Nanofluids with superhydrophobic nanoparticles for improved depressurization mechanism in low permeability reservoirs

Decreasing injection pressure and increasing water injection are crucial methods to enhance oil recovery in low permeability reservoirs. However, the high injection pressure, constrained by the reservoir's low porosity and permeability, limits the amount of injected water, consequently resulting in low recovery. In this study, inspired by the ''lotus effect'' of superhydrophobic wettability, we synthesized superhydrophobic nanoparticles by grafting fluorine-containing long chains onto the surfaces of SiO 2 nanoparticles. Nanofluids with small particle size (7 nm), high stability, and strong hydrophobicity (162°) were prepared by compounding modified SiO 2 nanoparticles with surfactants. The functional properties of the nanofluids revealed a depressurization rate of 23.13 % and the 23.90 % increase in flow rate at the channel center. Modified nanoparticles altered the surface wettability from hydrophilic to superhydrophobic. Surface free energy, determined using a three-probe-liquid method, demonstrated a significant reduction after hydrophobic modification. The surface hydrophobic interaction was tested and quantified by AFM measurements. The results show that the adhesion force is much larger than that of the unmodified hydrophilic surface. Through these analyses, we propose an efficient depressurization mechanism facilitated by the superhydrophobic layer formed by modified SiO 2 nanoparticles. This work offers technical and theoretical support for the efficient development of low permeability reservoirs.