液氮冷浸煤岩增透作用影响因素分析

Analysis of the influential factors on the ways for enhancing the coalmining rock permeability aroused by the liquified nitrogen soaking

为考察液氮冷浸煤岩后的增透效果,控制冷浸循环次数、冷浸时间、煤种和煤岩含水饱和度4种因素,通过渗流试验研究其对增透效果的影响,并分析了液氮冷浸煤岩的损伤增透机制。结果表明：循环作用和煤种对干燥煤岩渗透率的影响较弱;渗透率随冷浸时间先逐渐增大后趋于稳定,冷浸时间对渗透率的提升存在一定上限;液氮冷浸条件下,煤岩中的水分对渗透率的提升有很重要的作用,煤岩渗透率随含水饱和度的变化存在一个从增幅缓慢到迅速增加的临界含水饱和度,临界含水饱和度约70%;对含水煤样进行循环,可得到较好的增透效果,但渗透率增幅随循环次数的增加而逐渐降低;可通过在每次冷浸循环间隙尽量提高煤岩的含水饱和度,来达到理想的增透效果。

The paper is inclined to make an investigation of the effect of the permeability enhancement on the coal rock by the liquified nitrogen soaking through the permeability tests to be conducted pre--pro the liquid nitrogen soaking based on the control of the soaking cycle,the soaking time,types and humid saturation of the coal rock. And,then,we have done an analysis of the changes of the permeability to further our understanding of the fracturing mechanism of the liquid nitrogen in the paper. The results of our investigation and analysis show that the increase of the permeability caused by the temperature change,that is to say,the change related to the temperature drop or freezing,whose process may lead to a significant temperature drop,serious damage,and/or a considerable increase of permeability. As a result,the permeability of the coal rock increases significantly through the first cycle though there does not occur any serious change in the next five cycles. However,the permeability of the coal rock may tend to increase continuously in case the freezing time would be prolonging till the next cycle but later it could get stabilized.Nevertheless,the permeability would stop to grow when the temperature tends to fall and then decrease to the minimal level.Thus,it can be seen that the freezing time may also reach its upper limit with the permeability enhancement. Besides,since the water saturation of the coal rock may play a significant role in influencing the permeability enhancement,the variation of the water saturation has a critical effect on the water saturation from slow increase to rapid increase,particularly,when the critical water saturation remains at about 70%. On the other hand,though the permeability tends to increase remarkably with the freezing circulation of the hydrous coal rock,the increasing rate may tend to get minor and minor with the increase of the freezing cycle. However,it can also be possible to increase the water permeability significantly by improving the water saturation of the coal rock at intervals of each freezing cycle. It is just for the above reasons that we have made a further study of the two aspects of the fracturing mechanism of the liquid nitrogen,namely,the temperature shock and the pore water phase change,for the cold shock may tend to cause the thermal degradation of the coal rock and make the rock dry whereas the damage of hydrous coal rock can help to join the above mentioned two aspects.