利用GCMC分子模拟技术研究页岩气的吸附行为和机理

Study on Adsorption Behavior and Mechanism of Shale Gas by Using GCMC Molecular Simulation

揭示页岩气的吸附机理是阐明页岩气的吸附规律及转化条件、建立具有普适意义的定量评价模型的基础.采用GCMC(Grand Canonical Monte Carlo)分子模拟方法,对不同温压条件下CH_4和CO_2在不同孔径的伊利石狭缝形孔隙中的吸附行为进行模拟,结果表明,分子模拟与实验所得的吸附量归一化到单位表面积才具有相同的内涵和比较的意义.在此基础上进行的对比表明,分子模拟与实验结果相近,奠定了由分子模拟考察页岩气吸附行为和机理的基础:气体吸附于矿物表面的内因(机理)是气-固分子之间的范德华力和库仑力,伊利石表面对CO_2的吸附能力比其对CH_4的吸附能力强是其结合能更高的反映;CH_4和CO_2在伊利石表面的吸附虽然并非严格的单分子层吸附,但以一个强吸附层为主;孔径减小到微孔后吸附相密度将发生叠加,形成微孔填充,也是其结合能叠加的结果.

The mechanism of shale gas adsorption is the theoretical foundation for elucidating the adsorption and transformation conditions,and establishing a universal quantitative evaluation model.The adsorption behavior of CH4 and CO2 in illite slit pores with different sizes under various temperature and pressure conditions was simulated by GCMC（Grand Canonical Monte Carlo）method.It is found that adsorption capacities obtained from both molecular simulation and experiments have the same connotations and are comparable when being normalized to the surface area,under which conditions the molecular simulation results are consistent with the experimental measurements.In this way,the basis for the study of adsorption behavior andmechanism of shale gas is established by molecular simulation：the internal cause（mechanism）of gas adsorption on the mineral surface is van der Waals force and Coulomb force in gas-solid molecules,the larger adsorption capacity of CO2 than CH4 on the surface of the illite is the reflection of a higher binding energy;the adsorption of CH4 and CO2 on the illite is not rigorous monolayer-adsorption,but a strong adsorption layer mainly;the adsorption phase density will overlap when pore size reduced to micropore,and microporous filling is thus formed,which is also a result from the superposition of their binding energy.