A molecular insight into the mechanism of organic molecule detachment by supercritical CO2 from a water invasion calcite surface: Effect of water film and molecular absorbability

Abstract

Understanding the mechanism of organic molecule detachment by supercritical CO2 (scCO2) from a water-invaded calcite surface is crucial for CO2 enhanced oil recovery (EOR) and geological sequestration. In this study, a series of MD simulations were conducted to investigate the detachment performance of organic molecules from a water-invaded calcite surface under different reservoir conditions. The molecular configuration, relative concentration, interaction energy, H-bond number, COM distance and absorbed number were calculated to analyze the effect of water film and molecular absorbability on the detachment phenomenon at different pressure and temperature. The molecular configuration and relative concentration results manifest that scCO2 could break the water film and channel out a CO2 path to detach the organic molecules. The water molecules absorbed to the surface and dissociated in the CO2 phase simultaneously. High temperature and pressure could help the water molecules absorb on the surface and reduce the dissociative molecule number. The organics could be miscible with the CO2 molecules and escape from the surface through the CO2 channel. The COM distance results show that the detachment level of the organic molecules increased with pressure and temperature while decreased with water film thickness. The interaction energy results reveal that the toluene-calcite interaction and C8H18-calcite interaction are higher than the toluene-scCO2 interaction and C8H18-scCO2 interaction. In contrast, the pyridine-calcite and acetic acid-calcite interaction are weaker than the pyridine-scCO2 and acetic acid-scCO2 interaction. Thus, the scCO2 could detach the toluene and C8H18 while could not detach the pyridine and acetic acid.These findings can strengthen our understanding about some details of calcite-organics-water-CO2 interaction under reservoir conditions, which may provide some inspiration for CO2 EOR and CO2 geological sequestration.