基于重量法的页岩气超临界吸附特征实验研究

为了有效分析页岩气体的超临界吸附特征,利用重量法等温吸附仪,借助高精度的磁悬浮天平系统,直接测试了不同压力条件下甲烷气体密度及其过剩吸附量。实验测试结果表明,当压力较小时,过剩吸附量随着压力增大而增大;当压力大于8 MPa后,过剩吸附量会随着压力的增大而减小,这主要是由于甲烷吸附相密度与游离相密度差值随压力先增大后减小导致的。页岩中超临界甲烷的等温吸附曲线在压力较大时,必然存在下降的趋势,这并非异常现象,而是超临界甲烷过剩吸附量的本质特征。此外,利用高压段甲烷过剩吸附量随压力直线递减的规律,确定了甲烷吸附相体积的计算方法,并且采取定吸附相体积的方法对绝对吸附量进行了校正,校正结果表明,超临界甲烷在页岩中的绝对吸附量依旧能很好的利用Langmuir吸附模型进行拟合及分析,可以将该经典的吸附理论扩展到超临界温度领域。

Supercritical isothermal adsorption characteristics of shale gas based on gravimetric method

In order to analyze the supercritical adsorption characteristics of shale gas effectively,using the isothermal adsorption instrument based on gravimetric method,by means of the high precision magnetic suspension balance system,the density of methane and its excess adsorption were directly tested under the conditions of different pressures.The results show that when the pressure is low,the excess adsorption quantity increases with pressure；when the pressure is higher than 8 MPa,the excess adsorption quantity will decline with the increase of pressure.This is mainly due to the difference of methane density at adsorbed phase and free phase.When the pressure is very high,the isothermal adsorption curve of supercritical methane must have a downward trend.It is not an abnormal phenomenon,but the essence characteristics of the excess adsorption quantity of supercritical methane.In addition,the excess methane adsorption capacity decrease linearly with pressure at high pressure,so the method for calculating the methane adsorption phase volume is determined.And the absolute adsorption quantity are corrected by the assumption that the volume of methane at adsorbed phase is constant.The correction results show that the absolute adsorption quantity of methane on shale can still be simulated and analyzed by the Langmuir adsorption model.The existing adsorption theory can be extended to the field of supercritical temperature.