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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。
The low temperature generated by liquid nitrogen injection into the formation during liquid nitrogen fracturing can cause damage to the coal seam rock and lead to an increase in the permeability of the coal seam. In order to reveal the regularity of the influence of liquid nitrogen injection into formation on the permeability of coal seam, the permeability test of coal before and after low temperature treatment was carried out by pressure pulse decay method. Comparing the permeability tests of dry and saturated coal rocks at different treatment temperatures, the low temperature treatment of -10, -25, -40 ℃ and liquid nitrogen (-195.8 ℃) for 30 min all will lead to the increase of permeability of coal and rock, The permeability of coal is higher than that of dry coal. With the decrease of treatment temperature, the increase of permeability of coal and rock becomes larger, and the exponential relationship between the rate of permeability increase and coal processing temperature is fitted. Through the analysis of test results, the principle of low temperature lead to coal rock failure and increase coal permeability is discussed in detail.