Thermodynamic Interpretation of Coreflood Oil Recovery with Aqueous CO2 Nanobubble Dispersion

Summary In this paper, we present an experimental study of aqueous nanobubble (NB) dispersion of carbon dioxide (CO2-NB) for enhanced oil recovery (EOR). CO2-NB was compared with brine and slightly supersaturated carbonated water (CW) [enhanced CW (eCW)] in corefloods with Berea sandstone (BSS) cores and dead oil at 21°C. Coreflooding results showed that oil displacement by CO2-NB yielded a delayed breakthrough, with the oil recovery factor at breakthrough (RFBT) 9.1% original-oil-in-place (OOIP) higher than in the brine case. Oil displacement by eCW did not show such an increase in RFBT, but it exhibited a long-term, gradual increase in oil recovery after breakthrough. A detailed analysis of coreflooding data attributed the main difference among the corefloods to CO2 mass transfer during oil displacement. Multicontact equilibrium calculations using a calibrated thermodynamic fluid model demonstrated that the elevated CO2 content in the injected CO2-NB enhances CO2 mass transfer from the injected aqueous phase into the oleic phase (L1), thereby accelerating the nucleation of the CO2-rich liquid (L2) phase. The partially miscible displacement of dead oil by the in-situ-generated L2 phase could have enhanced RFBT by CO2-NB compared with the more immiscible oil displacement by water in other cases, where the CO2 content was lower or zero.