石墨狭缝吸附页岩气的分子模拟

为了深入了解页岩储层中有机质层状孔隙对甲烷的微观吸附机理，利用分子模拟软件构建了石墨狭缝模型来表征有机质层状孔隙，并运用巨正则蒙特卡罗、分子力学及分子动力学等方法模拟了扬子板块早古生代页岩储层在埋深为2～4 km 的条件下，石墨狭缝对甲烷的吸附性能。结果表明：石墨狭缝对甲烷的吸附是物理吸附；随温度和压力的增加，其吸附量呈现出先急剧增加后缓慢增加再减小的趋势；当页岩气藏埋深为2～4 km 时，页岩储层中有机质层状孔隙对甲烷的吸附量缓慢增加，并且在埋深为4 km 时达到最大，因此4 km 为页岩气最优埋深；甲烷沿石墨狭缝壁法线方向出现明显的吸附分层现象，其相对密度呈对称分布的趋势，而且随埋深的增加而有所减小；甲烷的自扩散系数随埋深的增加而增大，与吸附热及吸附量的变化原因一致。

Molecular simulation of shale gas adsorption in graphite slit-pores

In order to understand the methane adsorption mechanism in organic matter pores in shale, graphite slit-pores were established to characterize the organic matter pores by using molecular simulation software, the grand canonical Monte Carlo method, molecular mechanics and molecular dynamics were used to simulate methane adsorption in graphite slit-pores at the common shale burial depth of 2-4 km in Yangtze Plate. The results show that the adsorption was physical. With the increasing of temperature and pressure, the adsorption capacity in graphite slit-pores increased dramatically first, then increased slowly, and decreased at last, and the maximum adsorption capacity appeared at the buried depth of 2-4 km （4 km is the best buried depth for shale gas）. The relative density of methane along the normal direction of the graphite slit-pore wall shows a trend of symmetric distribution, which reflects apparent adsorption stratification, and it reduced with the increase of buried depth. The self-diffusion coefficient of methane increased with the increase of buried depth, which is consistent with the changes of adsorption heat and adsorption capacity.