Xu Shijing, Wang Jingyao, Wu Jiazhong, Liu Qingjie, Sun Chengzhen, Bai Bofeng
State Key Laboratory of Enhanced Oil Recovery, Research Institute of Petroleum Exploration and Development of PetroChina, Beijing, 100083, China.
State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an, 710049, China.
Nanoscale Res Lett. 2018 Apr 19;13(1):108. doi: 10.1186/s11671-018-2521-6.
Oil wettability in the water-oil-rock systems is very sensitive to the evolution of surface charges on the rock surfaces induced by the adsorption of ions and other chemical agents in water flooding. Through a set of large-scale molecular dynamics simulations, we reveal the effects of surface charge on the oil contact angles in an ideal water-decane-silicon dioxide system. The results show that the contact angles of oil nano-droplets have a great dependence on the surface charges. As the surface charge density exceeds a critical value of 0.992 e/nm, the contact angle reaches up to 78.8° and the water-wet state is very apparent. The variation of contact angles can be confirmed from the number density distributions of oil molecules. With increasing the surface charge density, the adsorption of oil molecules weakens and the contact areas between nano-droplets and silicon dioxide surface are reduced. In addition, the number density distributions, RDF distributions, and molecular orientations indicate that the oil molecules are adsorbed on the silicon dioxide surface layer-by-layer with an orientation parallel to the surface. However, the layered structure of oil molecules near the silicon dioxide surface becomes more and more obscure at higher surface charge densities.
在水-油-岩石体系中，油的润湿性对水驱过程中离子和其他化学剂吸附在岩石表面所引起的表面电荷变化非常敏感。通过一系列大规模分子动力学模拟，我们揭示了表面电荷对理想水-癸烷-二氧化硅体系中油接触角的影响。结果表明，油纳米液滴的接触角对表面电荷有很大的依赖性。当表面电荷密度超过临界值0.992 e/nm时，接触角可达78.8°，水湿状态非常明显。油分子数密度分布证实了接触角的变化。随着表面电荷密度的增加，油分子的吸附减弱，纳米液滴与二氧化硅表面的接触面积减小。此外，数密度分布、径向分布函数（RDF）分布和分子取向表明，油分子以平行于表面的取向逐层吸附在二氧化硅表面。然而，在较高的表面电荷密度下，二氧化硅表面附近油分子的层状结构变得越来越模糊。
