Barium Sulfate Kinetics on Steel Surfaces at Different Supersaturation Ratios

Barium sulfate surface deposition kinetics, at different supersaturation ratios in realistic oilfield brines, were investigated in a flow system at a constant temperature of 75 °C. In order to investigate the effect of one parameter (barium content), the supersaturation ratio of the mixed brines was varied over a wide range of Ba²⁺ ion concentrations (150 ppm, 100 ppm, 80 ppm, 50 ppm and 20 ppm). The expected barite formation was predicted using a theoretical approximation method. The barite surface deposition pattern was monitored by a sensitive differential pressure technique tool with respect to the change of pressure across the test capillary when scaling occurs. It was found that the barite surface induction period is inversely proportional to the supersaturation ratio and the whole process seems controlled thermodynamically at high supersaturation ratios (SR). This was obvious when plotting the reproducible observed induction time data versus the predicted supersaturation ratios and/or Ba²⁺ ion concentration. The exponential growth period was found to differ based on the saturation ratio. For each surface deposition measurement, the obtained growth factor is directly proportional to the Ba²⁺ concentration. The lowest SR was calculated at 20 ppm barium content and the role of barite on the whole deposition process was determined. Bulk assessment (turbidity, conductivity and ion selectivity for barium) was done to support the surface data. The bulk test provides information on the growth of scale crystals in the flow during the unstable mixing stage until surface deposition, indicating the time duration of this stage.