Study On The Gas Geological Law And Classification Control Of Coal And Gas Outburst In Xinyi Coal Mine

In China,coal and gas outburst has become the biggest obstacle to the health and safety of coal industry.In Xinyi Coal Mine,because of the influence of geologica l tectonic movement,the thickness of coal seam changes dramatically,gas exists differently,and the strength of coal body is extremely low,which makes the gas control work in the mine severe and complicated.Therefore,it is important for the gas control work of Xinyi mine to establish a gas control system for different outburst risk levels.This paper from nature of coal body and geological factors and combined with outburst examples to analyzes the control factors and Gas Geological Occurrence Law of coal and gas outburst in Xinyi Coal Mine.On this basis,the gas classification control system based on AHP-Fuzzy Probability Comprehensive Evaluation Method is established and its effect is tested.The main conclusions are as follows:?1?In Xinyi Coal Mine,the firmness coefficient of the only minable coal seam2₁#is between 0.19 and 0.30,the damage degree of the coal body is IV-V,and the?P is between 20.75 and 27.27mmHg,which has the coal conditions for outburst.The results of industrial component measurement of coal indicate that the geologica l structure does not change the metamorphic degree of coal,but the ash content of coal in different areas of coal seam thickness is obviously different,which can be used as an auxiliary index to judge the thickness of coal seam.Based on the observation of the pore structure characteristics of the micron level surface of coal,it is found that 2#coal samples have the most developed fissures,and the micron level large pores can be seen on the surface,and the opening of pores is good.3#coal samples have the most flat surface,and the fracture width is smaller when the magnification is 1000 times,which indicates that the pores and fissures are more developed when the coal seam is thinner under the influence of geological structure.In the N₂ and CO₂ adsorption experiments of coal,the desorption curves of three kinds of coal samples all have obvious H4 type hysteresis ring,and the desorption curves all appear sudden drop,which shows that the pore structure of the 2₁#coal in the micropore and micropore stage is open and the pore structure is mainly the narrow neck bottle type pore and contains a certain amount of layered slit pores.In the quantitative analysis of pore volume and specific surface area distribution of three coal samples,the pore volume of 1#and 2#coal samples is larger than that of 3#coal samples,the specific surface area,BET specific surface area and S_D-R surface area of 2#coal samples are the largest,and the data of 3#coal samples is the smal est,which shows that the development degree of pore in 2₁#coal seam increases with the decrease of coal thickness.The test results of coal adsorption and desorption performance show that the limit gas adsorption capacity is 2#>1#>3#,and the limit gas desorption capacity is 2#>1#>3#.Therefore,in Xinyi Coal Mine,the gas adsorption capacity and desorption capacity of the coal with thinner thickness are greater than that of the coal with thicker thickness.?2?Xinyi Coal Mine is located in the south central part of Xin'an Coal Field and the deep part of the north wing of Xin'an inclined syncline.The mine stratum belongs to stratigraphic minor region in Mianchi,stratigraphic subregion in western Henan,and stratigraphic region of Shanxi,Hebei,Shandong and Henan,stratigraphic major region in North China stratum area.21#Coal seam is a large part of minable coal seam,with floor elevation of-200m to-620m and buried depth of 580m to 960m.The dip angle of coal seam generally varies from 6°to 10°.The thickness of coal seam is 0m to15.47m and the average is 4.81m.Under the dual action of NS compressive stress in Indosinian and NW-SE structural stress in Yanshanian,the small undulation or secondary fold in the mine is relatively developed,and the fault structure is mainly NW and SN normal fault.After analyzing the control effect of geological factors such as buried depth,structure,coal thickness and coal quality on coal and gas outburst,it can be determined that structure is the main control factor of coal and gas outburst,which controls the uneven distribution of coal seam thickness and local stress concentratio n in the mine field,and leads to the differential distribution of gas content in the mine.Buried depth and coal seam thickness are the control factors of coal and gas outburst,but the mine is still in the first mining area,the change of coal seam buried depth is within 100m,so the importance of the buried depth should be ranked after the change of coal seam thickness.The change of coal thickness is the specific manifestation of geological structure in Xinyi Coal Mine,the area of coal seam thickening is not only the gas bag with high gas content,but also the area of structural stress concentratio n,so the area of coal seam thickness increase is the focus of gas control work.According to the analysis of the outburst data of each mine in Xin'an coalfield,in the geologica l unit of Xin'an coalfield,the initial outburst vertical depth is 290m.In the outburst coal quantity,small outburst accounts for a large proportion of 66.7%,and the outburst place mostly occurs in the driving face.Most of the outburst types are extrusion and outburst,and only two times of the pour out.All of the outbursts occur in coal seam thickening area,while the thickness of the coal seam decreases occurs extruding,which shows that the thickness of the coal seam has a crucial impact on the outburst of the coal field.?3?The self nature of 2₁#coal seam in Xinyi Coal Mine indicates that the risk of coal outburst in the area with thinner coal seam thickness is higher,while the actual outburst cases and geological factor analysis indicate that the risk of coal outburst in the area with thicker coal seam is higher than that in the area with thinner coal seam thickness.Therefore,for Xinyi Coal Mine,the self nature of coal is not the decisive factor of coal and gas outburst.Through comprehensive analysis and selection of 8main control factors,such as geological structure,coal seam buried depth,coal thickness variation coefficient,original gas content,original gas pressure,dynamic phenomenon,cuttings desorption index?H₂,initial velocity of gas emission from boreholes q,and initial velocity of gas emission?P,a gas governance classification model based on AHP-fuzzy probability comprehensive evaluation method is established.The coal and gas outburst risk level is divided into three levels from low to high:Level I,level II and level III.According to different outburst risk levels,the design standard,construction standard,acceptance standard and effect inspection standard of corresponding gas control measures are studied to form gas control closed-loops.?4?According to the AHP-fuzzy probability comprehensive evaluation model,it is determined that the 11090 working face belongs to the class III outburst risk working face,Therefore,the gas in the mining area is pre drained by using the floor roadway through layer drilling combined with the hydraulic drilling to increase the permeabilit y,and the gas in the mining area is pre drained by using the borehole along the layer as the auxiliary control measures.Through tracking the drilling construction of the working face and comparing with the design scheme,it is found that all the drilling holes in the area from the cutting to 520m of the working face constructed strictly according to the design,and the holes arranged evenly,and no blank area be left for treatment,which conforms to the design regulations.In addition,the average amount of coal produced by hydraulic drilling in the area from cut to 520m reaches 1.23t/m,exceeding the standard of 1.0t/m.The total amount of coal produced accounts for 3.17%of the control coal,which exceeds the standard of 2%.The calculated residual gas content of each evaluation unit from the cut of 11090 working face to 520m is 2.33-5.05m³/t,which meets the requirement that the calculated residual gas content is less than 6m³/t.the measured residual gas content is 2.06-5.88m³/t,and the residual gas pressure is 0-0.22MPa,which is less than the critical value.The sensitive indexes of working face during mining are tracked and measured.The measured maximum value of the desorption index of drilling cuttings is 160pa,the maximum value of the init ia l velocity Q of the gas emission from the drilling hole is 2.28l/min,the maximum value of the drilling cuttings S is 3.2kg/m,which are less than the critical value specified in?The Detailed Rules for Outburst Prevention?.And no other abnormal conditions are found during the measurement process.According to the measured data of the gas concentration in the return air roadway of the working face,the gas concentration in the return air roadway is not more than the critical value of 1%from November to December,and the working face has been mined safely.Finally,it is determined that the gas classified control measures are safe and reliable,and the expected control effect is achieved.