Abstract: In response to the problem of rapid rise of water injection pressure in the Weijialou tight reservoir, the nano-injection enhancing technology was introduced, and the principle and influencing factors of the nano-injection enhancing technology were analyzed through slim-tubes and core flooding experiment devices. The result shows that the nano-injection enhancer can change the wettability of rocks, which can change hydrophilic reservoir into neutral or oleophilic reservoir and reduce the thickness of water film formed on the surface of pore throat of hydrophilic reservoir; the nano-injection enhancer can also adsorb on the surface of pore throat to strip the hydration film on the surface of pore throat, so as to increase the effective radius of pore throat and reduce the fluid resistance, thus increasing the water absorption capacity of the formation. The slim-tube displacement experiments show that the nano-injection enhancing solution with a mass fraction of 0.010% has a better pressure reduction effect for slim-tubes with a diameter of 50-100 μm, with a maximum pressure reduction rate of 30.1%; the natural core flooding experiments show that the nano-injection enhancing solution has a better pressure reduction effect with a pressure reduction rate of 40.0% when the injection volume of the nano-injection enhancing solution is 1 times the pore volume and the adsorption time is greater than 36 h. The results of the field test of pressure reduction and injection enhancing in Weijialou Oilfield show that the nano-injection enhancer can reduce the injection pressure of water injection wells by 2.4MPa. The results of this study have good application value for high-pressure under-injection well governance in tight reservoirs;Weijialou oilfield

Key words: nano-injection enhancer, wettability, pressure reduction rate, hydration film, hydrophobic layer, contact angle, tight reservoir, Weijialou Oilfield