Molecular Simulation Study on Methane Adsorption Capacity and Mechanism in Clay Minerals: Effect of Clay Type, Pressure, and Water Saturation in Shales
Molecular Simulation Study on Methane Adsorption Capacity and Mechanism in Clay Minerals: Effect of Clay Type, Pressure, and Water Saturation in Shales
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DOI：
10.1021/acs.energyfuels.8b03462
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发表时间：
2019-02-01
期刊：
影响因子：
5.3
通讯作者：
Zhang, Xue
中科院分区：
文献类型：
--
作者：
Li, Wei;Pang, Xiongqi;Zhang, Xue
采用分子动力学和巨正则Monte Carlo模拟方法研究了甲烷在粘土矿物中的吸附行为和机理。根据延长组泥质岩样品的特征，建立了蒙脱石、蒙脱石和伊利石3种孔隙尺寸为6 nm的模拟模型。结果表明，甲烷在粘土上的吸附为物理吸附，吸附等温热为3.62 ~ 5.77kJ/mol，小于42 kJ/mol。粘土矿物类型、压力和含水饱和度影响甲烷吸附量。甲烷在蒙脱石、蒙脱石和伊利石中的扩散系数分别为1.521、1.635和1.693。不同粘土矿物对甲烷的吸附能力依次为蒙脱石>蒙脱石>伊利石。吸附面积和分子间相互作用力是影响甲烷吸附量的关键因素，它们受矿物晶体结构、化学组成和物理性质的控制。甲烷吸附量随压力的增加而增加，随含水饱和度的增加而减小。当含水饱和度增加到45%时，粘土矿物几乎没有甲烷吸附能力。水分子是极性分子，与非极性分子甲烷分子相比，它与粘土矿物之间具有更大的货车范德华力和静电力。此外，水分子之间存在氢键，而甲烷分子之间没有氢键。这些较强的相互作用力使水分子占据更有限的吸附位点，具有比甲烷更好的吸附能力。
The methane adsorption behaviors and mechanism in clay minerals are investigated by molecular dynamics and grand canonical Monte Carlo simulation methods. Simulation models of montmorillonite, chlorite, and illite with the pore size of 6 nm are built based on the characteristics of Yanchang Formation shale samples. The results show that the methane adsorption of clay is physical adsorption, for the adsorption isosteric heat of methane ranges from 3.62 to 5.77 kJ/mol, which is less than 42 kJ/mol. The types of clay minerals, pressure, and water saturation affect the methane adsorption capacity. The diffusion coefficients of methane in montmorillonite, chlorite, and illite are 1.521, 1.635, and 1.693, respectively. The methane adsorption capacity of different clay minerals decreases in the following order: montmorillonite > chlorite > illite. The adsorption area and intermolecular interaction forces are key factors affecting the methane adsorption capacity, and they are controlled by the crystal structure, chemical composition, and physical properties of minerals. The methane adsorption capacity increases as the pressure increases and decreases with increasing water saturation. When water saturation increases to 45%, clay minerals show almost no methane adsorption capacity. The water molecule is a polar molecule, and it has greater van der Waals force and electrostatic force with clay minerals than the methane molecule, the nonpolar molecule. Moreover, there are hydrogen bonds between water molecules and no hydrogen bonds between methane molecules. These stronger interaction forces make water molecules occupy more limited adsorption sites and have better adsorption capacity than methane.