Molecular Dynamics Simulation Study on the Interaction Between Gas and Asphaltene in Heavy Oil

The abstract Gases (CO₂/N₂) can diffuse and dissolve in crude oil, swelling the volume of crude oil, reducing its viscosity, and enhancing energy and sweep efficiency, which are widely applied in the auxiliary development technology of heavy oil. The content of asphaltene in heavy oil plays an important role in the physical properties of heavy oil. Therefore, it is necessary to carry out research on the mechanism of gas dispersion in crude oil asphaltene and the swelling of crude oil. In this paper, the molecular dynamics method was used to explore the microscopic dissolution process of N₂/CO₂ in crude oil asphaltene and its pores, revealing the mechanism of the dissolution and diffusion of gas in asphaltene. The results show that CO₂ and N₂ can diffuse into asphaltene and the pores of heavy oil, causing the volume expansion of heavy oil and having an extraction effect on the small-molecule components. Compared with N₂, CO₂ has a greater solubility in asphaltene, forming an adsorption layer at the oil-gas interface and even being able to break the lamellar structure of asphaltene. The peak value of the radial distribution function of asphaltene-CO₂ is approximately twice that of N₂, and the interaction energy between CO₂ and asphaltene is about 4 times that of N₂. When the gas dissolves in asphaltene, the diffusion coefficient of asphaltene is significantly increased.