Multi-scale Characterization Of Mesopores Of Liulin Coking Coal Under The Long-term Effect Of Stresses And Gas

The mining technology of coalbed methane resources in soft and low permeability coal seams in China is still imperfect.This not only restricts the industrial development of coalbed methane in China,but also poses a huge hidden danger to the safety of coal mines in China due to the serious problems of coal and gas outburst.In order to better extract the gas resources in this part of the coal seam and clarify the reasons for the formation of the soft and low permeability characteristics of the coal seam,it is necessary to study the gas storage mechanism and influencing factors of the coal microstructure.This thesis mainly takes China’s Shanxi Liulin Coking Coal as the main research object.Through in-depth study of Liulin Coking Coal’s pore structure in coking coal under the combined action of gas atmosphere and triaxial stress for a long time The evolution law qualitatively describes the evolution and characteristics of the gas pore structure of coking coal after the combination of gas atmosphere and triaxial stress.The quantitative characterization of multi-scale pore cracks in coal reservoirs is carried out,and the multi-scale pores of coal reservoirs in China are analyzed.Due to the influence of fissures,Zhaming understands the mechanism of coal reservoirs affected by gas and triaxial stress control evolution,which is conducive to fully understand and study the evolution and laws of coal reservoir pore fissures in China.Provide a theoretical basis for the cause of soft low permeability coal seam The theoretical analysis of gas safety prevention in coal mines is given from a micro perspective.The following are the main research results and understanding:(1)A microporous fissure characterization system of Shanxi coking coal reservoir was constructed,which was directly measured by low-temperature liquid nitrogen adsorption and high-pressure mercury intrusion test,combined with scanning electron microscope SEM and micro-CT scanning for three-dimensional reconstruction and mathematical fractal dimension.Clarifies the difference between the long-term effect of adsorbed gas and non-adsorbed gas on the microstructure of coal;(2)Through the low-temperature nitrogen adsorption experiment and mercury intrusion experiment,it was found that the gas and triaxial stress affect the internal pore shape,specific surface area and pore volume of the coking coal,thereby changing the adsorption and permeability of the coking coal.It is experimentally measured that the specific surface area of the Shanxi coking coal sample after the non-adsorbed gas helium and the triaxial stress are reduced,and the pore volume is increased;the pore shape of the Shanxi coking coal sample is complicated by the adsorption gas nitrogen and the triaxial stress.The specific surface area increases and the pore volume decreases.(3)Observe the changes of micro-nano pores on the sample surface through SEM electron microscope,and further clarify the main influencing factors of the micro-pore structure of the coal body.The comparative experiment found that the triaxial stress is the main influencing factor of the micro-pore structure of coking coal.Gap pressure is a secondary influencing factor,and gas adsorption promotes the influencing factors,aggravating the influence of both on the microscopic pore structure of coal.(4)Intuitively reveal the influence of adsorbed gas and non-adsorbed gas on the spatial structure of coal,CT scan and three-dimensional reconstruction of Shanxi coking coal samples,reducing the coking coal under the long-term gas atmosphere and triaxial stress,the change process of microscopic pores has refinedly characterized the influence of gas atmosphere and triaxial stress on the microscopic spatial structure of coal.(5)The adsorption gas mainly affects the micropores and small pores in the pore structure of coking coal,because the nitrogen atmosphere has a significant influence on the specific surface area of the coking coal under triaxial stress;The visible holes have an effect because the helium atmosphere and triaxial stress have a greater effect on the pore volume.There are many mines with high gas outburst in China,mainly distributed in soft and low permeability coal seam area.The research results of this paper can be used as a reference for the research on the prevention and control of gas disasters,gas outburst and coalbed methane extraction mechanism of this type of coal seam.