Performance and displacement mechanism of a surfactant/compound alkaline flooding system for enhanced oil recovery

摘要

Monoethanolamine and sodium carbonate were simultaneously applied with sulfonate surfactant to form a surfactant/compound alkaline flooding system, whose optimized composition is 0.20% SLPS, 0.15% Na2CO3, and 0.10% MEA. This system has better anti-salt performance. It can significantly decrease the oil/water interfacial tension (IFT) to ultra-low ( < 10(-3) mN/m) when NaCl concentration is lower than 40,000 mg/L, CaCl2 concentration is less than 400 mg/L, and the temperature is below 90 degrees C. Because of the synergistic effect among SLPS, MEA and Na2CO3, the flooding system shows obviously higher emulsion stability. Micro displacement experiments were performed to investigate the displacement mechanisms of the system. Results indicate that the oil/water IFT reduction and interfacial film softening are two fundamental micro mechanisms which can make crude oil easy to be emulsified by the flooding system. According to the flow velocity and the contact time between crude oil and the system, turbulent-emulsification and self-emulsification are main emulsification mechanisms. During the migration process of emulsion in porous media, the coalescence-entrainment and the coalescence-dispersion phenomena appear, which both can improve the displacement efficiency of remaining and irreducible oil and ultimately enhance the crude oil recovery.