Surfactant-Chelating Agent Based Formulations for Enhanced Oil Recovery

Abstract The presence of salts in reservoir brines and seawater can negatively impact surfactant performance. To address this challenge, chelating agents have been investigated as additives to stabilize surfactants. This study evaluates the stability, wettability alteration, and interfacial tension reduction performance of different types of surfactants, combined with chelating agent EDTA, in salt water for carbonate reservoirs. Tested surfactants include anionic, cationic, and nonionic, to cover different situations. A locally synthesized cationic gemini surfactant was also tested. The spinning drop method and sessile drop method were adopted to measure the IFT values. Static contact angle measurements were conducted to assess wettability changes induced by these EOR materials. Stability tests were conducted by monitoring the precipitations in the fluids in glass vials at varying temperatures in the oven. The application of EDTA requires a moderate pH condition. A low pH (3~5) causes EDTA precipitation while a high pH causes seawater instability. On the other hand, water with high pH can react with oil components to generate surfactants, thus reducing the interfacial tension. While surfactants with other ion types showed a synergic effect with EDTA in changing rock wettability, anionic surfactant (SDS) showed a negative impact that largely inhibited the wettability alteration induced by EDTA. Combinations between EDTA and commercial surfactants such as DTAB and Triton X100 can form stable EOR formulations that are efficient in both IFT reduction and wettability alteration at a proper pH condition. For surfactants largely impacted by salts in stability (SDS) or wettability alteration (GS), a combination with the chelating agent can significantly improve their performance at lifted salinity. In conclusion, this study provides valuable insights into the effectiveness of the combinations between chelating agents and surfactants as EOR materials. The findings highlight the importance of considering reservoir conditions (pH, temperature, salinity) and the synergistic effects of surfactant-chelating agent mixtures for optimizing oil recovery strategies in carbonate reservoirs.