A method of rapid determination of gas pressure in a coal seam based on the advantages of gas spherical flow field
2017
Abstract The gas pressure of a coal seam is one of the important parameters for studying gas reserves, law of gas flows, gas emissions, predicting coal and gas outburst risks and developing gas-control measures. In this study, the effects of the depth of the borehole drilled in a coal seam on the time required to determine the gas pressure and its value were discussed. Accordingly, elastic-plastic mechanics were applied to analyze the variation in the stress around the borehole, and the effective flow radii expressions of the spherical and radial flow boreholes were derived. The COMSOL Multiphysics numerical simulation software, was used to simulate the gas-flow range of the boreholes drilled at different depths in a coal seam, which were exposed for approximately 2 h. Finally, the boreholes of different depths was used to determine the gas pressure of No. 二 2 coal seam in the Xuehu coal mine (Henan Province, China). The results show that the time required in measuring the gas pressure is longer for boreholes drilled to a greater depth in a coal seam. For the same exposure times, the determined gas-pressure value will be smaller. Furthermore, the confined water and fractures in the roof and floor of the coal seam can be sealed by injecting high-pressure slurry into the borehole, which provides a reference for determining the gas pressure of the coal seam quickly under different geological conditions in future studies.
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