Аннотация
Residual oil saturation (Sor) after waterflooding is high in carbonate reservoirs, due to the wettability state, making them a lucrative candidate for novel enhanced oil recovery (EOR) methods such as engineered water/polymer flooding (EWPF).Initial wettability for such reservoirs must be considered during the preliminary screening for an effective EWPF application.This experimental study investigates the carbonate initial wettability criteria to achieve a successful EWPF design.Contact angles are measured at 80 o C to evaluate the temperature effect on wettability shift by engineered water (EW).Coreflood tests are conducted under different initial wettability conditions to analyse EWPF performance in weak, moderate, and strong oil-wet mediums.Capillary numbers and a corresponding reduction in Sor are estimated to develop a screening parameter.EW prepared by 10 times diluted Caspian seawater spiked with optimized active ions has caused a 40-55 o reduction in contact angle, making the rock more water-wet.Sor after waterflooding is 25% higher in a strong oil-wet carbonate sample in contrast with a weak oil-wet condition, implying such reservoirs are appropriate candidates for EWPF application.Ion-tuned water flooding has provided 8% of OOIC incremental recovery in strong oil-wet medium while it has given a negligible recovery in the weak oil-wet case.Despite having similar capillary numbers, EWPF has resulted in a 16% more reduction in Sor in the strong oil-wet system compared to the weak oil-wet system.This study presented a preliminary screening criterion for EW-based hybrid methods by considering the initial wettability of a reservoir.The results show that the hybrid EWPF method can reduce Sor more than that predicted by capillary desaturation curves.Hence, it has a higher capillary desaturation tendency and can be successfully applied to carbonate formations that are not water wet.