An Insight into Scale Inhibition Mechanism and the Development of an Inhibitor Package Against Extremely Severe Barium Sulfate Scale

Abstract Most kinetic scale inhibitors behave similarly in mild to severe scale risks by extending induction time. Induction time refers to the time from equilibrium shifting into supersaturation occurs until detectable scale forms. The higher a scale inhibitor dosage, the longer an induction time. However, in this study, different inhibition behaviors were observed under different scale inhibitor treatments in extremely severe barium sulfate (i.e., barite) conditions, with an associated saturation index (SI) of 2.79. Kinetic turbidity testing (KTT) was used to observe scale inhibition behaviors, including induction time and scale precipitation amount. The test temperature was 38°C (100°F). In KTT observations, the test brine (called blank hereafter) formed barite at <1 minute due to the extremely high SI. Many scale inhibitors could not inhibit barite even at 600 ppm or higher dose, while some inhibitors could inhibit barite for at least 2 hours at a dosage of 200 ppm or less. For the inhibitors that worked well, if dosed under their minimum inhibitor concentrations (MIC), some inhibitors extended induction time from <1 minute to 20 minutes or longer and then barite gradually formed. This phenomenon is typical for scale inhibition. However, for some other scale inhibitors if dosed under their MICs, it showed similar induction time as the blank, but the barite amount was significantly lower than the blank. The higher the inhibitor dose, the less barite formed. The obviously different inhibition behaviors reflect different inhibition mechanisms; nucleation inhibition and/or crystal growth inhibition or others. The barite that formed in test samples were further examined by Scanning Electron Microscopy (SEM) and Energy-dispersive X-ray spectroscopy (EDX) to investigate inhibition mechanisms. Based on the above observations, a barite inhibitor package was proposed by combing inhibitors with different inhibitor behaviors. It turned out that a strong synergism effect on barite inhibition was observed. The proposed package would significantly reduce chemical cost for barite control.