Micrometer-scale fractures in coal related to coal rank based on micro-CT scanning and fractal theory

Shi, Xinghua; Pan, Jienan; Hou, Quanlin; Jin, Yi; Wang, Zhenzhi; Niu, Qinghe; Li, Meng

doi:10.1016/j.fuel.2017.09.115

Cited by 149 publications

(60 citation statements)

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“…The fractal theory has been widely applied to quantitatively study the irregular structure of porous material, which has a certain degree of self‐similarity . The analysis via CO 2 adsorption is meaningless due to the narrow range of radius.…”

Section: Discussionmentioning

confidence: 99%

“…The fractal theory has been widely applied to quantitatively study the irregular structure of porous material, which has a certain degree of self-similarity. 48,49 The analysis via CO 2 adsorption is meaningless due to the narrow range of radius. In this paper, the fractal characteristics were investigated based on NMRC to discuss the heterogeneity of pore structure.…”

Section: Fractal Characterizations From Micropores To Mesopores Of mentioning

confidence: 99%

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Methane adsorption constrained by pore structure in high‐rank coals using FESEM, CO₂ adsorption, and NMRC techniques

Liu

Cai

Zhou

2019

Energy Science & Engineering

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To evaluate the impacts of nanopores of high‐rank coals on coalbed methane adsorption and storage, 12 anthracite and semianthracite coal samples from Yangquan and Shouyang blocks in the Qinshui Basin were investigated. Field emission scanning electron microscopy (FESEM) and CO2 adsorption combined with nuclear magnetic resonance cryoporometry (NMRC) experiments were used to evaluate the pore structure with diameters ranging from 0 to 500 nm and their impact on adsorption capacity based on qualitative and quantitative analysis. The results show that a coalification jump from semianthracite to anthracite occurred in the study area due to the magmatic intrusion. In the process, the volume of supermicropores and micropores largely increased while the volume of transition pores and mesopores decreased slightly. Additionally, vitrinite gets purified and enriched during the rapid maturation of coal reservoir, which is beneficial to the microporous structure development. The pore size distribution (PSD) of anthracite is mainly divided into two types, which are in serrated and decreasing forms, respectively. Higher vitrinite content can promote the formation of decreasing type (type II), which corresponds to a lower degree of complexity. The fractal dimensions indicate that the heterogeneity of coal samples is increasing with the decrease in pore size. Accordingly, the increase in pore heterogeneity corresponds to the lower adsorption capacity. The main pore sizes that contribute to CBM adsorption include two parts: 25‐30 nm and 50‐60 nm. For the supermicropores with large specific surface areas, the pore system detected by CO2 molecules is not conducive to CBM adsorption, while the increase in pore volume can improve the adsorption rate and capacity of CO2. These findings are vital for a precisely understanding of nanoscale pores as well as future CBM exploitation.

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Section: Discussionmentioning

confidence: 99%

Section: Fractal Characterizations From Micropores To Mesopores Of mentioning

confidence: 99%

Methane adsorption constrained by pore structure in high‐rank coals using FESEM, CO₂ adsorption, and NMRC techniques

Liu

Cai

Zhou

2019

Energy Science & Engineering

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“…(Liu and Nie 2016) employed a lowpressure nitrogen gas adsorption technique along with SEM to study methane adsorption in coal and demonstrated that the fractal dimensions of the pores comprehensively reflect the difference in the physical properties of the coal. (Shi et al 2018) investigated micrometer-sized fractures via micro-CT scanning and fractal analysis, with results showing high interconnectivity in the micro-fracture networks of low-grade coal and greater complexity in the micro-fracture structure of higher-grade coal.…”

Section: Introductionmentioning

confidence: 99%

Two-dimensional SEM image-based analysis of coal porosity and its pore structure

Zou

She

Peng³

et al. 2020

Int J Coal Sci Technol

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A quantitative analysis of the porosity, pore size distribution, and fractal dimensions of pores is significant for studying the pore structure characteristics of coal. This study utilized 12 anthracite coal samples from the Sihe mining area to explore the pore structure characteristics of the coal therein. Hundred randomly selected points on each sliced coal sample were imaged via scanning electron microscopy, and a total of 1200 images were used for the analysis. The porosity and fractal dimensions of the coal samples were analyzed via digital image processing and box-counting dimension methods. This method is characterized by extensive graphical analysis, and the results are based on statistical methods. These were also used to analyze the structural and development characteristics of the microscopic pores in the coal. The results reveal that the surface porosity obtained via digital image processing was 16.11% lower than that measured experimentally. The fractal dimension and porosity of the pore surface were fitted to a natural logarithmic curve. The rate of change in the pore fractal dimension depends on the porosity such that, to some degree, a greater porosity is associated with more complex pore structures, a higher degree of micropore development, and improved pore connectivity.

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“…The common practice relation was found incomprehensive to describe the relation of coal samples, and the mathematic practice has already been reported to be inaccurate. [34] found that the 2D fractal dimension of coal (R o from 0.59% to 2.25%) has positive correlation with coal rank, Zhou et al [35] used Sierpinski-like model to calculate the fractal dimension and the results showed that fractal dimension increases as the pressure on the coal sample increases. In our study, the relation between fractal dimension and porosity deduced theoretically and the results that calculated directly from samples were compared, the results show that these results fit well with each other.…”

Section: Introductionmentioning

confidence: 99%

Imaged based fractal characterization of micro-fracture structure in coal

Zhou

Yao

et al. 2019

Fuel

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To better understand the fractal characteristics of coal fracture network and find the relation between 2D and 3D fractal dimensions, we utilized the improved box counting method to calculate 2D and 3D fractal dimensions based on high resolution CT images of 4 coal samples (Ro from 2.915% to 4.69%). Based on the calculated 2D and 3D fractal dimension and porosity, the size of representative element volume (REV), the relationship between Df2 and Df3 and the relationship between porosity and fractal dimension are investigated extensively. It is noticed that the fractal dimension-based REV of coal is smaller than the porosity-based REV. As the complement of previous theoretical studies, it is proved that porosity has an exponential relationship with fractal dimension. By deducing formulas based on fractal theory, a new way to get the lower self-similar region size from relation between porosity and fractal dimension is provided. Evidently, the relation between 2D and 3D fractal dimension of coal could be expressed as Df3=CDf2+ φ, and the slope of the line, C, depends on the average 2D fractal dimension of the sample. Finally, the reference of the relation between Df2 and C of high rank coal is provided as C=-0.75Df2 +2.75.

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Micrometer-scale fractures in coal related to coal rank based on micro-CT scanning and fractal theory

Cited by 149 publications

References 50 publications

Methane adsorption constrained by pore structure in high‐rank coals using FESEM, CO₂ adsorption, and NMRC techniques

Methane adsorption constrained by pore structure in high‐rank coals using FESEM, CO₂ adsorption, and NMRC techniques

Two-dimensional SEM image-based analysis of coal porosity and its pore structure

Imaged based fractal characterization of micro-fracture structure in coal

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Micrometer-scale fractures in coal related to coal rank based on micro-CT scanning and fractal theory

Cited by 149 publications

References 50 publications

Methane adsorption constrained by pore structure in high‐rank coals using FESEM, CO2 adsorption, and NMRC techniques

Methane adsorption constrained by pore structure in high‐rank coals using FESEM, CO2 adsorption, and NMRC techniques

Two-dimensional SEM image-based analysis of coal porosity and its pore structure

Imaged based fractal characterization of micro-fracture structure in coal

Contact Info

Product

Resources

About

Methane adsorption constrained by pore structure in high‐rank coals using FESEM, CO₂ adsorption, and NMRC techniques

Methane adsorption constrained by pore structure in high‐rank coals using FESEM, CO₂ adsorption, and NMRC techniques