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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]

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]

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]

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]

Aiming at the problem of formation damage of synthetic-based drilling fluid to tight sandstone reservoirs in Yongjin Oilfield, the reservoirs damage mechanism is explored through core analysis, reservoirs sensitivity evaluation and solid particles /filtrate invasion experiment. The protection methods of plugging the pore space in matrix and micro-fracture in low permeability reservoirs are put forward. Therefore, a synthetic-base drilling fluid(SD-4) with extremely lower damage for tight sandstone reservoirs in Yongjin Oilfield is developed by optimizing the temporary plugging agent formula and the high pressure plugging agent. The results show that the average pore throat radius of the reservoirs is 0.1 µm, and the target layer has small pore throats and poor permeability. The mineral composition is mainly quartz, with an average content of 36.37%, and the average content of clay is 7.22%. Stress sensitivity, solid particles /filtrate invasion are the main factors that damage the reservoirs. The SD-4 drilling fluid has good rheological properties before and after hot rolling at 140 °C/16 h, with a temperature resistance of up to 160 °C . It can resist contamination from 1.5% CaCl2, 12% NaCl, and 12% poor quality clay. The plugging pressure capacity of 200 ^m fracture can reach 6 MPa, and the permeability recovery value after core contamination experiment is more than 89%. Field applications have shown that SD-4 drilling fluid has stable performance and excellent protective properties for tight sandstone reservoirs. [ABSTRACT FROM AUTHOR]

We report on the pore size distribution and water retention of Beacon sandstone from Antarctica that harbours a cryptoendolithic community, predominantly lichens, just below the surface. We measured the pore size distribution, drying time and equilibrium relative humidity of sandstone samples that were colonized by lichens. The incremental pore volume distribution peaks at ~10 μm radius, but ~20% of the pore volume occurs for a radius < 0.02 μm. Water from snowmelt fills ~20% of the total pore volume. It takes ~4–5 days of evaporation to lose 90% of the water. As the rock loses water, the equilibrium relative humidity remains at 99% until an appreciable amount (80–90%) of the pore water is lost, after which the equilibrium relative humidity starts to decrease. The relative humidity remains at > 80% (68 h) long after the water content falls to < 98% (19 h) - the point at which liquid water is estimated no longer to be present. Lichens can remain active in air with high relative humidity (> 80%). Thus, the pore size distribution of the sandstone may play a role in explaining why lichens dominate these sandstones. [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]

This study proposes a new algorithm to enhance the accuracy of measuring internal deformation, identify and quantify damage in rocks using digital volume correlation (DVC). This algorithm integrates the multimesh refinement technology into a mechanically regularized global DVC algorithm that incorporates nodal force equilibrium. The accuracy of different DVC algorithms was assessed through scanning experiments on particles with different sizes and digital virtual fracture models. The internal deformation and damage patterns of red sandstone were quantitatively analyzed using in-situ CT scanning during uniaxial compression experiments. The results indicate that the introduction of the mechanical regularization term reduced the measurement uncertainty of the global DVC method by 1-2 orders of magnitude. For the red sandstone specimens, the new algorithm was able to identify sub-voxel microcracks with an aperture of 0.15 voxels, while reducing the computational cost by 85.15%. The damage quantification analysis revealed that newborn cracks with a maximum aperture of 0.32 voxels occurred in the specimen when the axial stress reached 50.58% of its peak value, and these microcracks evolved into voxel-scale fractures when the stress increased to 84.27% of the peak value. The new algorithm not only improves the computational efficiency, but also demonstrates a strong capability in identifying sub-voxel scale newborn cracks, providing a novel method for quantifying internal deformation and damage in rocks. [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]

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]

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]

Copyright of Petroleum Geology & Oilfield Development in Daqing is the property of Editorial Department of Petroleum Geology & Oilfield Development in Daqing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Petroleum Geology & Oilfield Development in Daqing is the property of Editorial Department of Petroleum Geology & Oilfield Development in Daqing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Objective] The hydraulic coupling behavior of rocks is closely related to the safety and stability of various rock engineering projects, including tunnel excavation, dam construction, oil and gas extraction, and rock slope stability analysis. The failure of rock masses and the evolution of permeability are part of a gradual dynamic process that is interrelated. On the one hand, the external load applied to the rock mass alters its microphysical, macrophysical, and mechanical properties, thereby affecting its permeability. On the other hand, changes in permeability can alter the distribution of permeability pressure, affect the effective stress within the rock mass, and consequently influence its stability. Additionally, the rock mass contains numerous fractures and fissures resulting from diagenetic processes, tectonic movements, and excavation disturbances, which complicates the assessment of the stability and reliability of the rock mass. Therefore, fully quantifying the mechanical properties and permeability evolution of prefabricated fractured rocks under hydraulic coupling is essential for minimizing damage in rock engineering projects. Despite recent advances in rock mechanics testing technology, measuring the microstructural changes in rocks under hydraulic mechanical loads during laboratory tests remains a challenge. [Methods] The rock failure process is closely associated with acoustic emission (AE), which is defined as transient elastic waves generated by the rapid release of energy within a material. Owing to its high sensitivity to crack initiation, propagation, and coalescence in loaded rocks, AE monitoring is a powerful tool for studying brittle rock failure. This technology has been widely applied in rock mechanics research and engineering applications. This article employs AE technology to conduct triaxial hydraulic coupling tests on intact sandstone and prefabricated fractured sandstone samples. The primary objective is to explore the micro-mechanisms of permeability evolution under hydraulic coupling loads through a series of laboratory tests. The strength and deformation characteristics, macroscopic failure modes, and permeability evolution patterns of prefabricated fractured sandstone under hydraulic coupling were examined. Additionally, the spatiotemporal evolution of AE events and the statistical distribution of fracture types during the failure process of prefabricated fractured sandstone were analyzed using AE technology. [Results] The experimental results indicate the following: 1) Antiwing cracks occur when the inclination angles of prefabricated cracks are 45°, 75°, and 90°, whereas specimens with other prefabricated crack inclination angles predominantly exhibit wing crack failures. 2) During the spatiotemporal evolution of AE events, the compression events resulting from the closure of cracks and pores during the initial compression stage represent the primary microscopic mechanism for the decrease in permeability. 3) The increase in permeability is mainly attributed to tensile and shear microcracks associated with volume expansion, whereas the decrease in permeability is caused by shear microcracks associated with volume compression and compression microcracks. [Conclusions] Under triaxial hydraulic coupling, the strength and deformation characteristics, macroscopic failure modes, and permeability of prefabricated fractured sandstone specimens are influenced by the inclination angle of the prefabricated fractures. The decrease in permeability mainly results from compression events that lead to fracture closure and pore collapse, whereas the increase in permeability is attributed to the continuous accumulation of tensile and shear events, which is also influenced by the inclination angle of pre-existing fractures. [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]

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]

Terrestrial sedimentary basins are influenced by rapid changes in the clay content, resulting in significant differences in the lateral sealing capacity (shale gouge ratio, SGR) of different parts of the fault. In the present study, we used a method of setting virtual wells and using seismic inversion data to accurately calculate the SGR of faults in strata composed of interbedded sandstone and mudstone calculate the clay content of the strata and to compensate for the low level of the actual well control. Optimal well spacing was determined based on the variable clay content of the formation. The planar variation of the fault throw was characterized via seismic interpretation. We also examined the lateral sealing of faults. The Putaohua oil layer in the S14 area of the Sanzhao Sag in the Songliao Basin was chosen as an case study. Based on the calculation of fault SGR values and the oil distribution, the evaluation criteria for the fault sealing capacity were determined, and the changes in the lateral sealing capacity of the faults were analyzed. This approach accurately estimates fault SGR values and predicts the effective oil-bearing area within the fault zone. It is also suitable for evaluating the lateral sealing of faults in strata composed of interbedded sandstone and mudstone. Our findings provide an in-depth understanding of the lateral sealing of faults and can aid in further research on petroleum distribution patterns. [ABSTRACT FROM AUTHOR]

The study of fracture propagation in heterogeneous shale is a crucial prerequisite for the investigation of heterogeneous cluster and perforation parameters optimization. In this paper, we conduct a physical simulation fracturing experiment on heterogeneous shale to investigate the effects of various influencing factors, such as shale bedding, near-wellbore fractures, lithological changes, and the presence of fractures surrounding the perforation hole, on fracture propagation law and morphology. Our research demonstrates that during shale fracturing, shear dislocation typically occurs between layers, resulting in the separation of different layer planes. The main fracture primarily propagates through layers in a stepped manner. The presence of sandstone in heterogeneous shale significantly impedes fracturing fractures, causing significant distortion and deviation. As the scale of natural fractures increases, it tends to cause the fracturing fracture to twist and change direction. The natural fractures network can also lead to the distortion of fracturing fractures, albeit to a lesser extent than large-scale natural fractures. The presence of micro fractures parallel to the perforation axis surrounding the perforation hole enhances the ability of the main fracturing fractures to pass through natural fractures. [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]

Low salinity Waterflooding (LSWF) is a proven EOR technique which has emerged in the last few decades. In this, the salinity of the injected water is reduced. Studies have unveiled that the LSWF can improve about 5–38% of oil recovery. This work aims to study the effectiveness of LSWF by modeling Sea waterflooding (SWF) and LSWF using a commercial reservoir simulator and justifying the proposed mechanisms responsible for the incremental oil recovery due to LSWF. A critical parametric study has been undertaken, which led us to conclude that LSWF is a cost-effective, and environment-friendly method that results in additional oil recovery for sandstone reservoirs. [ABSTRACT FROM AUTHOR]

Formation damage caused by organic contaminates is one of the most important issues that undermine well injectivity and productivity. Anionic surfactants are commonly used to mobilize the organic contaminates trapped by capillary forces. The electrostatic repulsion between anionic surfactant heads reduces the surfactant density at the oil-water interface, consequently reducing the interfacial efficiency. In this paper, a novel surfactant blend of anionic-cationic surfactants (Sa/c) was designed and showed much higher efficiency than traditional ones because of the strong electrostatic attraction between anionic and cationic surfactants. The oil-water interfacial tension (IFT) was reduced to 3 × 10−4 mN/m, and the viscosity of crude oil was reduced by 92%. In addition, the freezing point of the residual oil was decreased by 20.9%. Moreover, Sa/c altered the wettability and inhibited the clay swelling. Field applications were conducted in sandstone reservoirs at temperatures of about 120 °C and permeabilities below 10 mD. The average injection pressure drops were greater than 30%. The findings of this study can help for better understanding the advantages of Sa/c with high interfacial activity and revealed that formation damage caused by the organic contaminates in high temperature and low permeability sandstone reservoirs can be effectively remediated by this novel surfactant blend. [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]

This paper systematically investigates the dynamic mechanical response and fragment characteristics of sandstone with asymmetrical conjugate fissures subjected to preexisting static stress based on the split Hopkinson pressure bar apparatus. The cross-fissured sandstone exhibits significant variations in mechanical behavior when exposed to higher dynamic strain rates under identical static pre-stress. The cross-fissured sandstone with a higher dynamic strain rate is characterized by a greater coupled strength under the same static pre-stress; for a given dynamic load, the highest coupled strength occurs under the static pre-stress of 60% UCS. The failure mode of the cross-fissured sandstone is predominantly governed by the dynamic strain rate, independent of static pre-stress variations considered in this investigation. At lower dynamic strain rates, the specimens typically exhibit a mixed tensile-shear failure mode, characterized by the dominance of larger fragments in the broken specimens. In contrast, under high dynamic impacts, the sandstone tends to fail in a shear-dominated manner, resulting in smaller fragments with a more uniform size distribution. Furthermore, the study explores how varying dynamic strain rates and static pre-stress influence the fragment characteristics of the cross-fissured sandstone. Higher dynamic strain rates and increased static pre-stress generally lead to smaller mean fragment sizes. This phenomenon is quantitatively described by fitting fragment size distributions using the Generalized Extreme Value (GEV) distribution, revealing a decrease in the location parameter (μ) and an increase in fractal dimension. These metrics indicate that higher dynamic strain rates and static pre-stress result in sandstone specimens breaking into smaller fragments with a more homogeneous size distribution. These findings contribute to a deeper understanding of rock dynamics, with potential implications for engineering applications involving similar geological configuration under dynamic loading conditions. [ABSTRACT FROM AUTHOR]

Tight sandstone reservoirs have extremely low porosity and permeability. Bedding-parallel fractures (BPFs) contribute prominently to the storage and seepage capability. However, the distribution of BPFs is remarkably heterogeneous, impeding the prediction and modeling of sweet spots. BPFs are controlled fundamentally by laminations, which are widely distributed in lacustrine tight reservoirs and provide most weakness planes. Based on core and thin section data, BPFs of the upper Triassic Chang 7 tight oil reservoir are characterized microscopically. The lamination combination unit, which is defined by distinctive lamination assemblage and relatively stable lamination thickness and space, is utilized as a homogeneous unit to measure the density of lamination and related BPFs. The influence of laminations on BPFs is discussed further. Results show that most bedding-parallel fractures are unfilled, with apertures generally <40 μιτι, mainly <10 μιτι. Larger apertures correlate with low filling degrees. The distribution of BPFs is intricately controlled by lamination type, density, and thickness. (1) BPFs tend to develop along different types by a priority sequence which reflects their mechanical strength. The development degree of BPFs also depends on the mechanical contrast with adjacent laminations; (2) When controlled by a single type of lamination, the density of BPFs increases with lamination density under a turning point and then decreases; (3) BPFs prefer to develop along the thinner lamination and are usually inside it, while controlled by thick lamination, BPFs tend to extend along the edge. The change in the thickness of laminations leads to a change in the development position of BPFs, indicating that the position of the weak plane controls the development position of BPFs; (4) When multiple types of lamination coexist, the type and thickness of laminations jointly influence the development of BPFs. Plastic thin laminations are conducive to the development of BPFs, while brittle thick laminations are not conducive. When the thickness of the plastic lamination is close to or less than that of the brittle, the influence of lamination type dominates BPFs, while the thickness of the plastic laminations is much larger than the brittle, the influence of lamination thickness will dominate. [ABSTRACT FROM AUTHOR]

Fractures play a crucial role in tight sandstone gas reservoirs with low permeability and low effective porosity. If open, they not only significantly increase the permeability of the reservoir but also serve as channels connecting the storage space. Among numerous fracture identification methods, seismic data provide unique advantages for fracture identification owing to the provision of three-dimensional information between wells. How to accurately identify the development of fractures in geological bodies between wells using seismic data is a major challenge. In this study, a tight sandstone gas reservoir in the Kuqa Basin (China) was used as an example for identifying reservoir fractures using deep-learning-based method. First, a feasibility analysis is necessary. Intersection analysis between the fracture density and seismic attributes (the characteristics of frequency, amplitude, phase, and other aspects of seismic signals) indicates that there is a correlation between the two when the fracture density exceeds a certain degree. The development of fractures is closely related to the lithology and structure, indirectly affecting differences in seismic attributes. This indicates that the use of seismic attributes for fracture identification is feasible and reasonable. Subsequently, the effective fracture density data obtained from imaging logging were used as label data, and the optimized seismic attribute near the well data were used as feature data to construct a fracture identification sample dataset. Based on a feedforward neural network algorithm combined with natural fracture density and effectiveness control factor constraints, a trained identification model was obtained. The identification model was applied to seismic multi-attribute data for the entire work area. Finally, the accuracy of the results from the training, testing, and validation datasets were used to determine the effectiveness of the method. The relationship between the fracture identification results and the location of the fractures in the target reservoir was used to determine the reasonableness of the results. The results indicate that there is a certain relationship between multiple seismic attributes and fracture development, which can be established using deep learning models. Furthermore, the deep-learning-based seismic data fracture identification method can effectively identify fractures in the three-dimensional space of reservoirs. [ABSTRACT FROM AUTHOR]

ABSTRACT The Erlangping back‐arc Basin separated the North Qinling Arc Terrane (NQAT) from the North China Block during Cambrian‐Ordovician. An enhanced knowledge on its evolutionary history would greatly improve our understanding on tectonic evolution of the Proto‐Tethys Ocean. In this study, we undertook sandstone petrologic and detrital zircon U–Pb geochronologic investigations on the Erlangping Group around the Tianshui Area. The Erlangping Group meta‐sedimentary rocks yielded two general types of zircon U–Pb age patterns. The first type is composed mostly of Neoproterozoic ages with a major age peak at ca. 900 Ma and has a youngest age population peaking at ca. 440 Ma. The second type is dominated by ca. 500–400 Ma components with a youngest age peak of ca. 380 Ma. The two contrasting age patterns and youngest peak ages, along with known ages of volcanic interbeds and intruded granites, allow us to subdivide the Erlangping Group to a Silurian unit and a Devonian unit, which are both stratigraphic higher than the Cambrian‐Ordovician ophiolitic unit of the Erlangping Group. In comparison with age spectra of coeval sediments in the nearby tectonic units, we found that sources of the Erlangping Group were from the Neoproterozoic NQAT basement rocks and associated Early Palaeozoic volcanic and plutonic rocks. The increasing numbers of younger zircons hint at a significant structural unroofing of the NQAT at the Silurian‐Devonian transition before having been subjected to greenschist‐facies metamorphism in the Devonian in response to the elimination of the Shangdan Ocean. [ABSTRACT FROM AUTHOR]

Acidizing constitutes a pivotal enhancement strategy for the effective exploitation of low-permeability sandstone oil reservoirs. The Silurian reservoirs in the Tarim Basin, characterized by numerous thin layers and pronounced heterogeneity, present challenges in acid treatment; specifically, acid fluids preferentially enter high-permeability layers, resulting in inadequate stimulation of low-permeability strata. Current techniques for sandstone reservoir acid diversion remain insufficient. This study introduces a fully water-soluble and degradable clean temporary plugging powder, combined with chelating acid, to address the uniform acidizing challenge in heterogeneous sandstone reservoirs. The research employs a parallel core acidizing flow instrument to investigate the blocking characteristics of the clean temporary plugging powder and its acid diversion capabilities under various differential pressures. Laboratory experiments demonstrate that the degradation of this powder is predominantly temperature-controlled, with complete degradation occurring above 90 ℃, resulting in a clear, acidic solution and effectively enhancing core permeability by 20%. A 0.1% concentration of the plugging powder, when injected with chelating acid into the rock, forms an internal and external barrier layer, increasing the temporary plugging skin factor. The maximum sealing pressure differential achieved is 1.87 MPa, 6.7 times that of chelating acid alone. Parallel core acidizing experiments reveal that 100-mesh clean temporary plugging powder at a 0.1% concentration is suitable for reservoirs with a permeability gradient less than 15, effectively reducing the heterogeneity in permeability and improving the transformation of low-permeability cores. Moreover, in the acidizing operation of well 11-9 in the Tarim Basin, the temporary plugging and diversion technique showed a notable increase in pressure and a substantial enhancement in production post-acidizing. Field trials and applications confirm that the temporary plugging and diversion acidizing technique achieves commendable production enhancement and transformation in Silurian reservoirs, offering significant insights for the uniform acidizing of long sections in heterogeneous sandstone reservoirs. [ABSTRACT FROM AUTHOR]

Engineering rock mass often involves bedding planes and U-shaped defects. Under the combined influence of bedding planes and defects, the fracture mode of engineering rock mass is more complicated. To better understand the failure law of U-shaped defects in rock mass with bedding planes and better control or predict the crack propagation morphology, three-point bending tests were conducted on semicircular disk specimens with U-shaped notches under three different notch radii. The load variation law, different stages of the load–displacement curve, and fracture characteristics of specimens under five bedding angles were analyzed. Then, numerical models of semicircular three-point bending tests were established in particle flow code 2D (PFC2D). The influence of notch radius and bedding angle on the failure path of semicircular specimens was simulated and analyzed, and the three failure modes were verified again. In addition, the stress at the notch tip of the model was monitored by the measurement circle in the discrete-element method, and the fracture toughness of the model specimen was calculated, which provides a new calculation idea for fracture toughness. The research results help us more comprehensively understand the mechanical behavior and failure characteristics of layered rock mass with notch under external load. [ABSTRACT FROM AUTHOR]

Lithological cycles with a repetitive pattern of sandstone overlain by limestone or shale comprise the middle Minnelusa Formation in the Black Hills region, USA. At least eight lithological cycles were observed at Boulder Canyon Road (BCR), eight at Vanocker Canyon Road (VCR) and four at Hot Brook Canyon (HBC). These rocks were deposited in a nearshore to offshore marine environment, and the shale and limestone intervals at the top of these cycles yielded conodonts. Five biostratigraphically distinct Middle to Upper Pennsylvanian conodont faunas were recovered from these marine units. An upper Desmoinesian assemblage was recovered from VCR cycle 1. Two Missourian assemblages were recovered, one indicative of the Idiognathodus cancellosus Zone from VCR cycle 3 and the other indicative of the Streptognathodus gracilis Zone from VCR cycle 6. Two Virgilian assemblages were recovered, one indicative of the Heckelina simulator Zone from VCR cycle 7, VCR cycle 8 and HBC cycle 2 and the other indicative of the lower part of the "Streptognathodus" group 4 virgilicus Zone from HBC cycle 3. Two conodont biofacies were recognized within the middle Minnelusa, the low energy, offshore, Idiognathodontidae-Idioprioniodus biofacies and the higher energy, nearshore Idiognathodontidae-Hindeodus biofacies. [ABSTRACT FROM AUTHOR]

Tight oil reservoirs require fracturing techniques to create complex fracture networks for efficient development. It is frequently accompanied by a dynamic matrix-fracture imbibition process, promoting enhanced recovery. At present, the mechanism of three dimensions (3D) matrix-fracture dynamic imbibition at the pore scale has not been fully elucidated. In this paper, the dynamic imbibition process of oil-water two phases in matrix-fracture was simulated based on the Navier–Stokes equations, and the level set method was used to capture the real-time interfacial changes between the two phases. It was found that during matrix-fracture dynamic imbibition process, oil-phase droplets in a single pore remain in the pore mainly due to the "stuck" effect. Cluster residual oil in the pore space is mainly retained due to the "flow around" effect. Continuous residual oil in the deeper regions of the matrix is due to insufficient capillary force. Water phase in the micro-confinement space of a tight reservoir intrudes into the pore space along the pore corners, forming the "fingering" phenomenon is beneficial for enhancing the efficiency of micro-dynamic imbibition. It differs from cognition obtained in the micro-view space during conventional water flooding. The enhancement of imbibition efficiency is often accompanied by the occurrence of fluctuations in the average pressure within the matrix. Therefore, a method involving impulse type of high-frequency and short-period for supplemental energy and imbibition is suggested to enhance recovery in tight sandstone reservoirs. This study reveals the detailed mechanisms of oil-water two-phase transport at different stages in the dynamic imbibition process and holds significant guiding implications for enhancing recovery in this type of reservoirs. [ABSTRACT FROM AUTHOR]

Tetrapod tracks from the Lower Jurassic strata of the Hartford Basin (Newark Supergroup) abound in areas of Massachusetts and Connecticut, USA. However, tetrapod skeletal fossils are uncommon, and the co-occurrence of tracks with skeletal material in the same bedding plane is exceedingly rare. Due to this paucity of skeletal material, spatiotemporal gaps and taxonomic incompleteness continue to hamper research on bones preserved as natural casts. Here we report on the discovery of new bone cast specimens and three grallatoroid (Anchisauripus) tracks on a single sandstone slab originating from Portland or Middletown, Connecticut. The Nash Specimen – BRCM 2021.10 – holds important implications for Early Jurassic dinosaur taphonomic history and the paleoenvironment in which dinosaur footprints and bones as natural casts were preserved. Results from this study describe three Anchisauripus tracks and five natural bone casts from an early theropod dinosaur. Judicious comparisons to the only comparable specimen of dinosaur bone casts (MOS.2001. 248) are made in describing the morphological structures and the taphonomic pathways leading to cast formation. The unique taphonomic circumstances of bone casts preserved alongside dinosaur tracks on the same substrate layer provide an intriguing case of the non-preservation of body fossils that merits further research in the Hartford Basin. [ABSTRACT FROM AUTHOR]

The Dina 2 gas field in the Kuqa Depression of the Tarim Basin is one of China's most critical oil and gas exploration areas. Natural fractures have played an important role in the low-permeability reservoirs in the Tarim area. Tectonic fractures are dominant in such reservoirs. In fact, the factors influencing tectonic fracture development have always been the source of important issues in tight reservoirs. Cores, thin sections, and borehole image logs were used to analyze the types, basic characteristics, and factors influencing tectonic fractures in the tight sandstone reservoirs of the Dina 2 gas field in the Tarim Basin. The results showed that the tectonic fractures are dominated by high-angle and upright shearing fractures, and they mainly show ENE–WSW strikes. The thin sections suggest that 60% of the fractures are fully filled with minerals, 20% are unfilled, and 20% are partially filled. The analysis also shows that lithology, faults, and in situ stress are the main factors controlling the development of the tectonic structures. Furthermore, the correlation between the unimpeded flow from a single well and the apertures of the tectonic fractures indicates that tectonic fractures play an important role in the production of hydrocarbons. [ABSTRACT FROM AUTHOR]

The H8 and S1 reservoirs in the lower Shihezi Formation and Shanxi Formation of the central block in the Sulige Gas Field are typical fluvial tight sandstone reservoirs. Due to frequent river channel migrations during deposition, the reservoirs exhibit complex spatial structures with developed intra-sand mudstone interlayers. As the field has entered the middle and late stages of development, the distribution of remaining gas is intricately controlled by these interlayers, necessitating research on their distribution to understand the remaining gas patterns and types for effective extraction enhancement. However, the thinness of interlayers presents a challenge for precise prediction. Addressing this, this study delineates different interlayer types and their origins, applies reservoir architecture theory, and utilizes bounding surfaces characterization, planar and sectional distribution studies, unit scale analysis, horizontal well data, and quantitative characterization methods to investigate the internal reservoir architecture bounding surfaces. The study finely portrays the interlayer distribution, analyzes the control of reservoir architecture bounding surfaces on remaining gas, and establishes a multi-tiered reservoir architecture model in the study area. Numerical simulation of the gas reservoir clarifies the types of remaining gas enrichment. This study also identifies and quantitatively characterizes the 5–3 level architecture bounding surfaces within the sandbody, categorizing the remaining gas into bounding surfaces-controlled, well-network uncontrolled, and single-layer unperforated types, proposing targeted enhancement measures for each type. Based on the findings, four vertical wells and three horizontal wells were deployed, improving the well network density to three wells per square kilometer. The first completed horizontal well encountered an effective drilling rate of 61.7%, marking significant implications for the exploitation and recovery enhancement of similar tight sandstone gas reservoirs. [ABSTRACT FROM AUTHOR]

The mechanical properties of fissured sandstone will deteriorate under water–rock interaction. It is crucial to extract the precursor information of fissured sandstone instability under water–rock interaction. The potential of each acoustic emission (AE) parameter as a precursor for instability in the failure process of fissured sandstone was investigated in this study. An experimental dataset comprising 586 acoustic emission experiments was established, and subsequent classification training and testing were conducted using three machine learning (ML) models: AdaBoost, MLP, and Random Forest (RF). The primary parameters for identifying the instability risk state of fissured sandstone include acoustic emission ringing count, energy (mV·ms), centroid frequency, peak frequency, Rise Angle (RA), Average Frequency (AF), b value, and the natural/saturated state of fissured sandstone: state. To enhance data utilization, a 10-fold cross-validation method was employed during the model training process. The machine learning models were developed and designed to identify the instability risk of fissured sandstone under the natural and saturated states. The results demonstrated that the established RF model was capable of identifying fissured sandstone instability risks with an accuracy of 97.87%. Feature importance analysis revealed that state and b value exerted the most significant influence on identification results. The Spearman correlation coefficient was utilized to assess the correlation between input features. This study can provide technical support to identify the risk of instability of fissured sandstones under both natural and saturated water conditions. Based on the models developed in this study, it is possible to implement an early warning method for instability in fissured sandstone that meets realistic working conditions. Compared with the traditional empirical and formulaic methods, the machine learning method can more quickly process huge amounts of AE data and accurately identify the damage state of fissured sandstone. [ABSTRACT FROM AUTHOR]

Sandstone-type deposits have emerged as the primary uranium deposits being mined in China, utilizing in-situ leaching technology. However, the leaching of uranium resources within sandstone formations faces significant constraints due to their extremely low permeability, accounting for approximately seventy percent of the total. This paper aims to present recent advancements in the field in enhancing seepage-leaching mass-transfer properties in in-situ leaching of uranium from low-permeability sandstone. We will provide an overview of the main factors influencing the in-situ leaching process in low-permeability ore layers, discussing the technical characteristics of applicable methods designed to enhance permeability in low-permeability uranium-bearing sandstone based on the existing research. Additionally, we will also explore the suitability of various approaches from other fields in the in-situ leaching of uranium process. Finally, we will outline the prospects regarding process methodologies, leaching agents, and enhancing permeability methods. [ABSTRACT FROM AUTHOR]

The isotonic point of the Chang-6 tight oil reservoir in the Qilicun Oilfield in the Ordos Basin cannot be determined from experimental data on the waterflooding permeability. Furthermore, there are missing data near the isotonic point. Previous research on phase permeability trends has uncovered significant uncertainties in the application of data normalization, standardization, and interpolation processing. In current research, there is a consensus on the existence of a relationship between the relative permeability and saturation indices. However, since measurements contain relative permeabilities of 0, coefficient indices cannot be directly derived. Researchers have theorized that the first data number in the wet phase relative permeability must be changed from a 0 to non-0 minimum in order to directly establish the relationship between the relative permeability and the water saturation index. The missing intervals after the first data point are not interpolated. Not only does this method incorporate the knowledge of the permeability indices obtained by researchers, but it also eliminates the processes of normalization, standardization, and interpolation of missing data intervals for permeability data in order to avoid errors introduced by these processes. Without introducing new parameters, interference with raw data was reduced and the accuracy was improved. The results indicate that the relative permeability is highly correlated with the water saturation indices. Furthermore, the relationships between the water content and relative permeability and between the water saturation and water content were analyzed using the Leverett displacement function and percolation theory. The water saturation corresponding to the water content of 17 samples was calculated under the condition of displacement, and the relationship between the critical water saturation and water content was further established. These results provide support for studies on the relationship between phase permeability and oil-water saturation within this area. [ABSTRACT FROM AUTHOR]

This paper presents a comparative analysis of the mechanical characteristics of claystone and sandstone soils of natural humidity and in a completely water-saturated state. The results of field and laboratory tests showed a significant decrease in the values of strength characteristics during saturation up to 65% for claystone and 33% for sandstone. The decrease in uniaxial compressive strength during water saturation reached 70% for claystone and 90% for sandstone, and the decrease in the deformation modulus was up to 80%. [ABSTRACT FROM AUTHOR]

Flood geologists linve been using tile Coconino Sandstone in the Grand Canyon to argue that a global flood rezoorked much of the plmietary geologic record. Flood geologists' arguments may seem convincing at first, but after analyzing their articles and videos tls well as the conventional geology literature, it is found t/mt the Coconino does not support a global flood. Flood geologists hai)e been largely directing their efforts toward re®ting generalized statements from critics in the popular science literature. By placing so much emphasis on finding data that could be used to refute critics, opportunities were missed to increase scient@ understanding of the Coconino. Flood geologists' filidings zoere consistently framed to argue for aqueous deposition, which they implicitly equate to global flood deposition. It is slioum flint an astronomical difference exists between the two. [ABSTRACT FROM AUTHOR]

This research investigated the effect of ion concentration on the performance of low salinity water under different conditions. First, the effect of injection water composition on interparticle forces in quartz-kaolinite, kaolinite-kaolinite, and quartz-oil complexes was tested and modeled. The study used two oil samples, one with a high total acid number (TAN) and the other with a low TAN. The results illustrated that reducing the concentration of divalent ions to 10 mM resulted in the electric double layer (EDL) around the clay and quartz particles and the high TAN oil droplets, expanding and intensifying the repulsive forces. Next, the study investigated the effect of injection water composition and formation oil type on wettability and oil/water interfacial tension (IFT). The results were consistent with the modeling of interparticle forces. Reducing the divalent cation concentration to 10 mM led to IFT reduction and wettability alteration in high TAN oil, but low TAN oil reacted less to this change, with the contact angle and IFT remaining almost constant. Sandpack flooding experiments demonstrated that reducing the concentration of divalent cations incremented the recovery factor (RF) in the presence of high TAN oil. However, the RF increment was minimal for the low TAN oil sample. Finally, different low salinity water scenarios were injected into sandpacks containing migrating fines. By comparing the results of high TAN oil and low TAN oil samples, the study observed that fine migration was more effective than wettability alteration and IFT reduction mechanisms for increasing the RF of sandstone reservoirs. [ABSTRACT FROM AUTHOR]

The majority of commercial kaolin deposits in Ethiopia originate from felsic igneous rock. On the other hand, the Adi-Hano kaolin deposit is a recently recognised kaolin deposit that was formed from sandstone. Nevertheless, this provides insight into potential deposit occurrences in the region's sedimentary sequence. This study aims to characterise the genesis, quality, quantity and potential industrial uses of Adi-Hano kaolin deposit. It was carried out by integrated field geological descriptions, thin-section interpretation, physical testing, mineralogical (X-ray diffraction, XRD) and geochemical investigations. An inductively coupled plasma mass spectrometer (ICP-MS) and an inductively coupled plasma atomic emission spectrometer (ICP-AES) were used to analyse the geochemistry. The main mineral phases in the deposit are quartz and kaolinite, while the minor mineral phases are rutile, cristobalite and tridymite. The elevated value of quartz, limits the quality of kaolin being as an impurity for its industrial use. The integrated result indicates that insitu weathering followed by leaching of the arkosic sandstone played a great role in kaolin deposit formation. The average chemical index of alteration (CIA; 94.18%) also shows that the source rock has experienced strong weathering and alteration. The deposit contains minor concentrations of Sr + Ba and Fe2O3 + TiO2, and high concentrations of Y + Ce + La and Nb + Cr values, which are indicative of a supergene type origin. Following treatment of the deposit, its similar grain size distribution, colour, relatively high Al2O3, relatively low TiO2, Fe2O3 and alkali components make it suitable for a variety of industrial uses, such as ceramics, refractory, paper coating and paint. [ABSTRACT FROM AUTHOR]

Since the dawn of civilization, sandstone has been a fantastic building material. Numerous causes have been observed in the past for sandstone damage or deterioration, one of which is sulphur-oxidizing bacteria (SOB) and cyanobacteria. In general, SOB is present in the soil, air, water, humidity, and human activity. The oxidation of sulphur compounds, such as hydrogen sulphide, thiosulphate, or elements of sulphur, provides energy for SOB. These microorganisms contribute to the decay of buildings materials, especially those made of stone, metal, or concrete. The sulphur oxidizing process affects the mechanical properties of sandstone. Mechanical properties are related to strength. Losses of mechanical properties may be the reason for deflection, cracking, collapse, and catastrophic failure of sandstone. Monitoring and evaluation gives an idea about the behavior of structure and the prevention of catastrophic failure. This research paper contains the application of electromechanical impedance with surface bonded Piezoelectric Lead Zirconate Titanate. The sandstone samples and soil samples have been collected from the historical site. Two sets of cylindrical types of sandstone specimens have been used in experimental work. The conductance signature and susceptance signature have been measured every six months. The variation and shifting of the signature curve have been used to identify the structural behavioral change. Statistical methods like the root mean square deviation have been used for the quantification of damage. An equitation has been generated on the basis of the percentage root mean square deviation to quantify the prediction of damages. [ABSTRACT FROM AUTHOR]

Chandarpur–Raipur sequence in Chattisgarh basin is represented as siliciclastic-dominated Chandarpur Group and carbonate-dominated Raipur Group. Here, we introduce 'Devsagar Sandstone Member', the only sandstone-dominated member in the carbonate-dominated Charmuria Formation of Raipur Group, that marks a period of rapid siliciclastic deposition identifying a phase of forced regression between two carbonate platforms of Charmuria–Chandi formations, thereby indicating a drastic change in palaeogeography of Raipur Group. In addition, this study revised the litho-stratigraphy of Mesoproterozoic Chattisgarh basin to clarify the confusion raised due to the existence of different stratigraphy in different basinal parts and different nomenclature for the same lithologic units. Detailed geological mapping with facies analysis in the eastern part of the basin manifests the entire basin-fill succession as part of the Chattisgarh basin itself, rather than sub-dividing some parts as Baradwar sub-basin and Singhora proto-basin. Singhora Group deposited in Singhora proto-basin has already been presented as equivalent of Chandarpur Group. Here we propose, Bamandihi–Saradih–Raigarh formations of Raipur Group in Baradwar sub-basin, as lateral equivalent of Gunderdehi–Chandi–Tarenga formations of Raipur Group and Sarnadih–Nandeli formations of Kharsiya Group in Chattisgarh basin. Inferred depositional environment and tectonic setting of Chattisgarh basin support the lithostratigraphic revision, which will help in basin analysis as well as intrabasinal–interbasinal correlation in regional and global contexts. Research highlights: Devsagar Sandstone Member introduced as the only sandstone-dominated member in carbonate-dominated Charmuria Formation of Raipur Group. Devsagar Sandstone Member represents a tidal shelf in between two carbonate ramp platforms (Charmuria and Chandi), marking a period of rapid siliciclastic deposition and the only phase of forced regression in overall sea-level rising scenario of the carbonate-dominated Raipur Group. Stratigraphy of Chattisgarh basin revised. The entire Chattisgarh succession is represented as deposits of Chattisgarh basin only, without further subdivision into sub-basin and/or proto-basin, thus resolving the stratigraphic and basinal correlation problem. [ABSTRACT FROM AUTHOR]

Amber appears in the archaeological material of the Eastern Baltic region in the Middle Neolithic and continues in intensive use until the end of the Neolithic. Four major amber-working centres are known in the Eastern Baltic, the least studied of which is the settlement of Siliņupe (4th mill. BC). Not yet widely applied in research on Stone Age amber technologies, but very promising, is an analytical approach combining experimental archaeology and traceology to study processing choices made in specific production stages (i. e., individual technological elements), revealing that fine-grained sandstone was favoured for surface grinding, while flint tools were most widely used for shaping and surface treatment, distinguishing three techniques, namely shaving, scraping and pressure flaking, each identifiable by characteristic features. The study suggests that amber and flint processing were largely intertwined, as pressure flaking along with indirect percussion (used for splitting amber) derive from flint processing, and in the case of pressure flaking, required specific know-how. [ABSTRACT FROM AUTHOR]

Fluid injection into subsurface reservoirs may cause existing faults/fractures to slip seismically. To study the effect of temperature on injection-induced fault slip, at a constant confining pressure of 10 MPa, we performed a series of injection-induced shear slip experiments on critically stressed sandstone samples containing saw-cut fractures (laboratory-simulated faults) under varying fluid pressurization rates (0.1 and 0.5 MPa/min, respectively) and temperatures (25, 80, and 140 °C, respectively). At 25 °C, slow fault slip events with a peak slip velocity of about 0.13 μm/s were observed on a tested sample in response to a low fluid pressurization rate of 0.1 MPa/min. In contrast, fluid injection with a high pressurization rate of 0.5 MPa/min caused fault slip events with a peak slip rate up to about 0.38 μm/s. In response to a given fluid pressurization rate, several episodes of slip events with a higher slip velocity were induced at an elevated temperature of 140 °C, indicating an appreciable weakening effect at elevated temperatures. We also experimentally constrained the rate-and-state frictional (RSF) parameters at varying effective normal stresses and temperatures by performing velocity-stepping tests. The obtained RSF parameters demonstrate that for a relatively high normal stress, increasing temperature tends to destabilize fault slip. Post-mortem microstructural observations reveal that elevated temperatures promote the generation of abundant fine-grained gouge particles associated with injection-induced shear slip. Our experiments highlight that injection-induced fault slip is affected by temperature-related wear production over the fault surface. [ABSTRACT FROM AUTHOR]

Stratigraphic subdivision of the Upper Cretaceous in Saxony and northern Bohemia has been significantly improved during the recent years, particularly on the Saxon side, and proposals for transboundary correlation were made. In the past few years, the hydrogeological exploration on the Czech side brought important new data (including several cored and well-logged boreholes; see Appendix) that facilitated more precise correlation of aquifer formations for groundwater modelling. Here, we present a revised stratigraphic correlation of sandstone-dominated areas of the Saxon-Bohemian Cretaceous Basin between Pirna and the Zittau Mts., supported by the new data and corroborated by thorough discussion of previously published stratigraphic correlation schemes. Correlation of the Cenomanian-Lower Turonian is relatively reliable with respect to the other most recent attempts, and only minor issues are discussed. The Upper Cenomanian Pennrich Fm. represents a locally developed, glauconite-rich lithofacies - as indicated by development of the Korycany Mb. The lower part of the Oybin Fm. (lower Turonian) has a markedly lower thickness, as indicated by its correlation to the Bílá Hora Fm. Thus, its actual top is either placed ca. 40 m higher or it contains two coarsening-upward cycles. The middle-upper Turonian Jizera Fm. largely correlates to the Postelwitz Fm. and middle-upper part of the Oybin Fm., respectively. The exact correlation of overlying sandstones c-d (upper Turonian) of the Postelwitz and Schrammstein formations, to individual coarsening-upward cycles within the Jizera Fm., is problematic for scarcity of fossil markers, rapid facies transitions and relatively limited database (number of boreholes and outcrops of certain units). Therefore, we present an alternative correlation of the Schrammstein Fm. based on the available borehole and outcrop data from both sides of the border, and consider plausibility of stratigraphic equivalence of sandstones d to f and the Teplice Fm. Sandstones d and e, compared to sandstones a to c, were likely deposited within significantly less extensive depositional space that gradually diminished from SW to NE, with the youngest Turonian Kyjov Sandstone (overlain by transgressive Chřibská Mudstone) being the least extensive. Lithostratigraphic correlation of the youngest Upper Cretaceous units in the Zittau and Lusatian Mts. revealed the following: (i) The upper Turonian Lückendorf Fm. combines lithologically contrasting successions with poorly defined boundaries and unknown thickness. It was described on discontinuous sections and does not reasonably correlate with the Czech stratigraphy; (ii) the overlying Waltersdorf Fm. lacks a proper definition (e.g. type section is missing), although it has been subdivided into three sandstone members thought to represent a stratigraphic succession; (iii) the Sonnenberg Sandstone that correlates to the Kyjov Sandstone, has clearly defined boundaries and distinct lithology and can be cartographically displayed. Both units can be combined and formally defined as a member within the Waltersdorf and Teplice formations, respectively; (iv) the Lausche and Hochwald sandstones as members of the Waltersdorf Fm. have no counterparts in the Czech territory due to a limited accessibility and impossibility of their recognition within a variable lithofacies succession of the Březno Fm. However, both units may be treated as informal stratigraphic units of local significance. [ABSTRACT FROM AUTHOR]

Borehole breakout is an important geological phenomenon that provides a significant reference for the estimation of the direction and magnitude of in situ stress. To better understand the water content effect on borehole breakouts, a series of experiments on red sandstone was conducted. The standard cylindrical samples and cubic samples containing a circular hole were loaded under uniaxial compression in four water states including dry, unsaturated, short-term saturated, and long-term saturated. Then, the water effect was discussed in terms of rock strength and deformation, initiation stress of borehole breakout, failure evolution process, geometries of breakout, fragments, and acoustic emission (AE) signals. In the water-bearing state, rock properties significantly deteriorate with the decline of strength, the enhancement of plastic deformation, and the restrain of the brittle failure mode. For cubic samples, the axial stress required for borehole breakout increases under the short-term saturated condition but decreases after the long-term immersion. In addition, obvious extrusion deformation of borehole walls toward the borehole space is observed in saturated samples, resulting in vague V-shaped void notches. Before the overall failure, more obvious AE signal fluctuation occurs in the water-bearing state and AE locations reveal a larger fracture concentration region. Two mechanisms are proposed to explain the water content effects on the borehole breakout initiation stress, involving strength weakening effect and stress redistribution mechanism. The shrinkage of borehole breakout geometries is discussed further on the influence on the in situ stress estimation. Highlights: The influence of water content on sandstone properties and borehole breakout is comprehensively investigated. Short-term immersion results in a slight rise of borehole breakout initiation stress, while it declines again after long-term immersion. Double mechanisms are proposed to explain the water content effect on borehole breakout initiation. Water induces the shrink of both breakout depth and angular span, which may further affect the in situ stress estimation. [ABSTRACT FROM AUTHOR]

In deep underground geotechnical engineering, water–rock interaction emerges as a critical factor influencing the stability of engineering rock masses. This study delves into the macroscopic nonlinear mechanical behavior and fracture characteristics of natural water-bearing and saturated sandstone samples under various true triaxial stress states. The objective is to systematically elucidate the impact of actual three-dimensional stress conditions and water content on the mechanical behavior and fracture mechanisms of sandstone formations. The findings reveal significant anisotropic deformation in sandstone under 3D stress, while saturated sandstone exhibits robust plastic deformation capacity. Moreover, changes in the strain ratio coefficient are identified as precursors to rock fracture. The dilatation behavior of sandstone weakens progressively with increasing σ2, indicating reduced expansion in saturated sandstone. To account for the influence of σ2, a novel dilation index is proposed. The true triaxial strength of sandstone demonstrates a close relationship with both σ2 and water content, with strength initially increasing before declining as σ2 rises. In addition, water significantly undermines sandstone strength, although this weakening trend moderates with increasing σ2. Morphological analysis and SEM observations unveil three-dimensional volume fracturing characteristics in rock fractures, primarily characterized by shear accompanied by tensile fractures. Saturated sandstone samples, in contrast, exhibit numerous tensile and intergranular fractures. Overall, this study holds paramount practical significance for the evaluation of rock stability and the design of water-bearing engineering rock masses, encompassing domains, such as geology, water conservancy, and mining. Highlights: The influence of the σ2 and water on the nonlinear mechanical behavior of sedimentary sandstone was studied. A new dilatation index and strength criterion considering the effect of the σ2 was proposed. The 3D fracture morphology and failure network characteristics of sandstone was analyzed. Mesoscopic fracture mechanism of the σ2 and water on sandstone was revealed. [ABSTRACT FROM AUTHOR]

To investigate the influence of joints on the rockburst process in the surrounding rock of deep tunnels, a free-face true-triaxial test was conducted on the rockburst of the jointed surrounding rock of a tunnel. The rockburst ejection failure process (i.e., failure mode, rock strength, and deformation characteristics), rockburst debris characteristics, and acoustic emission evolution characteristics of red sandstone specimens under different joint conditions were investigated. The experimental results indicate that the failure modes of red sandstone specimens with a joint condition perpendicular to the tunnel direction generally exhibit 'internal shear and external splitting', which can suppress the occurrence of rockbursts, whereas the failure mode of red sandstone specimens with a joint condition parallel to the tunnel direction is mainly shear fracture, which can also promote the occurrence of rockbursts. The variation trend of the peak strength and the joint angle of the specimen exhibits a 'U' type shape, and the debris pertaining to the joint specimen's rockburst exhibits fractal characteristics. With the increase of the joint inclination angle, the fragment's ejection kinetic energy exhibits a trend of decreasing first and subsequently increasing. There are significant differences in the total number pertaining to impacts of acoustic emissions during rockburst under different joint conditions. The distribution range pertaining to the dominant frequency signal of the acoustic emission signal at the time of rockburst is mainly a low-frequency signal, and the intermediate-frequency, high-frequency, and ultra-high-frequency signals also exist, thus indicating that the rockburst damage exhibits strong complexity. Finally, the strain rockburst mechanism of jointed rock is significantly different from that of jointless intact rock. The rockburst mechanism is mainly divided into two typologies: shear fracture and slab buckling-shear fracture. The research results contribute to a deeper understanding of the underlying mechanisms of rockburst disasters in jointed rock formations. Highlights: Successfully performed a free-face true-triaxial rockburst test in the jointed surrounding rock of a tunnel. The presence of different joints under true-triaxial conditions significantly alters the mechanism of strain-induced rockburst. Joints perpendicular to the tunnel direction reduce the occurrence of rockbursts, whereas joints parallel to the tunnel direction promote the occurrence of rockbursts. With the increase of the joint inclination angle, the fragments' ejection kinetic energy exhibits a trend of decreasing first and subsequently increasing, where the joint inclination angle of 30° is the transition's inflection point. [ABSTRACT FROM AUTHOR]