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基于X-ray μCT扫描的煤孔隙瓦斯微观渗流各向异性特征研究

Research on the anisotropic characteristics of gas microscopic seepage in coal pores based on X-ray μCT scanning

  • 摘要: 煤微观孔隙空间结构如同煤体的DNA,对煤层瓦斯的赋存状态和渗流特性起决定性作用。为了从微观角度揭示瓦斯渗流的各向异性特征,以鄂尔多斯盆地低阶煤为研究对象,通过X-ray μCT扫描重建煤孔隙微观空间结构模型,对煤微观孔隙表征单元(REV)内瓦斯渗流进行数值模拟,研究单向和多向瓦斯微观渗流的各向异性特征。研究结果表明:低变质程度煤微观孔隙中,孔隙压力只在某一个方向或某一段渗流长度内发生波动;单向瓦斯渗流过程中,羊场湾褐煤z方向渗透率最高,其值为0.64×10-3 μm2,而斜沟气煤y方向渗透率最高,其值为0.23×10-3 μm2;多向瓦斯渗流过程中,羊场湾褐煤+y、+x、-y方向为优势渗流方向,流量占比分别为41.89%、44.22%、38.43%,而斜沟气煤-y、+x方向为优势渗流方向,流量占比分别为51.67%、66.66%、41.56%。

     

    Abstract: The spatial structure of coal micro-pores is similar to the DNA of coal, it plays a decisive role in the occurrence state and seepage characteristics of coal bed methane. In order to reveal the anisotropic characteristics of gas seepage from a microscopic point of view, take the low-rank coal in the Ordos Basin as the research object, X-ray μCT scanning was carried out to reconstruct microscopic spatial structure model of coal pores.Numerical simulation of gas seepage in REV unit of coal micro-pores was carried out, the anisotropy characteristics of unidirectional and multidirectional gas micro-seepage were discussed. The results show that:in the micro-pores of low-rank coal, the pore pressure fluctuates only in a certain direction or within a certain seepage length; in the process of unidirectional gas seepage, the z direction permeability of Yangchangwan lignite is the highest, which is 0.64×10-3 μm2, inclined groove gas coal has the highest permeability in the y direction, which is 0.23×10-3 μm2; in the process of multi-directional gas seepage, the +y, +x and -y directions in Yangchangwan lignite are the dominant seepage directions, and the flowrate accounts for 41.89%, 44.22%, and 38.43% respectively. The -y, +x directions in inclined groove gas coal are the dominant seepage directions, and the flow rate accounts for 51.67%, 66.66%, and 41.56% respectively.

     

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