Effects of concentration, salinity and injection scenario of ionic liquids analogue in heavy oil recovery enhancement

• Effects of DESs concentration, salinity and injection scenarios were studied at reservoir conditions.
• The heavy oil recovery factors decreased, but still promising by diluting the DES solution.
• DESs flooding in tertiary mode always led to higher recovery compared to secondary mode.
• IFT measurements showed that there is a critical concentration in which the IFT value would be lowest.
• The DESs can tolerate wide range of reservoir’s salinities.

Recently, Deep Eutectic Solvents (DESs) have been demonstrated to be an effective analogue of ionic liquid in many applications. In our previous report, for the first time, two Chloride-based DESs were shown to have significant effects on different oil recovery mechanisms in heavy oil/formation brine/Berea sandstone system. In this report, the same DESs were used. The effects of DESs concentration, secondary and tertiary DES injections and brine salinity on recovery performance were examined through IFT measurements, contact angle measurements and core flooding experiments.Results of capillary number calculations indicated that although DESs solutions increased the IFT value, the capillary numbers in DESs flooding due to viscous forces and wettability alteration were higher than brine flooding case. Results showed that for both DESs, although the heavy oil recovery factors decreased by diluting the DES solution with brine from 50 vol% to 5 vol%, they were still promising between 6.3 and 8.7% for DES1 and DES2 respectively at lower concentrations of 5 vol%. Also, by reducing concentration from 50 to 25 vol%, there were no changes in recovery factors from 14 to 13.6% for DES1 and from 23.2 to 23.1% for DES2. The same trend was observed during wettability alteration study by contact angle measurements between oil droplet and aged surface of rock samples in the both DESs solutions at different concentrations. It verified that wettability alteration during DES injection has significant impact on oil recovery and it could be dominant and governing mechanism of heavy oil recovery enhancement. The DESs flooding in tertiary stage led to higher total recovery factors. The total recovery at tertiary mode compared to secondary mode were around 16% higher at 50 vol% concentrations and 3–6% higher at 5 vol% concentrations for both DESs. In addition, Results confirmed that the DESs can tolerate wide range of reservoir’s salinities and there were no big changes in oil recovery at different brine salinity during tertiary DESs injection.