Pore Structure Characteristics Research Articles

Multifractal Characteristics of Low-Field Nuclear Magnetic Resonance of Different Rank Coals and Its Permeability Predicting Method.

The permeability of methane in coal is a crucial factor in the production of coal-bed methane (CBM), which is dependent on the pore size distribution (PSD) of coal. The transverse relaxation time cutoff value (T2C) is a crucial parameter in nuclear magnetic resonance (NMR) techniques for converting NMR data into an absolute PSD. To investigate an appropriate approach for predicting the T2C and permeability of different rank coals, this study first revealed, through centrifuge experiments with a centrifugal force of 1.38 MPa, the T2C values of five coal samples: anthracite coal (3 ms), lean coal (8 ms), coking coal (12 ms), fat coal (11 ms), and lignite coal (13 ms). These T2C values were then employed to obtain the absolute PSD values of the coal samples. The results demonstrated that the pore structure characteristics of these coal samples are essentially identical, with micropores constituting the majority, varying between 63.47% and 93.74%. Subsequently, the multifractal analysis method was introduced to establish a new T2C value calculation model. A comparison of the model-calculated T2C values with those obtained from centrifugal experiments revealed an average deviation of only 5.26%. Finally, a new permeability model was developed by conducting multiple regressions on permeability and multifractal parameters. In comparison to classical models, such as the Timur-Coates (TC) model and the Schlumberger Dauer Research Center (SDR) model, the developed permeability model offers more accurate predictions. These results are applicable to pore structure characterization and methane permeability prediction in coal reservoirs of varying rank and other unconventional gas reservoirs.

Evaluation of MSA mortar pore structure characteristics in water-saturated curing environment based on Talbot gradation theory

To investigate the impact of aggregate gradation on the pore structure of manufactured sand aggregate (MSA) mortar and its fractal characteristics under water-saturated curing conditions. The static pore structure characteristics of the pore structure of MSA mortar with 10 aggregate gradations were explored. The analysis is based on the Talbot gradation theory, the NMR technique, and fractal theory. The surface area and roughness of aggregate particles contribute to a reduction in the porosity of MSA mortar. The aggregate gradation is quantified using the Talbot index. The correlation characteristics and intrinsic relationships between Talbot index and different pore structure parameters, such as total porosity, pore gradation, pore fractal dimension and permeability of MSA mortar, are analyzed. Two pore division methods are employed to explore the interrelationships among pore types, fractal dimensions and Talbot index. Additionally, A correlation model between Talbot index and permeability is developed to investigate the intrinsic correlation of parameter variations from a microscopic perspective. It is found that aggregate gradation is optimal with a Talbot index of 0.4, leading to the highest number of micropores and the lowest number of larger pores, thereby enhancing resistance to seepage and dissolution. Furthermore, The contribution of pore size, content and type to permeability varies with different aggregate gradations. Overall, this study serves as a valuable guide for the design and durability evaluation of mortar concrete projects in water-saturated curing environments.

Supercritical water synthesized Ni/ZrO2 catalyst and its application in the harmless treatment of oilfield wastewater in supercritical water

Supercritical water (SCW) catalytic gasification is a clean and efficient technology with prominent advantages in treating oily wastewater generated in oilfields. SCW synthesis is a promising one-step preparation method for nano-catalytic materials, while the influence of organic matter on SCW synthesis materials remains to be studied. This study focuses on the synthesis of the Ni/ZrO2 catalysts by the supercritical water synthesis (SCWS) method, particularly examining how different types and concentrations of organic matter affect the catalysts’ pore information and structural characteristics. It found that glycerol acted as a more effective precursor for generating reducing gases compared to glucose. This is attributed to glycerol’s capacity in SCW to generate reducing gases for activating a greater number of Ni site within the catalyst, and the 5 wt% glycerol should be a proper concentration for SCWS of Ni/ZrO2. When employed in SCW treatment of oilfield wastewater, the Ni/ZrO2 catalyst demonstrated impressive results, achieving the carbon gasification efficiency of 99.1 % and a chemical oxygen demand (COD) removal efficiency of 100 % at 500°C. These findings indicate that the SCW technique can effectively and harmlessly treat oilfield wastewater using the Ni/ZrO2 catalyst under relatively mild conditions, showing its potential as an innovative solution for wastewater management in the oil industry.

In-line granular filtration for mitigating gypsum scaling in membrane distillation

Mineral scaling and scaling-induced wetting are major challenges for the widespread application of membrane distillation (MD) in saline wastewater treatment. For the first time, an in-line modified activated alumina (AA) granular filtration coupled with MD process was proposed to achieve effective control of gypsum scaling. Firstly, the AA modified by NaOH impregnation with tuned pore structure and surface characteristics were supplied as the filter media. The optimized MD performance was obtained using in-line filtration with modified AA (MAA) with 20 g/L NaOH and the ratio of AA and NaOH solution of 1:3 for the duration of 24 h. Compared with severe scaling without granular filter, the optimized performance with a final normalized flux higher than 0.7 and a permeate conductivity less than 5 μS/cm at 70 % water recovery was observed. The MAA with rich pore, scale-like structures and high Na loading showed a superior ability in capturing gypsum scaling due to the enhanced heterogeneous scaling and the retention of scaling. In-line granular filtration-MD was also effective in mitigating gypsum scaling and scaling-induced wetting in saline solutions (e.g., 7–12 g/L NaCl). Our findings provide guidance for surface design of granular filter media and scaling control in membrane desalination technology.

Improved pore structure characterization and classification of strong diagenesis sandstones by data-mining analytics in Tazhong area, Tarim Basin.

The Silurian system in Tazhong area is characterized by extensive, low-abundance lithological reservoirs with strong diagenesis, resulting in significant heterogeneity. The complex pore structure in this area significantly impacts fluid control, making accurate characterization and classification of pore structures crucial for understanding reservoir properties and their influence on oil and gas distribution. Based on 314 Mercury Injection Capillary Pressure (MICP) samples in combination with core slices and thin casting slices observation, a pipeline of characterization and classification scheme by data-mining analytics of strong diagenesis sandstone pore structure types in the study zone is established, and the characteristics of different pore structures are clarified. According to the pore structure parameter abstracted by MICP data compression and variable analysis based on hierarchical clustering and principal component analysis (PCA) analysis, the variables are reasonably evaluated and screened, and the screened variables can be divided into three groups: mean pore throat radius-maximum pore throat radius-median pore throat radius-pore throat diameter mean variable group, microscopic mean coefficient variable group, and median pressure displacement pressure-relative sorting coefficient variable group. The combination of classification schemes analysed by decision tree model and linear discriminant analysis (LDA) model was determined. In the two-dimensional projection diagram of LDA model, a relatively obvious distribution of low displacement pressure, middle displacement pressure and high displacement pressure was obtained, and three distribution lines were nearly parallel. Based on the relevant information, 6 combined classification schemes suitable for final pore structure modelling were determined verified by microscopic observation. The correct characterization and classification of pore structure can be applied to the prediction of pore type, which can be used to improve the prediction of oil and gas distribution and oil and gas recovery in the future.

Characterization of Pore Structure and Fluid Mobility of Shale Reservoirs.

Accompanying the commercial exploitation of shale oil and gas in North America, shale oil has gradually become an important resource, sparking great interest among countries around the world in recent years. In this study, focusing on the Paleogene Shahejie Formation in Bohai Bay (Eastern China), techniques such as CT, nitrogen adsorption, mercury injection capillary pressure (MICP), and nuclear magnetic resonance (NMR) were used to characterize the pore structure and mobility of the shale reservoir. Based on the X-ray CT data, the pore radius of the shale reservoir is in the range 0.5-65 μm, and the pore coordination number is concentrated in the range of 1-4. The shale reservoir is poorly connected. The minimum size of the unit body for establishing the digital core model is 380 μm. Based on the experimental data of nitrogen adsorption and MICP, the pores of shale in the study area are mainly classified as ink-bottle-shaped pores, transition-shaped pores, and flat plate slit-shaped pores. The specific surface area and volume of pores are mainly attributed to meso- and macropores. The movable fluid saturation of shale is distributed from 23.59 to 44.42%, the pore throat radius is distributed from 0.001 to 6 μm, and the lower limit of the movable pore throat radius of shale is distributed between 9.0 and 20.1 nm. The movable fluid porosity is mainly distributed between 0.84 and 4.08%, with an average movable fluid porosity of 2.37%. The findings provide a theoretical basis for the efficient development of shale oil resources.

Layered double hydroxide assembled on a metal–organic framework coupled with polyaniline as pseudocapacitive anode for phosphorus capture

Excessive phosphorus is detrimental to supporting the proper function of aquatic ecosystems. Capacitive deionization (CDI) is an emerging, highly efficient, eco-friendly electrochemical technology that eliminates phosphorus from wastewater. In this work, a novel LDH@MOF/PANI composite was successfully fabricated by utilizing polyaniline (PANI) as a conductive substrate and metal–organic framework (MOF) as a self-sacrificial template for layered double hydroxide (LDH). The results demonstrated that LDH and PANI are favorable for improving the pore structure features, enriching the phosphorus binding sites, and strengthening the electrochemical performance of the electrode materials. Accordingly, the LDH@MOF/PANI electrode presented a superior phosphorus capture capacity than LDH@MOF and MOF. The isotherm and kinetic experiments revealed that the phosphorus capture by LDH@MOF/PANI is a chemisorption-dominated process associated with heterogeneous adsorption. The potential interference with phosphorus uptake was also assessed by focusing on several vital factors. Eventually, the possible mechanism suggested that ligand exchange, anion exchange, hydrogen bond, electrostatic attraction, and electric field assistance participate in the phosphorus uptake process. This work presents promising insight into the assembly design and rational construction of LDH-based pseudocapacitive anode for phosphorus capture.

Carbonation modelling of hardened cementitious materials considering pore structure characteristics: A review

Carbonation of cementitious materials is one of the most important reasons leading to the deterioration of steel-reinforced concrete structures. After years of research, different models have been developed to investigate and predict the carbonation process. This review paper provides a comprehensive overview of carbonation modelling approaches at different scales considering pore structure characteristics. As a typical porous material, the microscopic characteristics of hardened cementitious materials will greatly affect the carbonation rate, and the complex physicochemical carbonation process will alter the pore structure, which will, in turn, affect the carbonation process. Currently, the importance of considering the evolved pore structure and its influence on concrete durability modelling has also gained more and more attention. Therefore, this review paper first introduces the fundamental mechanism of carbonation process in cementitious materials and the existing models for carbonation modelling. By dividing these models into macro-, meso- and micro-scales, this review summarises the modelling approaches, assumptions, pore structure consideration approaches and current limitations of the empirical, kinetic, three-phase, neural network, voxel-based lattice, pore network, and thermodynamic models. The different features of carbonation modelling and ways to consider the effect of pore structure characteristics in those models are comprehensively compared. This review also discusses the future perspectives of different models, especially the pore structure-dependent analysis approaches, to better link the microscopic and macroscopic properties and improve the applicability of carbonation modelling at different scales.

Dynamic fractionation of methane carbon isotope during mass transport in coal with bidisperse pore structures: Experiments, numerical modeling, and applications

Gas-in-place (GIP) content and the in-situ free/adsorbed gas ratio are crucial factors for evaluating resource potential and optimizing production strategies of deep coalbed methane (CBM). While the prevailing notion that adsorbed gas predominates is widely accepted in shallow CBM, this idea has been contested in deep CBM. Various numerical models for calculating GIP content based on gas volume data from canister degassing experiments commonly suffer from low accuracy, strong multiplicity, and inability to evaluate critical parameters of free/adsorbed gas ratio. Isotope fractionation is an important tool for studying the occurrence state and transport mechanism of natural gas, and numerical modeling that considers both cumulative degassing content and carbon isotope data has proven effective in determining the GIP content and adsorbed gas ratio in shale. However, the applicability of the existing isotope fractionation models in deep CBM has yet to be demonstrated experimentally and theoretically. In this study, four coal samples from the Shanxi and Taiyuan formations in Ordos Basin were subjected to canister degassing, gas metering, and methane isotopic composition testing. The results revealed significant multi-stage carbon isotope fractionation characteristics throughout deep CBM degassing, reflecting the strong heterogeneous pore structure characteristics within the coal. Existing carbon isotope fractionation (CIF) models are unable to effectively characterize this complex phenomenon. Based on these findings, we innovatively developed a CIF model that considers bidisperse pore structures and multiple transport mechanisms. The model can better characterize the complex isotope fractionation behavior and reveal the mechanisms of carbon isotope transport in series structures of multi-scale pores. Using the model, we calculated the GIP content of four experimental samples from the Shanxi and Taiyuan formations on the southeastern edge of the Ordos Basin, ranging from 27.78 m3/t to 39.13 m3/t, with an average of 31.68 m3/t, and the in-suit free gas ratio ranges from 13.30 % to 32.89 %, with an average of 19.45 %. These research findings provided new insights for assessing the resource potential of deep CBM, screening sweet spots, and predicting gas well performance.

Characterization of anisotropic pore structure and dense selective layer of capillary membranes for long-term ECMO by cross-sectional ion-milling method.

Since the COVID-19 pandemic of 2020-2023, extracorporeal membrane oxygenator (ECMO) has attracted considerable attention worldwide. It is expected that ECMO with long-term durability is put into practical use in order to prepare for next emerging infectious diseases and to facilitate manufacturing for novel medical devices. Polypropylene (PP) and polymethylpentene (PMP) capillary membranes are currently the mainstream for gas exchange membrane for ECMO. ECMO support days for COVID-19-related acute hypoxemic respiratory failure have been reported to be on average for 14 or 24days. It is necessary to improve opposing functions such that promoting the permeation of oxygen and carbon dioxide and inhibiting the permeation of water vapor or plasma to develop sufficient durability for long-term use. For this purpose, accurately controlling the anisotropy of the pore structure of the entire cross section and functions of capillary membrane is significant. In this study, we focused on the cross-sectional ion-milling (CSIM) method, to precisely clarify the pore structure of the entire cross section of capillary membrane for ECMO, because there is less physical stress on the porous structure applied during the preparation of cross-sectional samples of porous capillary membranes. We attempted to observe the cross sections of commercially available PMP membranes using the CSIM method. As a result, we succeeded in fabricating fine-scale flat cross-sectional samples of PMP capillary membranes. The pore structures and the degree of anisotropy of the cross sections are quantitatively clarified. The achievements and the approaches of this study are being applied to the development of next-generation gas exchange membranes.

Innovative Deep Learning Approaches for High-Precision Segmentation and Characterization of Sandstone Pore Structures in Reservoirs

Innovative Deep Learning Approaches for High-Precision Segmentation and Characterization of Sandstone Pore Structures in Reservoirs

Comparison of Pore Structure Characteristics of Shale-Oil and Tight-Oil Reservoirs in the Fengcheng Formation in Mahu Sag

Despite the abundance of shale-oil and tight-oil reserves in the Fengcheng Formation within the Mahu Sag, exploration and development efforts for both types of reservoir are still in their early stages. A comprehensive examination and comparison of the pore structures of these reservoirs can establish rational classification and evaluation criteria. However, there is a dearth of comparative analyses focusing on the pore structures of shale-oil and tight-oil reservoirs within the Fengcheng Formation. This study addresses this gap by systematically analyzing and comparing the pore structures of these reservoirs using various techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), low-temperature nitrogen adsorption, and mercury intrusion capillary pressure experiments (MICP). The results show that the shale oil within the Fengcheng Formation exhibits a higher content of carbonic acid compared to the tight-oil samples. Furthermore, it demonstrates smaller displacement pressure and median pressure, a larger sorting coefficient, and superior permeability in contrast to tight oil. Notably, the shale oil within the Fengcheng Formation is characterized by abundant striated layer structures and micro-fractures, which significantly contribute to the microstructural disparities between shale-oil and tight-oil reservoirs. These differences in microstructures between shale oil and tight oil within the Fengcheng Formation in the Mahu Sag region delineate distinct criteria for evaluating sweet spots in shale-oil and tight-oil reservoirs.

Extracting salt from soil with ceramic sheets

The study investigates the drying behavior and desalination effectiveness of porous ceramic tiles made from fired clay materials like bricks or pottery on soil columns initially saturated with saline solution. Evaporation kinetics experiments compared the drying of saline soil with and without a ceramic tile. For soil without a ceramic cover, salt precipitation formed an efflorescent crust that initially (t ∼ 30 h) reduced the evaporation rate. However, with continued drying, the tensile stress caused cracks in the crust, allowing increased evaporation through the cracks (t > 200 h). When covered with a ceramic poultice, the saline solution was wicked into the porous ceramic by capillary action. Rapid salt efflorescence was observed on the ceramic surface. The ceramic layer initially reduced the soil evaporation rate due to pore clogging caused by salt precipitation. The pore structure characteristics of the ceramics significantly impacted their desalination performance. After an initial fast drying period controlled by evaporation, a reduced drying rate was observed as salt clogging effects became dominant, especially for the low porosity ceramic (t ∼20 h). The porous ceramic poultices could effectively extract salts from the soil, but their desalination efficiency depended critically on their pore structure properties. An industrial-based clay ceramic with large and more connected pores (porosity 0.33) was found to be around 62% more efficient in removing NaCl than a handmade pottery with small pores (porosity 0.18).

An investigation on enhancing the bonding properties of 3D printed concrete permanent formwork and post-casted concrete

Employing 3D-printed permanent formwork (3DPF) technology for rapidly manufacturing prefabricated components constructed with reinforced concrete represents a promising application of additive manufacturing technology in load-bearing constructions. Ensuring efficient bonding between 3DPF and post-casted concrete (PCC) is a prerequisite for the widespread adoption of this technology. This research aims to enhance the 3DPF-PCC interface through: physical (groove), chemical (cement paste) and composite methods. The interfacial bond strength was quantitatively analysed by splitting tensile strength and shear strength. X-ray computed tomography scanning was utilized for the quantitative characterization of pore structures. Digital image processing techniques were employed to monitor crack development during splitting tensile tests. The mechanism for strengthening the shear strength of the grooved interface was elucidated using a finite element model, and a modified formula for calculating the shear strength of the 3DPF-PCC grooved interface was proposed. The physical method improves shear strength by increasing interlocking structures significantly. The composite method weakens mechanical interlocking structures, increases interface porosity, and adversely affects interface bonding strength. It is recommended that future engineering applications adopt the physical process to improve mechanical interlocking structures and ensure interface bonding strength.

An Investigation on the Pore Structure Characterization of Sandstone Using a Scanning Electron Microscope and an Online Nuclear Magnetic Resonance System

An Investigation on the Pore Structure Characterization of Sandstone Using a Scanning Electron Microscope and an Online Nuclear Magnetic Resonance System

Effect of [C12mim][Cl]-NaCl compound solutions on pore structure and wetting characteristics of bituminous coal based on Pearson correlation coefficient

Water injection technology is a compelling technical measure to improve the water content of coal seams and reduce dust generation during mining. At present, the methods to enhance the wetting effect in the research progress are limited to increasing the dosage of a single wetting agent and using a variety of anionic and cationic wetting agents in large doses. More research is needed on the synergistic enhancement of the wetting effect by inorganic salts and ionic liquids. Aiming at this problem, this paper studies the influence of the combination of NaCl and surface active ionic liquid [C12mim][Cl] on the wetting effect and pore structure of bituminous coal. The influence of composite solution and ratio change on coal pore structure and wetting characteristics is studied based on Pearson correlation coefficient, combined with the experimental results of nitrogen adsorption at low temperature, scanning electron microscope and wetting characterization. The results show that bituminous coal exhibits different sizes of hysteresis rings after [C12mim][Cl] and NaCl treatments. With the change in composite ratio, the pore connectivity of coal samples is improved, and the surface roughness of modified bituminous coal is affected by the shift in composite ratio. With the enhancement of the wetting effect, the pore depth increases. On the other hand, adding 0.6 mol/L NaCl makes the composite solution reach a critical micelle concentration, which could synergistically enhance the surface activity and wetting effect of [C12mim][Cl] solution. There is a negative correlation between the volume of bituminous coal macropores and the contact angle, which indicates that the optimal solution ratio can be determined by analyzing the bituminous coal macropore volume change.

Electronic Properties of [Ru(NH3)6][M(CN)6] Double-Complex Crystals and Their Thermal Decomposition to Prussian Blue Analogs

The complex ions, [Ru(NH3)6]2+/3+ and [Fe(CN)6]3-/4-, are well known redox couples exhibiting fast interfacial and homogeneous electron transfer rates in aqueous solution. Here we show that when mixed together, they form insoluble double-complex Ax[Ru(NH3)6][Fe(CN)6] crystals with rhombohedral symmetry, where A is a cationic species and 0≤x≤2. The analogous interactions of [Ru(NH3)6]2+/3+ with [Ru(CN)6]3-/4- produces Ax[Ru(NH3)6][Fe(CN)6] crystals. Electrical measurements of these single crystals exhibit ohmic current-voltage responses, with corresponding conductivities on the order of 0.1 mS/m. We propose a solid-state charge transport mechanism based on Marcus theory for homogeneous outer-sphere electron transfer.Thermal decomposition at mild temperatures removes ammine ligands and transforms these crystals into nanopolycrystalline Prussian blue analogs (PBAs) that retain the macroscopic geometry of the double-complex crystals but adopt the familiar highly defected porous crystal structure and intervalence charge transfer characteristics of PBAs.

Characterization of effective moisture diffusivity based on pore structure of concrete

Concrete durability is greatly influenced by the transport rate of aggressive chemicals. Moisture diffusion plays a key role in the long-term performance of cementitious materials, as it facilitates the entry of aggressive chemicals into concrete. The pore size distribution plays a critical role in determining moisture diffusivity. However, the characteristics of the concrete pore structure have not been included comprehensively in the material models so far. In this paper, a theoretical model was developed to obtain the pore size volume fractions for each diffusion mechanism including Molecular, Knudsen and Surface diffusions. An effective moisture diffusivity in concrete was then obtained using the weighted average based on the diffusion mechanisms and pore size volume fractions. The model’s validity was demonstrated by comparing model predictions with available experimental data. The findings of this study provide valuable insights into the behavior of the concrete pore structure and its impact on moisture diffusivity.

Molecular Structural Characteristics and 3D Model Reconstruction of Organic Matter in Longmaxi Formation Shale.

The establishment of molecular structure modeling is an important means to study the pore characteristics of shale organic matter and is significant for molecular-level simulations of gas storage and diffusion. Using 13C NMR, FTIR, and XPS combined with the split-peak fitting technique, the structural characteristics of the aromatic structure, aliphatic structure, and oxygen functional groups of kerogen from the shale of the Longmaxi Formation, Wuxi County, Chongqing Municipality, were quantitatively characterized. A macromolecular structure model of the kerogen was also constructed by using the 2D macromolecular structure model construction method in combination with elemental analysis experiments. The results showed that the 2D single-molecule structural model of the sample consisted of 2 benzenes, 2 naphthalenes, 1 anthracene, 5 pyrenes, 1 pyridine, and 1 pyrrole. The C skeleton types were 93 protonated arylons, 39 bridged arylons, 6 carboxylons, 5 alkyl-substituted carbons, 2 oxygen-substituted carbons, 4 methylene carbons, and 3 methylons. The established 2D molecular structure formula was C152H82O12N2. The final 3D macromolecular structure model consisted of 14 2D molecular structures (structural formula C2128H1148O168N28), with the density set to 1.77 cm3/g, compressed in a cubic cell with an edge length of 3.05 nm. Finally, the adsorption results showed that the experimental adsorption of CO2 adsorption was less than the simulated adsorption, completing the validation of the model. The above study provides a method for determining the molecular structure of kerogen in the Longmaxi Formation shale, which can guide the study of the pore structure characteristics of the Longmaxi Formation shale.

Study on the permeability and capillary pressure of spiral woven mesh for flat-plate heat pipes

Due to its excellent capillary characteristics, spiral woven mesh is widely used as the wick structure in ultra-thin flat-plate heat pipes. The performance of these heat pipes surpasses that of conventional ones using sintered powder or multi-layer mesh structures. However, precise quantitative studies on the permeability and capillary pressure characteristics of this unique porous structure are lacking. In this work, we systematically investigated its permeability and capillary pressure, as well as their relationship with the structure. Based on experimental results, we demonstrated that numerical simulation of periodic microelements and subsequent area weighting can accurately predict the permeability of actual structures. Additionally, a parametric study was conducted, yielding a unified empirical relationship between permeability and the structural parameters. In the part of capillary pressure, U-shape tube gravity method was utilized and the relationship between capillary pressure and structure was also disclosed. This study will provide reliable data and theoretical guidance for calculating the capillary limit in heat pipes using spiral woven mesh as the wick.