(212a) Investigating the Coupled Effect of IFT Reduction and Wettability Alteration in Enhanced Oil Recovery from Carbonate Reservoirs

Carbonate reservoirs are often oil-wet and naturally fractured, leaving about 2/3 of the oil Carbonate reservoirs often retain around 2/3 of their oil after secondary recovery, necessitating the use of Enhanced Oil Recovery (EOR) techniques to improve oil recovery efficiency. Two of the most crucial mechanisms for EOR in carbonate reservoirs are Interfacial Tension (IFT) reduction and Wettability Alteration. Although both methods contribute to oil recovery when used separately, their combined effect can lead to confusion about whether they have a synergistic or offsetting impact. Some studies suggest that IFT reduction can enhance wettability alteration. In this research, the study compares the performance of wettability alteration with and without IFT reduction and concludes that IFT reduction has a negligible effect on wettability alteration. The research employed Indiana limestone outcrops, filtered crude oil, a commonly used chelating agent (DTPA), and a zwitterionic surfactant (ZS). The limestone outcrops were cut into 1-inch diameter and 3-4 mm thickness slices, smoothened using P500 sandpaper, and then aged in crude oil at 90°C. Different concentrations of DTPA solutions were diluted using synthetic seawater, and ZS was added to some solutions, while some only had ZS seawater solutions without DTPA. The IFT values between oil and solutions were measured, and the oil-aged slices were treated with different solutions to reflect on their wettability alteration performance. The IFT results showed that ZS is highly effective in reducing IFT values down to 0.01 mN/m, while having a negligible effect on wettability. On the other hand, DTPA is highly effective in changing rock from strongly oil-wet to water-wet conditions but has limited impact on IFT. When DTPA and ZS were combined, the solutions were effective in both reducing IFT and changing wettability. However, the wettability alteration performance of DTPA+ZS was similar to that of DTPA alone, indicating that even significant IFT reduction has negligible influence on the wettability alteration performance.