An experimental investigation of pore-scale distributions of nonaqueous phase liquids at residual saturation

A set of experiments was conducted to analyze the size distribution of nonaqueous phase liquid (NAPL) blobs as a function of aqueous phase velocities, NAPL densities, and interfacial tension between the aqueous phase and the NAPL. Blob size distributions were analyzed in a model cell after a state of residual saturation was achieved, using image analysis methods. Blob lengths parallel to the direction of flow and parallel to the direction of gravity ranged over about two orders of magnitude, while blob areas varied over about three orders of magnitude. Form factors, which are a measure of blob shapes, varied over a single order of magnitude, with a median form factor of about 0.6. Blobs with smaller areas occurred much more frequently than larger blobs. However, the few larger blobs contributed to the majority of the total NAPL saturation in the model cell. The geometric standard deviations of blob length parallel to the direction of gravity and square root of area exhibited inverse relationships to Bond number (Bo), for 1.3×10^–2–2. Blob length parallel to the direction of flow and area exhibited a weak inverse correlation with capillary number (Ca), for 3×10^–8–5.