钠基蒙脱石狭缝中CH_(4)-CO_(2)竞争吸附与CO_(2)埋存

CH_(4)-CO_(2) Competitive Adsorption and CO_(2) Sequestration in Na-Montmorillonite Silt

页岩主要由有机质干酪根和无机质黏土矿物等组成,其中干酪根和黏土矿物对CH_(4)的吸附作用是页岩吸附气的主要来源。为了研究无机质黏土矿物中CH_(4)吸附行为、CH_(4)-CO_(2)竞争吸附行为和CO_(2)埋存规律,利用钠基蒙脱石来表征页岩中的黏土矿物,基于巨正则蒙特卡洛方法,利用Lammps软件开展不同压力、温度和孔径下的流体吸附模拟。结果表明:随着压力增大,各孔径下CH_(4)超额吸附量先增加后减少,并在11~12 MPa间达到峰值;随着温度升高,各孔径下CH_(4)超额吸附量逐渐减少;随着孔径的增大,CH_(4)超额吸附量逐渐减少。小孔径下,CH_(4)在钠基蒙脱石中主要以吸附态赋存,随着孔径的增大,CH_(4)在钠基蒙脱石中处于吸附态和游离态共存的状态,并且钠基蒙脱石对CH_(4)的作用类型为物理吸附。CO_(2)的驱替效率随CO_(2)初始压力的升高而增大,随孔径的增大而增大。CO_(2)埋存量随温度的升高而降低,随注入压力的升高而升高,随孔径的增大而降低。CO_(2)与CH_(4)竞争吸附比随压力的增大而降低,随孔径的增大而升高。

Shale is mainly composed of organic kerogen and inorganic clay minerals,and the adsorption of kerogen and clay minerals on CH_(4) is the main source of shale adsorbed gas.In order to study the adsorption behavior of CH_(4),competitive adsorption behavior of CH_(4)-CO_(2) and the law of CO_(2) embedding in inorganic clay minerals,using Na-montmorillonite to characterize clay minerals in shale,and using Lammps software to simulate fluid adsorption at different pressures,temperatures and pore sizes based on the grand canonical Monte Carlo method.The results show that with the increase of pressure,the excess adsorption capacity of CH_(4) increases first and then decreases at each pore size,and reaches a peak value between 11 and 12 MPa.With the increase of temperature,the excess adsorption amount of CH_(4) decreased gradually at each pore size.With the increase of pore size,the excess adsorption amount of CH_(4) decreased gradually.At small pore size,CH_(4) mainly exists in the form of adsorption in Na-montmorillonite,and with the increase of pore size,the adsorption state and the free state of CH_(4) coexist in Na-montmorillonite,and the action type of Na-montmorillonite on CH_(4) is physical adsorption.The CO_(2) displacement efficiency increases with the increase of initial CO_(2) pressure and pore size.CO_(2) storage decreases with increasing temperature,increases with increasing injection pressure,and decreases with increasing pore size.The competitive adsorption ratio of CO_(2) and CH_(4) decreased with the increase of pressure and increased with the increase of pore size.