Molecular Dynamics Simulation of Transport and Structural Properties of CO₂–Alkanes

Abstract

Carbone dioxide emissions have imposed serious threats on the environment and health. As such, industrially viable CO2 storage and utilization technologies are of high demand. This study by performing a combined Monte Carlo and molecular dynamics simulations in osmotic and NPT ensembles aims to provide new insights into the complex CO2 interactions with two well-known alkanes (C10 and C20) over a pressure range of 5–30 MPa and a constant temperature of 311 K. The present study provides a quantitative understanding on the effect of CO2 solubility on density, specific volume, swelling, static structure, diffusion, and viscosity of CO2-saturated alkanes. According to results, CO2 dissolution into alkanes, alkane-specific volume, and swelling are a direct function of pressure and alkane chain length. The densities of CO2-saturated alkanes increase with increasing pressure via an increase in mechanical compaction and/or increase in CO2 mole fraction in solutions. As pressure increases, CO2 mole fraction in solution increases and, consequently, the solution viscosity decreases. It was found that the swelling of CO2-saturated alkanes is due to the stretching of the alkane molecules rather than the change in their average separation distance. Furthermore, the CO2 diffusion coefficient is closely related to the pressure and alkane chain length. The increase in the length of the alkane molecule chain leads to reduction in the CO2 diffusion coefficient. Finally, according to the results, it is expected that the swelling oil recovery and CO2 dissolution trapping mechanisms of CO2 injection act much stronger for lighter crude oils than medium to heavy ones, while the viscosity reduction oil recovery mechanism is more dominant for medium to heavy oils than light ones. These findings are useful for fast screening oil reservoirs to identify the most suitable one for CO2 enhanced oil recovery–storage applications.

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