| It is of great significance to pay attention to coal and gas outburst in coal mining for coal mine safety mining,and tectonic coal often exists in coal and gas outburst sites.Drilling gas is relatively easy to measure during mining.Therefore,it is of great significance to analyze the gas emission from structural coal drilling.In this paper,according to the difference between the properties and occurrence conditions of primary coal and tectonic coal,combined with the gas desorption characteristics of two kinds of coal at home and abroad,the gas emission characteristics of tectonic coal borehole are deduced,and the numerical simulation and field test are carried out.By analyzing the gas desorption law of native coal and tectonic coal at home and abroad,it is proposed that there will be great difference in gas emission during drilling.In order to further understand how the two types of coal affect the initial gas emission from boreholes,industrial analysis,X-ray fluorescence analysis,infrared spectroscopy,scanning electron microscopy,mercury injection and low-temperature liquid nitrogen adsorption experiments were carried out on coal samples.The main ash components of coal samples almost have little change,mainly S,Al and Si elements.The chemical elements of coal under tectonic stress change less,and the Ga element in primary coal is much higher than that in tectonic coal.Tectonic coal is subjected to tectonic stress,and some pores are blocked by broken particles,which affects the normal migration of gas in coal.The critical pore size of tectonic coal is smaller than that of primary coal.The primary coal pores are mainly concentrated in micropores,and the proportion of mesopores and macropores is small.Tectonic coal pores are mainly concentrated in small pores,and the proportion of mesopores and macropores is much larger than that of primary coal.The fractal dimension of tectonic coal is larger than that of raw coal.The pore structure is complex and the pore surface is rougher.The finite element software is used to establish the model of borehole containing tectonic coal in the coal body of single coal(only primary coal)and primary coal,and the derived control equation is used to modify the simulation.Through simulation,the laws of borehole gas,coal and rock properties and drilling depth are obtained : the initial gas emission increases with the increase of drilling depth,while the growth rate of gas emission decreases with time,and it will approach a certain value when the drilling depth is long enough;The initial gas emission of borehole is also affected by coal / gas properties.In the model of primary coal containing tectonic coal,there will be an abnormal area of borehole gas emission in the tectonic coal area.The instantaneous gas emission is more than two times higher than the normal level.When the drill pipe passes through the tectonic coal and returns to the primary coal curve,it will return to the normal level,but it is slightly improved compared with the previous part.The continuous flow prediction system was used to test the gas emission of boreholes in a mine in Henan Province.The correctness of the gas emission law of tectonic coal boreholes was verified by gas curve and later mining.And the range of tectonic coal is judged by the abnormal area of gas curve,which puts forward the basis for coal mine safety mining by predicting tectonic coal with rotary hole gas emission. |
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