Numerical investigation of optimum ions concentration in low salinity waterflooding

Injecting low saline water is one of the practices used to improve hydrocarbon production that has recently significantly grown due to its advantages over seawater and chemical flooding. Although many theories and mechanisms have been provided on how additional oil recovery has been achieved utilizing low salinity waterflooding, the principle fundamentals of the mechanism(s) are still ambiguous. This article investigates the potential use of low salinity waterflooding (LSWF) to improve oil production from a sandstone formation. A 3D field-scale model was developed using Computer Modeling Group (generalized equation-of-state model simulator) based on a mature oil field data. The developed model was validated against actual field data where only 8% deviation was observed. Simulation analysis indicated that multi-component ion exchange is a key factor to improve oil production because it alters rock wettability from oil-wet to water-wet. Simulation sensitivity studies showed that low salinity water flooding provided higher oil production than high water salinity flooding. Moreover, simulation showed early breakthrough time of low salinity water injection can provide high oil recovery up to 71%. Therefore, implementing LSWF instantly after first stage production provides recovery gains up to 75%. The determined optimal injected brine composition concentration for Ca²⁺, Mg²⁺ and Na⁺ are 450, 221, and 60 ppm, respectively. During LSWF, a high divalent cations and low monovalent cations' concentration can be recommended for injected brine and formation aquifer for beneficial wettability alteration. Simulation also showed that reservoir temperature influenced the alteration of ion exchange wettability during LSWF as oil recovery increased with temperature. Therefore, high temperature sandstone reservoirs can be considered as a good candidate for LSWF.