基于密度泛函理论致密油气吸附微观机理

发布时间：2018-04-02 03:35

本文选题：密度泛函理论　切入点：吸附　出处：《西南石油大学》2017年硕士论文

【摘要】：致密油气藏储量丰富,储层孔道小,比面大,流体分子与介质之间相互作用强,这种作用直接影响油气在储层中的赋存状态。常规渗流理论在致密油气渗流中描述已出现困难,而分子模拟能更好的描述流体分子与多孔介质矿物间的相互作用。吸附是描述油气分子与多孔介质相互作用的重要特征之一。由于致密储层具有复杂的孔隙结构和矿物成分,与实验方法相比,采用计算机模拟研究油气的微观吸附具有无法比拟的优势。本文旨在通过分析致密储层中油气分子在岩石矿物分子骨架结构上吸附能力的大小,从原子分子层面探讨致密油气的吸附机理,为了解致密油气在储层中的赋存状态、探讨吸附性能与矿物组成的相关性等提供有力依据。密度泛函理论是一种研究多电子体系电子结构的量子力学方法,与其他分子模拟方法相比,具有计算结果精确度更高的优点,在实际应用上非常方便。本研究采用基于密度泛函理论的第一性原理方法,对不同油气分子(CH4、C2H6、CO2、N2和C6H14)在不同矿物成分(CaCO3和SiO2)表面上不同位置(上位、桥位和表面四重洞位)的吸附进行了模拟计算,通过分析结构优化后的吸附能、物理结构和电子态密度,探讨了致密储层中油气组分在储层岩石基质上的吸附性能。研究结果表明:从吸附能力的大小来看,烃类气体的吸附能力较非烃类气体更强,分子量大的烃吸附能力比分子量小的强,CH4、C2H6、CO2、N2和C6H14分子在CaCO3(100)面和 α-SiO2(010)面的吸附能力大小依次为 C6H14C2H6CH4N2CO2,C6H14和C2H6的吸附能均小于-0.62eV,是较弱的化学吸附,CH4和N2的吸附能均大于-0.62eV,是物理吸附,CO2在α-SiO2(010)面是放热吸附,在CaCO3(100)面是吸热吸附;油气分子在不同高对称位上的吸附能差值越小,其流动性越好,甲烷在碳酸钙表面的流动性最强,己烷在二氧化硅表面最容易形成稳定流动;吸附后,油气分子的键长键角变化微小,CH4的电子态密度向低能量区域发生明显偏移,而CaCO3(100)面和α-SiO2(010)面的态密度几乎不变,甲烷在碳酸钙、二氧化硅表面的吸附作用较弱;C6H14在CaCO3(100)面、α-Si02(010)面吸附后,C6H14分子与 CaCO3(100)面、α-SiO2(010)面的电子态密度均出现成键态能量变低,反键态能量变高的特征,存在共价作用,己烷在碳酸钙、二氧化硅表面的吸附作用较强。因此,油气组分在致密砂岩、致密碳酸盐岩基质中具有吸附态的赋存形式,气组分的吸附是较弱的物理吸附,容易转变成游离态,油组分的吸附能力强,是化学吸附,容易产生稳定流动。
[Abstract]:Rich in tight oil and gas reserves, reservoir pore ratio of small, large, medium interaction between fluid molecules and strong, this effect directly affects the occurrence of oil and gas in the reservoir. Conventional seepage theory has difficulties in describing the tight oil and gas seepage, and the interaction of molecular simulation can better describe the fluid molecules with the porous medium between the minerals. The adsorption is an important feature of the molecular description of oil and gas interaction with porous medium. Because of tight reservoir with pore structure and mineral composition of the complex, compared with experimental methods, microscopic adsorption using computer simulation research on oil and gas has incomparable advantages. This paper aims to analyze the adsorption capacity of dense reservoir layer of oil and gas molecules in the molecular framework of rock mineral size, adsorption mechanism of tight oil and gas from the atomic and molecular level, in order to understand the existing shape of tight oil and gas in the reservoir of Fu State, the investigation of adsorption properties of mineral components and provide a strong basis. The correlation between the density functional theory of quantum mechanics is a method of electronic system of electronic structure, compared with other molecular simulation method has advantages of higher accuracy of calculation results, in the practical application is very convenient. In this study, by using the first principle density functional method based on the theory of different oil and gas molecules (CH4, C2H6, CO2, N2 and C6H14) in different mineral components (CaCO3 and SiO2) at various locations on the surface (upper surface, bridge and four hole bit) adsorption was simulated by adsorption analysis of the optimized structure, physical structure and the density of electronic states, the adsorption properties of dense reservoir oil and gas components in the reservoir rock matrix is discussed. The results show that: the adsorption capacity, adsorption capacity of hydrocarbon gases than non hydrocarbon gas molecules stronger. A large amount of hydrocarbon adsorption capacity than small molecule, CH4, C2H6, CO2, N2 and C6H14 molecules on CaCO3 (100) surface and a -SiO2 (010) surface adsorption capacity followed by the size of C6H14C2H6CH4N2CO2, C6H14 and C2H6 adsorption energy was less than -0.62eV, is a weak chemical adsorption, adsorption of CH4 and N2 it was more than -0.62eV, is physical adsorption, CO2 in alpha -SiO2 (010) surface is exothermic adsorption on CaCO3 (100) surface is endothermic adsorption; molecular hydrocarbon adsorption at different positions of the high symmetry energy difference is smaller, the better liquidity, the liquidity of methane in the surface of calcium carbonate, hexane on the surface of silica are most likely to form a steady flow of oil and gas; after adsorption, the molecular bond length and bond angle changes small, electron density CH4 to the low energy region was offset, and CaCO3 (100) surface and a -SiO2 (010) surface state density is almost the same, the methane adsorption on calcium carbonate, silica surface a Weak; C6H14 in CaCO3 (100), alpha -Si02 (010) surface adsorption, C6H14 molecules and CaCO3 (100), alpha -SiO2 (010) surface electron density appeared bonding state energy becomes low, the anti bonding states energy characteristics of high, there is the covalent interaction of hexane in calcium carbonate. Adsorption of two silicon oxide on the surface is strong. Therefore, oil and gas components in tight sandstone, with occurrence of adsorbed dense carbonate matrix. The adsorption of gas components and physical adsorption is weak, easily become a free state, the adsorption capacity of oil component is strong, is easy to produce stable chemical adsorption. Flow.

【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE31

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