Determinations of the multifractal characteristics of the pore structures of low-, middle-, and high-rank coal using high-pressure mercury injection

Zhang, Miao; Chen, Duan; Li, Guofu; Fu, Xuehai; Qiu, Zhong; Liu, Huihu; Dong, Zhibao

doi:10.1016/j.petrol.2021.108656

Cited by 45 publications

(37 citation statements)

References 54 publications

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“…According to the Washburn equation, the measurability of the mercury injection pore size and volume in coal depends on the mercury injection pressure. However, the coal matrix is compressible, which leads to the difference between the mercury injection amount and the actual pore volume of the coal sample under a certain pressure. ,, Generally, to obtain a more realistic pore size distribution curve, a mercury pressure of <15 MPa (corresponding to a pore size of about 100 nm) is used for the analysis. ,, The mercury injection–removal curve of the coal sample is shown in Figure , and the test results of the pore volume and the pore-specific surface area are shown in Tables and .…”

Section: Modeling and Experimental Methodsmentioning

confidence: 99%

“…As a porous medium, coal has a highly heterogeneous pore structure. Recent studies have shown that the pore structure remarkably affects gas diffusion in a porous media. ,,,, The fractal theory provides an effective method to study the effect of the complex pore structure on diffusion. ,,− In fractal structures, the diffusion process also exhibits some self-similarity (scaling property) due to the self-similar feature of the structure. In addition, the average diffusion distance of several particles is different for the same fractal structure due to the various starting points, which indicates that the diffusion in the fractal structure is uneven due to its uneven distribution of pores.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, the average diffusion distance of several particles is different for the same fractal structure due to the various starting points, which indicates that the diffusion in the fractal structure is uneven due to its uneven distribution of pores. The fractal structure and diffusion in Euclidean space are fundamentally different. ,,,,, To describe the natural heterogeneity of coal, scholars introduced a fractal dimension that can reflect the complexity of coal pores in the classical Fick diffusion model and considered real diffusion in nature. The classical Fick diffusion model with fractional partial-differential equations replaces the first-order partial-differential equation regarding time to obtain the fractional fractal-diffusion model. ,,,− The above-mentioned analysis indicated that the gas diffusion coefficient inside the coal body only remains constant or slightly changes in a certain period.…”

Section: Introductionmentioning

confidence: 99%

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Fractal-Time-Dependent Fick Diffusion Model of Coal Particles Based on Desorption–Diffusion Experiments

Ren

Wang

et al. 2022

Energy Fuels

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The diffusion coefficient is a crucial parameter to manifest the diffusivity of methane in coal, which is obtained by solving mathematical and physical equations that characterize the diffusion process. The diffusion model established by combining the pore structure parameters and time-dependent characteristics in Euclidean space cannot reflect the natural heterogeneity of coal. There is a fundamental difference between the fractal structure and time-dependent diffusion characteristics in Euclidean space. Based on the classic homogeneous spherical Fick diffusion model of coal particles, the full-aperture comprehensive fractal dimension and time-dependent diffusion decay coefficient are introduced, forming the fractal-time-dependent Fick diffusion (FTFD) model of coal particles. To verify the new model, we obtained model parameters by mercury injection, low-temperature liquid nitrogen adsorption, and desorption−diffusion experiments, and the model fitting curve was drawn, which was compared with the desorption−diffusion rate experimental points. In addition, the calculation method of lost-gas content based on the √t approach was also corrected. The results indicated that the new model could describe the whole process of gas diffusion in the heterogeneous coal with good accuracy and stability. The new model also covered the traditional classical homogeneous spherical Fick diffusion and dynamic diffusion-coefficient models with more general theoretical significance. The lost-gas content calculated by the new model was consistent with the actual lost-gas content, improving the accuracy of the lost-gas calculation. The investigation results have important theoretical significance for a comprehensive understanding of the diffusion and transport of pore gas in coal seams.

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Section: Modeling and Experimental Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fractal-Time-Dependent Fick Diffusion Model of Coal Particles Based on Desorption–Diffusion Experiments

Ren

Wang

et al. 2022

Energy Fuels

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“…Except for pore sizes, parameters used for numerical simulation are chosen from Table , which are used for validating adsorption kinetics of CO 2 in bituminous coals. Experimental observations on pore size distribution revealed that the pore volumes occupied by the pores with size less than 10 nm are significantly more than that by the pores with sizes larger than 10 nm for various rank coals. , To consider the permeation of coal matrices, the pore sizes of 0.6, 1, 3, and 8 nm are used in these simulations. The corresponding matrix intrinsic permeabilities range from 2.0 × 10 –24 to 3.6 × 10 –22 m 2 .…”

Section: Model Applicationmentioning

confidence: 99%

Modeling Adsorption and Transport behavior of Gases in Moist Coal Matrix

2021

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Water is ubiquitous in coalbeds, and its influence on coalbed carbon sequestration and/or methane recovery cannot be neglected. To investigate the roles of moisture content in gas transport and adsorption behavior, this paper presents a mass transport model for real gas transport in moist coal matrix based on multiple transport mechanisms. A modified kinetics in conjunction with Langmuir isotherm is proposed to incorporate the effects of moisture, and it is used to describe the mass change between bulk phase and adsorbed phase gases. The reliability of the model has been demonstrated through validation exercises.The results indicate that moisture in coal matrices alters both volume constant and pressure constant in conjunction with Langmuir isotherm. The presence of moisture can significantly reduce the gas adsorption capacity and hinder the loss of bulk gas diffusivity. The moisture effects on gas diffusion kinetics are associated with applied pressure, pore size, as well as the moisture contents. Larger pressures and pores can shorten the time for reaching equilibrium state. The moisture effects on the time required to reach equilibrium are more significant when pore sizes are smaller. The required time for adsorbed gas concentration reaching equilibrium is found to be shorter than that for the gas pressure due to the role of surface diffusion.

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“…In recent years, more and more studies have been carried out on the micro-characteristic parameters of soils, such as porosity, average pore diameter, pore volume, and other parameters. The main methods to detect pore characteristic parameters are the mercury intrusion method, the scanning electron microscope method, and the nitrogen adsorption method [ 13 , 14 ]. Some scholars have further classified the pores by the pore size, to further analyze the pores quantitatively [ 15 ].…”

Section: Introductionmentioning

confidence: 99%

Study on Crack Development and Micro-Pore Mechanism of Expansive Soil Improved by Coal Gangue under Drying–Wetting Cycles

Zhu

Zhang

et al. 2021

Materials

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Expansive soil is prone to cracks under a drying–wetting cycle environment, which brings many disasters to road engineering. The main purpose of this study is use coal gangue powder to improve expansive soil, in order to reduce its cracks and further explore its micro-pore mechanism. The drying–wetting cycles test is carried out on the soil sample, and the crack parameters of the soil sample are obtained by Matlab and Image J software. The roughness and micro-pore characteristics of the soil samples are revealed by means of the Laser confocal 3D microscope and Mercury intrusion meter. The results show that coal gangue powder reduces the crack area ratio of expansive soil by 48.9%, and the crack initiation time is delayed by at least 60 min. Coal gangue powder can increase the internal roughness of expansive soil. The greater the roughness of the soil, the less cracks in the soil. After six drying–wetting cycles, the porosity and average pore diameter of the improved and expanded soil are reduced by 37% and 30%, respectively, as compared to the plain expansive soil. By analyzing the cumulative pore volume and cumulative pore density parameters of soil samples, it is found that the macro-cracks are caused by the continuous connection and fusion of micro-voids in soil. Coal gangue powder can significantly reduce the proportion of micro-voids, cumulative pore volume, and cumulative pore density in expansive soil, so as to reduce the macro-cracks.

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Determinations of the multifractal characteristics of the pore structures of low-, middle-, and high-rank coal using high-pressure mercury injection

Cited by 45 publications

References 54 publications

Fractal-Time-Dependent Fick Diffusion Model of Coal Particles Based on Desorption–Diffusion Experiments

Fractal-Time-Dependent Fick Diffusion Model of Coal Particles Based on Desorption–Diffusion Experiments

Modeling Adsorption and Transport behavior of Gases in Moist Coal Matrix

Study on Crack Development and Micro-Pore Mechanism of Expansive Soil Improved by Coal Gangue under Drying–Wetting Cycles

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