Search Results (133)

In order to better understand the micropore structure of shale reservoir in Jiyang Depression, permeability damage test, low temperature nitrogen adsorption and scanning electron microscopy (SEM) were carried out on six cores in the target block. The adsorption isotherms were analyzed by Frenkel–Halsey–Hill (FHH) model, and the fractal dimensions of different layers were calculated. The results show that the shale pore system is mainly composed of organic nanopores, inorganic nanopores and micro-fractures. The inorganic pores are mainly distributed around or inside the mineral particles, while microcracks are commonly found between mineral particles or at the organic–mineral interface. Organic pores are located within or between organic particles. The results of nitrogen adsorption show that the shale pores are mainly H2/H3 hysteresis loops with wedge, plate or ink bottle shapes. The pore structure is highly complex, and the fractal dimension is high. The mean D1 fractal dimension, which represents pore surface roughness, is 2.3788, and the mean D2 fractal dimension, which represents pore structure complexity, is 2.7189. The fractal dimension is positively correlated with specific surface area and total pore volume and negatively correlated with average pore radius. The permeability damage rates of the N layer, B layer, and F layer are 17.39%, 20.2%, and 21.6%, respectively. The contact Angle of the core decreases with the increase in water skiing time. In this study, the micropore structure of different formations in Jiyang Depression is compared and analyzed, which provides valuable insights for the optimization and differentiated development of shale oil and gas resources. Full article

The fractal dimension quantitatively describes the complexity of the shale pore structure and serves as a powerful tool for characterizing the evolution of shale reservoirs. Thermal simulation experiments were conducted on the low-maturity transitional shale from the Shanxi Formation in the Ordos Basin. The initial samples consisted mainly of quartz (39.9%) and clay minerals (49.9%) with moderate-to-good hydrocarbon generation potential. Samples from different thermal maturation stages were analyzed through geochemical, mineralogical, and pore structure experiments to reveal the evolution of mineral compositions and pore structure parameters. The fractal dimensions of the pore structure were calculated using both the FHH and capillary bundle models. Correlation coefficients and principal component analysis (PCA) were employed to explore the factors influencing the fractal dimension and its evolutionary patterns during reservoir development. The results indicate that (1) with increasing thermal maturity, the quartz content gradually increases while the contents of clay minerals, carbonate minerals, pyrite, and feldspar decrease. (2) The evolution of porosity follows five stages: a slow decrease (0.78 < Ro < 1.0%), a rapid increase (1.0% < Ro < 2.0%), a relatively stable phase (2.0% < Ro < 2.7%), a rapid rise (2.7% < Ro < 3.2%), and a slow decline (Ro > 3.2%). The evolution of the pore volume (PV) and specific surface area (SSA) indicates that the proportion of pores in the 5–20 nm and 20–60 nm ranges gradually increases while the proportion of pores smaller than 5 nm decreases. (3) The fractal dimension of shale pores (D₁, average value 2.61) derived from the FHH model is higher than D₂ (average value 2.56). This suggests that the roughness of pore surfaces is greater than the complexity of the internal pore structure at various maturities. The D_M distribution range calculated from the capillary bundle model was broad (between 2.47 and 2.94), with an average value of 2.84, higher than D₁ and D₂. This likely indicates that larger pores have more complex structures. (4) D₁ shows a strong correlation with porosity, PV, and SSA and can be used to reflect pore development. D₂ correlates well with geochemical parameters (TOC, HI, etc.) and minerals prone to diagenetic alteration (carbonates, feldspar, and pyrite), making it useful for characterizing the changes in components consumed during pore structure evolution. (5) Based on the thermal maturation process of organic matter, mineral composition, diagenesis, and pore structure evolution, an evolutionary model of the fractal dimension for transitional shale was established. Full article

The dosage of mineral powder has a complex influence on the compressive strength of self-compacting concrete, among which the pore structure is a key determining factor. This study investigated the effects of different dosages of mineral powder (0%, 5%, 10%, 20%, and 30%) on the workability, mechanical properties, and pore distribution in C80 self-compacting concrete. The research results show that an appropriate dosage of mineral powder (0–20%) can significantly improve the spreadability and fluidity of C80 self-compacting concrete. This phenomenon is mainly attributed to the shape effect and micro-aggregate effect of mineral powder, which improve the fluidity of concrete, reduce the viscosity of the paste, and thereby increase the spreadability and gap-passing rate. By testing the BSD-PS1/2 series fully automatic specific surface area and pore size analyzer, we found that there are columnar pores and ink bottle-shaped pores in C80 self-compacting concrete, as well as a small amount of plate-like slit structures. Our observations with an SEM scanning electron microscope revealed that the width of micro-cracks and micro-holes is between 1 and 5 μm and the diameter is between 3 and 10 μm. These microstructures may have an impact on the mechanical properties of the structure. By applying fractal theory and low-temperature liquid nitrogen adsorption tests, this study revealed the relationship between the fractal characteristics of internal pores in C80 self-compacting concrete and the dosage of mineral powder. The results show that with the increase in mineral powder dosage, the fractal dimension first decreases and then increases, reflecting the change rule of the complexity of pore structure first decreasing and then increasing. When the dosage of mineral powder is about 20%, the compressive strength of SCC reaches the maximum value, and this dosage range should be considered in engineering design. Full article

The salt concentration of the pore solution can alter the micro-pore and particle structure of soil, thereby affecting its engineering properties. To investigate the compression characteristics of marine soil under different salt concentrations, one-dimensional compression and SEM scanning tests were conducted on marine reconstituted clay from the Yellow Sea with varying NaCl concentrations (0–5%). The effects of NaCl concentration on the compression characteristics and microstructure of marine sedimentary clay were analyzed. The results indicate that: (1) Compressibility increases up to a NaCl concentration of 2.5%, after which it declines. At 2.5% NaCl threshold concentration, the coefficient of compression, compressibility index, and consolidation coefficient reach their peak values, and the response becomes more pronounced with increasing compression pressure. During the secondary compression stage, as pore water is expelled, the impact of NaCl concentration on compressibility diminishes, while the rebound characteristics remain unaffected by NaCl concentration; (2) SEM analysis reveals that at a NaCl threshold concentration of 2.5%, the pore fractal dimension, particle fractal dimension, pore anisotropy, and particle anisotropy reach their maximum values, with the most complex shape and pores and particles aligning in the same direction. When the concentration is less than 2.5%, the soil exhibits narrow pores and rounded particles upon compression. When the concentration exceeds 2.5%, the microstructure changes in the opposite direction, confirming the particle rearrangement mechanism driven by surface contact under moderate salinity. At the threshold concentration of 2.5%, a balance between electrostatic forces and attractive forces enables stable surface-to-surface contacts, maximizing compressibility. The findings of this study provide valuable references for the foundation design of marine geotechnical engineering in specific sea areas, thereby enhancing the safety and reliability of related projects. Full article

The acidification modification of coal seams is a significant technical measure for transforming coalbed methane reservoirs and enhancing the permeability of coal seams, thereby improving the extractability of coalbed methane. However, the acids currently used in fracturing fluids are predominantly inorganic acids, which are highly corrosive and can contaminate groundwater reservoirs. In contrast, organic acids are not only significantly less corrosive than inorganic acids but also readily bind with the coal matrix. Some organic acids even exhibit complexing and flocculating effects, thus avoiding groundwater contamination. This study focuses on the 1/3 coking coal from the Guqiao Coal Mine of Huainan Mining Group Co., Ltd., in China. It systematically investigates the fractal characteristics and chemical structure of coal samples before and after pore modification using four organic acids (acetic acid, glycolic acid, oxalic acid, and citric acid) and compares their effects with those of hydrochloric acid solutions at the same concentration. Following treatment with organic acids, the coal samples exhibit an increase in surface fractal dimension, a reduction in spatial fractal dimension, a decline in micropore volume proportion, and a rise in the proportions of transitional and mesopore volumes, and the structure of the hydroxyl group and oxygen-containing functional group decreased. This indicates that treating coal samples with organic acids enhances their pore structure and chemical structure. A comparative analysis reveals that hydrochloric acid is more effective than acetic acid in modifying coal pores, while oxalic acid and citric acid outperform hydrochloric acid, and citric acid shows the best results. The findings provide essential theoretical support for organic acidification modification technology in coalbed methane reservoirs and hydraulic fracturing techniques for coalbed methane extraction. Full article

Coal dust seriously affects the underground working environment. The current water-spray dust reduction technology uses a large amount of water and has a poor effect on coal dust with poor wettability. This study proposed a clean and sustainable technology using plasma-activated water (PAW) to alter the wettability of coal dust and improve its dust control effect. The PAW was prepared and its physical and mathematical properties were tested by a device designed in-house. The influence of PAW on the wettability of coal dust was determined by the coal dust contact angle experiments. The effect of PAW on the surface morphology of coal dust was analyzed by a scanning electron microscope. The effect of PAW on the pore structure of coal dust was analyzed through the specific surface area and pore size experiments. The results showed that PAW contained a large number of active substances such as H₂O₂, NO₃⁻, and NO₂⁻, showing strong and stable oxidation. PAW could significantly reduce the instantaneous contact angle of coal dust, and the higher the degree of coal dust metamorphism, the more significant the reduction effect. The surface morphology, pore volume, specific surface area, and fractal dimension of the coal dust were significantly changed after PAW treatment. PAW could transform the non-uniform three-dimensional spatial distribution of the coal dust surface into an approximate two-dimensional planar distribution, thus enhancing the wettability of the coal dust. With the increase in PAW ionization intensity, the contact angle of long-flame coal was negatively correlated with the mesoporous pore volume. The contact angle of gas coal was negatively correlated with the micropore volume and micropore specific surface area, and was positively correlated with the mesopore volume. The contact angle of meager lean coal was positively correlated with the macropore specific surface area. The surface morphology, pore volume, specific surface area, and fractal dimension changes in coal dust treated with PAW can reveal the wettability enhancement mechanism to some extent. The results of the study can provide pre-theoretical guidance for the field application of PAW coal mine dust reduction technology. Full article

The pore–fracture structure of ultra-deep coal is critical for evaluating resource potential and guiding the exploration and development of deep coalbed methane (CBM). In this study, a coal sample was obtained from the Gaogu-4 well at a depth of 4369.4 m in the Shengli Oilfield of Shandong, China. A comprehensive suite of characterization techniques, including Field Emission Scanning Electron Microscopy (FE-SEM), X-ray diffraction (XRD), Mercury Intrusion Porosimetry (MIP), Low-temperature Nitrogen Adsorption (LT-N₂GA), and Low-pressure CO₂ Adsorption (LP-CO₂GA), were employed to investigate the surface morphology, mineral composition, and multi-scale pore–fracture characteristics of the ultra-deep coal. Based on fractal geometry theory, four fractal dimension models were established, and the pore structure parameters were then used to calculate the fractal dimensions of the coal sample. The results show that the ultra-deep coal surface is relatively rough, with prominent fractures and limited pore presence as observed under FE-SEM. Energy Dispersive Spectrometer (EDS) analysis identified the elements such as C, O, Al, Si, S, and Fe, thus suggesting that the coal sample contains silicate and iron sulfide minerals. XRD analysis shows that the coal sample contains kaolinite, marcasite, and clinochlore. The multi-scale pore–fracture structure characteristics indicate that the ultra-deep coal is predominantly composed of micropores, followed by mesopores. Macropores are the least abundant, yet they contribute the most to pore volume (PV), accounting for 70.9%. The specific surface area (SSA) of micropores occupies an absolute advantage, accounting for up to 97.46%. Based on the fractal model, the fractal dimension of the coal surface is 1.4372, while the fractal dimensions of the micropores, mesopores, and macropores are 2.5424, 2.5917, and 2.5038, respectively. These results indicate that the surface morphology and pore–fracture distribution of the ultra-deep coal are non-uniform and exhibit statistical fractal characteristics. The pore–fracture structure dominated by micropores in ultra-deep coal seams provides numerous adsorption sites for CBM, thereby controlling the adsorption capacity and development potential of deep CBM. Full article

Microbial-Enhanced Coalbed Methane (MECBM) is a technology that generates new methane gas in coal seams through the action of microorganisms, thereby improving the efficiency of coalbed methane development. In this study, low-temperature CO₂ adsorption, low-temperature N₂ adsorption, and isothermal adsorption experiments were conducted to systematically characterize the changes in the pore characteristics of low-rank coals in Xinjiang before and after degradation. The results show that microbial action increases the average pore diameter and enhances pore connectivity. Meanwhile, it reduces the fractal dimension of the pore surface and simplifies the complexity of the pore structure. The modification of the pore structure effectively promotes the efficiency of methane desorption and migration, thus improving the exploitation potential of coalbed methane. Microbial degradation avoids the risk of deterioration of reservoir physical properties through biological modification, and reduces carbon emissions and environmental pollution. This study provides an environmentally friendly solution for the low-carbon development of coal resources, and has important scientific significance for promoting the transformation of energy structures and achieving the goal of carbon neutrality. Full article

Based on the uniaxial compression tests and in situ CT scanning experiments of lignite with different dehydration times and the fractal theory, this paper qualitatively and quantitatively investigated the influence of the dehydration effect on the evolution of pore–fractures and the mechanical behavior of lignite under uniaxial compression conditions. The results show that the dehydration effect significantly affects the pre-peak deformation and post-peak failure behavior of lignite but has no significant impact on its peak strength. The pore–fracture parameters, such as the fractal dimension, surface porosity, and fracture volume, of three samples all exhibit an evolutionary pattern of “continuous decrease in the compaction and elastic stages–gradual increase in the plastic stage–sharp growth in the post-peak stage” with the dynamic evolution of the pore–fractures. However, the dehydration effect leads to an increase in the intensity of pore–crack evolution and a nonlinear rise in all the parameters characterizing the pore–crack complexity during uniaxial compression, which, in turn, leads to an increment in the fluctuation of the above evolutionary trends. The mechanism underlying the differential influence of the dehydration effect on the macroscopic mechanical behavior of lignite is follows: The dehydration effect non-linearly and positively affects the initial pore–fracture structure of lignite, thereby non-linearly and positively promoting the evolution of pore–fractures during the loading process. Nevertheless, since it fails to weaken the micro-mechanical properties of lignite and cannot form effective through-going fractures, it has no significant impact on the uniaxial compressive strength of the coal samples. The findings of this study can provide some references for the support design and deformation control of underground lignite roadways. Full article

Stabilizing sandy soil with inadequate engineering properties is essential for constructing infrastructure systems in all regions, especially in desertification-prone areas. Enzymatically Induced Carbonate Precipitation (EICP) offers an innovative solution, with advantages over conventional soil reinforcement methods due to its low energy consumption and carbon emission. This emerging reinforcement technique has proven effective in enhancing soil strength, yet the effects of variables such as curing time and cementation solution concentration, and their micro-mechanistic implications on sandy soil, remain understudied. This study conducted a series of unconfined compressive strength (UCS) tests and microstructural analyses on EICP-treated sand. The results showed that the optimal curing time for EICP-reinforced sand is seven days, with its strength being contingent upon soil density. The maximum UCS value was observed at a relative density of 0.7 and a cementation solution concentration of 1 mol/L. Mechanistically, EICP strengthens soil integrity through calcium carbonate-mediated cementation and particle bridging, thereby boosting soil strength. Micro-CT imaging and fractal dimension analyses reveal that the precipitation process decreases both the size and connectivity of the pores, while simultaneously increasing their surface heterogeneity and enhancing the overall toughness. This research establishes a foundational framework for advancing EICP applications in soil stabilization engineering. Full article

This study proposes a non-contact framework for evaluating the skid resistance of shared roadside pavements to improve cyclist and pedestrian safety. By integrating a friction tester and a laser scanner, we synchronize high-resolution three-dimensional (3D) surface texture characterization with friction coefficient measurements under dry and wet conditions. Key metrics—including fractal dimension (FD), macro/micro-texture depth density (HL_TX and WL_TX), mean texture depth (MTD), and joint dimensions—were derived from 3D laser scans. A hierarchical regression analysis was employed to prioritize the influence of texture and joint parameters on skid resistance across environmental conditions. Combined with material types (brick, tile, and stone) and drainage performance, these metrics are systematically analyzed to quantify their correlations with skid resistance. Results indicate that raised macro-textures and high FD (>2.5) significantly enhance dry-condition skid resistance, whereas recessed textures degrade performance. The hierarchical model further reveals that FD and MTD dominate dry friction (β = 0.61 and −0.53, respectively), while micro-texture density (WL_TX) and seam depth are critical predictors of wet skid resistance (β = −0.76 and 0.31). In wet environments, skid resistance is dominated by micro-texture density (WL_TX < 3500) and macro-texture-driven water displacement, with higher WL_TX values indicating denser micro-textures that impede drainage. The study validates that non-contact laser scanning enables efficient mapping of critical texture data (e.g., pore connectivity, joint depth ≥0.25 mm) and friction properties, supporting rapid large-scale pavement assessments. These findings establish a data-driven linkage between measurable surface indicators (texture, morphometry, drainage) and skid resistance, offering a practical foundation for proactive sidewalk safety management, especially in high-risk areas. Future work should focus on refining predictive models through multi-sensor fusion and standardized design guidelines. Full article

Granular samples are often used to characterize the pore structure of shale. To systematically analyze the influence of particle size on pore characteristics, case studies were performed on two groups of organic-rich deep shale samples. Multiple methods, including small-angle neutron scattering (SANS), low-pressure nitrogen gas adsorption (LP-N₂GA), low-pressure carbon dioxide gas adsorption (LP-CO₂GA), and XRD analysis, were adopted to investigate how the crushing process would affect pore structure parameters and the fractal features of deep shale samples. The research indicates that with the decrease in particle size, the measurements from nitrogen adsorption and SANS experiments significantly increase, with relative effects reaching 95.09% and 51.27%, respectively. However, the impact on carbon dioxide adsorption measurements is minor, with a maximum of only 8.97%. This suggests that the comminution process primarily alters the macropore structure, with limited influence on the micropores. Since micropores contribute the majority of the specific surface area in deep shale, the effect of particle size variation on the specific surface area is negligible, averaging only 16.52%. Shales exhibit dual-fractal characteristics. The distribution range of the mass fractal dimension of the experimental samples is 2.658–2.961, which increases as the particle size decreases. The distribution range of the surface fractal dimension is 2.777–2.834, which decreases with the decrease in particle size. Full article

The study of pore characteristics in tectonic coal is essential for a deeper understanding of gas diffusion, seepage, and other transport processes within coal seams, and plays a crucial role in the development of coalbed methane resources. Based on low-temperature N₂ and CO₂ adsorption experiments, this study investigated the pore structure characteristics of four tectonic coal samples collected from the Hegang and Jixi basins in China. The results show that the mylonitic coal sample exhibits a clear capillary condensation and evaporation phenomenon around a relative pressure (P/P₀) of 0.5. The degree of tectonic deformation in coal has a significant impact on its pore characteristics. As the degree of deformation increases, both the pore volume and specific surface area of the coal gradually increase. The pore volume and specific surface area of micropores are primarily concentrated in pores with diameters of 0.5–0.7 nm and 0.8–0.9 nm, while those of mesopores are mainly distributed in pores with diameters of 2.3–6.2 nm. The proportion of pore volume and specific surface area contributed by micropores is much greater than that of mesopores. The fractal dimension is positively correlated with the degree of tectonic deformation in coal. As the fractal dimension increases, the average pore diameter decreases, closely tied to the destruction and reconstruction of the coal’s pore structure under tectonic stress. These findings will contribute to a deeper understanding of the pore structure characteristics of tectonic coal and effectively advance coalbed methane development. Full article

Heterogeneity of adsorption pore volume distribution affects desorption and diffusion processes of coal reservoirs. In this paper, N₂ and CO₂ adsorption and desorption experiment tests were used to study the pore structure of middle and high rank coal reservoirs in the study area. The fractal theory of volume and surface area is used to achieve a full-scale fractal study of adsorption pores (pore diameter is less than 100 nm) in the study area. Firstly, adaptability and control factors of volume fractals and surface area fractals within the same aperture scale range are studied. Secondly, fractal characteristics of micro-pores and meso-pores are studied. Thirdly, fractal characteristics within different aperture scales and the influencing factors of fractal characteristics within different scale ranges are studied. The results are as follows. With the increase in coal rank, pore volume and specific surface area of pores less than 0.8 nm increase, and dominant pore size changes from 0.55~0.8 nm (middle coal rank) to 0.5~0.7 nm (high coal rank). As coal rank increases, TPV and average pore diameter (APD) decrease under the BJH model, while SSA changes are not significant under the BET model. Moreover, as the pore diameter decreases, the correlation between the integral dimension of pore volume and degree of coal metamorphism decreases. This result can provide a theoretical basis for the precise characterization of the target coal seam pore and fracture structure and support the optimization of favorable areas for coalbed methane. Full article

The pore structure and connectivity of coal are the primary factors influencing the permeability of coal reservoirs. However, clay and carbonate minerals are commonly found filling the pores and fractures within coal. To address the impact of these minerals on fracturing effectiveness, acidic fracturing technology has been introduced. This technique has proven to be an effective measure for enhancing the extraction rate of low-permeability coal seams with high mineral content. In this study, coal samples were treated with a 3% HCl solution, and the changes in the pore structure of the coal before and after acidification were analyzed through low-temperature nitrogen adsorption and X-ray diffraction (XRD) testing. The results were as follows: After acidification, the specific surface area, total pore volume, pore volume in different stages, and average pore size of the coal samples all significantly increased. Specifically, the BET specific surface area grew by an average of 4.8 times and the total pore volume expanded by an average of 7.7 times, with the pore volumes in the pore size ranges of <10 nm and 10–60 nm increasing by an average of 10.1 times and 7.7 times. The smoothness of the pore surface and connectivity of the pore structure in the coal samples improved, as indicated by decreased fractal dimensions D₁ (reflecting pore surface roughness) and D₂ (representing pore size distribution uniformity). The acidification mechanism was mainly attributed to the dissolution of carbonate minerals in the coal, which led to the removal of obstructive minerals such as ankerite and calcite that had accumulated in the coal pores. This resulted in the formation of new micropores and microfractures, achieving pore volume enhancement and pore expansion. Full article