The influence of CO2 on the structure of confined asphaltenes in calcite nanopores

Abstract

The effect of CO2 injection on the structure and transport properties of confined asphaltenes in 6 nm slit-shaped calcite nanopore was studied using molecular dynamics simulations. The difference between asphaltene behavior in confined and bulk fluids in the presence of CO2 were investigated. A higher number of CO2 molecules in confinement influenced the anisotropic distribution of the confined hydrocarbons by displacing the adsorbed hydrocarbons molecules away from the pore surface toward the center of the pore. The van der Waals and electrostatic affinity of toluene and asphaltene with calcite surface decreased with an increase in the CO2 mole fraction. Increase in the number of CO2 molecules in confinement enhanced the tendency of asphaltenes to form aggregates. Further, the diffusivities of hydrocarbons were influenced by the density of injected CO2 and were found to vary anisotropically in the calcite nanopores. The aggregation of asphaltenes in the absence of confinement is faster as opposed to being in confinement. The enhanced adsorption of CO2 to the pore surface reduces the concentration of CO2 in the center of the pore resulting in slower aggregation of asphaltenes in confinement. These results suggest that developing a fundamental understanding of asphaltene behavior in confinement is essential for developing more robust predictions of field-scale observations of asphaltene aggregation.