Pore fractal model applicability and fractal characteristics of seepage and adsorption pores in middle rank tectonic deformed coals from the Huaibei coal field

Middle rank tectonic deformed coal samples were screened from the Xutuan and Qinan coal mine in the Huaibei coal field, Anhui Province, North China. Based on mercury injection capillary pressure analysis and nitrogen sorption experiments using the Brunuaer-Emmett-Teller analysis, pore structure characteristics and applicability of the Sierpinski, Menger, Thermodynamics, and Frenkel-Halsey-Hill models for seepage and adsorption pore description were analyzed, as well as the fractal characteristics of the two types of pores. Several conclusions have been achieved. 1) The Sierpinski model can characterize the heterogeneity of seepage pores in tectonic deformed coals, and the thermodynamic model can be used for referencing and comparative analysis. The Frenkel-Halsey-Hill model can be used to describe the heterogeneity of adsorption pores, and the Sierpinski model can be a supplement. However, the Menger model is not suitable for characterizing the pore heterogeneity of coal because its fractal dimension exceeds three, and the standard deviation is larger than the others. 2) The fractal dimension of adsorption pores increases while seepage pores decreases, with the enhancement of tectonic deformation. The heterogeneity of adsorption pores in the cataclastic, schistose and scaly coals are weaker than that of seepage pores (Ds2Ds1).