甲烷在页岩黏土矿物中吸附行为的分子模拟  

Molecular simulation of methane adsorption behavior on clay minerals in shale

作　　者：吕兆兰 宁正福[1,2] 王庆[1,2] 黄亮 孟翰[1,2] 余雄飞 秦慧博 LU Zhaolan;NING Zhengfu;WANG Qing;HUANG Liang;MENG Han;YU Xiongfei;QIN Huibo(State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum,Beijing 102249,China;College of Petroleum Engineering,China University of Petroleum,Beijing 102249,China;State Key Laboratory of Heavy Oil Processing,China University of Petroleum,Beijing 102249,China)

机构地区：[1]中国石油大学(北京)油气资源与探测国家重点实验室,北京102249 [2]中国石油大学(北京)石油工程学院,北京102249 [3]中国石油大学(北京)重质油国家重点实验室,北京102249

出　　处：《煤炭学报》2019年第10期3117-3124,共8页Journal of China Coal Society

基　　金：国家自然科学基金资助项目(51774298)

摘　　要：为从微观角度研究页岩气在页岩黏土矿物中的吸附行为,利用分子模拟软件Materials studio构建了蒙脱石、伊利石及伊/蒙混层3种黏土矿物的模型,采用巨正则蒙特卡洛(GCMC)方法对页岩气主要成分甲烷在黏土矿物上的吸附行为进行模拟。研究表明,甲烷在不同孔径蒙脱石、伊/蒙混层和伊利石上的平均等量吸附热均小于42 kJ/mol,说明甲烷在黏土矿物表面发生物理吸附。甲烷在3种黏土矿物表面的吸附等温线呈现出相同的规律,均符合I型吸附曲线特征,Langmuir模型的拟合精度较高。3种黏土矿物对甲烷的吸附能力强度顺序为:蒙脱石>伊/蒙混层>伊利石。在伊/蒙混层矿物中,层间离子比甲烷分子更靠近黏土片层,蒙脱石片层一侧吸附的甲烷密度大于伊利石一侧,表明蒙脱石片层的吸附能力强于伊利石,但伊/蒙混层矿物中黏土片层的吸附作用对甲烷吸附层密度的影响随着压力升高而减弱。本文分别构建了孔径为1,2和4 nm的3种黏土矿物模型,从微观角度研究孔径对甲烷吸附的影响。模拟结果表明,黏土矿物孔径越小,甲烷吸附的等量吸附热越大,证明吸附更加牢固,对甲烷的吸附能力更强,但受到孔内有限空间的限制,甲烷在黏土矿物内的绝对吸附量及饱和吸附量随孔径减小而降低。To investigate factors that influence the adsorption behavior of shale gas in clay minerals from a microscopic perspective,the molecular models of smectite,illite and mixed-layer I/S were built using molecular simulation software Materials studio.Grand Canonical Monte Carlo method was used to simulate methane’s adsorption behavior on clay minerals.The research results found that the adsorption isotherms of methane on three clay minerals are lower than 42 kJ/mol,demonstrating that the adsorption of methane on clay minerals belongs to physical adsorption.The adsorption isotherms of methane also show the same trend,which conform to the characteristics of type I adsorption curve.The fitting accuracy of Langmuir model is high.The adsorption capacity of methane is in the sequence of smectite>mixed-layer illite/smectite>illite.In mixed-layer I/S,interlayer cations are closer to clay layer than methane.The density of methane adsorbed on the side of smectite is higher than that on the illite side,demonstrating that smectite has stronger affinity to methane compared with illite,but the effect of adsorption on density decreases with the increase of pressure.The authors constructed the clay models with the pore sizes of 1 nm,2 nm and 4 nm,respectively.As pore width decreases,the isosteric heat of methane increases,which means that the adsorption becomes stronger,the adsorption capacity of clay minerals increases,but the absolute and saturated adsorption amount decrease with pore size declining.

关 键 词：页岩 黏土矿物 伊/蒙混层 分子模拟 吸附 

分 类 号：TE319[石油与天然气工程—油气田开发工程]