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

The natural frequency of coal is one of the important technical parameters for the application of the permeability enhancement technology of coal and rock forced vibration. Aiming at exploring the dominant frequency of the permeability enhancement technology of coal vibration excited by vibration wave, the model of coal vibration excited by simple harmonic wave (SHW) was constructed. Furthermore, considering the three main control parameters, i.e., excitation force, coal sample size and mechanical parameters, the response characteristics of coal vibration excited by SHW were simulated and calculated. The calculation results demonstrate that when the frequency of excitation force equals the natural frequency of coal, the vibration occurs and the peak values of response parameters all increase significantly. The peak acceleration response of coal increases with the increase of excitation force, whereas it decreases with the increase of coal size. Under the same SHW excitation force, the mechanical parameters of coal determine the vibration response characteristics of coal, and the natural frequency of coal is proportional to the elastic modulus. Finally, the variation law of natural frequency response characteristics of coal vibration excited by SHW was verified by the response experiment on coal vibration under SHW excitation and related test results. The research results can serve as a theoretical basis for the application of the permeability enhancement technology of coal vibration excited by vibration wave.

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The Pore Structure Multifractal Evolution of Vibration-Affected Tectonic Coal and the Gas Diffusion Response Characteristics

Shen,

Huo,

Shu

et al. 2024

Processes

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Vibrations caused by downhole operations often induce coal and gas outburst accidents in tectonic zone coal seams. To clarify how vibration affects the pore structure, gas desorption, and diffusion capacity of tectonic coal, isothermal adsorption-desorption experiments under different vibration frequencies were carried out. In this study, high-pressure mercury intrusion experiments and low-pressure liquid nitrogen adsorption experiments were conducted to determine the pore structures of tectonic coal before and after vibration. The pore distribution of vibration-affected tectonic coal, including local concentration, heterogeneity, and connectivity, was analyzed using multifractal theory. Further, a correlation analysis was performed between the desorption diffusion characteristic parameters and the pore fractal characteristic parameters to derive the intrinsic relationship between the pore fractal evolution characteristics and the desorption diffusion characteristics. The results showed that the vibration increased the pore volume of the tectonic coal, and the pore volume increased as the vibration frequency increased in the 50 Hz range. The pore structure of the vibration-affected tectonic coal showed multifractal characteristics, and the multifractal parameters affected the gas desorption and diffusion capacity by reflecting the density, uniformity, and connectivity of the pore distribution in the coal. The increases in the desorption amount (Q), initial desorption velocity (V0), initial diffusion coefficient (D0), and initial effective diffusion coefficient (De) of the tectonic coal due to vibration indicated that the gas desorption and diffusion capacity of the tectonic coal were improved at the initial desorption stage. Q, V0, D0, and De had significant positive correlations with pore volume and the Hurst index, and V0, D0, and De had negative correlations with the Hausdorff dimension. To a certain extent, vibration reduced the local density regarding the pore distribution in the coal. As a result, the pore size distribution was more uniform, and the pore connectivity was improved, thereby enhancing the gas desorption and diffusion capacity of the coal.

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

Cited by 3 publications

References 35 publications

A New Permeability Model Under the Influence of Low-Frequency Vibration on Coal: Development and Verification

A New Permeability Model Under the Influence of Low-Frequency Vibration on Coal: Development and Verification

Study on natural frequency response characteristics of coal vibration excited by simple harmonic wave

The Pore Structure Multifractal Evolution of Vibration-Affected Tectonic Coal and the Gas Diffusion Response Characteristics

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