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The nanoscale pores in shale oil and gas are often filled with external nanomaterials to enhance wellbore stability and improve energy production. And there has been considerable research on discrete element blocking models and simulations related to nanoparticles. In this paper, the pressure transmission experimental platform is used to systematically study the influence law of different water activity salt solutions on shale permeability and borehole stability. In addition, the force model of the particles in the pore space is reconstructed to study the blocking law of the particle parameters and fluid physical properties on the shale pore space based on the discrete element hydrodynamic model. However, the migration and sealing patterns of nanomaterials in shale pores are unknown, as are the effects of changes in particle parameters on nanoscale sealing. The results show that: (1) The salt solution adopts a formate system, and the salt solution is most capable of blocking the pressure transmission in the shale pores when the water activity is 0.092. The drilling fluid does not easily penetrate into the shale pore space, and it is more capable of maintaining the stability of the shale wellbore. (2) For the physical blocking numerical simulation, the nanoparticle concentration is the most critical factor affecting the shale pore blocking efficiency. Particle size has a large impact on the blocking efficiency of shale pores. The particle diameter increases by 30% and the pore-blocking efficiency increases by 13% when the maximum particle size is smaller than the pore exit. (3) Particle density has a small effect on the final sealing effect of pore space. The pore-plugging efficiency is only increased by 4% as the particle density is increased by 60%. (4) Fluid viscosity has a significant effect on shale pore plugging. The increase in viscosity at a nanoparticle concentration of 1 wt% significantly improves the sealing effectiveness, specifically, the sealing efficiency of the 5 mPa-s nanoparticle solution is 16% higher than that of the 1 mPa-s nanoparticle solution. Finally, we present a technical basis for the selection of a water-based drilling fluid system for long horizontal shale gas drilling. [ABSTRACT FROM AUTHOR]

Shale gas exploration is continually developing in China. Diagenesis of shale influences the quality and productivity of its gas reservoirs. This study explored the characteristics and controlling factors of nanopores in organic-rich shale in the Niutitang Formation. Six samples were collected from the Upper Yangtze platform in Northern Guizhou Province, China, and experiments were conducted to investigate the pore structure of these high-maturity shale samples. Total organic carbon content varied between 4.81-17.51 % (average: 10.18 %). X-ray diffraction analysis showed that samples were dominated by quartz (44-71 %) with significant clay mineral content (8-27.5 % illite). Based on low-pressure liquid N2 sorption measurements, the pore structures were divided into groups. The first group was characterised by slit-like pores, mesopores, and macropores, while the second group contained narrow slit-like pores, providing extensive adsorption space for shale gas. The mesopores, macropores, porosity, and specific surface area of the second group were more developed than the first. Sample pore combinations shared similar features. By comparing shale pore structure with organic matter and mineral content, it was apparent that the dissolution of quartz and feldspar was an important factor controlling pore development. The results indicate that diagenesis processes have complex effects on the pores, including compaction, dissolution, and cementation. [ABSTRACT FROM AUTHOR]

Stability is a vitally important criterion to measure the effectiveness of a membrane, especially in the engineering fields. Although polymeric membranes are widely used, stability problems frequently arise in long-term applications. Two-dimensional atomically thin materials, especially graphene, have aroused wide interest from membrane science due to the excellent physical and chemical properties and, most importantly, the ability to simultaneously achieve high selectivity and high permeability. However, defects are generated in the growth and transfer process, impairing the desired properties and resulting in unstable performance of graphene membranes. Therefore, overcoming the negative effects from defects is urgent for their applications. Here, we report a facile route to produce stability-enhanced double-layer graphene membranes and provide an application paradigm of graphene in a membrane-based precision instrument, the membrane-based total organic carbon (TOC) analyzer. The first layer and the second layer of graphene were respectively transferred onto the polymer substrate through phase inversion and heat pressing methods. Then, Ar plasma was employed to accurately create high-density (1011–1012 cm–2) nanopores in the graphene lattice. The obtained double-layer graphene membranes could function normally in the TOC analyzer with a higher precision (signal linear correlation R2 of 99.64%) than the polymeric membranes (99.16% for poly-(vinylidene fluoride) and 99.33% for Teflon). Furthermore, the stability of double-layer graphene was evidently better (RSD (relative standard deviation) of 1.93%) than that of the single-layer graphene membrane (3.12%) in the continuous measurement for 7 days. Moreover, the stability-enhanced double-layer graphene membranes could work properly for more than 30 days (RSD of 2.50%), which have potential to satisfy the industry standards. Therefore, our work not only provides a solution to enhance the stability of membranes, which is significant in engineering fields, but also bridges the gap between the "proof-of-concept" in the laboratory and the application of graphene in membrane-based precision instruments. [ABSTRACT FROM AUTHOR]

For the clean and efficient extraction of coalbed methane (CBM), it is of great significance to understand the mechanism of the interaction between limonene, which is a natural organic solvent, and coal. In this study, the surface groups, nanoscale pore characteristics, and methane (CH 4) adsorption–desorption behaviors of selected rank coals were compared and analyzed to explore the effect of limonene leaching-induced evolution of the macromolecular structure of coal on its adsorption–desorption behaviors. The results showed that with the increase in the mass fraction of limonene, the contents of the aliphatic, aromatic hydrocarbons, and the cross-linking degree of the macromolecular structure of the coal decreased. This led to pore volume expansion of the SH and SQ coals, from a range of 0.3–7 nm to 7–36 nm. The pore volume in the 1.5–7 nm range in the LD coal increased significantly under the combined influence of the pore-expanding effect of the 0.3–1.5 nm pores and the porosity-enhancing effect of the 7–36 nm pores. Therefore, the promotion effect of limonene modification on the CH 4 adsorption-desorption behaviors of the coal was more evident in the medium- and high-rank coals than in the low rank-coals. • A new method for expanding nanoscale pores in coal has been proposed. • Non-polar solvents limonene are more likely to change the properties of coal. • Limonene leaching has dredging, expansion, and enhancing effects on coal pores. • The effect of limonene on pores of coal with different ranks is different. • Limonene is more beneficial to the coalbed methane extraction of high rank coal. [ABSTRACT FROM AUTHOR]

Cellular porous materials are frequently applied in the construction industry, both for structural and insulation purposes. The progressively stringent energy regulations mandate the development of better performing insulation materials. Recently, novel porous materials with nanopores or reduced gas pressures have been shown to possess even lower thermal conductivities because of the Knudsen effect inside their pores. Further understanding of the relation between the pore structure and the effective thermal conductivity is needed to quantify the potential improvement and design new optimized materials. This article presents the extension of a 3D numerical framework simulating the heat transfer at the pore scale. A novel methodology to model the reduced gas-phase conductivity in nanopores or at low gas pressures is presented, accounting for the 3D pore geometry while remaining computationally efficient. Validation with experimental and numerical results from the literature indicates the accuracy of the methodology over the full range of pore sizes and gas pressures. Combined with an analytical model to account for thermal radiation, the framework is applied to predict the thermal conductivity of a nanocellular poly(methyl methacrylate) foam experimentally characterized in the literature. The simulation results show excellent agreement with less than 5% difference with the experimental results, validating the model's performance. Furthermore, results also indicate the potential improvements when decreasing the pore size from the micrometre to the nanometre range, mounting up to 40% reduction for such high-porosity low-matrix-conductivity materials. Future application of the model could assist the design of advanced materials, properly accounting for the effect of reduced pore sizes and gas pressures. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical method to simulate gas-water relative permeability for nanoscale porous media utilizing fractal theory. The comparison between the calculation results and experimental data was performed to validate the present model. The result shows that the gas-water relative permeability would be underestimated significantly without interfacial effects. The thinner the liquid film thickness, the greater the liquid-phase relative permeability. In addition, both liquid surface diffusion and gas diffusion coefficient can promote gas-liquid two-phase flow. Increase of liquid surface diffusion prefer to increase liquid-phase permeability obviously as similar as increase of gas diffusion coefficient to increase gas-phase permeability. Moreover, the pore structure will become complicated with the increase of fractal dimension, which would reduce the gas-water relative permeability. This study has provided new insights for development of gas reservoirs with nanoscale pores such as shale.

The large amounts of natural gas in a dense solid phase stored in the confined environment of porous materials have become a new, potential method for storing and transporting natural gas. However, there is no experimental evidence to accurately determine the phase state of water during nanoscale gas hydrate dissociation. The results on the dissociation behavior of methane hydrates confined in a nanosilica gel and the contained water phase state during hydrate dissociation at temperatures below the ice point and under atmospheric pressure are presented. Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (PXRD) were used to trace the dissociation of confined methane hydrate synthesized from pore water confined inside the nanosilica gel. The characterization of the confined methane hydrate was also analyzed by PXRD. It was found that the confined methane hydrates dissociated into ultra viscous low-density liquid water (LDL) and methane gas. The results showed that the mechanism of confined methane hydrate dissociation at temperatures below the ice point depended on the phase state of water during hydrate dissociation.

The study on shale gas transport mechanisms plays an important role in shale gas production simulation. The majority of previous works neglected the body gas diffusion mechanism, and the multiple effects of stress sensitivity and multi-component of gas mixture system. In this paper, first, a model is built considering the multiple transport mechanisms of continuum flow, slippage flow, body gas diffusion and Knudsen diffusion. Then, the multiple effects of stress sensitivity and multi-component of gas mixture system are coupled into the model. Results show that: (a). For the body gas flow, both of the two weighted coefficients for items of body gas diffusion and slippage flow should be equal to one. And the ratio of one to Knudsen number is belong to the equation of body gas diffusion. (b). For a nanoscale pore of shale, the contribution of body gas diffusion on total mass flux cannot be neglected. The conductivities of continuum flow, slippage flow, modified slippage flow, Knudsen diffusion and weighted average flow decrease with decreasing of pressure due to shrinkage of nanopore radii and decrease in molecular concentration. (c). The decreasing of effective radii leads to the increase of the value of Knudsen number. The dominant transport mechanism is converting from modified slippage flow to Knudsen diffusion when the increase of stress sensitivity. (d). For methane confined in nanopores with extremely small effective transport radii, the injection of CO 2 can increase the mobility of methane. After a period of CO 2 injection, the methane molecules stored in nanopores can be flooded to fractures and then produced to the ground. • Multiple transport mechanisms, including body gas diffusion, are considered. • Multiple effect of stress sensitivity and multi-component are considered. • The injection of CO 2 can increase the mobility of methane confined in nanopores. [ABSTRACT FROM AUTHOR]

• The nanoscale storage spaces of the Da'anzhai carbonates are well developed. • The nanopore structure of the Da'anzhai carbonates is more complex than other rocks. • The Da'anzhai nanoscale storage spaces are mainly from terrestrial minerals. • The authigenic CaCO 3 minerals are negatively correlated with the nanoscale pores. • Weathering, salinity, climate and hydrodynamic conditions can control nanoscale pores. Compared with the studies of nanoscale pores in shale, coal, and tight sandstone, studies associated with lacustrine tight carbonate nanoscale pores and their control mechanisms, particularly quantitative studies combining reservoir evaluation and geochemistry, remain scarce. To address this disparity, lacustrine tight carbonate samples collected from the Jurassic Da'anzhai Member in the central Sichuan Basin of China were quantitatively investigated. Similar to other unconventional reservoirs, lacustrine tight carbonate reservoirs contain well-developed intraparticle pores, interparticle pores, and micro-cracks with nanoscale storage spaces that dominate the full-scale reservoirs. The relatively small pores (3–5 nm) make a dominant contribution to the nanoscale storage space. Isotherms and hysteresis loops are Type II and Type H 3 , respectively, indicating wedge-shaped pores. However, the hysteresis loops indicate more dead-end pores, larger pores, and more complex microstructures than those found in other unconventional reservoirs. The mineral in lacustrine carbonate provides a link between the reservoir and the formation environment. Strong paleo-weathering, low salinity, a humid (rainy) paleo-climate and poor hydrodynamic conditions are favorable to improve the storage spaces and terrestrial mineral contents but harmful to the formation of authigenic minerals. Terrestrial minerals, including primarily quartz, clay, and dolomite, have well-developed nanoscale pores and are positively correlated with the nanoscale storage space, whereas authigenic minerals, primarily calcite, have strong cementation and filling effects and are negatively correlated with the nanoscale storage space. [ABSTRACT FROM AUTHOR]

One of the challenges in evaluating and estimating the gas storage and migration of coal has been the investigation of complex pore structures, especially in the nanoscale. The present study provides new insights into nanoscale pore types, and the genesis, classification, and structure characteristics of high-rank coal by investigating 10 anthracite coals in the Shanxi Formation and Taiyuan Formation of the Xinjing Coal Mine in the Qinshui Basin, North China. A series of experiments that combined the qualitative observation method of argon ion polishing technology in combination with field emission-scanning electron microscope and quantitative analysis methods of low-pressure N2 gas adsorption and mercury intrusion porosimetry were performed to characterize nanoscale pore structures and its influence on gas behavior. The results revealed that various types of nanoscale pores exist in the coal matrix. Descriptive classifications for nanoscale pores consist of three major groups (organic matter pores, mineral-related pores, and micro-fractures), and nine subtypes was summarized to correlate pores to the networks. Furthermore, mercury intrusion porosimetry, low-pressure N2 gas adsorption, and image processing were combined to determine the pore size distributions, indicating that pore sizes are bimodally distributed with two broad peaks. The major peak at approximately 20–400 nm was mostly associated with isolated microscopic organic constituents interparticle nanopores, while a minor but prominent peak at the macro-pore to micro-fracture scale was more associated with epigenetic pores, mineral-related pores, and micro-fractures. Furthermore, image processing also provides a specialized approach to reveal the structure and diameter of different types of nanoscale pores. The combination of quantitative test and qualitative observation indicate that different major pore types dominate each size range of reservoir space in coal. These results lead to a feasible assumption that the poor connectivity of nanoscale pores and lack of seepage channels between the nanoscale pores and fracture-cleat networks may have led to the low "micro-permeability" of the coal matrix, which affects the productivity of coalbed methane in high-rank coal. [ABSTRACT FROM AUTHOR]

Ion flow in charged nanopores is strongly influenced by the ratio of the Debye length to the pore radius. We investigate the asymptotic behaviour of solutions to the Poisson–Nernst–Planck (PNP) system in narrow pore like geometries and study the influence of the pore geometry and surface charge on ion transport. The physical properties of real pores motivate the investigation of distinguished asymptotic limits, in which either the Debye length and pore radius are comparable or the pore length is very much greater than its radius This results in a quasi-one-dimensional (1D) PNP model, which can be further simplified, in the physically relevant limit of strong pore wall surface charge, to a fully 1D model. Favourable comparison is made to the two-dimensional (2D) PNP equations in typical pore geometries. It is also shown that, for physically realistic parameters, the standard 1D area averaged PNP model for ion flow through a pore is a very poor approximation to the (real) 2D solution to the PNP equations. This leads us to propose that the quasi-1D PNP model derived here, whose computational cost is significantly less than 2D solution of the PNP equations, should replace the use of the 1D area averaged PNP equations as a tool to investigate ion and current flows in ion pores. [ABSTRACT FROM AUTHOR]

Thermoelectric performance is proportional to the thermal conductivity reciprocal and power-factor, which are impacted by microstructures and electronic band structures, respectively. Herein, we study the effect of nanoscale pores on thermal conductivity. Within Cd-doped SnTe 1-x Se x , electron microscopy characterizations indicate the majority of pores are less than 200 nm, which is comparable to the phonon mean free path. Together with the point defects and nanoprecipitates, an ultra-low lattice thermal conductivity is obtained. Electrically, we find that the slight overdose of cation lone pair s2 character at L point of the first Brillion zone yields the energetically higher valence band edge at L point than at Σ point in rock-salt chalcogenides. As for SnTe 1-x Se x , Cd is a dopant free of lone pair s2 orbital. Cd doping decreases the energy offset of multivalence bands for SnTe 1-x Se x by partially reducing the cation lone pair s2 character. The refined band structures yield an enhanced power-factor. Combined with the decreased thermal conductivity, a figure-of-merit > 1.5 has been obtained. The demonstrated strategies of exploring nanoscale pores with size matching phonon mean free path to decrease lattice thermal conductivity and the computationally screening suitable dopants to modify band structures can enlighten the development of high-performance thermoelectric candidates in wide materials. Image 1 • Nanoscale pores with sizes matching phonon mean free path decrease the thermal conductivity. • The refined band structures lead to enhanced power-factor. • Dual valence band edges in rock-salt chalcogenides are ascribed to the weak contribution of cation lone pair s2 orbital. • Exploring the nanoscale pores extends the nanostructuring strategy for enhancing thermoelectric performance. [ABSTRACT FROM AUTHOR]

Highlights • 0.4–1.1 nm pores are considered to be formed inner the basic structural unit. • 2–150 nm pores are formed in the space between different basic structural units. • The volume of 2–150 nm pores increases with increasing the disorder degree. Abstract Nanoscale pores have been proven the major space for coalbed methane storage and important tunnels for coalbed methane transport. In this study, the influences of chemical composition, disorder degree and crystallite structure of coal macromolecule on the nanoscale pores were investigated by using different rank nature-matured coal samples via the methods of nuclear magnetic resonance (NMR), Raman spectroscopy, X-ray diffraction (XRD), low-pressure CO 2 adsorption experiment and N 2 adsorption experiment. The results show that the volumes of 0.4–1.1 nm pores in naturally-matured coals show strong correlations with coal crystallite structure and chemical composition, but a weak correlation with disorder degree of coal molecule. In contrast, the volumes of 2–150 nm pores have a good correlation with disorder degree of coal molecule, but have weak correlations with the crystallite structure and chemical composition. When aromatic carbon ratio is smaller than 63%, the volume of 0.4–1.1 nm pores decreases with increasing the aromatic carbon ratio of coal molecules. Beyond that, the volume of 0.4–1.1 nm pores continues increasing with an increase in the aromatic carbon ratio. In addition, when the vitrinite reflectance (R o) of the coal samples is >0.7%, volume of 0.4–1.1 nm pores increases with increasing the average lateral size (L a) and stacking height (L c). The effects of chemical composition and crystallite structure on 0.4–1.1 nm pores of naturally-matured coal samples obtained in this study are consistent to those of artificially-matured coals in our previous study (Liu et al., 2018). Based on the Raman data, the effect of disorder degree of coal molecule on nanoscale pores was also investigated. With D 1 /G ratio increasing, volume of 2–150 nm pores increases gradually. Considering that 0.4–1.1 nm pores are mainly related to the characteristics of single basic structural unit (BSU) (L a , L c and chemical composition) and 2–150 nm pores are related to arrangement of different BSUs (disorder degree), it is thought that 0.4–1.1 nm pores are formed inner BSUs and 2–150 nm pores are formed in the space between different BSUs. [ABSTRACT FROM AUTHOR]

The nanoscale pores in shale oil and gas are often filled with external nanomaterials to enhance wellbore stability and improve energy production. And there has been considerable research on discrete element blocking models and simulation about nanoparticles. However, nanomaterials are not just nanoparticles and there are few researches on fiber-based discrete element dynamics sealing calculations. Moreover, nanofibers have better sealing efficiency relative to nanoparticles. In this paper, a fiber-based discrete element fluid-solid coupling sealing model was established to clarify the dynamic migration and sealing process of nanofibers in shale pores. The innovative nanofiber model guarantees real-time force deformation and bendability during nanofiber flow process. The factors influencing sealing efficiency on shale pores with fiber concentration, aspect ratio, diameter, density, stiffness, rotation and Poisson's ratio have been conducted. Furthermore, the simulation results with and without fiber were certified by theoretical and experimental results which increased the credibility and applicability. Results indicate that the sealing efficiency increases by 69.40%, 139.12%, and 254.89%, respectively, as the fiber concentration increases from 0.5% to 1%, 1.5% and 2%. The increase in sealing efficiency is not linear for fiber concentration. The sealing efficiency is almost the highest as the ratio of aspect ratio is 1:15 in the initial stage of sealing. And fiber diameter with 1/15 of the pore outlet diameter is a reasonable choice if economical applicability is considered based on the sealing process. Furthermore, practice has proved that the sealing effect of bendable fibers is increased by 14.50% compared with non-bendable fibers. The bending of the fiber can improve the efficiency of shale pore sealing. And the research can provide theoretical and technical support for the nanofiber optimization of sealing nanopores of shale oil and gas. • Fluid-structure coupled nano model based on shale pores and fiber was presented. • Sealing effect with fiber concentration, aspect ratio and diameter are conducted. • Innovative nanofiber bending mode was proposed to ensure simulation accuracy. • The plugging influence of different nanofiber characteristics were discussed. • The simulation results were certified by theoretical and experimental results. [ABSTRACT FROM AUTHOR]

The formation and decomposition of gas hydrates in nanoscale sediments can simulate the accumulation and mining process of hydrates. This paper investigates the Raman spectra of water confined inside the nanoscale pores of silica gel, the decomposition characterizations of methane hydrate that formed from the pore water, and the intrinsic relationship between them. The results show that pore water has stronger hydrogen bonds between the pore water molecules at both 293 K and 223 K. The structure of pore water is conducive to the nucleation of gas hydrate. Below 273.15 K, the decomposition of methane hydrate formed from pore water was investigated at atmospheric pressure and at a constant volume vessel. We show that the decomposition of methane hydrate is accompanied by a reformation of the hydrate phase: The lower the decomposition temperature, the more times the reformation behavior occurs. The higher pre-decomposition pressure that the silica gel is under before decomposition is more favorable to reformation. Thus, reformation is the main factor in methane hydrate decomposition in nanoscale pores below 273.15 K and is attributed to the structure of pore water. Our results provide experimental data for exploring the control mechanism of hydrate accumulation and mining.

The gas transport in shale nanopores is always one of the major concerns in terms of the development of shale gas reservoirs. In this study, the gas flow regimes in shale nanopores were classified and analyzed according to Knudsen number. Then the gas flow model considering Darcy flow, slip flow, transition flow, molecular free flow and adsorption effect was proposed to evaluate the gas flow behavior in shale nanopores. The result shows that the contributions of Darcy flow, slip flow and transition flow in shale nanopores are reciprocal, and are mainly dominated by pore radius and pressure. The adsorption effect greatly influences the total mass flux. The total mass flux will increase as Langmuir pressure and temperature increase while it will decrease with reservoir pressure and the adsorption thickness. These results can provide insights for a better understanding of gas flow in the shale nanopores so as to optimize the production performance of shale gas reservoirs. [ABSTRACT FROM AUTHOR]

The application of relative permeability plays an important role in the development of shale gas reservoirs with nanoscale pores. An analytical model of relative permeability in nanoscale pores with interfacial effects has been developed according to the fractal theory. We verified our model with the classical models and experimental data and the results show good agreement with them. The proposed model considers the influence of surface diffusion and wettability, and establishes relationships between the relative permeability and the nanotube radius, fractal dimension, and contact angle. The results show that with an increase in film thickness, the fluid velocity in the spreading solid surface is decreased such that the surface diffusion coefficient is decreased and the flow resistance is increased in the nanoscale pores. Surface diffusion plays a positive role in promoting fluid flow, and the wettability effect has different influences with changes in the solid interfacial properties. This study has provided a new theoretical basis for gas-water two-phase flow in nanoscale pores ana may be beneficial in shale gas reservoir development. [ABSTRACT FROM AUTHOR]

This paper provides an analytical method for modeling and analyzing gas-water relative permeability in nanoscale pores with interfacial effects in terms of Hagen Poiseuille formula and capillary pressure curve. The flow models considering the interfacial effects in nanoporous shows good agreements with experimental data comparing with other models. The changing characteristics of gas-water relative permeability were analyzed under different conditions such as nanotube radius, film thickness, surface diffusion and contact angle. The results show that the larger the nanotube radius, the greater the relative permeability values because of decreasing both interfacial microstructure effect and the resistance of fluid flow. With the increasing of film thickness, surface diffusion which is positive for flow decreases in nanoscale pores. When the contact angle > 90° solid interface repel water and the hydrophobic of surfaces reduce the resistance to fluid flow, and the gas-water relative permeability increases with increasing contact angle. On the contrary when contact angle < 90°, the solid interface shows hydrophilic properties which play a negative effect to the fluid flow. This study has provided a new insight and theoretical basis for development of shale gas reservoirs with nanoscale pores. [ABSTRACT FROM AUTHOR]

In this article, a new technique combining polymer dynamic processing and low temperature foaming was proposed to fabricate isotactic polypropylene (iPP) foams with nano-scale cellular structures. A self-developed loop oscillating push–pull molding (LOPPM) device was first used to fabricate the highly oriented iPP samples with shish-kebab crystalline structure. A temperature-quench batch foaming device was used to foam the shish-kebab structured iPP sample at 100 °C with supercritical carbon dioxide (sc-CO 2 ) as blowing agent. Nano pores with average size of 55.3 nm were generated during foaming, attributing to the hindrance and nucleation synergistic effects of the shish-kebab crystalline structure. The LOPPM-PP foam samples showed high ultimate tensile strength (100% higher than PP) and strain-at-break (186% higher than LOPPM-PP), and excellent impact strength (658% higher than PP). [ABSTRACT FROM AUTHOR]

Special nanoscale storage mechanisms and pore radii create complex shale gas transport mechanisms. Shale gas reservoir production performance evaluations are challenging due to difficulties associated with microcosmic flow mechanisms, such as Knudsen diffusion, surface diffusion, adsorption and desorption. A thorough understanding of the effects of these transport mechanisms on shale gas production can help to develop new and improved shale gas production prediction models. This paper derives a unified apparent permeability equation based on the Knudsen number and four flow regimes, incorporating viscous, slip, transition and free molecule flows. The new apparent-permeability model also considers the surface diffusion, adsorption layer and tortuous diffusion path. Fully coupled differential equations were developed for a hydraulic fracture and matrix system based on these microcosmic transport mechanisms and using the finite difference method. A sensitivity analysis was performed to investigate the impacts of several parameters on production, including the nanopore radii, Langmuir parameters and bottom-hole flow pressure. The simulation results demonstrate that the microcosmic flow mechanisms significantly impact shale gas production. Gas production increases as the Langmuir parameters increase, but the rate of the increase decreases over time. Knudsen diffusion and surface diffusion become more prominent as the pore radius and reservoir pressure decrease. The adsorption layer cannot be ignored at sufficiently small pore radii. [ABSTRACT FROM AUTHOR]

• Deposition with confocal geometry induces fibrous-like nano-pores in VOx thin films. • Shape and distribution of nano-pores has an influence on electrical noise parameter. • Post-annealing at 200 °C favors electrical properties for thermal detector application. Structure-property correlation in vanadium oxide nanoscale thin films used in uncooled thermal detectors is a crucial question for device performance. The purpose of this work is to investigate the evolution of the nanoscale pores with post-annealing temperature and its correlation to electrical properties. It is observed that the as-deposited film has an amorphous matrix containing nanoscale crystal grains of VO 2 , V 2 O 5 , and V 6 O 13 phases, and additionally nanoscale fibrous-like pores. The film post-annealed at 200 C under high purity N 2 atmosphere for 3 h possesses nanoscale crystal grains predominantly with the VO 2 phase besides V 6 O 13 and nanoscale spherical pores. After post-annealing at 300 °C, a clear enhancement in crystallinity and diminishing of amorphous structure has been found, and the film contains VO 2 , V 2 O 3 , and V 6 O 13 phases, additionally larger pores and cracks. The electrical resistance and temperature coefficient of resistance increase with increasing temperature, whereas the electrical noise reduces after annealing at 200 °C and increases again at 300 °C. The best combination of values for 1/f noise corner frequency (5.7 kHz), electrical resistance (90 kΩ), and temperature coefficient of resistance (-2.71 %K−1) is obtained for the film after post-annealing at 200 °C, favorable for application. [ABSTRACT FROM AUTHOR]

• The effect of 50% THF in acidified coal is the most significant. • The trend of fractal dimension before and after coal acidification is opposite. • The trend of nitrogen adsorption of raw coal and acidified coal is opposite. As the most widely used reservoir stimulation method, hydraulic fracturing requires the injection of large volumes of fluid with certain viscosity, mainly formed by water and various additives in a certain proportion, into coal seam for the purpose of improving the permeability of coal reservoir, and thus the selection of appropriate fracturing fluid is very important to improve the fracturing effect. In the study, using a medium-volatile bituminous coal as the research object, solvent extraction experiments of coal samples before and after acidification under different solvent concentrations were carried out. After the soluble low molecular weight compounds in coal were extracted and dissolved, and the differences in pore structure parameters and their mechanisms in coal were investigated by using low-temperature liquid nitrogen adsorption apparatus and capillary coalescence theory. The research results show that, after tetrahydrofuran (THF) extraction with different concentrations, the pore volume (PV) of each pore size section for raw coal decreases, and with the increase of the pore size, the decreasing PV tends to be stable. The PV of acidified coal increases significantly in all pore size ranges, especially in the range of 5 ∼ 10 nm. Compared with unacidified coals, the low-temperature nitrogen adsorption isotherm of acidified coals after extracted with different concentrations of THF were more prominent in the relative pressure of 0.8 ∼ 1.0. As THF concentration increases, the fractal dimension D of raw coal and nitrogen adsorption capacity decrease, while the fractal dimension D of acidified coal and nitrogen adsorption capacity increase and are significantly bigger than those of raw coal. The nitrogen adsorption capacity of raw coal and acidified coal shows an inverted "N" and "N" trend, respectively, and the nitrogen adsorption capacity of the residue with 50%THF extraction after acidification reaches the maximum value of 1.47 cm3/g. This study suggests that adding a certain proportion of organic solvent (THF) and acid into fracturing fluids can be beneficial to improve reservoir porosity and thus increasing gas production. [ABSTRACT FROM AUTHOR]

Abstract: Design of nanocatalysts for efficient heterogeneous catalytic systems is needed to high ingredients for environmental cleanup of organic pollutant species. Here, well-defined order NiO–silica monolithic catalysts with hexagonal P6mm and cubic Pm3n mesostructures were successfully fabricated by using an instant direct-templating method of lyotropic and microemulsion phases of Brij 76 (C18H37(OCH2CH2)10OH, C18EO10). Ordered hexagonal P6mm NiO/HOM-2 monoliths could be fabricated in lyotropic system of Brij 76 at phase composition domains of TMOS/Brij 76 (50 wt%). However, periodically ordered cubic Pm3n NiO-supported monoliths were synthesized in microemulsion system formed by addition of C12-alkane to the hexagonal phase domains. This synthetic strategy also revealed that the NiO particles were well-dispersed into the silicate pore surface matrices of mesostructures. Monolithic NiO–silica composites with 2D hexagonal and 3D cubic geometries and with large particle morphologies show promise to act as catalysts. The current study revealed evidence of the advantages of nanoscale pore geometry and shape, and particle morphology of the supported silica monoliths in the design of nanocatalysts that can efficiently enhance the catalytic functionality in terms of stability, reversibility and reactivity. Furthermore, a key finding in our study was that 2D hexagonal and 3D cubic mesostructured NiO–silica catalysts retained the specific activity towards the oxidation reaction even after several regeneration/reuse cycles. Significant study of the mechanistic cyclization of the organic reactant using the density functional (DFT) calculations provided evidence of the key components of conformations of the functional model during the formation of the oxidation product. [Copyright &y& Elsevier]

The large amounts of natural gas in a dense solid phase stored in the confined environment of porous materials have become a new, potential method for storing and transporting natural gas. However, there is no experimental evidence to accurately determine the phase state of water during nanoscale gas hydrate dissociation. The results on the dissociation behavior of methane hydrates confined in a nanosilica gel and the contained water phase state during hydrate dissociation at temperatures below the ice point and under atmospheric pressure are presented. Fourier transform infrared spectroscopy (FTIR) and powder X-ray diffraction (PXRD) were used to trace the dissociation of confined methane hydrate synthesized from pore water confined inside the nanosilica gel. The characterization of the confined methane hydrate was also analyzed by PXRD. It was found that the confined methane hydrates dissociated into ultra viscous low-density liquid water (LDL) and methane gas. The results showed that the mechanism of confined methane hydrate dissociation at temperatures below the ice point depended on the phase state of water during hydrate dissociation. [ABSTRACT FROM AUTHOR]

Graphene holds great potential for fabricating ultrathin selective membranes possessing high permeability without compromising selectivity and has attracted intensive interest in developing high-performance separation membranes for desalination, natural gas purification, hemodialysis, distillation, and other gas-liquid separation. However, the scalable and cost-effective synthesis of nanoporous graphene membranes, especially designing a method to produce an appropriate porous polymer substrate, remains very challenging. Here, we report a facile route to fabricate decimeter-scale (∼15 × 10 cm 2 ) nanoporous atomically thin membranes (NATMs) via the direct casting of the porous polymer substrate onto graphene, which was produced by chemical vapor deposition (CVD). After the vapor-induced phase-inversion process under proper experimental conditions (60 °C and 60% humidity), the flexible nanoporous polymer substrate was formed. The resultant skin-free polymer substrate, which had the proper pore size and a uniform spongelike structure, provided enough mechanical support without reducing the permeance of the NATMs. It was demonstrated that after creating nanopores by the O 2 plasma treatment, the NATMs were salt-resistant and simultaneously showed 3-5 times higher gas (CO 2 ) permeance than the state-of-the-art commercial polymeric membranes. Therefore, our work provides guidance for the technological developments of graphene-based membranes and bridges the gap between the laboratory-scale "proof-of-concept" and the practical applications of NATMs in the industry.

The formation and decomposition of gas hydrates in nanoscale sediments can simulate the accumulation and mining process of hydrates. This paper investigates the Raman spectra of water confined inside the nanoscale pores of silica gel, the decomposition characterizations of methane hydrate that formed from the pore water, and the intrinsic relationship between them. The results show that pore water has stronger hydrogen bonds between the pore water molecules at both 293 K and 223 K. The structure of pore water is conducive to the nucleation of gas hydrate. Below 273.15 K, the decomposition of methane hydrate formed from pore water was investigated at atmospheric pressure and at a constant volume vessel. We show that the decomposition of methane hydrate is accompanied by a reformation of the hydrate phase: The lower the decomposition temperature, the more times the reformation behavior occurs. The higher pre-decomposition pressure that the silica gel is under before decomposition is more favorable to reformation. Thus, reformation is the main factor in methane hydrate decomposition in nanoscale pores below 273.15 K and is attributed to the structure of pore water. Our results provide experimental data for exploring the control mechanism of hydrate accumulation and mining. [ABSTRACT FROM AUTHOR]

Direct synthesis of graphene with well-defined nanoscale pores over large areas can transform the fabrication of nanoporous atomically thin membranes (NATMs) and greatly enhance their potential for practical applications. However, scalable bottom-up synthesis of continuous sheets of nanoporous graphene that maintain integrity over large areas has not been demonstrated. Here, it is shown that a simple reduction in temperature during chemical vapor deposition (CVD) on Cu induces in-situ formation of nanoscale defects (≤2-3 nm) in the graphene lattice, enabling direct and scalable synthesis of nanoporous monolayer graphene. By solution-casting of hierarchically porous polyether sulfone supports on the as-grown nanoporous CVD graphene, large-area (>5 cm 2 ) NATMs for dialysis applications are demonstrated. The synthesized NATMs show size-selective diffusive transport and effective separation of small molecules and salts from a model protein, with ≈2-100× increase in permeance along with selectivity better than or comparable to state-of-the-art commercially available polymeric dialysis membranes. The membranes constitute the largest fully functional NATMs fabricated via bottom-up nanopore formation, and can be easily scaled up to larger sizes permitted by CVD synthesis. The results highlight synergistic benefits in blending traditional membrane casting with bottom-up pore creation during graphene CVD for advancing NATMs toward practical applications., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Poly(lactic acid) (PLA) foams, with the combination of shish-kebab and spherulite nanoporous structure in skin and core layer respectively, was prepared using a novel technique comprising loop oscillating push-pull molding (LOPPM) and supercritical carbon dioxide low-temperature foaming process (SC-CO 2 LTFP). The foams present superior impact toughness which is 6-fold higher than that of neat PLA, and no significant decrease was observed for the storage modulus. Moreover, SC-CO 2 LTFP at soaking temperature ranging from 110 to 150 °C were performed to determine the evolution of pore morphology. The ultratough and supermoduli are unprecedented for PLA, and are in great need for broader applications.