Multiscale morphological and topological characterization of coal microstructure: Insights into the intrinsic structural difference between original and tectonic coals

Zhang, Kaizhong; Zou, Aoao; Wang, Liang; Cheng, Yuanping; Li, Wei; Li, Chun

doi:10.1016/j.fuel.2022.124076

Cited by 23 publications

(4 citation statements)

References 54 publications

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“…The R a and R q represent the mean distance and the root-mean-square distance from the reference surface, respectively. Calculated from eqs and . − R a = 1 N x N y ∑ i = 1 N x ∑ j = 1 N y | z ( i , j ) − z normalm normale normala normaln | where z normalm normale normala normaln = 1 N x N y ∑ i = 1 N x ∑ j = 1 N y z false( i , j false) N x and N y represent the number of points on the X and Y axes, respectively. R q = 1 N x N y ∑ i = 1 N x ∑ j = 1 N y false( z ( …”

Section: Experiments and Methodsmentioning

confidence: 99%

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Acidification-Induced Micronano Mechanical Properties and Microscopic Permeability Enhancement Mechanism of Coal

Xie,

Li,

Sui

et al. 2024

Langmuir

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An acid solution improves the pore-plugging problem in hydraulic fracturing, which in turn improves the permeability of the coal seam. The study aimed to investigate the effect of mixed acid on the micronano mechanical properties and permeability of the coal seam. The surface morphology of acidified coal was analyzed from the micronano scale using atomic force microscopy (AFM) and scanning electron microscopy. Additionally, the micronano scale mechanical characteristics of acidified coal were examined using the mechanical mode in an atomic force microscope. Furthermore, the complexity and connectivity of the micronano pores of samples were investigated using the low-temperature nitrogen adsorption and mercury intrusion porosimetry methods and the fractal theory. The results indicated that the surface minerals of acidified coal were dissolved, loosening the coal and increasing the complexity of the pore structure. Mineral deformation and pore deformation weakened the mechanical properties of coal at the micronano scale, and the mean elastic modulus of acidified coal (B# and E#) decreased by 28.78 and 25.66% compared to that of raw coal. The acid solution effectively enlarged the pore diameter, transitioning from micropores to mesopores and macropores, and the total pore volume of acidified coal increased by 1.88 times and 1.25 times, K n increased from 0.064 to 0.581 and 0.37, respectively. The type of methane diffusion in the diffusion pores changed from Knudsen diffusion to transition-type diffusion. The tortuosity of the pore structure of acidified coal decreased, the fractal dimension of the tortuosity of the pore structure decreased, and the permeability increased by nearly three times. The research results indicate that the mechanical properties of coal decrease after acidification and that the microstructural changes can promote methane migration (diffusion-seepage), which can provide theoretical guidance for coalbed methane extraction in low-permeability coal reservoirs.

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Section: Experiments and Methodsmentioning

confidence: 99%

“…The R a and R q represent the mean distance and the root-mean-square distance from the reference surface, respectively. Calculated from eqs and . − where N x and N y represent the number of points on the X and Y axes, respectively. …”

Section: Experiments and Methodsmentioning

confidence: 99%

Acidification-Induced Micronano Mechanical Properties and Microscopic Permeability Enhancement Mechanism of Coal

Xie,

Li,

Sui

et al. 2024

Langmuir

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show abstract

“…Coal is a graphitic carbonaceous material, and its overall structure can be viewed as a mixture of amorphous and heterogeneous crystalline materials. − The microporous structure of coal can be characterized by the interlayer spaces between the aromatic carbon atom network in the microcrystalline structure unit or the voids between the microcrystalline structures. , Therefore, from a microscopic perspective, the coal micropores are composed of macromolecular aromatic lamellar surroundings. Carbon nanotubes are considered an ideal model for the inner walls of cylindrical coal pores, and some of their properties can be used to characterize the coal micropores to a certain extent .…”

Section: Introductionmentioning

confidence: 99%

Modeling Methane Adsorption Distance Using Carbon Nanotubes and Bituminous Coal Pore Models

Zha,

Lin,

Liu

et al. 2024

Energy Fuels

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To simplify the analysis of the adsorption of methane by coal, single-walled carbon nanotubes (SWCNTs), slit graphene lamellae, and bituminous coal pore models were constructed, and the adsorption of methane molecules in the three models was studied using molecular dynamics and density functional theory. The results show that methane molecules cannot be adsorbed within carbon nanotubes with a pore size of 0.5 nm. In carbon nanotubes with a pore size of 1 nm, adsorbed methane is influenced by the inner wall of the SWCNTs to induce dipoles and to interact with nearby methane molecules. In large-pore-size carbon nanotubes and graphene sheets, methane molecules adsorb and accumulate on the wall surface to form adsorption rings, the thickness of which gradually increases with the pore size under the effect of curvature, ranging from 0.455 to 0.521 nm. This criterion for adsorption was applied to the pore model of bituminous coal, and 52 adsorbed methane states were determined. Furthermore, the Brunauer–Emmett–Teller equation was used to fit the methane isothermal adsorption curve of the bituminous coal pore model, and the adsorption quantity of methane in a single molecular layer was 54, confirming that the adsorption criterion of 0.521 nm is reasonable.

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“…Coal is a complex porous medium, and its pore characteristics have an important impact on gas storage (adsorption) and migration (desorption-diffusion-seepage) (Zhang et al 2022a). Coal pores can be divided into adsorption pores (< 100 nm) and seepage pores (> 100 nm).…”

Section: Introductionmentioning

confidence: 99%

Pore structure of low-permeability coal and its deformation characteristics during the adsorption–desorption of CH4/N2

Ji,

Lin,

Kong

et al. 2023

Int J Coal Sci Technol

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The pore structure of coal plays a key role in controlling the storage and migration of CH4/N2. The pore structure of coal is an important indicator to measure the gas extraction capability and the gas displacement effect of N2 injection. The deformation characteristic of coal during adsorption–desorption of CH4/N2 is an important factor affecting CH4 pumpability and N2 injectability. The pore structure characteristics of low-permeability coal were obtained by fluid intrusion method and photoelectric radiation technology. The multistage and connectivity of coal pores were analyzed. Subsequently, a simultaneous test experiment of CH4/N2 adsorption–desorption and coal deformation was carried out. The deformation characteristics of coal were clarified and a coal strain model was constructed. Finally, the applicability of low-permeability coal to N2 injection for CH4 displacement technology was investigated. The results show that the micropores and transition pores of coal samples are relatively developed. The pore morphology of coal is dominated by semi-open pores. The pore structure of coal is highly complex and heterogeneous. Transition pores, mesopores and macropores of coal have good connectivity, while micropores have poor connectivity. Under constant triaxial stress, the adsorption capacity of the coal for CH4 is greater than that for N2, and the deformation capacity of the coal for CH4 adsorption is greater than that for N2 adsorption. The axial strain, circumferential strain, and volumetric strain during the entire process of CH4 and N2 adsorption/desorption in the coal can be divided into three stages. Coal adsorption–desorption deformation has the characteristics of anisotropy and gas-difference. A strain model for the adsorption–desorption of CH4/N2 from coal was established by considering the expansion stress of adsorbed gas on the coal matrix, the compression stress of free gas on the coal matrix, and the expansion stress of free gas on micropore fractures. N2 has good injectability in low-permeability coal seams and has the dual functions of improving coal seam permeability and enhancing gas flow, which can significantly improve the effectiveness of low-permeability coal seam gas control and promote the efficient utilization of gas resources.

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Multiscale morphological and topological characterization of coal microstructure: Insights into the intrinsic structural difference between original and tectonic coals

Cited by 23 publications

References 54 publications

Acidification-Induced Micronano Mechanical Properties and Microscopic Permeability Enhancement Mechanism of Coal

Acidification-Induced Micronano Mechanical Properties and Microscopic Permeability Enhancement Mechanism of Coal

Modeling Methane Adsorption Distance Using Carbon Nanotubes and Bituminous Coal Pore Models

Pore structure of low-permeability coal and its deformation characteristics during the adsorption–desorption of CH4/N2

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