关键词: 双电层, 外电场, 电动效应, 分子动力学, 致密储层

Abstract: To address the lack of understanding of the electrokinetic phenomenon of the electric double layers at the surface of tight reservoirs under an external electric field and the difficulty in accurately characterizing the micro-characteristics of the interfacial electric double layers through macroscopic experiments,this study investigated the impact of the electrokinetic phenomenon of electric double layers on wettability and crude oil seepage under an external electric field from a microscopic perspective, established a model of the electric double layers on the surface of tight reservoirs under an external electric field by employing the molecular dynamics simulation to explore the influence mechanism of the electric double layers on the surface of tight reservoirs at 313 K and 20 MPa.The analysis results indicate that:after the application of an electric field, the diffusion of solution ions is reduced,the electric double layers undergo expansion,and the electrostatic interactions on the charged surfaces lead to a thicker and more stable water film, which is beneficial for the water wettability of rock surfaces.The greater the electric field intensity, the higher the ion density in the electric double layers,and the more pronounced the electroviscous effect.The oil-phase seepage velocity increases due to the interfacial viscous resistance,but the increase is limited.The formation water solution internally produces a stronger ion hydration effect under the electric field,and changes in ion hydration occur with different ions when the electric field intensity is altered.The research findings are of significant importance for the development of micro-theories of tight reservoirs under external electric fields.

Key words: electric double layers, external electric field, electrokinetic effect, molecular dynamics, tight reservoirs