煤、 页岩和砂岩孔隙结构差异性及对甲烷吸附的影响研究
Research on differences in pore structures of coal，shale and sandstone and their effects on methane adsorption
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摘要: 查明煤、页岩和砂岩孔隙结构差异性，对煤层气、页岩气和致密砂岩气的开发具有重要意义。采集煤、页岩和砂岩样品，利用压汞法、低温氮气吸附法、低温二氧化碳吸附法测试样品的孔隙结构，根据各测试方法的特点，提出了利用低温二氧化碳吸附法、低温氮气吸附法、和压汞法分别测试表征微孔（＜2 nm）、介孔（2～50 nm）和大孔（＞50 nm）的全孔径段表征方法，并进行了不同样品的甲烷等温吸附试验，分析孔隙结构对甲烷吸附的影响。试验结果表明：
① 所测样品中，煤中主要发育狭缝形孔隙，页岩和砂岩中主要发育墨水瓶形孔。② 煤、页岩和砂岩孔隙结构具有较大的差异性，煤微孔发育程度远远大于页岩和砂岩。煤中微孔为煤提供了大部分的孔容和比表面积，其中微孔孔容占总孔容的60%以上，微孔比表面积占总比表面积的95%以上；页岩和砂岩的孔容主要有介孔提供，介孔孔容占到总孔容的65%以上，比表面积由微孔提供，微孔比表面积占到总比表面积的61%以上。③ 不同样品对甲烷吸附能力顺序依次为煤＞页岩＞砂岩，对甲烷的吸附主要受控于孔比表面积，微孔为煤对甲烷的吸附提供了更多的空间和吸附点位，所以煤对甲烷吸附能力远远大于页岩和砂岩，最大吸附量与纳米孔隙比表面积大小具有强烈的正相关性。Abstract: A comprehensive understanding for the differences of pore structure among coal，shale and sandstone is of great significance for the development of coal bed methane，shale gas and tight sandstone gas. In this study，coal，shale and sandstone samples were collected，and pore structures of these samples were tested by mercury intrusion，low temperature N2 adsorption and low temperature CO2 adsorption. According to the characteristics of each test method, the joint characterization methods were used for multi-scale pore structures: micropore (<2 2="" was="" characterized="" by="" the="" low="" temperature="" mesopore="" 2-50="" adsorption="" and="" macropore="">50 nm) by the mercury intrusion method. Methane isothermal adsorption experiments were performed for different samples to analyze the influence of pore structure on methane adsorption. Experimental results show that：① in the tested samples，slit pores are mainly developed in coal，and spherical pores are mainly developed in shale and sandstone. ② Pore structures of coal，shale and sandstone are quite different，and the development degree of micropore in coal is much greater than that in shale and sandstone. In coal，most pore volume and specific surface area are provided by micropore，accounting for more than 60% of the total pore volume and more than 95% of the total specific surface area. The pore volume of shale and sandstone is mainly provided by mesopores，accounting for more than 65% of the total pore volume; and the specific surface area is provided by micropores，accounting for more than 61% of the total specific surface area. ③ The order of methane adsorption capacity of different samples is coal > shale > sandstone. The adsorption of methane is mainly controlled by the specific surface area of pores. Micropores provide more space and adsorption sites for methane adsorption in coal. Therefore，the adsorption capacity of coal is far greater than that of shale and sandstone. The maximum adsorption capacity has a strong positive correlation with the specific surface area of nanopores.
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