Scale Inhibition Efficiency of Chelating Agents Under High Temperature and Salinity

Inorganic scale formation presents a significant flow assurance challenge in oilfield operations, especially during seawater injection, where the interaction of seawater anions with cation-rich formation water leads to mineral precipitation. These effects are intensified under high-temperature and high-salinity conditions, where conventional scale inhibitors often lose effectiveness. This study investigates the performance of aminopolycarboxylic acid chelating agents—glutamic diacetic acid (GLDA), diethylene triamine pentaacetic acid (DTPA), and ethylene diamine tetraacetic acid (EDTA)—as alternative scale inhibitors. Static bottle tests were performed using 50:50 and 80:20 synthetic mixtures of seawater (TDS 58,550 ppm) and formation water (TDS 274,740 ppm), at 158 °F and 338°F, with inhibitor concentrations ranging from 0.1 to 1.0 wt%. After seven days, at 158 °F, 0.1 wt% GLDA achieved over 85% inhibition efficiency for calcium sulphate and strontium sulphate. At 338°F, 1.0 wt% DTPA maintained 86.2% inhibition efficiency, outperforming EDTA and GLDA. Ion chromatography and SEM–EDX analyses confirmed reduced scale nucleation and crystal growth. These findings highlight the effectiveness of chelating agents, particularly DTPA and GLDA, in scale management under extreme oilfield conditions. Their ability to perform at lower concentrations supports their potential to enhance oilfield seawater injection and application to reduce freshwater dependency in oilfield operations.