Abstract: The aim of this study is to quantitatively characterize the structural changes of effective seepage channels in water infusion coal body. The structure characteristics of the coal body under various confining pressures and water infusion pressures are measured via nuclear magnetic resonance (NMR) technology. The fractal characteristics of effective seepage channel in coal body are analyzed with fractal geometry theory. The results show that the coal body with water infusion has an intertwined internal fracture-pore structure and that the pore radius distribution is diverse under the influence of different water pressures and confining pressures. The variation of large pores volume is 13.72%, followed by transitional pores and medium pores of 8.12% and 5.39%, respectively. The smallest micro pores is 2.05%. Combined with the T2C test results, when the pore radius is greater than 270 nm, it is an effective seepage channel, and the pore structure affecting the seepage characteristics of the water infusion coal is mainly concentrated in the large pores and medium pores. In the process of test, the change of fractal dimension of test and theory is small, which shows that the structure of seepage passage of coal sample has obvious fractal characteristics under different pressure conditions. At the same time, the opposite change trend of the two verifies the different significance of their respective characterization.

Key words: coal seam water infusion, NMR experiments, effective seepage channel, fractal characteristics