Effect Of Liquid Nitrogen Freeze-thaw Action On The Seepage Characteristics Of Coal With Different Water Content

The exploitation of coalbed methane has the important significance of safety,high efficiency and green.How to increase the permeability of coalbed methane is the focus and difficulty of coalbed methane exploitation at present.Liquid nitrogen cracking technology is a hot topic in increasing the permeability of coalbed gas at present,but there are many factors that affect it.To this end,this thesis with liquid nitrogen crack caused by frost heave effect mechanism of water-ice phase transition of the moisture content as the main research contents,compound liquid nitrogen cycles and coal rank two influence factors,choice of yangquan coal anthracite and the admissible Tuan coal mine of huaibei mining coal for experimental research object,using "the loaded coal gas injection displacement gas testing system" axial flow experiments.The main research results are as follows:(1)The experiment shows that the Xanduan bituminous coal sample is easier to lose water than Yangquan anthracite and is difficult to absorb water.Liquid nitrogen fractured coal will improve the development degree of coal pore fissure and increase the permeability level of coal body,and the degree of improvement and improvement is positively correlated with the water content of coal body.The promoting effect of water on liquid nitrogen cracking coal is greater than the hindrance effect of water on gas adsorption and seepage,and the permeability increment of coal increases exponentially with water content.(2)The experimental results show that the influence law of coal seepage with different water content caused by liquid nitrogen cycle cracking: the macroscopic fracture development degree and permeability level of coal samples are positively correlated with the number of liquid nitrogen cycle,but the development degree of coal samples with higher water content is more obvious under liquid nitrogen cycle cracking.The increase of permeability increases exponentially with the increase of water content.The permeability growth of coal samples increases with the number of liquid nitrogen cycles approximately,but the average growth rate decreases slightly with the number of liquid nitrogen cycles.Within the appropriate number of cycles,the anti-reflection effect of liquid nitrogen of coal samples with the same moisture content is roughly the same at each cycle number.In the case of multiple cycles,increasing the number of cycles has limited effect on improving the permeability of coal samples,and the water content and the number of cycles do not promote each other.In the practical application of liquid nitrogen cracking technology,the appropriate number of cycles can be considered according to water content to maximize the cracking benefit.(3)Comparison of the influence of liquid nitrogen cracking on the seepage of bituminous coal and anthracite coal with different saturation degree: the permeability of both anthracite and bituminous coal samples caused by liquid nitrogen cracking increased,which was positively correlated with the saturation degree.However,the bituminous coal sample with low water saturation induced by liquid nitrogen can achieve better cracking effect,while the anthracite sample with high water saturation induced by liquid nitrogen can achieve better cracking effect.In the practical application of liquid nitrogen cracking technology,the coal samples with different liquid nitrogen cracking ranks should be selected according to the coal rank to maximize the cracking benefit.(4)Based on the experimental study of liquid nitrogen cracking in this paper and the research of related scholars,the current stimulation technology and the existing engineering practice and types are summarized,and on this basis,the direction of realizing engineering scale by liquid nitrogen cracking technology is prospected.There are 42 maps,24 tables,and 97 references in this paper.