Study On Gas Difference Mechanism Of Coal And Gas Outburst Coal Seam In Luling Coal Mine

Coalbed methane is present in the coal body.Understanding the gas distribution of the coal seam is meaningful for the safe production of mines and the efficient use of resources.In general coal seam gas content gradually increases with depth,with seam gas content was positively correlated with depth.Luling Coal Mine is a typical high gas outburst mine in China,However,the main coal seam in Luling#8,#9 shallow depth seam has a larger content of gas,coal seam gas content in#10 is less than the deep shallow coal seam.This paper takes 8#,9#and 10#coal seams of Luling Coal Mine as the research object,and analyzes the factors affecting the gas content of coal seams.The main conclusions are as follows:（1）The comprehensive regional structure,geological structure and gas occurrence conditions analyze the factors affecting the occurrence of coal seam gas,from the aspects of overall structural control,sequence stratigraphy,carbon isotope of coal seam,distribution of mine structure,storage conditions of caprock and aquifer.The regional tectonic activity controls the structure of the entire mine,so that the 8#and 9#coal seams are more seriously affected by the structure,and the 10#coal seam is lighter;According to the marking layer,the three main coal seams are divided into two sequences,which are composed of the transgressive system domain and the high water system domain,and the 8#and 10#coal seams are at the top of the sequence transgressive system domain,and the overlying strata are mudstones formed by sedimentation in the high-water system domain,but the top of the 10#coal seam in sequence I is partially sandstone;Carbon isotope measurements showed that the carbon isotope value(δ¹³C)of each layer of coal samples was-24.29‰^-23.91‰,which was not significantly different from other coal mines in Huaibei,and all belonged to C3 type coal-forming plants;According to the structure the Luling coal mine is divided into three sections,but in general,the geological structure is extremely complicated in the shallow part and simple in the deep part;From the sealing conditions of the cap layer,the 10#coal seam is worse than the 8#and 9#coal seams;The top and bottom plates of each coal seam are all sandstone fissure aquifers.The aquifer is mainly stored without other recharge,but the Taiyuan Formation limestone aquifer may have some hydraulic connection with the 10#coal seam sandstone aquifer and provide recharge.（2）The pore structure analysis of coal samples was carried out by combining liquid nitrogen adsorption experiments and scanning electron microscopy.The results of liquid nitrogen adsorption experiments show that:The adsorption and desorption isotherms of the three coal samples are similar,and the hysteresis loop of the 10#coal seam sample is less obvious,indicating that the pore connectivity of the 10 coal seams is poor;From the perspective of micropore pore size distribution,the distribution range is 8#>10#>9#,but the peak value of coal seam of 9#coal seam is higher,indicating that the pore development degree is good;8#,9#coal seams appear small peaks around20nm,indicating that 8#,9#coal seams develop pores at the pore size;From the perspective of microporous pore volume,the coal sample with small particle size has a large pore volume,indicating that the pore size makes the pore volume development better;from the specific surface area,the specific surface area of each coal seam is significantly correlated with the pore volume of micropores,the BET specific surface area of the size of 0.074⁰.2mm coal samples in each coal seam is several times larger than 1³mm coal samples;From the point of view of fractal characteristics,the degree of irregularity of the pores is 8#>9#>10#.Scanning electron microscopy（SEM）observation shows that the 8#coal-like fissures are basically in the same direction,and the fissures are relatively closed;the main fractures of the 9#coal samples are in the same direction,secondary cracks are developed,and the pore structure is obvious and not filled;The crack direction of the 10#coal sample crosses,and it develops well and has good openness.（3）Combined with isothermal adsorption experiments,120min desorption experiments and Fourier transform infrared spectroscopy（FTIR）,the adsorption and desorption characteristics and surface functional group structure of coal samples were analyzed:The isothermal adsorption curves of all coal seams are in accordance with the Langmuir equation.The relationship between the adsorption capacities of each coal seam is 8#>9#>10#.The smaller the coal sample size,the stronger the adsorption capacity;The cumulative gas desorption curve is a monotonous increasing trend with decreasing increments.The higher the pressure,the larger the desorption amount,and the longer the desorption time,the less the desorption amount per unit time.From the120min desorption curve,the higher the pressure,the larger the adsorption amount,and the smaller the particle size,the larger the adsorption amount.The isothermal adsorption curves of all coal seams are in accordance with the Langmuir equation.The relationship between the adsorption capacities of each coal seam is 8#>9#>10#.The smaller the coal sample size,the stronger the adsorption capacity.From the perspective of the proportion of oxygen-containing functional groups,the 8#coal seam is 61.9%,the 9#coal seam is 62.3%,and the 10#coal seam is 64%.In general,as the depth of burial increases,the proportion of oxygen-containing functional groups in each coal seam increases.Hydrophilic oxygen-containing functional groups inhibit gas adsorption,that is,as the proportion of oxygen-containing functional groups increases,the ability to inhibit gas adsorption by coal is stronger.