Pore fractal model applicability and fractal characteristics of seepage and adsorption pores in middle rank tectonic deformed coals from the Huaibei coal field

Lu, Guanwen; Wang, Jilin; Wei, Chongtao; Song, Yu; Gao, Yan; Zhang, Junjian; Chen, Guanghuan

doi:10.1016/j.petrol.2018.07.074

Cited by 62 publications

(37 citation statements)

References 37 publications

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“…Single fractal models such as Menger, thermodynamics, Sierpinski, FHH fractal model, SSA, and volume fractal model can all capture the heterogeneity information of nanopore structure in the corresponding pore size range. 46 Among these single fractal models, the Sierpinski model is suitable for describing the fractal characteristics of nanopores of TDCs. The FHH model is in favor of 8–100 nm in diameter.…”

Section: Samples Experiments and Fractal Dimensionsmentioning

confidence: 99%

Structural and Fractal Characterizations of Nanopores in Middle-Rank Tectonically Deformed Coals – Case Study in Panguan Syncline

Wen

Jiang

et al. 2020

ACS Omega

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The reservoir properties of tectonically deformed coals (TDCs) differ significantly compared with their neighboring primary coals which are also known as unaltered or underformed coals. However, the heterogeneity of nanopores in TDCs under the syncline control has been seldom reported, and also the middle-rank level was minimally investigated to date. Thus, in this paper, the structures and multiscale fractal characteristics of nanopores in middle-rank TDCs under the controlling effect from Panguan Syncline were investigated via high-pressure mercury injection (HPMI), low-pressure CO 2 /N 2 adsorption (LPCO 2 /N 2 GA), and fractal theory. The results show that both the pore volume (PV) and specific surface area (SSA) of macropores increase significantly in the stage of cataclastic–schistose coal. For ductile deformed coals, the PV increases, while the SSA remains stable. The SSA of mesopores increases slightly in the brittle deformation stage, but significantly in the ductile deformation stage. For micropores, both the PV and SSA for TDCs are significantly higher than primary coals. Moreover, the ductile deformation has a more significant promotion effect for the microporous PV and SSA than the brittle deformation. The fractal dimension of the adsorption pore (induced from the Sierpinski model) increases; however, that of seepage pores (Sierpinski model) decreases with the enhancement of tectonic deformation. The fractal dimension for mesoporous (induced from the FHH model, Frenkel–Halsey–Hill) at 2–6 nm keeps stable in the stage of cataclastic–schistose coal but significantly increases in the ductile deformation stage. For mesopores of 6–100 nm, their heterogeneities were also enhanced in the ductile deformation stage. The fractal dimension of 0.3–0.6 nm micropores is close to 3 and changes slightly with the enhancement of tectonic deformation, indicating that the heterogeneity of smaller micropores is stronger than that of larger micropores. The results are of broad interest for CBM exploration and gas outburst prediction.

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Section: Samples Experiments and Fractal Dimensionsmentioning

confidence: 99%

Structural and Fractal Characterizations of Nanopores in Middle-Rank Tectonically Deformed Coals – Case Study in Panguan Syncline

Wen

Jiang

et al. 2020

ACS Omega

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“…According to Menger Model and mercury intrusion test 37 , computational formula of the pore compressibility coefficient of coal specimens was shown as Eqs (3) and (4):where V P refers to the mercury intrusion volume, approximately equals to the sum volume of pores with diameter of greater than specified value (2r, r equals the pore radius). refers to the functional relation between the mercury intrusion volume and working pressure.…”

Section: Comprehensive Description Of Pore Characteristicsmentioning

confidence: 99%

Investigation on the pore characteristics of coal specimens with bursting proneness

Jiang

Zhang

et al. 2019

Sci Rep

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To achieve further insight into the pore characteristics, the coal specimens with different bursting proneness before and after uniaxial compression failure are tested and compared in this paper. The data of mercury intrusion test is corrected by that of low-temperature nitrogen adsorption and desorption test (LTNAD). The pore size distribution and pore volume of specimens are obtained. The pore compressibility coefficient is determined based on the fractal dimension of pore. Scanning electron microscope (SEM) and computed tomography (CT) are combined to evaluated the pore connectivity. The value of pore compressibility coefficient of specimens with high bursting proneness is larger than that of medium bursting proneness. It means more compressibility and abrupt failure under stress. The researches of both SEM and CT indicate that the pore connectivity of specimens with medium bursting proneness is better. The results show that great differences exist in the pore characteristics of specimens with high and medium bursting proneness, and uniaxial compression failure exacerbates the complexity of pore characteristics.

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“…e fractal characteristics of coal are also one of the important factors affecting the adsorption, desorption, and diffusion of gas in the coal matrix [13,37,46]. e influence of vibration on the pore-fracture structure of a coal sample will inevitably lead to a change in the surface morphology characteristics of the pore-fractures [38,47]. However, a few studies use fractal geometry to quantitatively characterize the complexity of the porefracture surface morphology of coal samples under VDF.…”

Section: Introductionmentioning

confidence: 99%

Effect of Mechanical Vibration with Different Frequencies on Pore Structure and Fractal Characteristics in Lean Coal

Shen

Chen

2021

Shock and Vibration

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The mechanical vibrations caused by underground operations can easily lead to coal and gas outbursts in coal mines. Using the MVGAD-I experimental platform that we designed, the raw coal (0 Hz) was treated with vibration frequencies of 25, 50, 75, and 100 Hz, and the coal samples with different frequency vibrations were obtained. The total pore volume (TPV), specific surface area (SSA), pore size distribution, and the pore fractal dimension (PFD) of five coal samples were analyzed by mercury intrusion porosimetry and low-pressure nitrogen adsorption data. We found that the TPV, SSA, and PFD of the coal samples fluctuate with the increase of vibration frequency. The changes of the TPV and SSA of coal samples treated with 25 and 75 Hz vibrations were significantly greater than those subjected to vibrations of 50 and 100 Hz. Compared with the raw coal (0 Hz), the TPV and SSA of macropores, mesopores, and micropores increased the most in 75 Hz vibration coal sample. Therefore, the 75 Hz vibration excitation can improve the permeability of a body of coal mass and is conducive to the diffusion and seepage of coalbed methane and its production.. The influence of 25 Hz vibration on the TPV and SSA of macropores and mesopores is not obvious, but the TPV and SSA of minipores and micropores decrease significantly, which is not conducive to gas diffusion and adsorption. In addition, 25 and 75 Hz vibrations obviously damaged the fractal characteristics of both mesopores and micropores, resulting in the change of gas adsorption and diffusion ability. The rational use of a 75 Hz vibration is beneficial to both the production of gas and the prevention of outbursts, while a 25 Hz vibration should be avoided. The results are expected to reveal the microscopic mechanism of a vibration-induced outburst and provide theoretical guidance for employing the appropriate frequency of vibration to improve the rate of gas drainage and reduce the risk of outbursts.

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Pore fractal model applicability and fractal characteristics of seepage and adsorption pores in middle rank tectonic deformed coals from the Huaibei coal field

Cited by 62 publications

References 37 publications

Structural and Fractal Characterizations of Nanopores in Middle-Rank Tectonically Deformed Coals – Case Study in Panguan Syncline

Structural and Fractal Characterizations of Nanopores in Middle-Rank Tectonically Deformed Coals – Case Study in Panguan Syncline

Investigation on the pore characteristics of coal specimens with bursting proneness

Effect of Mechanical Vibration with Different Frequencies on Pore Structure and Fractal Characteristics in Lean Coal

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