Polymer nanoparticles based nano-fluid for enhanced oil recovery at harsh formation conditions

Abstract The application of nano-fluids for enhanced oil recovery (EOR) has attracted noticeable attention and has formed a new research area in recent years. Currently the great challenge for this area is to formulate a stable nano-fluid for oil reservoirs with high-temperature and high-salinity, in particular, when divalent ions are present. In this paper, a novel nano-fluid was developed by using nano-composite formed with polymer nanoparticles (PolyNPs) and a betaine-type zwitterionic surfactant. The developed nano-composite was characterized using electron microscopies (TEM and SEM), Fourier transform infrared (FTIR) spectrometry, dynamic light scattering (DLS), etc. The nano-fluid showed noticeable stability at relatively high salinity (15 wt% simulated brine) and high temperature (80 °C) for more than 30 days. The potential of the nano-fluid in recovering oil was evaluated by investigating the interfacial tension with Bakken oil and the oil contact angle in the nano-fluid. The results showed that the water–oil interfacial tension of the Bakken crude oil decreased by 99.49% and the contact angle increased by 125.73% compared to the original values. Then, the EOR efficiency of the nano-fluid was tested using Berea rocks saturated with Bakken crude oil through core flooding experiments. The results showed that the total oil recovery by nano-fluid is 9.32% higher than that of the control. Finally, the possible mechanism of the nano-fluid for EOR was proposed based on the investigation of dynamic displacing processes. The results demonstrated that the developed nano-fluid is a highly promising oil displacement agent for enhanced oil recovery.