Fractal characteristics of coal samples utilizing image analysis and gas adsorption

Liu, Xianfeng; Nie, Baisheng

doi:10.1016/j.fuel.2016.05.110

Cited by 203 publications

(61 citation statements)

References 68 publications

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“…In recent decades, various constantly updated methods have been applied to evaluate the coal PSD characteristics, including direct observational methods and indirectly inferred methods. Direct observation methods are, for example, scanning electron microscopy (SEM) [5,6], X-ray computerized tomography (X-CT) [7,8] and atomic force microscope (AFM) [9,10], which can be used 2 of 18 to characterize the two-or three-dimensional distribution of coal PSDs. Indirectly inferred methods include mercury intrusion porosimetry (MIP) [11,12], gas adsorption (N 2 and CO 2 ) [13][14][15][16] and nuclear magnetic resonance (NMR) [17][18][19].…”

Section: Introductionmentioning

confidence: 99%

Insights into Multifractal Characterization of Coals by Mercury Intrusion Porosimetry

et al. 2019

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Mercury intrusion porosimetry (MIP) as a practical and effective measurement has been widely used in characterizing the pore size distribution (PSD) for unconventional reservoirs (e.g., coals and shales). However, in the process of MIP experiments, the high mercury intrusion pressure may cause matrix compressibility and result in inaccurate estimations of PSD. To get a deeper understanding of the variability and heterogeneity characteristics of the actual PSD in coals, this study firstly corrected the high mercury intrusion pressure data in combination with low-temperature N 2 adsorption (LTNA) data. The results show that the matrix compressibility was obvious under the pressure over 24.75 MPa, and the calculated matrix compressibility coefficients of bituminous and anthracite coals range from 0.82 to 2.47 × 10 −10 m 2 /N. Then, multifractal analysis was introduced to evaluate the heterogeneity characteristics of coals based on the corrected MIP data. The multifractal dimension D min is positively correlated with vitrinite content, but negatively correlated with inertinite content and mercury intrusion saturation. The multifractal dimension D max shows negative relationships with moisture and ash content, and it also emerges as a "U-shaped" trend with efficiency of mercury withdrawal. It is concluded that multifractal analysis can be served as a practical method not only for evaluating the heterogeneity of coal PSDs, but also for other unconventional reservoirs (e.g., shale and tight sandstone).

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Section: Introductionmentioning

confidence: 99%

Insights into Multifractal Characterization of Coals by Mercury Intrusion Porosimetry

et al. 2019

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“…Pore and fracture systems of coals have been comprehensively studied by constantly updated methods in recent years, including experimental techniques such as photoelectric observation, gas adsorption, and fluid intrusion, and reconstruction of three-dimensional structures (Chalmers et al, 2012;Clarkson et al, 2013;Li et al, 2017;Liu and Nie, 2016;Yao et al, 2010). The pores of coal can be classified into those <2 nm (micropores), 2-50 nm (mesopores), and >50 nm (macropores) in size according to the International Union of Pure and Applied Chemistry (IUPAC).…”

Section: Introductionmentioning

confidence: 99%

“…Among testing methods, the low-temperature nitrogen test (LPN 2 GA) has become an effective method to characterize adsorption pore structure (Francisco et al, 1996;Liu and Nie, 2016;Mahamud and Novo, 2008;Nie et al, 2015). However, this method has difficulty characterizing the structure of adsorption pores <2 nm in size accurately given the larger molecular kinetic diameter (0.36 nm) and instrument precision constraints ( Li et al, 2012a;.…”

Section: Introductionmentioning

confidence: 99%

Structural and fractal characterization of adsorption pores of middle–high rank coal reservoirs in western Yunnan and eastern Guizhou: An experimental study of coals from the Panguan syncline and Laochang anticline

Zhang

Wei

Gao

et al. 2018

Energy Exploration & Exploitation

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To better understand the structural characteristic of adsorption pores (pore diameter < 100 nm) of coal reservoirs around the coalbed methane production areas of western Yunnan and eastern Guizhou, we analyzed the structural and fractal characteristics of pore size range of 0.40-2.0 nm and 2-100 nm in middle-high rank coals (R o,max ¼ 0.93-3.20%) by combining low-temperature N 2 /CO 2 adsorption tests and surface/volume fractal theory. The results show that the coal reservoirs can be divided into three categories: type A (R o,max < 2.15%), type B (2.15% < R o,max <2.50%), and type C (R o,max > 2.15%). The structural parameters of pores in the range from 2 to 100 nm are influenced by the degree of coal metamorphism and the compositional parameters (e.g., ash and volatile matter). The dominant diameters of the specific surface areas are 10-50 nm, 2-50 nm, and 2-10 nm, respectively. The pores in the range from <2 nm provide the largest proportion of total specific surface area (97.22%-99.96%) of the coal reservoir, and

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“…(Mahamud and Novo 2008) used both porosity, obtained via mercury injection, and fractal analysis to assess the texture of coal: The fractal dimensions and fractal profiles were found to be sensitive to oxidation treatment; this information is useful to follow the changes in coal samples. (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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Fractal characteristics of coal samples utilizing image analysis and gas adsorption

Cited by 203 publications

References 68 publications

Insights into Multifractal Characterization of Coals by Mercury Intrusion Porosimetry

Insights into Multifractal Characterization of Coals by Mercury Intrusion Porosimetry

Structural and fractal characterization of adsorption pores of middle–high rank coal reservoirs in western Yunnan and eastern Guizhou: An experimental study of coals from the Panguan syncline and Laochang anticline

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

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