Study On Mechanism Of Coal And Gas Outburst In Tectonic Regions

With the rapid development of China's economy,energy demand continues to increase.Under the current situation that coal resources still occupy a dominant position,coal mining is increasingly extending deeper,and coal seam gas occurrence characteristics become more complex.Although the state has invested a lot of energy to prevent coal mine disasters,coal mine power disasters dominated by coal and gas outburst have not decreased.The existing outburst statistical data show that most of the outburst occurrences occur in geological structural areas such as faults,folds,igneous rock intrusion,coal seam thickness and dip angle change,indicating that geological structures are closely related to outburst disasters.Therefore,in this thesis,around the key disaster-causing factors of constructing coal and gas outburst,the self-developed experimental equipment is used to carry out the adsorption deformation test of the coal under the pressure of different carbon dioxide gas,the adsorption deformation law of coal sample under stress constraint is analyzed,and the deformation model of adsorption gas of coal sample under stress is constructed.The effects of gas and stress on coal and gas outburst were discussed by conducting outburst tests of coal under different carbon dioxide pressures,different axial pressures and confining pressures.Through the test of briquette and gas outburst under low stress and different gas pressures,the energy evolution law of the outburst process under gas-driven is obtained.The specific results are as follows:(1)The characteristics of the apparent morphology,pore structure and permeability of the coal samples were analyzed.It is found that its unique structural features can store a large amount of gas and provide a fast release channel for gas,resulting in strong coal and gas outburst.At the same time,it is confirmed that the gas in tectonic regions will be released more,easier and more quickly than the non-geological tectonic regions,and serious gas disasters are more likely to occur in tectonic regions.(2)Analyze the action law of the gas on the coal body before the occurrence of outburst,and derive the adsorption deformation model of the structural coal by combining the theoretical formula.Under the constraint of stress,the isothermal adsorption curve of the structural coal to carbon dioxide gas still satisfies the Langmuir equation,and its process of adsorption deformation has three distinct phase characteristics.(3)Through the experiments of coal and gas outburst in tectonic regions under different gas pressures and different stresses,the damage characteristics of coal samples after outburst under different conditions were obtained.When the gas pressure is 2.0 MPa,most of the coal samples after the test remain intact.With the increase of axial pressure or confining pressure,the damage degree of coal samples after outburst tends to decrease.However,when the gas pressure is 2.4 MPa,the coal sample is almost completely broken after the test,and as the axial pressure or the confining pressure increases,the intensity of outburst also becomes larger.At the same time,the change of gas pressure in the outburst carven and the distribution of coal powder were measured and analyzed,and a set of analysis methods for predicting the damage of coal samples after outburst was obtained.It can be found that as the intensity of outburst increases,the pulverization effect tends to be stable.But the micronization effect of gas on coal samples increases with the increase of the intensity of outburst.(4)The outburst test of the briquette made of structural coal powder is carried out.Through quantitative calculation,it is found that while the gas carrying energy to the coal is small and smaller than the crushing energy 2 to 3 orders of magnitude.Comparing the gas expansion energy with the crushing work of the coal,it is considered that the outburst process is the result of the interaction of the free gas and the adsorbed gas.In addition,it can be found that the expansion energy of free gas is closer to the size of the crushing energy as the gas pressure increases.When the gas is increased to a certain extent,most of the coal sample can be broken only by the action of free gas.Combined with the above results,it is believed that the presence of local high gas enrichment areas and soft stratified broken coal in the tectonic regions results in the formation of coal and gas outburst mainly affected by gas.Through the characteristics of the apparent morphology,pore structure and permeability of structural coal,it can be considered that the unique structure of the coal can accumulate rich gas,which is the basis of the occurrence of outburst;The strong permeability of the structured coal can provide a quick release channel for the gas,so that outburst can continue to occur.Through the evolution law of each stage of coal and gas outburst in tectonic regions,it can be considered that in the coal mining,when the stable environment of the coal seam is suddenly broken,the high-pressure gas inside the coal seam and the low-pressure external environment form a large pressure gradient,and the unloading wave generated by the pressure gradient will instantaneously destroy and throw the coal body.When the broken coal body is thrown to a certain extent,the remaining coal body desorbs less gas,which is not enough to destroy and throw a relatively complete coal body,and outburst is terminated.