Search Results (527)

By embedding optical fiber sensors into fiber preforms and utilizing liquid molding processes such as resin transfer molding (RTM), intelligent composite materials with self-sensing capabilities can be fabricated. In the liquid molding process of these intelligent composites, the quality of the final product is highly dependent on the resin flow and impregnation effects. The embedding of optical fibers can affect the microscopic flow and impregnation behavior of the resin; therefore, it is necessary to investigate the specific impact of optical fiber embedding on the resin flow and impregnation of fiber bundles. Due to the difficulty of directly observing this process at the microscopic scale through experiments, numerical simulation has become a key method for studying this issue. This paper focuses on the resin micro-flow in RTM processes for intelligent composites with embedded optical fibers. Firstly, a steady-state analysis of the resin flow and impregnation process was conducted using COMSOL 6.0 obtaining the velocity and pressure field distribution characteristics under different optical fiber embedding conditions. Secondly, the dynamic process of resin flow and impregnation of fiber bundles at the microscopic scale was simulated using Fluent 2022R2. This study comprehensively analyzes the impact of different optical fiber embedding configurations on resin flow and impregnation characteristics, determining the impregnation time and porosity after impregnation under different optical fiber embedding scenarios. Additionally, this study reveals the mechanisms of pore formation and their distribution patterns. The research findings provide important theoretical guidance for optimizing the RTM molding process parameters for intelligent composite materials. Full article

One of the hottest topics in current research is the creation of scaffolds for bone tissue restoration that are both biocompatible and tissue inducible. The aim of this work is to develop a numerical model to study the effects of temperature, velocity, and scaffold structure on flow and biomechanical properties, as well as to optimize design parameters to improve tissue engineering outcomes. The results show that the fluid transport properties of cylindrical unit cell architectures are superior. For effective mass transfer, pore diameters > 4 mm and porosity > 60% are ideal design parameters. With important clinical and financial implications, these discoveries offer theoretical direction and economical methods for developing bone tissue engineering. Full article

This study addresses the limitations of conventional evaluation methods caused by low porosity, strong heterogeneity, and complex pore structures in tight sandstone reservoirs. Through integrated rock physics experiments and multi-physical field modeling, the research systematically investigates the coupled response mechanisms between electrical and elastic parameters. The experimental approach includes pore structure characterization, quantitative mineral composition analysis, resistivity and polarizability measurements under various saturation conditions, P- and S-wave velocity testing, and scanning electron microscopy (SEM) imaging. The key findings show that increasing porosity leads to significant reductions in resistivity and elastic wave velocities, while also increasing surface conductivity. Specifically, clay minerals enhance surface conductivity through interfacial polarization effects and decrease rock stiffness, which exacerbates wave velocity attenuation. Furthermore, resistivity exhibits a nonlinear negative correlation with water saturation, with sharp increases at low saturation levels due to the disruption of conductive pathways. By integrating the Modified Generalized Effective Medium Theory of Induced Polarization (MGEMTIP) and Kuster–Toksöz models, this study establishes quantitative relationships between porosity, saturation, and electrical/elastic parameters, and constructs cross-plot templates that correlate elastic wave velocities with resistivity and surface conductivity. These analyses reveal that high-porosity, high-saturation zones are characterized by lower resistivity and wave velocities, coupled with significantly higher surface conductivity. The proposed methodology significantly improves the accuracy of reservoir evaluation and enhances fluid identification capabilities, providing a solid theoretical foundation for the efficient exploration and development of tight sandstone reservoirs. Full article

Accurate shear wave velocity is important for shale reservoir exploration and characterization. However, the effect of the ubiquitous preferred orientation of clay minerals on the velocities of shale has rarely been considered in existing S-wave velocity estimation methods, resulting in limited accuracy of the estimation method. In this study, a S-wave velocity estimation method is proposed for shale while considering the effect of the preferred orientation of clay. First, a compaction model is built by taking the effects of the orientation distribution of clay and the aspect ratio of pores into account. Then, the compaction model is utilized in a workflow to obtain the model parameters by fitting the estimated P-wave velocity with the bedding-normal P-wave velocity from well logging. Finally, the S-wave velocity is estimated using the compaction model and calculated model parameters. The proposed method is verified by laboratory data and successfully applied to a shale gas reservoir. The result shows that the root mean square error almost halves compared with the Xu–White model. Additionally, the correlation coefficient also improves. The improvement in S-wave velocity estimation indicates that the effect of the preferred orientation of clay on the velocities of shale is effectively corrected. The proposed method improves the accuracy of velocity modeling and reservoir characterization for shale. Full article

The deep carbonate reservoirs in the Tarim Basin, Xinjiang, China, are widely developed with multi-scale complex reservoir spaces such as fractures, pores, and karst caves under the coupling of abnormal high pressure, diagenesis, karst, and tectonics and have strong heterogeneity. Among them, fracture–cavity carbonate reservoirs are one of the main reservoir types. Revealing the petrophysical characteristics of fracture–cavity carbonate reservoirs can provide a theoretical basis for the log interpretation and geophysical prediction of deep reservoirs, which holds significant implications for deep hydrocarbon exploration and production. In this study, based on the mineral composition and complex pore structure of carbonate rocks in the Tarim Basin, we comprehensively applied classical petrophysical models, including Voigt–Reuss–Hill, DEM (Differential Effective Medium), Hudson, Wood, and Gassmann, to establish a fracture–cavity petrophysical model tailored to the target block. This model effectively characterizes the complex pore structure of deep carbonate rocks and addresses the applicability limitations of conventional models in heterogeneous reservoirs. The discrepancies between the model-predicted elastic moduli, longitudinal and shear wave velocities (Vp and Vs), and laboratory measurements are within 4%, validating the model’s reliability. Petrophysical template analysis demonstrates that P-wave impedance (Ip) and the Vp/Vs ratio increase with water saturation but decrease with fracture density. A higher fracture density amplifies the fluid effect on the elastic properties of reservoir samples. The Vp/Vs ratio is more sensitive to pore fluids than to fractures, whereas Ip is more sensitive to fracture density. Regions with higher fracture and pore development exhibit greater hydrocarbon storage potential. Therefore, this petrophysical model and its quantitative templates can provide theoretical and technical support for predicting geological sweet spots in deep carbonate reservoirs. Full article

Fluid dispersion directly influences the transport, mixing, and efficiency of hydrogen storage in depleted gas reservoirs. Pore structure parameters, such as pore size, throat geometry, and connectivity, influence the complexity of flow pathways and the interplay between advective and diffusive transport mechanisms. Hence, these factors are critical for predicting and controlling flow behavior in the reservoirs. Despite its importance, the relationship between pore structure and dispersion remains poorly quantified, particularly under elevated flow conditions. To address this gap, this study employs pore network modeling (PNM) to investigate the influence of sandstone and carbonate structures on fluid flow properties at the micro-scale. Eleven rock samples, comprising seven sandstone and four carbonate, were analyzed. Pore network extraction from CT images was used to obtain detailed pore structure parameters and their statistical measures. Pore-scale simulations were conducted across 60 scenarios with varying average interstitial velocities and water as the injected fluid. Effluent hydrogen concentrations were measured to generate elution curves as a function of injected pore volumes (PV). This approach enables the assessment of the relationship between the dispersion coefficient and pore structure parameters across all rock samples at consistent average interstitial velocities. Additionally, dispersivity and n-exponent values were calculated and correlated with pore structure parameters. Full article

In double-shield TBM tunnel construction, grouting plays a vital role in consolidating the gravel backfill and maintaining the integrity of the segmental lining. To investigate the permeation behavior of grout within the pea gravel layer, a fluid dynamics model was developed in this study. The model directly simulates the flow of grout through the porous medium by solving the Navier–Stokes equations and employs the level set method to track the evolving interface between the grout and air phases. Unlike conventional continuum approaches, this model incorporates particle-scale heterogeneity, allowing for a more realistic analysis of grout infiltration through the non-uniform pore structures formed by gravel packing. Three different grouting port positions and two boundary conditions are considered in the simulation. The results indicate that under pressure boundary conditions, the grout flow rate increases rapidly in the initial stage, and then decreases and stabilizes, with the flow rate peak increasing as the grout port moves upward. Under velocity boundary conditions, the injection pressure grows slowly in the early stage but accelerates with time. Additionally, the rate of pressure change is faster when the grout port is located lower in the backfilling layer. Through theoretical analysis, the existing analytical formula was extended by introducing a gravitational correction term. When the grouting port is near the upper part of the tunnel, the analytical solution aligns well with the numerical simulation results, but as the grout port moves downward, the discrepancy between the two increases. Full article

Understanding tortuosity is essential for accurately modeling fluid flow in complex porous media, particularly in the sub-surface reservoir rock; therefore, tortuosity estimation was evaluated using three approaches: Streamline streamline simulations via the Lattice Boltzmann Method (LBM), geometric pathfinding using Dijkstra’s algorithm, and empirical modeling based on pore-structure parameters. The analysis encompassed 1963 micro-Computed Tomography (micro-CT) images of Brazilian pre-salt carbonate and sandstone samples, with the effective porosity extracted from LBM velocity fields, isolating flow-contributing pores, establishing streamline tortuosity as the reference standard. Sandstones exhibited relatively narrow tortuosity ranges (Dijkstra: 1.29–1.75; Streamline: 1.18–2.61; Empirical: 1.18–4.42), whereas carbonates display greater heterogeneity (Dijkstra: 1.00–3.18; Streamline: 1.00–3.68; Empirical: 1.59–4.93). Model performance assessed using the corrected Akaike Information Criterion (AICc) revealed that the best agreement with the data was achieved by the semi-empirical model incorporating coordination number and minimum throat length (AICc = −113.11), followed by the Dijkstra-based geometrical approach (−99.74) and the empirical porosity-based model (202.23). There was a nonlinear inverse correlation between tortuosity and effective porosity across lithologies. This comprehensive comparison underscores the importance of incorporating multiple pore-scale parameters for robust tortuosity prediction, improving the understanding of flow behavior in heterogeneous reservoir rocks. Full article

We conducted ultrasonic (1-MHz) laboratory measurements on 210 samples from the Vaca Muerta Formation (Neuquén Basin, Argentina) to determine the factors influencing acoustic velocities in siliciclastic–carbonate mudstone. We quantitatively assessed the calcium carbonate and total organic carbon (TOC) content and qualitatively identified the quartz and clay mineralogy. For brine-saturated samples, P-wave velocities ranged from 2826 to 6816 m/s, S-wave velocities ranged from 1474 to 3643 m/s, and porosity values ranged from 0.01 to 19.4%. Carbonate content percentages, found to be critically important, vary widely from 0.08 to 98.0%, while TOC ranged from 0 to 5.3%. Velocity was primarily controlled by carbonate content and, to a lesser extent, by the non-carbonate mineralogy of the rock (e.g., quartz, clay minerals). TOC content had little effect on the acoustic properties. Due to the low porosity of most samples, mineral composition had a stronger influence on velocity than porosity or pore geometry. The V_p/V_s ratio of dry samples ranged from 1.38 to 1.97 and decreased as porosity increased. In saturated samples, the V_p/V_s ratio ranged from 1.46 to 2.06 and appeared independent of porosity. A clear distinction between carbonate and mixed lithofacies under both saturated and dry conditions was observed in all samples. Full article

Catalytic methane decomposition offers an attractive and sustainable pathway for producing CO_x-free hydrogen and valuable carbon nanotubes. This work investigates the innovative use of liquid metals, particularly gallium and indium, as promoters for iron catalysts based on a titanium dioxide and alumina composite to improve this process even more. In a fixed-bed reactor operating at 800 °C and atmospheric pressure, all catalyst activities for methane decomposition were thoroughly assessed while keeping the gas hourly space velocity at 6 L/g h. Surface area and porosity, H₂-temperature programmed reduction/oxidation, X-ray diffraction, Raman spectroscopy, scanning transmission electron microscopy, and thermogravimetry analysis were utilized to investigate the physicochemical properties of the catalyst. The result showed that iron supported on a titanium-alumina catalyst exhibited higher activity, stability, and reproducibility with a methane conversion of 90% and hydrogen production of 81% after three cycles, with 240 min for each cycle and stability for 480 min. In contrast, the liquid metal-promoted catalysts improved the metal-support interaction and textural properties, such as surface area, pore volume, and particle dispersion of the catalysts. Still, the catalytic efficiency significantly improved. However, the gallium-promoted catalyst displayed excellent reusability. The characterization of the spent catalyst proved that both the iron supported on a titanium-alumina and its gallium-promoted derivative produced graphitic carbon; on the contrary, the indium-promoted catalyst produced amorphous carbon. These results demonstrate how liquid metal promoters can be used to adjust the characteristics of catalysts, providing opportunities for improved reusability and regulated production of carbon byproducts during methane decomposition. Full article

Granitic faults within the crystalline upper-to-middle continental crust play a critical role in accommodating tectonic deformation and controlling earthquake nucleation. To better understand their frictional behavior, we review experimental studies conducted under both dry and hydrothermal conditions using velocity-stepping (VS), constant-velocity (CV), and slide-hold-slide (SHS) tests. These approaches allow the quantification of frictional strength, velocity dependence, and healing behavior across a range of conditions. Our synthesis highlights that the friction coefficient of granite gouges decreases with increasing temperature and pore fluid pressure, decreasing slip velocity, and increasing slip displacement. The velocity-weakening regime shifts to higher temperatures with increasing slip velocity or decreasing pore fluid pressure. Temperature, normal stress, pore fluid pressure, and slip velocity interact to modulate frictional stability. In particular, microstructural observations reveal that grain size reduction, pressure solution creep, and fluid-assisted chemical processes are key mechanisms governing transitions between velocity-weakening and velocity-strengthening regimes. These insights support the growing application of microphysical-based models, which integrate micromechanical processes and offer improved extrapolation from the laboratory to natural fault systems compared to classical rate-and-state friction laws. The collective evidence underscores the importance of considering fault rheology in a temperature- and fluid-sensitive context, with implications for interpreting seismic cycle behavior in continental regions. Full article

The selective catalytic reduction of NO_x with CH₄ (CH₄-SCR) holds the potential to simultaneously abate harmful NO_x and CH₄ greenhouse gases. In this study, a series of bimetallic M-In/H-SSZ-39 catalysts (where M represents Cr, Co, Ce, and Fe) were prepared via an ion exchange method and subsequently evaluated for their CH₄-SCR activity. The influences of the preparation parameters, including the metal ion concentration and calcination temperature, as well as the operating conditions, such as the CH₄/NO ratio, O₂ concentration, water vapor content, and gas hourly space velocity (GHSV), on the catalytic activity of the optimal Cr-In/H-SSZ-39 catalyst were meticulously examined. The results revealed that the Cr-In/H-SSZ-39 catalyst exhibited peak CH₄-SCR catalytic performance when the Cr(NO₃)₃ concentration was 0.0075 M, the In(NO₃)₃ concentration was 0.066 M, and the calcination temperature was 500 °C. Under optimal operating conditions, namely GHSV of 10,000 h⁻¹, 400 ppm NO, 800 ppm CH₄, 15 vol% O₂, and 6 vol% H₂O, the NO_x conversion rate reached 93.4%. To shed light on the excellent performance of Cr-In/H-SSZ-39 under humid conditions, a comparative analysis of the crystalline phase, chemical composition, pore structure, surface chemical state, surface acidity, and redox properties of Cr-In/H-SSZ-39 and In/H-SSZ-39 was conducted. The characterization results indicated that the incorporation of Cr into In/H-SSZ-39 enhanced its acidity and also facilitated the generation of InO⁺ active species, which promoted the oxidation of NO and the activation of CH₄, respectively. A synergistic effect was observed between Cr and In species, which significantly improved the redox properties of the catalyst. Consequently, the activated CH₄ could further interact with InO⁺ to produce carbon-containing intermediates such as HCOO⁻, which ultimately reacted with nitrate-based intermediates to yield N₂, CO₂, and H₂O. Full article

Shallow landslides are one of the main geological hazards that occur during heavy rainfall in Yuexi County every year, posing potential risks to the personal and property safety of local residents. A rainfall-induced shallow landslide named Baishizu No. 15 landslide in Yuexi Country was taken as a case study. Based on the field geological investigation, combined with physical and mechanical experiments in laboratory as well as numerical simulation, the failure mechanism induced by rainfall infiltration was studied, and the movement process after landslide failure was inverted. The results show that the pore-water pressure within 2 m of the landslide body increases significantly and the factory of safety (F_s) has a good corresponding relationship with rainfall, which decreased to 0.978 after the heavy rainstorm on July 5 and July 6 in 2020. The maximum shear strain and displacement are concentrated at the foot and front edge of the landslide, which indicates a “traction type” failure mode of the Baishizu No. 15 landslide. In addition, the maximum displacement during landslide instability is about 0.5 m. The residual strength of soils collected from the soil–rock interface shows significant rate-strengthening, which ensures that the Baishizu No. 15 landslide will not exhibit high-speed and long runout movement. The rate-dependent friction coefficient of sliding surface was considered to simulate the movement process of the Baishizu No. 15 landslide by using PFC^2D. The simulation results show that the movement velocity exhibited obvious oscillatory characteristics. After the movement stopped, the landslide formed a slip cliff at the rear edge and deposited as far as the platform at the front of the slope foot but did not block the road ahead. The final deposition state is basically consistent with the on-site investigation. The research results of this paper can provide valuable references for the disaster prevention, mitigation, and risk assessment of shallow landslides on residual soil slopes in the Dabie mountainous region. Full article

The study investigates the influence of an air-entraining admixture on the properties and pore structure of ordinary concrete. The aim was to examine how modifications to the concrete mix affect compressive strength, ultrasonic pulse velocity, and resistance to freeze–thaw cycles. Concrete samples with varying admixture dosages (0.00–1.50% of cement mass) were tested for mechanical properties and pore structure. Freeze–thaw resistance was assessed using both direct (PN-B-06265) and indirect methods (EN 480-11), while pore characteristics were evaluated via computer-aided image analysis. Results show that increasing the admixture dosage enhances freeze–thaw resistance by refining the pore structure—particularly by increasing the content of micropores below 0.3 mm—while simultaneously reducing compressive strength and ultrasonic velocity. Statistical analysis revealed that pore parameters such as total air content, specific surface area, and spacing factor significantly correlate with concrete performance. The regression models confirmed that compressive strength and ultrasonic velocity are negatively impacted by increased pore volume, while freeze–thaw resistance improves due to a more favorable pore size distribution. The findings demonstrate that optimizing the admixture dosage can effectively balance durability and mechanical performance, and that quantitative stereological parameters provide a valuable basis for predicting the behavior of air-entrained concrete. Full article

Dewatering and gas production are applied on a large scale in shale gas development. The fundamental mechanisms of water flow in shale nanoporous media are essential for the development of shale oil and gas resources. In this work, we use molecular dynamic simulations to investigate water flow in two different quartz surface ($(10\overline{1}0)\text{-}\alpha$ and $(10\overline{1}0)\text{-}\beta$) nanopores. Results show that the $(10\overline{1}0)\text{-}\beta$ surface exhibits stronger water molecule structuring with a structure arranged in two layers and higher first-layer adsorption density (2.44 g/cm³) compared to the ($(10\overline{1}0)\text{-}\alpha$ surface (1.68 g/cm³). The flow flux under the $(10\overline{1}0)\text{-}\alpha$ surface is approximately 1.2 times higher than that under the $(10\overline{1}0)\text{-}\beta$ surface across various pressure gradients. We developed a theoretical model dividing the pore space into non-flowing, adsorbed, and bulk water regions, with critical thicknesses of 0.14 nm and 0.27 nm for the non-flowing region, and 0.15 nm for the adsorbed region in both surfaces. This model effectively predicts velocity distributions and volumetric flow rates with errors generally below 5%. Our findings provide insights into water transport mechanisms in shale inorganic nanopores and offer practical guidance for numerical simulation of shale gas production through dewatering operations. Full article