Flow behaviors of nitrogen and foams in micro-visual fracture-vuggy structures

Nitrogen gas flooding and foam flooding have been widely used for oil and gas development in fracture-vuggy carbonate reservoirs. However, flow behaviors of nitrogen and foams are not very clear owing to the complex connectivity of fractures and vuggys. In this work, four types of micro-visual fracture-vuggy models were designed and fabricated to systematically investigate the dynamic flow behaviors of nitrogen and foam in fracture-vuggy structures. Results indicate that the swept volume and oil displacement efficiency can be improved more by foam flooding than by nitrogen flooding owing to the abilities of foams on mobility adjustment, IFT reduction, and oil emulsification. The presence of vuggy can strengthen the effect of gravity differentiation during nitrogen flooding, while foam flooding can diminish the gravity differentiation effect. Besides, pressure difference at the curved oil–gas interface plays a great role in the flow characteristics of nitrogen and foam. Moreover, the EOR rate is used to evaluate the EOR potential of nitrogen foam flooding technology over nitrogen flooding technology. This work systematically reveals the dynamic flow behaviors of nitrogen and foam in various micro visual fracture-vuggy structures, which can provide theoretical support for the development of the fracture-cavity reservoir.