Resistivity index measurement without the porous plate: A desaturation technique based on evaporation produces uniform water saturation profiles and more reliable results for tight North Sea chalk

Measurement of Archie's Resistivity Index 'RI' and saturation exponent 'n' can be very time consuming for low permeable core samples using the established porous plate techniques. An evaporation technique circumventing the porous plate difficulties has been developed, and is demonstra ted for the tight Lower Cretaceous carbonates in the Danish North Sea. Samples are saturated with a diluted formation brine and by evaporation water is removed from the diluted brine in the samples until the original brine concentration has been restored and the samples has attained a water saturation < 1. By this technique any water saturation down to approximately 0.1 can be imposed on the sample in less than a week. The movement of water in the sample during desaturation is documented by a tracer technique and core scanning, and data from the Lower Cretaceous carbonates are presented.