Research On Coal Gas Occurrence Characteristics Under The Influence Of Small Coal Seam Faults

With the increase of coal mining depth and mining intensity in China,the influence of geological structure on coal seam gas distribution is gradually enhanced,and the small fault of coal seam is one of the small structures widely developed in the mining working face,and the change of coal distribution characteristics in the tectonic influence area leads to the abnormal distribution of coal seam gas,which makes the abnormal change of gas outflow during the recovery process and the frequent occurrence of coal and gas power disasters,which seriously affects the safe and efficient coal mine production.Therefore,it is of certain significance to study the coal gas distribution characteristics under the influence of small coal seam faults for scientific and reasonable prevention and control of gas disasters.Based on the geological background that small coal seam faults are widely developed in Chenghe mining area,we collected samples of faulted coal rock and original coal rock under the influence of small coal seam faults of different scales and carried out the determination of basic parameters of coal samples,the results showed that the moisture and volatile matter of faulted coal samples did not change much,ash decreased and fixed carbon increased;the solidity coefficient of faulted coal samples ranged from 0.12 to 0.21,which was smaller than that of original coal samples;further determination of coal body Further determination of the particle size distribution of the coal body showed that the mass proportion of medium and small size coal particles increased,indicating that the physical properties of the coal body changed under the influence of the small fault.The pore structure of the coal body was studied by electron microscope scanning,mercury pressure test and nitrogen adsorption test,and it was found that the internal fracture and pore size of the faulted coal sample were more developed than those of the original coal sample;the pore volume of microporous and medium pores of the faulted coal sample increased,the pore volume of transition pores did not change significantly,and the pore volume of large pores decreased;the accumulated specific surface area of microporous,transition pores and medium pores of the faulted coal sample increased compared with that of the original coal sample,and the accumulated specific surface area of large pores decreased.Using gas adsorption and desorption instrument and coal core permeability measurement device to analyze the gas adsorption and desorption and permeability characteristics of coal body,it is concluded that the gas adsorption amount of fault coal sample is larger than that of the original coal sample,and the gas desorption amount of each stage is also larger than that of the original coal sample,the initial permeability of fault coal sample is lower than that of the original coal sample,and the difference between the two permeability values gradually decreases with the increase of gas pressure;with the increase of the scale of small fault of coal seam,the gas adsorption and desorption capacity of coal body,the coal permeability decreases gradually as the size of the small fault increases.By constructing a numerical model of coal seam containing small fault,we simulate and analyze the local stress characteristics of coal seam under the influence of small fault in coal seam,and the results show that the stress of coal seam on the upper plate of fault decreases rapidly with the increase of distance from the fault,then increases slowly and then stabilizes,and the stress of coal seam on the lower plate of fault increases slowly and slightly with the decrease of distance from the fault,and decreases rapidly when it is close to the fault surface,and there is a stress concentration area at the interaction of fault surface and coal seam.The stress concentration area exists at the interaction between the fault surface and the coal seam,and the peak stress gradually increases with the increase of the fault distance.The relationship between the small fault of the coal seam and the distribution of gas anomaly was obtained through the field gas content measurement,the gas content in the fault area was between 2.1197m3/t～5.6331m3/t,and the gas enrichment area was formed mainly in the upper plate of the small fault,and the influence of the fault on the gas anomaly overload distribution was enhanced as the scale of the fault increased.The research results can provide some theoretical basis for mine gas disaster prediction,coalbed methane mining and mine gas control.