Scale Inhibitors Designed for Zinc Bromide High-Density Completion Brines

Abstract Zinc bromide high-density brines are widely used in well completions, and zinc sulfide scale, which can cause formation damage and production decline, has been reported in some well completions. When severe scaling occurs, costly acid stimulation treatments are required to restore well production. Therefore, it is highly desirable to add an effective ZnS scale inhibitor directly to ZnBr2 brines before scaling can occur downhole. While scale inhibition methods for sulfates and carbonates in production equipment and reservoirs have been extensively studied, only limited literature for sulfide scales exists. Of the limited case, most are related to treatment in production tubing and topside process facilities, i.e., low zinc concentration in produced waters. Unlike traditional scale inhibitors which are typically applied in fresh water or very low salt solutions (~3 % salt), inhibitors designed for zinc brines need to be compatible with more than 50% dissolved salt. In zinc brines, the extremely high salt content and the limited amount of free-water severely restrict both the solubility and effectiveness of inhibitor candidates. Furthermore, most wells using high-density zinc brine are high-temperature high-pressure, and conventional scale inhibitor evaluation methods are not adequate. New evaluation methods were developed to test scaling tendencies and inhibition under downhole conditions. This research work was focused on the development and evaluation of ZnS scale inhibitors compatible with high-density zinc brines. Candidate chemicals were selected based on their potential ZnS scale-inhibition characteristics, and were studied in high-density zinc brines at high temperatures. Details of the test methods and results are presented for several ZnS scale inhibitors.