关键词: 中低煤阶, 孔隙结构, 分段分形, 特征, 煤层气开发

Abstract: 　In order to clarify the fractal features of the pore structure of coal rock in Hancheng and Baode block, a new fractal characterization method was derived based on matchstick model. The new method was validated by scanning electron microscopy (SEM) and mercury intrusion test data. On this basis, the fractal characteristics of pore structure in medium and low coal rocks were studied. The results show that the matchstick model can more accurately characterize the dual pore structure of middle and low coal rank coal rocks. In the bi⁃logarithmic coordinate, the mercury saturation is in a bilinear relationship with the capillary pressure, that is, the pore structure of medium⁃low rank coal rocks has the fractal characteristics of sections, and the pores and cracks have different fractal intervals and fractal dimensions by the dividing line of 1 μm. The pores fractal dimension ranges from 2.80 to 2.98 and the crack fractal dimension ranges from 2.17 to 2.33 for Hancheng and Baode block. The fractal dimension of fracture for coal sample increases with the increase of the fractal dimension of pores, and both fractal dimensions decrease with the increase of average pore radius, porosity and permeability. Fractal dimension of coal rock is the key index of reservoir evaluation and can characterize the heterogeneity of its pore structure. The larger the fractal dimension is, the stronger the heterogeneity of pore structure is. The fractal dimension of cleavage and fracture is much larger than that of pore in Hancheng and Baode Block.

Key words: Low?medium rank, Pore structure, Multi?fractal geometry, Features, CBM development