A Synergistic Chelating Approach for Hematite Filter Cake Removal in Carbonate Reservoirs Using DTPA and Citric Acid

Abstract Efficient removal of hematite-based filter cake is critical for restoring formation permeability while minimizing secondary formation damage. Conventional hydrochloric acid treatments often lead to severe corrosion and iron precipitation when reacting with carbonate formations. In this study, a combined chelating system consisting of 10 wt% diethylenetriaminepentaacetic acid (DTPA) and 10 wt% citric acid was developed to dissolve hematite-based filter cake under formation-friendly conditions. The solution, maintained at a pH of 2.25, achieved a solubility of 3.4 g of hematite per 100 cc of solution after 18 hours at 185 °F. The combination of DTPA and citric acid provided a synergistic chelating capability that stabilized the dissolved iron species, preventing reprecipitation during pH increase caused by calcite dissolution. The inclusion of citric acid significantly reduced the required DTPA concentration—addressing the economic limitation of DTPA's high cost—while maintaining high iron-chelating efficiency. A systematic series of solubility tests was conducted to evaluate the effects of solution pH, temperature, and treatment time on the dissolution performance. Results showed that solubility increased with temperature and prolonged exposure time, reaching optimal performance after 18 hours. Laboratory-prepared filter cakes formed on ceramic disks exhibited 85% removal efficiency under the optimized conditions. Additionally, corrosion testing revealed substantially lower metal loss compared with HCl-based treatments, confirming the system's practicality for downhole applications. The DTPA–citric acid system offers a cost-effective, corrosion-controlled, and formation-compatible alternative for removing hematite-based filter cakes in carbonate reservoirs.