Molecular dynamics simulation of solvation behavior and thickening properties of modified siloxanes in supercritical carbon dioxide under different pressure and temperature

[Display omitted] •The solvation behavior of modified siloxanes in supercritical CO2 was investigated.•High temperature and low pressure hinder the solvation of modified siloxanes.•Van der Waals forces and electrostatic interactions control intermolecular interactions.•The thickening mechanism of modified siloxanes in supercritical CO2 has been studied. Supercritical carbon dioxide (ScCO2) fracturing fluids have been limited in their application in unconventional reservoirs due to their weak proppant-carrying capacity resulting from their low viscosity. Consequently, numerous scholars have focused on modifying siloxanes to enhance their solubility and thickening performance in ScCO2. In this paper, the cohesive energy density, interaction energy, radial distribution function, shear viscosity and electrostatic potential distribution of modified siloxane with ScCO2 were calculated using molecular dynamics simulation. The effects of different temperatures and pressures on the dissolution and thickening ability of modified siloxanes in ScCO2 were investigated. The simulation results indicate that high temperature and low pressure have limited effects on promoting the solubility of modified siloxanes in ScCO2, with temperature exerting a more significant influence on solubility behavior than pressure. Additionally, PD4H+TMPTMA is less soluble in ScCO2 compared to PD4H+TAIC. The binding energy of ScCO2 and modified siloxanes decreases with increasing temperature but increases with increasing pressure. Van der Waals interactions and electrostatic interactions play decisive roles in the solubility of modified siloxanes in ScCO2. Finally, the thickening mechanism of modified siloxanes in ScCO2 was elucidated based on molecular structure and binding energy interactions. In summary, this paper aims to provide options and assistance in synthesis of better ScCO2 thickeners for unconventional reservoir fracturing applications through the study of modified siloxanes.