5 Summary
To evaluate the influence of viscosity ratio M and capillary number Ca on relative permeability k in a two-phase flow system, we calculated k for nonwetting and wetting fluids (k nw and k w) under variousM and Ca conditions using an LBM simulation. The main results of this study are as follows.
  1. In our simulations, the relative permeability of the nonwetting fluid increased as the viscosity ratio increased due to the lubricating effect and instability of the fluid interface. Specifically, at high viscosity ratios (M = 5), k nw could exceed 1 as a result of the lubricating effect.
  2. The relative permeability of the wetting fluid decreased as Mincreased due to the increase in shear drag force from the nonwetting fluid (viscous coupling effect).
  3. As M increased, the Euler number of the nonwetting fluid became higher, indicating that the nonwetting fluid became more disconnected and formed a larger number of clusters. In contrast, the Euler number of the wetting fluid decreased, signifying that the wetting fluid became more connected.
  4. At high capillary numbers (log Ca = 0.75 to −1.25),k nw did not respond to Ca , but did so at lower values of log Ca (<−1.25) due to the capillary force.
  5. As Ca decreased k w decreased, but at a negligible rate compared to k nw.
  6. k nw can change markedly in a wide range ofMCa parameter space, and theMCak nw correlation map created in this study can provide k nw estimates at various reservoir conditions.
  7. The color map produced from our results is useful for differentiating effects of M and Ca when both apply simultaneously.