The paper presents a systematic laboratory study to investigate the underlying physical mechanisms for improved oil recovery as a consequence of low-salinity water injection. Three sister plugs of Berea sandstone were used in the experiments. All three plugs were initially saturated with high salinity water (4 g/L NaCl). Single phase water flow test was performed in the first plug. The salinity of the injected water was decreased gradually (4 g/L to 0 g/L NaCl). In addition to observe the permeability reduction with reducing salinity, the particle concentration was also measured of the effluents at different stages of the experiment. Higher particle concentration was observed during low salinity injection period. The second plug was subjected to primary oil (Soltrol) drainage to the connate water saturation, followed by high salinity (4 g/L NaCl) water injection. After this connate water saturation was restored by a second oil flood. Finally, low salinity (0 g/L NaCl) injection was carried out. For both high and low salinity floods; oil recovery, pressure drop and effluent particle concentration was noted. Numerical modelling was used to interpret the waterflooding data. Five to ten times decrease in water relative permeability and some decrease in residual oil saturation were observed during the low-salinity waterflood. Treatment of the low-salinity coreflood data by a numerical model reveals the unusual decrease in water relative permeability with increasing water saturation at high water saturations. This observation is explained by the expansion of rock surface exposed to low-salinity water during the increase of water saturation. A reproducibility test was performed on the third sister plug which confirmed the observations of the second sister plug. The proposed laboratory-based mathematical model can be used to design the injected water concentration which is crucial for a low salinity waterflooding project.
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机译：本文提出了一个系统实验室研究，以研究潜在的物理机制，以改善溢油恢复的后果。在实验中使用了伯里亚砂岩的三个姐妹插头。所有三个塞子最初用高盐度水（4g / L NaCl）饱和。在第一塞中进行单相水流量试验。注入水的盐度逐渐降低（4g / L至0 g / l NaCl）。除了观察盐度的渗透性降低之外，还在实验的不同阶段测量颗粒浓度。在低盐度注射期间观察到更高的颗粒浓度。将第二个插头进行原油（Soltrol）引流到恶性水饱和，然后高盐度（4g / L NaCl）注水。在这种恶性水饱和后被第二次溢油恢复。最后，进行低盐度（0g / L NaCl）注射。对于高盐度洪水;注意到了采油，压降和流出物颗粒浓度。使用数值建模用于解释水上型数据。在低盐度水泡期间观察到水相对渗透率的5至10倍，并且在低盐度下观察到残留的油饱和度降低。通过数值模型处理低盐度内核数据，揭示了水相对渗透率的不寻常降低，随着高水饱和度的增加。在水饱和期间，通过暴露于低盐度水的岩石表面的膨胀来解释该观察。在第三姐妹插头上进行再现性测试，证实了第二个姐妹插头的观察。所提出的基于实验室的数学模型可用于设计注入的水浓度，这对于低盐度水塑料项目至关重要。
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