| Gas which seriously affects the safety production of mine is an important hazard source of coal mining in China, thus making it the most important part of coal mine disaster control. But gas is also a clean and high-efficient energy. Therefore, extracting coal and gas safely and simultaneously will be China’s future development trend of colliery gas calamity prevention and environmental protection. However, as the coalbed in China is characterized by high metamorphic degree, low permeability, high gas content and great gas pressure, it is difficult to extract gas from coal seamunder natural conditions in the vast majority of the mines. Considering the pore-fissure system of coal which generates permeability is very sensitive to in-situ stress, so fully understanding in-situ stress distribution characteristics in a region and developing a system of pressure relief antireflective drainage technology have important theoretical significance and practical value on simultaneous extraction of coal and gas.This article is on the background of Fengchun coal mine belong to Songzao coal power limited liability company. On the premise of analyzing regional stress field whole Songzao mining area, 5 measuring points for in-situ stress measurement in mining area have been taken by the hydraulic fracturing tests based on the present technique adapting to mine research, combining with theoretical analysis and acoustic emission experiment, to compare and analyze the measurement results so that we can master the in-situ stress field distribution in general. Taking the general in-situ stress field distribution for this basis, through the hydraulic fracturing field test, the laboratory experiments, theoretic analysis, numerical simulation and so on, this article studies the pressure relief antireflective mechanism of hydraulic fracturing. The majority work and research achievements are as follows:① Using the MTS815 Rock Mechanice Electro-Hydraulic Servo Testing System and SHIMADZU AGI-250 servo material testing machine to make Brazilian splitting test, uniaxial and triaxial compression tests on field sampling and office operation of the specimens, we can get the basic mechanical parameters of roof and floor rock specimens of fracturing coalbed. After modifying the experimental results by Hoak-Brown strength criterion, the basic data can be provided for the simulation test.② Maximum principal stress and minimum principal stress which arevertical to the plane of borehole are measured by hydraulic fracturing in 5 experimental points of the scene. Combined the theoretical formula for calculating the vertical stress and the lateral stress of experimental points with three-dimensional crustal stress formula and orientation of the maximum horizontal principal stress concluded by acoustic emission test on the standard rock specimens, the ground stress field distribution law of Fengchun coal mine has generated. It builds a good foundation for a follow-up study of fracturing initiation pressure, crack propagation and the mechanism of antireflection of coal and rock mass.③ On the basis of theoretical analysis of stress distribution around the borehole, by studying the theory of pressure relief antireflective mechanism of hydraulic fracturing technology, we can build up the theoretical calculation model and numerical model of hydraulic fracturing, thus making the fracturing space geometric form of cracks, tensile strength and thicknessin coal and rock influence on the effectof antireflection clear.④ Analyzing and studying the inner stress of fractured borehole, influence radius of fracturing and gas drainage effect in underground mine parameters, it can be confirmed that the antireflective effect of hydraulic fracturing process is obvious. Apparently it is beneficial to gas drainage, and plays a powerful role in the safe simultaneous extraction of coal and gas. |
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