Formation adaptability of combining modified starch gel and nitrogen foam in profile modification and oil displacement

Problems such as high permeability, serious heterogeneity, and ineffective water flooding exist in developing offshore oil fields. Integrating modified starch gel as profile control agent and foam to displace oil was investigated to improve production problems. Physical models with in-layer and interlayer heterogeneity, as well as different permeability ratios, were used in the physical simulation experiments. The feasibility and mechanism of this combined technology were discussed in detail. Experimental results indicated that the viscoelastic-modified starch gel with high viscosity could effectively block the high permeability channels, making foam migrate uniformly in the medium, and mobilize the remaining oil in the low permeability layers. For inner heterogeneous models, starch gel blocked the high permeability layer, as well as improved the sweeping volume of nitrogen foam. In addition, at permeability ratios exceeding 40, the foam sweeping efficiency and oil displacement effect became less significant. For interlayer heterogeneous models, the starch gel effectively blocked the high permeability layer. Based on the experimental results and theoretical analysis, the sweeping volume and displacement mechanism of the synergistic effects were discussed. The laboratory results can provide reference for optimizing nitrogen foam flooding and improving oil displacement.