气体吸附等温线法表征页岩孔隙结构的模型适用性初探

Preliminary verification of common calculation methods of pore size distribution of shale based on gas adsorption isotherm

针对常见的基于探针气体吸附等温线的孔隙表征方法,通过选择3件标准样品(介孔和微孔材料以及纳米碳管),对比分析了BJH法、HK法和QSDFT法的结果。研究发现BJH法和HK法分别仅适用于介孔和微孔的表征,而QSDFT法对介孔和微孔的表征都适用。鉴于页岩孔隙具有孔径分布广、孔隙结构复杂的特点,因此建议在分析页岩孔隙结构时宜采用QSDFT方法。同时,还分析了2件采自四川筇竹寺组的页岩样品,分析结果表明:该页岩富含微孔。按照BJH法得到的孔径分布进行的估算,所得甲烷吸附容量显著低于QSDFT方法的结果。

In this study,three standard samples（including one microporous sample,one mesoporous sample and one nanotube sample） were used to evaluate the applicability of three commonly used methods（BJH,HK and QSDFT） for the calculation of pore size distribution.The BJH method is found to be only valid for the characterization of mesopores and the HK is only valid for micropores.The QSDFT method works well for both mesopores and micropores and therefore is suggested to be used in characterizing the pores of shale samples due to the nature of the complexity in its pore structure.At the same time,two shale samples from Qiongzhusi formation of Sichuan basin were analyzed.According to the calculation results,the shale sample is rich in micropores（2 nm）.The gas potential would be greatly underestimated if the BJH method is used in the evaluation of shalemethane adsorption.