Volume 30, Issue 6 (November 2007)
Rapid Pseudo-Static Measurement of Hysteretic Capillary Pressure-Saturation Relationships in Unconsolidated Porous Media
An automated system was developed for a rapid measurement of detailed hysteretic capillary pressure-saturation (Pc-S) relationships, including primary drainage, main imbibition, and scanning loops. The method makes use of a slow-dynamic (pseudo-static) measurement method which is able to duplicate static results while expanding the pressure range over which high permeability capillary barriers can be applied, and increasing the quantity of hysteretic data that can be collected. The method is demonstrated for two sands and three silts for capillary pressures as high as 1000 cm water (98 kPa). For the experiments shown, primary drainage and main imbibition loops were completed within approximately 6.5 h for all materials, with full runs, including multiple scanning curves, completed in less than 20 h. A model for selection of pressure rates needed to duplicate static results is presented and is found to produce results consistent with empirically-determined rates. The model also predicts the effects of system resistance on dynamic response and is found to be in good agreement with experimental results, particularly for slower rates approaching those needed for pseudo-static conditions.