1M伊利石对甲烷吸附的分子模拟

发布时间：2018-04-22 19:39

本文选题：页岩气 + 伊利石　；参考：《太原理工大学》2015年硕士论文

【摘要】：页岩气工业的兴起，使得人们越来越重视对页岩气的成藏估计。随着对页岩气吸附机理认识的不断深入，很多学者开始将页岩气的吸附研究集中在粘土矿物上，特别是伊利石上。伊利石作为油气盆地储层中常见的粘土矿物之一，是致密储层的重要组成部分，由于其晶粒细小，比表面积大，对天然气具有较强的吸附性能，对油气的存储具有重要的作用。在伊利石对甲烷的吸附研究中，国内外学者主要集中于实验研究。但是粘土矿物和有机质常常形成有机复合体，，使得粘土矿物与有机质对甲烷的吸附上难以区分。为了更深层次的理解伊利石储层的吸附性能，以及甲烷在泥页岩中的扩散规律，本文从微观的角度模拟伊利石粒子对甲烷分子的吸附模拟。这对于页岩气盆地的资源估算和储层评价都有一定的现实意义。本文运用Material Studio6.0(MS)软件，对甲烷分子在1M伊利石中的吸附进行了模拟。首先，在伊利石的通用分子式的基础上，建立了伊利石1M-tv与1M-cv多型结构。通过分子力学方法建立了两种构型的最稳定结构，并对其进行了XRD反演及标准粉末衍射卡的物相匹配。结果表明所模拟的XRD图谱不仅符合前人对1M伊利石研究得出图谱特征而且与标准卡片也有较好的对应。在此基础上对所模拟结构中的d001与d002值进行了计算，在与前人文献中的理论值和实验值对比后发现了较好一致性，从而证明了所构建结构的合理性。通过蒙特卡洛方法模拟（MC）了实际储层条件下1M多型伊利石对甲烷的吸附，结果表明甲烷在1M伊利石中的吸附量均呈现出随着埋深先增大后减小的趋势，并且在2~3km下吸附量达到峰值。在1M多型中，tv构型与cv构型在类质同象作用上存在差异，使得二者的吸附量发生差异。不同埋深下cv构型较tv构型表现出对甲烷更好的吸附性能。这显示了贫Fe、Mg富Al的伊利石环境下更有利于对甲烷的吸附。为了进一步理解甲烷在两种1M伊利石构型中吸附量上的差异及扩散规律，本文通过分子动力学（MD）方法模拟了甲烷在伊利石中的扩散行为。结果表明：（1）1M伊利石吸附甲烷后，甲烷均集中在伊利石构型的中央和层中央两翼靠近粘土片层的位置。层间K离子均主要集中在两种构型的层中央，但随着温度压强的变化，tv构型中的K离子有小部分发生了震荡。（2）甲烷在伊利石中的聚集主要是受到了层间K离子与四面体的粘土片层的物理吸引作用。其中四面体片层是引起甲烷吸附量差异化的原因。（3）通过分析吸附后构型中粒子间的径向分布函数及层间粒子的自扩散系数，表明2~3km埋深下，伊利石两种构型对甲烷的束缚作用较强。此埋深下最适合页岩气的开采。
[Abstract]:With the rise of shale gas industry, more and more attention has been paid to the estimation of shale gas accumulation. With the deepening understanding of the mechanism of shale gas adsorption, many scholars begin to focus on clay minerals, especially Illite. Illite, as one of the common clay minerals in oil and gas basin reservoir, is an important part of tight reservoir. Because of its small grain size and large specific surface area, Illite has strong adsorption property to natural gas and plays an important role in oil and gas storage. In the study of Illite adsorption of methane, domestic and foreign scholars mainly focus on experimental research. However, clay minerals and organic matter often form organic complexes, which make it difficult to distinguish the adsorption of methane between clay minerals and organic matter. In order to better understand the adsorption performance of Illite reservoir and the diffusion of methane in shale, this paper simulates the adsorption of Illite particles to methane molecules from the microscopic point of view. This is of practical significance for resource estimation and reservoir evaluation in shale gas basins. The adsorption of methane molecules in 1m Illite has been simulated by Material Studio 6.0. Firstly, based on the general molecular formula of Illite, the polymorphic structures of Illite 1M-tv and 1M-cv were established. The most stable structures of two configurations were established by molecular mechanics method, and the XRD inversion and the matching of standard powder diffraction cards were carried out. The results show that the simulated XRD spectra not only accord with the previous studies on 1M Illite, but also correspond well with the standard cards. On this basis, the values of d001 and d002 in the simulated structures are calculated. The comparison with the theoretical and experimental values in previous literatures shows that the constructed structures are reasonable. The adsorption of methane by 1m polytype Illite in real reservoir is simulated by Monte Carlo method. The results show that the adsorption capacity of methane in 1M Illite shows a tendency of increasing at first and then decreasing with the depth of burial. The adsorption capacity reached the peak at 2~3km. In the 1m polyforms, there are differences between the tv and cv configurations in the homotypic effect, which leads to the difference of the adsorption capacity between them. Compared with TV configuration, cv configuration shows better adsorption performance for methane at different buried depths. The results show that the Illite with poor Fe, mg and rich Al is more favorable to the adsorption of methane. In order to further understand the difference in adsorption capacity and diffusion law of methane in two 1m Illite configurations, the diffusion behavior of methane in Illite was simulated by molecular dynamics (MD) method. The results show that: When Illite adsorbs methane, the methane is concentrated in the center of the Illite configuration and in the position near the clay lamellar between the two wings of the Illite configuration. The interlayer K ions are mainly concentrated in the middle of the two configurations, but a small part of K ions in the TTV configuration oscillates with the change of temperature and pressure. The accumulation of methane in Illite is mainly due to the physical attraction of interlaminar K ion and tetrahedral clay lamellae. The tetrahedron lamellar is the reason for the difference of methane adsorption. 3) by analyzing the radial distribution function of interparticle and the self-diffusion coefficient of interlayer particles in the adsorbed configuration, it is shown that the two configurations of Illite have strong binding effect on methane under the 2~3km buried depth. This depth is most suitable for shale gas mining.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P618.13

【参考文献】