(172b) Compatibility of the Surfactant-Chelating Agent Formulations for EOR Application

Surfactants are widely used in reducing the oil/water interfacial tension (IFT) so to get a favorable mobility ratio, enhanced oil removal, and microemulsions. However, the functionality of surfactants is largely dependent on conditions including temperature, salinity, hardness, etc. The exploration and exploitation of oil and gas resources has reached reservoirs of harsh conditions. Chelating agents are popular additives in EOR fluids to mitigate the negative impact of salts on the stability or functionality of chemicals. Studies have proven the potential of surfactant/chelating agent mixtures in increasing oil recovery. Apart from accommodating other chemicals, chelating agents themselves are found to reduce IFT, change rock wettability, improve conductivity, etc., exhibiting vast possibilities in EOR applications. This study aims at studying the compatibility of the surfactant-chelating agent-alkali compositions under harsh conditions.

Three types of commonly used chelating agents, EDTA, DTPA, and GLDA, are tested in this study. The tested surfactants include SDS, DTAB, and Triton X100, two locally synthesized zwitterionic surfactants, and two locally synthesized cationic Gemini surfactants. The brine of salinity ranging from 0 to approximately 214000 ppm was prepared by dissolving NaCl, MgCl₂, CaCl₂, NaHCO₃, and Na₂SO₄ in deionized water. The pH value of the compositions was controlled by adding diluted KOH or HCl solutions. Stability and IFT reduction performance of the solutions were tested at temperature varying from room condition (22°C) to high temperature (90°C).

Results showed that chelating agents themselves have a limited impact on the oil/water IFT. The significant IFT reduction results obtained come from the addition of surfactants. Increased salinity largely impacted the performance of all tested surfactants, both in IFT reduction and in wettability alteration. Chelating agents, however, have relatively consistent performance with lifted salinity. By adding chelating agents in surfactant solutions, the wettability alteration performance was significantly improved. Strongly oil-wet rock substrates were altered to water-wet conditions. The stability of surfactants under high temperature and high salinity conditions was largely improved with the addition of chelating agents. Though popularly used commercial surfactants showed improved performance when combined with chelating agents, locally synthesized cationic gemini surfactants managed to achieve comparable results at a much lower concentration, proving their high cost-efficiency compared to conventional commercial surfactants.

In-house developed cationic gemini surfactants emerged as cost-effective alternatives, offering comparable results at lower concentrations compared to conventional commercial surfactants. The combination of gemini surfactant and chelating agents, presents a potentially cost-effective EOR composition for oil-wet carbonate reservoirs.