Study on Fracture and Seepage Pore Fractal Characteristics of Tectonic Coal

The pore-fracture system of tectonic coal has control function on coalbed methane adsorption, migration and gas outburst. Based on microscopy and mercury testing of 12 different types of tectonic coal from Zhuxianzhuang Coal Mine in Huaibei Coalfield, pore system and fracture system and the relevance of both were studied by fractal method. Results showed that micro fracture information dimension of samples in study area distributed from 1.2 to 1.9, fractal dimension of pore system distributed from 2.6 to 3.0; with the increase of coal deformation degree, micro fractures fractal dimension D_l increases linearly, seepage pore fractal dimension D_k has little change in the brittle deformation stage and decreases linearly in brittle-ductile and ductile deformation stage. When D_l increases, pore volume and specific surface area increased exponentially, and average pore diameter of seepage pore reduced; seepage holes develop rapidly, and permeability increases. With the increasing of fractured fractal dimension, pore fractal dimension decreases in parabolic form; taking D_l=1.6 as the boundary point, deformation environment can be divided into brittle deformation environment (D_l＜1.6) and brittle-ductile/ductile deformation environment (D_l＞1.6) according to microscopic fractal dimension.