Low salinity water (LSW) flooding as an enhanced oil recovery (EOR) method is receiving attention from most oil field operators. Incremental oil recovery reported by different researchers is encouraging. While it is generally accepted that LSW changes rock wettability, the mechanism(s) by which this occurs remains debatable. CO2 flooding is a known EOR method and has been applied in different reservoirs. Synergy between LSW and CO2 are addressed in this paper.
Three major aspects are investigated: identifying the ion content boundary for the LSW which maximises oil recovery, assessing the ion ranking with LSW alternating CO2 injection (LSWACO), and assessing the synergies for oil recovery from applying LSWACO. Throughout the paper, ion tracking and pH are monitored using CMG GEM and Phreeqc Interactive 3.0 for simulating the fluid rock interactions recovered. Published EOR data for LSW and the simulation of core flooding which combines LSW and CO2 may shed light on the possible mechanism(s). Three dilution ratios of seawater (LSW5D, LSW10D and LSW25D) are investigated and ranked on the basis of the obtained incremental oil recovery.
It is interesting to see that the higher the dilution, the slower the oil recovery response from chalk reservoirs. The simulation also showed that the highest incremental recovery was obtained from LSW10D.
CO2 injection coupled with LSW (LSWACO) had a positive effect on oil recovery. It was interesting to observe that different LSW dilution ratios during LSWACO injection yield similar recovery response times and ultimate oil recovery. However, the order of the various LSW dilutions differs from that without CO2.