Promising combination of CO2 enhanced oil recovery and CO2 sequestration in calcite nanoslits: Insights from molecular dynamics simulations.

[Display omitted] • The displacement and miscible behaviors of CO 2 and octane in calcite nanoslits are investigated by molecular dynamics simulations. • Increase of the temperature and slit aperture could promote the miscible progress of CO 2 and octane. • The calcite nanoslits have a remarkable ability to store CO 2 even at high temperatures and pressures. CO 2 -Enhanced recovery has attracted extensive attention, meanwhile reducing greenhouse gas emissions via CO 2 geological sequestration is causing global concern in recent years, combining CO 2 -EOR and CO 2 sequestration has been recognized as one of the CCUS approach with high potential, and tight reservoirs such as shale oil are the most promising resource in this respect, which has become one of the hot topics unsurprisingly. The understanding about the microscopic molecular behaviors and interaction mechanisms between CO 2 , shale oil, and reservoirs is critical for the development of the techniques, while still incomplete, which makes it challenging for efficient large-scale application in the world. In this paper, molecular dynamics (MD) simulations are used to investigate the displacement and miscible behaviors of CO 2 /octane in calcite nanoslits under reservoir conditions, the effects of temperature, pressure and slit apertures on the molecular behaviors have been studied comprehensively. The interaction energy between CO 2 and octane molecules and calcite surface were calculated to quantitatively analyze the mechanisms in the process of CO 2 flooding. The significant strong interactions between calcite surface and CO 2 on one hand benefit the displacement of octane by CO 2 increasing the miscible flooding efficiency, on the other hand ensure the high adsorption capacity of CO 2 inside the calcite nanoslits, thereby plenty of CO 2 can be stored inside the calcite nanoslits after the flooding. It could be concluded that the carbonate reservoir could be the most promising field combining CO 2 -EOR and CO 2 sequestration. This work provides theoretical guidance for both the optimization of the CO 2 -enhanced oil recovery and effective CO 2 sequestration in unconventional tight reservoirs, especially carbonate reservoir. [ABSTRACT FROM AUTHOR]