黔北无烟煤孔隙结构特征及甲烷吸附特性研究

Study on pore structure characteristics and methane adsorption characteristics of Qianbei

  • 摘要: 煤作为一种复杂多孔介质,其孔隙结构特征对决定了煤中甲烷的吸附特性。本文以黔北煤田无烟煤为研究对象,综合运用低温CO?吸附、低温N?吸附与高压压汞实验,利用分形理论分析了煤的孔隙结构特征,并结合高压甲烷等温吸附实验,研究孔隙结构特征对甲烷吸附性能的影响。结果表明,黔北无烟煤孔隙结构以微孔和介孔为主,宏孔占比较小,微孔比表面积占总比表面积的75%~80%,孔体积占比为48%~57%,是甲烷吸附的主要场所;介孔在气体扩散与运移过程中发挥重要的过渡作用;分形维数分析显示,介孔与宏孔的结构复杂度(D2、D3)高于微孔(D1),表明孔隙结构随尺度增大趋于复杂。Langmuir体积(VL)与微孔体积和比表面积呈显著正相关,而与分形维数之间存在一定的负相关趋势,说明孔隙结构过于复杂可能抑制甲烷的有效吸附。通过多尺度孔隙结构与分形特征的关联分析,为揭示无烟煤中甲烷的赋存机制与煤层气高效开发提供了理论依据。

     

    Abstract: As a complex porous medium, coal's pore structure characteristics determine its methane adsorption behavior. This study investigates anthracite from the Qianbei Coalfield through a combination of low-temperature CO? adsorption, low-temperature N? adsorption, and high-pressure mercury intrusion experiments. Fractal theory was employed to analyze the pore structure characteristics, and high-pressure methane isothermal adsorption experiments were conducted to study the impact of pore structure on methane adsorption capacity. The results indicate that the pore structure of Qianbei anthracite is predominantly composed of micropores and mesopores, with macropores constituting a relatively small proportion. Micropores contribute 75%–80% of the total specific surface area and 48%–57% of the total pore volume, representing the primary sites for methane adsorption. Mesopores play a significant transitional role in gas diffusion and transport. Fractal dimension analysis reveals that the structural complexity of mesopores and macropores (D?, D?) is higher than that of micropores (D?), indicating that pore complexity increases with scale. The Langmuir volume (VL) shows a significant positive correlation with micropore volume and specific surface area, but a certain negative correlation with fractal dimension, suggesting that overly complex pore structures may inhibit effective methane adsorption. The association analysis between multi-scale pore structure and fractal characteristics provides a theoretical basis for understanding methane occurrence mechanisms in anthracite and guiding efficient coalbed methane extraction.

     

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