黏土矿物微观孔隙对甲烷吸附行为的分子模拟

为了研究黏土矿物对CH_4的吸附规律和页岩储层对CH_4的最小储集空间界限,利用Materials Studio软件构建三种黏土矿物伊利石、蒙脱石和高岭石的微观模型,运用蒙特卡洛方法和分子动力学方法,研究在不同压力、不同孔径空间下三种黏土矿物对CH_4的吸附规律。结果表明:随着孔径和压力的增大,CH_4气体在三种黏土矿物层间的吸附量逐渐增大;不含水的黏土矿物对CH_4的最小储集空间为0. 4 nm,三种黏土矿物对甲烷的吸附能力随孔隙大小的变化而不同;随着孔径的减小或压力的增大,CH_4气体在三种黏土矿物孔径中吸附越稳定;随着孔径的增加,CH_4气体在黏土矿物孔径中出现多层吸附;三种黏土矿物中吸附的CH_4分子之间的距离均大于0. 075 nm,距离CH_4分子0. 125 nm处出现另一个CH_4分子的概率最大。研究结果对页岩气赋存特征和渗流规律具有重要基础认识作用。

Molecular Simulation on the Adsorption behaviors of Methane in Clay Minerals Micro-pore

In order to study the adsorption rule of clay minerals for CH4 and the minimum reservoir space limit of shale reservoir for CH4, three molecular models including illite, montmorillonite and kaolinite were established by using Material Studio software, the Monte Carlo and molecular dynamics method were used for studying the adsorption of CH4 at different aperture spaces and different pressures in the three kinds of clay minerals.The results show that with the increasing of pore size and pressure,the adsorption capacity of CH4 gas between three clay mineral layers increases gradually. The minimum reservoir space of non-aqueous clay minerals for CH4 is 0.4 nm.The relationship between the adsorption capacity of three clay minerals varies with the pore size. With the decreasing of pore size or the increasing of pressure, the adsorption of CH4 gas in the pore size of three clay minerals becomes more stable.With the increasing of pore size, multi-layer adsorption of CH4 appears in the clay minerals.The distance between CH4 molecules adsorbed in the three clay minerals is greater than 0.075 nm,and another CH4 molecule is most likely to appear at 0.125 nm away from CH4 molecule. The research results play an important role in understanding the occurrence characteristics and seepage law of shale gas.