High-temperature and high-salinity performance of chelating agents for oilfield scale inhibition with dynamic scale loop.

Scale formation in oil and gas operations reduces production efficiency and increases costs, especially in high-salinity and high-temperature environments. Conventional inhibitors often fail in such harsh conditions. This study examines diethylenetriaminepentaacetic acid (DTPA) and glutamic acid diacetic acid (GLDA) as primary scale inhibitors under dynamic flow conditions. The experiments use a dynamic scale loop (DSL) that mimics reservoir conditions, with a commercial phosphonate scale inhibitor acting as a comparison benchmark. Experiments were performed at temperatures of 200 °F, 275 °F, and 338 °F, using high salinity water (TDS of 58,500 ppm) representing seawater and formation water (TDS of 274,740 ppm) at mixing ratios of 50:50 and 80:20, with injection rates of 1 and 10 cc/min, and inhibitor concentrations ranging from 0.1 to 1.0 wt%. Scale formation was strongly accelerated by increasing temperature, flow rate, and ion interaction in the 50:50 brine mixture. All inhibitors delayed scale formation relative to the uninhibited case; however, performance varied significantly with operating conditions. Inhibitor effectiveness was evaluated using a normalized improvement factor relative to prescale conditions. DTPA demonstrated strong performance at elevated temperatures, while GLDA showed more consistent performance at higher flow rates. The phosphonate inhibitor performed well under moderate conditions but showed reduced effectiveness under more severe HTHS conditions. Notably, GLDA at 338 °F, with a 50:50 brine mixture and a flow rate of 10 cc/min, delayed scale formation by 11-fold, the most significant improvement observed. These findings demonstrate that inhibitor performance is governed by both thermodynamic stability and kinetic effects and highlight the importance of condition-specific inhibitor selection. Overall, this study provides a systematic framework for evaluating scale inhibitors under realistic dynamic HTHS conditions and demonstrates the potential of chelating agents as effective alternatives for challenging environments.