The Sulfate Removal Unit (SRU), a nanofiltration system, reduces seawater's Sulfate ions from approximately 2,800 mg/L for 100 mg/L or less. This technology minimizes the formation of Sulfate scales in the oil production. This process uses pressure as a driving force and it uses membranes with nanometric pores that are composed of polymeric material. Decrease in permeability is frequently observed in this nanofiltration process due to the deposition in the surface of the membrane (biofouling and inorganic deposits). The objective of this study is the evaluation of scale inhibitors for Calcium Sulfate that can be formed in the membrane as a consequence of the concentration of the seawater in the SRU. The feed, permeate and concentrate fluids of the SRU were characterized. The chemical composition of the seawater in the polarization region (fluid located in the membrane surface) was estimated considering mass transference between permeate and feed fluids of the SRU, and Fick Law. The chemical composition of the seawater in the polarization region presents higher concentration of Calcium, Magnesium and Sulfate than the one in the concentrate fluid (reject). So the polarized seawater is highly saturated regarding Calcium Sulfate. Thermodynamic model MultiScale was applied to assess the scaling tendency (saturation ratio and precipitate mass) in specific points of the SRU under temperature and pressure conditions. The performance of different chemical classes of scale inhibitors was evaluated. Chemical compatibility of these chemicals with seawater in the polarization region, as well as their inhibition efficiency to Calcium Sulfate precipitation in the conditions of the surface of the membrane were evaluated.

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