Search Results (237)

Lacustrine shale oil in the Chang 7 Member of the Ordos Basin is controlled by a multi-scale pore–throat system in which oil occurrence, spontaneous imbibition, and pore-structure evolution are tightly coupled. In this study, nitrogen adsorption and micro-computed tomography (μCT) were employed to characterize pore-size distribution and connectivity, whereas nuclear magnetic resonance (NMR) T₂ relaxation was utilized to classify oil occurrence states, and X-ray diffraction (XRD) and total organic carbon (TOC) analyses were performed to determine mineralogical and organic compositions. Spontaneous imbibition experiments were conducted at 60 °C and subsequently extended to temperature–pressure sequence tests. The Chang 7 shale exhibits a stratified pore system in which micropores, mesopores, and macropores jointly define a three-tier “micropore adsorption–mesopore confinement–macropore mobility” pattern. As pore size and connectivity increase, the equilibrium imbibed mass and initial imbibition rate both rise, while enhanced wettability (contact angle decreasing from 81.2° to 58.7°) further strengthens capillary uptake. Temperature elevation promotes imbibition, whereas increasing confining pressure suppresses it, revealing a “thermal enhancement–pressure suppression” behavior. μCT-based network analysis shows that imbibition activates previously ineffective pore–throat elements, increasing coordination number and connectivity and reducing tortuosity, which collectively represents a capillary-driven structural reconfiguration of the pore network. When connectivity exceeds a threshold of about 0.70, the flow regime shifts from interface-dominated to channel-dominated. Building on these observations, a multi-scalecoupling framework and a three-stage synergistic mechanism of “pore-throat activation–energy conversion–structural reconstruction” are established. These results provide a quantitative basis for predicting imbibition efficiency and optimizing capillary-driven development strategies in deep shale oil reservoirs. Full article

Reliable performance of TRISO (tristructural isotropic) nuclear fuel depends on the interplay between its multilayer architecture and the buffer-layer microstructure, which are difficult to isolate experimentally. We implement a multiscale, multiphysics model in the open-source MOOSE (Multiphysics Object-Oriented Simulation Environment) framework that couples particle-scale thermo-mechanical finite-element analysis with mesoscale phase-field fracture to link microstructure to effective stiffness and strength. The model resolves the combined influence of pore volume fraction, size, and aspect ratio and explicitly separates the effects of reduced load-bearing capacity from stress concentrations in the porous buffer. Simulations reveal substantial hoop stresses across coating layers under nominal thermal conditions due to material property mismatches and temperature gradients. In the buffer, stiffness and strength decrease with porosity; morphology is decisive: as aspect ratio decreases, strength degrades far more rapidly than stiffness, consistent with crack-like pores that amplify local stresses. The framework reproduces logarithmic trends with aspect ratio and explains the higher sensitivity of strength, providing parameters that can inform design and acceptance criteria (e.g., limits on pore elongation and porosity gradients). Implemented within MOOSE, the approach is readily extensible to irradiation-dependent kinetics, interface debonding, and uncertainty-quantified 3D analyses to support risk-informed TRISO fuel development. Full article

Zeolite is a popular soil amendment capable of improving physical and chemical properties of soils. This study investigates how zeolite concentration affects the hydrological connectivity of sandy loam soil. Soil samples with different zeolite concentrations C_z (0, 1, 1.5, 2.5, 5, 10, 15, and 30%) were analyzed for changes in water dynamics through Fast Field Cycling Nuclear Magnetic Resonance (FFC-NMR) relaxometry. FFC-NMR data revealed that the investigated zeolite can modify the pore size distribution in a wide range (1–15%) of C_z, as the zeolite particle size distribution has a percentage of coarse particles (56%) appreciably higher than that of the original soil (37%). Moreover, a concentration of 1% produces a more relevant increase in the soil’s meso- and macropores, while for C_z > 1.5%, the change in pore size distribution is damped by the increase in water retention that occurs upon increasing zeolite concentration. The analysis also demonstrated that C_z = 1% is sufficient to achieve the highest values of both structural and functional connectivity indexes. In conclusion, for sandy loam soil, adding a zeolite concentration of 1% is sufficient to improve the soil’s physical characteristics, with significant effects on soil hydrological behavior, and can be considered a valid practice to manage the addition of a water resource to the soil. Full article

The exploration potential, storage capacity, and exploitability of the deep shale-gas reservoirs are governed by various characteristics of their pore networks. Conventional methods cannot fully capture these features across scales, highlighting the need for an integrated, multi-technique approach. In this study, pore structure and connectivity of the Wufeng–Longmaxi Formation (Luzhou Block) were investigated using Scanning Electron Microscopy (SEM) with the Mosaic Acquisition and Positioning System (MAPS), ImageJ (ImageJ 2.14.0)-based pore analysis, Mercury Intrusion Porosimetry (MIP), and Nuclear Magnetic Resonance (NMR). Based on the samples from eight reservoir layers of Wufeng-WF and Longmaxi-LM1₁^1–7, shale pore connectivity was classified into three grades. Grade A layers, with connected pore volumes above 0.0067 cm³/g and porosity exceeding 1.75%, showed trimodal NMR pore-size distributions and strong connectivity among micro, meso, and macropores. Grade B layers exhibited bimodal pore distributions, moderate pore connectivity (0.0057–0.0067 cm³/g; 1.55–1.75% porosity), and sponge-like organic pores with isolated mineral pores. Grade C layers, with connected pore volumes below 0.0057 cm³/g, showed poor connectivity and unimodal NMR responses. Connected pores (1–100 nm) contributed 20–35% of total pore volume, reflecting the strong heterogeneity of the formation. Interconnected inorganic mineral-hosted pores were found to link locally connected organic pores, forming continuous pore networks. The qualitative and quantitative identification of the pore connectivity of shale reservoirs with MAPS, MIP, and NMR approach provides a robust framework for evaluating shale pore connectivity and identifying high-quality reservoir targets. Full article

The Middle Jurassic Lianggaoshan and Shaximiao Formations are the primary crude oil reservoirs in the central Sichuan Basin, offering significant resource potential. However, studies on reservoir characterization across different lithologies remain limited. This study focuses on fluvial–deltaic sandstones, siltstones, and lacustrine shales, analyzing pore types, structures, pore size distribution, and connectivity using various methods, including X-ray diffraction (XRD), thin-section analysis, scanning electron microscopy (SEM), high-pressure mercury injection, low-temperature nitrogen adsorption, and nuclear magnetic resonance (NMR) spectroscopy. The results show that sandstones exhibit the largest pore space, followed by siltstones, while shales have the smallest pore space. These reservoirs are relatively tight, with poor connectivity and high heterogeneity. Sandstone reservoirs, with their high quartz content, represent high-quality reservoirs because of their relatively good connectivity. Therefore, areas with well-developed natural fractures in sandstone are considered high-quality targets. For nanoscale reservoirs in siltstone and shale, horizontal fracturing is essential to improve reservoir properties, provided that source–reservoir matching is adequate. This study offers a detailed reservoir characterization across different lithologies, providing new insights for the optimization of favorable crude oil zones in the central Sichuan Basin. Full article

Understanding the microscopic occurrence states of shale oil—particularly the distribution between adsorbed and free phases—is essential for optimizing the development of unconventional reservoirs. In this study, we propose an integrated methodology that combines experimental techniques with molecular dynamics simulations to investigate shale oil behavior within kerogen nanopores. Specifically, pyrolysis–gas chromatography–mass spectrometry (PY-GC-MS), solid-state ¹³C nuclear magnetic resonance (¹³C NMR), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) were performed to construct a representative kerogen molecular model based on shale samples from the Lianggaoshan Formation in the Sichuan Basin. Grand Canonical Monte Carlo (GCMC) simulations and a theoretical occurrence model were applied to quantify the adsorption characteristics of n-dodecane under varying pore sizes, temperatures, and pressure. The results show that temperature exerts a stronger influence than pore diameter on adsorption capacity, with adsorption decreasing by over 50% at higher temperatures, and pressure has a limited effect on the adsorption amount of dodecane molecules. This study offers a robust workflow for evaluating shale oil occurrence states in complex pore systems and provides guidance for thermal stimulation strategies in tight oil reservoirs. Full article

Elucidating the characteristics of methane adsorption in coal is essential for accurately assessing coalbed methane (CBM) potential. Methane adsorption is primarily governed by the compositional complexity of coal and its pore structure. Molecular simulation enables characterization of coal’s molecular composition at the microscopic level and facilitates the construction of nanoscale pore models. In this study, Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Photoelectron Spectroscopy (XPS) were used to characterize the molecular structure of coal. Pore models of various sizes were constructed in Materials Studio (MS) to simulate methane adsorption under different temperatures and pressures. To further clarify the influence of molecular structure, a reconstructed macromolecular model (RMM) was compared with a graphite model, revealing differences in methane adsorption behavior across varying pore sizes, temperatures, and pressures. The results show that absolute methane adsorption increases with pore size, while excess adsorption behavior is strongly associated with the adsorption layer. In the pore size range of 0.4 nm to 1.2 nm, excess adsorption increases due to spatial confinement, but decreases as pore size exceeds 1.2 nm. Structural differences between the RMM and graphite models also resulted in distinct temperature responses, with the graphite model underestimating methane adsorption capacity, highlighting the importance of realistic macromolecular representations in adsorption studies. Full article

This study is based on an experiment and a molecular dynamics simulation to investigate the distribution states and property variation laws of crude oil in nanopores, aiming to provide theoretical support for efficient unconventional oil and gas development. Focus is placed on the distribution mechanisms of multicomponent crude oil in oil-wet siltstone (SiO₂) and dolomitic rock (dolomite, CaMg₃(CO₃)₄) nanopores, with comprehensive consideration of key factors including pore size, rock type, and CO₂ flooding on crude oil distribution at 353 K and 40 MPa. It is revealed that aromatic hydrocarbons (toluene) in multicomponent crude oil are preferentially adsorbed on pore walls due to π-π interactions, while n-hexane diffuses toward the pore center driven by hydrophobic effects. Pore size significantly affects the distribution states of crude oil: ordered adsorption structures form for n-hexane in 2 nm pores, whereas distributions become dispersed in 9 nm pores, with adsorption energy changing as pore size increases. Dolomite exhibits a significantly higher adsorption energy than SiO₂ due to surface roughness and calcium–magnesium ion crystal fields. CO₂ weakens the interaction between crude oil and pore walls through competitive adsorption and reduces viscosity via dissolution, promoting crude oil mobility. Nuclear magnetic resonance (NMR) experiments further verified the effect of CO₂ on crude oil stripping in pores. This study not only clarifies the collaborative adsorption mechanisms and displacement regulation laws of multi-component crude oil in nanopores but also provides a solid theoretical basis for CO₂ injection strategies in unconventional reservoir development. Full article

The complexity of tight sandstone reservoirs challenges effective oil and gas exploration. The Chang 8 Member of the Yanchang Formation in the Longdong area of the Ordos Basin has significant exploration potential. However, its reservoir characteristics are controlled by two distinct provenance systems and diverse sedimentary microfacies. The specific impacts of these factors on reservoir quality and their relative importance have remained unclear. This study employs an integrated analytical approach combining casting thin sections, conventional porosity-permeability measurements, and Nuclear Magnetic Resonance (NMR) to systematically investigate the petrological characteristics, pore structure, and physical properties of the Chang 8 reservoirs. Our findings reveal that the entire section of Chang 8 is a delta front subfacies, with sub sections of Chang 8¹ and 8² developing microfacies such as underwater distributary channels, underwater natural levees, sheet sand and mouth bars. The tight sandstone reservoir is mainly composed of lithic arkose and feldspathic litharenite, with its porosity dominated by dissolution and intergranular types. These secondary pores, particularly those resulting from feldspar dissolution, are of great importance. The underwater distributary channels have the best pores, followed by sheet sands, and underwater natural levees the worst. Compaction in Chang 8² is stronger than in Chang 8¹, leading to smaller pores. The northwest provenance is characterized by high clay content and small pores, while the southwest provenance has coarser grain size and better-preserved intergranular pores. Reservoir properties improve toward the lake but deteriorate at the lake-proximal end due to more small pores. This study reveals the control laws of sedimentary microfacies, provenance, and diagenesis on the pore development of tight sandstone in the Longdong area, providing theoretical guidance for the exploration and development of tight sandstone oil and gas in the region. Full article

This study investigates the air filtration capabilities of fibrous membranes fabricated via electrospinning, with a focus on optimizing processing parameters. Specifically, Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), a well-characterized biodegradable polyester, was electrospun to produce membranes exhibiting precisely controlled surface microstructures. The optimal fiber morphology was attained under conditions of a 20 kV applied electric field, a solution flow rate of 0.5 mL·h⁻¹, a polymer concentration of 13 wt.%, and a needle inner diameter of 0.21 mm. The microstructural features of the electrospun PHBV membranes were characterized using scanning electron microscopy (SEM). Complementary analysis via ¹³C nuclear magnetic resonance (NMR) spectroscopy confirmed that the membranes comprised pure 3-hydroxyvalerate (3HV) copolymerized with 3-hydroxybutyrate (3HB) terminal units, with 3HV mole fractions ranging from 17% to 50%. The incorporation of different molar percentages of 3HV in PHBV membrane significantly enhances its durability, as evidenced by Ball Burst Strength (BBS) measurements, with an elongation at burst that is 65–86% greater than that of ASTM F2100 level 3 mask. The nanofibrous membranes exhibited a controlled pore size distribution, indicating their potential suitability for air filtration applications. Particle filtration efficiency (PFE) assessments under standard atmospheric pressure conditions showed that the optimized electrospun PHBV membranes achieved filtration efficiencies exceeding 98%. Additionally, the influence of 3HV content on biodegradation behavior was evaluated through soil burial tests conducted over 90 days. Results indicated that membranes with lower 3HV content (17 mol.%) experienced the greatest weight loss, suggesting accelerated degradation in natural soil environments. Full article

The oil content in a produced fluid plays a crucial role in oil production engineering. In this paper, a predictive model for the oil and water proportions in produced fluid was established through nuclear magnetic resonance coupling displacement. This model successfully predicts the oil proportion in the produced fluid from each block within the Gaotaizi oil reservoir of the Songliao Basin and elucidates the reasons for its variation across different blocks. The production of pure oil in a vertical well area was attributed to the reservoir fluid exhibiting high bound water saturation, resulting in oil being the primary movable phase. In the testing and extended areas, variations in oil saturation combined with the pore size distribution governing oil and water occupancy are likely responsible for the differing oil-water ratios observed in the produced fluid. Specifically, a higher oil-to-water ratio (7:3) was produced in the testing area, while the extended area yielded a lower oil-to-water ratio (3:7). Furthermore, the model predicts an oil-to-water ratio of 4:6 for the produced fluid in the Fangxing area. To enhance oil production in the extended area, narrowing the fracture interval is proposed. However, this measure may not prove effective in other blocks. Full article

To investigate the flow characteristics of movable water in coal under the influence of micro-nano pore fractures with multiple fractal structures, this study employed nuclear magnetic resonance (NMR) and multifractal theory to analyze gas–water seepage under different injection pressures. Then, the scale threshold for mobile water entering coal pores and fractures was determined by clarifying the relationship among “injection pressure-T₂ dynamic multiple fractal parameter seepage resistance-critical pore scale”. The results indicate that coal samples from Yiwu (YW) and Wuxiang (WX) enter the nanoscale pore size range at an injection pressure of 8 MPa, while the coal sample from Malan (ML) enters the nanoscale pore size range at an injection pressure of 9 MPa. During the water injection process, there is a significant linear relationship between the multiple fractal parameters log X(q, ε) and log(ε) of the sample. The generalized fractal dimension D(q) decreases monotonically with increasing q in an inverse S-shape. This decrease occurs in two distinct stages: D(q) decreases rapidly in the low probability interval q < 0; D(q) decreases slowly in the high probability interval q > 0. The multiple fractal singularity spectrum function f(α) has an asymmetric upward parabolic convex function relationship with α, which is divided into a rapidly increasing left branch curve and a slowly decreasing right branch curve with α₀ as the boundary. Supporting evidence indicates the feasibility of a methodology for identifying the variation in multiple fractal parameters of gas–water NMR seepage and the critical scale transition conditions. This investigation establishes a methodological foundation for analyzing gas–water transport pathways within porous media materials. Full article

With the increasing demand for soil modification technologies in the field of civil engineering, this study employed cement-stabilized soil and MBER (Material Becoming Earth into Rock) stabilized soil as controls to investigate the modification effects of an N-MBER (nanosilica reinforced MBER) stabilizer on the mechanical properties and microstructure of loess. The mechanical and water stability characteristics of N-MBER-stabilized loess under varying moisture contents and compaction degrees were analyzed through unconfined compressive strength (UCS) tests, softening coefficient tests, falling-head permeability tests, and wet–dry cycle tests. Combined with scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and nuclear magnetic resonance (NMR) techniques, the underlying mechanism of the N-MBER stabilizer in loess stabilization was thoroughly revealed. The results indicate that the N-MBER stabilizer significantly enhances the UCS and softening coefficient of loess. Particularly, under conditions of 28-day curing, a moisture content of 16%, and a compaction degree of 1, the compressive strength achieves a local optimum value of 3.68 MPa. Compared to soils stabilized with MBER stabilizers and cement stabilizers, the N-MBER-stabilized loess exhibits superior water resistance and microstructural density, with a significant reduction in the proportion of pore defects. Specifically, after five wet–dry cycles at a curing age of 28 days, the strength loss rates for MBER-stabilized soil and cement-stabilized soil were 24.4% and 27.54%, respectively, while that for N-MBER-stabilized soil was 18.23%, demonstrating its enhanced water resistance. Additionally, compared to cement-stabilized soil, the N-MBER-stabilized soil exhibited a 21.63% reduction in total pore number, with a 41.64% reduction specifically in large pores. The extremely small particle size and large specific surface area of the nanomaterial enable more effective interactions with soil particles, promoting hydration reactions. The resulting ettringite (AFt) and three-dimensional networked C-S-H gel tightly interweave with soil particles, forming a stable cemented structure. Compared to traditional concrete roads, stabilized soil roads enable the utilization of locally available materials and demonstrate a significant cost advantage. This study provides theoretical support and experimental evidence for the application of nanomaterials in loess improvement engineering. Full article

This review provides a comprehensive examination of porosity and permeability as key parameters governing the durability and performance of construction materials, including natural stone, mortar, concrete, and other cementitious composites. It highlights the pivotal role of pore structure in transport phenomena and degradation mechanisms, examining how the variations in pore architecture, encompassing total vs. effective porosity, pore size distribution, and pore connectivity, dictate a material’s response to environmental stressors. A comparative evaluation of advanced pore characterization techniques is presented, including helium pycnometry, mercury intrusion porosimetry (MIP), nitrogen adsorption (BET/BJH), nuclear magnetic resonance (NMR) relaxometry, and imaging methods such as optical microscopy, scanning electron microscopy (SEM), and X-ray micro-computed tomography (micro-CT). Furthermore, it assesses how these porosity and permeability characteristics influence durability-related processes like freeze–thaw cycling, chloride ingress, sulphate attack, and carbonation. Case studies are discussed in which various additives have been employed to refine the pore structure of cement-based materials, and pervious concrete is highlighted as an example where deliberately high porosity and permeability confer functional benefits (e.g., enhanced drainage). Overall, these insights underscore the importance of tailoring porosity and permeability in material design to enhance durability and sustainability in construction engineering. Full article

Although coagulation can enhance sludge dewatering performance, it often leads to dense flocs, hindered water release, and secondary pollution of the sludge cake. In this study, three types of biochar-based skeleton materials, tea waste-derived biochar (TB), PAC sludge-derived biochar (PB), and their mixture (MB), were employed in combination with polyaluminum chloride (PAC) to improve sludge permeability and water release capacity. The results showed that PAC alone reduced the water content (Wc) and capillary suction time (CST) of raw sludge (RS) from 79.07% and 97.45 s to 69.45% and 42.30 s, respectively. In contrast, biochar–PAC composite conditioning achieved further enhancement. Among them, the TBP group (10% DS TB + 4% DS PAC) exhibited the best performance, with Wc and CST reduced to 58.73% and 55.65 s, reaching the threshold for deep dewatering (Wc < 60%). Low-field nuclear magnetic resonance (LF-NMR) analysis revealed an enhanced transformation from bound to free water, improving water mobility. Zeta potential and particle size analysis indicated that biochar promoted electrostatic neutralization and adsorption bridging. Rheological and EPS measurements demonstrated significant reductions in yield stress and apparent viscosity, alongside the enhanced release of proteins and polysaccharides into soluble EPS (S-EPS). Scanning electron microscopy and pore structure analysis further confirmed that biochar formed a stable porous skeleton (pore diameter up to 1.365 μm), improving sludge cake permeability. In summary, biochar synergizes with PAC through a “skeleton support–charge neutralization–adsorption bridging” mechanism, reconstructing sludge microstructure and significantly improving deep dewatering performance. Full article