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Bogor Trough in the West Java are typified by turbidity deposits with the source are mostly characterized by volcanoclastic materials from the southern area. The Trough actually receipt the sediment from both volcanoclastic materials from the south and continental source from the north. But, the discussions of sediments in term of composition and temporal variation are rare to be reported, especially the sediments from the north. This manuscript intends to discuss the temporal variation in detrital compositional and depositional facies of the Neogene sediments that delivered from the north (i.e., Sundaland) into the Bogor Trough, which is represented by Miocene Jatiluhur Formation. A total of 36 selected samples have been taken for identifying the minerals using a polarization microscope. Modal analysis of the Gazzi-Dickinson method was applied for this provenance study of sandstones samples, which are consisting largely of quartz and feldspar, then sedimentary rock and volcanic rock fragments, glaucony, mud chips and skeletal fragments. Sundaland, a continental block highland area in the north, is interpreted to have been the provenance of sediments of the Jatiluhur Formation, which is also considered to be the source area for the Paleogene sediments. Granitic igneous rocks are interpreted as the source of dominance of monocrystalline quartz grains, or the product of long-distance transport of polycrystalline quartz from metamorphic rocks But, however late Miocene samples (upper part of formation) represent that the size and amount of glauconite grains are increasing, and texturally mud supported. Volcanic rocks materials are also observed. The upper part of Jatiluhur Formation records the starvation of sediment discharge into the basin, which has been also promoted for development of carbonate reef Klapanunggal Formation in the self-margin setting, and suggesting that the basin have directly received or indirectly some contemporaneous volcanic provenances sediment from the southern area.

This paper is a literature review on marine hardbottom environments (MHE) that emerge in coastal regions in the Brazilian state of Ceará. This stretch of the Brazilian coast houses several rock formations, which are widely distributed in the intertidal zone. These formations have various origins and composition, ranging from crystalline rocks to biogenic structures, but most are composed by sandstones. These substrates support biodiverse ecosystems that produce valuable environmental goods and services, which have historical and socioeconomic relevance for the state. Despite their importance, they are currently threatened by various types of local and global stressors, and a consistent government effort to protect them is still lacking. There are many knowledge gaps regarding these formations and new studies are needed to support conservation actions involving these ecosystems. Este artigo é uma revisão da literatura sobre ambientes marinhos rochosos que surgem em regiões costeiras do estado brasileiro do Ceará. Esse trecho da costa brasileira abriga diversas formações rochosas, que estão amplamente distribuídas na zona entremarés. Essas formações possuem origens e composições diversas, que vão desde rochas cristalinas até estruturas biogênicas, mas a maioria é composta por arenitos. Esses substratos sustentam ecossistemas biodiversos que produzem bens e serviços ambientais valiosos, que têm relevância histórica e socioeconômica para o estado. Apesar de sua importância, eles estão atualmente ameaçados por vários tipos de estressores locais e globais e ainda falta um esforço consistente do governo para protegê-los. Existem muitas lacunas de conhecimento a respeito dessas formações e novos estudos são necessários para subsidiar ações de conservação envolvendo tais ecossistemas

Three new species of Elatostema (Urticaceae) from Thailand, E. kaweesakii Triyutth. & L.F.Fu, sp. nov., E. rubricaule Triyutth. & L.F.Fu, sp. nov. and E. saxatile Triyutth. & L.F.Fu, sp. nov., are newly described and illustrated. These new species can be distinguished by the presence of rhizome. Elatostema kaweesakii is similar to E. atroviride. Elatostema kaweesakii is a lithophyte growing in limestone crevices. It differs from E. atroviride by its large swollen rhizome, glabrous stem, glabrous receptacle, number of tepal in staminate flower, absence of tepal in pistillate flower, presence of staminodes in pistillate flower and smooth achene. Elatostema rubricaule and E. saxatile are found on sandstone habitats. They have distinct flattened and disk-like rhizome. Elatostema rubricaule is distinguished by its distinct sulcate and reddish stem with flattened and disc-like rhizome and chartaceous leaves with entire margin. Elatostema saxatile resembles E. bulbiferum but differs by its flattened and disc-like rhizome, acute leaf apex, glabrous receptacle in pistillate inflorescences, presence of staminodes in pistillate flower, and its sandstone habitat. Descriptions, distribution, ecological and phenological data are provided.

Актуальность исследования обусловлена необходимостью предотвратить введение в прифильтровую зону объема породы с большей однородностью и большего размера по сравнению с крупной фракцией пластового песка - попытка добиться улучшения фильтрационных свойств прифильтровой зоны, т. е. снижения [zeta]2фк и [zeta]2n. Конструкция гравийной набивки одновременно должна исключать вынос частиц пласта в скважину. Решение этой проблемы позволит улучшить работу фильтрации пластовой жидкости из пласта в скважину и сократить затраты на дополнительное применение методов интенсификации притока пластовой жидкости к скважине. Цель: разработать методику, позволяющую при выборе конструкции фильтра, одновременно с возможностью обеспечения им надежной гидравлической связи в системе пласт-фильтр, предотвращать вынос песка в скважину. Объекты. Для предотвращения поступления песка из пласта и удержания гравия на забое скважины при создании гравийных набивок применяют щелевые, проволочные, кольцевые, титановые, металлокерамические и другие фильтры. Эти фильтры, установленные в интервале перфорации обсадной колонны без образования гравийной наружной кольцевой набивки (а именно таким образом в большинстве скважин устанавливаются фильтры на месторождениях России), очень часто забиваются пластовым песком, что приводит к снижению продуктивности скважин. Если для задержания песка используются щелевые фильтры, то эффективность их применения зависит от соответствия размера щелей гранулометрическому составу выносимого песка. Фильтры с ракушечной набивкой более эффективны, но также не всегда отвечают поставленной цели, поскольку прочность и качество ракушечника, закачиваемого в прискважинную часть пласта, довольно низкие. Кроме того, примененные на промыслах проволочные фильтры не имеют фиксации каждого витка, в результате чего при механическом повреждении одного из витков происходит срыв всей намотки. Методы. При применении предложенной методики полученные результаты экспериментальных работ по оценке способов снижения выноса песка из несцементированных неоднородных пластов показывают, что применение фильтров в обсаженном стволе требует создания гравийной набивки в кольцевом зазоре между фильтром и колонной, в перфорированном канале и за обсадной колонной. Причем размер гравия должен быть выбран таким, чтобы исключить перемешивание гравийной обсыпки с пластовым песком за счет миграции и интрузии песка, т. е. D/d=4-5. Снижения производительности скважин можно в этом случае избежать путем увеличения размера и количества перфорационных отверстий. Следует отметить, что предотвращение выноса песка означает, что при оптимальном установившемся режиме работы скважины фильтр удерживает частицы скелета пласта, но пропускает мелкодисперсные и глинистые частицы. В период запуска скважины картина несколько иная - пропускается и часть скелетообразующих частиц до того момента, пока на фильтрующей оболочке не образуется естественный фильтр из отсортированных крупных фракций. Результаты. Частицы, которые составляют структуру породы, не должны выносится из пласта за счет применения фильтра. Практически это означает, что фильтр должен не пропускать 75-85 % (по весу) более крупных фракций песка. Для сохранения общей устойчивости скелета пласта можно допустить вынос мелких частиц не более 15-25 % (во весу). The relevance of the study is caused by the need to prevent the introduction of a volume of rock with greater homogeneity and larger size into the near-filter zone compared to the coarse fraction of formation sand - an attempt to improve the filtration properties of the near-filter zone, i. e. decrease in [zeta]2фк and [zeta]2n. The design of the gravel pack should simultaneously exclude the removal of formation particles into the well. The solution to this problem will improve the work of filtration of formation fluid from the formation into the well and reduce the cost of additional application of methods for stimulating the inflow of formation fluid to the well. Purpose: to develop a methodology that allows, when choosing a filter design, simultaneously with the ability to provide them with a reliable hydraulic connection in the reservoir-filter system, preventing sand removal into the well. Objects. To prevent the flow of sand from the formation and retain gravel at the bottom of the well, when creating gravel packs, slot, wire, ring, titanium, cermet and other filters are used. These screens, installed in the casing perforation interval without the formation of gravel outer annular packing (and this is how screens are installed in most wells in Russian fields), are very often clogged with formation sand, which leads to a decrease in well productivity. If slot filters are used to retain sand, then the effectiveness of their application depends on the correspondence of the slot size to the granulometric composition of the sand being removed. Filters with shell packing are more effective, but they also do not always meet the set goal, since the strength and quality of shell rock pumped into the near-wellbore part of the formation are rather low. In addition, wire filters used in the fields do not have fixation of each turn, as a result of which, if one of the turns is mechanically damaged, the entire winding breaks down. Methods. When applying the proposed technique, the results of experimental work on evaluating ways to reduce sand production from unconsolidated heterogeneous formations show that the use of filters in a cased hole requires the creation of gravel packing in the annular gap between the filter and the string, in the perforated channel and behind the casing. Moreover, the size of the gravel should be chosen so as to exclude the mixing of the gravel packing with the formation sand due to the migration and intrusion of sand, i.e. D/d=4-5. A decrease in well productivity can in this case be avoided by increasing the size and number of perforations. It should be noted that sand avoidance means that under optimal steady state well operation, the filter retains formation backbone particles, but allows fines and clay particles to pass through. During the well start-up, the picture is somewhat different - part of the skeletal particles is also passed through until a natural filter of sorted coarse fractions is formed on the filtering casing. Results. The particles that make up the rock structure should not be carried out of the formation by applying a filter. In practice, this means that the filter should not pass 75-85 % (by weight) of the larger sand fractions. To maintain the overall stability of the formation skeleton, it is possible to allow the removal of small particles not more than 15-25 % (in weight).

Backfilling is a common practice in the mining industry and the backfilling performance plays a significant role in supporting the surrounding rock mass. To evaluate the backfilling performance, an experimental apparatus has been developed to understand how backfill affects the compressive strength of sandstone specimens in the laboratory. Pebbles were selected to model the backfill and divided into six groups with different particle sizes using a set of standard sieves. The backfilling pebbles with three types of particle size compositions were then produced, i.e. single gradation, two adjacent gradations, and increasingly widening gradations. A series of compressive tests were carried out to study the mechanical behavior of the sandstone specimens confined by these pebbles. The effects of the gradations of the filled pebbles on the peak and residual compressive strengths were analyzed. It is found that the increasing amount of the compressive strength is over 10% in most cases, even up to 20%. Based on the experiment data, the increasing amount was also estimated theoretically under some assumptions and it further confirmed the experimental results. The effects are closely related to the gradations of the filled pebbles except for their dense degree.

Considering the storage capacity and already existing infrastructures, underground porous reservoirs are highly suitable to store green energy, for example, in the form of green gases such as hydrogen and compressed air. Depending on the energy demand and supply, the energy-rich fluids are injected and produced, which induces cyclic change of state-of-the-stress in the reservoir and its surrounding. Detailed analyses of the geo-mechanical deformations under variable storage conditions i.e., storage frequency and fluid fluctuating pressures, are crucially important for safe and efficient operations. The present work presents an integrated analysis, based on experimental and constitutive modeling aspects, to investigate sandstones’ geomechanical response to cyclic loading relevant to underground energy storage (UES). To this end, sandstone rock samples were subjected to cyclic loading above and below the onset of dilatant cracking under different frequencies and loading amplitudes. Axial strains and Acoustic Emissions (AE) were measured in both regimes to quantify the total deformation (strain) of the rock and its AE characteristics. It is found that the inelastic strain and number of AE events is the highest in the first cycle and reduce subsequently cycle after cycle. Moreover, cyclic inelastic deformations are affected by the mean stress, amplitude, and frequency of the stress waveform. On the one hand, the higher the mean stress and the amplitude, the higher the total inelastic strains. On the other hand, the lower the frequency, the higher the total inelastic strain. From the modeling perspectives, five types of deformation mechanisms were identified based on the governing physics: elastic, viscoelastic, compaction-based cyclic inelastic, inelastic brittle creep, and dilatation-based inelastic deformation. To model elastic, viscoelastic, and brittle creep, the Nishihara model was used. A cyclic modified cam clay model (MCC) and hardening–softening model were applied to capture plastic deformation. The results show a very good fit of the constitutive model with the experimental results, which could help in studying the response of reservoirs to injection and production.

The Murchison and Maruia basins are situated on the Australian Plate adjacent the Alpine Fault, an ideal place to study Cenozoic Australian–Pacific plate boundary evolution. Sandstone provenance was investigated using petrographic and detrital zircon U–Pb geochronologic methods and primarily varies geographically. Secondary up-section variation tracks spatiotemporal changes in basement exhumation. Eocene–middle Miocene western Murchison Basin sandstone is arkosic, derived locally from Devonian–mid-Cretaceous granitoids. Early Miocene–?Pliocene eastern Murchison and Maruia basin sandstone is lithic-/plagioclase-rich, reflecting a mixed provenance: proximal Carboniferous–mid-Cretaceous granitoids, and distal mid-Cretaceous Median Batholith and Permian–Triassic Eastern Province metasedimentary sources in the Pacific Plate. This confirms early Miocene Pacific Plate exhumation during initial Alpine Fault evolution began in northern Fiordland/western Otago but the contrast between eastern and western Murchison Basin indicates limited westward sediment dispersal. Higher proportions of Brook Street Terrane (BST) detrital zircon in middle Miocene eastern Murchison Basin sandstone suggests accelerated Pacific Plate exhumation at c. 15 Ma. By c. 10 Ma, the eastern Murchison Basin BST source had switched to the Australian Plate due to Waimea–Flaxmore fault reverse reactivation and dextral plate boundary strike-slip displacement, which by the late Miocene/Pliocene led to Rakaia Terrane-affinity Haast Schist replacing Caples Terrane as the main Maruia Basin sediment source.

The reliability of disc cutters has a significant influence on the safety and working efficiency of tunnel boring machines (TBMs). To investigate the reliability of disc cutters under different geological and operational conditions, we conducted a series of novel rolling cutting tests on intact and jointed sandstone blocks using different dip angles and interlayers. Different normal forces and rotational speeds of the cutterhead were also applied during the experiment. A novel reliability estimation method, based on a logistic regression model, was then proposed, and the influence of dip angle, strata, normal force, and rotational speed on the reliability of the disc cutter were analyzed. The reliability estimation method consisted of data acquisition regarding the normal force and cutter wear, feature extraction using wavelet packet transform and correlation analysis, and the estimation of the logistic regression model. To obtain the spectrum and normalized wavelet energy for each frequency band, we decomposed the time domain of the normal force by the wavelet packet transform. A correlation analysis was employed to determine the feature frequency bands that were sensitive to wear loss. On the basis of salient feature parameters and wear loss, the logistic regression model was established to evaluate the reliability of disc cutters. The analytical results indicated that the optimal dip angle for rock cutting was 30°. In the presence of mixed-face and single ground, the reliability of disc cutters was primarily affected by the difficulty of TBM excavation and wear loss, respectively. An increase in normal force and rotational speed aggravated wear on the cutter, thus reducing reliability. Furthermore, compared with Rabinowicz’s formula, the proposed method considers various geological and operational conditions, making the proposed method more applicable to estimate the reliability of disc cutters.

Identifying the fate of contaminants (such as barium) during gas field produced water reinjection could be a feasible method to evaluate the environmental risks of the reinjection project and thus improve its sustainability. To assess the barium sorption behaviors during gas field produced water reinjected into sandstone reservoirs, a series of water–rock interactions experiments were conducted to systematically investigate the effects of brine/rock ratio (5:1~500:1), pH (3~10), temperature (20, 50 and 80 °C), brine salinity (NaCl solution, 0~100 g/L), competitive cations (Sr and Mg, 0.5 g/L), and organic compound (methanol, 0~5 g/L) on the sorption of barium in sandstone. The rock samples were collected from the Triassic formation of the Yanchang Group in the northern Ordos Basin, China. The results indicated that the sorption of barium in sandstone strongly depends on the brine/rock ratio. Under the same brine/rock ratio, the severity of the impact on the barium sorption from high to low was competitive cation, salinity, pH, temperature, and methanol concentration. The sorption process of barium onto the sandstone could be well fitted by a pseudo-second-order kinetics model. The presence of competitive cations would restrain the sorption of barium, while the existence of methanol hardly affects the barium sorption. The chloro-complexation reaction and the reduction of rock surface electrical potential are mainly responsible for the inhibition effects of NaCl salinity on barium sorption, and the corresponding relationship can be characterized by an exponential function. Barium sorption in sandstone decreases with increasing temperature, while it is positively correlated to the initial pH of the solution. The water-rock system is weakly alkaline with a value of 7.7–8.5 when the barium sorption reaches an equilibrium state, regardless of the initial pH of the reactive solution. The results are meaningful in understanding and predicting the fate of barium after the gas field produced water was reinjected into the underground.

The success rate of matrix acidizing in hydraulic fractured sandstone formation is less than 55%, much lower compared to the more than 91% success rate in carbonate formation. The need for alternative approaches to help the success ratio in matrix acidizing is crucial. This paper demonstrates a modeling technique to improve the success ratio of matrix acidizing in a hydraulic fractured sandstone formation. Supervised machine learning with 4 models of a neural network, logistic regression, tree, and random forest was selected to predict the successfulness of matrix acidizing in hydraulic fracturing. In parallel, multivariate analysis of principal component regression and partial least square regression approach were utilized to predict the oil gain of the job. For qualitative prediction, the results showed that the random forest was the best model to predict the successfulness of the job with the area under the curve (AUC) of 0.68 and precision of 0.73 in the training model with 70% of the data. Subsequently, the validation test with the rest of the data (30% data) gave 0.51 AUC and 61% precision. For quantitative prediction, the net oil gain was evaluated by using principal component regression (PCR) and partial least square regression (PLS-R). The PCR and PLS-R model gave a coefficient of determination (Rsquare) of 0.22 and 0.35, respectively. The p-value of PLS-R was 0.047 (95% confidence interval) which indicates that the model is significant. The results of this work demonstrate the potential application of supervised machine learning, principal component regression, and partial least square regression to improve candidate selection of oil wells for matrix acidizing especially in hydraulic fractured wells with limited design data.

The new genus Bryorutstroemia is established for the red-brown, stipitate, bryoparasitic discomycete Helotium fulvum Boud. Combined phylogenetic analysis of ITS and LSU rDNA and EF1α revealed that Bryorutstroemia fulva belongs to the sclerotiniaceous clade, which comprises the paraphyletic families Rutstroemiaceae and Sclerotiniaceae. Bryorutstroemia formed with Clarireedia a supported clade (Rutstroemiaceae s.l.), though with high distance. Bryorutstroemia closely resembles other Rutstroemiaceae in having uninucleate ascospores with high lipid content and an ectal excipulum of textura porrecta, but is unique because of its bryophilous lifestyle and is extraordinary with its thick-walled inamyloid ascus apex. Although B. fulva was described in 1897, very few records came to our notice. The present study summarizes the known distribution of the species, including 25 personal collections from the years 2001–2022. Bryorutstroemia fulva was most often encountered on Dicranella heteromalla, and rarely on other members of Dicranales or Grimmiales, while inducing necrobiosis of the leaves. A detailed description based on mainly fresh apothecia is provided together with a rich photographic documentation. Six new combinations are proposed based on our phylogenetic results and unpublished personal morphological studies: Clarireedia asphodeli, C. calopus, C. gladioli, C. henningsiana, C. maritima, and C. narcissi.

Sandstones have been widely used in construction for their abundance, aesthetics, and ease of extraction. To determine sandstones’ quality, it is essential to analyse their petrographic and petrophysical properties and sensitivity (durability and conservation) to environmental agents. This paper evaluates the physical-mechanical changes undergone by Sierra de la Demanda (Burgos, Spain) sandstone under combined and induced water and salt aggression and assesses ESTEL 1100’s effectiveness and suitability as a treatment. This sandstone is porous, permeable, dense and quartz-rich with high hardness and strength. The treatment improved its petrophysical properties by modifying its pore geometry and connectivity, reducing absorbency, permeability and anisotropy, and further increasing its hardness and resistance. Salts did not substantially modify its properties as its porosity type absorbed the crystallisation pressure. Ultimately, its pore system and predominantly quartz composition make it a high-quality, weather-resistant material compatible with the treatment applied., Las areniscas han sido uno de los materiales de construcción más utilizados por su abundancia, estética y fácil extracción. Para determinar su calidad es esencial analizar sus propiedades petrográficas y petrofísicas, así como su sensibilidad (durabilidad y conservación) a los agentes medioambientales. Este trabajo evalúa tanto los cambios físico-mecánicos sufridos por una arenisca de la Sierra de la Demanda (Burgos, España), ante la agresión combinada e inducida de agua y sales, como la eficacia e idoneidad del tratamiento ESTEL 1100. Esta arenisca es porosa, permeable, densa, rica en cuarzo, y con alta dureza y resistencia. El tratamiento mejoró sus propiedades petrofísicas, modificando la geometría y conectividad de sus poros, y reduciendo su absorción, permeabilidad y anisotropía. Las sales no modificaron sustancialmente sus propiedades, ya que su porosidad absorbió su presión de cristalización. El sistema poroso y el abundante cuarzo hacen de esta arenisca un material de alta calidad, resistente a la intemperie y compatible con el tratamiento aplicado.

It is generally accepted that the uniaxial compressive strength (UCS) and P-wave velocity of rocks tend to decrease simultaneously with increasing temperature. However, based on a great number of statistical data and systematic analysis of the microstructure variation of rocks with temperature rising and corresponding propagation mechanism of elastic wave, the results show that (1) There are three different trends for the changes of UCS and P-wave velocity of sandstone when heated from room temperature (20 °C or 25 °C) to 800 °C: (i) Both the UCS and P-wave velocity decrease simultaneously; (ii) The UCS increases initially and then decreases, while the P-wave velocity decreases continuously; and (iii) The UCS increases initially and then fluctuates, while the P-wave velocity continuously decreases. (2) The UCS changes at room temperature–400 °C, 400 °C–600 °C, and 600 °C–800 °C are mainly attributed to the discrepancy of microstructure characteristics and quartz content, the transformation plasticity of clay minerals, and the balance between the thermal cementation and thermal damage, respectively. (3) The inconsistency in the trends of UCS and P-wave velocity changes is caused by the change of quartz content, phase transition of water and certain minerals.

This study aims to determine the field and petrographic properties of sandstones observed in Arsuz-İskenderun (Hatay) region and micro-size porosity changes in acidizing stages. The fine-grained sandstones of the Aktepe formation have more quartz grains than the other components and the binding material is matrix. Rock fragments that consist of fossil shells, limestone and igneous fragments are observed relatively to quartz and feldspar grains in the Kızıldere formation sandstones. The first step of reservoir rock acidizing is HCl acidizing and the process is experimentally provided by capillarity experiment. HCl with dilution rates of 7.5% - 15% - 30% was absorbed into the samples at room temperature and after 100 minutes, effective distances were observed as 0.6-0.8-1.1 cm and dissolved rock amounts as 32.82-34.02-35.54 g, respectively. In acidizing process, the average porosity analysed with Micro-CT is 39.6% of acidified samples with 15% diluted acid and non-acidified samples, equivalent results were obtained with porosity values measured by well logs. There is an increase in the porosity of about 16% with acidizing. Pores were bonded together by acidizing and pore size increase about 20%. The change in the pore throat by acidizing is 105%. Calculation of porosity of rocks by Micro-CT and image processing methods can be performed faster compared to the other methods.

The Camel site is located in the north of Saudi Arabia in the province of al- Jawf and is characterized by three decaying sandstone hillocks on which ancient craftsman have carved high and bas-reliefs depicting camels and equids of life-size stature dating possibly to the Late Neolithic (Guagnin et al. 2021). In 2019, an international team of specialists conducted excavations and surveyed the immediate vicinity of the sandstone formation as well as documenting the engravings/reliefs. Survey in the central area of the site identified clusters of flakes and knapping debris in the lower areas between the sandstone spurs as well as larger silcrete tools directly underneath the animal reliefs. Some of these tools presented abraded edges, possibly from prolonged contact with the soft and abrasive sandstone that constitutes the rock spurs. To test this hypothesis and in order to have a reference collection for further traceological analysis experiments were performed. Here we will present the results of these exploratory experiments conducted to classify traces from sandstone carving using silcrete tools. We will compare the traces from the experimental sample with the archaeological material in order to address the function of the tools found at the Camel site. The chaine opératoire of the experimental engraving tools, from raw material procurement, tool manufacture and use was conducted on site with locally available materials comparable to the archaeological specimens. Specific experimental variables including how the force was applied, in what direction the movement took place and the orientation of the stone tool during the experiment were also recorded. Three different time intervals were used to perform the activities and understand wear development during use. Macro and microscopic analysis of the experimental collection and of a sample of twelve artefacts was performed in order to assess if the ancient tools where used in the making of the camelid and equid reliefs at the site.

In underground engineering, such as geological CO2 sequestration, unconventional oil and gas exploration, and radioactive waste storage, permeability of rock is important to evaluate the potential CO2 storage capacity, improve oil and gas production, and prevent leakage of radioactive waste. In this study, hydrostatic stress tests and triaxial compression tests with gas permeability measurements were carried out on intact and damaged sandstone specimens. Three series of experiment were designed to evaluate the permeability evolution laws of sandstone under different testing conditions. They included triaxial seepage tests on intact specimens under different confining pressures, triaxial seepage tests on damaged specimens with different extents of damage, and hydrostatic seepage tests on damaged specimens under increasing and decreasing gas pressures. Based on the experimental results, the effects of effective confining pressure, extent of damage and increasing and decreasing gas pressure on permeability of sandstone were investigated. It shows that the permeability of the intact sandstone specimens first decreased and then increased, followed by a constant value with increase in axial strain. The permeability of the sandstone specimens was observed to decrease with increase in effective confining pressure. The extent of damage affects the permeability evolution, but does not influence the failure patterns of damaged sandstone. As the gas pressure increased, the permeability of the damaged sandstone specimen increased. Under the same gas pressure condition, the permeability during the decreasing process is generally higher than that during the increasing process. These experiments are expected to enhance our understanding of seepage behavior in underground rock masses.

Stimulation of the sandstone reservoir requires a mixture of acids such as mud acid, which assist in enlarging the microscopic paths by dissolving the siliceous fines or clays near the well-bore region. As a result, the formation permeability and porosity can be enhanced. In deeper wells, the temperature exceeds 200 °F, at these temperature ranges, problems can arise. For example, the use of mud acid mixtures can lead to issues like precipitations, corrosion, early consumption of acids, leading to lesser acid efficiency. In this study, the core flooding apparatus was used for acidizing experiments, designed to dissolve minerals and to analyze the changes in petrophysical parameters such as porosity, permeability, and mineralogy. Conventional and tight sandstone core samples were acidized using different chelating acids such as Hydroxyethylethylenediaminetriacetic acid (HEDTA), Ethylenediaminetetraacetic acid (EDTA) and Glutamic acid (GLDA) at high-temperature conditions. Analytical studies (mineral mass, pore size distribution, topology, grain size distribution, and density distribution were conducted using Tescan Integrated Mineral Analysis (TIMA). The obtained results showed that chelating agent HEDTA created more pore spaces in the core samples and is effective in dissolving positive ions. Also, the permeability was observed to be doubled by its application which could be effective in alteration of pore topology of the sandstone cores.

Reservoir characterization carried out for the quantitative representation of a reservoir leads to effectively managing the hydrocarbon reservoir. There have been few attempts made to characterize the reservoir and assess the potential of a reservoir for the sweet spots using seismic, geomechanical, and petrophysical characteristics where a combination of seismic and petrophysical characters is often ignored given the complexity of such integration. To the best of our knowledge, none of the studies have provided overall reservoir characterization workflows using the combination of petrophysical and geomechanical attributes for sweet spot detection. This study aims to adopt a new color transformation overlay scheme to assess the potential of reservoirs by identifying the sweet spots that can guide to propose a location for a new well. The core scale measurements and well log interpretation were used to determine the petrophysical and geomechanical properties of a highly complex sandstone reservoir which were used as the input to build a 3D reservoir model. The results obtained indicated that predicting the distribution of sweet spots is an effective scheme for well-planning and field development in the region. Four sweet spots are identified in the studied reservoir based on the color transformation overlay approach which has heterogeneous continuity behavior in vertical and horizontal directions. The identification of sweet spots based on top view is not enough for the complete understanding of spreading in all directions. Cross-sectional analysis of the color transformation overlay model revealed that there is a sweet spot near Well-E in west which has ideal reservoir potential and place to consider another proposed well.

The macroscopic engineering properties of sandstone are dominated primarily by mineral features in a microscopic scale. This study will investigate the microscopic physical and mechanical properties of the main minerals (quartz, K-feldspar, Na-feldspar and kaolinite) in Yungang Grottoes sandstone, using the molecular mechanics and the molecular dynamics simulations. The microscopic physical properties were represented by density and volume. The microscopic mechanical properties were represented by Young’s modulus and Poisson’s ratio. The microscopic mechanical properties of the minerals in various directions were then explored. The influences of water molecules and the surrounding temperature on the microscopic physical and mechanical properties of the minerals were furthermore investigated. It is found that the differences in the microscopic densities between the simulated results and those from the open data set are, respectively, 0.37%, 1.15% and 9.16%, for the quartz, Na-feldspar and kaolinite cells; the microscopic mechanical properties of various minerals have a significant anisotropy; the Young’s modulus of halloysite decreases by 75.86% compared with that of kaolinite; as the water molecule number increased from 0 to 5, the Young’s moduli of K-feldspar, Na-feldspar and kaolinite cells decreases by 31.31%, 55.05% and 42.60%, respectively; for each mineral, as the temperature increases from 243.15 to 303.15 K under one atmospheric pressure, the volume increases and the density decreases. Those results may have a theoretical significance for the analysis of microscopic mechanism of hydration in the Yungang Grottoes sandstone.

In rock mechanics, the dilatancy point is always occurring before rock failure during loading process. Water content plays a significant role in the rock physiomechanical properties, which also impact the rock dilatancy point under loading process. This dilatancy point significantly plays a warning role in the rock engineering structures stability. Therefore, it is essential to predict the rock dilatancy point under different water contents to get an early warning for effective monitoring of engineering projects. This study investigates the water contents effects on sandstone dilatancy point under loading in the presence of infrared radiation (IR). Furthermore, this IR was used for the first time as an input parameter for different artificial intelligence (AI) techniques to predict the dilatancy point in the stress-strain curve. The experimental findings show that the stress range in stress-strain curve stages (crack closure and unstable crack propagation) increases with water content. However, this range for deformation and stable crack propagation stages decreases with water content. The dilatancy stress, crack initiation stress, and elastic modulus are negatively linearly correlated, while peak stress and stress level are negatively quadraticaly correlated with a high (R2). The absolute strain energy rate, which gives a sudden increase at the point of dilatancy, is used as the dilatancy point index. The stress level is 0.86 σmax at the dilatancy point for dry rock and decreases with water content. This index is predicted from IR data using three computing techniques: artificial neural network (ANN), random forest regression (RFR), and k-nearest neighbor (KNN). The performance of all techniques was evaluated using R2 and root-means-square error (RMSE). The results of the predicted models show satisfactory performances for all, but KNN is remarkable. The research findings will be helpful and provide guidelines about underground engineering project stability evaluation in water environments. © 2022 Liqiang Ma et al. All Rights Reserved. This paper was supported by the National Natural Science Foundation of China (51874280) and the Fundamental Research Funds for the Central Universities (2021ZDPY0211).

Mineral segmentation is an equally important and difficult task in the quantification of mineral composition. Difficulties come from the process of determining boundaries of distinctive mineral grains necessary for further analysis and mineral identification. Done by hand, the task is very time-consuming and higher accuracies are burdened with the possible human fatigue factor. The presented method is a fully automated solution to the problem that uses a superpixel approach and feature-based merging. The method is validated by comparison with the manual approach. Analyzed data consist of photos taken by a Nikon Eclipse LV100N POL polarizing microscope at 200× magnification, in transmitted light, with crossed polarizers. Images are first prepared by Gaussian filter and meanshift operations, then the initial segmentation is provided by the superpixel algorithm. Oversegmentation is resolved by feature-based merging. The last step consists of counting the individual grain boundaries and preparing the results as easily readable visual data.

With the increasing demand for resource consumption, the mining depths gradually increase, resulting in increases of temperature at tens or even hundreds of degrees. High temperature could damage to interior structures and alter the mechanical properties of rock mass. Therefore, studying the effects of temperature on dynamic mechanical properties and failure behaviors are of great significance for deep resources exploitation. In this study, to study the effects of high temperature treatment on the strength and failure behavior of typical sandstones, specimens were prepared and heated to different degrees. The longitudinal wave velocity, volume, and density of specimens before and after high-temperature treatment were examined. Then, the Thomas Hopkinson (SHPB) test was conducted on specimens with different air pressures and the dynamic stress-strain curve, peak stress, peak strain, and other dynamic characteristics were obtained. The variations regulations and failure behavior of sandstone under the effects of high-temperature treatments and different impact loads were analyzed and discussed from the aspects of stress-strain, peak strength, and peak strain. It was observed that with the increase of heating temperature, the average density, average wave velocity, peak strength, and average elastic modulus of the sandstone specimens all showed a decreasing trend and the highest decreasing rated occurred at the temperature between 600 °C and 800 °C. The obtained results provided a certain theoretical basis for deep mine exploitation, especially for mines with high temperature.

Over the past tens of years, glacial sandstone erratics variably enriched in Zn, Pb and Cu have been collected from the coast south of Raahe, but their source has remained ambiguous. In these non-metamorphosed and non-deformed boulders, detrital grains of quartz and minor feldspar are cemented by calcium carbonate, which is partly or wholly replaced by ore minerals, including sphalerite, galena, pyrite, marcasite, and chalcopyrite. Analyzed mineralized boulders have yielded total base metals contents between 1 and 19 wt.%. The FeS content in sphalerite is low and variable, ranging commonly between 0.5 and 15 mol.%, which is in harmony with its coexistence with pyrite. Galena shows very radiogenic Pb isotope compositions, with 206Pb/204Pb and 207Pb/204Pb falling in the ranges of 20.55−21.06 and 15.90−15.94, respectively. These compositions are similar to those measured for the Laisvall MVT Pb-Zn deposit in the Swedish Caledonides, being consistent with a similar Ordovician age of ore formation. However, S isotope analyses yielded heterogeneous compositions, with pyrite showing mostly negative δ34S values from −15.6 to −7.6‰, indicating partly a strong bacteriogenic signature, which are distinctly different from the generally heavy sulfur isotope compositions (avg. δ34S +24‰) reported from the Laisvall-type deposits, pointing to a different source of sulfur. These results together with some mineralogical differences (relatively abundant chalcopyrite, scarcity of fluorite and barite) suggest that the boulders were not derived from the eastern front of the Caledonian orogen but their provenance occurs much closer, potentially in a so-far-undiscovered occurrence of stratabound base metal mineralization in Cambrian sediments under the Bothnia Bay. The direction of transportation of the sandstone boulders can be estimated using associated carbonate and mafic metavolcanite boulders whose carbon isotope and major and trace element compositions, respectively, indicate their derivations from the Kalix area, northern Sweden.

The main building material in the past was stone. Geological composition influenced the choice and type of building stone, which was used for the construction of the buildings. In eastern Slovakia sandstone was used in large quantities for its good compressive properties, good workability and aesthetic appearance. Sandstones were used for decorative but mainly construction purposes. The most common problem in historical stone structures is missing waterproofing insulation. Transmission and storage parameters of heat and water of historical materials are needed to assess the moisture condition of buildings and to correctly design measures. In this article are presented researches of sandstones properties abroad and locations of selected sandstones of eastern Slovakia, which were used for construction of historical buildings.

In underground engineering, reinforcement is a necessary means to ensure the stability of surrounding rock. Due to the stress redistribution caused by excavation disturbances, the reinforced rock mass is frequently subjected to loading and unloading, and its mechanical properties change accordingly. Based on the above engineering practice, using pasted circular CFRP, an approximate simulation of the rock reinforcement effect of bolt and shotcrete support was performed. Triaxial cyclic loading and unloading tests of reinforced sandstone were carried out, and the influence of different reinforcement schemes on the mechanical properties was compared and analyzed. Furthermore, the strengthening mechanism, damage evolution, and energy transformation mechanism of CFRP are discussed. The results showed that the peak strength increased about 14.2% and 23.8% with the two reinforced schemes, and the residual strength increased about 27.3% and 52.8% with the increase in the area reinforced by CFRP. Under the same confining pressure and strain conditions, the characteristic energy density and elastic energy ratio increased with an increase in the reinforcement area, but the damage variable decreased. It is proved that CFRP can improve energy absorption efficiency, enhance the energy storage limit, and reduce dissipation efficiency. By inhibiting the propagation of internal fissures and limiting the energy dissipation during fractures, the rock mass can be restrained and strengthened.

The Upper Pannonian (UP) sandstone formation has been utilised for thermal water production in Hungary for several decades. Although sustainable utilisation requires the reinjection of cooled geothermal brine into the host rock, only a fraction of the used water is reinjected in the country. UP sandstone formation is reported to exhibit low injectivity, making reinjection challenging, and its petrophysical properties are poorly known, which increases uncertainty in designing operational parameters. The goal of the study is to provide experimental data and to gain a better understanding of formation characteristics that control injectivity and productivity issues in Upper Pannonian sandstone layers. Petrographical characterisation and petrophysical laboratory experiments are conducted on cores retrieved from two wells drilled in the framework of an R&D project at the depth of between 1750 m and 2000 m. The experiments, such as grain density, porosity, permeability, and ultrasonic velocity, as well as thin section, grain size distribution, XRD, and SEM analyses, are used to determine Petrophysical Rock Types (PRT) that share distinct hydraulic (flow zone indicator, FZI) and petrophysical characteristics. These are used to identify well intervals with lower potential for injectivity issues. The results imply that fines migration due to formation erosion is one of the key processes that must be better understood and controlled in order to mitigate injectivity issues at the study area. Future investigation should include numerical and experimental characterisation of formation damage, including water–rock interaction tests, critical flow velocity measurements, and fines migration analysis under reservoir conditions.

Due to the location of the Yungang Grottoes, freeze–thaw cycles contribute significantly to the degradation of the mechanical properties of the sandstone. The factors influencing the freeze–thaw cycle are classified into two categories: external environmental conditions and the inherent properties of the rock itself. Since the parameters of rock properties are inherent to each rock, the effect of rock properties on freeze–thaw degradation cannot be investigated by the control variates method. An adaptive multi-output gradient boosting decision trees (AMGBDT) algorithm is proposed to fit nonlinear relationships between mechanical properties and physical factors. The hyperparameters in the GBDT algorithm are set as variables, and the Sequential quadratic programming (SQP) algorithm is applied to solve the hyperparameter optimization, which means finding the maximum Score. The case study illustrates that the AMGBDT algorithm can precisely determine the effect of each independent factor on the output. The patterns of mechanical properties are similar when the number of freeze–thaw cycles and porosity are used as variables separately and when both are used simultaneously. The uniaxial compressive strength decay rate is positively correlated with the number of freeze–thaw cycles and porosity. The modulus of elasticity is negatively correlated with the number of freeze–thaw cycles and porosity. The results show that the number of freeze–thaw cycles is the main factor influencing the freeze–thaw cycling action, and the porosity is minor. In addition, the fitting accuracy of the AMGBDT algorithm is generally higher than neural networks (NN) and random forests (RF). Studying the influence of porosity and other rock properties on the freeze–thaw cycle will help to understand the failure mechanism of rock freeze–thaw cycles.

This research aims to shed light on an experimental study to evaluate acrylic, silicone materials and nano additives used to consolidate the sandstone with an application to a statue in Sphinxes Avenue at Luxor, Egypt. Samples of sandstone were taken from one of the statues of Sphinxes Avenue to determine their com-ponents and current status by X-Ray Diffraction analysis (XRD), scanning electron microscope's examination (SEM) and EDAX elemental analysis to choose the standard sample which should be very close to the sand-stone of the statue. Six materials were selected to the experimental study; two of them belong to acrylic group (Addicon and Paraloid B72), Kemtekt and Wacker (OH 100) which are silicone materials, Nano silica which is an additive material to Paraloid B72 and Wacker (OH 100). The selection of the best material by the evaluation of visual examination, measuring physical properties such as density, porosity and water absorption as well as mechanical properties (compressive strength) of standard and treated samples in addition to examination by scanning electron microscope (SEM). The treated samples were subjected to artificial aging (thermal and salt weathering) and the results were also evaluated by previous methods before weathering, the best consolidation material is Wacker (OH 100)+ Nano silica which achieved the best results comparing to the other materials in physical and mechanical properties and scanning electron microscope 's examination. It's found that high temperatures have good effect on some hydrophobic materials like Siloxanes which make them Superhydrophobic, also nanoparticles improve the performance of some consolidation materials like Wacker (OH 100) and Paraloid B72.

Although quartz crystallinity index (QCI) was developed more than four decades ago, it remains a relatively new tool used in provenance studies. This study examines QCI values of Arabian sands (Quaternary sands from Nafud, Dahna, and AlRub'AlKhali deserts), and Arabian sandstones (Paleozoic and Mesozoic sandstones from northern and central Arabia). QCI values of sandstones range from 8.2 to 9.8. For Quaternary occurrences, QCI values of Nafud sands range from 7.4 to 9.5, Dahna sands range from 7.9 to 9.4, and AlRub'AlKhali sands range from 8.8 to 9.4. The data confirm that Arabian sands are derived mainly from early Paleozoic sandstones, with subordinate contributions from late Paleozoic and Mesozoic sandstones. They also highlight the role that sediment homogenization plays in narrowing QCI values of AlRub'AlKhali sands. Highest and lowest QCI values raise questions about the role of chert in controlling of QCI values of Arabian sands and sandstones. Arabian sandstones of Late Ordovician, Late Devonian, Late Permian, Late Triassic, and Cretaceous age possess the highest QCI values (>9.5). These time intervals coincide with lower abundances of siliceous sponges, and therefore fewer potential sources of chertification/silicification. Cambrian sandstones and Quaternary sands possess the lowest QCI values (

The stress–strain characteristics of compressed sandstone are affected by many different factors. The study on the evolution law of the strain field of compressed sandstone is of great significance for disaster prediction and warning during the construction process of geotechnical engineering. In this paper, uniaxial compression tests of red sandstone of 100 mm height and 50 mm length and width were carried out under the conditions of (1) different loading rates, (2) different particle sizes and (3) different inclination angles of prefabricated fractures. Stress–strain curves corresponding to different conditions were presented, the evolution of strain field on the sample surfaces was analyzed with the help of Digital Image Correlation technology and the relationship between the stress–strain curves and the strain field was preliminarily given. This study may be helpful for obtaining a deeper understanding of the deformation and failure mechanism of sandstone under uniaxial compression.

Thin sandstone is a widely used building material; however, its compressive behavior is not well understood. Four groups of cylinders were manufactured in a factory to investigate the uniaxial compressive behavior of red sandstone. Uniaxial compression tests were performed to determine the compressive behavior and failure mode of the specimens. The geometry of the stress–strain diagram varied among the four groups. The critical strain generally increased with a decrease in the height of the cylinder, whereas the compressive strength exhibited an inverse trend. The experimental diagrams were normalized with the peak stress and corresponding critical strain to represent the stress–strain diagram of each group of cylinders. A formula consisting of two parabolas was employed for regression to obtain a representative mathematical expression of the diagram. The correlations between porosity, compressive strength, and elastic modulus were evaluated based on empirical expressions. Normalized strength was employed to evaluate the size effect on the diameter and length–diameter ratio (L/D) of the cylinder; the latter provided a better prediction of the experimental results than the former. A new expression in terms of L/D was proposed based on the regression analysis of the experimental results. This study is beneficial for the engineering application of sandstone as a construction material.

A constitutive model able to describe both tensile damage and plastic deformation under confinement is a prerequisite to numerically simulate the behaviour of sandstone rock under an impact loading induced in a percussive drilling process. Therefore, model identification under both tensile and high confinement states is needed. In the present work, an experimental investigation was carried out in order to determine the mechanical properties of a sandstone rock for the purpose of advanced constitutive model identification. Different testing methods were used in quasistatic and dynamic loading regimes. This first part of the study is dedicated to static experiments, whereby three-point bend tests were first performed to evaluate the quasistatic tensile strength of the rock and its distribution by employing the Weibull statistics. Secondly, direct compression tests were conducted to evaluate the stiffness and strength in an unconfined condition. Afterwards, quasioedometric compression (QOC) tests were carried out in order to obtain the deviatoric and volumetric behaviours of the material as a function of the hydrostatic pressure (up to 375 MPa). In these QOC tests, the metallic confinement cell was instrumented with strain gauges to deduce the state of the stress and strain within the sample. A linear volumetric response along with a continuous increase of strength with the level of hydrostatic pressure was observed. This experimental work points out that, under unconfined loading (three-point bending and uniaxial compression), pre-existing structural defects play a major role leading to a highly scattered behaviour in terms of sample stiffness and ultimate applied load. On the other hand, under high confinement levels (QOC tests), beyond the nonlinear response of the curve foot, the influence from structural defects was observed to be small.

Due to the complexity of the sedimentary and diagenetic processes, natural rocks generally exhibit strong heterogeneity in mineral composition, physicochemical properties, and pore structure. Currently, 3D printed (3DP) rock analogs fabricated from sandy materials (silica sand) are widely applied to study the petrophysical and geomechanical characteristics of reservoir rocks, which provides an alternative and novel approach for laboratory tests to calibrate the environmental uncertainties, resolve up-scaling issues, and manufacture customized rock specimens with consistent structure and controllable petrophysical properties in a repeatable fashion. In this paper, silica sand with various grain sizes (GS) and Furan resin were used to fabricate rock analogs with different layer thicknesses (LTs) using the binder-jetting 3DP technique. A comprehensive experimental study was conducted on 3DP rock analogs, including helium porosity measurement, micro-CT scanning, SEM, and uniaxial compression. The results indicate that the LT and GS have a great influence on the physical properties, compression strength, and failure behavior of 3DP rock analogs. The porosity decreases (the difference is 7.09%) with the decrease in the LT, while the density and peak strength increase (showing a difference of 0.12 g/cm3 and 5.67 MPa). The specimens printed at the 200 and 300 μm LT mainly experience tensile shear destruction with brittle failure characteristics. The ductility of the 3DP rocks increases with the printing LT. The higher the content of the coarse grain (CG), the larger the density and the lower the porosity of the specimens (showing a difference of 0.16 g/cm3 and 8.8%). The largest peak compression strength with a mean value of 8.53 MPa was recorded in the specimens printed with CG (i.e., 100% CG), and the peak strength experiences a decrease with the increment in the content percentage of the fine grain (FG) (showing a difference of 2.01 MPa). The presented work helps to clarify the controlling factors of the printing process and materials characteristics on the physical and mechanical properties of the 3DP rock analogs, and allows for providing customizable rock analogs with more controllable properties and printing schemes for laboratory tests.

In order to explore the mechanical response characteristics of fractured sandstone under true triaxial different medium principal stresses, matdem particle flow software was used to study the mechanical response characteristics, fracture mechanism and damage evolution characteristics of sandstone specimens under the conditions of 30 MPa, 40 MPa and 50 MPa respectively. The simulation results are verified by true triaxial test. The results show that under true triaxial stress, the increase of medium principal stress is beneficial to increase the strength of sandstone. The fracture degree of the specimen increases with the increase of the intermediate principal stress, and finally the interlacing macroscopic cracks are formed. When the intermediate principal stress is perpendicular to the fracture strike, the fracture mode of sandstone is that the macroscopic fracture plane is perpendicular to the fracture strike, and the fracture mechanism of sandstone under true triaxial compression is mainly shear failure, accompanied by tensile failure. With the increasing of the intermediate principal stress, the fractal dimension of the fracture of sandstone specimen increases significantly and the degree of fracture deepens. Combined with the true triaxial test results, the rationality of particle flow simulation test is proved.

Mining-induced hydromechanical behavior of sandstone is critical to mining safety and disaster prevention. To investigate the evolution behavior of the mechanical and permeability properties of sandstone, mining-induced stress was imitated by increasing axial stress and decreasing confining stress, and a set of hydromechanical experiments were further performed, incorporating the effect of in situ stress, pore pressure, and mining stress. The results show the similar variation tendencies of the deformation and permeability of sandstone under different loading paths of in situ stress and pore pressure. Most sandstone samples maintain a compression state for the peak stress condition. The failure mode evolved from shear failure to shear–tension failure with the increase in in situ stress. The stress-relief effect significantly effects the permeability, since the permeability of sandstone increases exponentially with decreasing effective confining stress. The growth rate of permeability in Stage II is significantly greater than that in Stage I. One order of magnitude of permeability was presented at the peak stress situation. A fitting exponential model based on the alteration of effective confining stress was proposed to describe the permeability evolution dominated by the stress-relief effect, and the discovered permeability model can accurately describe the experimental results. The research results provide significant guidance for understanding the hydromechanical behavior and water hazard prevention for underground coal mines.

The tunnels in present-day cities are experiencing varying degrees of loading conditions ranging from static to extreme loading. Therefore, the stability of underground tunnels needs to be analyzed and understood for safer and strengthened design. The present study was conducted to simulate the impact loading conditions due to a missile traveling at a velocity of 5 Mach for different rock tunnels. The nonlinear continuum finite element analysis has been carried out through Abaqus and Explicit. The four different types of sandstones considered in the present study include Kota, Jamrani, Singrauli, and Jhingurda sandstones. An elastoplastic Mohr–Coulomb constitutive material model has been considered to model the behavior of rock surrounding the tunnel opening. The tunnel has an opening of 7 m in diameter (d), and 50 m in height and breadth, with 50 m of longitudinal length. The deformation and stress in the rock and the damage to the concrete lining have been compared in different cases. The Concrete–Damage–Plasticity (CDP) model and the Johnson–Cook model were considered for modelling of the RC lining and steel reinforcement. It was concluded that Jhingurda sandstone has maximum deformations due to impacts caused by missiles.

Funder: bp International Centre for Advanced Materials (bp-ICAM), Artificially bio-cemented sands treated with microbially induced calcite precipitation are weakly cemented rocks representing intermediate materials between locked and carbonate sands. Variations in cementation significantly affect the strength of sample, particularly tensile stregth. The modes of fracture and the surface characteristics resulting from the indirect tensile strength tests (Brazilian tests) are strongly correlated with the specimen strength and consequently the degree of cementation. This study examines the tensile strength of bio-cemented fine and coarse sands (average particle diameter 0.18 and 1.82 mm, respectively) and investigates failure modes by recording fracture evolution at both sides of specimen and surface characteristics of the reconstructed surfaces. The dimensionless slope parameter Z2 provided the best fit with respect to tensile strength while the power spectral density was a good indicator of surface anisotropy. Finally, wavelet decomposition allowed for comparison of fracture surface characteristics of the two sands ignoring the grain size effects.

X-ray micro-tomography combined with a high-pressure high-temperature flow apparatus and advanced image analysis techniques were used to image and study fluid distribution, wetting states and oil recovery during low salinity waterflooding (LSW) in a complex carbonate rock at subsurface conditions. The sample, aged with crude oil, was flooded with low salinity brine with a series of increasing flow rates, eventually recovering 85% of the oil initially in place in the resolved porosity. The pore and throat occupancy analysis revealed a change in fluid distribution in the pore space for different injection rates. Low salinity brine initially invaded large pores, consistent with displacement in an oil-wet rock. However, as more brine was injected, a redistribution of fluids was observed; smaller pores and throats were invaded by brine and the displaced oil moved into larger pore elements. Furthermore, in situ contact angles and curvatures of oil–brine interfaces were measured to characterize wettability changes within the pore space and calculate capillary pressure. Contact angles, mean curvatures and capillary pressures all showed a shift from weakly oil-wet towards a mixed-wet state as more pore volumes of low salinity brine were injected into the sample. Overall, this study establishes a methodology to characterize and quantify wettability changes at the pore scale which appears to be the dominant mechanism for oil recovery by LSW.

Since prehistoric times stones have been widely employed in the construction of historic buildings, floors, and claddings in rural and urban areas. Among the Italian natural stones, the sandstone belonging to the Gorgoglione Formation, known as the Gorgoglione Stone, quarried and worked near the homonymous village in Basilicata (Southern Italy), is usually used as a building material. The Gorgoglione Stone consists of well-cemented turbidite sandstones deposited in a Middle-Upper Miocene thrust-top basin unconformably resting on the external nappes of the Southern Apennine thrust belt. In the Gorgoglione area, it can be observed in either numerous natural outcrops or quarries. This study aims to highlight the geological peculiarities of the Gorgoglione Stone and, in particular, it is focused on its mechanical characterization for assessing the most effective use when employed in construction, such as public and civil buildings, road construction, paving, and small works of art. Based on the experimental results, obtained by samples collected from different quarries, axial stress-strain curves have been plotted, whose analysis has delivered the deformation behavior and the strength characteristics of the stone. The elastic modulus, uniaxial compressive strength, and axial strain at stress peak have been estimated for several specimens. The measured values are typically of a medium-high-strength sandstone. The tested specimens of sandstone exhibit a typical behavior of an elastic-brittle rock, characterized by a linear path and a failure typically of axial splitting. With regard to the results of the physical tests, they showed that the analyzed sandstone is characterized by quite low density and by medium-high porosity and water absorption.

A multidisciplinary integrated approach for the study of heterogeneous rock masses is presented herein with the aim of providing a characterization of one of the widest flysch formations of northeastern Sicily. The Capo d'Orlando Flysch is indeed affected by a geotechnical heterogeneity arising from the alternation of sandstone banks and siltstone layers occurring in different proportions and showing peculiar features. This is the main responsible of the uneven mechanical strength offered by these different lithological compartments and deserves an in-depth study. To this purpose, an integrated sedimentological-geomechanical study is the focus of this research, which was initially carried out through rock mass surveys aimed at recognizing the different facies associations and their distribution along selected outcrops. Sedimentological logs were followed by rock mass geomechanical surveys for the assessment of the quality of the rock and its discontinuities. All these elements concurred in the definition of the Geological Strength Index, which is preparatory for the estimation of the main mechanical properties of the rock mass through the Hoek and Brown failure criterion. Results show that the lithological compartments occurring within flysch rock masses strongly condition their mechanical attitude. In fact, sandstone portions behave as massive/fractured rock mass characterized by specific geomechanical properties, which are lowered by the presence of siltstone layers. For this reason, the definition of the facies associations (F.A.) affecting the rock mass, along with their geomechanical characterization, is a useful integrated activity to avoid overestimating or underestimating the mechanical attitude of flysch rock masses, especially when engineering geological works have to be designed.

The present article focuses on the study of different physical-mechanical parameters; it presents the results of a preliminary investigation aimed at experimental characterization. To simulate the mechanical behavior of the rock, a reference material needs to be chosen. The reference material selected is Sandstone, which is commonly used in this field of study. The behavior of sandstone from the region of Hassi Messaoud, which is well known for its petroleum operations, deals mainly with different mechanical sandstone properties and their varying strengths. The relationships between different depths and both of the mechanical sandstone properties were evaluated. As a result, useful relationships were found for different depths and the following properties: uniaxial compressive and triaxial test, Young's modulus and Poisson ratio.

International audience; The aim of this collection is to record a snapshot of our current state of understanding of the impact of fluids on the evolution and monitorability of subsurface rock formations during anthropogenic fluid injection/withdrawal operations, accounting for scale and frequency effects. In this introduction we provide a summary of the key challenges and findings reported in these 23 articles. This suite of articles addresses a variety of issues related to the impact of fluids on subsurface rocks, which can be grouped in three themes: (i) impact of fluids on wave velocity and attenuation/dispersion (five articles); (ii) fluids, fractures, and seismicity (nine articles); and (iii) dynamic fluid injection and substitution (nine articles).

The upper Beetaloo Sub-basin of the McArthur Basin, Northern Territory, Australia, records over 500 myr of tectonic history of the North Australian Craton from c. 1.45 to 0.9 Ga. The basin sequences include shallow-water clastic sedimentary rocks that preserve the oldest global commercial hydrocarbon reserves. New detrital zircon U–Pb age and Lu–Hf isotopes, compiled with published data, provide constraints on the basin provenance and reveal the dynamic tectonic evolution of Mesoproterozoic northern Australia. Data from the oldest formation examined, the c. 1.4 Ga Bessie Creek Sandstone, suggest provenance from (present-day) eastern sources (e.g. the Mount Isa Province and the palinspastically adjacent Curnamona and Georgetown provinces) with considerable spatial heterogeneity. These eastern source regions are interpreted as uplifted rift-shoulder highs, formed by contemporaneous extension between Proterozoic Australia and Laurentia. Progressively younger formations (the Velkerri Formation, the Moroak Sandstone and the Kyalla Formation) demonstrate a rapid swamping of the basin by detritus from southerly sources (e.g. the Arunta Region) that occurred at c. 1.4–1.3 Ga. This is particularly characterized by the up-section reduction of c. 1.6–1.5 Ga detrital zircon grains. This change in provenance is interpreted to relate to closure of an ocean basin during the period 1.35–1.25 Ga, which resulted in uplift of the southern margin of the North Australia Craton. Three ungrouped latest Mesoproterozoic to Neoproterozoic sedimentary units, the lower and upper Jamison sandstone and the Hayfield mudstone, were deposited after the emplacement of the Warakurna Large Igneous Province and are sourced from the Musgrave Province. Detrital zircon U–Pb and Hf isotope affinities between the lower and upper Jamison sandstone and the Hayfield mudstone and the latest Mesoproterozoic to early Neoproterozoic successions along the eastern margin of the North China Craton suggest that they share a similar provenance. This supports correlations between the Mesoproterozoic of the North China Yanshan Basin and the greater McArthur Basin. Supplementary material: Sample descriptions, details of data and concordia plots are available at https://doi.org/10.6084/m9.figshare.c.4444790

Pore pressure reduction in sandstone reservoirs generally leads to small elastic plus inelastic strains. These small strains (0.1%–1.0% in total) may lead to surface subsidence and induced seismicity. In current geomechanical models, the inelastic component is usually neglected, though its contribution to stress-strain behavior is poorly constrained. To help bridge this gap, we performed deviatoric and hydrostatic stress cycling experiments on Slochteren sandstone samples from the seismogenic Groningen gas field in the Netherlands. We explored in situ conditions of temperature (T = 100 °C) and pore fluid chemistry, porosities of 13% to 26% and effective confining pressures (≤320 MPa) and differential stresses (≤135 MPa) covering and exceeding those relevant to producing fields. We show that at all stages of deformation, including those relevant to producing reservoirs, 30%–50% of the total strain measured is inelastic. Microstructural observations suggest that inelastic deformation is largely accommodated by intergranular displacements at small strains of 0.5%–1.0%, with intragranular cracking becoming increasingly important toward higher strains. The small inelastic strains relevant for reservoir compaction can be described by an isotropic, Cam-clay plasticity model. Applying this model to the depleting Groningen gas field, we show that the in situ horizontal stress evolution is better represented by taking into account combined elastic and inelastic deformation than it is by representing the total deformation behavior using poroelasticity (up to 40% difference). Therefore, inclusion of the inelastic contribution to reservoir compaction has a key role to play in future geomechanical modelling of induced subsidence and seismicity.

Lefke stone is a sandstone that has been widely used in mosques, madrasas, churches, and houses as building stone. The geological features and engineering properties of Lefke stone outcropped in the southern part of Osmaneli/Bilecik were investigated in field and laboratory studies. Samples acquired during the fieldwork were tested to determine the physical, mechanical, durability, and hygrothermal properties in the laboratory. The mean physico-mechanical properties of Lefke stone yielded apparent density of 2.38 g/cm3, specific gravity of 2.68 g/cm3, total porosity of 11.26%, 2.93% water absorption by weight, uniaxial compressive strength of 94 MPa, flexure strength of 11.45 MPa, a 3.90 MPa point load strength, 4.5–5 Mohs hardness, and field Schmidt hammer rebound value of 36. According to durability tests, Lefke stone is resistant to CaCl2 salt mist but has low resistance to SO2 aging. Salt crystals placed in the discontinuities of the rock caused slight crack growth. The stone’s resistance to crystallization of sodium sulphate salt is low, and an increase in the volume of salts crystallized in the rock results in low corner strengths. A capillary water-absorption value of 0.0016 kg/m2.h places Lefke stone into the category of very low water absorption capacity and permeability. The water vapor diffusion resistance factor (?) less than 1 indicates that the sandstone has high breathability. Its performance in historical buildings, field observations, and values obtained through laboratory tests confirm that Lefke sandstone can be used as a building stone. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature. 2017/16-024 -- The authors would like to thank the Istanbul Commerce University YAPKO unit for financing the project (grant number 2017/16-024), the Osmaneli (Bilecik) Municipality for logistical support during the fieldwork, and ITU-GAL and AKU-NSL laboratories. --

High‐speed neutron tomographies (1‐min acquisition) have been acquired during water invasion into air‐filled samples of both intact and deformed (ex situ) Vosges sandstone. Three‐dimensional volume images have been processed to detect and track the evolution of the waterfront and to calculate full‐field measurement of its speed of advance. The flow process correlates well with known rock properties and is especially sensitive to the distribution of the altered properties associated with observed localized deformation, which is independently characterized by Digital Volume Correlation of X‐ray tomographies acquired before and after the mechanical test. The successful results presented herein open the possibility of in situ analysis of the local evolution of hydraulic properties of rocks due to mechanical deformation. (Less)

CO2 storage capacity in saline aquifers can dramatically be reduced by pressure build up due to the CO2 injection process. In this paper, a novel optimisation strategy that maximises the CO2 storage capacity utilisation and net profits before tax is presented in a scenario of simultaneous CO2 injection and brine production to help control pressure build up and increase the effective storage capacity. The strategy is tested at the region surrounding the Forties and Nelson fields, assuming both as pure saline aquifer traps. The optimisation was performed considering constraints such that the CO2 plume distribution does not migrate outside the license boundaries, the fracture pressure is not reached within the reservoir, and the CO2 injection and brine production rates occur within feasible limits. The problem was first formulated analytically with the aid of surrogate models, and then optimised using the SIMPLEX and Generalized Reduced Gradient methods. Results for the Forties and Nelson fields show that by allowing five brine production wells producing up to 2.2 MMtonnes/year, the CO2 storage capacity increased between 112-145% compared to the case where no brine production is practiced.

The stress sensitivity of reservoir rocks has captured considerable attention in the field of oil and gas development. In this paper, nuclear magnetic resonance (NMR) was employed to measure the T2 spectra of sandstone samples from Dongfang X gas field under different confining pressures. According to T2 values, the pores in sandstone samples were divided into macropores (right peak of T2 spectra) and micropores (left peak of T2 spectra), and the stress sensitivity of macropores and micropores were discussed separately. The results show that the increase of net effective stress will lead to the pore deformation of rock samples, and the pore deformation characteristics of rocks in different blocks under different net effective stress can be effectively analyzed by the NMR. As the net effective pressure increases, the compression amplitudes of rock samples in different blocks are almost equal, indicating that the reservoirs in the Dongfang X gas field have good homogeneity. In addition, the study rocks have a weak stress sensitivity, the general stress sensitivity of micropores is stronger than that of macropores. For the samples with high permeability (over 80mD), the compression amplitudes of macropores and micropores are relatively small and close, and the porosity losses are almost the same.

Inspection of the deterioration of both natural outcrops and historical built stone facades reveals that patterns of disruption are not uniform, indicating the influence of material and environmental properties. Sandstones have a spatial variability in weathering response. For this reason, geostatistical techniques have been applied to studies of sandstone properties, mineralogical and structural, that influence susceptibility to decay. For this study, a comparative analysis of permeability data acquired from a ‘quarry fresh’ stone and a weathered sample is undertaken.The depositional processes that resulted in the formation of sandstone also create structures of spatial variation such as laminations or larger bedding planes within the material. Using geostatistical techniques, the permeability variance observed within ‘quarry fresh’ blocks of sandstone indicates the subsampling of larger geological structures when cut from the quarry face. Once blocks have been emplaced within a building they will be subjected to the increased stress of the urban environment. These conditions result in exacerbated weathering through processes such as salt and chemical weathering. Weathering can alter material properties such as permeability with the creation of a secondary permeability produced by the opening pores and alteration of pore connectivity. Through the application of geostatistics in the analysis of permeability data observed from the weathered block, variography reveals the presence of smaller scale structures. This suggests that alteration of the sandstone’s permeability has led to the creation of new weathering structures within the stone, overwriting the initial sedimentary structures.These weathering related structures will affect both the magnitude and spatial distribution of permeability within the weathered block. The interconnected pathways of permeability, created by past weathering, facilitate the migration of moisture and salts in solution through the substrate. This work has demonstrated that through a geostatistical approach with the application of co-kriging, these potential moisture pathways can be identified and visualised.

The research of pore and permeability characteristics of tight sandstone reservoirs in coal-measure is critical for coal-measure gas development. In this study, the pore systems of tight sandstones were studied based on low-field nuclear magnetic resonance (LF-NMR) data. The permeability of tight sandstones was obtained by the tester based on the pulse transient method. The permeability variation with the effective stress, grains, and pore characteristics was analyzed. The results show that the tight sandstone reservoirs in the coal-measure have low total porosity (2.80–4.14%), low effective porosity (0.51–1.56%), and low permeability (0.351 × 10−6–13.910 × 10−6 um2). LF-NMR T2 spectra of the testing sandstones show that the micropores are the most developed, but most of the micropores are immovable pores. The pore characteristics are significantly affected by the grain size of sandstones. The pore connectivity ranks from good to poor with decreasing sandstone particle size. The total porosity and effective porosity increase with the grain size. There is a near-linear negative relationship between permeability and effective stress when the effective stress is between 405 psi and 808 psi. The greater the number of movable pores and the larger the effective porosity, the bigger the permeability of the sandstone. The effective porosity of sandstones is a sensitive indicator for evaluating the permeability of tight sandstone reservoirs. The stress sensitivity coefficient of permeability (Ss) increases with the increase of the effective stress. The sandstone with lower permeability, smaller effective porosity, and finer grains has a higher Ss. The particle size of sandstone from coal-measure has a great influence on both permeability and Ss. The findings will provide a better understanding of the characterization of pore structure and permeability in the process the coal-measure gas extraction, which is useful for the efficient development of coal-measure gas.