Novel expandable modified graphite for water plugging in deep oil reservoirs

Objective The aim is to solve the problem of water channeling which is easy to occur due to complex geological conditions and harsh reservoir conditions in the process of water injection and oil recovery in deep reservoirs, and then lead to the decline of recovery rate. In particular, considering that the existing plugging agents cannot adapt to the harsh conditions such as high temperature and high salt in deep oil reservoirs, a water plugging system for deep reservoirs with expandable modified graphite was developed.

Method Using natural flake graphite as the base material, a new type of expandable modified graphite was prepared by ultrasonic coordinated oxidation multi-component composite intercalation method for channeling and water plugging in deep reservoirs; the optimal synthetic formula and conditions were determined by an orthogonal experiment. The synthetic formula was that the mass ratio of natural flake graphite, potassium permanganate, concentrated nitric acid, perchloric acid, glacial acetic acid and expander in turn, was 1.0∶0.2∶2.0∶4.0∶2.0∶0.2; the optimal synthesis conditions were oxidation reaction time of 60 min, reaction temperature of 30 ℃; enhanced intercalation reaction time of 30 min, reaction temperature of 30 ℃. The structure of the synthesized expandable graphite was characterized by IR and X-ray diffraction.

Result The results of IR, X-ray diffraction and scanning electron microscopy showed that the synthesized expandable modified graphite was the expected structure, and the intercalation agent was successfully inserted between the graphite layers, and the expanded graphite particles still retained the sheet structure. The initial particle size of natural flake graphite used in this study is 300 μm. It can expand 6.0 times in the wet phase environment at 200 ℃, and has good expansion performance.

Conclusion The synthesized expandable graphite can be fully expanded in fractures and firmly combined with the rough wall, which can effectively plug the channeling channel, and the plugging rate reaches 96%. The research results can provide new ideas for the regulation of deep oil reservoirs.