The Impact of Initial Water Saturation and Temperature on Oil Recovery during Spontaneous Imbibition and Injection of Low Salinity Water and Smart Water in Carbonate Reservoir Rocks

In recent years, low salinity water-flooding has received much attention as one of the enhanced oil recovery methods because of its cheapness and low operating limitations. Tuning of injected water composition and concentration can induce a significant effect on the oil recovery during the spontaneous imbibition process and forced oil displacement in the fractured reservoirs. Numerous lab and field studies have been conducted to realize the mechanisms and factors affecting the low salinity and smart water injection. Despite these researches, some of the related mechanisms and determining factors in carbonate reservoirs, such as the initial water saturation and temperature, have not yet been fully understood. Therefore, extensive experiments are needed to optimize the conditions of injected water. In this study, the oil recovery of spontaneous imbibition by low salinity and smart water containing divalent ions has been investigated when the initial water saturations were in relatively small and high amounts in carbonate cores. Then, the coreflooding experiments were conducted with various temperatures, including equivalent and below the reservoir temperature. Based on relative permeability and capillary pressure measurements, the mechanism leading to higher oil recovery during smart water injection was also investigated. The results showed that the oil recovery was increased during spontaneous imbibition of low salinity and smart water under ambient conditions as the initial water saturation increased. It was also observed that elevating the temperature from 80 °C to 105 °C in secondary water injection could improve oil production significantly. The reduction of residual oil saturation in the relative permeability and capillary pressure diagrams due to the presence of sulfate and magnesium ions confirmed that the carbonate rock became more water-wet at the ambient temperature.