Capillary pressure overshoot as a function of imbibition flux and initial water content

Infiltration into well‐sorted sands can show an anomalous behavior called saturation overshoot where the saturation at the infiltrating front is higher than the saturation behind the front for certain fluxes and initial water contents. Similarly, capillary pressure overshoot is defined as when the capillary pressure is greater behind the front than it is at the front, which is contrary to normal infiltration. In this paper, pressure profiles are reported for water infiltrating into sand for a range of fluxes and initial water content. Capillary pressure overshoot is observed for sands with an initial water saturation of 0.06 and less, while no overshoot is observed for greater initial saturations. Capillary pressure overshoot does not show much dependence on flux, but the capillary pressure at the front does decrease with increasing flux. These results are combined with the previous saturation measurements, and it is found that the capillary pressure‐saturation imbibition curve is not dependent on the velocity of the front. The implications of the results on the stability of three‐dimensional flows are discussed.