Fractal characteristics of pores and microfractures of coals with different structure and their effect on permeability

The characteristics of pores and fractures in coal are the basis to study permeability. In this study, the micro-pores and fractures of coal samples with different structure taken from Guojiahe coal mine were analyzed using mercury injection experiment and scanning electron microscope. The micro-pores and fractures of intact coal and cataclastic coal samples were quantitatively analyzed by using Menger sponge and box-counting dimension. The comprehensive fractal dimension was calculated by pore volume weights. Based on fractal theory, the relationship between fractal dimension of coal samples and coal permeability have been discussed. The results show that brittle deformation adds complexity of pores, fracture pores, seepage pores and microfractures, while the deformation uniforms the structural characteristics of adsorption pores. Micro-fracture dimension has a nonlinear relationship with permeability. The cataclastic coals deformed by brittle deformation have the suitable ratio of fractal dimensions of pores and microfractures determine their high permeability. Thus, cataclastic coal deformed by weak brittle deformation at fault, syncline and anticline are favorable to gas extraction.