Pore-scale mechanisms of two-phase flow in porous materials: Volume-of-Fluid method and pore-network modelling

We present direct simulations of several experiments with different geometries using Volume of Fluid (VOF) method. Pressure-flow rate correspondence and flow patterns are compared between numerical and experimental data. For a simple geometry, wecan reproduce experimental results satisfactorily, while significant disagreement with experiment are observed for complex geometries. Possible reasons for these findings are analyzed.
A two-pressure dynamic drainage algorithm is developed for three-dimensional unstructured network model. The impact of time step is discussed through drainage simulations. Dynamic effects in average phase pressure for fluid phases with different viscosity ratios are explored using the developed code as an upscaling tool. For cases where two fluids have significant viscosity differences, the viscous pressure drop within one fluid may be neglected. This dynamic algorithm can be further simplified into a single-pressure algorithm. This simplifications have been done for both drainage and imbibition. Saturation pattern during imbibition for different boundary pressure drops are studied. With increase of boundary pressure, invasion becomes less capillary dominant with a wetting front. The single-pressure algorithms for drainage and imbibition have been employed to simulations of sandbox experiments and liquid penetration into paper coating layer.