Middle East reservoirs are usually characterized as high temperature and high salinity (HTHS). In chemical EOR, interfacial tension (IFT) is a key parameter that alters the reservoir environment. IFT measurements are challenging specially at high temperatures due to its dynamic nature. Viscoelastic surfactants are introduced because of their dual capability of lowering the IFT and improving the sweep efficiency of the reservoir. In this paper, the main objective is to determine ultralow IFT's and thermal stability that can be obtained from viscoelastic surfactants in the presence of heavy crude oil using spinning drop tensiometer (Kruss), thermogravimetric analyzer (TGA), nuclear magnetic resonance (NMR) and fourier transform infrared (FTIR) spectroscopy. Investigation of VES is performed with heavy reservoir oil (12cp at 90°C) and using high salinity formation brine (234,189 ppm). The solutions were prepared by the combination of viscoelastic surfactant and undiluted sea water and stirred until they attain equilibrium. Density and IFT at high temperatures are determined. Equilibrated solutions are used with heavy reservoir oil to determine the IFT reduction capability of viscoelastic surfactant at various concentrations from 0.1 to 1%. Results show a considerable reduction in IFT with viscoelastic surfactant up to 10−1 mNm−1 range. IFT reduction usually depends on the concentration of solutions used. Results also show that ultralow IFT was obtained at 50°C and 80°C. Encouraging results with TGA demonstrated that VES is thermally stable and show high resistance to temperatures up to 250°C. Long-term thermal stability up to 30 days at 90°C and 120°C temperatures was evaluated. 1H NMR show stability in structure while 13C NMR results show minor structural changes in the aliphatic region. FTIR results indicated good thermal stability with strong bonding between C-H and C=O. Static adsorption is evaluated by shaking the powdered core samples with VES at two different high temperatures for 24 hours. Concentration measurements are performed using total organic carbon (TOC) analysis. Static adsorption results give less adsorption when we have higher temperatures compared to lower temperatures. Experimental results indicate two major effects. Firstly, ultralow IFT obtained with the novel viscoelastic surfactant and it is thermal stable at high temperatures. Secondly, viscoelastic surfactant significantly reduces retention at high temperatures when compared with low temperatures. They are excellent additives in chemical EOR for HTHS conditions. They are also very useful when we have heavy reservoir oil and where IFT reduction is required to mobilize the oil and improve the sweep efficiency of the reservoir.

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