Assessment of Oil Production for Low-Salinity Water Based Polymer Injection Method in Carbonate Oil Reservoir

Abstract

This study experimentally investigates the effect of pH and SO42- on oil production in carbonate reservoir applying low-salinity water based polymerflooding (LSWPF), which has additional synergetic effect by altering the wettability and improving the mobility ratio. Particularly, SO42- ions contained in injection water not only decrease electrical potential of rock surface, but also retain stability of polymer chain. Therefore, it is essential to analyse the potential of sulfate on oil production in LSWPF. From the results of viscosity analysis and zeta potential measurement of polymer solution, it was confirmed that Ca2 yielded precipitation with polymer molecule, leading to viscosity reduction, while SO42- stretched the polymer chains. In the results of coreflooding experiments for LSWPF, injecting polymer solution containing higher concentration of sulfate with neutral pH revealed less degradation and affected wettability alteration, resulting in enhancing oil recovery. In overall, we demonstrated the interaction between low-salinity waterflooding and polymerflooding, especially the impact of sulfate ions on polymer degradation and consequently enhanced oil recovery. In field application of low-salinity polymerflooding method to carbonate reservoir, pH and PDI of injection water should be designed in advance to maximize the oil recovery.