Deformation-Failure Characteristics of Coal with Liquid CO 2 Cryogenic-Freezing Process: An Experimental and Digital Study

Gaoming Wei (), Li Ma (), Hu Wen, Xin Yi, Jun Deng, Shangming Liu, Zhenbao Li and Duo Zhang
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Gaoming Wei: College of Energy Science and Engineering, Xi’an University of Science and Technology, Xi’an 710054, China
Li Ma: College of Safety Science and Engineering, Xi’an University of Science and Technology, Xi’an 710054, China
Hu Wen: College of Safety Science and Engineering, Xi’an University of Science and Technology, Xi’an 710054, China
Xin Yi: College of Safety Science and Engineering, Xi’an University of Science and Technology, Xi’an 710054, China
Jun Deng: College of Safety Science and Engineering, Xi’an University of Science and Technology, Xi’an 710054, China
Shangming Liu: College of Safety Science and Engineering, Xi’an University of Science and Technology, Xi’an 710054, China
Zhenbao Li: College of Petro-chemical Engineering, Lanzhou University of Technology, Lanzhou 730050, China
Duo Zhang: College of Safety Science and Engineering, Xi’an University of Science and Technology, Xi’an 710054, China

Energies, 2023, vol. 16, issue 17, 1-19

Abstract: The aim of this paper is to analyze the deformation-failure degree and microstructure variations in coal under the cryogenic-freezing effect of liquid CO 2 . In this paper, X-ray CT scanning technology is adopted to measure the microscopic-morphological parameters of coal. Drawing support from the image processing and three-dimensional (3D) visualization functions of Avizo software, 3D spatial structure variation rules, as well as the deformation and permeability parameters, are quantitatively calculated. Under the effect of LCO 2 cryogenic freezing, the macroscopic mechanical properties and deformation-failure degree of coal are thoroughly analyzed. The results show that fracture-scale parameters of treated coal are significantly increased, resulting in spatial structure parameters including the coal plug total volume (V t ), fracture network volume (V 0 ), and proportion of fracture network (μ 0 ) to increase by 17.11%, 56.57%, and 55.59%, respectively. A comparison analysis indicates that the coverage area of a single value function from the percolation theoretical model for treated coal plugs becomes larger, and its percolation curves are more intensive; the quantitative coal permeability coefficients are increased to more than 40% on average, which further proves that the permeability of coal by using LCO 2 cryogenic freezing is significantly improved. Under the same uniaxial stress loading rate, the peak stress threshold value required by treated coal in the compaction and elastoplastic deformation stage is decreased. The corresponding output acoustic emission energy is apparently increased, owing to the increased brittleness of coal, and deformation failure of coal occurs more easily. Simultaneously, the fracture network and matrix surface of treated coal are more complex, and the corresponding fractal characteristic is obvious. It could be thus concluded that the coal plugs have deformation-failure changes under cryogenic freezing by using LCO 2 , increasing the proportion of coal microstructure and enhancing coal permeability. Therefore, the capability of gas migration through the coal microstructure becomes easier, which is favorable for coalbed methane recovery.

Keywords: coal permeability; mechanical property; X-ray CT image; 3D reconstruction; liquid CO 2 (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2023
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