关键词: 疏水纳米SiO₂, 防膨机理, 吸附, 隔离作用, 减阻

Abstract:

Drag reduction technology of nano-materials is an effective new technique to solve the problem of under-injection in high pressure in oilfields，however, its drag reduction mechanism is not well understood. Hydrophobic nano-particles inhibiting clay swelling is one of the drag reduction mechanisms of nano-materials. A new testing method of the anti-swelling effect, suitable for strongly hydrophobic nano-powder, was applied to test the anti-swelling rate of bentonite with various hydrophobic nano-SiO₂ materials. Adsorption features of nano-SiO₂ particles on core surface were studied by means of adsorption experiments and scanning electron microscope (SEM). The result of anti-swelling experiments shows that most of the nano-SiO₂ materials have certain anti-swelling properties，which however show a big difference in the anti-swelling effect. The anti-swelling effect is greatly influenced both by the surface modifier of nano-SiO₂ particles and by the proportion of nano-SiO₂ particles to bentonite，therefore, an appropriate modifier or an optimum proportion can achieve a good anti-swelling effect. The anti-swelling rate of nano-HNP2 is about 46.9% when the proportion is 1∶25，while the anti-swelling rate of nano-HNP4 becomes about -25.8% when the proportion is 1∶25. The SEM photos show that hydrophobic nano-SiO₂ particles can form nano-particle layers on cores through adsorption and make core surface highly hydrophobic, here the water contact angle is 138.3°. The investigation indicates that through adsorption on clay mineral surface, hydrophobic nano-SiO₂ can form isolation layers with high hydrophobicity, which separate clay minerals from water to produce an anti-swelling effect. This anti-swelling mechanism is somewhat different from that of commonly used clay stabilizers.

Key words: hydrophobic nano-SiO₂ material, anti-swelling mechanism, adsorption, isolation, drag reduction