Preparation and performance evaluation of an active nanofluid for enhanced oil recovery in ultra-low permeability reservoirs

The presence of nano-pore throats results in oil recovery of less than 15% in ultra-low permeability reservoirs. In this work, a new type of nanofluid was developed using chemically modified ultra-small silicon dots (SiDots) dispersed in water for enhanced oil recovery (EOR) of ultra-low permeability reservoirs. First, the ultra-small SiDots were synthesized by the hydrothermal method. Then, active SiDots were obtained by grafting sodium p-aminobenzene sulfonate onto the surface of the SiDots at room temperature with glutaraldehyde as a crosslinking agent. The active SiDot nanoparticles spontaneously dispersed in water; thus, the active SiDot nanofluid could be prepared without an external force. The active SiDot nanofluid exhibited high interfacial activity, reducing the interfacial tension and increasing the expansion modulus of the oil–water interfacial film. In addition, the active SiDot nanofluid showed excellent temperature (110 °C) and salinity resistance (12 × 104 mg/L). The result of imbibition experiments showed that the maximum recovery rate of the active SiDot nanofluid was 38%. The recovery rate of the active SiDot nanofluid was>15% higher than that of brine water and 5% higher than that of surfactants. The active SiDot nanofluids exhibited excellent application potential for EOR in ultra-low permeability reservoirs.