PNNL

Abstract

A numerical model based on smoothed particle hydrodynamics (SPH) was used to simulate pore-scale liquid and gas flow in synthetic two-dimensional porous media consisting of non-overlapping grains. The model was used to study effects of pore scale heterogeneity and anisotropy on unsaturated flow and the saturation-pressure relationship. Pore scale anisotropy was created by using co-oriented non overlapping elliptical grains, and heterogeneity was created by inserting a micro-fracture in the middle of the porous domain consisting of non-overlapping circular grains. The effect of wetting fluid properties on drainage was also investigated. Capillary-pressure saturation curves resulting from fluid drainage through boundaries parallel and perpendicular the fracture alignment were qualitatively similar to those observed in gap-graded sediments with bimodal grain-size and pore-size distributions. Those derived from drainage on a boundary oriented perpendicular to particle and fracture alignment were qualitatively similar to those for mono-modal pore-size distributions. It is shown that pore-scale heterogeneity and anisotropy can gave rise to capillary pressure-saturation relationships and entry (bubbling) pressures that depend on flow direction suggesting that these properties should be described by tensor rather than scalar quantities.