Oil Recovery and Fluid Configuration in High- vs Low-Salinity Waterflooding Followed by Polymer Flooding: Pore-Scale Insights

Increasing attention is being given to low-salinity waterflooding (LSW) due to its environmental and economic advantages. While numerous scholars have researched LSW, the comprehension of its synergistic effect with other recovery techniques, such as polymer flooding, remains incomplete especially in the pore-scale remaining oil configuration. This study conducted two sets of two-phase displacement flow experiments in carbonate samples using high-salinity brine, low-salinity brine, and polymer. The high-salinity polymer flooding (HSPF) experiment served as a control to highlight the efficiency of combining low-salinity brine with polymer. A high-resolution micro-CT machine was used to acquire images of rock samples during the displacement processes. We found that the polymer after injection of the low-salinity brine was more efficient. Low-salinity brine significantly altered the wettability (from 125.13 to 104.80°) of the rock, while there was no change in the average contact angle during polymer flooding. Polymer flooding resulted in more significant ruptures of the largest clusters. Additionally, a substantial increase in the oil–water interfacial area was observed after low-salinity polymer flooding (LSPF). The synergy of LSW with polymer flooding may greatly improve oil recovery.