| Mine gas is not only the main hidden danger of safety production, but also is an efficient clean energy, gas control has been the focus of various coal enterprises and research institutes. Development of gas drainage method is becoming more and more mature, there are two standards to judge effect of coal seam gas drainage,one is the energy provided by internal or external to gas molecules to break free from the adsorption of coal matrix, the second is the external mechanical action to promote the development of fissures of coal, and original crack formation of fracture network, and provide the circulation channel for gas migration. Based on this principle, the relatively mature technology is hydraulic fracturing, the principle is using the fracturing fluid inject into the coal, and ensure the fracturing fluid flow rate greater than coal filter loss rate, and the pressure is greater than minimum weak tearing stress required for, and quartz sand proppant continued support crack channel, ensuring the sustained development of the fracture network.The subject of the study of ground shaft fracturing technology strengthens the antireflective effect, ground drilling fracturing and hydraulic fracturing cooperate with each other, not only can be taken before unloading pressure to increase permeability and increase coal seam permeability performance, and has a good effect of preventing rockburst of working face and recovering extraction.so as to achieve with one well has three purposes and comprehensive utilization of objective. This topic based on Yuwu Coal S2107 shaft hydraulic fracturing engineering practice, combined with related theoretical research, numerical simulation and laboratory verification means to research shaft hydraulic fracturing technology, specific research work includes the following aspects:(1) Analyse the failure types of ground drilling, and analyse the changing law of the main section of the surface moving basin. The paper focus on the shear failure which has greatest impact on the gas effect. Explanation of the "S" shape deformation mechanism of the well body from the angle of horizontal displacement and the stress of rock stratum. From perspective of horizontal displacement, the start time of the horizontal movement of the upper and lower strata in the well, the velocity change rate and the maximum horizontal displacement are the main reason of "S" shape deformation. From the angle of stress, the paper establish the shear failure beams with web model, let formation in complex mechanical analysis attributed to simple rock beam structure analysis, under the random medium and probability integral method and analyse failure mechanism of layer at the surface of the drilling, given displacement equation of drilling micro sections. Analysis the impact of thickness, elastic modulus, strength of interface of the upper and lower strata to horizontal movement. Using numerical simulation software Midas to simulate these conclusions, and the simulation results consistent with theoretical results. The stability of drilling is analyzed, and the reinforcement measures are given.(2) Analysis of the mechanism of hydraulic fracturing in vertical shaft. Analysis of the initiation and propagation mechanism of hydraulic fracturing. When the total stress is larger than the tensile strength of the weak plane, the crack starts to crack. The initiation direction is related to the size of the earth stress. The migration characteristics of fractured water in coal seam are analyzed. The hydraulic fracturing make gas migration channel full growth and change trend of gas flow, the role is positive. When the fluid flow pattern is non Darcy and nonlinear, the water can increase the pressure gradient of gas flow, restrain gas desorption and occupy the gas molecular diffusion channel, the role is negative.(3)The seepage law of coal samples with different water content under stress conditions is studied by means of the electro-hydraulic servo seepage test device. The change rules of permeability and seepage velocity of given coal samples with different moisture content under the condition of varying confining pressure are nonlinear decreasing, which have high fitting degree with quadratic polynomial. The decreasing trend of low water content coal sample(<1%).along with the increase of the moisture content of coal, also has high fitting degree with negative power function, the fitting curve equation is k = a2-, a, b are fitting coefficients. With the increase of effective stress, the permeability and seepage velocity of coal sample has a trend of nonlinear decreasing. The trend of change has high degree of fitting with quadratic polynomial, the equation is y = a2+ + , a, b, c are fitting coefficients.Under the condition of the same effective stress, the permeability and seepage rate of low moisture content coal sample decreased significantly, another word, the low water content coal sample permeability has higher sensitivity to the effective stress. The permeability nonlinear decreases with the water content, and the decreasing rate decreases gradually, and have high degree of fitting with quadratic polynomial. The negative effect of water content on gas migration in coal is proved.(4) S2107 work surface of Yu Wu coal mine carried vertical well hydraulic fracturing engineering practice, given hydraulic fracturing design and construction scheme, given shaft hydraulic fracturing effect assessment program, analyze shaft fracturing antireflective effect by borehole drainage data.(5) The effect of shaft hydraulic fracturing of Yu Wu Coal Mine’s S2107 Face were assessed in order to provide standardized solutions for Yuwu coal mine’s other Face fracturing. By analyzing the flow of single drill gas within the range of fracture zone 1-52,1-54 and non-fracture zone, result showed that within the influencing range of 1-52 drilling extraction rate is significantly higher than the non-fracturing zone, and the maximum increase of 7.3 times and 3.7 times the minimum raise. Within 1-54 fracture influencing area, the effect of extraction of measuring point from 1-54 zone 87 m and 42 m did not change significantly, however extraction effect of the other measuring point is obvious,and the biggest increase 9.2 times and the minimum two-fold increase. In general, Yuwu Coal Mine’s S2107 Face fracturing effect is obvious. Throughout the observation period, by analyzing the change of the hole gas flow along with extending distance, it is determined that during the entire 50 days two fracturing shaft impact on different points’ s degree, moreover analysis indicated radius of influence of fracturing shaft 1-52 is between 85 and 100 m and radius of influence of fracturing shaft 1-54 is between 39 and 42 m. |
PDF Full Text Request