The evolution characteristics of seepage channel during water infusion in deep coal samples

In coal mining,coal seam water infusion can effectively prevent coal outburst,dust and rock burst.In order to study the evolution process of pore structure and seepage channels during water infusion in deep coal samples,the coal at the No.310130 working face of the Ji15 coal seam in No.12 Pingdingshan Coal Mine was sampled for this study.The T2 spectrum and water content distribution of three raw coal samples under different water infusion pressures were tested online by low-field nuclear magnetic resonance imaging equipment.By analyzing the T2 spectra under different water infusion pressures,the pore size distribution and pore structure evolution process of the coal sample during water injection were obtained.Through the nuclear magnetic resonance imaging technology,the visualization of the evolution of the pore structure and seepage channels during the water infusion process of coal samples was initially realized,the dynamic evolution process of the coal samples during the water infusion process was observed more intuitively,and the internal reasons for the similarities and differences of the T2 spectrum evolution process of different coal samples were more deeply understood.A method for calculating the permeability contribution of pores with different pore diameters based on the T2 spectrum was proposed,and the contribution of pores with different pore diameters to the water permeability process during the water infusion process of coal samples was quantitatively analyzed.The fractal dimension calculation of T2 spectrum was performed,and the content and heterogeneity of the seepage space of coal samples were quantitatively analyzed.The test results show that the T2 spectrum of the deep coal sample in the No.12 Pingdingshan Coal Mine shows the characteristics of three peaks during the water injection process.The content and connectivity of mesopores,macropores,and microcracks are all greater than those of micropores.In the process of water infusion of coal samples,macropores and microcracks contribute more than 99% of the permeability.The micropores and pores with poor connectivity are mainly involved in water storage rather than water transport.During the water infusion process,when the pore connectivity of the coal sample is poor and there is no obvious dominant seepage channel,increasing the water injection pressure can make more pores participate in the seepage process.However,when the coal sample has better connectivity and has dominant seepage channel,it is difficult to increase the water infusion pressure to make more pores participate in the seepage process.Therefore,it is worth noting it during the design of coal seam water infusion parameters.