A novel method for modeling oil-water two-phase flow in fractured-vuggy carbonate reservoirs considering fluid vertical equilibrium mechanism

Fractured-vuggy carbonate reservoirs have great potential for development with diverse reservoir space types and very complicated fluid flow dynamics. The height of high-angle fractures and cavities in fractured-vuggy carbonate reservoirs can reach several meters and fluids are extremely prone to transport and mass exchange along the vertical direction. The vertical equilibrium phenomenon can significantly affect the oil-water spatial distribution in this type of reservoir. However, the existing numerical simulation methods do not consider the effect of fluid vertical equilibrium mechanism, and the predicted results often have large deviations from the actual situation. In this paper, considering the connectivity structure of typical fractured-vuggy unit, several visualized fractured-vuggy physical models are firstly prepared by 3D printing technology, and the vertical equilibrium time of oil and water under different fractured-vuggy combination modes are determined using the vertical equilibrium experiments. 'Dynamic reconstruction', a multi-scale vertical equilibrium method, is employed for the decoupling calculation of fluid saturation and pressure profiles in coarse-scale and fine-scale grids of fractured-vuggy reservoirs. Compared with indoor experiments, the simulated results when considering the fluid vertical equilibrium are much closer to the experimental phenomena than that calculated by the traditional method, proving the proposed method's reliability. Finally, the vertical equilibrium model is applied to study two-phase fluid flow in a typical fractured-vuggy unit of Tarim oilfield. The proposed method has been proven to reveal the flow characteristics of oil-water two-phase and remaining oil distribution in fractured-vuggy carbonate reservoir more accurately.