A visualization method for obtaining capillary pressure relationships during centrifuge experiments was tested.It consists of recording and processing the video images of a rock sample at every spin rate.From these images,the local saturation at any location on the sample is obtained using a correlation that relates gray level to saturation.The capillary pressure is calculated using the measured average distance from the center of spin to the location of the local saturation measurement.With the visualization method,gas-water capillary pressure curves for sand packs and for Berea rock were obtained that agree with those determined with the algorithm of Hassler and Brunner.The irreducible water saturations were observed to be quite low in experiments at high spin rates for Bond numbers greater than 0.00001.Using video images,it was possible to explore the failure of the standard outlet boundary condition for centrifuge experiments,which maintains that the saturation of the displaced wetting phase during a drainage experiment is 100% at the outlet face of the sample.Results suggest that the standard outlet boundary condition fails for Bond numbers in excess of 0.0012.
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