Waterflooding has been applied for many years as secondary recovery method with no or little regard to the effect of the injected water salinity on oil recovery. However, in the last decade, there has been an increasing interest in understanding the effects of changing injected water salinity on reservoir performance. The potential of low-salinity waterflooding (LSWF) has been studied in sandstone reservoirs by numerous core-flooding experiments. These experiments have shown diverse results. This paper aims to investigate the effects of changing water salinity on oil recovery. A comprehensive review and analysis of the results of more than 500 core-flood experiments from published work were investigated to study the effects of several parameters such as clay content, clay type, and temperature on oil recovery. The relation between incremental oil recovery and sodium adsorption ratio SAR, and exchangeable sodium percentage (ESP) parameters which control clay swelling was illustrated. The analysis of the results revealed that there is an optimum composition and optimum salinity for waterflooding in secondary flooding stage. However, for tertiary flooding stage, the results showed that the controlling factor may be not decreasing the salinity but rather changing the salinity (e.g., either increasing or decreasing) with minor improvement in oil recovery. It was clear also that applying the optimum salinity in the secondary recovery stage is more effective than applying it in the tertiary recovery stage. This study aims to develop important guidelines for screening and designing optimum salinity for waterflooding projects in sandstone reservoirs.

中文翻译：

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砂岩油藏低盐度注水综合研究

注水作为二次采油法已经应用了很多年，几乎没有考虑注入的盐度对采油的影响。但是，在过去的十年中，人们对理解改变注入水盐度对储层性能的影响的兴趣日益浓厚。通过大量岩心驱油实验研究了砂岩储层中低盐度水驱的潜力。这些实验显示出不同的结果。本文旨在研究改变水盐度对石油采收率的影响。对发表的工作进行的500多次岩心驱油实验结果进行了全面回顾和分析，以研究黏土含量，黏土类型和温度等几个参数对采油率的影响。说明了增量油采收率与钠吸附率SAR以及控制粘土溶胀的可交换钠百分比（ESP）参数之间的关系。结果分析表明，二次注水阶段存在最佳的注水组成和盐度。然而，对于第三次驱替阶段，结果表明，控制因素可能不是降低盐度而是改变盐度（例如，增加或减少），而采油率略有提高。同样清楚的是，在二次采油阶段应用最佳盐度比在三次采油阶段应用最佳盐度更为有效。这项研究的目的是为筛选和设计砂岩储层注水项目的最佳盐度制定重要的指南。