LAUSR

Abstract Fast depletion in oil reserves has steered the petroleum industry towards developing novel enhanced oil recovery (EOR) techniques. The standalone EOR methods have associated merits and demerits. For example, the chemical EOR (CEOR) methods have very limited applications in high salinity, high temperature carbonate reservoirs because of increased chemical adsorption and high project costs. In this study, hybrid approaches utilizing engineered water (EW) and CEOR were investigated for carbonate reservoirs. The synergetic effects of EW and chemicals such as polymer, alkali, and surfactant were analyzed. Phase behavior analysis, aqueous stability study, surfactant static adsorption test, and polymer rheological characterization were conducted to select the optimum alkali/surfactant/polymer formulation. To evaluate the increase in oil recovery, wettability alteration, and extent of mobility control, various EW/CEOR combinations were designed for oil displacement experiments, including EW/surfactant flooding (EWSF), EW/polymer flooding (EWPF), EW/surfactant/polymer flooding (EWSPF), and EW/alkali/surfactant/polymer (EWASP) flooding. The EWASP flooding was executed in both continuous and slug-wise injection modes, and the best hybrid EW/CEOR design was selected. 10 times diluted Caspian seawater spiked with optimized active ions was used as the EW. Based on phase behavior and static adsorption tests, 1 wt% Soloterra 113-H was used as a surfactant, while 1 wt% sodium carbonate was used as an alkali. Flopaam 5115 was employed as a polymer with an optimum concentration of 1500 ppm, as established from rheological experiments. The best combination in terms of oil recovery, stability of polymer and surfactant, and chemical consumption was the hybrid EWASP flooding in slug-wise injection mode. This injection scheme resulted in 36% OOIP incremental recovery, 7% higher than the EWPF and EWSPF scenarios and 3% higher than hybrid EWASP flooding in continuous injection mode. Hybrid designs proved to be more effective in recovering residual oil because of better mobility control, reduced capillary trapping, wettability modification, lower surfactant adsorption, and ultra-low interfacial tension (IFT). Our studies showed that the application of hybrid EW/CEOR for carbonate formations, as a novel approach, can expand the application envelope of chemical methods to challenging carbonate formations by making the EOR projects technically and economically viable.