Study On Structural Evolution And Dynamic Desorption Of Coal Driven By High Temperature

High gas outburst coal seams in China are characterized by high gas,low permeability and strong adsorption.Gas extraction is difficult,it is need to adopt enhanced anti-reflection measures.Methods commonly today used to improve the permeability of coal seams include hydraulic cutting,hydraulic fracturing and hydraulic punching,but they have little effect.In this paper,the heat-driven gas desorption flow is the main line,with the aid of theoretical research,modern testing instruments and physical experiment means,the structural evolution and adsorption and desorption laws of coal under high temperature thermal action were studied from molecular level,pore level and fracture level.The following important conclusions have been drawn.(1)The evolution of molecular structure of coal was studied by infrared spectroscopy,the study found that by raising the temperature of coal,will change the composition of the molecular structure of coal.On the one hand,the high temperature thermal effect can reduce the content of hydroxyl and oxygen-containing functional groups,and cause the thermal decomposition of aliphatic hydrocarbons,which leads to the decrease of the water-bearing capacity of coal and the weakening of the gas adsorption performance.The gas generated by the decomposition can open closed pores,develop and connect pores,and improve the methane migration ability.On the other hand,improve the aromaticity of coal,reduce coal adsorption of methane,so comprehensive function leads to a decline in coal gas adsorption capacity.(2)The pore structure of coal was analyzed by nuclear magnetic resonance(NMR): It is found that increasing the temperature of coal can effectively promote pore development,and the higher the temperature,the greater the influence on pore development.(3)The high temperature heating experiment was designed,Using modern testing methods such as scanning electron microscopy,ultrasonic sonic velocity meter and Matlab,the paper makes a qualitative and quantitative analysis on the comparison of the macro and microscopic cracks of coal when high temperature is applied to the coal,The results show that high temperature thermal action can effectively change the fracture structure of coal body and increase the number and size of fractures in different amplitude.The higher the temperature of thermal action is,the larger the fracture can be expanded,and the more obvious the blocking effect of fractures on ultrasonic wave is leading to the decrease of transverse and longitudinal wave velocity.(4)The influence of desorption diffusion of coal at 25? and 80~200? were studied.The adsorption amount of two coal samples increased to different degrees after heating at different temperatures.Increasing the temperature is conducive to promoting coal desorption of gas.Finally,an engineering application of gas extraction in shallow and deep coal seams by heat injection and stimulation is put forward.Published 2 papers of core journals and apply for one invention patent during the postgraduate period.