New Insights into Geochemical Modeling of Hybrid Low Salinity/Engineered Water and Polymer Injections in Carbonates

For decades, polymer flooding proved to be one of the most effective enhanced oil recovery (EOR) methods. In addition, low salinity/engineered water injection (LSWI/EWI) has been gaining momentum over the last few years. Both techniques seem to be cheaper than other EOR methods. This resulted in an increased interest among operators in these techniques. Moreover, low-salinity water is usually less viscous compared to formation fluids, which warrants a lower volumetric sweep efficiency, especially at high temperatures and in highly heterogeneous formations. The reduction in macroscopic sweep efficiency impairs the improvement in recovery efficiency by low-salinity water. In addition, experimental studies showed that polymer viscosity is considerably improved in less saline water. In this study, hybrid polymer and LSWI/EWI flooding performance is numerically evaluated in carbonate formations under conditions of mixed-to-oil wettability, high temperature, high salinity, and low permeability. A numerical 1D model was constructed using a commercial compositional simulator. The model captures the polymer rheology of a newly developed and commercially available synthetic polymer. Also, the effect of LSWI/EWI on polymer rheology and performance was studied. Oil recovery, pressure drop, and in-situ saturation data were history matched for seawater, polymer, and low salinity water injection cycles. Furthermore, the matched experimental data were utilized to examine the combined polymer and low salinity water effect on the improvement in microscopic displacement efficiency of linear models under reservoir flow conditions. The simulation results showed that hybrid polymer and LSWI/EWI is a viable EOR method for carbonate reservoirs under harsh conditions. Moreover, this work provides new insights into the hybrid application of LSWI/EWI and polymer flooding in carbonates under harsh conditions, the impact of low-salinity water on in-situ polymer rheology, and it promotes further field-scale applications of hybrid polymer-LSWI/EWI to improve volumetric sweep efficiency and overall recovery efficiency.