孔隙未冻水含量和分布特征可以反映煤体融化程度,融化程度影响冰孔隙大小,直接决定 孔隙渗透性,影响煤层气开采效率。 研究冻结条件下煤体冰水相变过程特征,对精准评价煤层低温 致裂效率具有重要意义。 实验以冻结态饱水烟煤为研究对象,使用核磁共振技术研究煤样融化过 程孔隙特征,综合测量 T2 曲线、累计孔隙度以及累计孔喉分布,定量分析煤样融化过程孔隙结构。 实验结果表明,液氮循环冻结煤体融化过程中,首先融化出小孔结构,后融化出中大孔结构,且融化 前期孔隙连通性较差。 通过计算 T2 曲线面积,验证了融化过程未冻水含量与温度呈指数关系,并 建立拟合函数。 同时,根据煤样累计孔隙度与累计孔喉分布将融化过程划分为 3 个阶段,分别为加 速融化阶段(-196~-30 °C)、稳定融化阶段(-30~-5 °C)以及快速融化阶段(-5~10 °C)。 热力学 分析表明,低温下煤样未冻水含量同时受到孔隙压力与孔径分布影响,孔隙压力越大、小孔结构越 丰富的煤样未冻水含量越多。 总结了基于液氮循环冻融孔隙扩张收缩以及局部导热特性分析体 系,涉及 T2 图谱分析、导热组分划分、融化速度计算等关键问题,进而分析液氮循环次数造成的煤 样融化速度差异。 计算结果表明,液氮循环冻结 10 次时煤样平均融化速度最快,小孔、中孔与大孔 冰的最大融化速度分别为 0.632% / °C 、0.582% / °C 和 0.521% / °C 。

The content and distribution characteristics of unfrozen water in the pores of coal seams can reflect the de- gree of coal thawing. The degree of coal thawing affects the size of ice pores,directly determines the pore permeability and affects the efficiency of coalbed methane extraction. It is of great significance to study the ice-water phase transfor- mation characteristics in coal under freezing conditions for accurately evaluating the efficiency of cryogenic fractu- ring technology. Taking the frozen saturated bituminous coal as the research object, the nuclear magnetic resonance technology was used to study the pore characteristics of coal samples during thawing process. The pore structure was comprehensively analyzed by measuring T2 curve,cumulative porosity and cumulative pore throat distribution. The results show that in the thawing process of liquid nitrogen cyclic frozen coal,the micropore structure is thawed first, and then the mesopore and macropore structures are thawed,and the pore connectivity is poor in the early thawing stage. By calculating the area of T2 curve,the exponential relationship between unfrozen water content and temperature was verified,and the fitting curve was established. Simultaneously,the thawing process of coal samples was divided in- to three stages according to the cumulative porosity and pore throat distribution,which were the accelerated thawing stage (-196--30 °C),the normal thawing stage (-30--5 °C) and the rapid thawing stage (-5-10 °C). Thermody- namic analysis shows that the unfrozen water content of coal samples at low temperature is affected by both pore pres- sure and pore size distribution,that is,the higher the pore pressure and the richer the micropore structure,the high- er the unfrozen water content of coal samples. The analysis system of pore expansion and contraction and local ther- mal conductivity characteristics based on liquid nitrogen cycle freeze-thaw technology was summarized,involving key issues such as the analysis of T2 spectrum,the division of thermal conductivity components,and the calculation of tha- wing speed. The differences in the thawing speeds of coal samples caused by different liquid nitrogen cycles were ana- lyzed. The calculation results show that the average thawing speed of coal sample was the fastest when the liquid nitro- gen frozen for 10 times. The maximum thawing speed of ice in micropore,mesopore and macropore were 0.632% / °C , 0.582% / °C and 0.521% / °C ,respectively.