Numerical simulation of gas migration tule in mining-induced fractures field

Abstract

Gas extraction practice has proved that the vast majority of the mining area in China is unfavorable use gas drainage technology such as ground drilling hole, and should use the mining-induced fractures for gas extraction. Therefore, research the gas migration rule in mining-induced fractures field above the goaf, can provide a technical support for optimizing system arrangement of pressure-relieved gas extraction, and increasing the rate of gas extraction.

At present, scholars by utilizing numerical simulation to study the gas migration rule in working face and goaf without considering the influence of the mining-induced fractures, and there have not a better simulation software which can simulate not only the space-time evolution of the mining-induced fractures field, but also the rule of gas migration. This study takes one mining face of 10th mine in Pingdingshan Coalmine Group in Henan China as the research background. Firstly establishes numerical calculation model, and uses UDEC software to calculate the evolution formation of the mining-induced fracture field. And then gets the spatial diagram by image processing method, imports it into COMSOL MULTIPHYSICS software to simulate the process of gas migration.

By combining the UDCE and COMSOL software, the gas migration rule in mining-induced fractures above goaf is numerically simulated, and the results are shown as follows: When the working face advances to a certain distance, goaf overburden gradually form a mining-induced fractures trapezoid table, and with the working face advancing, the height of the mining-induced fractures trapezoid table increased; Compare with the gas migration in the overburden matrix, the gas flow in abscission layer crack and vertical fracture of mining-induced fractures is directional, the gas enrichment area is located in the biggest abscission layer crack area in upper end of mining-induced fractures trapezoid table; When drilling for gas extraction in mining-induced fracture field, the gas concentration declines in the whole region during the process of gas drainage, and the rate of gas concentration decline faster in fractured zone, it is shown that with the gas drainage, the velocity of the gas flow in the mining-induced fracture is faster.