Improvement of waterflooding sweeping efficiency of the well patterns in low-permeability oil reservoirs with plane heterogeneity based on injection and production optimization

Unstable water injection is widely applied to the waterflooding development of heterogeneous oil reservoirs. In order to further improve the waterflooding effect of low-permeability oil reservoirs with plane heterogeneity, this paper adopted the radial-flow physical model corresponding to the target oil reservoir to analyze the production performance and recovery factor of the production wells of the well group in the plane heterogeneous oil reservoirs in three kinds of injection/production modes. Then, the mechanisms of improving the waterflooding effect in these three kinds of injection/production modes were clarified, and their applicability was pointed out. It is indicated that by means of unstable water injection, unstable pressure field can be formed and oil-water mutual flow and elastic drive are realized, so that the oil displacement effect in the low-permeability areas is improved. The injection/production method with synchronously balanced liquid production rate can improve the overall waterflooding sweeping efficiency and make use of the unstable water injection to increase the recovery factor of low-permeability areas, so as to improve the overall recovery factor. The injection/production method with asynchronously balanced liquid production rate can increase the oil displacement efficiency of low-permeability areas by adjusting the injection/production pressure difference after the unstable water injection. In the meantime, it increases the sweeping efficiency of the injected water in low-permeability areas, so as to improve the recovery factor of low-permeability areas greatly. The experimental results provide the theoretical support for optimizing the injection and production mode of waterflooding development of the target oil reservoir.