Thermal shocking effect occurs when the coalbed methane (CBM) reservoirs meet liquid nitrogen (LN2) of extremely low temperature. In this study, 3D via X-ray microcomputer tomography (µCT) and scanning electron microscope (SEM) are employed to visualize and quantify morphological evolution characteristics of fractures in coal after LN2 thermal shocking treatments. LN2 thermal shocking leads to a denser fracture network than its original state with coal porosity growth rate increasing up to 183.3%. The surface porosity of the μCT scanned layers inside the coal specimen is influenced by LN2 thermal shocking which rises from 18.76% to 215.11%, illustrating the deformation heterogeneity of coal after LN2 thermal shocking. The cracking effect of LN2 thermal shocking on the surface of low porosity is generally more effective than that of high surface porosity, indicating the applicability of LN2 thermal shocking on low-permeability CBM reservoir stimulation. The characteristics of SEM scanned coal matrix in the coal powder and the coal block after the LN2 thermal shocking presented a large amount of deep and shallow progressive scratch layers, fracture variation diversity (i.e. extension, propagation, connectivity, irregularity) on the surface of the coal block and these were the main reasons leading to the decrease of the uniaxial compressive strength of the coal specimen.

当煤层气（CBM）储层遇到极低温度的液氮（LN2）时，就会发生热冲击作用。在这项研究中，通过X射线微型计算机断层扫描（µCT）和扫描电子显微镜（SEM）进行的3D可视化和量化了LN2热冲击处理后煤中裂缝的形态演化特征。LN2热冲击导致的裂缝网络比其原始状态更致密，煤的孔隙率增长率高达183.3％。煤样品内部μCT扫描层的表​​面孔隙度受LN2热冲击的影响，其从18.76％上升至215.11％，说明了LN2热冲击后煤的变形非均质性。LN2热冲击在低孔隙度表面上的开裂效果通常比高表面孔隙度更有效，这表明LN2热冲击在低渗透煤层气储层增产中的适用性。LN2热冲击后，煤粉和煤块中SEM扫描的煤基质的特征表现出大量深浅的渐进刮痕层，并且在其表面上出现了裂缝变化的多样性（即扩展，扩展，连通性，不规则性）。煤块，这是导致煤样单轴抗压强度降低的主要原因。