Formation Damage Assessment and Waterflooding Incompatibility Study for Reduced Sulfate Injection Water

Abstract

Waterflooding has always been considered as a favorable technology to support reservoir pressure during production and enhance recovery. The main challenge that needs to be addressed is the increase in scale potential due to incompatibility of mixing two different waters of different physical and chemical properties. Calcium sulfate scaling can form as a result of the reaction of high calcium produced water with high sulfate injection water. Since there is no feasible method that can efficiently be used to reduce the high calcium content in the formation water, treating the injection water by adding scale inhibitor or lowering its sulfate content is of high interest. Reducing the sulfate content physically through RO membranes or chemically through ion exchange methods can be considered a solution. In this study, different scenarios for using reduced sulfate simulated injection water (SIW) in addition to untreated SIW have been examined as options for waterflooding prior to field application recommendations. Three different concentrations of reduced sulfate SIW (100, 200 and 300 SO4− ppm) in addition to the untreated SIW with almost 4000 ppm of SO4− were used to study water-water reaction and water-rock interaction. The study scheme included static bottle testing for compatibility of the synthetic flooding water and SPW at different mixing ratios and coreflooding at different temperatures for the water-rock interaction. Water-water interaction tests revealed that the reduced sulfate SIW was found to be compatible, and no sign of precipitatation was observed. Untreated SIW showed white precipitates of calcium sulfate when mixed with the high calcium synthetic simulated production water (SPW) at different ratios and temperature. Coreflooding formation damage assessment indicated a reduction in the commercial core plug permeability of less than 12%. Reduced sulfate waterflooding can eliminate the risk of calcium sulfate scale formation damage and minimizing scaling mitigation and challenges requirements.