Implementing ASP Without Water Softening in Reservoirs With Low Concentrations of Divalent Ions

Alkaline Surfactant Polymer (ASP) flooding has proven to be an effective method to recover residual oil after waterflood. Yet, there are several complications that limit a wide implementation of ASP. The source water needs to be softened to avoid injectivity issues due to scale formation when alkali is mixed with divalent cations. Even when softened water is used as base water, scaling can still be an issue in producing wells due to mixing of waters with different compositions in-situ. Scale control by means of scale inhibitor squeezes on the production side or scale inhibitor on the injection side have been reported to be successful for some cases. Carbonate scaling issues are most severe when sodium carbonate is used as alkali. Even if alkalis other than carbonate are used, carbonate scale remains an issue as bicarbonate that is present in almost any formation water, will convert to carbonate at high pH and will subsequently precipitate with the divalent ions present. Ethanolamine has been proposed as an effective alkali in ASP application with high TAN oils for reservoirs that contain relatively low concentrations of divalent ions in their produced water that is reinjected. ASP implementation could significantly be simplified if softening of the produced water could be avoided. Results of a study that involved determination of scaling tendencies, compatibility testing, tube blocking tests, and core floods with and without the addition of scale inhibitor will be presented together with implications for field implementation. A potential additional advantage of adding scale inhibitor on the injection side is that the scale inhibitor travels with the components to be inhibited. This might eliminate the need for scale control measures at the production side.