Sequential deep eutectic solvent and steam injection for enhanced heavy oil recovery and in-situ upgrading

Recently, Deep Eutectic Solvents (DESs) have been introduced and investigated as new EOR agents for heavy oil recovery enhancement. In this study, sequential DES and steam flooding was proposed and experimentally investigated as a new scenario for heavy oil recovery enhancement and having potentials for in-situ heavy oil upgrading. DESs used in this study are Choline Chloride:Glycerol (DES1) and Choline Chloride:Urea (DES2). Primary and secondary DES flooding at different concentration followed by high-temperature steam flooding were conducted using 16.5 °API heavy oil and Berea sandstone core plugs. DES thermogravimetric analysis (TGA) performed and results verified the relatively high thermal stability of the selected DESs. Maximum decomposition temperature was found to be 320 and 370 °C for DES1 and DES2, respectively. This improves their potential for use as chemical additives or pre-flooding agents in thermal EOR methods. Sequential steam flooding after undiluted and 2-fold diluted DES injection recovered an additional heavy oil of 12% IOIP compared to steam flooding alone. However, using more diluted solutions (i.e., 20-fold diluted DESs) caused the same and in some cases lower total recovery factor by secondary steam flooding. When followed by steam flooding, DES2 exhibited superior heavy oil recovery enhancement (8–12%) compared with DES1 (1.5–6%) at the same concentrations. Analysis of physicochemical properties of produced oil for different cases revealed the favorable role of DES in upgrading the in-situ heavy oil. Heavy oil upgrading were quantified through various measurements including increase in API gravity up to 3.5 °API, 16.6% reduction in sulphur content or desulphurization and increase in the yields of saturate hydrocarbons. Comparatively, DES1 exhibited better overall performance than DES2 in terms of in-situ heavy oil upgrading.