煤中CH4渗透率估算方法研究

煤体内部气体流通路径主要由裂隙和孔隙构成，是典型的双重气路结构。为便于量化不同尺度气路的气体传输视渗透率，一般采用单一气路的孔隙或裂隙气路结构来建立渗透率数学模型。随着微结构表征技术的发展，对煤体内部裂隙和孔隙结构的表征更加精确，基于单一气路建立的渗透率模型显然不够精确。因此，本文将微米级气路结构简化为裂隙和孔隙两种形态，运用高精度CT技术获取孔隙、裂隙结构在总气路中的体积占比，即孔隙率、裂隙率；将参数代入渗透率统计分布模型，进而求得孔-裂隙整体视渗透率；将基于单一气路结构的孔隙视渗透率、裂隙视渗透率和双重气路结构的总视渗透率计算结果进行比较分析。结果表明:裂隙视渗透率会高估实际视渗透率，孔隙视渗透率会低估实际视渗透率，孔-裂隙双重结构视渗透率处于二者之间。从单一气路结构与双重气路结构的视渗透率计算相对偏差均值来看，基于孔隙气路的视渗透率相对偏差均值都未超过50 %，更接近于实际双重气路结构的视渗透率。

Study on estimation method of methane permeability in coal

The gas flow path in coal body is mainly composed of slits and pores, which is a typical dual gas flow path structure. Generally, in order to quantify the apparent permeability of gas transport in different scale flow paths, mathematical models of permeability are established using the pore or slit structure of single flow path. With the development of microstructure characterization technology, the characterization of slits and pores in real coal is more accurate, and the permeability model based on single flow path is obviously not accurate enough. Therefore, in this paper, the micron scale gas flow path is simplified into two geometric forms of slit and pore. High-precision CT technology is used to obtain the volume proportion of pore and slit structure in the total gas flow path, namely pore porosity and slit porosity. Then, the parameters are substituted into the statistical distribution model of permeability, and the overall apparent permeability with slits and pores is obtained. Finally, the calculation results of apparent permeability of single flow path pores-based model, slits-based model and the dual flow path pore-slit-based model are compared and analyzed. The results show that the slit-based apparent permeability model overestimates the actual apparent permeability, but the pore-based apparent permeability model underestimates it, and the mixed pore-slit-based permeability is in between. From the mean value of relative deviation of apparent permeability calculated for single gas path structure and dual gas path structure, the mean value of relative deviation of pore-based apparent permeability is no more than 50 %, which is closer to that of the real dual flow path pore-slit-based apparent permeability.