Influence of Immersion Time on the Frequency Domain Characteristics of Acoustic Emission Signals in Clayey Mineral Rocks.

The frequency domain characteristics of acoustic emission can reflect issues such as rock structure and stress conditions that are difficult to analyze in time domain parameters. Studying the influence of immersion time on the mechanical properties and acoustic emission frequency domain characteristics of muddy mineral rocks is of great significance for comprehensively analyzing rock changes under water-rock coupling conditions. In this study, uniaxial compression tests and acoustic emission tests were conducted on sandstones containing montmorillonite under dry, saturated, and different immersion time conditions, with a focus on analyzing the effect of immersion time on the dominant frequency of rock acoustic emission. The results indicated that immersion time had varying degrees of influence on compressive strength, the distribution characteristics of dominant acoustic emission frequencies, the frequency range of dominant frequencies, and precursor information of instability failure for sandstones. After initial saturation, the strength of the rock sample decreased from 53.52 MPa in the dry state to 49.51 MPa, and it stabilized after 30 days of immersion. Both dry and initially saturated rock samples exhibited three dominant frequency bands. After different immersion days, a dominant frequency band appeared between 95 kHz and 110 kHz. After 5 days of immersion, the dominant frequency band near 0 kHz gradually disappeared. After 60 days of immersion, the dominant frequency band between 35 kHz and 40 kHz gradually disappeared, and with increasing immersion time, the dominant frequency of the acoustic emission signals increased. During the loading process of dry rock samples, the dominant frequency of acoustic emission signals was mainly concentrated between 0 kHz and 310 kHz, while after saturation, the dominant frequencies were all below 180 kHz. The most significant feature before the rupture of dry rock samples was the frequent occurrence of high frequencies and sudden changes in dominant frequencies. Before rupture, the characteristics of precursor events for initially saturated and immersed samples for 5, 10, and 30 days were the appearance and rapid increase in sudden changes in dominant frequencies, as well as an enlargement of the frequency range of dominant frequencies. After 60 days of immersion, the precursor characteristics of rock sample rupture gradually disappeared, and sudden changes in dominant frequencies frequently occurred at various stages of sample loading, making it difficult to accurately predict the rupture of specimens based on these sudden changes.

Optimized artificial neural network application for estimating oil recovery factor of solution gas drive sandstone reservoirs.

The most crucial aspect in determining field development plans is the oil recovery factor (RF). However, RF has a complex relationship with the reservoir rock and fluid properties. The application of artificial neural networks is able to produce complex correlations between reservoir parameters that affect the recovery factor. This research provides a new approach to improve the accuracy of the ANN model in the form of steps including removing outlier data, selecting input parameters, selecting transferring functions, selecting the number of neurons, and determining hidden layers. By applying these steps, an ANN model was selected with nine input parameters consisting of oil viscosity, water saturation, initial oil formation volume factor, formation thickness, initial pressure, permeability, specific gravity of oil, porosity, and original oil in place. Furthermore, based on the correlation coefficient, a tangent sigmoid transferring function, 30 neurons, and two hidden layers were determined. The proposed ANN correlation gives the best accuracy compared to the previous correlations. This is proved by the highest correlation coefficient of 0.91657.

Kinetics of Alkali-Silica Reaction: Application to Sandstone.

Despite extensive research, the relationship between the progression of the alkali-silica reaction (ASR) and the expansion of concrete due to ASR, particularly for the heterogeneous aggregate with slow reactivity, is not thoroughly understood. In this paper, the dissolution kinetics of reactive silica present in sandstone when exposed to NaOH solutions, alongside the expansion characteristics of rock prisms under ASR conditions, were studied. The experimental results indicate that ASR behaves as a first-order reaction, accompanied by an exponential decrease in the concentration of OH- over time, and the dissolution rate of silica is predominantly governed by diffusion dynamics. Notably, increasing the temperature accelerates ASR, which augments the expansive pressure in a confined and limited space, leading to more significant aggregate expansion. Conversely, higher temperatures also result in a diminished retention of ASR gels within the aggregate, leading to the mitigation of ASR expansion. Our findings underscore that larger aggregates retain a greater quantity of gels, resulting in more pronounced expansion. To establish an ASR prediction model based on the relationship of the ASR expansion of concrete to high and low temperatures, the parameters such as the range of curing temperatures and the grading size of aggregates should be carefully considered for the experiments.

Seabuckthorn (Hippophae rhamnoides L.) plantation degradation aggravates microbial metabolic C and P limitations on the Northern Loess Plateau in China.

Vegetation degradation in arid and semi-arid regions reduces plant C inputs to the soil, which can impede soil nutrient cycling because of the limited C source for microbial metabolism. However, whether vegetation degradation aggravates microbial nutrient limitation in degraded ecosystems in arid and semi-arid regions is not fully understood. Here, we investigated changes in soil enzyme activity and microbial nutrient limitation along a well-documented gradient of degraded seabuckthorn (Hippophae rhamnoides L.) (slightly degraded, canopy dieback <25 %, moderately degraded, canopy dieback 25 %-75 %, and severely degraded, canopy dieback >75 %) in Liang (long ridge) and gully channel locations in the Pisha Sandstone region of the Loess Plateau, China. We found that as the magnitude of seabuckthorn degradation increased, activities of C-acquiring enzymes and ratios of C:N and C:P enzymes (0.54-0.80 and 0.52-0.77, respectively) increased whereas the N:P enzyme ratio (0.93-0.99) decreased. Stoichiometric modelling further indicated that microorganisms were limited by soil C and P (vector angle >45°) in the seabuckthorn plantation region, and the degradation of seabuckthorn plantation aggravated microbial C and P limitations. Partial least squares path modelling revealed that seabuckthorn degradation (canopy dieback) was the main factor explaining microbial C limitation variations, while soil physicochemical properties (pH and soil moisture content) and understory plant parameters (litter biomass) were the major factors underlying microbial P limitation of long ridge and gully channel formations, respectively. Our findings highlight synergistic changes between aboveground and belowground processes, suggesting an unexpected negative effect of vegetation degradation on soil microbial community and nutrient cycling. These insights offer a direction for the development of plantation nutrients management strategies in semi-arid and arid areas.

Imaging porosity evolution of tight sandstone during spontaneous water imbibition by X-ray Micro-CT.

Water imbibition is an important process in reservoir rocks during hydraulic fracturing and water-based enhanced oil recovery operations. However, the water imbibition behavior in tight sandstones has not been fully understood due to their complex pore structure, including the presence of nano and micron-sized pores and throats, surface properties, and wide variation in mineralogy. The present study focuses on the effect of spontaneous water imbibition on the porosity evolution of a tight sandstone. Within this context, a core of Torrey Buff sandstone was characterized by using a combination of multiscale imaging methods (X-ray Computed Tomography, Scanning Electron Microscopy), laboratory experiments (porosity-permeability measurements), and analytical techniques (X-ray Diffraction, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy-Energy Dispersive Spectroscopy, and Thermogravimetry). The studied tight sandstone core has a porosity of 12.3 % and permeability of 2.05mD with minerals of quartz (58 %), clays (kaolinite and illite, 23 %), K-feldspar (7 %), dolomite (7 %) and calcite (5 %). Primary and secondary pores, ranging in size from 60 to 140 µm and 30-50 µm, respectively, are mostly filled with highly-soluble carbonate minerals and hydrophilic illite, which influence the spontaneous water imbibition capacity of the tight sandstone. The multiscale imaging technique indicates that after a 10-h long water imbibition experiment, the average pore size of the tight sandstone increased by 1.28 %, reaching 2.35 % at the rock-water contact and 0.13 % at the top of the core. In other words, throughout the core, the porosity changes upon water imbibition are not uniform but show an almost linear trend. This observation could be explained by the significant contribution of highly-soluble carbonates and hydrophilic illite on the microstructure of the tight sandstone. This study implies that multiscale imaging techniques, crucial in examining spontaneous water imbibition, hold promise for further research in enhanced oil recovery or hydraulic fracking in tight sandstones.

Investigating the impact of the quantity of wet and dry cycles on the mechanical characteristics and fracture variations of sandstones.

The sandstone is in a state of dry-wet cycle under the repeated action of rainfall, and its mechanical properties are deteriorated to varying degrees, which causes cracks in the sandstone. Therefore, it is of great significance to study the mechanical properties and fracture propagation of sandstone under the action of dry-wet cycles. Currently, there are limited studies using numerical simulation methods to study the fracture extension of rocks under various dry and wet cycling conditions.Therefore, in this paper, the effects of different amounts of dry and wet cycling on the mechanical properties and fracture behavior of sandstone are investigated through uniaxial compression tests and numerical simulations of fracture extension. The findings indicate that the deformation stage of sandstone remains unchanged by the dry-wet cycle. The uniaxial compressive potency and coefficient of restitution gradually diminish as the quantity of cycles rises, while the Poisson's ratio exhibits the opposite trend, and the impact on the mechanical performance of sandstone wanes with cycle increments, and the correlation coefficient surpasses 0.93, signifying a substantial influence of the dry-wet cycle on sandstone's mechanical performances. The discrepancy between the numerical simulation and experimental results is minimal, with a maximum error of only 3.1%, demonstrating the congruence of the simulation and experimental outcomes.The mesoscopic examination of the simulations indicates that the quantity of fractures in the sandstone specimens rises with the escalation of dry-wet cycles, and the steps of analysis linked to crack inception and fracture propagation are accelerated, and the analysis steps from fracture initiation to penetration are also reduced.

Study on Fracture Characteristics of Layered Sandstone under Asymmetric Loading.

In engineering practice, layered rock masses often display obvious anisotropy while deforming and failing, and the failure mode directly impacts the engineering construction stability. In this study, the fracture failure load, fracture toughness, crack deflection angle, and failure mode of a layered rock mass under different fracture modes were analyzed by utilizing improved asymmetric semi-circular disc specimens. According to the constitutive model of transversely isotropic materials, the maximum tensile stress (MTS), maximum energy release rate (MERR), and maximum strain energy density (MSED) calculation formulas were modified, and the calculation formulas of the three prediction criteria under anisotropic materials were derived. The calculation results were compared with the experimental results. The results show that the fracture toughness and crack deflection angle were significantly affected by the weak bedding plane. As a result of applying the MTS criterion, the results are closer to the experimental results, providing a solid foundation for engineering deformation, failure, and fracture analyses.

Mechanism and deterioration pattern of sandstone surrounding rock voiding at bottom of heavy-haul railway tunnel.

This study combines laboratory experiments and discrete element simulation methods to analyze the mechanism and deterioration patterns of sandstone surrounding rock voiding the bottom of a heavy-haul railway tunnel. It is based on previously acquired measurement data from optical fiber grating sensors installed in the Taihangshan Mountain Tunnel of the Wari Railway. By incorporating rock particle wastage rate results, a method for calculating the peak strength and elastic modulus attenuation of surrounding rock is proposed. Research indicates that the operation of heavy-haul trains leads to an instantaneous increase in the dynamic water pressure on the bottom rock ranging 144.4-390.0%, resulting in high-speed water flow eroding the rock. After 1-2 years of operation, the bottom water and soil pressures increase by 526.5% and 390.0%, respectively. Focusing on sandstone surrounding rock with high observability, laboratory experiments were conducted to monitor the degradation stages of infiltration, particle loss, and voiding of rock under the action of dynamic water flow. The impact of water flow on the "cone-shaped" bottom rock deformation was also clarified. The extent of rock deterioration and voiding was determined using miniature water and soil pressure sensors in conjunction with discrete element numerical simulations. The measured rock particle loss was used as a criterion. Finally, a fitting approach is derived to calculate the peak strength and elastic modulus attenuation of surrounding rock, gaining insight into and providing a reference for the maintenance and disposal measures for the bottom operation of heavy-haul railway tunnels.

Experimental study on I/II/III mixed mode fracture characteristics of a combined rock mass under creep loading.

I/II/III mixed mode fractures of intersecting joint fissures often occur in natural rock masses, and jointed rock masses are prone to rockbursts in deep underground engineering when subjected to long-term crustal stresses. However, most studies of the mechanical mechanisms of these intersected joints have been conducted by simplifying two-dimensional joint model tests. Furthermore, the fracture mechanisms of two-dimensional intersected joints under tension and compression are completely different from those of three-dimensional joints. This paper presents a novel prefabricated specimen with combinations of intersecting joints capable of detecting the failure behaviours of rock I/II/III mixed mode fractures under creep loading. Uniaxial compression and multistage creep tests are performed on prefabricated sandstone specimens with intersecting joints of 0°/0°, 0°/30°, 0°/60°, and 0°/90°. The experimental results show that with the increase in the number of prefabricated intersecting joints, the uniaxial compressive strength and elastic modulus values of the sandstone specimens gradually decrease. In addition, the sandstone specimens experience relatively few AE events and minor axial strain variations in the first creep stage and the second creep stage of the multistage creep test. The axial strain increases sharply due to the sharp increase in the number of AE events in the third creep stage. The 0°/60° sandstone specimen undergoes accelerated creep failure, resulting in mixed X-shaped tensile‒shear rupture. The RA value is high based on the quantification of the creeping cracks using the acoustic emission parameters of the rise angle (RA) and average frequency (AF). The AF values of the 0°/0°, 0°/30°, and 0°/90° sandstone specimens are high. The experimental results show that a larger joint intersection angle leads to greater mutual restraints and greater effects of prefabricated crack propagation in the rock specimens, thus increasing the final failure strength. Finally, based on the acoustic emission count, a characteristic variable D suitable for characterizing the creep damage evolution of a joint rock mass is established. The findings of this paper can facilitate an effective understanding of the creep effect of I/II/III mixed mode fracture and its micromechanism. The research results will have a certain reference value for the detection and risk mitigation of instantaneous and time-delayed rockbursts.

Appraisal of reservoir quality for hydrocarbon-bearing deep-water Miocene sandstones incised valley, south-east Asian offshore Indus: An application of seismic attributes and instantaneous spectral porosity quantitative reservoir simulations.

Incised marine valleys (IVS) are hot topics in exploring the stratigraphic oil and gas-bearing plays. Multiple channelized sandstone lenses at varying depths [m], thicknesses [m], and porosities [%] constrain seismic impedance. The presence of hydrocarbon-bearing resources affects the seismic impedance (density (g/cc) and velocity (m/s)). Therefore, a quantitative prediction has been carried out for determining the thickness [m], porosity [%], and depths [m] of laterally distributed channelized sandstone lenses (SLS) for IVS, Indus offshore Basin (IOB), Pakistan, using 2-D instantaneous spectral porosity quantitative modelling (2DSSM), continuous wavelet transforms-based (CWT) 2-D instantaneous spectral density modelling (2DSSDM), and spectral decomposition tools. The 2DSSM remained limited in predicting the number of channelized sandstone lenses and their quantitative stratigraphic attributes. The 45-Hz-based processing of conventional 2DSSM has resolved the two channelized sandstone lenses of the stratigraphic trap. The deepest channelized sandstone lens has attained 1-6 m thickness with a lateral extent of 3 km, within the porosity range of 18-33 %. The highest confidence level for predicted petrophysical attributes such as 13 m-thick pay zones, -0.08, -0.067, and -0.07 acoustic impedances [g/c.c.*m/s], and 28 % porosities with R2 > 0.85 have validated interpretations. The response of 45-Hz CWT waveform-based inverted density and thickness simulations has predicted the highest thicknesses and lowest densities of reservoir sandstones within the meandering channel belt of the deepwater depositional system. The predicted densities and thicknesses for the coarse-grained sandstone lenses of point bars were 1.8-1.9 g/cc and 15 m, respectively. In the same way, the quantitative estimates of predicted density and simulated thickness have shown a strong coefficient correlation (R2 > 0.80), which confirms the presence of gas-bearing prospects within the IVS. The facies-controlled migration is thought to be the movement of the reservoir facies of the point bars and channelled sandstone-filled lenses to the side.

Green and Low-Cost Modified Pisha Sandstone Geopolymer Gel Materials for Ecological Restoration: A Phase Review.

Pisha sandstone (PS) is a special interbedded rock in the middle reaches of the Yellow River that experiences severe weathering and is loose and broken. Due to severe multiple erosion events, the Pisha sandstone region is called "the most severe water loss and soil erosion in the world" and "the ecological cancer of the earth". As a special pozzolanic mineral, PS has the potential to be used as precursors for the synthesis of green and low-carbon geopolymer gel materials and applied in ecological restoration. This paper aims to undertake a phase review of the precursors for geopolymer gel materials. The genesis and distribution, physical and chemical characterization, erosion characteristics, and advances in the ecological restoration of PS are all summarized. Furthermore, current advances in the use of PS for the synthesis of geopolymer gel materials in terms of mechanical properties and durability are discussed. The production of Pisha sandstone geopolymer gels through the binder jetting technique and 3D printing techniques is prospected. Meanwhile, the prospects for the resource application of PS in mine rehabilitation and sustainable ecology are discussed. In the future, multifactor-driven comprehensive measures should be further investigated in order to achieve ecological restoration of the Pisha sandstone region and promote high-quality development of the Yellow River Basin.

Characteristic evaluation and environmental validation of self-compacting concrete containing sandstone slurry waste for sustainable usage.

This study aims to understand the impact of concrete ingredients on the environment. To analyze the effect of, three significant indexes have been taken into consideration, which are embodied carbon dioxide index (e-CO2), embodied energy consumption (e-energy), and embodied resource consumption (e-resource) index. The life cycle assessment (LCA) methodology has considered veto comprehending the probable application of sandstone waste in the form of a slurry (Sslurry) and powder (Spowder) for the development of self-compacting concrete (SCC). This study can be proven beneficial to evaluate the potential adverse effects from environmental and energy perspectives. One reference mix and eighteen design mixes of SCC have been designed and developed to perform an experimental program. An environmental impact comparison of the "hybrid" SCC was performed using the OpenLCA life cycle analysis software with Ecoinvent LCIA methods. The outcomes of this experimental program reveal that the partial replacement of pozzolana Portland cement (PPC) with Sslurry can reduce e-CO2 emission along with the e-energy and e-resource parameters. When Spowder was used as the partial substitution of fine aggregate (FA), only the e-resource index decreased, and e-CO2 and e-energy increased. Minimalist impact on the environment has been noticed when SCC is prepared with Sslurry and Spowder. A detailed LCA analysis study justifies the utilization of Sslurry and Spowder in SCC, which exhibits encouraging results concerning strength and quality. Hence, it was observed that Sslurry and Spowder in developing green and sustainable SCC with moderate strength characteristics are beneficial from an environmental impact perspective.

Reservoir damage mechanism and "Double protection" drilling fluid of tight sandstone gas reservoir in central SiChuan Basin.

It is very important to clarify the reservoir damage characteristics and damage characteristics and damage mechanism of tight sandstone gas reservoirs in Jinhua-Zhongtai mountain area of central SiChuan Basin, and put forward the technical countermeasures of "Double protection" drilling fluid to protect the reservoir and the environment, which is very important for the efficient well construction in this area. Through X-ray diffraction, scanning electron microscopy, casting thin sections and other testing methods, the mineral composition and microstructure characteristics of the block were analyzed, and the potential damage factors of the reservoir were clarified. Based on the sensitivity evaluation, it was revealed that the overall sensitivity damage of the block was weak. The main damage type was salt-sensitive damage, and the critical salinity was 9472.5 mg/L. On the basis of the environmental protection drilling fluid system used in this block, the surfactant which can effectively prevent gas invasion and reduce surface tension is selected, and the "Double protection" drilling fluid system is constructed. Through comprehensive performance test and reservoir protection performance evaluation, the core permeability damage rate of the optimized drilling fluid system is reduced from 88.77 to 18.66%, and the cuttings recovery rate is increased to more than 66%, and the cuttings expansion rate is reduced to less than 3.2%, which can effectively solve the problem of reservoir damage in drilling in Jinhua-Zhongtai mountain block in central Sichuan.

Geochemical indicators to constrain weathering, provenance and tectonic setting of the Pisha Sandstone (Early-Middle Triassic) in Northeast Ordos Basin, China.

The Pisha Sandstone is widely exposed in the northeastern margin of the Ordos basin. Since the Mesozoic the basin was subjected to uneven uplift several times, strong weathering and erosion have been occurring and a large amount of sediments derived from these erosional strata are input into the lower Yellow River, posing a fragile ecological environment along the river. However, the geochemical characteristics of the Pisha Sandstone have remained poorly understood. In this study, we focus on the Pisha Sandstone from Early-Middle Triassic Liujiagou, Heshanggou and Ermaying Formation, present a very first petrographic and geochemical data together with detailed field geological characteristics, aiming to place geochemical indicators on weathering, provenance and tectonic setting of the Pisha Sandstone. The results show that sandstones in Pisha Sandstone are classified as arkose, litharenite and wacke. The geochemical proxies including Chemical Index of Alteration (CIA = 67.2), Chemical Index of Weathering (CIW = 80.1), Plagioclase Index of Alteration (PIA = 75.6) and Index of Compositional Variability (ICV = 1.6) indicate Pisha Sandstone experienced first-cycle deposit and moderate to strong chemical weathering. Trace element and rare earth element concentrations together with their ratios (La/Sc, La/Co, Th/Sc, Th/Co, Cr/Th) reveal a felsic provenance, and source rock compositions are predominantly granodiorite and granite from the north margin of the Inner Mongolia Paleo-Uplift (IMPU), with a small amount of mafic or intermediate components. The geochemical signatures and tectonic discrimination diagrams display a collision setting for the Pisha Sandstone and further reveal the sediments had been deposited in a continental island arc setting. The results of this work may provide new theoretical basis for environmental protection in the Pisha Sandstone area.

Hydrochemical characteristics and genetic mechanism of porous sandstone geothermal water in northern Jinan, Shandong, China.

Porous sandstone geothermal water is an important geothermal resource, which is a low-carbon and clean resource, but lacks systematic research on a regional scale. The northern part of Jinan City is rich in geothermal resources, specifically porous sandstone thermal reservoirs. However, there is still incomplete research on the mechanism of geothermal genesis and the hydrochemical characteristics of geothermal water in porous sandstone. This study aims to address this gap by collecting 21 groundwater samples from northern Jinan and comparing their conventional ion and isotope characteristics to investigate the hydrochemical characteristics during the formation of geothermal water and uncover the genesis mechanism of porous sandstone geothermal water. The results indicate that the geothermal water is classified as Na-Cl type and Na-SO4-Cl type. The hydrochemical characteristics of geothermal water are primarily influenced by water-rock interaction and groundwater mixing. The water source primarily comes from the atmospheric precipitation in the Taiyi mountains, with an altitude of 910.75-1542.2 m.s.a.l.. The estimated temperature of the thermal reservoir ranges from 51 to 78 °C, and the depth of geothermal water circulation is estimated to be between 1316 and 2216 m. Based on the characteristics of the geothermal field, including the "cap rock, water source, heat source, reservoir, and channel," a conceptual model of the porous sandstone geothermal water flow system is proposed. This model offers novel insights into the genesis mechanism of geothermal water under similar geological conditions.

Experimental and numerical investigation of the mechanical properties and energy evolution of sandstone-concrete combined body.

Studying the mechanical properties of rock-concrete combined body is crucial to ensure the safety and stability of engineering structures. In this paper, laboratory tests and numerical simulations are used to investigate the mechanical properties of the sandstone-concrete combined body. Uniaxial compression tests and an acoustic emission monitoring system are used to analyze the failure characteristics of the sandstone-concrete sample and to validate the accuracy of the numerical model. The mechanical properties of the composite body were further analyzed by integrating energy and damage theories. The results of the sandstone-concrete study suggest that the combined sandstone-concrete body exhibits synergistic deformation and failure when subjected to uniaxial compression. The peak stress and elastic modulus fall between those of sandstone and concrete. The interface's shape causes the stress in the y-direction to transition from tensile stress to compressive stress. Energy is stored before reaching the peak stress and released after reaching the peak stress. The damage curve indicates that the damage increases gradually with the strain, and it results in plastic failure. In the numerical simulation of triaxial compression, the stress and displacement at the interface are evenly distributed. Compared to uniaxial compression, the energy of each component is higher and shows a linear positive correlation with confining pressure. Additionally, the rate of energy dissipation increases with higher confining pressure. The damage variable also increases with the increase in confining pressure, and the plastic failure process is also apparent under triaxial compression.

Electrical facies of the Asmari Formation in the Mansouri oilfield, an application of multi-resolution graph-based and artificial neural network clustering methods.

Electrofacies analysis conducted the distribution effects throughout the reservoir despite the difficulty of characterizing stratigraphic relationships. Clustering methods quantitatively define the reservoir zone from non-reservoir considering electrofacies. Asmari Formation is the most significant reservoir of the Mansouri oilfield in SW Iran, generally composed of carbonate and sandstone layers. The stratigraphical study is determined by employing 250 core samples from one exploratory well in the studied field. Five zones with the best reservoir quality in zones 3 and 5 containing sandstone/shale are determined. Moreover, multi-resolution graph-based and artificial neural network clustering involving six logs are employed. Utilizing Geolog software, an optimal model with eight clusters with better rock separation is obtained. Eventually, five electrofacies with different lithological compositions and reservoir conditions are identified and based on lithofacies describing thin sections, sandstone, and shale in zones 3 and 5 show high reservoir quality. According to the depth related to these zones, most of the facies that exist in these depths include sandstone and dolomite facies, and this is affected by the two factors of the primary sedimentary texture and the effect of the diagenesis process on them. Results can compared to the clustering zone determination in other nearby sandstone reservoirs without cores.

Influence of activator ratios and concentration on the physio-mechanical and microstructural characteristics of the geopolymers derived from sandstone processing waste.

Natural stones have been utilized to meet various needs of human civilization since ancient times. The exploitation of any resource is associated with the production of redundant materials called wastes. Sandstone waste (SW) is one such waste obtained during the industrial processing of sandstones. Due to its siliceous composition, extensive yield, and disorganized dumping, noxious conditions related to land and human health are promoted. However, the lack of comprehensive engineering studies, mineralogical analysis, and design methodologies associated with the utilization of sandstone processing wastes restricted their applicability only to fillers or partial substitutes with pozzolans and traditional cement in meager volumes. In the past, limited efforts have been made to utilize SW as a construction entity, particularly for binding purposes. Thus, to enhance the scope of its utilization, a comprehensive investigation has been performed in this research to transform sandstone waste into a novel construction material by geopolymerization. Mix design tailoring and laboratory tests were implemented to understand the effects of sodium hydroxide concentration and sodium silicate to sodium hydroxide ratio on the dissolution and physio-mechanical characteristics of SW-based geopolymers. The activator-to-binder ratio was restricted to 0.4 to obtain pastes with sufficient workability without hindering the properties of the matrix. Besides, a high temperature-curing regime was selected based on SW's crystallographic and reactivity analysis. Subsequently, a total of 48 samples were prepared and tested at the curing age of 28 days. Detailed characterization of SW and SW-based geopolymer samples was performed using optical, X-ray, and infrared spectroscopies aided by electron imaging and thermogravimetric techniques. SW-based geopolymer samples showed compressive strengths in the range of 6-12 MPa, ~2 to 3 times higher than those obtained in previous experimentations. Phase analysis and microstructural examinations confirmed SW's participation in geopolymerization. Overall, it could be advocated that geopolymerization is an innovative approach for solving issues related to the disposal and re-utilization of SW, extending its possible application to the fields of cement mixes, wall tiles, mortars, and masonry as per the commendations of ASTM and ACI committee.

A Laboratory Experimental Study on Enhancing the Oil Recovery Mechanisms of Polymeric Surfactants.

In order to evaluate the physical and chemical properties of polymer surfactants and analyze their oil displacement mechanisms, three types of poly-surfactant used in the Daqing oil field were chosen to be researched, and the oil displacement effects were studied using poly-surfactants of different viscosity, dehydrating rate, and core permeability. The main purpose is to determine the reasonable range of different characteristic indexes of polymeric surfactant flooding. The oil displacement effect of 15 cores was analyzed, and the effects of viscosity, the dehydrating rate of emulsion, and permeability on EOR (Enhanced Oil Recovery) were analyzed. The oil displacement mechanisms of polymeric surfactants were researched using a photolithographic glass core. This paper explores the mechanism underlying production enhancement as an EOR target, while simultaneously conducting laboratory tests to assess the physical and chemical properties of polymeric surfactants. The poly-surfactant agents exhibit a notable increase in viscosity, with the optimal displacement effect observed at a core effective permeability exceeding 400 mD, resulting in a potential EOR of 15% or higher. Moreover, at a viscosity ranging between 40 and 70 mPa·s, the total EOR can reach 73%, with the peak efficiency occurring at a viscosity of 60 mPa·s. The water loss rate of the emulsion, ranging between 30% and 70%, achieves optimal performance at 50%. The poly-surfactants' higher viscosity extends the oil sweep area, enhancing recovery efficiency, and noticeably reducing residual oil compared to water flooding. During poly-surfactant flooding, a substantial amount of residual oil is extracted and transformed into droplets. The rapid emulsification of the polymeric surfactant solution with crude oil forms a stable emulsion, contributing to its significant oil recovery effect. This research provides valuable technical support for EOR in thin and low-quality reservoirs of onshore multi-layered sandstone reservoirs.

Experimental research on compressive strength deterioration of coal seam floor sandstone under the action of acidic mine drainage.

In sulphur-coal symbiotic coal seams, after the mining of sulphide iron ore, when the coal resources are mined, the mine water accumulated in the roadway mining area will have a certain impact on the stability of the surrounding rock of the coal seam roadway. Taking the floor sandstone of sulfur coal symbiotic coal seam as the research object, the roof fissure water with pH values of 7.48, 4.81 and 2.62 was used as the experimental solution. 10 experimental schemes were designed to measure the compressive strength of the samples under the action of AMD, and the hydrochemical analysis of AMD was conducted. The pore structures of the samples before and after the action of AMD were analyzed. Based on the hydrochemistry and pore structure, the deterioration mechanism of compressive strength of the coal seam floor sandstone under the action of AMD was explained. The results indicated that the compressive strength of the samples decreased with the increasing action time of AMD. The compressive strength decreased with the increment of the porosity. The concentration of H+ ion in AMD was relatively small. Na2O in albite dissolved and reacted with water, leading to an increase in the concentration of Na+ ion. Soluble substances such as MgCl2 and CaSO4 in the pore structure dissolved, leading to an increase in the concentration of Ca2+ and Mg2+ ions. The dissolution of soluble substances and the physical-chemical reactions between solutions and minerals were the essential causes of the continuous deterioration of the compressive strength of the coal seam floor sandstone. The results of this study can provide a theoretical basis for the deterioration of the mechanical properties of the peripheral rock in the roadway of the sulphur coal seam, and can also provide a certain engineering reference for the sulphur coal seam roadway.