Numerical simulation of gas injection for stable gravity flooding after polymer flooding

Residual oil after polymer flooding is very scattered, and residual oil in top sections of reservoir formations is extremely difficult to develop, yet there is no prevailing technology suitable for development after polymer flooding. Based on analysis of stress on crude oil, the idea of injecting gas at the top section of the reservoir and conducting ASP flooding in bottom section has been proposed in this paper. Performances of different displacement modes have been predicted for some blocks of Daqing Oilfield after polymer flooding.The research results show gas injection for stable gravity flooding has the best performance, with a EOR increment of 13.53%. Comparing residual oil saturation obtained through application of different displacement modes, gas injection for stable gravity flooding can effectively develop low-permeability formations in the top section and reduce residual oil significantly. Vertical distribution of residual oil saturation at different time points was analyzed. After gas injection in the top section, differential pressure in vertical direction may drive residual oil to migrate downward, while ASP flooding conducted in bottom section may drive residual oil by horizontal differential pressure, thus realizing 3-dimensional flooding. Gas injection for stable gravity flooding may provide a viable option for EOR after polymer flooding.