LAUSR

Nano-fluids in recent years showed great potential as a chemical enhanced oil recovery (EOR) technology thanks to their excellent performance in altering interfacial properties. However, due to the great challenge in preparing stable systems suitable for elevated temperature and high salinity environment, expanding the application of nano-fluids was greatly restrained. In this work, a novel nano-fluid was prepared by integrating positively charged amino-terminated silica nanoparticles (SiNP-NH2) with negatively charged anionic surfactant (Soloterra 964) via electrostatic force. The resulted nano-fluid could be stored at relatively high salinity (15 wt.% NaCl solution) and high temperature (65 °C) for more than 30 days without aggregation. Successful coating of the surfactant on target SiNPs was verified by FTIR spectrometry and the surface charge and size distribution. In addition, the potential of the nano-fluid in recovering oil was investigated by analyzing the nano-fluid/Bakken oil interfacial tension and the variation tend of oil contact angle when brine was replaced by nano-fluids. Experimental results showed that the water-oil interfacial tension of the Bakken crude oil decreased by 99.85% and the contact angle increased by 237.8% compared to the original value of 13.78 mN/m and 43.4°, respectively indicating strong oil displacement efficiency and obvious wetting transition from oil-wet towards water-wet. Spontaneous imbibition tests conducted on Berea rocks showed that the nano-fluid yielded a high oil recovery rate of 46.61%, compared to that of 11.30%, 16.58% and 22.89% for brine, pure SiNP-NH2 and pure surfactant (Soloterra 964), respectively. In addition, when core flooding was applied, total 60.88% of the original oil in place could be recovered and an additional oil recovery of 17.23% was achieved in the chemical flooding stage. Moreover, a possible mechanism of the EOR using the nano-fluid was proposed. Overall, the developed nano-fluid is a promising new material for enhanced oil recovery.