Mechanical Mechanism And Application Of Gas Occurrence And Migration In Coal-seam

The gas is one of the important factors in causing coal mine disasters, meanwhile being an important clean energy. The fundamental cause of frequent gas disasters is unclear-understanding to gas occurrence law, and its direct reason is that the unclear-understanding to gas migration law. In this thesis, the issue was researched by taking advantage of the theories of gas geology, rock mechanics, seepage mechanics, and numerical simulation, as well as adopting the combined research methods of theoretical analysis, numerical analysis and site testing. Based on the stress analysis with different geology pertains, we discussed the mechanical mechanism and application of gas occurrence and migration in coal-seam, and then obtained some meaningful achievements.Based on the previous research results, a mechanics explanation of the geological structure gradual control of the gas occurrence is raised in this paper. The gas occurrence is controlled by the geological structure evolution. Tectonic extrusion shearing zone and extensional rift zone is confirmed through research on the effect of the tectonic stress field in different periods for the tectonic formation and property, physical and mechanical properties of coal. Tectonic coal formed easily when the geological structure is compressed and sheared, permeability of coal seam is low, gas will be kept and enriched, and these also control the distribution of the dangerous zones of coal and gas outburst. The stress is released because of the extensional structure, permeability of coal seam is good, and gas will be escaped easily.Influence of the faults and fold structures on gas occurrence especially coal and gas outbursts at modern stress field is studied systematically. The outburst risk nearby the fault depends on the relationship between fault strike and the modern stress and the thickness of tectonic coal. When the fault strike is parallel to the maximum principal stress, it’s good for the stress release and gas escape, but gas storage conditions are good and stress concentrate at the end of fault, it’s easy to occur for gas accidents. Along with the increase of included angle between fault strike and principal stress direction, extruding shear stress concentration zone increases, and so does outburst dangerous zone. When fault strike is vertical to maximum principal stress, compression shear stress concentrates in a large scope with low permeability of coal seam, it is easy to form the large gas enrichment zone. There is the largest outburst risk in these zone. Shear stress concentration at a certain range of the anticline wings, it’s maybe the cause of the serious coal and gas outburst in this region.The method of gas content confirm by using the mine gas emission is established. The gas resources calculation method based on the gas geological map is also proposed in the paper. These have been applied in coal mine gas geological map working led by the national Energy Administration. The gas resources of22provinces (autonomous regions and municipalities) are calculated by this method, and the total quantity of the national resources are29.17trillion m3. Based on the gas-solid coupling effect model using in the coal and rock fracture process, RFPA-GAS software was used to simulate the extract process of the upper protective layer. The results proved that there is a good consistency between the numerical simulation results and the actual measurements. Coal and gas outburst will be caused easily if the tectonic failure zone is encountered, or the interlayer spacing to the protected layer is small, during the protective layer excavation. Shear failure will be caused easily at floor rock of pressure-relief and the expansion abrupt change belt during the mining, and coal and gas outbursts will be induced easily if the tectonic failure zone is encountered or the interlayer spacing to the protected layer is small. The floor of the short-distance upper protective layer is divided into4seepage zones:the original seepage zone (original stress zone)-seepage velocity and flow reduction zone (compression zone)-rapid increase zone of seepage velocity and flow (stress relief and sudden expansion zone)-stable increase zone of seepage flow (stress relief and steady expansion zone).By using of the above research results and the actual situation of the mine5#of China Pingmei Shenma Group, gas extraction and related measures are formulated during the exploitation period of the protective layers. These ensured the exploitation safety of the protective and protected layers, and obtained the high-efficient extraction both of the coal and gas.