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. However, the related reservoir-engineering problems to these techniques such as formation damage and fluid mobility control are still uncertain and have 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 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 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, anhydrite scale is the main controlling solid specie for formation damage. In addition, high temperature water injection should be avoided in carbonate reservoirs due to the likelihood of anhydrite precipitation and formation damage. This precipitation occurs because of the low-solubility of anhydrite at high temperature. Moreover, water dilution could decrease the scale formation while sulfate spiking might increase scale 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 anhydrite precipitation by sulfate spiking, oil production is expected to decrease by around 23% in the selected case study. The dissolution and precipitation mechanisms during LSWI are very case-dependent and subject of pore distribution, crude oil/brine/rock compositions, and thermodynamic conditions. Hence, the findings of this study cannot be generalized.

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