Determining water content and saturation from dielectric measurements in layered materials

Abstract

Measurements of the dielectric constant in regions of the subsurface are commonly made to determine water content and in turn to determine water saturation. The accuracy with which water content or saturation information can be obtained from dielectric data is very dependent upon the model used to relate dielectric constant to water content or saturation. Most models assume that the material can be described as a homogeneous mixture of solids and fluids. While this may be valid in the interpretation of laboratory data, we suggest that in the interpretation of field data, improved accuracy in water content and saturation estimates can be obtained by accounting for the presence of layering. We present three relationships for determining water content or saturation from dielectric constant for layered materials. These three layered averages take into account both the layer thickness and measurement direction. We numerically model the relationship between the dielectric constant and both the fine fraction and water content or saturation in sand‐fine systems. We calculate dielectric constant as a function of water content or saturation using these three relationships for layered systems and compare the results to those calculated using two relationships for homogeneous systems. There are considerable differences between the dielectric constants predicted from the relationships for layered and homogeneous media. There are also differences between the individual relationships for the layered media due to the geometries of the systems. The numerical results illustrate the inaccuracy that can result in water content and especially saturation estimates if an inappropriate relationship is used to interpret dielectric data from a layered system.