页岩矿物不同润湿性表征与吸附微观机理

The influence of mineral wettability on the adsorption of shale gas

无机矿物作为页岩气吸附的重要载体,其表面性质对甲烷吸附能力有着重要影响,而润湿性作为固体重要表面性质之一,对矿物气体吸附能力的影响不可忽视.文章以蒙脱石和石英作为研究对象,通过对矿物表面甲基化(-CH_(3))和羟基化(-OH)处理来改变其润湿性,以探究无机矿物表面润湿性对甲烷吸附能力的影响.采用分子动力学方法研究矿物体系的润湿性,用接触角对润湿性进行定量表征,并构建纳米狭缝,结合巨正则蒙特卡罗方法模拟润湿性改变前后,CH4在矿物中的吸附变化.研究结果表明,水滴在羟基化矿物表面迅速破裂并铺展在矿物表面,而在甲基化表面铺展程度较小,普遍呈半球形.羟基化蒙脱石和石英表面的润湿接触角分别为12.7°和26.5°,均小于其甲基化表面接触角62.5°和85.7°.甲基化矿物甲烷吸附量均高于其羟基化,气体几乎大都以吸附状态位于孔隙壁面,随着矿物亲水性的减弱,其对甲烷吸附能力增强.

As an important carrier for shale gas adsorption,the surface properties of inorganic minerals have an important impact on the methane adsorption capacity,while wettability,as one of the important surface properties of solids,can not be ignored.In this paper,montmorillonite and quartz are taken as the research objects,and their wettability is changed by methylation(-CH_(3))and hydroxylation(-OH)on the mineral surface,so as to explore the effect of inorganic mineral surface wettability on methane adsorption capacity.The wettability of min⁃eral system was studied by molecular dynamics method,the wettability was quantitatively characterized by contact angle,and the nano slit was constructed.Combined with the grand canonical Monte Carlo method,the adsorp⁃tion changes of CH4 in minerals before and after the change of wettability were simulated.The results show that water droplets rupture rapidly on the surface of hydroxylated minerals and spread on the mineral surface,while the spread degree on the methylated surface is small and generally hemispherical.The wetting contact angles of hydroxylated montmorillonite and quartz are 12.7°and 26.5°respectively,which are less than those of methyla⁃ted surface 62.5°and 85.7°.The methane adsorption capacity of methylated minerals is higher than that of hy⁃droxylated minerals,and most of the gases are located on the pore wall in the adsorption state,with the weakening of mineral hydrophilicity,its adsorption capacity for methane increases.