Observations of water and oil infiltration into soil: Some simulation challenges

Experiments were performed to test the ability of multiphase flow theory to predict the flow behavior of an immiscible organic liquid entering an unsaturated soil medium. The infiltration and redistribution behavior of water followed by oil, and of oil followed by water, in soil columns was observed. Experiments involved both liquid entry at the top of columns with downward flow and entry at the base of columns with upward flow. Two oils (specific gravity, 0.80 and 0.86; viscosity ratio relative to water, 4.7 and 77) were used in three soils: a silt loam, a sandy loam, and a sand. The results from 17 different infiltration scenarios, each about 8 hours in duration, are compared with the predicted results obtained from a simplified explicit finite difference code for three‐phase flow in a one‐dimensional system. Code input required only the soil water release curve, the bulk density, the initial water content, the saturated water conductivity, the oil viscosity, and the interfacial tensions between oil and air and water and oil. The code made reasonably good predictions of water and oil redistribution in the silt loam and loamy sand, when oil followed water infiltration. It made less than satisfactory predictions for the sand, possibly because hysteresis was neglected. Infiltration time for small amounts of oil was often shorter than the code predicted for the silt loam and loamy sand. The code, which did not account for hysteresis or unstable liquid flow, also did a poor job of predicting oil and water contents when water followed oil into the soils. Visual evidence of unstable flow of the more viscous oil entering the water wet loamy sand is presented, and the implications for one‐ and two‐dimensional experiments are discussed. The experimental results are presented to facilitate the preliminary validation of other immiscible flow codes.