Synthesis of an Amphiphobic Nanofluid with a Novel Structure and Its Wettability Alteration on Low-Permeability Sandstone Reservoirs

To address the water-blocking and water-sensitivity issues in low-permeability sandstone reservoirs, this paper describes a simple method to synthesize amphiphobic nanofluids by combining nanosilica, multi-walled carbon nanotubes (MCNTs), and trichloro(1H,1H,2H,2H-perfluorooctyl)silane. These fluids process bead chain structures with a special chemical property that alters the sandstone core surface from amphiphilic to amphiphobic. To examine the wettability alteration of the sandstone core surface after treatment with amphiphobic nanofluids, contact angle tests, calculations of the surface free energy, liquid level measurements, spontaneous imbibition tests, permeability recovery experiments, and oil recovery experiments were carried out. The results showed that the contact angle of deionized water on the sandstone core surface reached up to 160°, 120°, and 110° and the contact angle of hexadecane reached up to 133°, 88°, and 91° after treatment with the amphiphobic nanofluids, the modified nanosilica nanofluids, and the modified MCNT nanofluids, respectively. Meanwhile, these three nanofluids decreased the surface free energy to 0.73, 6.80, and 9.70 mN/m; in addition, they reduced the liquid level from 40 to −46, −30, and −16 mm in deionized water and from 24 to −16, −2, and 1 mm in hexadecane, respectively. The amphiphobic nanofluids lowered the spontaneous imbibition volume more effectively than the other two nanofluids. As the wettability in the sandstone core surface was altered from amphiphilic to amphiphobic, well recovery of the sandstone core permeability increased and resulted in an approximately 9% enhancement of the oil recovery.