正己烷在CaCO3(100)面吸附的第一性原理研究

致密油在储层多孔介质中的吸附研究多以定量的实验研究为主,定性的机理研究较少。以正己烷为对象,从原子分子层面定性研究其在碳酸钙表面的吸附能力,为解释致密油在储层岩石基质上的吸附性提供了有力依据。采用基于密度泛函理论的第一性原理方法,计算了C_6H_(14)分子在CaCO_3(100)面的吸附能,对比分析了吸附前后的物理结构和电子态密度。结果表明:C_6H_(14)分子在B11位吸附最稳定,吸附能为-0.782 4 eV,吸附后键长键角变化率均小于1%,是一种弱化学吸附。不同吸附位的能量差值很小,仅为0.017 8 e V,C_6H_(14)分子容易在CaCO_3表面发生稳定流动。吸附后,C_6H_(14)分子的电子态密度向低能量区域整体偏移约3.1 e V,而CaCO_3(100)面的电子态密度曲线基本重合,吸附作用对C_6H_(14)分子的电子结构影响显著,对CaCO_3(100)面电子结构影响甚微。

First principles calculation of adsorption for n-hexane on CaCO3 (100) surface

The study on the adsorption of tight oil in porous media is mainly based on the quantitative experimental study, but there is little qualitative mechanism study. It provides a strong basis for the interpretation of the adsorption of tight oil in reservoir rock matrix by the qualitative study of the adsorption capacity of n-hexane on the surface of calcium carbonate from the atomic and molecular level. By using the first principles calculation method based on density functional theory, the adsorption energy of C6H14 molecule on CaCO3(100) surface was calculated, and the physical structure and electronic density of states before and after adsorption were compared. The results show that the C6H14 molecule has the most stable adsorption at B11 site, its adsorption energy is -0.782 4 eV, and the bond length and bond angle change rate are less than 1%, which is a kind of weak chemical adsorption; The energy difference of different adsorption sites is very small, only 0.0178 eV, which indicates that the C6H14 molecule is easy to flow stably on the CaCO3 surface; After adsorption, the electronic density of states of the C6H14 molecule shifts to the low energy region by about 3.1 eV, while the electronic density of states curve of CaCO3(100) surface was coincident, so the effect of adsorption on the electronic structure of C6H14 molecule is significant, and it has little effect on the electronic structure of CaCO3(100) surface.