Multiscale Pore Structure Research Articles

Effects of Supercritical Carbon Dioxide Saturation Temperature on the Multiscale Pore Structure of Coal

Effects of Supercritical Carbon Dioxide Saturation Temperature on the Multiscale Pore Structure of Coal

Tunable honeycomb-hierarchical multiscale structures of 2D/3D porous PLA/CCN composite films fabricated by the breath figure method

Highly ordered porous structures of PLA composite films can be designed with the addition of calcium carbonate nanoparticles (CCN) in polymeric film formation using the breath figure (BF) technique at controlled humidity. Both 2D and 3D monodispersed honeycomb-like porous structures of the PLA composite films are achieved by the adding CCN at the concentration of up to 1.00 phr, whereas hierarchically multiscale porous structures of the PLA/CCN films are obtained when the CCN concentration in the composites increases to more than 1.00 phr. These structures can be fabricated due to three mechanisms: water absorption and condensation, nano-Pickering emulsion, and capillary flow by self-assembly of the nanoparticles. Moreover, the nano effects of CCN on polymeric film fabrication are maximized by increasing the relative humidity to 90%, resulting in the formation of porous multilayers up to 95–120 μm in thickness. The application of the prepared porous composite films of PLA/CCN in the food and medical industries was illustrated. A model colorimetric sensor is made from PLA/CCN composite films enriched with bromothymol blue. The color of the films quickly changes from yellow to blue within 10 min after coming into contact with histamine, a representative gas generated from spoiled food.

Hydraulic conductivity and multi-scale pore structure of polymer-enhanced geosynthetic clay liners permeated with bauxite liquors

A study was conducted to investigate the multi-scale pore structure-based mechanism controlling the hydraulic conductivity of polymer-enhanced geosynthetic clay liners (GCLs) prepared by the wet-mixed method to bauxite liquors (BLS and BLA). The multi-scale pore structures were evaluated using MIP and N2GA tests quantitatively. Conventional GCL permeated with BLS had a larger flow path volume than with DI water (0.194 > 0.119 cm³/g), attributed to the bentonite swelling inhibition and the montmorillonite dissolution, leading to the higher hydraulic conductivity (3.0 × 10−7 > 2.7 × 10−11 m/s). Polymer-enhanced GCLs developed more micropores and had a smaller quantity proportion and volume of flow paths since polymer formed more micropores to clog pores, contributing to a lower hydraulic conductivity than conventional GCL to BLS. The hydraulic conductivity of polymer-enhanced GCL to BLS (ionic strength: 622.5 mM) was higher than that to BLA (156.9 mM) (2.6 × 10−9 > 6.0 × 10−12 m/s), given that the coiled or contracted polymer conformation left a smaller quantity proportion (5.54% < 6.71%) and volume (0.0002 cm3/g < 0.0035 cm3/g) of micropores.

Lightweight, thermal insulation, hydrophobic mycelium composites with hierarchical porous structure: Design, manufacture and applications

Mycelium composites offer a sustainable alternative to lightweight petroleum-based plastic products and are attracting great attention in various fields. However, creating a mycelium composite with both superior thermal insulation and mechanical strength remains a significant challenge. Here, different sizes of poplar or birch sawdust arranged in a loose and disordered manner are employed to construct mycelium composites with multiscale hierarchical porous structure, including both meso- and microscale pores. The morphological, biological, and physicochemical properties of the filamentous mycelium and the resulting composites are discussed in terms of how they are influenced by the substrate features and the way they interact with the fungus. Mycelium composites with high porosity (∼93%) demonstrate energy absorption of 32 kJ m−3, cushioning coefficient of 5, thermal conductivity of 0.044 W m−1 K−1, and contact angle of 123°, which is comparable to or even better than expanded polystyrene. Lightweight, thermally insulating, hydrophobic mycelium composites with excellent mechanical properties show broad prospects in construction and packaging.

Investigation of cross-scale characterization of porous structure and fluid index in bituminous coal via microwave-LN2 freeze-thaw cycles

Microwave-LN2 cyclic processing (MLCP) is a clean and high-efficiency anhydrous fracturing technology. The change in the porous structure of coal after freeze-thaw cycles significantly affects development efficiency of coalbed methane (CBM) in low porosity and permeability reservoirs, while there is a lack of in-depth macro-meso-micro studies. The damage mechanism of coal under microwave-LN2 cold and thermal shock and the evolution of pore fluid reservoir space is based on cross-scale pore characterisation. This paper evaluates the multi-scale porous structure variations of coal before and after MLCP was assessed by hydrogen nuclear magnetic resonance (1H NNR) and field emission scanning electron microscopy (FE-SEM). The evolutionary trends in coal pore fluid fugacity space under freeze-thaw cycles was indirectly characterised by T1-T2 spectra. Additionally, utilizing T2 distribution, peak area and pore throat changes reflect the evolution trend of coal pore space. The results indicate that as the cycles increased, the coal free water and total fluid reservoir space gradually expanded beyond the cycle threshold (n > 10), the free-fluid index rose to 25.68 %, and the free fluid saturation increased by 20.39 %. Additionally, the NMR permeability of the coal increased by 98.37–1471.65 %, and the pore throat distribution increased by 28.05 %. Comprehensive analysis showed that as the cycles progressed, the free water space in the pore space increased significantly, the proportion of bound water gradually decreased, and the internal pores and fluid space of the coal were improved. This study provides fundamental support for multidimensional evaluation of the porous structure of microwave-LN2 freeze-thaw cycles.

Construction of a reduced graphene oxide/polyvinyl alcohol (PVA)-natural rubber (NR) porous rubber sponge toward solar-driven sustainable water purification

Solar-driven evaporation is an environmentally benign and sustainable technology to address the global water crisis. The abundant and renewable solar energy as its sole input energy, thus leading to zero-carbon emission and minimum environmental impact. Thus, in this work, a hydrophilic reduced graphene oxide (rGO)/polyvinyl alcohol (PVA)-natural rubber (NR) porous rubber sponge was obtained by emulsion ice template and vulcanizing at high temperature. The cross-linked NR rubber and the robust PVA endow rGO/PVA-NR sponge with excellent flexibility integrated outstanding mechanical robustness. The water evaporation rate of the resultant rGO/PVA-NR evaporator can reach up to 2.11 kg·m−2·h−1 under 3 sun illumination. Moreover, benefitting from the multi-scale porous structure and hydrophilicity of the rGO/PVA-NR sponge, water is continuously transported from the bulk water to the evaporation surface in whole evaporation process, ensuring a continuous water supply and salt self-cleaning. Moreover, the results of practical solar-driven interfacial evaporation under outdoor conditions indicated that rGO/PVA-NR evaporator has overall multifunctional purification for inorganic ions and wastewater contaminated with organic dyes. This investigation provides a convenient and environmentally friendly strategy toward developing high-performance solar steaming technologies based on rubber sponge for effective water purification to address the global water crisis.

Multiscale topology optimisation for porous composite structures with stress-constraint and clustered microstructures

While porous composites are drawing growing attention for their excellent lightweight and multifunctional characteristics, inherent stress concentration in these porous composites often presents a main concern of structural integrity. This study aims to develop a multiscale topology optimisation (MTO) method for design of porous composites with clustered microstructures under a prescribed stress constraint. First, the concurrent topology optimisation (TO) for both macrostructures and microstructures are implemented via a multiscale algorithm. Meanwhile, a clustering technique is implemented based on a so-called k-means method to simultaneously determine the allowable volume fraction and microstructural configuration. Second, a consistent density-and-strain based clustering technique is developed for both 2D and 3D multiscale TO. Finally, two benchmark design examples, namely Messerschmitt–Bölkow–Blohm (MBB) and L-bracket structures, are implemented using the presented MTO method by considering either 2D or 3D situations to demonstrate the design effectiveness. The results indicate that, when optimising a high-stiffness porous composites subject to the stress constraint, the maximum von Mises stresses of the 2D MBB and L-bracket structures are well restrained, which are respectively 20% and 29% lower than those without the stress-constraint. In design of a 3D L-bracket, the present MTO method can achieve around 19% reduction in the maximum stress. The study demonstrates the importance of stress constraint to the topological design of multiscale porous composite structures.

Low-temperature deposition manufacturing technology: a novel 3D printing method for bone scaffolds.

The application of three-dimensional printing technology in the medical field has great potential for bone defect repair, especially personalized and biological repair. As a green manufacturing process that does not involve liquefication through heating, low-temperature deposition manufacturing (LDM) is a promising type of rapid prototyping manufacturing and has been widely used to fabricate scaffolds in bone tissue engineering. The scaffolds fabricated by LDM have a multi-scale controllable pore structure and interconnected micropores, which are beneficial for the repair of bone defects. At the same time, different types of cells or bioactive factor can be integrated into three-dimensional structural scaffolds through LDM. Herein, we introduced LDM technology and summarize its applications in bone tissue engineering. We divide the scaffolds into four categories according to the skeleton materials and discuss the performance and limitations of the scaffolds. The ideas presented in this review have prospects in the development and application of LDM scaffolds.

Rapid evaluation of capillary pressure and relative permeability for oil–water flow in tight sandstone based on a physics-informed neural network

Efficient and accurate evaluation of capillary pressure and relative permeability of oil–water flow in tight sandstone with limited routinely obtainable parameters is a crucial problem in tight oil reservoir modeling and petroleum engineering. Due to the multiscale pore structure, there is complex nonlinear multiphase flow in tight sandstone. Additionally, wetting behavior caused by mineral components remarkably influences oil–water displacement in multiscale pores. All this makes predicting capillary pressure and relative permeability in tight sandstone extremely difficult. This paper proposes a physics-informed neural network, integrating five important physical models, the improved parallel genetic algorithm (PGA), and the neural network to simulate the two-phase capillary pressure and relative permeability of tight sandstone. To describe the nonlinear multiphase flow and the wettability behavior, five physical models, including the non-Darcy liquid flow rate formula, apparent permeability (AP) formula, and contact angle-capillary pressure relationship, are coupled into the neural network to improve the prediction accuracy. In addition, the input parameters and the structure of the physics-informed neural network are simplified based on analyzing the change rule of the oil–water flow with the main controlling factors, which can also save training time and improve the accuracy of the neural network. To obtain the data for training the coupled neural network, the dataset of tight sandstone in Ordos Basin is constructed with experimentally measured data and various fluid flow properties as constraints. The test results demonstrate that the estimated capillary pressure and relative permeability from the physics-informed neural network are in good agreement with the test ones. Finally, we have compared the physics-informed neural network with the quasi-static pore network model (QSPNM), dynamic pore network model (DPNM), and conventional artificial neural network (ANN). The calculation time of QSPNM and DPNM are hundreds of times longer than that of the physics-informed neural network. The coupled neural network has also performed much better than the conventional ANN. As the heterogeneity of pore spaces in tight sandstone increases, the advantages of the physics-informed neural network over ANN are more prominent. The prediction models generated in this study can estimate the capillary pressure and relative permeability based on only four routine parameters in a few seconds. Therefore, the physics-informed neural network in this paper can provide the potential parameters for large-scale reservoir simulation.

Characterizing multi-scale shale pore structure based on multi-experimental imaging and machine learning

An accurate and comprehensive understanding of shale pore structure is fundamental and critical for accurate reserves evaluation and efficient hydrocarbon development. Thus, by taking the shale of Paleogene Eocene Shahejie Formation in the Jiyang Depression, Bohai Bay Basin, as an example, the 2D and 3D multi-resolution images of the shale microstructure are obtained by multiple imaging technologies, including X-ray computed tomography, large-field scanning electron microscopy, scanning electron microscopy and focused ion beam scanning electron microscopy. By integrating image processing and machine learning algorithms, the shale pore structure is characterized at a single scale and multi scales. The results are obtained as follows. First, the shale pore space in the study area is mainly composed of microfractures, inorganic pores, organic matters and organic pores, and exclusively shows multi-scale characteristics. Second, there are various types of inorganic pores, and abundant dissolution pores; organic matters are distributed as strips and patches, and no organic pores are found in some organic matters. Third, pores with radius less than 20 nm account for 25%, those with radius between 20 and 50 nm account for 19%, those with radius between 50 and 100 nm account for 29%, those with radius between 100 and 500 nm account for 14%, those with radius between 500 nm and 20 μm account for 11%, and those with radius between 20 and 50 μm account for 2%. Fourth, the organic pores are less connected than the inorganic pores. The connectivity between organic pores and inorganic pores plays a crucial role in hydrocarbon migration, and microfractures control fluid flow channels. Fifth, pores with radius less than 50 nm are dominantly organic pores, those with radius between 50 and 500 nm are mainly organic and inorganic pores, and microfractures mainly contribute to the pores with radius more than 500 nm. It is concluded that a single imaging experiment cannot accurately and comprehensively reveal the multi-scale micro pore structure of a shale reservoir. Through integration of multiple imaging technologies and machine learning algorithms, the shale pore structure can be recognized and characterized at both single scale and multi scales. The proposed new method provides accurate and comprehensive information of multi-scale pore structures.

Limiting pathways and breakthrough pressure for CO2 flow in mudstones

The sealing and integrity of caprocks is a critical issue in the geological sequestration of CO2. In this work, we integrate multiscale pore-size measurements and imaging techniques, to characterize macropores, microporosity, and their spatial connectivity of intact mudstone cores from an Enping oilfield in the South China Sea. Together with the information on mineral compositions, we propose clay regions in the absence of organic matter as limiting pathways for supercritical CO2 flows in the cores, which primarily consist of nanopores ranging from tens to hundred nm in diameter. The FIB-SEM tomography is used to obtain nanoporous structures of a representative domain of those limiting pathways. We simulate the primary drainage of supercritical CO2 displacing brine in the domain by using an in-house quasi-static pore-network model. The numerical predictions of capillary breakthrough pressure match the experimental data well. Our proposed method of determining capillary breakthrough pressure can substantially complement experimental measurements. Moreover, it has the potential to quantitatively link the multiscale porous structures of mudstone to its CO2 sealing.

Photocurable 3D-Printed PMBG/TCP Scaffold Coordinated with PTH (1-34) Bidirectionally Regulates Bone Homeostasis to Accelerate Bone Regeneration.

Bone defect repair remains a major clinical challenge that requires the construction of scaffolds that can regulate bone homeostasis. In this study, a photo-cured mesoporous bioactive glass (PMBG) precursor is developed as a tricalcium phosphate (TCP) agglomerant to obtain a double-phase PMBG/TCP scaffold via 3D printing. The scaffold exhibits multi-scale porous structures and large surface areas, making it a suitable carrier for the loading of parathyroid hormone (PTH) (1-34), which is used for the treatment of osteoporosis. In vitro and in vivo results demonstrate that PMBG/TCP scaffolds coordinated with PTH (1-34) can regulate bone homeostasis in a bidirectional manner to facilitate bone formation and inhibit bone resorption. Furthermore, bidirectional regulation of bone homeostasis by PTH (1-34) is achieved by inhibiting fibrogenic activation protein (FAP). Thus, PMBG/TCP scaffolds coordinated with PTH (1-34) are viable materials with considerable potential for application in the field of bone regeneration and provide an excellent solution for the design and development of clinical materials.

Multiscale pore structural alteration in gas shale by supercritical water stimulation

Hydraulic fracturing can induce high conductive fracture networks to stimulate shale gas well production. Large amounts of fracturing fluid generally retained in shale matrix after hydraulic fracturing will limit the shale gas well production. Reusing retained fracturing fluid by in-situ transformed into supercritical water (SCW) via formation heat treatment (FHT) is a state-of-the-art method to improve the shale gas well production by further altering shale multiscale pore structure. In this study, the changes in shale multiscale pore structure was visually and quantitatively characterized. The pore volume with a size range of 2 nm–5000 nm increased significantly. Inducing intragranular dissolution pores, pyrite dissolution pores, interparticle dissolution pores, and hydrothermal fractures stimulated the multiscale pore structure alteration during supercritical water stimulation (SCWS). Additionally, the advantage of SCWS in altering shale pore structure was systematically summarized, including further extend the hydraulic fracturing stimulation scale, enhancing multiscale shale gas flow capacity and ultimately improving well production. This work sheds light on the influence of supercritical water stimulation on the pore structure evolution in shale matrix, which is expected to be an innovative method for increasing the estimated ultimate recovery of a shale gas reservoir.

Relationship between multiscale nanopore structure and coal connectivity during coalification process

The complex nanopore structures in coal provide the space for gas adsorption and migration, which is crucial for the development of coalbed methane. However, the mechanism of the evolution of multi-scale nanopore structures during coalification is still unclear. In this work, a combined method of CO2/N2 adsorption and synchrotron radiation Nano-CT experiments were used to reveal the multi-scale pore structure characterization during coalification. The synchrotron radiation Nano-CT experiment reconstructed the 3D pore network model for different rank coal and revealed the effective diameter is less than 0.5 μm, accounting for 97.4%–99.6% of the total number of macropores. The combination of these methods, including CO2/N2 adsorption and Nano-CT, accurately characterizes the multi-scale pore distribution in coal, ranging from <2 nm, 2–300 nm and 64 nm - 3.5 μm. The ultra-micropores occupy the primary advantage, accounting for approximately 60.3%–95.2% of the total pore volume and the micropores, mesopores and macropores are more poorly developed than ultra-micropores. During the coalification process, the proportion of porosity contributed by ultra-micropores to the total porosity gradually increases, with the contribution rising by 57.9%. The proportion of porosity contributed by micropores, mesopores and macropores to the total porosity gradually decreases, with the contribution decreasing by 81.0%, 82.8% and 93.6%, respectively. Besides, with growing coal maturity, the total permeability gradually decreases by 9.26 × 10−3 - 3.05 × 10−1 mD, which is negatively correlated with coal maturity during coalification. And the total permeability is mainly provided by macropores, which account for about 99% of the total permeability. This research provides an in-depth understanding of the storage and transport of coalbed methane in a multi-scale nanopore structure.

Stress sensitivity of multiscale pore structure of shale gas reservoir under fracturing fluid imbibition

Stress sensitivity of multiscale pore structure of shale gas reservoir under fracturing fluid imbibition

Multi-Scale and Multi-Region Pore Structure Analysis on Sandy Conglomerate Whole Core With Digital Rock Model

Abstract Based on industrial computed tomography (CT), the whole core sandy conglomerate is scanned with a resolution of 0.5 mm/voxel, and the representative debris region and filling region subsample is selected to be scanned with a resolution of 15 µm/voxel using micro-CT. Then, four regions of the whole core sandy conglomerate image are segmented with the multi-threshold segmentation algorithm including macro pore, debris, filling, and gravel regions, while binary segmentation is performed on the debris and filling subsamples to segment the debris pores and filling pores respectively. Finally, the multi-scale and multi-region pore network model of the sandy conglomerate was constructed by the integration method to analyze the different types of pore characteristics. It can be found that the integrated sandy conglomerate model can reflect the structural characteristics of macro pore, debris pore, and filling pore at the same time. Meanwhile, the porosity and permeability of the integrated sandy conglomerate model are calculated and they are basically consistent with that of lab test results, which greatly increase the accuracy of the multi-scale multi-region pore network model.

Highly sensitive photodetector based on laser-generated graphene with 3D heterogeneous multiscale porous structures

Graphene holds great promise in optoelectronics because of its high broadband light absorption across a wide range of wavelengths. Despite low optical absorption, various techniques have been devised to address this challenge. This study presents a new highly sensitive, photodetector based on three-dimensional (3D) porous graphene derived from fluorinated polyimide (fPI-3DPG). This material is produced via a laser photothermal process and features micro- and nanopore structures that increase the light absorbing area and support optically resonant structures. The resulting fPI-3DPG photodetectors display high photoresponsivity of 4.4 mA W−1 in the visible light range, an ultrahigh signal-to-noise ratio of ∼208, and a noise equivalent power of 0.54 × 10−11 W Hz−1/2. These photodetectors are also mechanically durable, surviving 10,000 cycles of bending and twisting. The laser photothermal method used in this study enables fast, cost effective production of wearable and flexible optical sensors for imaging and spectroscopy applications, making this 3D graphene a promising functional material for sensing technologies.

Reuse of coal gangue to prepare adsorbent with multiscale pore structure for emulsified water removal

Reuse of coal gangue to prepare adsorbent with multiscale pore structure for emulsified water removal

Multi-scale pore structure transformation of shale under mixed acid acidification method

Most of the acid fluids used in the existing acidfrac process have the shortcomings of plugging pores, polluting formation and poor effect. The method of adding nitric acid in a specific proportion to conventional acid can avoid the above problems to a certain extent. A mixture of HCl: HF: HNO3 (3:1:1) was used to acidize the shale of the Longmaxi Formation in Sichuan and the Piyuancun Formation in Jiangxi for 24 h. The mineral fractions and pore structures of the samples were then analyzed using scanning electron microscopy-energy dispersive spectrometry, X-ray diffraction, low-pressure nitrogen adsorption, and nuclear magnetic resonance. The results showed that by reducing the mineral constituents of shale, the 2–15-nm sized pores decreased, 1–10-μm sized pores increased, and fractal dimensions decreased. The mixed acid solution caused cross-scale porosity expansion in the shale and increased gas circulation within the matrix. The process of acid mixing in the shale pore structure was divided into four stages: surface dissolution, macroporous dissolution, meso–microporous dissolution, and feedback dissolution.

Multiscale reconstruction of porous media based on multiple dictionaries learning

Digital modeling of the microstructure is important for studying the physical and transport properties of porous media. Multiscale modeling for porous media can accurately characterize large-pores and fine-pores in a large-FoV (field of view) high-resolution three-dimensional pore structure model. This paper proposes a multiscale reconstruction algorithm based on multiple dictionaries learning, in which edge patterns and fine-pore patterns from homology high-resolution pore structure are introduced into low-resolution pore structure to build a fine multiscale pore structure model. The qualitative and quantitative comparisons of the experimental results show that the results of multiscale reconstruction are similar to the real high-resolution pore structure in terms of complex pore geometry and pore surface morphology. The geometric, topological and permeability properties of multiscale reconstruction results are almost identical to those of the real high-resolution pore structures. The experiments also demonstrate the proposal algorithm is capable of multiscale reconstruction without regard to the size of the input. This work provides an effective method for fine multiscale modeling of porous media.