Experimental Investigation of Hydrophobically Modified α-ZrP Nanosheets for Enhancing Oil Recovery in Low-Permeability Sandstone Cores

Highly crystalline α-zirconium phosphate (α-ZrP) nanoparticles were synthesized and exfoliated into nanosheets, and then the hydrophilic nanosheets were modified into hydrophobic nanosheets with octadecyltrichlorosilane (OTS). Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analysis were applied to confirm the morphology and chemical structure of the nanosheets. Contact angle measurement was conducted to explore the wettability alteration of the hydrophobically modified α-ZrP nanosheets, and the result showed that the wettability of the core was changed into hydrophobicity. When ZrP-OTS nanosheets were injected during water-flooding, a Pickering emulsion will be formed. The droplet diameters and viscosities of the Pickering emulsions were measured. The hydrophobically modified α-ZrP nanosheets were applied in low-permeability sandstone cores and various concentrations were tested. The injectivity of the hydrophobically modified α-ZrP nanosheets was also studied and the result indicated that the nanosheets exhibit good injectivity. The mechanisms for enhancing oil recovery by utilizing hydrophobic α-ZrP nanosheets were analyzed: forming Pickering emulsions and increasing the viscosity of the displacing phase. Forming emulsions and increasing the viscosity of the flooding phase can enhance the microdisplacement efficiency, while good injectivity can also enhance the macrodisplacement efficiency. The result indicated the possibility of using hydrophobically modified α-ZrP nanosheets for enhancing oil recovery in a low-permeability reservoir.