Study on Fluid Behaviors of Foam-Assisted Nitrogen Flooding on a Three-Dimensional Visualized Fracture-Vuggy Model

Tahe Oilfield, located in northwest China, is an unconventional fracture-vuggy carbonate reservoir. The foam-assisted nitrogen gas flooding technology has been proven to be a potential EOR technology. However, the flow behaviors of foam-assisted nitrogen gas in fracture-vuggy structures are not clear due to the complex fracture-vuggy structures and their strong heterogeneity. In this work, a three-dimensional visualized fracture-vuggy model is designed and fabricated to investigate the fluids behaviors of foam-assisted N-2 flooding and classify the residual oil types after foam-assisted N-2 flooding. Experimental results reveal that foam slug can enlarge the sweep efficiency, suppress the formation of nitrogen gas channeling, and detach the oil film. Additionally, the evolution processes of the gas-oil and oil-water interfaces are investigated and analyzed. Moreover, the residual oil types after foam-assisted N-2 flooding and nitrogen gas flooding, respectively, are classified and summarized. Compared to nitrogen gas flooding after water flooding, 12.36% more oil can be recovered through foam-assisted N-2 flooding. This work further studies the fluid flow behaviors of foam-assisted N-2 in the three-dimensional visualized fracture-vuggy carbonate model and also confirms the previous achievements.