Low Salinity Waterflood in Combination with Surfactant/Polymer: Effect of Brine Composition
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The effect of low salinity water (LSW) on enhanced oil recovery has been known for decades. Although much research is done on the topic, a general agreement of the prevailing mechanism for the low salinity effect has still not emerged. The present study compares the effect of LSW in secondary and tertiary mode in six Berea cores. Following tertiary mode LSW injection, low salinity surfactant polymer (LSSP) floods were conducted. In addition, measurements of density, pH, viscosity and interfacial tension was executed on the fluids used. In secondary mode, aged and unaged cores were used for injection of synthetic seawater and diluted synthetic seawater (10%). The results show a higher production (1-12% OOIP) when injecting synthetic seawater compared to the diluted synthetic seawater (10%) in secondary mode. No fines or pH variation was observed during the floods. In tertiary mode the cores were flooded with a sequence of brines with different composition (synthetic seawater without divalent ions, diluted synthetic seawater (10%) and 3000 ppm NaCl). Some enhanced production (5-9% ROIP) was observed when altering ion composition or reducing total salinity. The extra oil production was observed in some of the cores, but seems no to be reproduced in all parallel experiments. No fines or significant pH increase was observed during the floods. Combining low salinity brine with surfactants and polymers yielded varying production, ranging from 11-32% ROIP. It was observed that the aged cores generally had a higher recovery compared to unaged cores.