Optimization of Low Salinity Water/Surfactant Flooding Design for Oil-Wet Carbonate Reservoirs by Introducing a Negative Salinity Gradient

Engineered water surfactant flooding (EWSF) is a novel EOR technique to reduce residual oil saturation; however, it becomes quite challenging obtain Winsor Type III microemulsion and the lowest IFT under actual reservoir conditions if only low salinity used. The main objective of this study was design negative gradient optimize performance hybrid method. Three corefloods were performed on carbonate outcrop samples. injection sequence in first test conventional waterflooding followed by optimum engineered (2900 ppm) finally an EWSF stage. second third tests conducted using varying gradient. for designed 10 times dilution Caspian Sea spiking with key active ions. A higher used test. total 4300 ppm brine 1 wt% injected as pre-flush after further reduced (~1400 ppm). consisted three post-waterflooding stages salinities 4600, 3700, 290 ppm, respectively. Up 8% 16% more incremental recovery obtained tests, respectively, compared descending order helped create environment despite adsorption. This provided successful LSSF adjusting creating during flooding. reduction saturation can be achieved carefully designing test, improving project economics.