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Directed at creating fractures and extracting methane in low permeability, high gas-outburst coal seams, this paper presents the results of a comprehensive integration trial of under panel cross strata drilling with a new coal seam stimulation technique: the Cardox system in a colliery located in a major high gas content and outburst prone coal field in the central part of China. On the basis of the coal seam parametric measurements, the precise designation of under panel cross strata borehole patterns and the arrangement of the fracturing and monitoring procedures, the advantages of the Cardox system in creating fractures and improving gas drainage efficiency of low permeability coal seams are: (1) Changing the trend of gas concentration and/or pure gas quantity over time; (2) Maintaining the uptrend of gas concentration and/or pure gas quantity in a relatively long time period, which, in the current case, is ninety days and counting; and (3) Elevating gas drainage to a higher level. Stimulation mechanisms of the highly pressurized gas system have been proposed, and based on these mechanisms, the crushing and fracturing radii created by the highly pressurized gas have been calculated and corroborated well with the field monitoring data. [ABSTRACT FROM AUTHOR]

Abstract: Most of the coal seams currently mined in the Southwest part of China have high gas content, are soft and prone to outbursts, which significantly influences the rate of gate road development and mining safety. It is believed that an outburst is mainly due to the internal energy stored in the coal seam, so it is necessary to release the energy to prevent the occurrences of coal and gas outbursts, which in turn improves the rate of gate road development. This paper presented herein discusses the usage of the waterjet slotting technique to prevent the occurrence of outbursts during gate road development, on the basis of the laboratory tests, numerical modeling and field work. The numerical modeling indicated that the internal effective stress levels can be reduced up to 70% and 45% for the vertical and horizontal stresses, respectively, when waterjet slotting is applied, and the field monitoring results showed that the gas concentration released from the face of excavation can be increased up to five times compared with the traditional borehole drainage method. As a result, the values S mix and K 1, which are determined by drill cuttings to describe the possibility of outburst occurrences, have been kept below the critical limits 70% of the excavation time and the rate of gate road development increases from 30m to 70m per month. [Copyright &y& Elsevier]

Abstract: Traditional methane drainage methods, including conventional ventilation and boreholes drilled in the coal seam, are widely used in modern coal mining operation in China. However, it is often noted that the gas drainage presents low efficiency in most coal mines due to low permeability of the coal seam, which not only affects the safety, but also the productivity of the coal mine. This paper describes the development and application of the waterjet cutting system, which is used to create artificial fractures and increase the permeability of coal seam for the improvement of methane drainage in underground coal mines in China. According to underground monitoring, a significant improvement of methane drainage efficiency of up to 3 to 6 times over the traditional methods has been achieved. [Copyright &y& Elsevier]

Nowadays, the water jet technique has been more frequently used for coal bed methane stimulation. As the ultimate component of the water jet system, the nozzle has important influence on the rock breaking ability of water jet. To optimize the nozzle, a simplified model for impinging water jet was established. The effects of geometric structure (cylindrical, conical, and conical‐straight) and parameters (outlet diameter d, conical angle α, and length L) on the flow field of the impinging water jet are simulated through computational fluid dynamics software Fluent14.0. Besides, the effects of inlet pressure (Pin) and target distances (S) on the jet dynamics are also discussed based on the simulation results. The results show that the jet dynamic parameters including dynamic pressure, velocity, and impinging pressure vary with different nozzles. The jet dynamic parameters linearly increase with the inlet pressure, while they first increase then decrease with the increase in target distance. Additionally, the optimal nozzle designed based on the numerical simulation was used in the field test, and the results indicate that this technique can effectively improve the gas drainage efficiency. [ABSTRACT FROM AUTHOR]