液氮超低温作用引起煤体渗透率变化规律的实验研究

Experimental study on the feasibility of the technology of increasing permeability in the cracked coal seam caused by liquid nitrogen

为探究液氮致裂煤层增渗技术的可行性,对其技术原理进行了理论分析,并采用实验测试的方法研究了液氮超低温作用对煤体孔隙率与渗透率的影响。结果表明:液氮超低温的作用使得煤样试件的内部温度骤然降低,因液氮的超低温作用而产生的应力已超过了抗拉强度,形成新的裂隙,使得煤样的渗透率增加了2倍以上,孔隙率增加了近1.5倍;在液氮超低温作用时间超过一定阈值后,两者数值增大的趋势减缓。结合热力学和断裂力学的理论,构建了液氮超低温作用下煤体温度分布的数学物理模型,进一步获得了液氮作用下煤体温度场与应力场解析解,阐释了液氮对煤体内裂隙发育、发展的作用机制。

In order to explore the feasibility of the technology of increasing permeability of coal seam caused by liquid nitrogen,the theory of the technology is analyzed,and the effect of ultra-low temperature of liquid nitrogen on the porosity and permeability of coal body is studied by the method of experimental test.The results show that the effect of ultra-low temperature of liquid nitrogen makes the internal temperature of coal sample suddenly reduce,and the stress produced by ultra-low temperature of liquid nitrogen has exceeded the tensile stress the permeability and porosity of coal samples increased by more than 2 times and nearly 1.5 times,respectively.When the time of ultra-low temperature action of liquid nitrogen exceeded a certain threshold,the trend of increase of the two values slow down.Combined with the theory of thermodynamics and fracture mechanics,the mathematical and physical model of coal temperature distribution under the action of liquid nitrogen at ultra-low temperature is constructed,and the analytical solution of coal temperature field and stress field under the action of liquid nitrogen is obtained,and the mechanism of liquid nitrogen on the development and development of coal fracture is explained.