Oilfield scale deposition is a common problem causing production deferment, safety issues, and equipment damage. This paper presents the laboratory testing data and some field data for barium sulfate (barite) and zinc sulfide (ZnS) scale control. It demonstrates possible synergetic scale inhibition effects and successful field implementation based on laboratory results in a produced water stripping system. Literature shows barite scale can be effectively prevented by phosphonate inhibitors and polymer inhibitors. Effective ZnS scale inhibitors are not commercially available, so dispersants are commonly used to suspend the ZnS scale particles in production fluids carrying the particles through the system without deposition.

Ten scale inhibitors were evaluated for this system: Product A (combination of phosphonate inhibitor and ZnS dispersant); Product B (polymer inhibitor), Product C (polymer inhibitor), Product D (chelator), and Product E (chelator), Product F (phosphonate inhibitor + polymer inhibitor), Product G (phosphonate inhibitor + polymer inhibitor), Product H (phosphonate inhibitor + polymer inhibitor), Product I (phosphonate inhibitor + polymer inhibitor), and Product J (phosphonate inhibitor). Aerobic bottle tests, anaerobic bottle tests, and kinetic turbidity tests evaluated the potential scale risk at various scaling conditions including ∼3,000 mg/L SO42-, 1.1-78 mg/L Ba2+, 0.56 -5.6 mg/L Zn2+, 25-250 mg/L H2S, and pH (3.2-7.5). Product F (phosphonate/dispersant) prevented barite and ZnS most effectively in lab testing but was incompatible with the process system, so Product G, the second best performer, was field trialed. Product C prevented barite scale formation at low dosage and eventually prevented ZnS formation at very high concentrations.

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