Lattice-Boltzmann simulations of the capillary pressure–saturation–interfacial area relationship for porous media

Hysteresis in the relationship between capillary pressure (Pc)(Pc), wetting phase saturation (Sw)(Sw) and nonwetting–wetting interfacial area per volume (anw)(anw) is investigated using multiphase lattice-Boltzmann simulations of drainage and imbibition in a glass bead porous system. In order to validate the simulations, the Pc–SwPc–Sw and anw–Swanw–Sw main hysteresis loops were compared to experimental data reported by Culligan et al. [Culligan KA, Wildenschild D, Christensen BS, Gray WG, Rivers ML, Tompson AB. Interfacial area measurements for unsaturated flow through porous media. Water Resour Res 2004;40:W12413]. In general, the comparison shows that the simulations are reliable and capture the important physical processes in the experimental system. Pc–SwPc–Sw curves, anw–Swanw–Sw curves and phase distributions (within the pores) show good agreement during drainage, but less satisfactory agreement during imbibition. Drainage and imbibition scanning curves were simulated in order to construct Pc–Sw–anwPc–Sw–anw surfaces. The root mean squared error (RMSE) and mean absolute error (MAE) between drainage and imbibition surfaces was 0.10 mm−1 and 0.03 mm−1, respectively. This small difference indicates that hysteresis is virtually nonexistent in the Pc–Sw–anwPc–Sw–anw relationship for the multiphase system studied here. Additionally, a surface was fit to the main loop (excluding scanning curves) of the drainage and imbibition Pc–Sw–anwPc–Sw–anw data and compared to the surface fit to all of the data. The differences between these two surfaces were small (RMSE = 0.05 mm−1 and MAE = 0.01 mm−1) indicating that the Pc–Sw–anwPc–Sw–anw surface is adequately represented without the need for the scanning curve data, which greatly reduces the amount of data required to construct the non-hysteretic Pc–Sw–anwPc–Sw–anw surface for this data.