The Study Of Low Permeability Coal Seam Pore Structure Fractal Characteristics And Mechanical Properties

This paper is aimed at the problems of hydraulic fracturing engineering in XinJiang low permeability coal seam, through low temperature nitrogen absorption and SEM experiments, the fractal theory is applied to study the fractal characteristics of low permeability coal seam B1~B6 coal samples; based on micro pore SEM experiments, multipoint statistical method is uesd to build the three-dimensional porous model; mainly studying the relationships between pore fractal dimensions and pore structure, micro pore structure characteristics and macro physical and mechanical properties; the researches can be applied to the hydraulic fracturing engineering of XinJiang low permeability coal seam, it is meaningful and value for the scientific research of fracturing fluid loss and gas release, the main contents are as follows:(1) The common models and application range of measurement methods are summarized, analyzing the pore distribution dimension with its value is 1~2, the pore volume, the specific surface area and surface dimensions with their values are 2~3.(2) Through low temperature nitrogen absorption and SEM experiments, B1~B6 pore structure parameters are measured then structure characteristics are analyzed; based on the pore SEM experiments, building the cylinder three-dimensional reconstruction models, whose porosities are 1.86%, 3.7%, 7.4%, 11.2% respectively.(3) Pore dimension expressions are applied to calculate the pore volume, the specific surface area and surface dimensions of B1~B6 coal samples; the relationships between pore structure parameters and dimensions are analyzed, which show that the pore volume, specific surface area and surface dimensions can better characterize the heterogeneity and complexity of the pore structure; Grey Relational Theory is applied to analyze the impact factors of all pore dimensions.(4) The porosity and permeability of B1~B6 coal samples are measured by experiments; studying the relationships between coal pore structures and macro properties; confirming that pore distribution dimensions can be used to calculate the permeability of porous media and analyzing the absorption capability of coal samples for coal gas; the numerical simulation is used to analyze the process of uniaxial compression of models and stress distributions of models rupture; studying the relationships between porosity and compressive strength, fractal dimension.