EFFECTS OF CARBON DIOXIDE CONCENTRATION ON THE DIFFUSION OF n-PENTANE BY MOLECULAR SIMULATION

Molecular diffusion affects the miscibility of carbon dioxide and crude oil in the process of carbon dioxide enhanced oil recovery. The study of diffusion of carbon dioxide in crude oil is important to grasp the mechanism of enhanced oil recovery. Molecular dynamics simulation of the diffusion behaviour of pure n-pentane and carbon dioxide/n-pentane mixture is investigated in this article. Viscosity and Pressure Temperature phase diagram of the mixture and pure component are obtained by reservoir numerical simulation. Based on the result of reservoir numerical simulation, the range of pressure applied during the molecular dynamics simulation is obtained. For the first time, the effects of carbon dioxide concentration and pressure on the radial distribution function of ethyl, self-diffusion coefficient of n-pentane and system potential energy are discussed. We find that carbon dioxide molecules reduce the potential energy of mixture and increase the distance of n-pentane molecules. The viscosity calculated by molecular simulation matches well with the numerical simulation result and this proves that our model used is correct. It is also confirmed from microscopic simulation that carbon dioxide injection is an efficient way to reduce the oil viscosity and improve the self-diffusion coefficient of oil component.