Variation Of Pore Structure Research Articles

A systematical comparation of Cu (II) adsorption behavior and mechanism between biomass fly ash and biogas residue pyrolysis char

Biomass fly ash (BFA) and biogas residues are the main by-products of biomass direct-fired power generation and biogas production. This study compares the Cu(II) adsorption mechanisms of BFA and biogas residue pyrolysis char (BRPC) through systematic tests. BFA exhibited a significantly higher adsorption capacity (75.34 mg/g) than BRPC (42.80 mg/g). The pseudo-first-order kinetic model best described BFA, while the Elovich model was optimal for BRPC. Both materials fit the Freundlich isotherm model. BFA's superior mineral co-precipitation and ion-exchange capacity are due to its rich mineral content, particularly calcium. BRPC benefits from an additional functional group complex adsorption due to its pyrolytic charcoal content. Variations in pore structure of BFA and BRPC did not demonstrate a significant effect on the adsorption. The results of this study provide essential data support for the potential of high-value utilization of BFA and BRPC and the innovative modification of high-performance biomass-based heavy metal adsorbent materials.

Effects of crosslinker concentration on curing process and performances of needled fiber preform reinforced phenolic aerogel composite using process simulation and comprehensive experiments

A kind of needled quartz/carbon fiber preform reinforced phenolic aerogel composite (NQCF/PR) was fabricated through impregnating needled fiber preform with phenolic resin precursor solution, followed by sol–gel polymerization and solvent drying. The needled fiber preform serves as lightweight quasi-three-dimensional reinforcement, while phenolic aerogel matrix provides high porosity and low thermal conductivity. During fabrication of aerogel composite part using vacuum-assisted resin infusion process, distribution of crosslinker hexamethylenetetramine (HMTA) in precursor solution can be problematic, as precipitated crosslinker particles may be filtered by fibrous preform. In this study, the impact of HMTA filtration induced heterogeneous structure on subsequent curing process was investigated using process simulation. Temperature effects of sol–gel polymerization and solvent evaporation were considered through establishment of corresponding kinetic models. Impacts of heterogenous structure on distribution of temperature, resin curing degree and solvent conversion degree in large hemispherical aerogel composite structure were investigated. This leads to variations in gel network and pore structure of aerogel, thereby affecting final material performance. Based on experimental results, as HMTA concentration increases, compressive performance of NQCF/PR obviously increases. Among these, NQCF/PR with 4.7 wt% HMTA provides a balance of lightweight nature (0.25 g/cm3), excellent thermal insulation property (0.052 W·m−1·K−1) and compressive performance (strength of 0.35 MPa).

Influence mechanism of further hydration on the compressive strength of ultra-high performance concrete with coarse aggregates

A further hydration test was conducted to study the effects of temperature and humidity conditions on the compressive strength and microstructure of ultra-high performance concrete with coarse aggregates (UHPC-CA), while analyzing the mechanisms influencing its compressive strength. The results indicated that the higher temperatures resulted in more significant strength and pore structure variations, with strength and pore structure changes being greater in liquid water environments compared to water vapor environments. The hardness of interfacial transition zone (ITZ) increased initially and then declined. The influence of further hydration on the strength of UHPC-CA was primarily divided into three stages: enhancement, damage and filling. These findings provide a theoretical foundation for the evaluation and design of UHPC materials for long-term service in aquatic environments.

Variation of soil pore structure and predication of the related functions following land‐use conversion identified by multi‐scale X‐ray tomography

AbstractLand‐use conversion profoundly influences the soil pore structure, consequently modifying the soil functions. Investigating the variation of multiscale soil pore structure and their associated functions following land‐use change is critical for evaluating land management strategies. However, this topic has not yet been extensively explored in recent studies. In this study, the pore structure of soil following land‐use conversion was quantitatively investigated by multiscale X‐ray tomography. Intact soil aggregates and undisturbed soil cores were collected from paddy fields (PF) and from vegetable fields were converted from paddy fields for 5 years (VF‐5), 13 years (VF‐13), and 20 years (VF‐20), respectively. Results revealed that the connected porosity of both aggregates and soil cores was significantly increased after land‐use conversion. The isolated porosity of soil aggregates increased, while, conversely, it decreased for soil cores. The variance in pore structure was attributed to the development of new pores, including channels created by vegetable roots, fissures, earthworm holes, and packing pores resulting from the decomposition of soil organic matter and the rearrangement of soil particles. The altered pore structure influenced the soil exchangeability and reservation ability. For aggregates, the isolated porosity of PF and VF‐5 accounted for over 70% of the total imaged porosity. These aggregates displayed a larger water and carbon reservation ability, but limited exchangeability of air, water, and nutrients. The isolated porosity of VF‐13 and VF‐20 aggregates accounted for approximately 50% of the total imaged porosity, suggesting they could effectively balance the exchange and storage of air, water, and nutrients. As for soil cores, isolated pores became negligible (<0.2%) following land‐use conversion, leading to the emergence of a drainable pore system suitable for vegetable plantation. These findings offer insights into the development of pore structures and the prediction of soil function variations at multiple scales, both of which are crucial for optimizing soil management protocols.

Pore-Scale Formation Characteristics of Impermeable Frozen Walls for Shallow Groundwater Contamination Remediation

Impermeability and water blocking are crucial for remediating shallow groundwater contamination. Traditional methods often employ curtain-grouting technology to create impermeable layers. However, cement slurry curing is irreversible, leading to permanent closure of underground aquifers and secondary pollution. This study employs an innovative approach by fabricating cylindrical models that simulate actual strata and utilizing a high-temperature and high-pressure displacement device. It systematically analyzes the variations in soil pore structure, distribution, porosity, and permeability under different temperatures, pressures, and freezing durations. The microscopic characteristics of the freezing process in water-bearing soils were studied. Results demonstrate that longer freezing time improves the effectiveness of soil freezing, reaching complete freezing at temperatures as low as −4 °C for samples with low water content. For water-saturated samples, freezing below −6 °C results in nearly zero porosity. Increased pressure at a certain freezing temperature significantly reduces permeability. When freezing temperature falls below −4 °C, water permeability in saturated samples after freezing reaches near-zero levels, while unsaturated samples experience complete freezing. These findings provide a theoretical foundation for constructing freezing curtains in remediating shallow groundwater pollution.

Intrinsically Conductive and Cu-Functionalized Polymer-Composite Membranes as Gas Diffusion Electrodes for CO2 Electroreduction.

We introduced a new class of gas diffusion electrodes (GDEs) with adjustable pore morphology. We fabricated intrinsically conductive polymer-composite membranes containing carbon filler, enabling a pore structure variation through film casting cum phase separation protocols. We further selectively functionalized specific pore regions of the membranes with Cu by a NaBH4-facilitated coating strategy. The as-obtained GDEs can facilitate the electrochemical CO2 reduction reaction (CO2RR) at Cu active sites that are presented inside a defined and electrically conductive pore system. When employing them as free-standing cathodes in a CO2 flow electrolyzer, we achieved >70% Faradaic efficiencies for CO2RR products at up to 200 mA/cm2. We further demonstrated that deposition of a dense Cu layer on top of the membrane leads to obstruction of the underlying pore openings, inhibiting an excessive wetting of the pore pathways that transport gaseous CO2. However, the presentation of Cu inside the pore system of our novel membrane electrodes increased the C2H4/CO selectivity by a factor of up to 3 compared to Cu presented in the dense layer on top of the membrane. Additionally, we found that gaseous CO2 could still access Cu in macropores after wetting with electrolyte, while CO2RR was completely suppressed in wetted nm-scale pores.

Bayesian linearized inversion for petrophysical and pore-connectivity parameters with seismic elastic data of carbonate reservoirs

Abstract Carbonate reservoirs are important targets for promoting the oil and gas reserve exploration and production in China. However, such reservoirs usually contain the developed complex pore structures, which heavily affect the precision in seismic prediction of petrophysical parameters. As one of the most important parameters to characterize reservoir rock, pore-related parameters can not only describe the pore structure, but also be used to evaluate the oil/gas bearing capabilities of potential reservoirs. The conventional rock-physics models (e.g. Gassmann's model) are formulated assuming fully-connected pores, which is unable to accurately capture the geometrical complexity in real rocks. In order to characterize the influences of multiple pores on the elastic properties, this work presents a rock-physics modelling method for carbonates, wherein the percentage composition of connected pores is equivalently quantified as the pore-connectivity factor. The method treats the pore-connectivity factor as an objective variable to characterize the spatial variations of pore structure. Specifically, the method combines the differential equivalent medium theory and Gassmann's model, and derives a linearized forward operator to quantitatively link porosity, water saturation, and pore-connectivity factor to seismic elastic parameters. According to the Bayesian linear inverse theory, the simultaneous estimation of petrophysical and pore-connectivity parameters is achieved. To characterize the statistical variations with multiple lithofacies, the Gaussian mixture model is employed to quantify the prior distribution of the objective variables. The posterior distribution of the objective variables is analytically expressed with the linearized forward operator. Numerical experiments show that the accuracy of the proposed method in predicting elastic parameters is improved. Compared with the conventional Xu-White model and the varying pore aspect ratio method, the accuracy of predicted P-wave velocity increases by 10.29% and 1.33%, respectively, and the predicted S-wave velocity increases by 6.44% and 0.03%, in terms of correlation coefficient. The application to the field data validates the effectiveness of the method, wherein the porosity and water saturation results help indicating the spatial distribution of potential reservoirs.

Comparative Pore Structure and Dynamics for Bacterial Microcompartment Shell Protein Assemblies in Sheets or Shells.

Bacterial microcompartments (BMCs) are protein-bound organelles found in some bacteria that encapsulate enzymes for enhanced catalytic activity. These compartments spatially sequester enzymes within semipermeable shell proteins, analogous to many membrane-bound organelles. The shell proteins assemble into multimeric tiles; hexamers, trimers, and pentamers, and these tiles self-assemble into larger assemblies with icosahedral symmetry. While icosahedral shells are the predominant form in vivo, the tiles can also form nanoscale cylinders or sheets. The individual multimeric tiles feature central pores that are key to regulating transport across the protein shell. Our primary interest is to quantify pore shape changes in response to alternative component morphologies at the nanoscale. We used molecular modeling tools to develop atomically detailed models for both planar sheets of tiles and curved structures representative of the complete shells found in vivo. Subsequently, these models were animated using classical molecular dynamics simulations. From the resulting trajectories, we analyzed the overall structural stability, water accessibility to individual residues, water residence time, and pore geometry for the hexameric and trimeric protein tiles from the Haliangium ochraceum model BMC shell. These exhaustive analyses suggest no substantial variation in pore structure or solvent accessibility between the flat and curved shell geometries. We additionally compare our analysis to hydroxyl radical footprinting data to serve as a check against our simulation results, highlighting specific residues where water molecules are bound for a long time. Although with little variation in morphology or water interaction, we propose that the planar and capsular morphology can be used interchangeably when studying permeability through BMC pores.

Optimisation of mechanical properties and pore structure of lightweight geopolymer concrete

Lightweight geopolymer has good physical and mechanical properties, thermal and chemical stability and low carbon dioxide emissions. The development of high-strength lightweight geopolymer concrete (LGC) for load-bearing structures can expand geopolymer applications. The use of ground granulated blast-furnace slag (GGBFS) to improve the mechanical properties and pore structure of LGC was investigated. The ultimate compressive stress of LGC containing GGBFS were analysed, as well as the variation in microscopic pore structure. Specimens of LGCs with different strengths (LC20, LC30 and LC40) were investigated. As the GGBFS content increases, the ultimate compressive stress and specific strength of LGC increases, while the strain corresponding to the peak stress decreases, indicating that the mechanical properties and deformation resistance of LGC are improved. The carbon dioxide emissions of LGC are less than those of cement-based lightweight concrete, indicating that LGC has good sustainability. Moreover, the addition of GGBFS can produce more gel and reduce the volume proportion of capillary pores and air pores, resulting in LGC densification. Recommended GGBFS contents for strength grades LC20, LC30 and LC40 are 0–12.7%, 12.7–24.6% and 24.6–30%, respectively. The LGC is lightweight and has high strength, and has potential for application in civil engineering.

Mechanisms underlying variations in pore structures and permeability in response to thermal treatment and their implications for underground coal utilization

Coal remains a predominant energy source in today's society. However, the coal mining process is associated with severe environmental hazards, and combustion for power generation leads to pollution and carbon dioxide emissions. As a result, many countries have imposed restrictions on underground coal mining. Underground coal gasification, direct combustion for heat recovery and thermal treatment provides serval promising way for cleanly and safely utilizing coal resources. However, the successful operation of these technologies needs to comprehensively understand the physical and chemical properties of coal responding to high temperature. In particular, the pore structures and permeability of coal which are closely related to the transport of gas and liquid in coal seams. Therefore, serval advanced instruments were employed to investigate the variation of the functional groups, pore structures, permeability from room temperature to 500 °C. Their connection was discussed in detail to reveal the mechanism of thermal treatment on the pore structures and permeability of coal. The variations of all physical properties with temperature demonstrated a trend of gradual change followed by a sudden change. This indicated that coal samples possess relatively good stability up to 300 °C. Experimental results revealed significant alterations in the pore structure and permeability of the coal at 400 °C and 500 °C. Correspondingly, the mass of coal samples and the CC functional groups, which constitute the main molecular structure of coal, underwent significant changes at these temperatures. This suggested that the pyrolysis of coal beyond 400 °C led to an increase in both pore volume and permeability. Moreover, observations through scanning electron microscopy indicated that the increase in pore volume at 400 °C and 500 °C also resulted from the thermal stress induced cracks between minerals and organic matters. These mechanisms significantly enhance the pore volume and permeability of coal seams, facilitating the transport of coalbed gases and liquids during the production process of underground coal utilization.

Variations in pore structures and permeabilities of ion adsorption rare earth ores during simulated in-situ leaching: Effect of newly formed clay particles and their swelling

In-situ leaching is essential for mining rare earth elements (REEs) from ion-adsorption rare earth (RE) ores. The efficiency of RE mining is dependent on the permeabilities of ion-adsorption RE ores, and the permeabilities are controlled by their pore structures. However, the current understanding of the pore structures and permeabilities of the RE ores during leaching is limited, particularly their dynamic variations, the controlling roles of different pore structure parameters on the permeability, the roles of the influencing factors and the mechanisms causing the variations. To investigate the above-mentioned issues, we conducted an experimental study of simulated in-situ leaching on undisturbed ion-adsorption RE ore samples under different conditions via constant waterhead permeability tests. The leaching conditions included leaching time, concentration and waterhead of the (NH4)2SO4 solution. Three-dimensional (3-D) pore structures of the RE ores before, during, and after leaching were constructed via X-ray computed tomography, and their pore structure parameters were measured using 3-D image computation. It was observed that the dynamic variations in both the pore structure parameters and permeability coefficients of the RE ores occurred in three distinct stages: rapid reduction, less rapid reduction, and little reduction. The experimental results also revealed that the permeability coefficients of the RE ores were primarily dependent on the average coordination number among the seven pore structure parameters examined, and that the pore throats larger than 30 μm in diameter served as the most effective seepage channels within the RE ores. The waterhead of the leaching solution had a stronger influence on the variations in pore structures and permeabilities compared to that of the concentration. Analysis of the particle/aggregate size distribution and mineralogical compositions of the RE ores before and after leaching indicated that the decreases in the pore structure parameters and permeabilities were largely attributed to clogging of the pore throats and pores by migrated and newly formed clays, as well as swelling of the latter. The newly formed clays were the products of the decomposition of K-feldspar and mica resulting from chemical reactions with the leaching solution. The clays from the two sources occurred in disaggregated and aggregated forms. The results of this study provide an important reference for the mining of RE ores via leaching.

Long-term durability investigation of basalt fiber-reinforced geopolymer concrete in marine environment

The long-term durability of basalt fiber-reinforced geopolymer concrete (BFRGC) in marine environments is importance for the development of sustainable construction practices. This study examines the long-term durability of basalt fiber-reinforced geopolymer concrete exposed to dry-wet cycles and immersion treatment in marine conditions. A geopolymer concrete with 1% fiber content was prepared and subjected to dry-wet cycles and immersion treatments in a 5% sulfate solution (Tehmina et al., 2014; Nasir et al., 2016; John et al., 2016) [1-3]. Density measurements, ultrasonic pulse velocity tests, and uniaxial compression tests were conducted on the BFRGC after various treatment durations. The mechanical properties of BFRGC were compared with geopolymer concrete without fibers in marine environments. Additionally, the changes in compressive strength of geopolymer concrete with and without fibers in different immersion environments were further discussed. Using low-field nuclear magnetic resonance (LF-NMR) technology, the variations in pore structure were also analyzed. The results show that the mechanical property loss from dry-wet cycles was greater than from immersion treatment. In BFRGC, strength decreased by 10.1% after 192 days of dry-wet cycles, compared to a smaller decrease of 5.6% in immersion environments. The inclusion of basalt fibers effectively enhances stability. When in dry-wet cycle tests, BFRGC strength decreased from 49.6 MPa to 44.6 MPa, a reduction of 10.1%. Conversely, geopolymer concrete without fibers dropped from 49.7 MPa to 42.1 MPa, a reduction of 15.5%. LF-NMR test results show that the porosity of geopolymer concrete without fibers increased by 21.6% and 17.5% in dry-wet cycles and immersion environments, respectively. In contrast, the porosity of BFRGC increased by 16.1% and 12.7%.

Polymer-fiber combined effect for improving sand mechanical and micro-damage response

Sand instability is always an intractable problem in geotechnical engineering and its reinforcement using additives is an effective method. This paper introduces the organic polymer reinforcer (OPR) and the recycled polypropylene fiber (RPF) to modify sand. The unconfined compression and corresponding numerical tests were performed to investigate mechanical properties, deformation failure behavior, and microscopic response. Results showed that both materials positively affect the mechanical and deformation properties of modified sand synergistically. Optimized particle structure by the inter-particle polymer membrane linked the loose sand into a whole with fibers as a framework. Strain-softening properties were reduced with less strain localization under loading. This is also clearly related to the improvement of the micro-damage based on numerical results. OPR-RPF reinforcement transformed the bond failure from unidirectional concentration to multilocal dispersion by improving force chain construction, microcrack propagation, and energy allocation. Thus, the failure of modified sand showed a macroscopic progression from shear-faulting via ductile-faulting to ductile flow. Future research lies in further considering the particle shape and pore structure variations to provide new insights for a deeper understanding of sand stabilization mechanisms and engineering applications.

Study of the mutual coupling characteristics of the oxidation thermal effect and microstructural evolution of gas-containing coal

Besides be affected by coal confining pressure, coal seams are also be affected by the surrounding pressure during mining. To understand the heat release characteristics and microstructural evolution of oxidization within coal under different gas pressures is of great significance. For this reason, a combination of theoretical research and test analysis was adopted, which includes differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR) and mercury intrusion method (MIP). The influences of gas phase transformation and migration on the oxidation and spontaneous combustion processes of gas-containing coal under different gas pressures were explored. The distributions and variations in heat release, gas derivation, pore structure and functional group characteristics during the oxidation of gas-containing coal were analysed. We clarified the cross-coupling attributes of heat, seepage and chemical properties in the oxidation of gas-containing coal. The experimental results show that the methane within coal migrates outward in pores with the increase of temperature, which inhibits the penetration and adsorption of oxygen, thereby inhibiting the coal‑oxygen composite reaction and delaying the heat accumulation within coal. There is a positive correlation between loose and porous characteristics of coal and gas pressure. With the continuous increase of coal temperature, the pore connectivity of high-pressure gas-containing coal is enhanced, which increases the risk of coal spontaneous combustion. The research results are of great significance to the theoretical research on the prevention and prediction of spontaneous combustion of gas-containing coal.

Effect of temperature and fluid on rock microstructure based on an effective-medium theory

Abstract Temperature and pressure variations during the geologic diagenesis process can lead to complex pore structures in tight rocks. The effective-medium theory, based on the stress–strain relationship in combination with pore structure parameters, can be used to describe the elastic-wave responses of rocks. In this work, the differential effective medium (DEM) and self-consistent approximation (SCA) models are combined to invert the pore-crack spectrum. The Voigt–Reuss–Hill average is used to estimate the elastic moduli of the minerals. Then, based on SCA, the pore structures are incorporated into the rock matrix to create a new host phase. Subsequently, the DEM theory is used to add cracks with different volume fractions and aspect ratios to the host phase. To predict the structure of pores and cracks (crack density and aspect ratio), an objective function is defined as the sum of variances between experimentally measured and predicted wave velocities. The results show that the modeling predictions of P- and S-wave velocities at different temperatures and pressure ratios agree well with the experimental measurements. Variations in pore structure are determined at a zero effective pressure and different temperatures. We analyze the characteristics of how cracks change with variations in temperature and confining pressure, providing a theoretical basis for characterizing the structure of tight rocks.

Experimental study of hydraulic properties of the granite fracture under heating-cooling cycles

The fracture within the surrounding rock will suffer heating-cooling process for the high-level radioactive waste (HLW) geological repository after the disposal of the HLW, and the conductivity variation of fracture to the heating-cooling process is crucial for the long-term safety of the HLW repository. To study the response of hydraulic properties to temperature of granite fracture, the hydraulic conductivity measurement of granite fracture was carried out during heating-cooling cycles (25 °C-120 °C-25 °C) with different confining pressures (3 MPa, 5 MPa and 8 MPa). In addition, the variation of morphology, pore structure and mineral distribution of fractured granite were analyzed using nuclear magnetic resonance and digital image processing technology. Results show that the hydraulic aperture continuously decreased with increasing temperature, then slightly recovered with the decrease of temperature during the first heating-cooling process. For the second heating-cooling process, the evolution of the hydraulic aperture with temperature is similar to the first heating-cooling cycle, while the variation magnitude was decreased significantly. The confining pressure affect the recovery ability of hydraulic aperture during the cooling process, the hydraulic aperture recover decreased with the increasing confining pressure. Combined effects of the confining pressure and thermal effect control the plastic deformation and fracture aperture of granite fracture. A formula considering the influence of temperature and confining pressure was developed to characterize the hydraulic aperture of granite fracture. In addition, variations in morphyology and mineral distribution were analyzed of granite fracture before and after the test. Result shows that the roughness of fracture surfaces decreased, and biotite and feldspar increased while quartz decreased after tests. Findings from the study could provide important reference for the HLW geological disposal engineering.

Development of pore structure and related driving factors following land‐use change by dual‐scale x‐ray tomography

AbstractLand‐use conversion has a great impact on soil pore structure. However, the variation of pore structure and the related driving factors following land‐use conversion are still in need of further interpretation. In this study, the pore structure of millimetric intact aggregates as well as centimetric undisturbed soil cores collected from paddy fields (PF) and vegetable fields converted from paddy fields for 5 years (VF‐5), 13 years (VF‐13), and 20 years (VF‐20) was quantified by dual‐scale x‐ray tomography. Results revealed that the pore structure at the aggregate and soil core scales responded differently after the paddy fields were converted to vegetable fields. Imaged porosity and pore connectivity of aggregates increased slightly following land‐use conversion. Those properties increased significantly within soil cores. Compared with the paddy field aggregates, the porosity of elongated pores with larger diameters markedly increased in vegetable field aggregates, suggesting an enhancement in the accessibility of air, water, and nutrients. At the soil core scale, the alteration of pore structure was mainly attributed to the shift of the soil environment, the change of tillage operation, and the plantation of different crops. The shift of rice to vegetable plantation significantly altered the length and tortuosity of the intermediate branch pores. Importantly, the land‐use change created a more drainable pore structure due to the significant increase of pore connectivity at the soil core scale, which is suitable for vegetable plantations. These findings are crucial for evaluating and interpreting the microscale pore structure change following land‐use conversion.

Pore connectivity and microfracture characteristics of Longmaxi shale in the Fuling gas field: Insights from mercury intrusion capillary pressure analysis

Assessing the connectivity of pores and the characteristics of microfractures is essential for comprehending gas migration mechanisms and effectively implementing development strategies in deep shale gas plays. The Fuling gas field, a prominent shale gas reservoir in China, holds promise for deep shale development. This requires a better understanding of variations in pore connectivity among shale samples from different depths of the Fuling gas field. To achieve this goal, this study employs innovative methodologies based on mercury intrusion capillary pressure (MICP), a recognized technique for evaluating material pore structures. In this research, we conducted MICP tests on shale samples of varying sizes to examine variations in pore structure and quantify inaccessible pores. Additionally, repeated MICP tests were performed on the same sample to investigate the spatial distribution of residual mercury and distinguish different pore types associated with flow conduits and storage spaces. Furthermore, a directional MICP experiment was carried out to quantitatively characterize the degree of pore development and anisotropy of microfractures by considering the direction of mercury intruding the sample (parallel or perpendicular to lamination). Our findings revealed that deep shale samples exhibited a higher proportion of inaccessible pores compared to mid-deep ones. Regarding accessible pores, a greater proportion of connected pores was observed in the deep shale samples, while the mid-deep shale samples exhibited a lower proportion. The results from the directional MICP experiment indicated that samples with anisotropy in mercury intrusion volume possessed finer and denser microfractures. However, no evidence was found to correlate the ratio of dead-end and connected pores with sample anisotropy. Overall, this study presents a novel approach for experimentally evaluating pore connectivity and microfracture characteristics in shale reservoirs using MICP. The outcomes contribute to enhancing our understanding of shale gas migration mechanisms, particularly in deep ultra-low-permeability reservoirs, and hold significant implications for future developments in the field.

Macro-micro characteristics of geopolymer-stabilized saline soil in seasonal frozen soil region

Chemical stabilization is an effective approach to address various engineering problems related to saline soil, including salt heaving, frost heaving, dissolution, and corrosion. Through unconfined compression strength (UCS) test, x-ray diffraction (XRD) test, scanning electron microscope (SEM) tests and mercury intrusion porosimetry (MIP), this research investigates the macroscopic strength characteristics, microscopic mineral composition, and pore structure variation of quicklime, fly ash and sodium silicate joint solidifying sulfate saline soil under various freeze-thaw cycles, and discusses its solidification mechanism. The results indicate that when the contents of fly ash and sodium silicate are held constant, the unconfined compressive strength of the solidified soil increases first and then decreases with the increase of quicklime content. Additionally, the peak strength occurred at a quicklime content of 3 %; The strength of all the solidified soils decreased with the increase of the freeze-thaw cycles and the solidified soils with the optimum quicklime content has a relatively strong ability to resist freezing and thawing; The influence of quicklime content on solidification is reflected in the formation of hydrate gels and the variation of pore structure; The influence of freeze-thaw cycle on solidification is reflected in the destruction of solidified pore structure.

Pore structure characterization of solvent extracted shale containing kerogen type III during artificial maturation: Experiments and tree-based machine learning modeling

Shale samples with type III kerogen from the Damoguaihe formation were exposed to hydrous and anhydrous pyrolysis (HP and AHP) in the temperature range of 300–450 °C. Next, soluble organic matter (OM) and the liquid yield were removed from the pyrolyzates after each step of thermal maturation. N2 adsorption tests were performed to assess the pore structures of the samples. Furthermore, deconvolution and fractal dimension analyses were executed to unveil pore clusters and discern the complexity of the pore network within each sample. Finally, two tree-based machine learning algorithms, random forest (RF) and extra trees (ET) were applied to model the N2 adsorption/desorption data of pyrolyzates to predict pore structure variations. Based on the results, HP pyrolyzates had higher bitumen reflectance (BRo%) values than AHP ones at all temperature sequences, which confirms water controls thermal maturity. AHP pyrolyzates exhibited larger average pore diameters across all temperatures, while HP pyrolyzates displayed higher BET surface areas in contrast to AHP pyrolyzates. Also, the average pore diameter of HP pyrolyzates with soluble OM and liquid yield extracted did not change significantly during thermal maturation, while the average pore diameter of AHP ones increased, peaking at 400 °C in post-mature stage. The largest total pore volume of HP samples was observed at the end of the wet gas window, while this was observed for AHP samples in the dry gas window. Three mesopore and four macropore clusters were identified in the original sample. Moreover, pore clusters of the pyrolyzates underwent diverse changes during thermal maturation, without following a specific trend, influenced by both temperature and pyrolysis conditions. Abundance of micropores, finer mesopores (2–10 nm), and a smaller average pore diameter in HP pyrolyzates compared to the AHP is the main reason for the higher fractal dimensions showing a more complex pore structure and/or rougher pore surface. Intelligence modeling exhibited that RF outperformed ET in estimating N2 adsorbed/desorbed volumes for the samples. Ultimately, sensitivity analysis revealed that water exerted a more significant influence on pore development in shales during thermal progression, outweighing the impact of temperature.