The novel use of malonic acid-based deep eutectic solvents for enhancing heavy oil recovery

This study investigates the potential of deep eutectic solvents (DES) to recover the residual oil left after waterflooding. For the first time to our knowledge, the effectiveness of two DESs - choline chloride-malonic acid of molar ratios 1:1 and 1:0.5 - in enhancing oil recovery was investigated. The solvents were characterised by measuring density, viscosity, conductivity and pH at different temperatures. Also, measurements of interfacial tension, wettability alteration, spontaneous water imbibition, emulsification, core flood and formation damage tests were conducted at different temperatures. The core flood tests were carried out at reservoir condition using Berea sandstone cores and fluids from the field of interest. Results showed the solvents produced 7%-14% of the residual heavy oil after brine flooding as tertiary recovery stage and without causing any formation damage. Both DESs showed better performance at higher temperatures. Wettability alteration was found to be the dominant mechanism for the oil recovery enhancement.