Molecular Dynamics Simulation of CO2 Diffusion in a Carbonated Water–Decane System

Carbonated water injection (CWI) is a technology with significant sweep efficiency advantages in enhanced oil recovery (EOR), but the mechanism of the microscopic diffusion of CO2 is still unclear. In this study, the diffusion mechanism of CO2 from the aqueous phase to the oleic phase in a carbonated water (CW)–decane system was investigated by the molecular dynamics simulation method. This investigation also explored the diffusion capacity and interface properties of the CW–decane system. We found that the movement of CO2 from the aqueous phase to the oleic phase can be divided into two processes: the accumulation behavior of CO2 moving from the aqueous phase to the interface, and the dissolution behavior of CO2 moving from the interface to the decane phase. The increase in the temperature and CO2 concentration in carbonated water can improve the decane phase’s diffusion ability and reduce the water–decane interfacial tension. The difference in the interactions between water–CO2 and decane–CO2 provides a driving force for the diffusion of CO2 between aqueous and oleic phase. The temperature increase intensifies the degree of diffusion and improves the diffusion rate of CO2 from the aqueous phase to the oleic phase. The diffusion coefficient results show that CO2 significantly enhances the oleic phase’s diffusion properties. In addition, the affinity of water for CO2 is increased by the hydrogen bond, and it provides a mechanism for the accumulation behavior of CO2. Further, the temperature significantly improves the CO2 diffusion ability at the interface, which promotes CO2 leaving the interface and weakens the accumulation behavior. This work provides useful information for guiding carbonated water injection to improve the recovery mechanism of enhanced oil.