Pressure Measurement of Coal Seam with Active Nitrogen Injection: Model and Experimental Analysis

Coal seam gas pressure is the core index of coal mine gas disaster prevention and control. Research on active nitrogen injection pressure measurement can effectively shorten the pressure measurement time and is of great significance to improve the pressure measurement efficiency. The purpose of this paper is to study the variation in gas pressure in the process of active nitrogen injection and the influence of different gas injection pressures on pressure measurement. Through the design of active pressure test device, pressure measurement experiments with different nitrogen injection pressures were carried out. The multicomponent gas migration model of active pressure measurement was constructed, and the active pressure numerical solver was developed based on OpenFOAM and C++ language. The borehole gas pressure equation was verified by field pressure data. The results show that when the injected nitrogen pressure is closer to the original coal seam gas pressure, the borehole gas pressure balance time is shorter. The gas change rate in this process depends on the pressure difference and concentration difference between the borehole and the surrounding coal. When the nitrogen injection pressure is greater than the gas pressure around the borehole, N2 will percolate, diffuse, and adsorb into the coal. In contrast, it is dominated by the desorption, diffusion, and seepage of CH4 to the borehole. The correlation coefficient R2 between the borehole gas pressure equation and the field pressure measurement data is more than 0.88. Therefore, the equation can verify the reliability of the measurement results of active gas injection pressure in the field. The research results provide a reference for further understanding the mechanism and application of pressure measurement in coal seam injected with active nitrogen.