Study Of A Multifunctional Decompression And Augmented Injection System In Low Permeability Reservoir Of Changqing Oilfield

According to the problems Changqing Oilfield faced when developing low permeability reservoir, a decompression and augmented injection system with multifunctions such as reducing the interfacial tension, changing rock wettability, preventing the migration or swelling of clay grains, lightening scaling problem and so on was studied and its formula was optimizatised as 0.05%HA-1+0.10%MEA+0.10%methanol+2.0%DMDAAC+5.0%ATMP. The system’s performance on changing wettability and lightening scaling were investigated. The results show that the system can convert the oil-wet surface to wet surface observably from 129°to 60°and the tendency to scaling is well controled. It has better performance of the interface under the conditions of NaCl concentration of 5000mg/L~30000mg/L, CaCl2 concentrations of less than 600mg/L, and it has good adaptability for temperatures below 40℃~70℃.The Core displacement experiment showed that the depressurization rate of the decompression and augmented injection system can reach up to 20%, and the system has a good decompression and augmented injection effect for the examined low permeability reservior. What’s more, the more the amount of slug injection is and the slower the injection speed is, the larger the decompression extent will be. Besides, the flooding effect of the system was also evaluated. The result shows that, when inject 1.0PV decompression and augmented injection system after first water drive, which is followed by the second water flooding, the EOR can totally reach up to 70.59%, among which 19.25% was contributed by the system. The mechanism of decompression and augmented injection was studied, which is, greatly reducing oil-water interfacial tension, well changing the wettability of the rock and preventing the migration or swelling of clay grains.