页岩油在有机质孔隙赋存特征的分子模拟研究

Study on characteristics of shale oil in organic matter pores based on molecular simulation

利用分子动力学模拟方法研究了页岩油在页岩纳米有机质孔隙中的赋存特征。在OPLS全原子力场下模拟了353 K、30.7 MPa条件下正辛烷在石墨烯壁面的吸附特征,并分析了不同孔隙尺寸、温度、压力、碳链长度、烷烃极性等5个影响因素对正辛烷在有机质壁面吸附的影响。结果表明,正辛烷在有机质孔隙壁面有4个吸附层,吸附层密度峰值逐渐降低,吸附层厚度为0.4~0.5 nm;沿z方向垂直扩散系数和平行扩散系数均逐渐增大并在孔隙中央处达到稳定,且平行扩散系数大于垂直扩散系数;压力对烷烃分子的吸附量几乎没有影响,孔隙尺寸越大,温度越高,碳链越短,分子极性越低的烷烃分子在纳米有机质孔隙中的吸附态体积分数越小。

The occurrence characteristics of shale oil in the pores of shale nano organic matter are studied by molecular dynamics simulation.The adsorption characteristics of n-octane on graphene wall at 353 K and 30.7 MPa are simulated under OPLS all atomic force field,and the effects of different pores size,temperature,pressure,carbon chains length and alkane polarity on the adsorption of n-octane on organic matter wall are analyzed.The results show that n-octane has four adsorption layers on the pores wall of organic matter,the peak density of the adsorption layer decreases gradually,and the thickness of the adsorption layer is 0.4-0.5 nm.The vertical diffusion coefficient and parallel diffusion coefficient increase gradually along the z direction and reach stability at the center of the pores.And the parallel diffusion coefficient is greater than the vertical diffusion coefficient.The pressure has little effect on the adsorption capacity of alkane molecules.The larger the pores size,the higher the temperature,the shorter the carbon chains and the lower the molecular polarity,the smaller the adsorption volume fraction of alkane molecules in the pores of nano organic matter.