低温流体液氮对煤冷冲击的作用范围、煤内部因温差形成的热应力变化规律及其对煤形成损伤的力学作用机理，均是液氮在煤岩增透领域应用中亟待研究的关键问题。利用非接触式全场应变测量装置、红外温度场测量装置和热电偶温度测量装置，测得开放环境下液氮冷冲击煤样钻孔后，钻孔周边煤体温度场及应变场随冷冲击时间的变化规律。通过建立包含弹性模量、泊松比、热膨胀系数、测点温差及测点所在半径参数的热应力模型，设计实验测得模型各参数并代入其中求解，计算得到煤岩内部不同位置处的热应力及其随冷冲击距离和时间的变化规律，并针对3类不同变质程度煤的上述规律进行对比。研究结果表明，在液氮冷冲击过程中，3类煤样内部各测点处的温度均呈现出快速降低—缓慢降低—稳定的变化规律，各测点处的热应力均经历了快速增长—缓慢增长—无增长3个阶段。距离冷冲击钻孔越近，相邻测点间的温度相差越大，所产生的热应力越大。液氮冷冲击1 800 s后，3类煤样各测点处的热应力均基本达到稳定阶段，距离冷冲击钻孔1 cm处所产生的热应力均≥1.84 MPa。液氮冷冲击能够使煤内部产生4类变形进而对煤造成损伤，其中“因压致拉”所产生的II、III、IV类变形及3者相互组合的复合型变形，是煤体形成损伤产生复杂裂缝的根本原因。然而，液氮冷冲击对不同煤的降温及变形范围虽存在差异，但总体作用范围有限，仅能够在钻孔周边产生损伤，因此，液氮冷冲击技术建议结合压裂工艺进行应用，冷冲击所产生的损伤可用于降低起裂压力，并使压裂裂缝更为复杂。

The range of the cold shock of low-temperature liquid nitrogen on coal, the variation law of thermal stress in coal caused by temperature difference and the mechanical action mechanism of coal damage are the key issues to be studied urgently in the application of liquid nitrogen in the field of coal and rock permeability enhancement. Using the non-contact full-field strain measuring device, infrared temperature distribution measuring device and the thermocouple temperature measuring device, the variation laws of the coal temperature field and strain field around the borehole with time are measured after the liquid nitrogen cold shock on the borehole of coal samples in the open environment. By establishing a thermal-stress model including elastic modulus, Poisson’s ratio, thermal expansion coefficient, temperature difference of measuring points and radius parameters of measuring points, the experiments are designed to measure the parameters of models and the parameters are input into the models for solution. The thermal stress at different positions in coal and rock and its variation law with cold shock distance and time are calculated, and the above laws of three types of coals with different metamorphic degrees are compared. The results show that in the process of liquid nitrogen cold shock, the temperature at each measuring point of three types of coal samples all shows a variation law of rapid decrease-slow decrease-stability, and the thermal stress at each measuring point has experienced three stages: rapid growth-slow growth-zero growth. The closer to the cold shock borehole, the greater the temperature difference between adjacent measuring points, and the greater the thermal stress. After 1 800 s of liquid nitrogen cold shock, the thermal stress at each measuring point of three kinds of coal samples basically reached a stable stage, and the thermal stress at 1 cm from the cold shock drilling hole was ≥ 1.84 MPa. The cold shock of liquid nitrogen can cause four kinds of deformation in the coal, and then damage the coal. Among them, the type II, III, IV deformation caused by “pressure-induced tension” and the compound deformation of three are the fundamental reasons for the formation of complex cracks in the coal. However, although the range of cooling and deformation of different coals is different, the overall range of action is limited, and it can only produce damage around the borehole. Therefore, the liquid nitrogen cold shock technology is suggested to be applied in combination with fracturing technologies, and the damage around the borehole after cold shock can effectively reduce the initiation pressure and make the fracturing fracture more complicated.