Petrophysical Characterization of Swelling and Non-Swelling Clays by Geoelectrical Measurements

Abstract:

Geophysical techniques may provide noninvasive and cost-effective alternatives to direct methods for characterization and monitoring of soil moisture content. We conducted an experiment to determine changes in electrical conductivity with variations in moisture content in swelling and non-swelling soils. Soil samples were packed into cylindrical columns equipped with 8 electrodes equally spaced around the circumference of a cross section on both columns. Both soils were fully saturated with a saline solution and maintained at room temperature for the duration of the study. Soils were mounted on a scale to monitor water loss due to evaporation with shrinkage visually monitored. Electrical conductivity measurements were collected continuously over the period of 12 to 17 (swelling and non-swelling clay) days. Soil shrinkage in response to drying was recorded on a daily basis. Archie’s second law was fitted in an attempt to find representative saturation exponents for both soils. The non-swelling clays follow a power-law fit of Archie’s second law. In contrast, the swelling clays do not obey Archie’s Law even after the measured soil shrinkage is used to correct soil porosity. This work indicates that modified petrophysical relationships are needed to account for changes in pore geometry with moisture content variation in swelling soils.