Molecular dynamics study on hydration characteristics of expansive clay minerals by temperature and inorganic salts

Abstract

Most strata rock minerals have hydrophilic characteristics and the mineral surface is negatively charged. It can adsorb water molecules to form hydration layers on the mineral surface. The existence of hydration layer will reduce the effective pore diameter of rock pore microchannel. Thus, the development efficiency of crude oil is affected. Hydration layer compared to free water, water molecules are arranged in a highly ordered manner, with higher density and more stable toughness. Therefore, it is very important to study the structure of hydration layer adsorbed on rock wall and its influencing factors. Four different rock and mineral types are selected in this paper: Na-montmorillonite, quartz, kaolinite, calcite. Molecular dynamics method was used to simulate different temperature conditions and adding different inorganic salts. Study the influence of temperature and inorganic salts on the hydration layer structure of rock wall. The simulation results show that the increase of temperature and the addition of inorganic salts of different components have a great influence on the adsorption of water molecules on the rock wall, and it changes the original structure of the hydration layer. The adsorption of water molecules on different rock surfaces and the effect of different rock walls on the adsorption of hydration layer are described in molecular form. This study explains the mechanism of temperature and inorganic salts inhibiting water molecules from a microscopic perspective. It is of great significance to study the physical properties of hydration layer. It provides a theoretical basis for the field well wall stability research.