| Magmatic intrusion phenomenon in the coal measure strata is widespread in the world’s major coal-producing countries. The occurrence, thickness and distribution form of magmatic intrusions have very important influence on the coal mining safety, in our country’s coal mine disasters, there are a great many of accidents caused by magmatic intrusion. The high temperature and high pressure environment built by the magmatic intrusion promotes the thermal evolution of coal seam, changes the metamorphic degree, the pore-fracture structure and the adsorption-desorption characteristics of coal, thus has control effect on the coal seam gas occurrence and the outburst disaster. This dissertation takes the Haizi coal mine of the Huaibei mining area as the research object, which is seriously influenced by magmatic intrusion, adopts the research method of combining the theoretical analysis, laboratory test, the similar simulation, the numerical simulation and the field engineering practice, systematically carries out the basic research of the thermal evolution mechanism of magmatic intrusion on underlying coal seams, the entrapment effect of the extremely thick magmatic rock bed on the coal seam gas and the fracture evolution and seepage characteristics of the unloading coal and rock under the extremely thick magmatic rock bed etc., on this basis, puts forward and practices zoning and grading comprehensive control technology on gas disaster in the magmatic intrusion mine. The main conclusions and innovation points of this dissertation are embodied in the following four aspects:(1) The mathematical model of the heat conduction effect after the magma intruded in the coal measures strata is built, by comprehensively considering the geothermal gradient, the solution of the two-dimensional heat conduction model is obtained. Through the numerical calculating by MATLAB and COMSOL and the laboratory verification method, the thermal evolution mechanism of magmatic intrusion on underlying coal seams is analyzed, the main controlling factors on the temperature distribution of the surrounding rock which influences the cooling process of magmatic rock(the cooling duration of the magmatic rock, the thickness and the initial temperature of the magmatic rock, etc.) are contrastive analyzed. The results show that: With the increase of the distance from the magmatic rock, the maximum effective temperature and the continuous high temperature duration of coal seam decrease, through the thermal history simulation, it can be known that the maximum thermal evolution temperature of No.8~10 coal seams underlying the magmatic rock in the Haizi coal mine is 258 ℃ and 228 ℃ respectively, the continuous duration of the maximum thermal evolution temperature of the coal evolution is 600 a and 500 a respectively. At the same time, combining the coal bearing formation evolution characteristics and magmatic intrusion space-time evolution process of Huaibei, the characteristics of hydrocarbon generation induced by thermal evolution of magmatic intrusion in the coal seam in the field of the Huaibei mining area are obtained, after the magmatic intrusion of the Yanshanian period, the maximum hydrocarbon regeneration of the coal seam is about 340 m3/t.(2) The entrapment effect of different thickness of the magmatic intrusions on the coal seam gas occurrence is obtained. It turned out that, with the increase of the thickness of the magmatic rock, the metamorphic degree of the underlying No.10 coal seam significantly rises, the pore-fracture degree continuously increases, thus the ability of coal seam generating, absorbing and reserving gas is enhanced. The permeability of the dense and hard magmatic rock intrusion is low, when occurrence in the coal seam roof in the form of rock bed or rock lid, a natural “gas storage tank” is formed to trap the underlying coal seam gas, and the gas trap effect performs more apparently with the increase of the thickness of the rock, making the original gas pressure and gas content of the coal seam surpass the outburst critical value, thus it is more likely to occur outburst accident under the influence of mining.(3) The dynamic evolution rule of the separation layer fissures of the overlying rock in the stope and the storage and transportation characteristics of the unloading gas after the mining of the remote protective layer(No.10 coal seam) which is under the extremely thick magmatic rock are systematically analyzed. It turned out that, under the support of the extremely thick magmatic rock, a large number of separation layers which are not completely closed in the bending zone of the overlying rock in the stope could be formed, the separation zone becomes a enrichment region of unloading gas(even groundwater), provides the theoretical basis for the selection of the efficient extraction method of long distance unloading gas. At the same time, due to the extremely thick magma rock is in a whole block structure, mechanical strength meets the requirements of the main key stratum of the mine, the caving interval calculated can be up to 332 m. However, with the increase of the mining area, after collapse and breakdown, the magmatic rock releases a great deal of elastic energy, which forms impact effect and acts on the separation space and the underlying coal seams, the impact energy can be up to, which often leads to the happen of the gas outburst, rock burst, water burst, surface subsidence etc. multivariate dynamic disasters.(4) For the difference phenomenon presented by the gas occurrence characteristics and the outburst danger degree in different regions of the mine, which is induced by the thermal evolution and trap effect of the extremely thick magmatic rock, according to the distribution form of magmatic rock, the occurrence characteristics of coal measures strata and the grade of the gas dynamic disaster, the zoning and grading comprehensive control technology on gas disaster in the magmatic intrusion mine is put forward, which is successfully applied in the field. At the same time, based on the causation analysis of the multivariate dynamic disasters induced by the extremely thick magmatic rock breakdown and impact, the concept of reasonable filling height of the goaf is put forward, under the condition of extremely thick magmatic rock occurrence, the coexist of efficient extraction of unloading gas and the goaf filling technology in the process of protective layer mining is realized, which provides technical support for the control of multivariate dynamic disasters under the extremely thick magmatic rock. |
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