温度与应力对原煤、型煤渗透特性影响的试验研究

EXPERIMENTAL STUDY OF EFFECT OF TEMPERATURE AND STRESS ON PERMEABILITY CHARACTERISTICS OF RAW COAL AND SHAPED COAL

通过试验分析尺寸效应、温度和应力对原煤及型煤的渗流特性的影响,结果表明,对岩芯直径相同而高度不同的均质试样,尺寸效应对渗透率的测试值误差一般在10%以内;非均质煤样尺寸效应对渗透率的测试值误差范围为4%～40%,甚至可能更高;微裂缝的发育程度是导致煤样渗透率变化较大的主要因素。不同直径的煤样,直径相对较小的煤样在围压加压、卸压条件下渗透率变化比大尺寸煤样更为敏感,渗透率对应力的敏感性大于孔隙度。当煤体经历较高的围压后,孔隙结构将发生塑性变形,煤体会遭受永久性不可逆的损害,表现在孔隙度及渗透率的值无法恢复到初始值。煤在经历高温后,大孔被压缩,但微孔更加发育,比表面积增加,同时煤体的强度将有所降低,当围压增加时,存在一个围压临界点,当围压达到临界点,渗透率会大幅降低。原煤与型煤在加压、卸压条件下渗透率的变化规律一致,均与围压成指数关系。

The effects of size effect,temperature and stress on the permeability characteristics are analyzed by the experiments.The results show that for homogeneous samples with the same diameter and different lengths,the error of testing value of permeability rate induced by the size effect is less than 10%,while for the heterogeneous coal core,the error is 4% to 40%,or even higher.The development degree of microcrack is the main factor that leads to permeability rate to change greatly.Under loading and unloading of confining pressure,the permeability rate of coal samples with small diameter is more sensitive than that of large-size coal samples;and the permeability rate is more sensitive to the stress than the porosity.When the coal body experiences higher confining pressures,plastic deformation occurs for the pore structure,the coal suffers permanent irreparable damage,and the porosity and permeability rate cannot restore to the initial values.After the coal experiences high temperature,big holes are compressed,but more micropores are developed.Meanwhile,the specific surface area of the coal increases,and the strength decreases.For the confining pressure,there is a critical point.When the confining pressure reaches the critical point,the permeability rate will be greatly reduced.The permeability rate change of raw coal and shaped coal under loading and unloading is consistent,which is an exponential function of the confining pressure.