气体压力降低对煤岩变形和渗流的影响机制

Influence mechanism of gas pressure reduction on coal deformation and seepage

为探究瓦斯抽采过程中压力降低引起的煤岩变形和气体渗流行为,基于气体压力降低的渗流试验及三轴压缩试验,得出煤岩变形和渗流变化特性;考虑吸附损伤修正基质收缩变形,构建煤岩渗透率模型,并用试验结果验证模型的合理性。研究结果表明:随气体压力降低,煤岩渗透率呈现出“V”型变化趋势,轴向变形和径向变形线性升高,且通入CO_(2)的煤岩比通入CH_(4)的煤岩变形更大,径向变化量是轴向变形量1.89倍;通入CO_(2)煤岩的弹性模量、峰值主应力差比通入CH_(4)的有不同程度降低;为保证安全生产,使用CO_(2)驱替或CO_(2)致裂增透技术时,应重视CO_(2)注入煤层后所引起的煤岩强度降低问题。

In order to study coal deformation and gas seepage behaviors caused by pressure reduction in gas extraction process,based on seepage test and triaxial compression test of gas pressure reduction,coal deformation and seepage characteristics were obtained.Then,matrix shrinkage deformation was modified by considering adsorption damage,and a permeability model was constructed before its rationality was verified by experimental results.The results show that with the decrease of gas pressure,coal permeability presents a"V"shaped change trend.The axial and radial deformation increase linearly,and coals injected with CO_(2) produce larger deformation than that with CH_(4),with radial deformation being 1.89 times of axial deformation.Moreover,the elastic modulus and peak principal stress difference in coal with CO_(2) are lower to different extent than those with CH_(4).In order to ensure safe production,attention should be paid to the issue of coal strength reduction caused by CO_(2) injection into coal seam when using CO_(2) displacement or CO_(2) fracturing anti-reflection technology.