页岩甲烷吸附等温线拟合模型对比分析

Comparison Analysis on Model of Methane Adsorption Isotherms in Shales

对四川南部下寒武统牛蹄塘组黑色页岩样品进行了甲烷等温吸附试验,测定了35、65℃下页岩甲烷吸附等温线,采用Langmuir、Freundlich、Langmuir-Freundlich、D-R、Toth方程对吸附等温线进行拟合,检验了各模型的拟合精度。结果表明:这些模型都能较好地拟合页岩甲烷吸附平衡数据,模型的参数越多拟合精度越高,三参数的Toth方程和Langmuir-Freundlich方程的拟合结果比两参数的Langmuir方程、Freundlich方程和D-R方程拟合结果要好;页岩组成非常复杂,表面吸附位的能量分布不均匀,这影响吸附模型在低压下的拟合效果,采用Toth方程可以较为准确地模拟甲烷在页岩不均匀表面上的等温吸附行为。

Isothermal adsorption experiments of methane on Lower Cambrian Niutitang black shales from the south of Sichuan Basin at 35 ℃and 65 ℃ have been conducted.Five different adsorption models （Langrnuir,Freundlieh,Langmuir-Freundlieh,D-R and Toth adsorption equations） were used to fit the experimental data, and fitting degree of these models were investigated.The results showed that all these models fit the experimental data well, and the more parameters were used in these models, the better matching results could be obtained. The Toth and Langmuir-Freundlieh equations with three parameters fit better than Langmuir, Freundlich and D-R equations which all had two parameters.The composition of shale was complex,resulting in energy heterogeneity of the adsorption sites on the surface of shale, which affected the fitting results in low pressure, and Toth equation could describe methane adsorption in shales with heterogeneous surface very well.