This study investigates the potential of chemical solvent called deep eutectic solvents (DES) to recover the residual heavy 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 heavy oil recovery was thoroughly investigated. As preliminary investigations, the two solvents were characterized by measuring density, viscosity, conductivity and pH at different temperatures (20 – 80°C). In order to investigate the EOR potential of the solvent, measurements of interfacial tension, wettability alteration, spontaneous water imbibition, emulsification, core flood and formation damage tests were conducted at different temperatures. The core flood test was carried out at reservoir condition (pressure = 1200psi, temperature = 45 - 80 °C) using Berea sandstone core samples and fluids from the field of interest (formation brine and crude oil). Results of the core flood test showed the solvents produced 7-14% of the residual heavy oil after brine flooding as tertiary recovery stage and both DESs displayed better performance in enhancing the oil recovery at higher temperatures. Measurements of absolute permeabilities before and after injection of DESs/brine solutions showed no damage to the formation. Wettability alteration was found to be the dominant mechanisms for the tertiary oil recovery enhancement.

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