Investigation of the effect of CO2 on asphaltene deposition and flow mechanism under nano-confined environment

Abstract

Through the molecular dynamic simulation, the effect of CO2 on asphaltene deposition behavior and fluid flow mechanism under nano-confined conditions has been investigated. The dynamic of asphaltene deposition indicates that the maximum deposition effect is achieved when the CO2 mass fraction exceeds 40%. The solvent composition is a crucial factor in asphaltene aggregation and deposition morphology. The competition between CO2 and asphaltene molecules for surface adsorption is the main factor for the detachment of aromatic core from the surface, which further determines the deposition structure of the surface asphaltene. The flow simulation demonstrates that deposited asphaltene molecules adhere to the pore surface, resulting in a negative slip boundary condition. Additionally, the increase in CO2 concentration further reduces the pore permeability, which is attributed to asphaltene volume swelling, CO2 adsorption, and the change in asphaltene structure. The volume correction method based on Hagen-Poiseuille formula cannot accurately predict the nanopore permeability under asphalt deposition, while the prediction of pore permeability using the thickness of the adhesive layer introduced by MD results has a relative error less than 3%. This study provides a theoretical basis for predicting the nanopore permeability under asphaltene deposition.