The formation of silica and silicate scales caused troublesome issues in various water-handling systems, including steam generators, geothermal wells, and waste-water disposal systems. Recently, a produced water with over 300 ppm of silica, and a spent brine off the strong acid cation (SAC) softeners containing high levels of calcium (Ca), barium (Ba), and magnesium (Mg) were commingled in the production wells. The mixing of these two waters induced silicate as well as other scales, including calcite, barite, etc. In order to provide effective scale inhibition when these waters are mixed, effective scale inhibitors for both silicate and other scales were requested for evaluation.

In this paper, scale inhibitor chemistries for preventing both silica/silicate and other scales were reviewed and the possible synergistic effects were assessed by Design of Experiment (DOE) software. DOE is a systematic method to determine the relationship between several factors, i.e. various chemistries and the performance of formulations under designed application conditions. Selected chemicals were formulated for control of both silica/silicates and other scales, and their performances were evaluated by a Kinetic Turbidity Test (KTT). The KTT is a novel laboratory test method using an Ultraviolet-Visible (UV-Vis) spectrophotometer to monitor the formation of scales at various dosages of tested products. Bottle tests were also conducted for the comparison of inhibition performance.

Based on the lab testing results from the KTT and the bottle tests, the combined products exhibited good scale inhibition performance for both silicate and other scales. The product was recommended for field applications. Subsequent field applications of this product have provided the desired scale control.

This paper presents the laboratory testing data for scale inhibitor selection for the combination products on both silica/silicate control and other scale control by using the efficient performance evaluation method. It also provides an effective product formulation approach for finding synergetic effects of different products. Successful scale inhibitor implementations in the field applications are also presented in this paper. Both laboratory and field testing results show a good case history for the optimization of the silica/silicate and other scale treatment.

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