Multi-phase flow process in porous medium are generally simulated with in introduction of relative permeability, which is assumed to be a scalar function of phase saturation. Previous research have demonstrated this assumption might not be suitable for capillary force dominated heterogeneous porous medium. Similarly, in vugular porous medium, the free flow region in vugs would introduce vertical velocity component, causing the flow field to differ. Two-dimensional experiments are conducted to examine such effect. The physical model are artificial homogenous and isotropic porous medium square plates, and vugs are designated as cylindrical holes. A group of models with axisymmetric vug distribution are designed so that the fluid flow in two principal directions are the same if the plate is placed horizontally but different if the plate is placed vertically. Also for general purpose another group of models with random placed vugs are designed to simulate actual reservoirs. The upscaled relative permeability curves in two principal directions are measured and compared. Supplemental numerical simulation are also conducted on two simulators. The first is a finite volume simulator KarstSim with the assumption of gravity segregation and instantaneous establishment of steady-state in vugs, the second is a commercial finite element software. The experiment result indicates that the direction of upstream fluid flow have a significant influence on the flow field within the physical model, and is presented in the relative permeability curves. This effect is pronounced in the cases where the vugs are distributed in specific orders. The numerical result are in good agreement with the result of experiments. Based on the results, we prompt the need to introduce a secondary variable in the relative permeability function, which is the angle between the upstream flow direction and the vertical direction to better simulate the multi-phase flow process in vugular porous medium.
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