Investigation on Water-Oil Displacement Efficiency in Heterogeneous Porous Media Based on Voronoi Tessellations

The pace of research on tight oil exploration and development has been accelerating in recent years. However, the tight reservoir has the characteristics of stronger heterogeneity, more complex pore-throat structure, and smaller pore-throat radius, which hinder their development. Therefore, research on porous media with strong heterogeneity and complex pore-throat structure has important engineering value. In this work, the water-oil displacement process in heterogeneous porous media is simulated by coupling the Navier-Stokes equation with the phase field method to track the interface between two phases in real time. In the past, the classical spherical grain was often used to study the displacement efficiency of porous media. However, with Voronoi tessellations embedded in porous media as the research object, it is possible to observe new pore-scale phenomena not seen in classical spherical grains. The influence of capillary number (Ca), oil-water viscosity ratio (M), and wettability on displacement efficiency has been investigated. The results demonstrate that at high viscosity ratio and low Ca, the strong heterogeneity caused by vugs makes the dominant channel more unstable, which is the main reason increasing the capillary number does not guarantee higher displacement efficiency under strong heterogeneity. In addition, a phenomenon of self-imbibition is observed due to strong heterogeneity, which leads to the coexistence of capillary fingering and viscous fingering at the crossover. A neutral wetting condition is an optimal condition for tight oil reservoir production.