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In order to study the mixed permeability characteristics of broken coal medium, the parameter changes during water-gas permeation are analyzed and discussed in this study. It includes the law of two-phase flow state transformation, the law of permeability evolution and the principle of effective stress action. Firstly, the water-gas mixed permeation test system was designed by independent design. Then the gas and liquid two-phase permeation parameters were measured in real time by using multiple sets of sensors. The results are as follows: In one hand, the two-phase seepage process in broken coal medium, the seepage apparent Reynolds number is mainly distributed between 1230–2207. The difference of two orders of magnitude between the kinematic viscosities of the two fluids leads to an asynchronous transition process between the liquid and gas phase flow regimes. On the other hand, there is a competitive relationship between the relative permeability ratio of water and gas phases. When the proportion of gas phase relative permeability is distributed in the interval 71.7%–85.1%, the proportion of gas phase relative permeability is dominant, and it is most sensitive to the influence of the compaction deformation process of the initial pore structure. At the same time, the permeability k decreases with the increase of the effective stress σovin all three stages of the compaction deformation of the skeleton of the broken coal medium, in accordance with the relationship: σov=0.678/k+0.608. The effective stress will directly determine the pore deformation process of the structure of the broken coal medium.

Three-dimensional porous network encapsulation strategy is an effective means to obtain composite phase-change materials (PCMs) with high heat storage capacity and enhanced thermal conductivity. Herein, macroporous reduced graphene oxide (rGO) aerogels with adjustable pore size are prepared by the emulsion template method and hydrothermal reduction process. Further, the shape-stabilized rGO-aerogel-based composite PCMs are constructed after the combination of 3D porous rGO supports and paraffin wax (PW) through vacuum melting infiltration. By regulating the pore structure of the rGO aerogel network, the rGO-based composite PCMs achieve excellent energy storage properties with a phase-change enthalpy of 179.94 J/g for the loading amount of 95.61 wt% and an obvious enhancement in thermal conductivity of 0.412 W/m−1·K−1, which is 54.89% higher than pristine PW and enduring thermal cycling stability. The obtained macroporous rGO-aerogel-based composite PCMs with high thermal storage and heat transfer performance effectively broaden the application of PCMs in the field of thermal energy storage.

This study explored the potential of granite stone powder (GSP) as a supplementary cementitious material (SCM). The 72 h early hydration process stages of GSP-mixed slurry were analyzed in depth, and the mechanical properties of manufactured sand concrete (MSC) mixed with GSP were investigated. Physical phase types, morphological characteristics, and pore structure evolution were investigated using an X-ray diffractometer, scanning electron microscope, and mercury intrusion approach (MIP). Atomic force microscopy was used to show the interface transition zone between aggregate and slurry in phase images, height images, and 3D images, allowing quantification of ITZ and slurry by calculating the roughness. Gray entropy analysis was used to evaluate the significance of the effect of pore size distribution parameters on mechanical strength, and the GSP-content-mechanical-strength gray model GM (1, 1) was established to predict mechanical strength. The results indicate that, compared with the reference group, the GSP cement slurry system exhibited a delayed hydration process acceleration rate, with a 1.04% increase in cumulative heat of hydration observed in the 5% test group and an 11.05% decrease in the 15% test group. Incorporating GSP in MSC led to decreased mechanical properties at all ages, with significant decay observed when incorporation ranged from 10% to 15%. Although the type of hydration products remained unchanged, there was a decrease in the number of C-S-H gels and gel pores, while large pores increased, resulting in increased porosity and roughness of the interface transition zone and slurry. Large pores (>1000 nm) were found to have the greatest influence on mechanical strength, with gray correlation above 0.86. The GM (1, 1) model yielded accurate predictions, showing good agreement with measured data and thus it can be identified as belonging to a high-precision prediction model category. These findings provide theoretical support and a reference for applying GSP as an SCM, laying the groundwork for data-based specification development.

To elucidate the reservoir characteristics of organic-rich siliceous shale of the Upper Permian Dalong Formation in western Hubei, this study focused on the drilling cores of Well ED-2. Various techniques, including a mineral composition analysis, an organic carbon content analysis, a vitrinite reflectance measurement, a total porosity determination, field emission scanning electron microscopy (FE-SEM), and low-pressure CO2 and N2 physical adsorption tests, were employed to analyze the mineralogy, organic geochemistry, total porosity, and pore structure characteristics. Additionally, the factors influencing the reservoir performance of the Dalong Formation shale were investigated. The results indicated that the Dalong Formation’s shale was characterized as an organic-rich siliceous shale. Organic matter was mainly of sapropelic type, with a relatively high thermal evolution degree and Ro ranging from 2.59% to 2.76%. The total porosity of the Dalong Formation’s siliceous shale was low, indicating poor reservoir properties. Organic matter pores were highly developed, mainly the ones formed after the hydrocarbon generation of solid asphalt. Micropores and mesopores were the dominant pore types in the shale, with macropores being significantly less abundant. The study further revealed that the pore volume and specific surface area exhibited a significantly positive correlation with total organic carbon (TOC) content and clay minerals, while demonstrating a weak negative correlation with quartz content. The comprehensive analysis revealed that there were two factors contributing to the poor physical properties of organic-rich siliceous shale in the Dalong Formation. Firstly, in siliceous shale with a high quartz content, the siliceous component was partly derived from the siliceous cementation of hydrothermal fluids. This process led to the formation of secondary quartz that filled intergranular pores, resulting in a decrease in macropore volume, total porosity, and a weak negative correlation with quartz content. Secondly, in siliceous shale with a relatively high clay mineral content, the organic matter was subjected to stronger compaction due to the relatively low content of brittle minerals. This compaction caused the destruction of most macropores, leaving behind primarily micropores and mesopores. Consequently, the average pore size decreased, leading to poor physical properties.

The present study aims to scrutinize the flexural behavior and engineering properties of beams reinforced with amorphous metallic fiber (AMF) at varying dosages (0%, 0.25%, 0.50%, and 0.75% AMF according to the volume of mortar) and lengths (5 mm, 10 mm, 15 mm, and 20 mm). A total of fourteen mortar mixes, i.e., seven mixes for water curing (immersed in fresh tap water) and seven mixes for carbonation curing (60% relative humidity, 20 °C, and 10% CO2 concentration) were considered. The load–deflection behavior, flexural strength, pore structures, voids, and water absorption of the beams were investigated. The outcomes were justified with the mix containing 0.5% steel fiber (SF) and a length of approximately 20 mm. The results reveal that the load–deflection behavior and flexural strength were dramatically augmented for the beams with AMF as compared to the control beam (fiber-free beam), and the difference was more pronounced with an increase in both the dosage and the length of the AMF. Greater flexural strength with a lower deflection at failure was registered for the beam with AMF compared to that with SF. The voids and water absorption increased with an increase in the dosage and length of the AMF compared to the control specimen. It was also revealed that the carbonation-cured beams exhibited lower load–deflection behavior and lower flexural strength than those cured in water due to the substantially increased number of voids and greater water absorption driven by the better-connected pores. This study demonstrates that 0.50% AMF with a length of 20 mm can be used in cement-based materials due to the outstanding performance among all mixes.

Shale pore systems are the result of the geological evolution of different matrix assemblages, and the composition of gas shale is considered to affect the pore systems in shale reservoirs. This study aimed to investigate the impact of both organic and inorganic constituents on the shale pore system, including specific surface area (SSA) and pore volume in Wufeng–Longmaxi Shale. Multiple linear regression (MLR) was employed to examine the contributions of different components to shale pore structure. The pore structure parameters, including pore SSA and pore volume, were obtained by gas adsorption experiments in 32 Wufeng–Longmaxi Shale (Late Ordovician–Early Silurian) samples. Both pore SSA and pore volume were calculated by the density functional theory (DFT) model on shale samples, and the pore types were determined by high-resolution field emission scanning electron microscopy (FE-SEM). The results of the X-ray diffractometer (XRD) analysis indicate that the Wufeng–Longmaxi Shale is dominated by quartz, clays, carbonates, feldspar, pyrite, and organic matter. Four models were made using SPSS software, all of which showed significant correlation between shale pore size and organic matter (OM) and clays. The content of organic matter played the biggest role in determining the size and structure of the pores. Although the content of quartz is the highest and serves as a rigid skeleton in shale reservoirs, it has complicated effects on the pore structure. In this study, most of the quartz is biogenetic and part of it is transformed from clays in deep shale. Therefore, these two parts of quartz are, respectively, related to organic matter and clays. In essence, the pores related to these two parts of quartz should be attributed to organic matter and clays, which also support the conclusion of the MLR models.

A precise evaluation of the fluid movability of coal sedimentary rock is crucial to the effective and secure utilization of coal measures gas reserves. Furthermore, its complex pore structure and diverse mineral components impact the flow properties of fluids in pore structures, causing accurate evaluation of fluid mobility to be extremely challenging. Nuclear magnetic resonance (NMR) technology is currently a prevalent technique to assess unconventional reservoirs due to its capacity to acquire abundant reservoir physical property data and determine fluid details. The free-fluid volume index (FFI) is a crucial factor in assessing fluid movability in the application of NMR technology, which can only be derived through intricate NMR saturation and centrifugation experiments This research utilized nuclear magnetic resonance (NMR) tests on 13 classic coal-measure sedimentary rock samples of three lithologies to reveal the FFI value. Moreover, the association between mineral components, pore structure parameters, and FFI was then extensively analyzed, and a prediction model for FFI was constructed. The results indicate that the T2 spectra of sandstone and shale own a bimodal distribution, with the principal point between 0.1 and 10 ms and the secondary peak between 10 and 100 ms. The majority of the T2 spectra of mudstone samples provide a unimodal distribution, with the main peak distribution range spanning between 0.1 and 10 ms, demonstrating that the most of the experimental samples are micropores and transition pores. The calculated results of the FFI range from 7.65% to 18.36%, and depict evident multifractal properties. Porosity, the content of kaolinite, multifractal dimension (Dq), and the FFI are linearly positively correlated. In contrast, the content of chlorite, illite, multifractal dimension subtraction (Dmin − Dmax), multifractal dimension proportion (Dmin/Dmax), and singularity strength (Δα) possess a negative linear correlation with the FFI, which can be further used for modeling. On the basis of the aforementioned influencing factors and the FFI experimental values of eight core samples, an FFI prediction model was constructed through multiple linear regression analysis. The accuracy of the prediction model was validated by utilizing this approach to five samples not included in the model development. It was revealed that the prediction model produced accurate predictions, and the research findings may serve as a guide for the classification and estimation of fluid types in coal reservoirs.

The continuous development of urban areas around the world led to an increase in construction material use and demand, with concrete seeing significant market uptake. Although significant progress has been made to reduce the environmental impact of concrete, there is still a stringent need for improvement. One of the most widely used methods to reduce the environmental impact of the cement industry and the construction industry alike is the replacement of ordinary Portland cement (OPC) by supplementary cementitious materials (SCM). Aside from by-products of industry, SCMs could also come from natural sources. Taking into account the porous structure of zeolites and their contribution to the improvement of the mechanical and durability properties of cement-based materials, the analysis of pore structure in cement pastes incorporating micronized natural zeolite is deemed necessary. In this research, the OPC was replaced by zeolite in three different percentages: 10%, 20%, and 30% by mass. The evolution of pore structure was investigated by means of nuclear magnetic resonance relaxometry at the curing ages of 1, 7, and 28 days. The microstructure of cement pastes was assessed by scanning electron microscopy investigations at 1, 7, 14, 21, and 28 days. The obtained results show that smaller pore sizes are present in cement pastes containing zeolites during the first 7 days. However, at the age of 28 days, the reference mix exhibits a similar pore structure to the mix containing 10% micronized zeolite due to the presence of larger amounts of hydration products. Increasing the replacement percentage to 30% results in larger pores, as indicated by larger values of the relaxation time.

In this paper, we report the preparation of a gas diffusion layer (GDL) with different gradient pore size structures. The pore structure of microporous layers (MPL) was controlled by the amount of pore-making agent sodium bicarbonate (NaHCO3). We investigated the effects of the two-stage MPL and the different pore size structures in the two-stage MPL on the performance of proton exchange membrane fuel cells (PEMFC). The conductivity and water contact angle tests showed that the GDL had outstanding conductivity and good hydrophobicity. The results of the pore size distribution test indicated that introducing a pore-making agent altered the pore size distribution of the GDL and increased the capillary pressure difference within the GDL. Specifically, there was an increase in pore size within the 7–20 μm and 20–50 μm ranges, which improved the stability of water and gas transmission within the fuel cell. The maximum power density of the GDL03 was increased by 37.1% at 40% humidity, 38.9% at 60% humidity, and 36.5% at 100% humidity when compared to the commercial GDL29BC in a hydrogen-air environment. The design of gradient MPL ensured that the pore size between carbon paper and MPL changed from an initially abrupt state to a smooth transition state, which significantly improved the water and gas management capabilities of PEMFC.

The pore structure of low-rank coal reservoirs was highly complex. It was the basis for predicting the gas occurrence and outburst disasters. Different scale pores have different effects on adsorption–desorption, diffusion, and seepage in coalbed methane. To study the pore structure distribution characteristics, which are in different scales of low-rank coal with different metamorphism grade, the pore structure parameters of low-rank coal were obtained by using the mercury injection, N2 adsorption, and CO2 adsorption. These three methods were used to test the pore volume and specific surface area of low-rank coal in their test ranges. Then, the fractal dimension method was used to calculate the fractal characteristics of the pore structure of full aperture section to quantify the complexity of the pore structure. The experimental results showed that the pore volume and specific surface area of low-rank coal were mainly controlled by microporous. The pore fractal characteristics were obvious. With the influence of coalification process, as the degree of coal metamorphism increases, fluctuations in the comprehensive fractal dimension, specific surface area, and pore volume of the pore size range occur within the range of Rmax = 0.50% to 0.65%.

In response to the high water sorptivity of alkali-activated slag–red mud–steel slag cementitious material (AASRSS), water and aggressive ions are easily transferred to the interior of cementitious materials, which poses a significant threat to their durability. In order to limit the transfer of moisture and aggressive ions to the interior of AASRSS, sodium stearate (NaSt) was utilized in this paper to reduce its water sorptivity. The aim of this study was to elucidate the role of NaSt in the AASRSS system. The changes in the compressive strength and water sorptivity of AASRSS mortar were tested by mixing different amounts of NaSt into the mortar. The changes in the hydration process and microstructure of AASRSS after mixing with NaSt were analyzed by using the test methods of the isothermal calorimetry, resistivity, SEM and MIP. The results showed that NaSt plays an important role in the pore structure characteristics of AASRSS and that the use of NaSt significantly reduces its water sorptivity. The improvement in the water sorptivity was caused by two main mechanisms, namely the optimization of the pore structure (reduction in defects of the microstructure and alteration of pore size distribution) and the introduction of a hydrophobic film on the pore surface. The addition of NaSt did not change the type of AASRSS hydration product, but it inhibited the hydration reaction, leading to a reduction in the hydration product. The combination of the increased porosity and reduced hydration products mainly accounts for the decrease in the compressive strength of AASRSS due to NaSt.

Desired retention and depth into wood are necessary for wood preservatives to provide long-term durability. In general, heartwood of wood is difficult to treat, and bioincising was investigated as a potential technique to improve the treatability of refractory wood and heartwood. In order to study the effects of bioincising treatment with white-rot fungus Trametes versicolor on the pore structure and treatability of radiata pine heartwood, this research conducted tests of mass loss, microscopic structures, pore structure parameters, uptake, and penetration of preservative of radiata pine heartwood specimens incubated by T. versicolor for 4, 8, and 12 weeks. The results showed that the optimal inoculation time of T. versicolor bioincising on radiata pine heartwood was 4 to 8 weeks. At this time, the retention of injected preservatives increased by 5.01%–17.73%, the penetration depth of preservatives increased significantly, and the corresponding mass loss was 3.04%–6.45%. The results of microstructure and pore structure showed that T. versicolor entered the adjacent tracheids via apertures, with less impact on the cell wall, mainly degrading pit membranes and ray parenchyma cells early in the inoculation of radiata pine heartwood. As the structures impeding fluid flow were connected, the porosity of the wood and the range of the main pore size distribution increased significantly, thus increasing the treatability of radiata pine heartwood.

Aluminum foam that is lightweight with high specific strength, high energy absorption and other characteristics can be used in aerospace, transportation, machinery manufacturing and other fields. The PCM method is usually used to prepare closed-cell aluminum foams. The microsized aluminum foams made by this process can solve the non-uniform pore structures caused by liquid drainage during the foaming process of large aluminum foams. The surface morphology and internal pore structure of microsized aluminum foams are affected by the quality of the precursor used for foaming. In this paper, foamable precursors were obtained via either hot rolling or hot extrusion and subsequently foamed. By analyzing the micromorphology and foaming process of the precursor, the influence of the technological method on the macroscopic pore structure of the final aluminum foam was studied. The results show that the aluminum powder particles in the precursor prepared with the hot rolling method had metallurgical bonding, and the outer surface was dense, with almost no porosity and holes in the interior. The microsized aluminum foam obtained after foaming was smooth in appearance, and the internal pore structure was round and uniform. The reason is that during the foaming process of microsize aluminum foam, the foaming agent was evenly distributed in the precursor of the hot rolling process because of its compact structure. During the foaming process, the decomposed gas of the foaming agent will not escape, and the evenly distributed foaming agent tends to nucleate in situ. In the process of rapid foaming, the pressure in the bubble is enough to resist the liquid drainage phenomenon caused by gravity, and the growth direction of the gas core is isotropic, which promotes the foam structure to be more rounded and uniform.

The properties of concrete can be significantly affected by sodium gluconate (SG) at very small dosages. In this paper, the effects of SG on the fluidity, setting time, heat of hydration, and strength of ultra-high-performance concrete (UHPC) were studied. The results show that (1) in the plastic stage, SG inhibited the formation of early ettringite (AFt) and delayed the hydration of tricalcium silicate (C3S) and dicalcium silicate (C2S). SG increased the initial fluidity of UHPC without decreasing within 1 h. When the SG dosage was ≥0.06%, the slumps at 30 min and 60 min increased slightly. (2) In the setting hardening stage, the addition of SG inhibited the formation of calcium hydroxide (CH), which significantly extended the setting time of UHPC. When the dosage of SG was 0.15%, the initial and final setting times were 5.0 times and 4.5 times that of the blank group, respectively. SG had no obvious effect on the hydration rate of cement in the accelerated period, but the peak hydration temperature of UHPC was increased when the SG dosage was 0.03~0.12%. (3) In the strength development stage, the 1 d and 3 d strength of UHPC decreased significantly with the increase in the SG dosage. However, SG could promote the formation of AFt at the pores and aggregate interface in the later stage, reduce the porosity of cementite, and improve the compressive strength of UHPC in 28 d, 60 d, and 90 d. When the SG dosage was 0.12%, the 90d strength increased by 13%.

Analyzing and mastering the fractal features of coal-measure sedimentary rocks is crucial for accurately describing the pore structure of coalbed methane resources. In this work, mercury intrusion porosimetry (MIP) and nuclear magnetic resonance (NMR) are performed on coal-measure sedimentary rocks (i.e., shale, mudstone, and sandstone) to analyze their pore structure. Pore size distributions (PSDs) and the multifractal dimensions of the investigated samples are discussed. Moreover, multivariable linear regression models of multifractal dimensions are established through a comprehensive analysis of multifractal characteristics. The results show that sandstone (SS-1) and clay rocks are dominated by nanopores of 0.01 to 1 μm, while sandstone (SS-2) is mostly mesopores and macropores in the range of 1 to 10 μm. The fractal characteristics of the investigated rock samples show a prominent multifractal characteristic, in which DA reflects the surface structure of micropores, while DS represents the pore structure of macropores. Multifractal dimension is affected by many factors, in which the DA is greatly influenced by the pore surface features and mineral components and the DS by average pore diameters. Moreover, multivariate linear regression models of adsorption pore and seepage pore are established, which have a better correlation effect on the multifractal dimension.

The column leaching experiments, CT, numerical simulation and fractal theory were adopted to study the continuously weakening mechanism of the heap leaching velocity of weathered rare earth ores with the increase of ore burial depth. The variation characteristics of pore structure and the seepage law of solution in ore samples at different depths during leaching were explored, respectively. The results showed that the variation of characteristic parameters of the pore structure in the lower ore samples was the main reason for the decrease in the leaching velocity. For the lower ore samples after leaching, the number of pores with a pore volume of less than 0.01 mm3 and a pore radius of less than 0.8 mm increased, while pore connectivity, the fractal dimension of the pore shape, the ratio of pore length to width and pore throat length reduced. The solution paths of the upper and middle ore samples were concentrated while that of the lower samples were few, even interrupted. The pore pressure of the ore samples decreased after leaching, especially that of the lower ore samples. The research results are helpful to enrich the basic theory on the heap leaching of weathered rare earth ores.

To adapt porous material for its application as low noise trailing edge, a special rolling process, using a time-varied rolling gap, was used in previous research to produce a porosity gradient in the direction of rolling. Investigations suggest that a gradient in porosity may also be produced in the thickness direction of the material, i.e., in the rolling gap direction, without using a specialized rolling mill. Such a gradient may help to further increase acoustic efficiency of porous materials. The aim of this study was to analyze the dependency of such a gradient on the rolling parameters, and to clarify which stress components are significantly responsible for an increased near-surface compaction. Experiments using different relative compressed lengths were performed to analyze shear-dominated and friction-dominated rolling. The material was characterized using compression tests, computed tomography and flow resistance measurements. It is shown that the compressed length is an important parameter for adjusting a porosity gradient. Rolling with small values of compressed length during all rolling passes leads to increased compaction of near-surface regions, compared to interior ones. The difference in porosity achieved was up to 15%. Furthermore, the results suggested that a gradient in hydrostatic stress is responsible for the porosity gradient. Validation of the results by FE simulation is forthcoming, but not part of this publication.

Wood, as a naturally green and environmentally friendly material, has been widely used in the construction and decoration industries. However, the flammability of wood poses serious safety problems. To improve the fire resistance of wood, In this study, it is proposed to use calcium chloride (CaCl2) and disodium hydrogen phosphate (Na2HPO4, DSP) to impregnate wood for multiple cycles. The experimental results show that phosphate mineral precipitation can be deposited on the surface of the wood. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) are used to analyze the micromorphology of mineral precipitation and use the MIP test to analyze the treated wood pore structure. The results show that with the increase in the number of cycles, the phosphate deposited on the surface of the wood increases, and the cumulative pore volume and water absorption rate of the wood after 10 cycles are 54.3% and 13.75% lower than that of untreated wood respectively. In addition, the cone calorimeter (CONE) confirmed that the total heat release (THR) and total smoke production (TSP) of wood treated in 10 cycles have decreased by 48.7% and 54.2% respectively compared with the untreated wood. Hence, this treatment method not only improves the mechanical properties of wood. It also improves fire resistance.

The Pinghu Formation is a low permeability sandstone reservoir in the KQT Region, East China Sea. Its porosity ranges from 3.6 to 18.0%, and permeability is distributed from 0.5 to 251.19 mD. The relationship between porosity and permeability was poor due to strong heterogeneity. This led to the difficulty of quantitatively evaluating effective reservoirs and identifying pore fluids by using common methods. In this study, to effectively evaluate low permeability sandstones in the Pinghu Formation of KQT Region, pore structure was first characterized from nuclear magnetic resonance (NMR) logging based on piecewise function calibration (PFC) method. Effective formation classification criteria were established to indicate the “sweet spot”. Afterwards, several effective methods were proposed to calculate formation of petrophysical parameters, e.g., porosity, permeability, water saturation (Sw), irreducible water saturation (Swirr). Finally, two techniques, established based on the crossplots of mean value of apparent formation water resistivity (Rwam) versus variance of apparent formation water resistivity (Rwav)—Sw versus Swirr—were adopted to distinguish hydrocarbon-bearing formations from water saturated layers. Field applications in two different regions illustrated that the established methods and techniques were widely applicable. Computed petrophysical parameters matched well with core-derived results, and pore fluids were obviously identified. These methods were valuable in improving low permeability sandstone reservoirs characterization.

Shale gas is one of the hot spots of energy development. Due to the strong heterogeneity and low physical properties of shale gas reservoirs, and the complex influencing factors of pore development, it is necessary to conduct a comprehensive analysis of the control factors of high-quality reservoirs. The sedimentary characteristics, mineral composition, pore structure and controlling factors of high quality reservoir development are studied on the basis of thin section, scanning electron microscopy (SEM) and QEMSCAN analysis, X-ray diffraction (XRD), total organic carbon (TOC), Nano-CT scanning and Low-pressure N2 adsorption (N2GA) analysis on shale samples from the Longmaxi Formation in South Sichuan Basin. The results show the following: (1) According to lithology, sedimentary structure, organic carbon content and mineral composition, six sedimentary microfacies can be divided. (2) Organic matter pores are developed in organic-rich siliceous shale and organic-rich silty shale at the bottom of the first member of the Longmaxi formation, with average porosity of more than 5% and permeability of more than 2 × 10−3 μm2, which is conducive to the formation of high-quality shale gas reservoirs. (3) The contents of siliceous and TOC are positively correlated with porosity and specific surface area, while the contents of carbonate and clay minerals are negatively correlated with reservoir quality. (4) In the first member of the Longmaxi formation, the sedimentary water depth becomes shallower from bottom to top, and the sedimentary environment changes from a reduction to an oxidation environment. The contents of siliceous and organic matter decrease, while the contents of clay minerals and carbonate minerals show the opposite trend. The difference in sedimentary microfacies affects the distribution of mineral and organic matter and controls the heterogeneity of the shale reservoir.

The evaluation of pore characteristics in lacustrine shales is of significance for shale oil and gas exploration in terrestrial sedimentary basins. However, due to the complex depositional environments, there have been few reports on the quantitative evaluation of lacustrine pores. In this study, we carry out experiments, e.g., scanning electron microscopy (SEM), nitrogen adsorption, X-ray diffraction (XRD), and rock pyrolysis, on sixteen lacustrine shale core samples of the Late Cretaceous Nenjiang Formation (K2n1+2) in the Songliao Basin. At the same time, we bring in the fractal dimensions to quantitatively characterize the pores of shale samples in K2n1+2. The kerogen type of shales in the Nenjiang Formation is mainly type Ⅰ. The shales of K2n1+2 develop a large number of mineral intergranular pores and a small number of organic pores and mineral intragranular pores. The primary minerals of the samples are clay minerals and quartz. The total organic carbon (TOC) has a correlation with the pore physical parameters, whereas the content of minerals does not correlate significantly with pore development. The average pore fractal dimensions obtained from the analysis of nitrogen adsorption data are D1 = 2.5308 and D2 = 2.6557. There is a significant negative correlation between the fractal dimensions (D1 and D2) and the TOC content: the lower the fractal dimensions, the higher the TOC, and the more the free oil. In low maturity shales with higher TOC content, due to hydrocarbon generation, larger pores with a regular shape (small fractal parameters) can be produced, which can store more free oil. The shale reservoir evaluation of K2n1+2 in the Songliao Basin should be focused on shales with higher TOC and lower pore fractal parameters. Our work provides a reference for the shale oil evaluation of K2n1+2 in the Songliao Basin and complements studies on lacustrine pore characteristics.

Pore space of tight sandstone samples exhibits fractal characteristics. Nuclear magnetic resonance is an effective method for pore size characterization. This paper focuses on fractal characteristics of pore size from nuclear magnetic resonance (NMR) of tight sandstone samples. The relationship between the fractal dimension from NMR with pore structure and water saturation is parameterized by analyzing experimental data. Based on it, a pore structure characterization and classification method for water-saturated tight sandstone and a water saturation prediction method in a gas-bearing sandstone reservoir have been proposed. To verify the models, the fractal dimension from NMR of 19 tight sandstone samples selected from the gas-bearing tight sandstone reservoir of Shahejie Formation in Nanpu Sag and that of 16 of them under different water saturation states are analyzed. The application result of new methods in the gas-bearing tight sandstone reservoir of Shahejie Formation in Nanpu Sag shows consistency with experimental data. This paper has facilitated the development of the NMR application by providing a non-electrical logging idea in reservoir quality evaluation and water saturation prediction. It provides a valuable scientific resource for reservoir engineering and petrophysics of unconventional reservoir types, such as tight sandstone, low porosity, and low permeability sandstone, shale, and carbonate rock reservoirs.

This study analyzes the mechanical properties of high ductility concrete (HDC) under different ambient temperatures to provide a parameter basis for the design of HDC bridge deck link slabs. Five temperatures (−30, 0, 20, 40, and 60 °C) were designed to investigate the compressive, tensile, and flexural properties of HDC after temperature treatment and analyze the pore structure. The results show that, compared with the HDC performance at room temperature (20 °C), the compressive strength, ultimate tensile strength, and flexural strength decreased after treatment at low temperatures (−30 and 0 °C), while the strength increased after treatment at high temperatures (40 and 60 °C). After experiencing low- and high-temperature treatments, the ultimate tensile strain and ultimate deflection of the HDC increased. The tensile and flexural failures of the HDC exhibited multiple cracking, and the stress–strain/deflection curve showed a strain/deflection hardening stage. The tensile constitutive relationship can be simplified as a bilinear two-stage relationship. As the temperature increased, the porosity of harmless and less harmful pores in HDC gradually increased, while the porosity of harmful and more harmful pores gradually decreased, resulting in an increase in HDC strength. Based on the influence of temperature on HDC properties, design parameters for the HDC bridge deck link slab structure are proposed.

Reactive magnesia cement is considered an eco-efficient binder due to its low synthesis temperature and CO2 absorption properties. However, the hydration of pure MgO–H2O mixtures cannot produce strong Mg(OH)2 pastes. In this study, nesquehonite (Nes, MgCO3·3H2O) was added to the MgO–H2O system to improve its strength properties, and its hydration products and pore structure were analyzed. The experimental results showed that the hydration product changed from small plate-like Mg(OH)2 crystals to interlaced sheet-like crystals after the addition of a small amount of Nes. The porosity increased from 36.3% to 64.6%, and the total pore surface area increased from 4.6 to 118.5 m2/g. At the same time, most of the pores decreased in size from the micron scale to the nanometer scale, which indicated that Nes had a positive effect on improving the pore structure and enhancing the compressive strength. Combined with an X-ray diffractometer (XRD), a Fourier transform infrared spectrometer (FTIR), and a simultaneous thermal analyzer (TG/DSC), the hydration product of the sample after Nes addition could be described as xMgCO3·Mg(OH)2·yH2O. When Nes was added at 7.87 and 14.35 wt%, the x-values in the chemical formula of the hydration products were 0.025 and 0.048, respectively. These small x-values resulted in lattice and property parameters of the hydration products that were similar to those of Mg(OH)2.

In membrane-based water purification technology, control of the membrane pore structure is fundamental to defining its performance. The present study investigates the effect of the preparation conditions on the final pore size distribution and on the dye removal efficiency of cellulose acetate membranes. The membranes were fabricated by means of phase inversion (using different speeds of film casting and different thicknesses of the casted solution) and introducing modifications in the preparation conditions, such as the use of a coagulation bath instead of pure water and the addition of a surfactant as a solution additive. Both isotropic and anisotropic membranes could be fabricated, and the membranes’ pore size, porosity, and water permeability were found to be greatly influenced by the fabrication conditions. The removal capacity towards different types of water contaminants was investigated, considering, as model dyes, Azure A and Methyl Orange. Azure A was removed with higher efficiency due to its better chemical affinity for cellulose acetate, and for both dyes the uptake could be fitted using a pseudo-second order model, evidencing that the rate-limiting step is chemisorption involving valency forces through the sharing or exchange of electrons between the dye and the membrane.

In a humid environment, the stray current generated by subway operation will corrode the underground pipe network and the internal steel structure of the track plate, which will seriously affect the service life of the subway track plate and increase the maintenance cost later. Groundwater in subway projects mainly enters the concrete interior through capillary action and affects the concrete resistivity, and there is a lack of research on the mechanism of groundwater effect on concrete resistance. In this study, the variation of cement mortar resistivity with capillary water absorption time for cement mortar with different amounts of mineral admixtures (fly ash, ground-granulated blast furnace slag, and silica fume) was measured by the four-electrode method, and the mechanism of the influence of the electrical properties of cementitious materials under the effect of capillary water absorption was analyzed based on the mercury-pressure method (MIP) and thermogravimetric method (TG-DTG). The results show that with the increase in capillary water absorption time, the change curve of cement mortar resistivity can be divided into two stages; in the first stage, capillary water absorption leads to gel pores and transition pores quickly connecting to capillary pores and other large pores to form a water-saturated conductive pathway, resulting in a rapid decrease in resistivity, when the gel pores and excessive pores have a greater impact on resistivity. The second stage is that of capillary water absorption, to a certain extent, after the specimen’s internal water upward development rate slows down; at this time, the formation speed of the conductive pathway decreases, resulting in the rate of change in resistivity decreasing and gradually stabilizing. The incorporation of silica fume can effectively improve the resistivity of cementitious materials under the action of capillary water absorption, in which the resistivity of specimens incorporated with 15% silica fume after 36 days of capillary water absorption is 10.39 times that of the reference group, which is mainly due to its lower porosity and a higher percentage of gel pores.

The alkali-free accelerator based on aluminum sulfate is widely used in shotcrete in tunnels. Long-term Ca-leaching of shotcrete may adversely affect the tunnels in a water-rich mountain. It is necessary to examine further the impact of the AS accelerator and w/c on cement hydration and leaching. In this study, all the cement pastes were cured in the environment with R.H. > 95% and 20 ± 1 °C for 60 days and leached in a running water test with 6 M NH4Cl at 1 cm/s. The hydration kinetics was characterized by isothermal calorimetry. Additionally, the microstructural and mineralogical alterations were characterized by XRD, SEM, MIP, and N2 absorption. The results show that (1) the AS accelerator affected the hydration kinetics of cement by stimulating early hydration and delaying the late silicate hydration, resulting in AS-accelerated cement pastes with rougher pore structure. As a result, the higher the dose of AS accelerator, the faster the cement pastes will leach. (2) Hydration kinetics of the accelerated cement are not affected by the w/c. The AS-accelerated cement pastes with lower w/c have a denser pore structure. So, the reduction in the w/c contributes to leaching resistance.

Nitrogen adsorption experiments have been extensively applied to shale pore structure research and evaluation. The pore structure can be quantitatively characterized in accordance with the nitrogen adsorption–desorption isotherm using various calculation models, whereas the results obtained using different models can more effectively indicate the pore characteristics of shale remains unclear. Further, there has not been any unified process in the optimization of calculation models for pore size distribution (PSD). In this study, the Barret–Joyner–Halenda adsorption (BJH-AD) and BJH desorption (BJH-DE) models were used with Longmaxi Formation shale as an example. Subsequently, the density functional theory (DFT) calculations were conducted on different shale lithofacies samples. Next, the pore structure parameters and heterogeneity obtained using different models were compared, and the consistency parameters of different models were obtained in accordance with Cronbach’s alpha. The results indicated that the pore structure parameters obtained using the BJH-AD model were underestimated since the macroscopic thermodynamic theory was not applicable to this study. The DFT model showed multiple peaks in the range of 1–10 nm, whereas the BJH-DE model had a significant artificial peak in the range of 3.8 nm due to the tensile strength effect, thus suggesting that the DFT model is more capable of characterizing the pores with a pore size 10 nm lower than the BJH model. The PSD curves generated using the three models exhibited multifractal characteristics, whereas the results of the heterogeneity achieved using different models were different. Moreover, the consistency of the results of different models can be studied in depth by combining Cronbach’s alpha with various heterogeneity parameters. The DFT model exhibited high consistency in pore structure parameters and pore heterogeneity, thus suggesting that the DFT method of N2 is the optimal physical adsorption data analysis method in the shale mesoporous range. Accordingly, the nitrogen adsorption curve, the hysteresis loop shape, multifractal parameters, and Cronbach’s alpha were integrated to generate a working flow chart of the nitrogen adsorption model for N2-adsorption-model optimization.

During diagenesis, the transformation of unconsolidated sediments into a sandstone is usually accompanied by compaction, water expulsion, cementation and dissolution, which fundamentally control the extent, connectivity and complexity of the pore structure in sandstone. As the pore structure is intimately related to fluid flow in porous media, it is of great importance to characterize the pore structure of a hydrocarbon-bearing sandstone in a comprehensive way. Although conventional petrophysical methods such as mercury injection porosimetry, low-pressure nitrogen or carbon dioxide adsorption are widely used to characterize the pore structure of rocks, these evaluations are based on idealized pore geometry assumptions, and the results lack direct information on the pore geometry, connectivity and tortuosity of pore channels. In view of the problems, X-ray micro-CT was combined with ImageJ software (version 1.8.0) to quantitatively characterize the pore structure of Berea Sandstone. Based on its powerful image processing function, a series of treatments such as contrast enhancement, noise reduction and threshold segmentation, were first carried out on the micro-CT images of the sandstone via ImageJ. Pores with sizes down to 2.25 μm were accurately identified. Geometric parameters such as pore area, perimeter and circularity could thus be extracted from the segmented pores. According to our evaluations, pores identified in this study are mostly in the range of 30–180 μm and can be classified into irregular, high-circularity and slit-shaped pores. An irregular pore is the most abundant type, with an area fraction of 72.74%. The average porosity obtained in the image analysis was 19.10%, which is fairly close to the experimental result determined by a helium pycnometer on the same sample. According to the functional relationship between tortuosity and permeability, the tortuosity values of the pore network were estimated to be in the range of 4–6 to match the laboratory permeability data.

The success of shale oil exploration and production is highly dependent on the heterogeneous nature of the reservoir pore structure. Despite this, there remains limited research on the heterogeneity characteristics of pores at different scales in lacustrine shale oil reservoirs and the factors that impact them. This study aims to quantitatively characterize the multi-scale pore heterogeneity differences of the lacustrine shale found in the Funing Formation in Gaoyou Sag. Additionally, the study seeks to clarify the impact of the total organic carbon (TOC) and lithofacies type on pore structure heterogeneity. To achieve this, nitrogen adsorption, scanning electronic microscope (SEM), mercury intrusion porosimetry (MIP), and other experimental means were adopted in combination with the fractal dimension model of FHH and capillary. The results show that the predominant lithofacies of the Funing Formation shale samples are mixed shale (MS) and siliceous shale (SS), with a limited presence of calcareous shale (CS). The micro-pores of lacustrine shale are dominated by inorganic mineral pores and fewer organic pores. Intragranular pores and clay mineral pores are two types of inorganic mineral pores that are widely found. Small pores (pore diameter < 50 nm) make up 89% of the pore volume (PV) and 99% of the specific surface area (SSA). The fractal dimensions D1, D2, and D3 were calculated to characterize the roughness of the pore surface, the structural complexity of small pores, and the structural complexity of large pores (pore diameter > 50 nm), respectively. The increase in the total organic carbon (TOC) resulted in a decrease in the D1, D2, PV, and SSA, while connectivity showed a slight improvement. The fractal dimension of shale across all lithofacies followed the pattern: D3 > D2 > D1. The pore structure is more complex than the pore surface, and the large pores showed a greater heterogeneity than the small pores. Among the three lithofacies, CS had the largest PV, SSA, D1, and D2, indicating the development of a more complex pore structure network. This expands the space required for shale oil occurrence. However, the connectivity of the CS lithofacies is the lowest among the three, which hinders shale oil production. Although the PV of SS is slightly lower than that of CS, its average pore diameter (AVE PD) and connectivity are significantly advantageous, making SS an ideal shale reservoir. This study provides an important reference for the reservoir evaluation required to better develop lacustrine shale oil around the world.

Reducing solid waste emission is the development direction of cleaner production in the future. This paper proposes to use the agricultural solid waste rice husk ash (RHA) as an alternative cementitious material for the underground filling of mines. The pore structure and mechanical properties of cemented paste backfill with different RHA dosages (RCPB) are analyzed. The results reveal that: (1) The pore structure of RCPB is divided into three types: micropores (100 μm). The total number of micropores accounts for the largest proportion, followed by secondary pores and main pores. The total volume of secondary pores accounts for the largest proportion, followed by micropores and main pores. (2) The porosity decreases and the UCS increases with the increase of RHA dosage and curing time. The UCS decreases linearly with the increase of RHA dosage. The UCS has a linear negative correlation with porosity. (3) The cracks of RCPB initiated at the yield point, gradually expanded at the peak point, and finally penetrated at the post-peak point. The failure mode of RCPB is mainly a tensile failure, accompanied by a small number of secondary tensile cracks. (4) The hydration products of RCPB are mainly C–S–H and AFt gels. The greater the RHA dosage and CT, the more hydration products, the fewer pores, the greater the strength, and the greater the average gray value. The outcome of this work will afford a new ideas and methods for using solid waste (Rice husk) as backfilling.

To study the performance of recycled aggregate pervious concrete (RAPC) in severe cold regions, the influence of the water–binder ratio, design porosity, micro silica fume (SF) and enhancer agent (EA) on the permeability and mechanical properties of the RAPC were evaluated using the orthogonal design method. Based on the optimal mixture proportion, freeze–thaw (F-T) experiments were carried out to investigate the effect of different media (water, 3.5 wt% NaCl solution) on the mechanical properties, permeability and anti-frost durability of the RAPC. Moreover, the porosity and pore structure characteristics of RAPC were evaluated after frost damage using an X-ray CT technique. The results indicate that the influence of the salt solution on the deterioration of the RAPC specimen is greater than water. The deterioration degree of the mass loss ratio, relative dynamic elastic modulus (RDEM), average compressive strength and porosity of the RAPC increase with increasing F–T cycles. Based on the two-parameter Weibull probabilistic distribution function, damage evolution models of RAPC are established, which can be used to quantitatively characterize the damage degree of the RAPC specimens under different F–T media. The results obtained can provide an experimental reference and data support for the promotion and application of RAPC pavement in severe cold regions.

In previous research, many scientists and researchers have carried out related studies about the spontaneous combustion of coal at both the micro and the macro scales. However, the macroscale study of coal clusters and piles cannot reveal the nature of oxidation and combustion, and the mesoscale study of coal molecule and functional groups cannot be directly applied to engineering practice. According to our literature survey, coal is a porous medium and its spontaneous combustion is a multi-scale process. Thus, the mesoscale study of coal’s spontaneous combustion is essential. In this manuscript, the mesoscale of the coal body (such as pore size, pore volume, and specific surface area), and the meso-scale structural morphological characteristics of the coal surface are finely analyzed and characterized. On this basis, the meso-scale structure of pores and fractures are digitally reconstructed. Furthermore, velocity and pressure distributions of the flow field in the pores of the scan plane are outlined and described by numerical simulation. The results indicate that, because of the pore structure characteristics and fluid viscosity, not all fluids in the pores demonstrate flow. This conclusion well explains the source of CO gas in methane extraction pipes, which is one of the main index/indicator gases of the spontaneous combustion of coal.

Diatomite is a siliceous sedimentary rock containing amorphous silica, which can be used as a green mineral admixture to improve the properties of concrete. This study investigates the affecting mechanism of diatomite on concrete performance by macro and micro tests. The results indicate that diatomite can reduce the fluidity of concrete mixture and change its water absorption, compressive strength, resistance to chloride penetration (RCP), porosity, and microstructure. The low fluidity of concrete mixture containing diatomite can reduce workability. With increasing diatomite as partial replacement for cement in concrete, water absorption of concrete decreases before increasing, while compressive strength and RCP rise first and then drop. When diatomite is added to the cement at a content of 5% by weight, the concrete has the lowest water absorption and the highest compressive strength and RCP. Through the mercury intrusion porosimetry (MIP) test, we determined that the addition of 5% diatomite reduces the porosity of concrete from 12.68% to 10.82% and changes the proportion of pores with different sizes in concrete, the proportion of harmless and less harmful pores increases, and the proportion of harmful pores reduces. Based on the microstructure analysis, the SiO2 in diatomite can react with CH and produce C-S-H. C-S-H is responsible for developing concrete because it fills pores and cracks, forms a platy structure, and makes the concrete much denser, thereby improving its macroscopic performance and microstructure.

The Jurassic shale in the northeastern Sichuan Basin is one of the main target intervals for continental shale gas exploitation. Research on the pore structure and gas-bearing properties of shales is the key issue in target interval optimization. Through core observation, geochemistry, bulk minerals, scanning electron microscopy, nitrogen adsorption, and isothermal adsorption experiments, various lithofacies with different pore structure characteristics were clarified. In addition, the factors that control gas-bearing properties were discussed, and a continental shale gas enrichment model was finally established. The results show that the Jurassic continental shale in the northeastern Sichuan Basin can be classified into six lithofacies. Organic pores, intergranular pores, interlayer pores in clay minerals, intercrystalline pores in pyrite framboids, and dissolution pores can be observed in shale samples. Pore structures varied in different shale lithofacies. The contact angle of shales is commonly less than 45°, leading to complex wettability of pores in the shales. Free gas content is mainly controlled by the organic matter (OM) content and the brittleness in the Jurassic shale. The adsorbed gas content is mainly controlled by the OM content, clay mineral type, and water saturation of the shales. The enrichment mode of the Lower Jurassic continental shale gas in the northeastern Sichuan Basin is established. Paleoenvironments control the formation of organic-rich shales in the center part of lakes. The “baffle” layer helps the confinement and high pressure, and the complex syncline controls the preservation, forming the enrichment pattern of the complex syncline-central baffle layer.

The Silurian Longmaxi (S1l) marine shale and Jurassic Dongyuemiao (J1d) lacustrine shale in the Sichuan Basin, West China have attracted considerable attention from the oil-and-gas industry in China. Currently, the differences in pore types and pore structures between them are poorly understood, which has limited shale-resource exploration in the Sichuan Basin. This paper systemically compares the pore characteristics of Longmaxi shale and Dongyuemiao shale and investigates their impact on shale-gas enrichment by integrating field-emission scanning electron microscopy (FE–SEM), X-ray diffraction (XRD), low-pressure gas (CO2 and N2) adsorption and mercury-intrusion porosimetry, high-pressure sorption isotherms, gas-saturation measurement, molecular-dynamics simulation, etc. The results show that the S1l organic-rich marine shale and the J1d lacustrine shale have different pore types and pore structures. The S1l shale is dominated by organic pores, mainly micropores and mesopores with ink-bottle-like pore shapes, while the J1d shale is primarily composed of clay-mineral pores, mainly mesopores and macropores with slit- or plate-like pore shapes. Organic pores can provide considerable storage space for shale-gas enrichment in S1l marine shale, which also determines the adsorption capacity of shale reservoirs. Although organic pores are not the most prevalent in the Dongyuemiao lacustrine shale, they also play an important role in enhancing reservoir quality and absorbed-gas enrichment. Clay-mineral pores contribute weakly to the storage space of J1d-lacustrine-shale reservoirs. Mesopores are the most important form of storage space in both S1l shale and J1d shale, contributing significantly to shale-gas enrichment. Micropores are secondary in importance in S1l marine shale, while macropores are secondary contributors to pore volume in J1d lacustrine shale.

The chloride diffusion of marine high-performance concrete under a couple of actions, flexural load and freezing–thawing, was investigated by a fast freezing and thawing test in NaCl solution. Concrete specimens of 100 × 100 × 515 mm were tested under bending load and 300 freeze–thaw cycles under the stress levels of 15%, 30%, and 50% of the ultimate fracture modulus. The change in the microstructure of the concrete was analyzed by SEM and MIP. The results indicated that the chloride diffusion coefficient of concrete under the coupling effect of flexural load and freezing–thawing or simple flexural load increased with the increasing in the flexural stress level, and the chloride diffusion coefficient was approximately exponential to the flexural stress level, as D = 0.8777e1.668σ for a couple of actions of flexural load and freezing–thawing, and D = 0.8336e1.3231σ for a simple flexural load. The resistance ability of concrete to chloride diffusion was reduced by the freezing–thawing procedures, the resisted ability dropped more severely under a couple of actions of flexural load and freezing–thawing than simple flexural load at the same stress level. Micro-cracks at the interfacial transition zone between the aggregate and the paste matrix in concrete was induced under a couple of actions of flexural load and freezing–thawing, which increased the average pore size and total pore volume, resulting in the modification of the pore size distribution in the concrete. The influence of a couple of actions of flexural load and freezing–thawing on the concrete was greater than that of simple flexural load.

To evaluate the reservoir characteristics of siliceous shale in the Dalong Formation within the late Permian intra-platform rift trough in Western Hubei (China), we studied a drill core from well ED-2 in Western Hubei. To analyze the physical characteristics, pore structure, methane adsorption performance, and their influences on the siliceous shale reservoir, we performed X-ray diffraction, total organic carbon (TOC) content, vitrinite reflectance (Ro, indicating thermal evolution), total porosity and permeability, field emission scanning electron microscopy, CO2 and N2 physical adsorption, and methane isothermal adsorption analyses, among others. Our results show that the Dalong Formation in Western Hubei is an organic-rich (2.6–14.3 wt.%), highly thermally evolved (Ro = 2.59–2.76%), siliceous shale containing mainly type-I and type-II1 organic matter. The Dalong siliceous shale has low porosity and permeability and belongs to a larger reservoir with low horizontal permeability (0.002–335.209 mD) and porosity (1.2–7.8%). Pores in the shale are mainly organic, inorganic, and microfractures; the organic pores are very developed. The pore volume and specific surface area of the shale are mainly due to micropores and mesopores and are positively correlated with TOC and clay mineral contents and weakly negatively correlated with quartz and carbonate contents. The micropores and mesopores are well developed, improving the methane adsorption capacity, which, in turn, is strongly positively correlated with TOC content. Comprehensive analysis shows that the high organic matter content of the Dalong siliceous shale has the greatest influence on its pore structure; the many organic pores generated after hydrocarbon generation have controlled the development of micropores and mesopores, which is conducive to the adsorption and storage of shale gas. The development of brittle minerals resistant to compaction, such as siliceous minerals, helps preserve organic pores. This study is informative for basin-scale petroleum system investigations, which are essential for understanding oil and gas exploration possibilities and regional petroleum systems.

With the gradual shift of coal mining to deeper levels in recent years, rock burst has become one of the primary dynamic hazards faced in deep mining. It has been shown that the pore structure in rocks affects the mechanical properties, but the relationship with the rock burst phenomenon still needs to be clarified. In this paper, we investigated the causes and effects of pore structure on impact mechanical properties using RFPA2D numerical simulation software, established several numerical models with different porosities and pore diameters, and analyzed the stress-strain curves, the relationships between porosity and pore diameter and each the bursting liability indices of the coal rock body were elaborated, and the fitting equations in the range of porosity (0%~10%) and pore diameter (0.25~2.0 mm) were obtained. The results showed that the increase in porosity and pore diameter effectively attenuated the bursting ability of coal rocks, which has some reference significance for the study of early warning and prevention of rock burst phenomenon.

Authigenic chlorite is a common clay mineral in clastic rock reservoirs, and it has an important influence on the pore structure of tight clastic rock reservoirs. In this paper, the tight clastic reservoirs in the Lower Cretaceous Yingcheng Formation in the Longfengshan subsag in the Changling fault depression in the Songliao Basin were investigated. Polarized light microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), high-pressure mercury injection (HPMI), and low temperature nitrogen adsorption (LTNA) were used to study the influence of authigenic chlorite on the pore structure of tight clastic reservoirs. The results show that the authigenic chlorite in the study area was mainly generated in the form of pore linings. The formation of the authigenic chlorite was mainly controlled by the parent rock type and the sedimentary microfacies in the provenance area. The hydrolysis and dissolution of the iron- and magnesium-rich intermediate-mafic magmatic rocks and the high-energy, open, weakly alkaline reducing environment in the delta-front underwater distributary channel were the key factors controlling the formation of the authigenic chlorite in the study area. The pore-lining chlorite slowed down compaction and inhibited quartz overgrowth, protecting the original pores. Moreover, there are a large number of intercrystalline pores in the chlorite, which provided channels for the flow of acidic water and thus the formation of secondary pores, playing a positive role in the physical properties of the tight clastic rock reservoirs. However, the pore-filling chlorite also blocked the pore throats, playing a negative role in the physical properties of the tight clastic rock reservoirs. The tight clastic rock reservoirs with pore-lining chlorite generally had low displacement pressures and large pore throat radii. The morphology of the nano-scale pores was mainly parallel plate-shaped slit pores. There were many primary pores and a small number of secondary pores in the reservoir. Some of the pores were connected by narrow-necked or curved sheet-like throats, and the pore structure was relatively good. A higher relative content of chlorite led to a larger nano-scale pore throat radius, a smaller specific surface area, a smoother pore surface, and stronger homogeneity. Authigenic chlorite played a positive role in the formation of the tight clastic reservoirs in the study area.

Grout sleeve splicing of rebar is a major technology in prefabricated buildings, and cementitious grout for rebar sleeve splicing (hereinafter called grout) is an essential material for this technology. Grout, with its excellent mechanical properties, improves the stability of rebar sleeve splicing. In this study, the mechanical properties of grout were improved by introducing an admixture in the form of a defoamer, and the influence of the defoamer on the fluidity, loss rate of fluidity, wet apparent density and strength of the grout was investigated. The action of the defoamer in regulating the pore structure of the grout was further analyzed using the mercury intrusion porosimetry (MIP) method. The results showed that when the dosage of defoamer was increased from 0 to 0.025%, the fluidity of the grout initially increased and then decreased, but there was no change in the loss rate at 30 min. The wet apparent density increased continuously, whereas the flexural and compressive strength generally increased initially and then tended to stabilize. The MIP test results showed that the defoamer increased the pore volume of the grout in the range of 6 nm to 30 nm and decreased the pore volume in the range of 30 nm to 60 μm. However, in the 60 μm to 300 μm pore size range, the pore volume increased when the dosage of the defoamer was 0.0025% and 0.0075%, and decreased when the dosage was 0.005% and 0.001%. The porosity of the grout initially decreased and then increased slightly as the dosage of the defoamer increased from 0 to 0.01%. The introduction of defoamer can optimize the pore structure of grout and then improve its mechanical properties. The influence of defoamer on grout properties and pore structure were systemically studied with a view to providing technical and theoretical guidance for rebar sleeve-splicing technology in prefabricated construction.

The production of shale gas plays an important role in the global oil/gas industries, which is considered to approach about 1/3 of the total natural gas production at 2040. In recent years, Wufeng–Longmaxi Formation shale in Sichuan Basin has become a key target of gas development in China. The detection of high-quality gas-producing areas based on the relation between pore structure, mineralogy and elastic properties is the main research direction. However, the effects of depositional environment and diagenetic processes are rarely considered in the studies of these petrophysical properties. We select core samples from the two boreholes to perform X-ray diffraction experiments together with another set of cores from the target formation to obtain scanning electron microscope images and ultrasonic velocities. The mineralogy, pore structure and elastic properties are analyzed. The formation is divided into two sections based on the reservoir characteristics and sedimentary environments. Then, we study the different diagenetic processes of the upper and lower sections. Three-dimensional rock-physics templates of the shale in the two sections are built by using equivalent medium theories and elastic attributes. The templates are calibrated with the samples and well-log data. A 2D survey line and a 3D seismic block of the upper and lower sections are selected, respectively, to map the mineral component, porosity and microcrack density. The good match between the predictions and log interpretation and actual gas content reports suggests that the rock-physics template based on differential diagenesis can be effectively used for further interpretation of seismic inversion results.

Renewable energy sources are indispensable to meet the rising demand of energy usage while reducing the negative environmental impact of utilising fossil fuels. Gasification is an efficient technology to convert biogenic waste into valuable gaseous products. The rate of conversion of char, produced in an intermediate step in the conversion, plays an essential role in the conversion of biogenic materials. The conversion of char is significantly affected by properties such as the structure of the char and its alkali content. This thesis presents findings related to the influence of char pore structure development and alkalis content on char gasification, as well as the alkali release during gasification and co-gasification. Experimental results show that the generation of micropores are directly proportional to the observed reactivity up to 70% of char conversion, after which the catalytic effects of potassium become the dominating factor. Furthermore, investigations of the effect of different intrinsic potassium contents on woody char reactivity demonstrate that no alkali surface saturation point is reached, as is the case for high-ash chars. Application of a modified random pore model enabled a successful capture of the later stages of char conversion in comparison to other kinetic models applied. Alkali release and sample mass changes were monitored simultaneously, using a thermogravimetric analyser together with a surface ionization detector (TGA-SID). The studies revealed a significant release of alkali as woody char conversion approaches completion during CO2 gasification. For straw char the release of alkali decreased continuously throughout the conversion process. Similar results were obtained for biochar gasification under steam conditions in a fixed bed reactor. However, in this case the process is more complex, including transfer of alkali between particles inside the fixed bed, which influences char conversion. Co-gasification of different types of biomass can substantially affect char conversion efficiency. In comparison to pure wood, mixing wood and straw had positive effects on the char conversion for rates below 90% of conversion, while exceeding this degree of conversion resulted in negative effects. The most significant positive effect was observed at a gasification temperature of 900 °C, particularly when using a wood-straw blend of 75 wt%:25 wt%. The above findings are important for the understanding of the mechanisms of char conversion and are valuable in the design of gasifiers. The research provides with a deeper understanding of char structure development, alkali release, and migration during gasification of biogenic materials. Förnybara energikällor behövs för att möta den ökande efterfrågan på energianvändning, samtidigt med behoven av att minska den negativa miljöpåverkan som användningen av fossila bränslen medför. Förgasning är en effektiv teknologi för att omvandla biogent avfall till värdefulla gasformiga produkter. I omvandlingsprocessen förkolas biomassan till biokol i ett intermediärt steg. Hastigheten för omvandlingen av biokolet spelar en avgörande roll vid förgasningen av biogena material. Denna omvandling påverkas väsentligt av biokolets egenskaper såsom kolstruktur och dess alkaliinnehåll. I denna avhandling presenteras resultat som relaterar till inverkan av kolstrukturens utveckling och innehåll av alkalier vid förgasningen av biokol samt frigörandet av alkali under förgasning och samförgasning. Experimentella resultat visar på att genereringen av mikroporer är direkt proportionellt mot observerad reaktivitet upp till 70 procents kolomvandling. Därefter är de katalytiska effekterna huvudsakligen relaterade till kaliumhalten. Vidare så observerades ingen effekt av alkalimättnad av kolytan på biokolets reaktivitet vid studier med biokol från trämaterial med olika halter av kalium, något som observerats tidigare för biokol med högre innehåll av aska. Tillämpning av en modifierad randomiserad modell för utvecklingen av porer resulterade i en lämplig beskrivning av de slutliga stadierna i omvandlingen av biokol jämfört med andra kinetiska modeller. Frigörandet av alkalier och förändringar i provernas massa undersöktes med hjälp av termogravimetrisk analys tillsammans med en ytjonisationsdetektor (TGA-SID). Studierna visar att en betydande mängd alkalier frigörs mot slutet av biokolets omvandling under koldioxidförgasning. För biokol från halm observerades däremot ett fortsatt minskat frigörande av alkalier under hela omvandlingsprocessen. Liknande resultat erhölls för biokolförgasning under ångförhållanden i en reaktor med en fast bädd. I detta fall är dock processen mer komplex och omfattar även överföring av alkalier mellan partiklar inne i den fasta bädden, vilket påverkar kolomvandlingen. Samförgasning av olika typer av biomassa kan avsevärt påverka kolomvandlingens verkningsgrad. I jämförelse med rent trä så resulterade en blandning av trä och halm i positiva effekter på kolomvandlingen för omvandlingsgrader under 90 %, medan högre omvandlingsgrader resulterade i negativa effekter. Den mest betydelsefulla positiva effekten observerades vid en förgasningstemperatur på 900°C, särskilt vid en trä-halm-blandning med viktprocentförhållandet 75:25 Resultaten är viktiga för förståelsen av mekanismerna för omvandlingen av kol och är värdefull vid konstruktion av förgasare. Forskningen har gett en djupare förståelse för utvecklingen av kolstrukturen, frigörande av alkalier och migration under förgasning av biogent material. QC 2023-04-26

Shale of the Middle–Upper Permian Dalong Formation and Gufeng Formation in the Lower Yangtze region is characterized by large thickness, high total organic carbon (TOC), wide distribution and moderate organic thermal evolution degree, so it may be the next important field of shale gas exploration. In order to point out the target and direction of shale gas exploration and development in this region, this paper selects the Dalong Formation and Gufeng Formation shale in the Xuanjing area of Lower Yangtze as the research object to quantitatively describe the development characteristics of shale pores of different scales by means of scanning electron microscopy (SEM), high pressure mercury injection, CO2 and N2adsorption. Then, the fractal dimension of sample pores is calculated by using the FHH (Frenkel–Halsey–Hill) model. Finally, combined with TOC and mineral compositions, the relationship between pore structure and fractal dimension is discussed. And the following research results are obtained. First, dominant lithofacies of Dalong Formation are argillaceous-rich siliceous shale and argillaceous-rich/siliceous mixed shale, which has smaller specific surface area and pore volume, larger average pore diameter. The pore development is mainly controlled by clay mineral content. Dominant lithofacies of Gufeng Formation is siliceous shale, which has a larger specific surface area and pore volume, and smaller average pore diameter. The pore development is controlled by organic matter and brittle mineral content. Second, the influencing factors of fractal dimension can be attributed to the controlling factors of micropore development. The fractal dimension D1of Dalong Formation ranges from 2.4515 to 2.5513 (average 2.5227), and D2ranges from 2.5817 to 2.6578 (averagely 2.6246). The fractal dimension D1of Gufeng Formation ranges from 2.5817 to 2.6578 (averagely 2.6246), and D2ranges from 2.7227 to 2.871 (averagely 2.813). Gufeng Formation shale presents the characteristics of more complex pore structure. Third, the fractal dimension D1is more sensitive to specific surface area, pore development and mineral composition, while D2is more effective in characterizing the average pore diameter. In conclusion, Dalong Formation shale with high D1and D2and Gufeng Formation shale with low D1and high D2can be taken as the favorable exploration targets of Permian marine shale gas in the Lower Yangtze region, and the regional overpressure zones (belts) with weaker structural deformation in hydrocarbon rich sags will be the favorable shale gas exploration targets in this area.

The accurate determination of the coal slime filter cake pore structure has always been a problem in the field of solid–liquid separation. An innovative measurement method for the pore structure of filter cake after filtration dehydration of coal slime water, including the preparation of coal slime filter cake, the solidification of the filter cake, and the preparation and measurement of test filter cake, was established in this paper. Epoxy resin and curing agent can ensure the strength of the filter cake, and red colorant can realize the accurate separation of coal particles and pores. The most suitable perfusate consists of epoxy resin, red colorant, and curing reagent, and the optimal ratio is 12:3:5. The application of the method to the study of the effect of filtration time on the coal slime filter cake pores shows that the modified method is effective. At the initial stage of filtration, intergranular pores formed by coarse particles are the main pores. With increasing filtration time, the macropores formed by the coarse particles are mainly filled with fine particles, and the pore size of the filter cake rapidly decreases. These measuring results and rules are accurate. This method can be conveniently used to study the microstructure of filter cake, pore channel regulation, filtration dehydration mechanisms, etc.

The research on pore structure and heterogeneity of shale reservoirs has always been a hotspot in the study of unconventional reservoir characteristics. China is a country dominated by continental shale. Compared with marine shale, continental shale has lower maturity and stronger reservoir heterogeneity. In this study, Sha-4 shale in the Liaohe Western Depression was selected for low-temperature nitrogen adsorption, scanning electron microscopy and other experiments revealing the pore structure and fractal characteristics of continental low mature organic-rich shale. The fractal dimension was calculated by the FHH model and the effects of TOC and mineral composition on pore structure and fractal characteristics were discussed. The results show that the Sha-4 shale in the study area is mainly mesoporous and the main pore types are inorganic pores with relatively large pore diameters, such as intergranular pores and inter-crystalline pores. The pore morphology is very complex, mainly narrow slit and flat pore, and the pore is often filled with organic matter. The fractal dimensions D1 range from 2.58 to 2.87 and D2 range from 2.18 to 2.55, and the pore structure shows obvious dual fractal characteristics. The pore structure and fractal characteristics of shale are mainly affected by TOC and quartz due to the low degree of the thermal evolution of shale and their effects are different from those of marine shale reservoirs. The increase in TOC reduces the heterogeneity of the shale reservoir. In addition, mineral particles with strong weathering resistance and stability such as quartz can protect the pore structure of shale, improve the pore structure and reduce the reservoir heterogeneity. This study can provide support for the study of low maturity continental shale reservoir heterogeneity in the Sha-4 member of the Liaohe Western Depression.

The disposal of industrial by-product tailings has become an important issue in solving environmental pollution. In this study, 15%, 30%, 50%, and 70% iron tailings were used to replace the natural sand in concrete, and 1.5% steel fiber and 0–0.75% PVA fibers were added to the iron tailings concrete. The effects of the iron tailings replacement rate and the fiber content on the mechanical properties, carbonization depth, and concrete porosity were studied in a carbonization environment. The results demonstrated that the compressive and splitting tensile strengths of concrete first increased and subsequently decreased with an increase in the iron tailings replacement rate, while the carbonation depth and porosity initially decreased and subsequently increased. When the replacement rate of iron tailings was 30%, the compressive strength and split tensile strength were increased by 7.6% and 17.7%, respectively, and the porosity was reduced by 8.9%. The compressive strength, carbonation depth and porosity of single-doped steel-fiber concrete were superior to those of ordinary iron tailings concrete. However, compared with single-doped steel fiber, the performance of steel-PVA fiber was further improved. Based on the mechanical properties, the carbonation depth test results of the three aforementioned types of concrete, the mathematical expression of the uniaxial compression stress–strain curve of iron tailings concrete, and the prediction equation of the carbonation depth of mixed-fiber iron tailings concrete were proposed. This study provides a reference for the application and popularization of fiber-reinforced iron tailings concrete in carbonization environments.

Silicon-based ceramic aerogels obtained by the polymer pyrolysis route possess excellent thermophysical properties, but their poor mechanical properties limit their broader applicability in thermal insulation materials. Herein, SiCN(O) ceramic aerogels were prepared under the toughening effect of a crosslinker (hexamethylene diisocyanate, HDI), which maintains the structural integrity of the aerogel during the wet gel-to-aerogel conversion. The aerogel maintained a high surface area (88.6 m2 g−1) and large pore volume (0.21 cm3 g−1) after pyrolysis. Based on this, mullite-fiber-reinforced SiCN(O) aerogels composites with outstanding thermal insulation properties and better mechanical performance were synthesized via ambient pressure impregnation. Furthermore, the effect of the impregnation concentration on the mechanical and insulation properties of the composites was investigated. The results revealed that the composite prepared with a solution ratio of 95 wt.% exhibited a low density (0.11 g cm−3) and a low thermal conductivity (0.035 W m−1 K−1), indicating an ~30% enhancement in its thermal insulation performance compared to the mullite fiber; the mesoporous aerogel structures wrapped on the mullite fibers inhibited the gas thermal conduction inside the composites.

Hydraulic fracturing of shale gas reservoirs is characterized by large fracturing fluid consumption, long working cycle and low flowback efficiency. Huge amounts of fracturing fluid retained in shale reservoirs for a long time would definitely cause formation damage and reduce the gas production efficiency. In this work, a pressure decay method was conducted in order to measure the amount of fracturing fluid imbibition and sample permeability under the conditions of formation temperature, pressure and adsorbed methane in real time. Experimental results show that (1) the mass of imbibed fracturing fluid per unit mass of shale sample is 0.00021–0.00439 g/g considering the in-situ pressure, temperature and adsorbed methane. (2) The imbibition and flowback behavior of fracturing fluid are affected by the imbibition or flowback pressure difference, pore structure, pore surface properties, mechanical properties of shale and mineral contents. (3) 0.01 mD and 0.001 mD are the critical initial permeability of shales, which could be used to determine the relationship between the formation damage degree and the flowback pressure difference. This work is beneficial for a real experimental evaluation of shale formation damage induced by fracturing fluid.

In this study, a series of experiments was conducted to examine the mechanical and damage properties of cemented paste backfill (CPB) with different water saturations (ws = 0%, 22.1%, 47.0%, 65.3%, 82.8%, and 100%). The results reveal that the UCS, peak strain, and elastic modulus first increased and then decreased, and the porosity and fractal dimension of cracks first decrease and then increase with the increase of ws. In addition, the UCS, peak strain, and elastic modulus is maximum, and the porosity and fractal dimension are minimum when the ws is 65.3%. The UCS increases with the increase of peak strain and elastic modulus, and decreases with the increase of porosity and fractal dimension, and the UCS present good quadratic polynomial functions relationship with the porosity and fractal dimension. The SEM images show that with the increase of ws from 0% to 65.3%, the hydration products increases and the pore structure decreases. When the ws exceeds 65.3%, and the pore structure begins to increase. The failure mode of the CPB is mainly tensile failure. A new damage constitutive model of CPB with different ws was constructed. The total damage D of the CPB is composed of initial damage Dp and load damage DL. The total damage evolution curve shows an S-shaped distribution, and the total damage rate evolution curve shows a normal distribution. With the increase of ws, the damage rate and the peak value of damage rate of CPB first increases and then decreases.