcomes can accurately represent the distribution characteristics of deep coal seam gas content. After a year of application, the prediction results have consistently met on-site requirements, providing a scientific foundation for the implementation of effective gas prevention and control measures in the mining area. Furthermore, this approach can effectively guide the formulation of medium- and long-term gas prevention and control plans for mines. [ABSTRACT FROM AUTHOR]

The purpose of this study is to locate groundwater-saturated aquifers in the Vindhyan fringe belt in the Mirzapur district of Uttar Pradesh, India, and evaluate their protection using geoelectrical indices. The Schlumberger electrode layout, with a maximum half-current distance between electrodes of 300 m, was used to perform three gradient profilings and six geoelectrical soundings. The inversion IPI2win program and the traditional partial curve matching approach were used for geoelectrical sounding data interpretation. Four to five geologic units are identified in the research region based on the interpretation of the geoelectrical sounding data. These are the top-surface soil, clay, kankar/laterite and sand, weathered sandstone, and compact sandstone. The research region is characterized by HA-type sounding curves, and the obtained findings suggest the presence of groundwater-saturated zones and cracks in the area. The weathered sandstone saturated with water shows resistivity ranges between 375.4 and 407.1 Ω-m and depth ranges from 96.8 to 97.6 m. Thematic maps were prepared for total longitudinal conductance, transverse resistance, overburden thickness, and electrical anisotropy. The protective capacity of the aquifer is measured using the transverse resistance (Tr) and longitudinal conductance (Lc) of the Dar Zarrouk parameters. Based on the longitudinal conductance of the aquifers, the results obtained indicate that the research region is dominated by a good aquifer protective capacity rating. [ABSTRACT FROM AUTHOR]

With the continuous development of underground engineering construction in China, it is particularly important to study the identification of structural plane characteristics of rock masses. In this study, three types of pseudo-rock specimens with structural plane interlayers were fabricated to analyze the patterns of drilling parameter changes in rock bodies with structural planes during the drilling process and to explore the characterization and identification methods of rock body structural planes. Gneiss, granite, and sandstone were used as rock materials, with gypsum mortar as the interlayer material for the structural planes in these three types of specimens. The indoor digital drilling equipment was utilized for conducting indoor digital drilling experiments. The variation patterns of drilling parameters in rock bodies with structural surfaces under different interlayer inclinations and thicknesses were analyzed. The relationship between the ratio of the change in rotational speed and drilling speed during the stable phase of the upper rock mass and the peak torque and peak drilling pressure has been established. The relationship between the structural plane inclination angle and the ratio of change in rotational speed and drilling speed has been determined. By utilizing the variation in these ratios, the impacts of the structural plane inclination angle and the thickness of the structural plane on the peak torque and peak drilling pressure have been elucidated. The research results provide a theoretical basis for the stability evaluation of rock masses with structural planes under drilling action. [ABSTRACT FROM AUTHOR]

The location of the investigation area is in Oben Village, Nekamese District, Kupang Regency, East Nusa Tenggara Province with coordinates 123° 40'40” E - 123° 41'20” E and 10° 16'0” S - 10° 16'40” S. The geology of the study area is generally occupied by mixed rocks dominated by a gray clay, blackish brown, reddish brown, with foreign chunks consisting of peridotite, sedimentary rock consisting of brown and reddish reddish limestone, silt, micaceous sandstones, metamorphic rock: chlorite schist, with quartzite veins. Of the five samples analyzed, namely four samples of soil matrix and one sample of Peridotite, the following results were obtained: six rare earth elements were contained in 4 samples of the soil matrix, namely Yttrium (Y): 3.63 – 68.75 ppm, Praseudymium (Pr): 7.38 – 38.38 ppm, Scandium (Sc): 4.83 – 4.93 ppm, Lanthanum (La): 21.48 – 91.03 ppm, Cerium (Ce): 32.48 – 184.85 ppm, and Neodymium (Nd): 9.4 – 57 ppm specifically for sample 1 also contains 3 rare earth elements, namely: Gadolinium (Gd): 3.48 ppm concentration the average is lower than its abundance in nature, Samarium Sm: 13.1 ppm, and Dysprosium: (Dy): 6.88 ppm. For rock samples only contain Praseudymium (Pr): 7.78 ppm and Cerium (Ce): 87.88 ppm. [ABSTRACT FROM AUTHOR]

The resistivity difference between oil and gas layers and the water layers in low contrast tight sandstone reservoirs is subtle. Fluid identification and saturation calculation based on conventional logging methods are facing challenges in such reservoirs. In this paper, a new method is proposed for fluid identification and saturation calculation in low contrast tight sandstone reservoirs. First, a model for calculating apparent formation water resistivity is constructed, which takes into account the influence of shale on the resistivity calculation and avoids apparent formation water resistivity abnormal values. Based on the distribution of the apparent formation water resistivity obtained by the new model, the water spectrum is determined for fluid identification in low contrast tight sandstone reservoirs. Following this, according to the average, standard deviation, and endpoints of the water spectrum, a new four-parameter model for calculating reservoir oil and gas saturation is built. The methods proposed in this paper are applied to the low contrast tight sandstone reservoirs in the Q4 formation of the X53 block and X70 block in the south of Songliao Basin, China. The results show that the water spectrum method can effectively distinguish oil-water layers and water layers in the study area. The standard deviation of the water spectrum in the oil-water layer is generally greater than that in the water layer. The new fourparameter model yields more accurate oil and gas saturation. These findings verify the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

Fissure fillings are critical to the hydro-mechanical properties of jointed rock masses in rock engineering. In this study, triaxial seepage tests were performed on standard cylindrical fissure-filled sandstone. The characteristics of stress–strain relationships, absorption and consumption of energy, variations in deformation resistance, and permeability evolution during the experimental process, along with the crack development observed in post-failure computed tomography scan images of the sandstone specimens were analyzed. The results demonstrate that the fillings improve the energy capacity and reduce the damage accumulation of sandstone specimens, with sand-filled specimens performing better than mud-filled specimens, especially at lower bridge angles. The fillings can reduce the depth of crack extension and lessen the influence of prefabricated fissures on sandstone failure, with this effect diminishing as the rock bridge angle increases. Permeability decreases in the pre-peak failure stage as the fillings improve the deformation resistance of the sandstone specimens. In the post-peak failure stage, the fillings and rock debris generated by the sandstone failure move within the developed fractures, causing significant fluctuations in permeability. These findings deepen the understanding of the hydro-mechanical properties of jointed rocks and provide a scientific basis for stability analysis in rock engineering. [ABSTRACT FROM AUTHOR]

The Carboniferous strata in the northeastern Junggar Basin are an important exploration field for natural gas in the basin. However, volcanic rocks have long been the primary exploration target. In contrast, the exploration and research of clastic rocks associated with source formations have been largely overlooked, resulting in an insufficient understanding of the reservoir forming conditions and exploration potential of Carboniferous clastic rocks. Through the evaluation of Carboniferous source rocks, effective source stove characterization, clastic reservoir evaluation, oil and gas source correlation, and reservoir formation model construction in this region, three key findings have been made. First, the Carboniferous in the northeastern Junggar Basin has developed three sets of high-quality gas source rocks: the Dishuiquan Formation, the Songkalsu B Member, and the Shiqiantan Formation. These formations correspond to three hydrocarbon source centers: the Sannan--Dishuiquan Sag, the Wucaiwan Sag--Dajing area, and the Dongdao Haizi Sag--Baijiahai High. Second, the Carboniferous system in the northeast has developed multiple types of large-scale reservoirs, including sand conglomerates, sandstones, turbidites, dolomitic rocks, and shale. These reservoirs are generally characterized by low porosity to ultra-low porosity and low permeability to ultra-low permeability reservoirs. There is a dissolution pore development zone at depths of 2900-4500 m. Third, a comparison of oil and gas sources reveals that all three sets of gas source rocks contribute to the natural gas found in the northeast, with obvious characteristics of near-source reservoir formation. The Carboniferous clastic rocks host two types of natural gas reservoirs: unconventional and conventional near-source reservoirs. It is predicted that there is an orderly accumulation pattern of shale gas, tight sandstone gas, and conventional natural gas reservoirs. This study reveals that the Carboniferous clastic rock source and reservoir configuration in the northeastern Junggar Basin is highly favorable, and the natural gas reservoirs in source and near-source clastic rocks represent important exploration directions. [ABSTRACT FROM AUTHOR]

This paper studies the influence of the staged particle sieving-out method on the seepage characteristics in loose sandstone heap leaching. The staged sieving out of ore sample particles was conducted according to particle size, and ground pressure was applied to them. Subsequently, parameters such as the permeability, particle distribution, and pore distribution characteristics of the rock samples were obtained to investigate the influence of the staged particle sieving-out method on the seepage effect of loose sandstone heap leaching. The results indicate that sieving out particles smaller than 0.15 mm can significantly reduce the probability of hole blockage and increase the overall pore size, greatly enhancing permeability. Sieving out particles with sizes between 0.15 mm and 1.2 mm can result in the loss of skeleton particles, reducing the amount of flow channels and thereby decreasing permeability. Sieving out particles larger than 1.2 mm can reduce the overall particle size of rock samples, improve strength and pressure stability, and help maintain permeability. In the surface heap leaching of loose sandstone ore, by sieving out particles smaller than 0.15 mm during deep heap construction and sieving out particles larger than 1.2 mm during mid-level heap construction, and by using vat leaching for sieved-out particles, the seepage effect of the ore heap can be significantly optimized, and complete utilization of resources can be ensured. [ABSTRACT FROM AUTHOR]

Petrographic studies have been carried out on the Early Miocene Darnó Conglomerate Formation, which consists only of debris of ophiolitic mélange and is found today on Darnó Hill in SW Bükk, NE Hungary. The studied sediments are bounded by the Darnó line from Darnó Hill. The aim of this work was to show if it is possible to reconstruct the petrographic composition of the source area only from its debris. The rock types were determined in thin sections using a polarizing microscope, and a quantitative analysis of the different rock types was carried out using the grain counting method, the results of which were interpreted as volume ratios. The main rock types observed in the studied samples (textural varieties of basalt, dolerite/microgabbro, claystone, siltstone, and radiolarite) are similar to the rock types of the mélange assemblage of Darnó Hill. Based on the volume calculations of basaltic detrital grains with different textures characteristic for pillow basalts, it could be established that pillow basalts dominated the igneous rocks in the source area of the Darnó Conglomerate on Darnó Hill already in the Miocene. Thus, this work shows that the lithological composition of a source area can be precisely outlined by a detailed petrographic analysis of the debris eroded from the immediate vicinity. [ABSTRACT FROM AUTHOR]

During the assembly of Pangea, peri-Gondwanan terranes collided with the eastern and southern margins of Laurentia and brought with them unique detrital zircon U-Pb signatures. Discriminating between individual peri-Gondwanan terranes in the detrital record is difficult due to their similar geologic histories. However, characterization of this provenance is critical for understanding late Paleozoic sediment routing during development of Pangea. Along southeastern Laurentia, in the Arkoma Basin (present-day Arkansas and eastern Oklahoma, southeastern United States), we identified Middle Pennsylvanian (Desmoinesian) strata that exhibit a concentrated peri-Gondwanan detrital zircon signature (e.g., ca. 800–550 Ma). Although several southern peri-Gondwanan terranes (e.g., Maya, Suwannee) are closer to the Arkoma Basin, geologic data, such as predominantly north-to-south paleocurrents and proximal-to-distal facies relationships in these Desmoinesian strata, support a northern source (e.g., Ganderia, Avalonia, Meguma). Further evidence of a northern source comes from detrital zircon source mapping, which reveals the persistence of this peri-Gondwanan signal in depocenters to the north of the basin after the signal had diminished in the Arkoma Basin. To this end, bottom-up detrital zircon source modeling, source mapping, regional stratigraphy, paleocurrent data, and sandstone petrography allow us to reconstruct the evolution of this Middle Pennsylvanian (Desmoinesian) sediment pathway in the context of intraplate and plate-margin tectonic activity. This reconstruction documents processes affecting Earth’s surface (e.g., tectonics, climate) during the assembly of Pangea and describes in detail part of a dynamic continental-scale drainage system. [ABSTRACT FROM AUTHOR]

In this work, we present several new materials collected at the pink sandstone levels from the Las Flores Formation at the Cerro Pan de Azúcar (Gaiman, Chubut Province, Argentina) and compare them with taxa present in other localities of similar age. The Metatheria taxa described here are 1) the 'Ameridelphia' Sternbergiidae indet; 2) the Didelphimorphia Protodidelphis cf. mastodontoides and Guggenheimia glykeia sp. nov. (Protodidelphidae); 3) the Polydolopimorphia Pliodolops rothi and Pliodolops cf. kamektsen (Polydolopidae); and 4) the Microbiotheria Eomicrobiotherium diluculum sp. nov. (Microbiotheriidae). On the other hand, the Cingulata Dasypodidae is represented by the Astegotheriini Prostegotherium astrifer. This fauna shares more species with those occurring in the localities from Paso del Sapo than with any other early – middle Eocene localities. However, at the generic level, it shares several taxa with the Itaboraian fauna from Sao José de Itaboraí. Finally, the faunal associations from Pan de Azúcar, Paso del Sapo, Cañadón Hondo, and Bajo de la Palangana could be, at least in part, synchronous, representing locally the Riochican SALMA, with an age spanning from 51 to 45 Ma (early Ypresian- early Lutetian). [ABSTRACT FROM AUTHOR]

Rocks have a softening effect under the long-term physical and chemical action of water, resulting in a reduction in the strength of rock and a weakening of the safety performance of project, which may have destructive effects for the wellbore instability, borehole contraction, leakage, and reservoir protection at a certain time. To investigate the effect of water-induced rock softening on its anisotropy for reservoir protection, the digital experiment was conducted on three types of rocks with four different saturation levels in five different directions. A digital drilling response model was employed to determine the drilling strength and specific energy at the critical point. The drilling parameters of the three types of rocks were recorded to calculate the softening coefficient and the anisotropy of the softening coefficient. The reliability of the proposed anisotropy of the softening coefficient was verified by introducing strength parameters based on the water-induced rock softening. The results show that the softening coefficient decreased with increasing saturation levels. The highest decrease with 43% was observed in mudstone. The anisotropy of the softening coefficient increased with an increasing saturation levels. The highest increase with 12% was observed in mudstone. Both fine-grained sandstone and mudstone exhibited the phenomenon of strength rebound with increasing saturation levels. A comparison with the previous studies reveals that this method can provide a reliable basis for determining the degree of rock softening using drilling strength. Highlights: The effect of water-induced rock softening on rock anisotropy is investigated during drilling process. The digital experiment was conducted on rocks with four different saturation levels. The reliability of the anisotropy of the softening coefficient was verified by introducing strength parameter. [ABSTRACT FROM AUTHOR]

Fracturing of rocks subjected to cryogenic treatment significantly impacts the stability and permeability of underground storage facilities for liquefied natural gas (LNG). However, existing fracturing damage models lack coverage across the entire spectrum of practical engineering conditions, spanning potential temperature ranges from room temperature to − 160 °C and saturation levels from 0 to 100%. Addressing this gap, this study utilizes cracked sandstone disks to investigate the fracture toughness of sandstone following cryogenic treatment to − 160 °C using the Brazilian splitting test. In the experimental setup, treatment temperatures are specified at 15, − 40, − 80, − 120, and − 160 °C, while saturations range from 0 to 100%. The experimental findings reveal that ultralow temperatures reduce the fracture toughness of saturated sandstone by approximately 30%, whereas for dry sandstone, this reduction is approximately 7.4%. This suggests a significant influence of different pore saturations on fracture toughness. A damage model, based on the Boltzmann function, is established to incorporate the effects of both temperature and saturation. This model accurately predicts the damage variable concerning treatment temperature and saturation. Generally, as temperature decreases, the damage variable also decreases, exhibiting two stages: rapid decrease followed by gradual decrease. The transition temperature, marking the division between these stages, tends to be lower in sandstone with higher saturation levels. The experimental results are further discussed within the context of the mineral compositions present in the sandstone, elucidating the thermal–mechanical mechanisms at play. Although the current damage model is specific to sandstone, the methodological approach is generalizable to generic rock types. The damage model's adaptability allows for testing fitting parameters for specific rock types or adjusting the relevant thermal coefficients. These findings and the developed model offer valuable insights for the reliable analysis of stability and permeability in LNG storage facilities or similar geologic engineering projects. Highlights: The Mode-I fracture toughness of sandstone under variable saturation conditions subjected to cryogenic temperatures of − 160 °C is investigated. Saturated sandstone experiences more than four times the amount of damage compared to dry sandstone under ultralow temperatures. A damage model is developed to incorporate the influences of both temperature and saturation. [ABSTRACT FROM AUTHOR]

The petrographic and geochemical attributes of the Oligocene Barail Group of rocks are used to decipher the likely source area(s) or tectonic domains, as this sequence of rocks was deposited in a foreland basin governed by orogenic domain, namely the North-east Arunachal Himalayas. The river system that gave rise to the Brahmaputra River (Yarlung-Tsangpo), which flowed through several tectonic domains of the Himalayan ranges, primarily from Bomi-Chayu, Gangadese Granitoid, Higher Himalayan Leucogranites, and Namche Barwa into the proto Bengal Basin now a part of Assam Arakan Basin and Naga Schuppen Belt, was the main source of the sandstone formation of the Barail Group. The purpose of sandstone petrography, which combines modal analysis with XRF (Major Oxides) and HR-ICP-MS (Trace & Rare Earth Elements) research, is to identify the type of source rock(s), their weathering pattern, and its paleo-environmental circumstances. These sandstones were formed from recycled orogen and include lithic and sublithic arenite variants with advanced texture and chemical maturity. The sediments were felsic (Th/Co: 1.38, Cr/Th: 9.78, La/Lu: 11.58, Th/Sc: 0.99, Eu/Eu*: 0.66, La/Sc: 3.05, La/Co: 4.18), with contributions from intermediate source rocks and low-rank metamorphics deposited in an active continental margin to a continental island arc setting. Climatic conditions impacted the sediments of Barails, characterised by being warm and semi-humid to humid which resulted in moderate to a high degree of chemical weathering, as shown by weathering indices like CIA (79.14), PIA (85.47), CIW (86.9), WIP (32.50), ICV (0.71), and Th/U (6.03), which were further additionally supported by C-Value (1.01), PF (1.20), Sr/Cu (2.04), and Rb/Sr (0.97). [ABSTRACT FROM AUTHOR]

The Mamonia Mélange in the Ayia Varvara area (southwestern Cyprus) is characterized by a matrix supported mélange which is composed of tectonized siltstones and mudstones with numerous blocks that were derived from the Mamonia Allochthonous Complex (Petra tou Romiou Formation reefal limestones, Phasoula Formation volcanics, Kholetria Member pelagic limestones, Akamas Member sandstone, Parekklisha Member sandstone, Ayia Varvara Formation metamorphics and Episkopi Formation radiolarian cherts). Subordinate blocks were derived from the Troodos Ophiolite Complex: serpentinites, gabbro, pillow lavas and cherty umbers (Perapedhi Formation). Radiolarian assemblages from chert blocks display a broad spectrum in age, ranging from the Late Triassic (latest Carnian–early Norian) to the youngest Cenomanian. The composition of the mélange in the Ayia Varvara area differs from the one described in the Petra tou Romiou area (SW Cyprus), as various lithologies were recorded (like Akamas Member sandstone and Parekklisha Member sandstone) which were not detected previously. The Mamonia Mélange was formed during the Late Cretaceous, most probably after the end of deposition of the Perapedhi Formation (late Santonian–early Campanian). [ABSTRACT FROM AUTHOR]

In subsurface energy extraction, permeability or conductivity is the vital parameter for quantifying fluid flow in porous media. Three-dimensional digital core technique is widely used to calculate flow parameters and to analyze the internal structure and properties of rocks. However, one major problem is its high computational cost associated with fine-scale simulation of porous media, especially for large and complex rock samples. In this study, we propose to use subvolume properties to increase computational efficiency. Specifically, we first construct digital cores of dune sand and sandstone by CT scanning technology, and divide the whole core into multiple subvolumes and calculate their permeabilities. Then, we reassemble the subvolumes and compute the permeability for the whole core. This approach may lead to underestimation as the connectivity between subvolumes could be lost. To address this issue, we divide the whole core into different-sized subvolumes, and then use curve fitting to deduce the permeability of whole rock sample via extrapolation. The results show that the proposed method has improved accuracy, and is significantly faster than simulating the whole digital core, since the computation on subvolumes can be easily parallelized. This approach provides new ideas for accurate and efficient permeability estimation for digital porous media. [ABSTRACT FROM AUTHOR]

Considering the problems in the discrimination of fracture penetration and the evaluation of fracturing performance in the stimulation of thin sand-mud interbedded reservoirs in the eighth member of Shihezi Formation of Permian (He-8 Member) in the Sulige gas field, a geomechanical model of thin sand-mud interbedded reservoirs considering interlayer heterogeneity was established. The experiment of hydraulic fracture penetration was performed to reveal the mechanism of initiation-extension-interaction-penetration of hydraulic fractures in the thin sand-mud interbedded reservoirs. The unconventional fracture model was used to clarify the vertical initiation and extension characteristics of fractures in thin interbedded reservoirs through numerical simulation. The fracture penetration discrimination criterion and the fracturing performance evaluation method were developed. The results show that the interlayer stress difference is the main geological factor that directly affects the fracture morphology during hydraulic fracturing. When the interlayer stress difference coefficient is less than 0.4 in the Sulige gas field, the fractures can penetrate the barrier and extend in the target sandstone layer. When the interlayer stress difference coefficient is not less than 0.4 and less than 0.45, the factures can penetrate the barrier but cannot extend in the target sandstone layers. When the interlayer stress difference coefficient is greater than 0.45, the fractures only extend in the perforated reservoir, but not penetrate the layers. Increasing the viscosity and pump rates of the fracturing fluid can compensate for the energy loss and break through the barrier limit. The injection of high viscosity (50-100 mPa·s) fracturing fluid at high pump rates (12-18 m3/min) is conducive to fracture penetration in the thin sand-mud interbedded reservoirs in the Sulige gas field. [ABSTRACT FROM AUTHOR]

In order to predict phase distributions within complex pore structures during two-phase capillary-dominated drainage, we select subsamples from computerized tomography (CT) images of rocks and simulated porous media, and develop a pore morphology-based simulator (PMS) to create a diverse dataset of phase distributions. With pixel size, interfacial tension, contact angle, and pressure as input parameters, convolutional neural network (CNN), recurrent neural network (RNN) and vision transformer (ViT) are transformed, trained and evaluated to select the optimal model for predicting phase distribution. It is found that commonly used CNN and RNN have deficiencies in capturing phase connectivity. Subsequently, we develop a higher-dimensional vision transformer (HD-ViT) that drains pores solely based on their size, regardless of their spatial location, with phase connectivity enforced as a post-processing step. This approach enables inference for images of varying sizes and resolutions with inlet-outlet setup at any coordinate directions. We demonstrate that HD-ViT maintains its effectiveness, accuracy and speed advantage on larger sandstone and carbonate images, compared with the microfluidic-based displacement experiment. In the end, we train and validate a 3D version of the model. [ABSTRACT FROM AUTHOR]

PT. Singlurus Pratama operates four mining blocks: Sungai Merdeka, Argosari, Margomulyo, and Mutiara. The Sungai Merdeka block has three voids with significant potential as a source of clean water for Nusantara Capital City (IKN), given its location within the city's development area. Surface water flows from the southern ridge to the north, accumulating in the voids of the Sungai Merdeka block, with a total inflow of 449,218,750 m2 per day. This volume can meet the needs of 1,796,875 to 4,492,187 people. One of the geological formations of the Sungai Merdeka block is the Balikpapan Formation, composed of alternating sandstone and clay with intercalations of shale and limestone, which is likely an aquifer. The water quality in voids 1 and 2 falls into the fairly good category (WQI = 70.07 and 70.77), while void 3 has moderate quality (WQI = 64.76). Thus, the water from the Sungai Merdeka voids can be used for personal and household hygiene, as well as raw water for drinking. Additionally, it can be utilized for recreational water facilities, freshwater aquaculture, livestock, and irrigation. However, the void water in the Sungai Merdeka block is indicated to have formed acid mine drainage, as the exposed void walls are contaminated with oxygen and leached by water. This leads to increased acidity, as indicated by the low pH values of the water. The increased acidity also results in higher concentrations of dissolved metals within the voids, necessitating careful management and treatment to ensure the water's safety and usability for various applications. [ABSTRACT FROM AUTHOR]

Water-bearing fractured rock masses are prone to geological hazards due to freeze–thaw (FT) damage, which brings adverse effects on the stability of rock engineering. In order to study the FT damage characteristics of rocks, the intact and pre-cracked cyan sandstone samples were taken as the research objects, with pre-crack inclination angles β of 0°, 45°, and 90°, respectively. The effects of FT cycle on stress–strain curve, peak strength, apparent stiffness and FT coefficient of cyan sandstone samples were studied by uniaxial compression test. Based on macroscopic damage variables, a damage constitutive model of cyan sandstone is proposed combined with strain equivalence hypothesis and Weibull distribution hypothesis. Considering that the strain equivalence hypothesis is difficult to reflect the compaction effect of microcracks, the damage constitutive equation is modified by taking the ratio of the secant modulus of the actual stress–strain curve to that of the classical Lemaitre damage constitutive curve as the correction coefficient. The application results show that the modified constitutive model can well describe the stress–strain relationship of cyan sandstone before the peak strength, which verifies the reliability of the model parameters derived from the test data, and the practicability of the damage characterization method and correction coefficient. The results can provide theoretical reference for the study of FT damage of rocks in cold regions. [ABSTRACT FROM AUTHOR]

Water content and primary fractures can change the mechanical characteristics of rock, making it easy to induce geological disasters. Therefore, direct shear tests of red sandstone under the action of water-fracture were carried out in this paper. The results show that shear strength of rock samples with fractures is less than that of intact rock samples. With the increase of primary fracture dip angle, shear strength and macroscopic crushing area of the rock sample increases first and then decreases with 20° as the boundary. It shows that the primary fractures weaken the shear mechanical properties and change the macroscopic failure mode. The shear performance of water-bearing rock samples is weaker than that of intact rock samples, and the weakening degree of water-saturated on shear performance of rock samples is lower than that of unsaturated water state. The fracture surfaces of rock samples are divided into 'shortest path single through type', 'longest path single through type' and 'cross path through type'. The failured rock samples are divided into 'single through type' and 'cross through type'. The research results can provide reference for geological disaster management under relevant conditions. [ABSTRACT FROM AUTHOR]

Sand production poses a substantial challenge in the oil and gas field, particularly in formations lacking the requisite strength to withstand pressure differentials during extraction. Many wells produce much less than their capacity due to the need to mitigate sand production and prevent well completion and wellhead erosion. The choice of sand control method depends on various factors, such as reservoir conditions, operational methods, and economic considerations, encompassing both mechanical and chemical approaches. In response to this challenge, this study investigates the application of a novel polymer nanofluid for chemical consolidation in clay-rich sandstone reservoirs, an area of exploration yet to be fully tapped. The research aims to assess the potential of polymer nanofluids as a promising solution for sand control in clay-rich reservoirs, with the overarching goal of bolstering well productivity and mitigating the adverse impacts of sand production. Conducted at a laboratory scale, the experiments involved the injection of 1 Pore Volume of consolidation fluid into sandstone cores with 15% and 30% clay content. Subsequently, the cores were subjected to reservoir temperature and pressure conditions for a period of 24 h. The obtained results show a significant enhancement in compressive strength, exceeding 700 psi, facilitated by the polymer nanofluid. Furthermore, permeability restoration reached approximately 89%, a notable improvement compared to preceding studies. Moreover, the introduction of foam injection rendered the core surface water-wet, suggesting potential advantages for reservoir management. These findings illuminate the promise of polymer nanofluids as an effective tool for sand control in clay-rich sandstone reservoirs. [ABSTRACT FROM AUTHOR]

Reservoir quality prediction in deeply buried reservoirs represents a complex challenge to geoscientists. In sandstones, reservoir quality is determined by the extent of compaction and cementation during burial. During compaction, porosity is lost through the rearrangement and fracture of rigid grains and the deformation of ductile grains. During cementation, porosity is predominantly lost through the growth of quartz cement, although carbonate and clay mineral growth can be locally important. The degree of quartz cementation is influenced by the surface area of quartz available for overgrowth nucleation and thermal history. Clay grain coats can significantly reduce the surface area of quartz available for overgrowth nucleation, preventing extensive cementation. Using a coupled-effect compaction and cementation model, we have forward-modelled porosity evolution of surface sediments from the modern Ravenglass Estuary under different maximum burial conditions, between 2000 and 5000 m depth, to aid the understanding of reservoir quality distribution in a marginal marine setting. Seven sand-dominated sub-depositional environments were subject to five burial models to assess porosity-preservation in sedimentary facies. Under relatively shallow burial conditions (<3000 m), modelled porosity is highest (34 to 36%) in medium to coarse-grained outer-estuary sediments due to moderate sorting and minimal fine-grained matrix material. Fine-grained tidal flat sediments (mixed flats) experience a higher degree of porosity loss due to elevated matrix volumes (20 to 31%). Sediments subjected to deep burial (>4000 m) experience a significant reduction in porosity due to extensive quartz cementation. Porosity is reduced to 1% in outer estuary sediments that lack grain-coating clays. However, in tidal flat sediments with continuous clay grain coats, porosity values of up to 30% are maintained due to quartz cement inhibition. The modelling approach powerfully emphasises the value of collecting quantitative data from modern analogue sedimentary environments to reveal how optimum reservoir quality is not always in the coarsest or cleanest clastic sediments. [ABSTRACT FROM AUTHOR]

The geological storage of carbon dioxide (CO2) in offshore saline aquifers stands as a primary option for reducing CO2 emissions in coastal regions. China's coastal regions, particularly Shandong and Jiangsu provinces, face significant challenges in CO2 reduction. Therefore, evaluating the feasibility of CO2 geological storage in the adjacent seas is critical. To assess the suitability of a CO2 storage site, understanding its structural and reservoir characteristics is essential to mitigate injection and storage risks. In this study, we analyzed the structural characteristics and potential traps of the Yantai Depression in the South Yellow Sea Basin based on seismic data interpretation. We further conducted well logging analysis and post-stack seismic inversion to obtain lithological data, including acoustic impedance and sandstone content percentages from the Cenozoic Funing Formation, Dainan–Sanduo Formation, and Yancheng Formation. Our findings highlight that the Yantai Depression in the South Yellow Sea Basin exhibits diverse structural traps and favorable reservoir–caprock combinations, suggesting promising geological conditions for CO2 storage. This area emerges as a suitable candidate for implementing CO2 geological storage initiatives. [ABSTRACT FROM AUTHOR]

Sandstone is the fundamental material in various engineering and construction projects. However, the mechanical integrity of sandstone can be compromised by initial unloading damage resulting from activities such as engineering excavations. Furthermore, this degradation is further exacerbated under periodic dry-wet environmental conditions. This study investigated the effects of dry-wet cycles and unloading on the mechanical properties of jointed fine sandstone using uniaxial and triaxial compression tests. These tests were performed on rock samples subjected to varying unloading degrees and different numbers of dry-wet cycles. The results demonstrate that with an increase in the unloading degree from 0% to 70%, there is a corresponding decrease in peak stress ranging from 10% to 33%. Additionally, the cohesion exhibits a reduction of approximately 20% to 25%, while the internal friction angle experiences a decline of about 3.5% to 6%. These findings emphasize a significant unloading effect. Moreover, the degree of peak stress degradation in unloading jointed fine sandstone diminishes with an increase in confining pressure, suggesting that confining pressure mitigates the deterioration caused by dry-wet cycles. Additionally, as the number of dry-wet cycles increases, there is a notable decline in the mechanical properties of the sandstone, evidencing significant dry-wet degradation. Utilizing the Drucker Prager criterion, this study establishes a strength criterion and fracture criterion, denoted as σ1(m, n) and KTII(m, n), to quantify the combined impacts of dry-wet cycles and unloading on jointed fine sandstone, which provides a comprehensive understanding of its mechanical behavior under such conditions. [ABSTRACT FROM AUTHOR]

One of the major factors impacting on drill bit performance during rock drilling is interface temperature. The performance of the drill bit during drilling operations not only depends on operations parameters but also the properties of rock during drilling in laboratory and field investigations. Hence the present study focused on interface of bit-rock, the temperature had been determined by developing a specially grounded thermocouple. Over 500 different test conditions were performed in each rock sample's case during experimental drilling on a cylindrical block of UCS of 17.83 MPa (fine-grained sandstone grey-FG), 13.70 MPa (medium-grained sandstone-MG), and 51.67 MPa (fine-grained sandstone pink-FGP). The results revealed that the average increase in interface temperature for MG is about 53.74%, FG is about 93.26%, and FGP is about 165.22%. The significant parameters such as uniaxial compressive strength (26%), depth (33%), rate of penetration (15.2%), diameter of the bit (5.26%), and thrust (5.04%) are the most influenced parameters on temperature, followed by spindle speed (1.04%), and torque (0.23%) respectively. The proposed regression models successfully predict the temperature with an R2 value of 91.74%, 90.30%, and 90.95% for MG, FG, and FGP, respectively. Finally overall regression model is developed by considered operational parameters with rock properties to predict temperature and R2 value of 80.8% for all three types of rock samples considered. [ABSTRACT FROM AUTHOR]

ABSTRACT Carbonate cementation in the Upper Permian sandstones informs the timing and temperature of hydrothermal activity in the south‐western Ordos Basin. This study presents a detailed examination of these hydrothermally influenced carbonate cements, constraining their age, carbonate diagenesis and relationship with regional geodynamic evolution. Sedimentological analyses demonstrate the development of deltaic plain and front sand bodies in the study area, which resulted in interbeds of volcanic matrix‐rich sandstones with matrix‐free sandstones. Petrography and electron microprobe analysis reveal four carbonate mineral growth phases of matrix‐free sandstones in the following sequence; scarce pure siderite, scarce Mg‐rich siderite, abundant blocky calcite and moderately abundant grain‐replacing calcite. The fluid inclusion data show anomalies of homogenization temperature of blocky carbonate cements during early diagenesis, over a wide range of ca 148 to 228°C. In addition, blocky carbonate cements show low δ13C (−5.9 to −13.1‰ Vienna PeeDee Belemnite) and δ18O (clustered tightly from −12.4 to −14.6‰ Vienna PeeDee Belemnite) values, interpreted to result from elevated temperatures during cementation, associated with activation of basement faults and concomitant hydrothermal fluid intrusion triggered by oceanic crust subduction in the south‐west margin of the Ordos Basin. Using in situ calcite U–Pb geochronology, the timing of hydrothermal activity was constrained to ca 247.0 ± 11 to 248.2 ± 4.7 Ma. This work provides a case study for applying intergranular calcite U–Pb dating to determine the absolute timing of fluid flow in sedimentary basins, offering tremendous potential to capture snapshots of various diagenetic evolution stages in sediments. The proposed diagenetic model can also provide new insights and understanding regarding hydrothermally influenced sediments. More importantly, hydrothermal activity may have commenced earlier than previously thought. The North Qinling Orogen uplift and associated Mianlue oceanic crust subduction may have begun at the Permian–Triassic transition with a protracted hydrothermal event in the south‐western Ordos Basin. [ABSTRACT FROM AUTHOR]

Tunnel stability is influenced by the rheological properties of the surrounding rock. This study, based on the Ganshen high-speed railway tunnel project, examines the rheological characteristics of siltstone and sandstone through laboratory tests and theoretical analysis. Rheological curves and parameters are derived, revealing the time-dependent deformation mechanisms of the surrounding rocks. A numerical simulation model is created using these parameters to analyze deformation and stress characteristics based on different rock levels and inverted arch closure distances. Results indicate that sandstone follows the Cvisc model, with the Maxwell elastic modulus increasing under higher loads while the viscous coefficient decreases. The vault displacement is mainly affected by the surrounding rock strength; lower strength leads to greater displacement, which also increases with the closure distance of the inverted arch. These findings are crucial for determining the optimal closure distance of inverted arches in sandstone conditions. [ABSTRACT FROM AUTHOR]

Undercutting anchors are structural elements used in construction and geotechnics to stabilize both structures and soils. Their main applications include stabilizing slopes and embankments, reinforcing foundations, and providing support during tunnel construction and other underground works. The authors propose the use of these anchors in rock mass detachment technology. This article presents a comprehensive analysis of the mechanism behind rock mass detachment using an undercutting anchor. Particular attention is given to the influence of parameters such as the fracture energy of the medium and the coefficient of friction between the medium and the anchor head on the detachment process of rock elements during anchor expansion in the drilled hole. Numerical FEM analysis was employed to model the effect of changes in the shape and size of failure cones under varying simulation conditions. The discussed problem is crucial for evaluating the effectiveness of this anchor design under non-standard conditions, particularly in the unconventional destruction of rock media. [ABSTRACT FROM AUTHOR]

ABSTRACT Despite a growing interest, few studies integrate quantitative supercritical‐flow deposit (SFD) distribution into paleoenvironmental reconstructions in deep‐marine settings. We present a re‐evaluation of the Oligocene Annot Sandstones (SE France) in terms of flow criticality, by examining the spatial distribution of SFDs. Proximal settings exhibit SFD proportion varying from ~90% to 40% with a common occurrence of cyclic steps, whereas distal environments show <40% SFDs with antidunes and upper‐plane beds prevalent. Comparing SFD spatial distribution to other proxies in the Annot Sandstones and published proxies from the Eocene Ainsa‐Jaca basins (Spanish Pyrenees), SFD trends appear more consistent than those in sandstone percentages, or the distribution of the Bouma sequence divisions. Our approach achieves two goals: (1) establishing the reliability of quantitatively analysing SFDs as a proxy for paleoenvironment reconstructions, characterising the proximal‐to‐basin floor transition at ~40% SFDs and (2) providing fundamental insights into the formation processes compared to other proxies. [ABSTRACT FROM AUTHOR]

Well workover operation in some blocks of the Tarim Basin resulted in mud leakage to the gas-producing formation, resulting in damage to gas well production. Therefore, refracturing of mud leakage wells in the future is necessary. To explore the means of refracturing to promote the recovery of gas well productivity, studying the evolution law of the production-induced stress field is necessary. Therefore, in this study, a prediction model of the production-induced stress field of fractured high-yield gas wells was established, and the evolution law of the stress field under the set production conditions of high-yield gas wells was clarified. The results show that with an increase in matrix permeability, main fracture conductivity, and natural fracture density, the decrease in the amplitude of stress decreases under the set production. At lower matrix permeability and natural fracture density, the low-stress areas on both sides and the front end of the main fracture are larger. At a higher main fracture conductivity, the low-stress area at both sides and the front end of the main fracture is larger. The change in the in situ stress of the gas well is smaller under set production than constant-pressure production. [ABSTRACT FROM AUTHOR]