Conductivity Measurements of Sand-Clay Mixtures: A Modified Experimental Method

Abstract

We present experimental results of electrical conductivity measurements on sand-clay mixtures saturated with brines and on sand saturated with trichloroethylene (TCE). These experiments were conducted to aid in the study of detecting common groundwater contaminants and to expand the database of conductivity measurements made on unconsolidated sediments. Our experimental apparatus is based on the standard four-point electrode measurement technique utilizing removable unconsolidated sample “cores.” We can change saturating fluids and make seismic measurements in the same apparatus without disturbing the sample. Our brine data show little change in magnitude with frequency and follow Archie’s law with Archie’s cementation exponents ranging from approximately 1.5 to 2.5. Samples with higher clay content show a lower bulk conductivity. This trend may be due to both incomplete saturation and∕or the clay packing. This finding may affect the interpretation of common field methods, as it is contrary to results on consolidated shaley sandstones. Measurements made on a sand sample saturated with TCE do not follow Archie’s law. This deviation may be due to a thin conductive water layer and∕or incomplete flushing of the sample.