Microscopic Characteristics Of Coal Bodies In Thermal Metamorphic Zones Of Igneous Rocks And The Evolution Of Gas Dispersion

Coal seams will undergo different degrees of metamorphism due to igneous rock intrusion.The microstructure changes,and the adsorption and diffusion characteristics are changed macroscopically,thus changing the outburst risk of coal seam.Under the action of mining disturbance,the change of geological environment and internal energy coupling of coal body,gas-bearing coal medium will lose stability and produce coal and gas outburst.Therefore,it is of great significance to reveal the microscopic coal structure and macroscopic gas disaster-causing outburst mechanism for accurately predicting and preventing outburst disasters under the condition of igneous rock intrusion.Coal samples were collected from different positions of igneous rock thermal contact coal in the experimental area,and the characteristics of industrial components and geochemical components of different metamorphic degrees were analyzed.It was found that the intrusion of igneous rock reduced the moisture and volatile matter in coal,and increased the ash content and fixed carbon content in coal.The composition of metamorphic coal mine is mainly silicate minerals and quartz.The intrusion of igneous rock has a negative effect on the occurrence of trace elements in coal seam.The correlation analysis of multi-scale pore parameters was carried out by using scanning electron microscope（SEM）and pore-fracture analysis system（PCAS）,and the law of full pore parameters was obtained by BET specific surface area test.The results show that the large and medium pores of thermal metamorphic coal are developed,while the pore volume and specific surface area of micropores are greatly reduced,which leads to the weakening of adsorption capacity and the enhancement of desorption capacity;The continuous diffusion curve was measured by developing a precision diffusion experimental device,and the60-second gas diffusion process was divided and analyzed.The results show that the 60-second diffusion velocity curve of coal shows a negative exponential function relationship,and the V₁values from large to small are:composite metamorphic coal,power metamorphic coal,thermal metamorphic coal,normal coal.The attenuation of composite metamorphic coal is the fastest and that of normal coal is the slowest.This sort is very different from the sort of?P values.V₁is more sensitive to compound metamorphic coal;combined with the time-space evolution process of coal and the change law of pore fissure under the evolution of geological activities such as magmatic intrusion in the experimental area,the control effect of micro-structure of composite metamorphic coal on gas emission is analyzed.The results show that the high temperature dissolution of igneous rock blocks the micropores on the surface of coal matrix,and the large and medium pores are not affected.After the equilibrium pressure difference is broken by macroscopic disturbance,the free gas in large and medium pores gushes instantaneously,and the instantaneous gas release rate of composite metamorphic coal is the fastest.Finally,according to the index comparison and parameter sensitivity analysis,the composite index X=V₁/f is proposed.The results show that the coal pore characteristics,geochemical characteristics and gas emission characteristics within 5 meters from the igneous rock in the experimental area are significantly different from those of the normal coal far away from the igneous rock area.The average thermal evolution zone in the experimental area is 5 meters,and the X index of the structural composite zone in the igneous rock intrusion area increases.Compared with the?P index,the X index has better sensitivity.The paper has 38 figures,11 tables,and 87references.