煤岩孔隙率与渗透率变化规律试验研究

煤岩的渗透率与孔隙率密切相关,而煤岩的应力状态对孔隙率具有显著的影响。本文基于对韩城3#、5#和11#煤的单轴和三轴压缩试验结果,根据煤岩的变形特性与孔隙率之间的关系,得出了各类煤岩在压缩条件下孔隙率随应力状态改变的变化规律;然后,利用Palmer等提出的煤岩孔隙率对渗透率的影响关系,计算得出了渗透率随煤岩应力状态改变的变化规律;通过三类煤岩计算结果的对比分析,确定了煤岩类型对渗透率随应力状态变化规律的影响。研究表明,煤岩孔隙率和渗透率随应力状态改变呈先减小然后逐渐增大的趋势,在反弹点处,煤岩的应力值为峰值强度的20%～40%;峰值强度后孔隙率随有效应力增大的速率比峰值强度前大2～3倍,并受煤岩类型的影响较大。研究成果可为煤层气工程排采过程中确定和分析渗透率的变化规律提供参考。

Experimental Research on Variations of Permeability and Porosity for Coals

Permeability is closely related to the porosity of coals, and the stress state has a significant impact on porosity. In this paper, based on the uni-axial and tri-axial compression tests to 3#, 5# and 11# coal of Hancheng mine, the variation of porosity with its stress state is obtained; and then, using the relationship between porosity rate and permeability rate proposed by Palmer et al, the variation of permeability with the stress state is calculated. Through the comparative analysis on three kinds of coals, the difference of stress state to the permeability change affected by the coal type is recognized. The research results show that the changes of porosity and permeability with the stress state, at first, decline slowly and then increase significantly, and the stress value at the rebounding point is 20%～40% of the peak strength; The increase rate of porosity with stress state after peak strength is 2～3 times larger than that before the peak. The research results can supply some references to analyze and determine the permeability change in the process of production for coalbed methane work.