A novel amphiphilic Janus nano-silica for enhanced oil recovery in low-permeability reservoirs: An experimental study

The hydrophilic nano-silica (HNS) has become a research hotspot in multiple fields due to its cost-effectiveness and environmental protection. However, due to the lack of the amphiphilic structure, the HNS is unable to reduce interfacial tension (IFT), which is adverse to the recovery of residual oil from reservoirs. Therefore, it is of great significance to prepare amphiphilic Janus nano-silica similar to surfactant for enhanced oil recovery (EOR). In this present work, a sulfonic/alkane composite amphiphilic Janus nano-silica (SAJNS) was fabricated through the Pickering emulsion template approach under specific conditions, and its surface structure was confirmed through related characterization techniques. Then, 500 ppm of the SAJNS was dispersed in different based fluids to prepare corresponding nanofluids. The prepared nanofluids could remain stable at 50 degrees C during storage for one week. Benefiting from the amphiphilic characteristic, the SAJNS migrated from the aqueous phase to the oilwater interface and thus reduced the IFT, which made the residual oil remobilize inside the pore throats. The measurement result of the contact angle illustrated that the oil-wet thin slice treated with the nanofluid became water wet. SEM and EDS techniques indicated that the adsorption of the SAJNS on the surface of the thin slice was responsible for the wetting alteration. Besides, almost all the crude oil adsorbed on the glass slide face was stripped after immersion in the nanofluid. The core flooding experiment demonstrated that the injected nanofluid helped to recover residual oil and decrease injection pressure. The NMR results presented that most recovered residual oil was from the micropores.