Influence of water composition on formation damage and related oil recovery in carbonates: A geochemical study

Abstract Several benefits of low salinity/engineered water injection (LSWI/EWI) have been reported in the literature including its ability to increase oil recovery at low cost and with least environmental impact. Nevertheless, the related reservoir-engineering problems to this technique such as formation damage is still uncertain and has not been thoroughly investigated. This study investigates the effect of water composition on formation damage and the related oil recovery from a geochemical prospective. The study presents coupling of the IPhreeqc geochemical engine with Matlab to simultaneously solve the oil-water multiphase flow in 1-D and the related geochemical reactions. Using this coupling technique, the geochemical capabilities of Phreeqc were successfully incorporated in a multiphase flow simulator. The latter enabled modeling of reactive transport and formation damage in subsurface multiphase reservoir. The developed model was validated against single phase geochemical simulator, analytical solution of Buckley-Leverette equation, commercial reservoir engineering simulator, and experimental data. The results showed that the temperature, sulfate concentration, and dilution of injection water have a pronounced effect on formation dissolution and precipitation during LSWI/EWI. Also, anhydride scale is the main controlling solid specie for formation damage in the investigated case study. In addition, high temperature water injection should be avoided in carbonate reservoirs due to the likelihood of anhydride precipitation and formation damage. This precipitation occurs because of the low-solubility of anhydride at high temperature. Moreover, water dilution could decrease scale formation while sulfate spiking might increase anhydride precipitation. Hence, sulfate concentration should be optimized as a wettability alteration agent to enhance oil recovery while avoid formation damage. Furthermore, as a sequence of anhydride precipitation by sulfate spiking, oil production is expected to decrease by around 10% in the selected case study. The dissolution and precipitation mechanisms during LSWI/EWI are very case-dependent and hence, the findings of this study cannot be generalized.