液氮压裂过程向地层注入液氮而产生的低温会对煤层岩石造成破坏，导致煤层渗透率升高。为揭示液氮注入地层过程对煤层渗透率影响的规律，采用压力脉冲衰减法开展了低温处理前、后煤岩渗透率测试试验。对比干燥与饱水煤岩在不同处理温度下的渗透率测试结果，-10、-25、-40 ℃及液氮（-195.8 ℃）低温处理30 min都会导致煤岩渗透率升高，饱水煤岩渗透率升高幅度高于干燥煤岩；随着处理温度的降低，煤岩渗透率升高幅度变大，拟合得到了渗透率升高率与煤岩处理温度之间的指数关系。通过试验结果分析，详细论述了低温导致煤岩破坏并提高煤层渗透率的原理。

Liquid nitrogen fracturing is a technique using liquid nitrogen as a fracturing fluid to stimulate the reservoir. During the treatment of liquid nitrogen fracturing, the cryogenic nitrogen is injected into formation, which leads coal rocks damage and increases coal rocks permeability. To reveal the laws of permeability variation after cryogenic nitrogen injection, the permeability tests are conducted on coal rocks before and after cryogenic treatment with pressure pulse decay method. By comparing the permeability results of dry and saturated coal rocks at different temperatures, it is found that the permeabilities of coal rock are all improved after 30 minutes cryogenic treatment respectively at -10 ℃, -25 ℃, -40 ℃ and liquid nitrogen (-195.8 ℃). Saturated coal rocks have a higher increasing rate of permeability than dry coal rocks. With the decrease of temperature, the permeability of coal rocks increases by a large amplitude. An exponential relation between the increasing rate of coal rock permeability and the temperature is obtained. The test results are analyzed to reveal the principles of coal rocks damage and permeability enhance influenced by low temperature.