Numerous studies have been carried out to ascertain the mechanisms of low-salinity and smart water flooding technique for improved oil recovery. Focus was often on brine composition and, specifically, the cationic content in sandstone reservoirs. Given the importance of the salt composition and concentration, tweaking the active ions which are responsible for the fluids–rock equilibrium will bring into effect numerous mechanisms of displacement which have been extensively debated. This experimental study, however, was carried out to evaluate the extent of the roles of chloride- and sulphate-based brines in improved oil recovery. To carry this out, 70,000 ppm sulphates- and chloride-based brines were prepared to simulate formation water and 5000 ppm brines of the same species as low-salinity displacement fluids. Core flooding process was used to simulate the displacement of oil by using four (4) native sandstones core samples, obtained from Burgan oil field in Kuwait, at operating conditions of 1500 psig and 50 °C. The core samples were injected with 70,000 ppm chloride and sulphates and subsequently flooded with the 5000 ppm counterparts in a forced imbibition process. Separate evaluations of chloride- and sulphate-based brines were carried out to investigate the displacement efficiencies of each brine species. The results showed that in both high- and low-salinity displacement tests, the SO₄ brine presented better recovery of up to 89% of the initial oil saturation (Soi). Several mechanisms of displacement were observed to be responsible for improved recovery during SO₄ brine displacement. IFT measurement experiments also confirmed that there was reduction in IFT at test conditions between SO₄ brine and oil and visual inspection of the effluent showed a degree emulsification of oil and brines. Changes in pH were observed in the low-salinity flooding, and negligible changes were noticed in the high-salinity floods. These results provide an insight into the roles of chloride and sulphate ions in the design of smart “designer” water and low-salinity injection scenarios.

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研究氯化物和硫酸盐对砂岩油藏低盐注入性能的作用：实验方法

为了确定低盐度和智能注水技术改善油采收率的机理，已经进行了大量研究。通常将重点放在盐水成分上，尤其是砂岩储层中的阳离子含量上。考虑到盐的组成和浓度的重要性，调整负责流体-岩石平衡的活性离子将使人们广泛讨论了许多位移机理。然而，进行了该实验研究以评估基于氯化物和硫酸盐的盐水在改善采油率中的作用程度。为此，准备了70,000 ppm的基于硫酸盐和氯化物的盐水，以模拟与低盐度驱替液相同种类的地层水和5000 ppm盐水。通过使用四（4）种天然砂岩岩心样品（从科威特的Burgan油田获得），在1500 psig和50°C的操作条件下，使用岩心驱油工艺来模拟油的驱替。核心样品中注入了70,000 ppm的氯化物和硫酸盐，然后在强制吸水过程中注入了5000 ppm的对应物。对基于氯化物和硫酸盐的盐水进行了单独评估，以研究每种盐水种类的驱替效率。结果表明，在高盐度和低盐度位移测试中，SO 000 ppm氯化物和硫酸盐，随后在强制吸水过程中被5000 ppm对应物淹没。对基于氯化物和硫酸盐的盐水进行了单独评估，以研究每种盐水种类的驱替效率。结果表明，在高盐度和低盐度位移测试中，SO 000 ppm的氯化物和硫酸盐，随后在强制吸水过程中被5000 ppm的对应物淹没。对基于氯化物和硫酸盐的盐水进行了单独评估，以研究每种盐水种类的驱替效率。结果表明，在高盐度和低盐度位移测试中，SO₄盐水的回收率最高可达初始油饱和度（Soi）的89％。观察到有几种驱替机制可导致SO ₄盐水驱替过程中提高采收率。IFT测量实验还证实，在测试条件下，SO ₄盐水和油之间的IFT有所降低，并且目视检查废水显示油和盐水的乳化程度。在低盐度洪水中观察到pH的变化，而在高盐度洪水中观察到的变化可忽略不计。这些结果提供了对氯离子和硫酸根离子在智能“设计器”注水和低盐度注入方案设计中的作用的见解。