The Oil/Water Two-Phase Flow Behavior of Dual-Porosity Carbonates

Dual-porosity carbonates exhibit abundant macropores and micropores, yet the mechanisms governing oil/water flow at the dual-porosity scale remain inadequately understood. This study investigates the flow behavior in dual-porosity carbonates during forced imbibition. Initially, carbonate characteristics were extracted using a random field method to generate two types of porous media. Subsequently, the multiple-relaxation-time color-gradient lattice Boltzmann method, validated by experimental and analytical solutions, was employed to systematically evaluate the effects of wettability, capillary number, and oil/water viscosity ratio on oil displacement efficiency in dual-porosity carbonates during forced imbibition. The reliability of the simulated oil displacement efficiency was verified through core waterflooding experiments. The results reveal that under water-wet conditions, fluid flow paths in dual-porosity carbonates are strongly influenced by the blockage of micrite particles at low capillary numbers, while at high capillary numbers, the fragmentation of large continuous oil droplets interacting with micrite particles leads to more unstable interfaces. Under non-water-wet conditions, dominant capillary forces enhance oil displacement within macropores of dual-porosity carbonates. Under the same conditions, water-wet conditions are more favorable for improving oil displacement efficiency. As the capillary number increases, oil displacement efficiency exhibits a pronounced non-monotonic trend under non-water-wet conditions, attributed to the alternating dominance of viscous and capillary forces. Additionally, with an increase in oil/water viscosity ratio, the decline in oil displacement efficiency is less pronounced for dual-porosity carbonates compared to single-porosity carbonates, particularly under non-water-wet conditions at high capillary numbers.