Evaluation of Polyamidoamine-Assisted Scale Inhibitors to Mitigate Silicate Scale Formation in Near Wellbore Region

Abstract

Abstract Silicate scaling is a concern that could result in formation damage and flow assurance issue. Phosphonates and phosphino-polyacrylates are widely used to treat many types of scale but they are not intended to treat silicate scale. Besides that, these inhibitors may have been considered as harmful substances due to their reported inherent biodegradability. Synergistic silicate scale inhibitors are current trends since cationic or anionic polymers alone is found not effective for silicate scale inhibition. The objective of this work is to assess the performance of polyamidoamine-assisted scale inhibitors for silicates. The experiment settings are simulating the environment in near wellbore region, such that higher temperatures and brine that is mostly pH neutral. The effectiveness of scale inhibitors is investigated through static bottle test and dynamic scale loop (DSL) test. The scale inhibitors are also characterized to determine their functional groups in aqueous state. The tendency of scale inhibitors to impede silicate polymerization process is also determined through the remaining concentration of monomeric silica in water after 72 hours. FTIR revealed that all scale inhibitors exhibit amine characteristic in water. Experimental results show that the polyamidoamine-assisted scale inhibitor, PAMAM G-2/PteGlu, is the most effective in mitigating silicate scale formation. It reduces scaling brine's turbidity as much as 94.8% after 72 hours at 90°C. In addition, it also minimizes silicate polymerization process by retaining almost half of the initial monomeric silica concentration. This also implies that PAMAM G-2/PteGlu inhibitor could reduce the tendency of silicate scale formation to 46% as compared to 97% of silicate scale formation without any inhibition at 95°C. From DSL test, PAMAM G-2/PteGlu inhibitor is also the most effective inhibitor. It prolongs the scaling time from 7 minutes to 339 minutes at 0.01 g/L inhibitor concentration. It is also 7% more effective than PAMAM G-1/PteGlu inhibitor in DSL test. In general, the performance of scale inhibitors for silicates can be arranged as: PAMAM G-2/PteGlu > PAMAM G-1/PteGlu > PteGlu > PAMAM G-2 > PAMAM G-1 from top to bottom. In this work, these environment-friendly products had demonstrated good silicate scale inhibition as well as synergistic effect. They could offer as alternatives to commercial scale inhibitors.