Adaptation study on nitrogen foam flooding in thick reservoirs with high water cut and high permeability

Abstract

Most of the oilfields in China are in high- or ultrahigh-water-cut stages, and the impacts of water flooding developments have declined due to the increase in reservoir heterogeneity, the rapid increase in the water cut and the discontinuous distribution of crude oil under these conditions. Based on this phenomenon, an experimental study of nitrogen foam flooding is conducted in this paper. The oil displacement characteristics of nitrogen foam in oil and water layers of thick, high-porosity and high-permeability reservoirs are studied through one-dimensional core tube experiments, and the mechanisms of profile control and water plugging are analyzed. Through two-dimensional visualization experiments, we observe the migration and diffusion patterns of nitrogen foam, analyze the effects of different degrees of vertical foam production on the residual oil after water flooding, clarify the production effect of gas overburden on the residual oil at the top of the reservoir, and summarize the mechanisms of nitrogen foam flooding involved in improving the recovery factor. The results show that in the core tube experiment, the recovery factor of the high-permeability core is 93.73%, the recovery factor of the low-permeability core is 71.33%, and the total recovery factor reaches 83.23% in the stage of nitrogen foam flooding, which is 28.96% higher than that of water flooding. In the visualization experiment, the recovery factor of the nitrogen foam flooding stage is 57.12%, which is 24.99% higher than that of water flooding. The recovery degrees of the layers are similar; by comparing the increase in the recovery degree of each layer before and after the two stages, it is found that the increase in recovery degree increases from the bottom to the top. The foam system exhibits a good selective plugging ability under the conditions of severe heterogeneity and low residual oil in the high-permeability zone. Nitrogen foam flooding can effectively improve the recovery factor in the late-stage reservoir development of the ultrahigh-water-cut stage, and it shows good adaptability to these types of reservoirs.