注水煤体有效渗流通道结构分形特征核磁共振试验研究

Fractal characteristics of effective seepage channel structure of water infusion coal based on NMR experiment

为定量表征注水煤体有效渗流通道结构变化特征,基于核磁共振试验测试了注水过程中,不同围压及水压作用下煤体孔隙结构特征,并结合分形几何理论对煤体有效渗流通道结构分形特征进行了分析。结果表明:注水煤体内部孔径分布差异明显,在不同水压及围压影响下,各孔径孔隙体积占比变化明显,大孔体积变化幅度最大为13.72%,其次为过渡孔及中孔分别为8.12%和5.39%,最小的微孔为2.05%。结合T2C测试结果,当孔隙半径大于270 nm时为有效渗流通道,则影响注水煤体渗流特性的孔隙结构主要集中于大孔及中孔尺度内;试验过程中,试验及理论分形维数变化较小,表明煤样在不同承压条件下,渗流通道结构均具有明显的分形特征,同时两者相反的变化趋势验证了各自表征意义的不同。

The aim of this study is to quantitatively characterize the structural changes of effective seepage channels in water infusion coal body.The structure characteristics of the coal body under various confining pressures and water infusion pressures are measured via nuclear magnetic resonance(NMR)technology.The fractal characteristics of effective seepage channel in coal body are analyzed with fractal geometry theory.The results show that the coal body with water infusion has an intertwined internal fracture-pore structure and that the pore radius distribution is diverse under the influence of different water pressures and confining pressures.The variation of large pores volume is 13.72%,followed by transitional pores and medium pores of 8.12%and 5.39%,respectively.The smallest micro pores is 2.05%.Combined with the T2C test results,when the pore radius is greater than 270 nm,it is an effective seepage channel,and the pore structure affecting the seepage characteristics of the water infusion coal is mainly concentrated in the large pores and medium pores.In the process of test,the change of fractal dimension of test and theory is small,which shows that the structure of seepage passage of coal sample has obvious fractal characteristics under different pressure conditions.At the same time,the opposite change trend of the two verifies the different significance of their respective characterization.