| In the new situation, the development of coal industry in China is facing a severe challenge. The state attaches great importance to the work of coal mine gas control, there is great technical bottlenecks and difficulties in coal mine gas extraction. According to statistics, more than 95% of the country's high gas and gas outburst mine mining coal seam belongs to low permeability coal seam, the permeability in 10-3~10-4md. The influence of mining gas extraction scope is very small, the attenuation speed and extraction difficult. However, mining technology can not effectively solve the problem of efficient extraction of low permeability coal seam now, the direct cause of mine gas extraction efficiency is low, and led to the "pumping, mining and excavation" imbalance.In order to control gas, low permeability of high outburst mine have to invest a lot of manpower, material and financial resources for gas drainage, but due to the lack of extraction technology breakthrough, or struggling to develop mine, or is due to drainage not thoroughly cause gas overrun frequent, serious security risks, gas accident frequency and a serious threat to coal mine production safety.Therefore, coal seam gas drainage can not only effectively solve the problem of gas disasters, but also conducive to the utilization of gas as an energy source, can reduce greenhouse gas emissions, to achieve the purpose of environmental protection. Due to the understanding insufficiency to the change mechanism of the coal seam parameters in the process of extraction, therefore China's coal seam gas drainage effect is not ideal. The physical simulation experiment system of multi-field coupling of coal seam gas extraction developed by Chongqing University was used to simulate the different conditions of coal seam, different gas conditions and different extraction methods.Through the analysis of evolution law of coal seam parameters in the process of gas extraction, so as to reasonably provide the basis for the mining work in the field of gas extraction. The main results are shown as followed:(1)In the process of gas extraction, coal seam gas pressure in the early decreased fast and in late decreased slowly; in each stratification plane, vertical surface and section, the gas flow is large where close to borehole; the stress concentration zone and primitive area that less affected by mining with relatively low permeability in the gas extraction process, the gas pressure decreases slowly, extractiion is difficult;(2)The influencing factors of coal seam deformation include stress, drainage area, drainage time and coal seam gas pressure. At the early stage of extraction, the coal seam deformation rate is larger; the deformation of coal body ?1 direction is generally greater than ?2 and ?3 direction; because of the Poisson effect caused by coal deformation limit deformation of coal body that far from extraction place; The gas pressure in coal seam is bigger, the faster the rate of deformation of coal seam, the gas pressure in the reduced and stabilized after the coal seam deformation reaches a steady state;(3)Coal seam methane desorption endothermic leads to the temperature drop and temperature and gas flow rate has a good correlation. These parametersare shown decrease rapidly at early stage and decreased slowly later, the decrease of temperature with time logarithmic function relationship; from drill hole near the gas desorption velocity and temperature decreased more quickly, the greater the temperature gradient and the vertical direction is greater than the parallel direction of drilling; initial gas pressure increases, the desorption rate of gas and coal temperature drops more quickly, the temperature decrease is greater, gas desorption speed and temperature decreased more slowly, the initial gas pressure is more significant effect on the stress of coal seam temperature desorption process. |
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