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| Experiment study on influence of liquid nitrogen freeze-thaw on pore structure of coal based on nuclear magnetic resonance technology and
mercury intrusion methods |
| CHU Yapei1，2，3，4，ZHANG Dongming2，3，WANG Man4，LIU Heng1，WU Xuyang1，ZHAI Panpan1，SHEN Tong1 |
| (1. School of Civil and Traffic Engineering，Henan University of Urban Construction，Pingdingshan，Henan 467000，China；
2. School of Resource and Safety Engineering，Chongqing University，Chongqing 400044，China；3. State Key Laboratory of Coal Mine Disaster Dynamics and Control，Chongqing University，Chongqing 400044，China；4. State Key Laboratory of Coking Coal Exploitation and Comprehensive Utilization，Pingdingshan，Henan 467000，China) |
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Abstract To study the damage characteristics of the pore structure of coal samples under the action of liquid nitrogen (LN2) freeze-thaw，image analysis，nuclear magnetic resonance(NMR) technique and mercury intrusion were used to analyze the evolution law of fracture expansion，porosity，bound fluid volume，free fluid volume，pore volume，specific surface area and pore size distribution of coal samples under LN2 freeze-thaw. The experimental results show that：(1) The primary fracture gradually expands and connects to form secondary fracture with increasing the number of LN2 freeze-thaw cycles，and the isolated fractures are connected to form fracture network with primary and secondary fractures after the number of freeze-thaw cycles reaches a certain level. (2) LN2 freeze-thaw can promote the development of pores，and the micropores and minipores of coal samples gradually expand，develop and connect to form mesopores and macropores after LN2 freeze-thaw，resulting in enhanced pore connectivity of coal samples，a decrease in the proportion of the bound fluid and increase in the proportion of the free fluid，and the increase of the total porosity，the residual porosity and the effective porosity. (3) The number of pores and the pore size increases after LN2 freeze-thaw，and the pore density in some areas continues to increase and expand to form microfractures. (4) The total pore volume and the specific surface area of coal samples increases after LN2 freeze-thaw，and the change of the pore volume is mainly concentrated in the mespores and macropores. The micropres of coal sample gradually transform to the mesopores and macropores，which leads to the increase of proportion of mesopores and macropores.
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2022, Vol. 41 
