Remaining oil after polymer flooding is very scattered, and the remaining oil in top sections is extremely difficult to develop, yet there is no prevailing technology suitable for developing the reservoirs after polymer flooding. Gas injection for stable gravity combination flooding is studied by force analyses and numerical simulation.

The force condition of oil droplets in porous media was studied in this paper, and the action of buoyancy on oil droplets was considered during different stages of oilfield development. Based on the analyses of stress on oil, the idea of injecting gas at the top sections of the reservoir and conducting ASP flooding at the bottom sections has been proposed in this paper. Performances of different displacement modes have been predicted for the block in Daqing oil field after polymer flooding.

The research results showed that gas injection for stable gravity combination flooding had the best performance with an EOR increment of 13.53%. Comparing the remaining oil saturation of different displacement modes, the low permeability formations in the top section was effectively flooded and the remaining oil of whole formation was reduced significantly by gas injection for stable gravity combination flooding. Vertical remaining oil distribution at different time points was analyzed. Because of differential pressure in vertical direction, the remaining oil was driven to migrate downward after injecting gas in the top sections, and then the remaining oil was flooded by horizontal pressure of ASP flooding conducting at the bottom sections, thus realizing 3-dimensional flooding.

Gas injection for stable gravity combination flooding may provide a viable option for EOR after polymer flooding. The method of this paper will provide the necessary support for future applications.

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