Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

Experimental Study on Methane Diffusion Characteristics of Different Metamorphic Deformed Coals Based on Counter Diffusion Method

Jiangang Ren
* ORCID logo ,
Liang Gao
,
Zhihui Wen
ORCID logo ,
Hongbo Weng
,
Jianbao Liu
,
Runsheng Lv
ORCID logo ,
Yanwei Qu
,
Zhimin Song
ORCID logo ,
Yongwang Zhang
,
Bing Li
* ORCID logo
Version 1 : Received: 20 August 2023 / Approved: 21 August 2023 / Online: 22 August 2023 (02:32:47 CEST)

A peer-reviewed article of this Preprint also exists.

Ren, J.; Gao, L.; Wen, Z.; Weng, H.; Liu, J.; Lv, R.; Qu, Y.; Song, Z.; Zhang, Y.; Li, B. Experimental Study on Methane Diffusion Characteristics of Different Metamorphic Deformed Coals Based on the Counter Diffusion Method. Processes 2023, 11, 2808. Ren, J.; Gao, L.; Wen, Z.; Weng, H.; Liu, J.; Lv, R.; Qu, Y.; Song, Z.; Zhang, Y.; Li, B. Experimental Study on Methane Diffusion Characteristics of Different Metamorphic Deformed Coals Based on the Counter Diffusion Method. Processes 2023, 11, 2808.

Abstract

The diffusion coefficient (D) is a key parameter characterizing gas transport in coal seams. Usually, the D is calculated from the desorption curve of particle coal, which cannot accurately reflect the diffusion characteristics under the stress constraint conditions of in-situ coal seams. In this paper, based on Fick's law of counter diffusion, different metamorphic deformed coals of medium and high coal rank are taken as the research object. The change laws of D under different confining pressure, gas pressure, and temperature conditions are tested and analyzed, and the influencing mechanisms on the D are discussed. The results show that the D of different metamorphic deformed coals decreases exponentially with the increase of confining pressure, and increases exponentially with the increase of gas pressure and temperature. There is a limit diffusion coefficient. The influence of confining pressure on the D is essentially determined by the change of effective stress, and the D has a negative effect of effective stress similar to permeability. The effect of gas pressure on the D involves two mechanisms, namely, mechanical and adsorption effects, which are jointly restricted by effective stress and coal particle shrinkage and expansion deformation. The effect of temperature on the D is mainly achieved by changing the root mean square speed and average free path of gas molecules. Under the same temperature and pressure conditions, the D increases first and then decreases with the increase of deformation degree, and the D of fragmented coal is the largest. Under similar deformation conditions, the D of high-rank anthracite is greater than that of medium-rank fat coal. It is considered that porosity is the key factor affecting the change of D in different metamorphic deformed coals.

Keywords

Counter diffusion method; Confining pressure; Gas pressure; Temperature; Diffusion coefficient

Subject

Environmental and Earth Sciences, Geophysics and Geology

Copyright: This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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