注入低矿化度水是用于提高采收率的开发方式之一，由于其优于海水和化学驱。 模拟分析表明，多组分离子交换使岩石润湿性由油湿变为水湿，是提高原油产量的关键因素。敏感性研究表明，低矿化度水驱比高矿化度水驱提供了更高的石油产量。此外，低矿化度注水的早期突破时间可以提供高达71%的采收率。因此，在第一阶段生产后立即实施LSWF可提供高达75%的开采收益。所确定的Ca2+、Mg2+和Na+的最佳注入盐水成分浓度分别为450、221和60ppm。在LSWF期间，可建议注入盐水和地层含水层采用高二价阳离子和低单价阳离子浓度，以利于润湿性的改变。模拟还表明，储层温度影响LSWF过程中离子交换润湿性的变化，因为采收率随温度的升高而增加。因此，高温砂岩储层可以被认为是LSWF的良好候选者。
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.
