Study on the Technology of Composite Nano Depressurization and Augmented Injection for Water Injection Well in Offshore Oil Field

In order to solve the rapid increase of pressure and under injection of water injection wells in offshore oilfeld, a composite nano depressurization and augmented injection system for water injection well in offshore oilfeld was developed. The stability, interfacial activity, anti-swelling property, change of the rock wettability, and the ability to reduce the migration and damage of the particles were evaluated. Meanwhile, the effect of depressurization and augmented injection was demonstrated by the displacement experiment. The results show that the composite nano depressurization and augmented injection has a good stability and interfacial property, and the interfacial tension can be stabilized at 10^-2 mN/m when placed under the simulated reservoir temperature for 50 days. The anti-swelling rate of core powder can reach 96.7%, which can effectively change the surface wettability of rock. The total number of the particles and the median diameter of the flooding particles were signifcantly decreased after treating by the system, it means the possibility of blockage caused by particle migration can be reduced to some extent. Core flooding experiments showed that the depressurization rate reaches more than 35% after taking the augmented injection measure. It can be concluded that the drag reducing effect of the composite nano depressurization and augmented injection system is obvious, and can meet the needs of longterm depressurization and augmented injection of water injection wells in offshore oilfeld.